Lost foam casting process

Lost foam casting, also called solid casting, is a model of a foam model with the same shape and shape as the casting. After brushing the refractory paint and drying it, it is buried in the dry sand and is molded under vacuum and under vacuum. The gasification of the model, the liquid metal occupying the position of the model, and the emerging casting method of forming the casting after solidification and cooling, the idea of ​​the process as the core, is still the soul of the industry, which affects the future of the lost foam casting industry and the mold manufacturing industry.

Lost foam casting process

1. Make foam plastic white mold, combined pouring system, gasification mold surface brush, spray special high temperature resistant paint and dry.

2. Place the special compartment sand box on the vibrating table, fill in the bottom sand (dry sand), tap it, scrape the flat, put the dried gasification mold on the bottom sand, fill the dry sand, and shake the appropriate time. Scrape the box mouth.

3. Cover with plastic film, put on the pouring cup, connect the vacuum system to vacuum, dry sand is formed and then cast, the white mold gasification disappears, and the molten metal replaces its position.

4. Release the vacuum. After the casting is condensed, turn the box and remove the casting from the loose dry sand.

Lost foam casting process control

First: the choice of foam beads

1. There are three types of foam beads for foam casting.

(1) Expandable polystyrene resin beads (abbreviated as EPS);

(2) Expandable methyl methacrylate and styrene copolymer resin beads (STMMA for short);

(3) Expandable polymethyl methacrylate resin beads (abbreviated as EPMMA).

2. Commonly used expandable polystyrene resin beads (EPS) for casting non-ferrous metals, gray iron and general steel casting.

3. bead characteristics: translucent beads, pre-expansion multiple 40 ~ 60, particle size of 0.18 ~ 0.80 亳 m (6 sizes).

4. The particle size of the original bead generally selected is less than or equal to 1/9 to 1/10 of the minimum wall thickness of the casting.

Second: About the production of models

1. Made of foamed beads: pre-foaming – curing – foam molding – cooling out of the mold.

(1) pre-foaming

Before the EPS beads are added to the mold, they are first foamed to expand the beads to a certain size. The foaming process determines the density, dimensional stability and accuracy of the model and is one of the key links. There are three methods for pre-expansion of EPS beads: hot water pre-expansion, steam pre-expansion and vacuum pre-expansion. The vacuum pre-expanded beads have a high foaming rate, and the beads are dried and used more.

(2) ripening

The pre-foamed EPS beads are placed in a dry, ventilated silo for a certain period of time. In order to balance the external pressure in the beads, the beads have elasticity and re-expansion ability to remove the moisture on the surface of the beads. The ripening time is between 8 and 48 hours.

(3) Foam molding

The foamed and matured EPS beads are filled into the cavity of the metal mold, heated, and the beads are expanded again to fill the voids between the beads, and the beads are fused to each other to form a smooth surface, that is, a mold. Cooling must be carried out before the mold is released to cool the model below the softening temperature. After the model is hardened and shaped, the mold can be released. After the mold is released, there should be time for the model to be dry and dimensionally stable. The equipment has two kinds of steaming cylinders and automatic forming machines.

2, made of foam plastic sheet: foam plastic sheet – resistance wire cutting – bonding – model. For a simple model, a foam wire cutting device can be used to cut the foam sheet into the desired model. For complex models, first use a resistance wire cutting device to divide the model into several parts and then glue them into a whole model.

Third: the model is combined into clusters

It is a combination of a self-processed (or purchased) foam model and a pouring riser model to form a model cluster, which is sometimes carried out before the coating, sometimes in the case of a buried shape after the coating is prepared. It is an indispensable process for lost mold (real) casting. Currently used bonding materials: rubber emulsion, resin solvent and hot melt adhesive and tape paper.

Fourth: model coating

The surface of the solid casting foam model must be coated with a certain thickness of paint to form the inner shell of the mold. The role of the coating is to improve the strength and rigidity of the EPS model, improve the surface erosion resistance of the model surface, prevent the surface damage and vibration modeling of the model during sanding and the deformation of the model during negative pressure setting, and ensure the dimensional accuracy of the casting. A commercially available special coating for lost foam casting, which is stirred with water in a paint mixer to obtain a suitable viscosity. The agitated paint is placed in a container, and the model group is coated by dipping, brushing, pouring, and spraying. It is usually applied twice to make the coating thickness 0.5~2mm. It is selected according to the type, structure and size of the casting alloy. The coating is dried at 40 to 50 °C.

Fifth: vibration modeling

We introduce a commonly used modeling method (one of two methods). The process includes the following steps: sand bed preparation – placing the EPS model – sand filling – sealing and setting.

1. Sand bed preparation

Place the flask with the pumping chamber on the shaker and clamp it. Put a certain thickness of bottom sand at the bottom (generally the thickness of the sand bed is above 50~100mm), and the vibration is tight. The molding sand is dry quartz sand without binder, no filling, and no water. The ferrous metal has a high temperature and can be made of coarser sand. The aluminum alloy is made of fine sand. The sand is used repeatedly after being treated. The sand box is a sand box with a single opening, a pumping chamber or an air suction pipe, a lifting or walking mechanism.

2. Place the EPS model

After the tapping, the EPS model group is placed according to the process requirements, and the sand is fixed.

3. Sand filling

Add dry sand (several sanding methods) and apply vibration (X, Y, Z directions) for 30~60 seconds, so that the sand fills all parts of the model and increases the bulk density of the sand.

4. Sealed stereotypes

The surface of the sand box is sealed with a plastic film. The vacuum pump is used to draw a certain vacuum into the sand box. The sand is “bonded” together by the difference between the atmospheric pressure and the pressure inside the mold to keep the casting process from collapsing. “Negative pressure setting. More commonly used.

Sixth: casting replacement

The EPS model generally softens around 80 °C and decomposes at 420-480 °C. The decomposition products are gas, liquid and solid. The thermal decomposition temperature is different, and the contents of the three are different. In solid casting, under the action of liquid metal, the EPS model undergoes pyrolysis gasification, generates a large amount of gas, continuously discharges through the coated sand, and forms a certain pressure in the mold, model and metal gap. The metal constantly occupies the position of the EPS model and advances, causing a replacement process between the liquid metal and the EPS model. The end result of the displacement is the formation of a casting. The pouring operation is slow-fast-slow. And keep pouring continuously to prevent the pouring process from breaking. After pouring, the mold vacuum is maintained for 3 to 5 minutes and then the pump is stopped. The pouring temperature is 30 to 50 ° C higher than the temperature of the sand casting.

Seventh: cooling and cleaning

After cooling, the real casting sand falling is the simplest. The sand box can be slanted out of the casting or the casting can be directly hoisted from the sand box. The casting is naturally separated from the dry sand. The separated dry sand is treated and reused.
The above is the introduction of the lost foam casting process.

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Defects and preventive measures in the heat treatment of lost foam molds!

Although the application of lost foam casting technology in China has been slow, it has developed rapidly in recent years. In particular, due to the low investment in lost foam casting equipment and short process routes, many original small and medium-sized foundry companies are increasingly adopting this technology.

However, some companies have failed to pay attention to some operational problems. Today we will understand the defects and preventive methods in the heat treatment of lost foam molds:

1. The surface of the mold has soft spots

After the heat treatment of the mold, there are soft spots on the surface, which will affect the wear resistance of the mold and reduce the service life of the mold.

(1) Cause

The mold has scale, rust and local decarburization on the surface before heat treatment. After quenching and heating, the cooling and quenching medium is improperly selected, and the impurities in the quenching medium are excessive or aged.

(2) Preventive measures

Before the heat treatment of the mold, the scale and rust spots should be removed. When the mold is heated during quenching, the surface of the mold should be properly protected. Vacuum furnace, salt bath furnace and protective atmosphere furnace should be used for heating. When quenching and heating, select a suitable cooling medium, and filter the long-term cooling medium frequently, or replace it regularly.

2. The mold is poorly organized before heat treatment

The final spheroidized structure of the mold is coarse and uneven, and the spheroidization is imperfect. The structure has mesh, ribbon and chain carbides, which will cause the mold to be cracked after quenching, resulting in scrapping of the mold.

(1) Cause

There is serious carbide segregation in the original structure of the die steel material. Poor forging process, such as forging heating temperature is too high, deformation is small, stop forging temperature is high, and the cooling speed after forging is slow, so that the forged structure is coarse and there are mesh, band and chain carbides, so that spheroidizing annealing It is difficult to eliminate. The spheroidizing annealing process is not good, such as the annealing temperature is too high or too low, the isothermal annealing time is short, etc., which may result in uneven spheroidizing annealing or poor spheroidization.

(2) Preventive measures

Generally, according to the working conditions of the mold, the production batch and the toughening performance of the material itself, try to select a good quality mold steel material. Improve the forging process or use normalizing heat treatment to eliminate the non-uniformity of the network and chain carbides and carbides in the raw materials.

High-carbon die steel with severe segregation of carbides that cannot be forged can be subjected to solution heat treatment. The correct spheroidizing annealing process specification for the forged blank can be tempered heat treatment and rapid uniform spheroidizing annealing. The furnace is properly installed to ensure the uniformity of the temperature of the mold blank in the furnace.

3. The mold produces quenching cracks

The cracking of the mold after quenching is the biggest defect in the heat treatment process of the mold, which will cause the processed mold to be scrapped, causing great loss in production and economy.

(1) Reasons for the cause

There is severe network carbide segregation in the mold material. There are mechanical or cold plastic deformation stresses in the mold. Improper heat treatment (heating or cooling too fast, improper selection of quenching cooling medium, low cooling temperature, too long cooling time, etc.).

The mold has a complicated shape, uneven thickness, sharp corners and threaded holes, which cause excessive thermal stress and tissue stress. The quenching heating temperature is too high to cause overheating or overheating. After quenching, the tempering is not timely or the tempering time is insufficient. When the quenching is heated, the quenching is performed again without intermediate annealing. Heat treatment, improper grinding process. When subjected to electrical discharge machining after heat treatment, high tensile stress and microcracks are present in the hardened layer.

(2) Preventive measures

Strictly control the intrinsic quality of the mold raw materials, improve the forging and spheroidizing annealing process, eliminate the network, ribbon, and chain carbides, and improve the uniformity of the spheroidized structure. The mold after mechanical processing or after cold plastic deformation shall be subjected to stress relief annealing (>600 ° C) and then subjected to heat quenching. For molds with complex shapes, asbestos should be used to block threaded holes, and the dangerous section and thin wall should be wrapped, and graded quenching or austempering should be used.

Annealing or high temperature tempering is required when reworking or refurbishing the mold. Preheating should be adopted during quenching heating, pre-cooling measures should be taken during cooling, and suitable quenching medium should be selected. The quenching heating temperature and time should be strictly controlled to prevent overheating and over-burning of the mold.

After the mold is quenched, it should be tempered in time, the holding time should be sufficient, and the high alloy complex mold should be tempered 2-3 times. Choose the right grinding process and the right grinding wheel. Improve the mold EDM process and perform stress relief and tempering.

4. After the mold is quenched, the structure is coarse.

After the mold is quenched, the coarse structure will seriously affect the mechanical properties of the mold. When used, the mold will be broken, which will seriously affect the service life of the mold.

(1) Reasons for the cause

The mold steel is confused, and the actual steel quenching temperature is much lower than the quenching temperature of the required mold material (such as GCr15 steel as 3Cr2W8V steel). The steel was not properly spheroidized before quenching, and the spheroidized structure was poor. The quenching heating temperature is too high or the holding time is too long. Improper placement in the furnace and overheating in the vicinity of the electrode or heating element area. For molds with large cross-section changes, the quenching heating process parameters are not properly selected, and overheating occurs at thin sections and sharp corners.

(2) Preventive measures

Before the steel is put into storage, it should be strictly inspected to prevent the steel from being confused. Proper forging and spheroidizing annealing should be performed before the mold is quenched to ensure good spheroidization. Correctly formulate the mold quenching heating process specification and strictly control the quenching heating temperature and holding time. Regularly test and calibrate the temperature measuring instrument to ensure the normal operation of the instrument. Keep the proper distance from the electrode or heating element when heating in the furnace.

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Improvement of design of cylinder liner centrifugal casting mold

Large cylinder diameter wet diesel engine cylinder liner (≥φ125), usually used for single casting. According to the traditional mold design process, the produced blank is heavier, the casting cost is higher, and the machining allowance is large. Therefore, it is imperative to reduce the weight of the cast blank and thus reduce the machining allowance.

Before the improvement, the inner hole design of the mold, the traditional design is a diagonal line from the big end to the small end of the mold. This design makes the coating performance of the coating better, the cooling speed of the blank is uniform, and the big end and small end quality of the blank are produced. More uniform. However, due to the limited design, the slope is not too large (otherwise, the coating performance of the coating is poor, resulting in waste), so the processing margin of the produced blank is large.

After the improvement, there are three steps from the big end to the small end on the inner hole surface of the mold. Therefore, there are three steps in the outer round surface of the blank, which are substantially the same as the outer circular surface of the finished cylinder sleeve, so that the blank The machining allowance and weight are greatly reduced.

After the cylinder liner centrifugal casting mold was changed, we found two problems:

1. The wall thickness of the small end of the blank is reduced. When pouring, the cooling rate of the molten iron is accelerated, and the graphite form does not meet the standard requirements.

2. At the large end of the blank, due to the large step difference below the supporting shoulder, the speed of the molten iron in the solidification process is different, and it is easy to produce shrinkage on the inner hole surface of the blank.

Casting mold process adjustment:

Through the implementation of the second incubation process and the adjustment of the casting process, the qualified products are successfully produced. The second inoculation treatment process, before the pouring of molten iron, under certain conditions (such as a certain superheat temperature, a certain chemical composition, a suitable addition method, etc.), a certain amount of substance (referred to as an inoculant) is added to the molten iron. In order to change the solidification performance of the molten iron, improve the as-cast structure, and thereby achieve the purpose of improving the performance of the treatment method, said the inoculation treatment.

The purpose of the inoculation treatment is to promote graphitization, reduce the tendency of white mouth; improve the uniformity of the section; control the morphology of graphite, reduce the formation of D, E type symbiotic graphite and ferrite to obtain medium size A type graphite.

After the mold change is analyzed, the wall thickness of the small end of the blank is thinned, and the cooling rate of the molten iron is accelerated. During the solidification process, the degree of supercooling of the molten iron (0 T) is increased, and the transformation from ΔT1 to ΔT2 and ΔT3 causes the graphite structure to become smaller. It is tapered and transformed from type A graphite to type B, D, and E graphite. In addition, due to the long casting route, 12 sets of molten iron should be poured into 12 centrifugal casting machines, and the pouring time is relatively long. Obviously, a single inoculation process can no longer meet the quality requirements. A second inoculation process must be carried out, that is, an appropriate amount of inoculant is added to the small pouring bag before the centrifugal pouring machine. This treatment method, from the melting of the inoculant to the pouring time is very short, maximizes the role of inoculant, reduces the decline of pregnancy, in the actual production, the rational choice of the size and amount of inoculant is the key to success.

Adjustment of the casting process of the centrifugal casting machine to eliminate shrinkage:

The reason for the formation of the shrinkage is various, and the most fundamental reason is that when the molten iron in the shrinkage portion is solidified, the shrinkage is not obtained. After the casting mold structure is changed, the step of the large end of the blank supports the shoulder. Because the wall thickness of the blank differs greatly, the solidification speed of the molten iron is different, and the molten iron at the thin wall first solidifies, causing the molten iron at the thick wall after solidification to solidify. Feeding, forming a shrink.

Therefore, for the reasons of shrinkage formation, after repeated experiments, the following countermeasures are taken: increasing the rotational speed of the centrifugal casting machine (N); appropriately extending the rotation time of the centrifugal casting machine (TI); appropriately extending the molten iron from the small pouring bag to the pouring Machine pouring time (T2). Through calculation, it is found that there is a mathematical correspondence between (N) . ( T1 ) . ( T2 ) and the blank inner diameter (D). That is, the inner diameter (D) of the blank and the rotational speed (N) of the mold are proportional to each other; and the relationship between the rotation time (TI) of the mold and the casting time (T2). When the inner diameter of the blank is constant, if the actual rotation speed of the mold is lower than the theoretically required rotation speed of the mold corresponding to Fig. 8, shrinkage will occur; similarly, if the actual rotation time of the mold (T1), the pouring time (T2) is lower than the theoretically required rotation time (TI) of the mold corresponding to Fig. 8, and the shrinkage is also generated when the pouring time (T2).

Cost reduction:

The improved liner blank has a reduced wall thickness and a reduced weight, which saves the casting raw materials. At the same time, due to the reduction of machining allowance, the machining tool wear is reduced and the service life is prolonged. With an average weight loss of 3.6 per blank, the tool can save 0.02 yuan / piece. Since the improvement of the cylinder liner was put on the market, it has been more than a year since the production of a large cylinder bore diesel engine cylinder casing of about 50,000. The raw materials and tools saved a total of 614,000 yuan, reducing costs and improving economic efficiency.

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Application Analysis of Aluminum Alloy Gravity Casting Mould

While advanced equipment is an indispensable factor in ensuring product quality, the role of molds in casting is also very important. Especially for aluminum alloy and aluminum alloy auto parts manufacturers, the accuracy and durability of aluminum alloy casting molds have an obvious impact on product quality.

For ferrous metal casting, the mold is more for the formation of the mold cavity. In general, the mold itself is not directly in contact with the molten metal, especially for the non-metal mold castings with complicated shapes, and the contact with the hot metal liquid is the shape. The material, mainly the molding sand, makes the modeling material a major factor affecting the quality of the casting. The aluminum alloy gravity casting is different. Because of the lower melting point of the aluminum alloy, the casting performance is good. In the mass production, the shape of the casting is generally formed directly by the mold, such as the aluminum alloy cylinder and the cylinder head of the engine. It is beneficial to improve labor productivity, and more importantly, to control the structure and grain size of castings by adjusting the temperature distribution of different parts of the mold, improve the quality of castings, and at the same time avoid environmental pollution caused by the use of modeling materials. The labor conditions of the workshop.

As the shape of the casting is different, the aluminum alloy gravity casting molds are also different. Even in the same part, different casting processes are used, and the mold forms are often different, but in any case, aluminum alloy gravity casting molds have their commonalities.

First, you must choose the right casting process.

The quality of the casting process is directly related to the quality of the casting and the rate of the production. Some mold manufacturing factories in China have begun to use the solidification simulation to carry out the casting process auxiliary design. Through the computer simulation of the filling and solidification process, the hot junction parts which are easy to produce casting defects are found and overcome, which is reliable for improving the casting process design. Sex, it is very important and effective to effectively prevent the mold from being reworked during the debugging process.

Second, the mold must have good heat capacity.

The thicker formwork and modules that meet the requirements are not only an effective guarantee for the life of the mold, but also have a very important role in the adjustment of the temperature field during continuous working of the mold. In order to reduce the cost and save the materials, some mold factories blindly reduce the effective thickness of the mold to achieve the purpose of reducing the weight. However, this not only greatly reduces the service life of the mold, but also makes the casting easy to deform and affects the dimensional accuracy of the casting. Will lead to the scrapping of castings, causing damage to the foundry, and more seriously damage the reputation of the mold factory itself.

Third, the mold must have a more reliable cooling system and a gas extraction system.

Through cooling, not only can labor productivity be effectively improved, but also the temperature field of the casting can be adjusted, and the cooling rate of the casting can be controlled, thereby affecting the internal structure and grain size of the casting and achieving the purpose of effectively controlling the mechanical properties of the casting. As the name implies, the gas is extracted artificially to discharge the gas inside the cavity to the cavity to reduce the possibility of pore defects in the casting. At the same time, the mold temperature can be adjusted in a small area by adding a vent plug, which plays an important role in preventing and overcoming the cracking and collapse of the aluminum alloy.

Fourth, there must be a mold positioning device and a convenient mold mounting system that match the casting machine.

The positioning device not only ensures the casting size, reduces the crevice and burr, but also ensures the normal operation of the casting machine. It can be said that there is no good positioning device without a good positioning device. The mold must be easy to install and disassemble. Because aluminum alloy>aluminum alloy gravity casting, the mold must be removed and repainted and repaired at regular intervals. If the disassembly is inconvenient, it will increase the labor intensity of the workers and take up more labor. Time, reduce production and efficiency.

For foundries, high-quality molds mean high-quality castings, which means lower costs, higher output and profits.

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The advantages and disadvantages of metal casting and sand casting!

Sand casting, as the name suggests, uses the sand mold as the basic mold, and the metal solution is poured to form the desired casting. At present, iron, steel and many non-ferrous metals can be obtained by this method. Its advantages are: low material prices, easy access, adaptability, and a wide range of applications, whether it is single or large-scale production.

Metal casting, also known as die casting. Unlike sand casting, which uses a metal mold, the mold can be reused hundreds of times. However, it has certain limitations, such as casting weight, shape and thickness.

The following are the specific advantages and disadvantages of metal casting and sand casting.

1. Advantages:

(1) Castings produced by metal type have higher mechanical properties than sand castings. The same alloy, the tensile strength can be increased by 25% on average, the yield strength is increased by about 20% on average, and the corrosion resistance and hardness are also significantly improved;

(2) The precision and surface finish of the casting are higher than that of the sand casting, and the quality and size are stable;

(3) The process yield of the casting is high, and the liquid metal consumption is reduced, generally saving 15 to 30%;

(4) No sand or less sand is used, generally 80-100% of the molding material can be saved; in addition, the production efficiency of the metal casting is high; the cause of the defects of the casting is reduced; the process is simple, and the mechanization and automation are easily realized.

2. Disadvantages:

(1) Metal type manufacturing cost is high;

(2) The metal type is airtight and has no retreat, which may cause defects such as insufficient washing of the casting, cracking or white cast iron parts;

(3) During metal casting, the working temperature of the mold, the casting temperature and casting speed of the alloy, the time the casting stays in the mold, and the coating used are sensitive to the quality of the casting and require strict control. .

Therefore, when deciding to use metal casting, the following factors must be considered: the shape and weight of the casting must be appropriate; there must be sufficient batch size; the deadline for completing the production task is permitted.

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Importance of casting molds in sand casting

The factory refers to the casting mold as the “mother of casting”, which can be said to be a high-level summary of the role and status of casting molds in casting production. It is called “mother”. One of them is because in the factory, all the castings are made by molding the sand mold, and there is no casting mold without casting. Second, the castings always have the “hereditary” of the casting mold. The dimensional accuracy of the casting, the surface roughness and even some casting defects are directly related to the quality of the casting mold.

(1) Dimensional accuracy

 

The castings are made according to the mold, and the dimensional error of the mold is reflected on the casting without exception. Especially for some complex castings, due to the use of multiple casting molds (outer mold and core box), the cumulative error will seriously affect the dimensional accuracy of the casting. The pursuit of “zero error” in casting molds is very important.

(2) Surface roughness

 

The smooth surface of the casting mold can not only improve the mold release performance, thereby reducing the core rejection rate, improving the production efficiency, and obtaining a smooth cavity or sand core, which is advantageous for obtaining a smooth surface casting.

(3) Casting defects

 

Some casting defects may be caused by poor quality of casting molds. For example, the surface of the mold has a negative degree of unevenness and unevenness, which will result in poor mold release, damage to the surface of the mold and even blisters; mold mounting deviation or locating pin (set) wear Causes misalignment, extrusion, and blisters; the random fabrication or installation of the gating system causes the metal flow to deviate from the process design requirements, which may cause defects such as porosity, shrinkage, and the like.

In casting production, process-casting mold-equipment is an inseparable system, and good process design relies on casting molds.

Similarly, a crappy process design may result in a well-machined casting mold being scrapped due to the inability to produce a qualified casting. The proper fit of the casting mold and equipment is just as important. Therefore, in determining the process plan and designing the process, it is necessary to start the preparation of the casting mold and equipment at the same time, that is, it is necessary to implement parallel engineering. Because of this, some domestic enterprises have introduced core boxes at the same time as the introduction of core making machines, and introduced some complex casting molds (such as cylinders) as well as process design.

In the modern society where innovation is becoming the main theme of economic development, the product renewal cycle is shortening and new products are emerging one after another. This requires the manufacturing industry to adapt to it and develop rapidly. High-quality, high-precision molds are an important guarantee for the production of high-quality castings.

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Heat treatment technology and method for casting mold

With the continuous improvement of science and technology, the mold industry has gradually become an indispensable product in the manufacturing and manufacturing enterprises, resulting in a large increase in the number of molds. As the number of molds increases, people gradually become more and more demanding. Among them, the casting mold is a typical representative of the mold, which uses the cavity to cast a fluid liquid, and after the liquid is cooled and solidified, the parts having the same shape and shape as the mold can be formed, and after the casting is completed, the products need to be taken out. The heat treatment is carried out in a heat treatment electric furnace, which not only affects the production efficiency, but also generates an oxide layer on the surface during the removal process, which not only affects the quality of the subsequent heat treatment, but also increases the loss of the material.

Mold manufacturing precision: Unevenness, incompleteness of the microstructure transformation and excessive residual stress caused by heat treatment cause deformation of the mold after heat treatment, assembly and mold use, thereby reducing the accuracy of the mold and even scrapping.

Mold strength: The heat treatment process is improperly formulated, the heat treatment operation is not standardized, or the state of the heat treatment equipment is not perfect, resulting in the strength (hardness) of the treated mold not meeting the design requirements.

Working life of the mold: Unreasonable structure caused by heat treatment, excessive grain size, etc., leading to the decline of main properties such as mold toughness, hot and cold fatigue performance, anti-wear performance, etc., affecting the working life of the mold.

Mold manufacturing cost: As the intermediate or final process of the mold manufacturing process, the cracking, deformation and poor performance caused by heat treatment will cause the mold to be scrapped in most cases, even if it can be used through repair, it will increase the working hours. , to extend the delivery time and increase the manufacturing cost of the mold.

It is the heat treatment technology that has a very close relationship with the quality of the mold, which makes these two technologies promote each other and improve together in the process of modernization. In recent years, the field of rapid development of international mold heat treatment technology is vacuum heat treatment technology, surface strengthening technology of molds and pre-hardening technology of mold materials.

First, the vacuum heat treatment technology of the mold

Vacuum heat treatment technology is a new type of heat treatment technology developed in recent years. Its characteristics are urgently needed in mold manufacturing, such as preventing oxidation and non-decarburization, vacuum degassing or degassing, eliminating Hydrogen embrittlement, thereby improving the plasticity, toughness and fatigue strength of materials (parts). Factors such as slow vacuum heating and small temperature difference between the inside and outside of the part determine the deformation of the parts caused by the vacuum heat treatment process.

According to the different cooling medium used, vacuum quenching can be divided into vacuum oil quenching, vacuum gas quenching, vacuum water quenching and vacuum nitrification. The main application of mold vacuum heat treatment is vacuum oil quenching, vacuum gas quenching and vacuum tempering. In order to maintain the excellent characteristics of vacuum heating of workpieces (such as molds), it is very important to select and formulate coolants and cooling processes. The mold quenching process mainly uses oil cooling and air cooling.

For the working face of the mold which is no longer machined after heat treatment, vacuum tempering is used as much as possible after quenching, especially vacuum hardened workpiece (mold), which can improve the mechanical properties related to surface quality. Such as fatigue performance, surface brightness, corrosion and so on.

The successful development and application of computer simulation technology (including tissue simulation and performance prediction technology) of the heat treatment process makes the intelligent heat treatment of the mold possible. Due to the small batch (even single piece) of the mold production, the characteristics of multiple varieties, and the high requirements for heat treatment performance and the fact that waste products are not allowed, the intelligent processing of the mold becomes a necessity. The intelligent heat treatment of the mold includes: clarifying the structure, material and heat treatment performance requirements of the mold: computer simulation of the temperature field and stress field distribution of the mold heating process; computer simulation of the temperature field, phase transformation process and stress field distribution of the mold cooling process; heating and Simulation of the cooling process; formulation of the quenching process; automated control technology for the heat treatment equipment. In developed countries, such as the United States and Japan, in the field of vacuum high-pressure gas quenching, technology research and development in this area has been carried out, mainly aimed at molds.

Second, the surface treatment technology of the mold

In addition to the reasonable cooperation of the mold with sufficient strength and toughness, the surface properties of the mold are crucial to the working performance and service life of the mold. These surface properties are: abrasion resistance, corrosion resistance, friction coefficient, fatigue properties, and the like. These performance improvements, relying solely on the improvement and improvement of the matrix material, are very limited and uneconomical, and surface treatment techniques can often achieve twice the result with half the effort, which is why surface treatment technology has developed rapidly.

The surface treatment technology of the mold is to systematically change the morphology, chemical composition, microstructure and stress state of the mold surface by surface coating, surface modification or composite treatment technology to obtain the desired surface properties. From the way of surface treatment, it can be divided into: chemical methods, physical methods, physical and chemical methods, and mechanical methods. Although new treatment technologies are being developed to improve the surface properties of molds, most of the major nitriding, carburizing and hardening film deposits are used in mold manufacturing.

The nitriding process includes gas nitriding, ion nitriding, liquid nitriding and the like. In each type of nitriding method, there are several kinds of nitriding techniques, which can adapt to the requirements of different workpieces of different steel types. Because the nitriding technology can form a surface with excellent performance, and the nitriding process has a good coordination with the quenching process of the die steel, and the nitriding temperature does not require intense cooling after low nitriding, the deformation of the mold is extremely small, so the surface strengthening of the mold The use of nitriding technology is earlier and the most widely used.

The purpose of mold carburizing is mainly to improve the overall strength and toughness of the mold, that is, the working surface of the mold has high strength and wear resistance. The technical idea introduced here is to reduce the manufacturing costs by replacing the higher-grade materials with lower-grade materials, ie by carburizing and quenching.

The most mature sclerosing film deposition technology is CVD and PVD. In order to increase the bonding strength of the surface of the film workpiece, various enhanced CVD, PVI) technologies have been developed. The hardened film deposition technology was first applied to tools (tools, cutting tools, measuring tools, etc.), and the effect was excellent. A variety of tools have been coated with a cured film as a standard process. Molds have been coated with hardened film technology since the 1980s. Under the current technical conditions, the cost of hardened film deposition technology (mainly equipment) is still high, and it is still only applied to some precision and long-life molds. If the method of establishing a heat treatment center is adopted, the cost of coating the cured film will be greatly reduced. If more molds adopt this technology, they can improve the overall level of mold manufacturing in China.

Third, the pre-hardening technology of the mold material

The heat treatment of the mold during the manufacturing process is a process that most molds use for a long time. Since the 1970s, the idea of ​​pre-hardening has been proposed internationally, but due to the rigidity of the machine tool and the constraints of the cutting tool, the pre-hardening The hardness of the mold cannot reach the hardness of the mold, so the research and development of the pre-hardening technology is not large. With the improvement of the performance of machine tools and cutting tools, the development of pre-hardening technology for mold materials has accelerated. By the 1980s, the proportion of pre-hardened modules used in plastic molds in industrialized countries in the world has reached 30% (currently More than 60%). In the mid-to-late 1990s, China began to use pre-hardened modules (mainly imported products).

Pre-hardening technology for mold materials is mainly developed and implemented by mold material manufacturers. By adjusting the chemical composition of the steel and equipped with the corresponding heat treatment equipment, it is possible to mass produce pre-hardened modules of stable quality. In China, the pre-hardening technology of mold materials started late and has a small scale. At present, it cannot meet the requirements of domestic mold manufacturing.

The use of pre-hardened mold materials can simplify the mold manufacturing process, shorten the manufacturing cycle of the mold, and improve the manufacturing precision of the mold. It is foreseeable that as processing technology advances, pre-hardened mold materials will be used for more mold types.

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Lost mold of motor casing

R&D background：

As of 2017, China’s total installed capacity of electric motors has reached more than 400 million kW, and the annual power consumption has reached 1.2 trillion kWh, accounting for 60% of the country’s total electricity consumption, accounting for 80% of industrial electricity consumption, including fans, pumps and compressors. The total installed capacity has exceeded 200 million kW, and the annual power consumption has reached 800 billion kWh, accounting for about 40% of the country’s total electricity consumption. Therefore, the energy saving requirements on the motor are extremely great, and it is also the place where the energy saving effect can best be reflected.

As an important device for electromechanical energy conversion, the motor is the basic component of electric drive. It has a wide range of applications, many varieties of products and complicated specifications. Its product characteristics determine that the concentration of the industry is not high, and the production enterprises and the sub-sectors involved are more. Obvious periodic, regional, seasonal characteristics. As of 2018, the domestic production and supporting manufacturers of differential and medium-sized motors are more than 2,000, which has become an indispensable basic product in the national economy and national defense modernization. There are many manufacturers in the domestic differential and small and medium-sized motor industry. The market competition is mainly reflected in the technical content, price and production scale of the products. Due to the imperfect market mechanism, the price competition in the industry is fierce and has been a benign development of the industry. To adverse effects. With the enforcement of the motor energy efficiency label, the emergence of the market’s survival of the fittest and the further strengthening of the industry barriers, the price competition will gradually weaken. Foreign host manufacturers also purchase motor housings in large quantities in China, Siemens, ABB, Dongyuan, South Korea Hyosung and so on.

In this context, the invigorating motor casing production plant has sprung up on the land of China, and the various motorized areas in China’s motor market have been approved by the motor main engine factory. , Taizhou, Jingjiang, Wuxi, Jiamusi, Nanyang, etc., the construction of large and small lost foam production line thousand, Y series 80-400 model motor shell lost foam casting technology is mature and stable, lost foam process The casting process of the motor casing is fully embodied and the advantages are strong. First, the heat sink is straight and smooth, the spacing is the same, the appearance of the casting has no stitching line, smooth and smooth. Second, the casting precision reaches the CT8 standard, the roundness is high, and the machining allowance is small, as long as the white mold is not affected, the weight can be controlled. Third, the entire production process is small, the amount of castings is small, the corresponding labor cost of the production of castings is low, and the casting price has a large advantage. The commonality of the remaining lost foam casting advantages is the same for the lost flame casting of the motor casing, such as good casting environment, green and environmental protection, simplified process, high density of castings and so on.

Motor housing mechanism diagram

Process requirements：

According to the above analysis, the six-point requirement for casting the motor casing using the lost foam process:

First, the direction of the heat sink is preferably horizontal and vertical, that is, the orientation of the heat sinks in four directions is uniform, although the radial heat sink can also open the mold, but the motor shell of this structure is recommended to be a manual mold. .

Second, the top thickness of the heat sink is guaranteed to be 3.2-5mm, and the height of the rounded fins reserved for R1.5-2mm is 30-60mm higher than the outer round surface.

Third, try to simplify the molding difficulty of the motor casing, and straighten the screw cover of the fixed end cover in four directions.

4. The grounding mark is placed in four orientations.

5. Optimize the inner core structure and try to avoid the possibility of undercutting.

6. The position and orientation of the junction box are as consistent as possible with the core pulling direction, simplifying the structure and avoiding bonding.

According to the casting process requirements of the motor casing, it is not difficult to find that the lost foam casting is more difficult.

First, the heat sink around the motor casing is thinner and taller, and the casting is prone to cold separation.

Second, the same roundness of the stator surface of the intermediate installation should be ensured to prevent deformation and excessive rounding.

Third, the motor shell casting generally adopts the top casting process, and the exhaust slag in the casting process is well treated. Based on the above analysis of the difficulty of the lost foam casting of the motor casing, the design points of the lost mold of the motor casing are mainly reflected in the classification, processing and insert material selection of the heat sink around the motor casing product. material.

Mold design：

In order to solve the above problem of the lost foam casting process of the motor casing, it is necessary to design a lost foam mold for the motor casing, so that the white mold of the motor casing can meet three requirements:

First, the heat sink is fully formed, evenly matured, without gas traces, and without jagged.

Second, the motor shell white mold body looks beautiful, smooth, no granular or superheat caused by uneven heating.

Third, the molding operation is simple, the product consistency is good, the foam pattern has high precision, and the molding effect is good.

Mold assembly drawing

According to the mold assembly diagram:

Design a three-open mold motor shell lost mold, the mold mechanism includes automatic gun, upper mold, side core insert, core cylinder, lower mold, lower mold, upper core, upper mold sealing, positioning Plate and spring mechanism. The upper mold sealing plate is connected to the upper mold cavity of the upper end surface of the upper mold to form a sealing structure; the upper mold core is hollow and communicates with the inner cavity of the upper mold air chamber and the mold cavity; the lower mold includes a lower mold air chamber , the lower mold chamber 2 and the core; the lower mold chamber is a double-layer structure; the lower mold chamber 1 and the lower mold chamber are connected by a spring mechanism; the lower core is fixed to the lower mold chamber 2 and the upper core Symmetrically disposed; the inner cavity of the lower die chamber has four side core inserts uniformly distributed along the circumference for forming the heat sink around the motor casing; and the corresponding four side core inserts are respectively provided with core pull cylinders; The four core pulling cylinders are respectively fixed on the outer side of the lower mold one; the side core pulling inserts are respectively connected with the pistons of the corresponding core pulling cylinders through the guiding columns to form four side core pulling inserts. Under the action of four core-pulling cylinders, the inward movement is closed to form a mold cavity or an outwardly moving structure; the top of the upper mold sealing plate is fixed with an automatic material gun; the lower end of the automatic material gun passes through the inner cavity of the upper mold air chamber. The upper core is slidably connected to the upper mold chamber by bolts and springs; one end of the spring is connected with the upper mold core, and the other end is connected with the upper mold air chamber by bolts, and the lost mold is used in the automatic mold. When the gun is filled, the upper core and the lower core are closely adhered under the action of the spring force, and the upper mold chamber and the lower mold chamber are not in contact, thereby realizing the structure of double pre-opening.

The upper mold chamber has a positioning table around the chamber, and the lower mold chamber has a positioning groove that cooperates with the positioning table on the upper mold chamber; the positioning chamber and the lower mold chamber on the upper mold chamber The positioning grooves have a guiding mechanism for positioning and guiding the mold when the lost mold is closed.
The parting surface of the upper mold chamber has a reserved hole for the passage of hot steam and cooling water.

The outer side of the upper mold chamber, the lower template and the lower mold chamber, the lower template and the lower mold chamber, and the lower mold and the lower core contact surface each have a reserved hole through which hot steam and cooling water pass.

The three-opening structure of the motor casing is to make the lower die chamber closed without leaking and to achieve the effect of the limit side core insert. The three-opening structure of the motor casing is composed of an upper die, a lower die 1 and a lower die 2. The lower die 1 and the lower die 2 are combined by a spring mechanism to form a lower die chamber. The finite-position bosses at the two ends of the four side core inserts are inserted into the upper die limit groove and the lower die limit groove respectively in the mold clamping state, and the side draw is prevented. The core insert is retracted. When filling, the upper mold is lifted by 20mm, then the lower mold spring mechanism bounces the lower mold. The lower side of the 12mm insert is separated from the lower mold. At this time, the 20mm pre-opening of the filling is performed, which will make the motor shell foam-like. The heat sink is full and flawless. When the mold is opened, the upper mold is lifted, and the upper mold limit groove is separated from the four side core inserts, the spring structure springs up the lower mold, and the core cylinder structure causes the four links to drive the side core insert to retreat. When the motor shell foam is taken out, the side of the motor shell is formed. The three-opening structure of the motor casing is composed of an upper die, a lower die 1, a lower die 2 and a spring mechanism. The spring structure is composed of a lower die, a lower limit hole, a lower die second limit hole, a guide post and a spring. The spring structure realizes the first opening of the lower mold 1 and the lower mold 2. The molding machine drives the upper mold to move upward to make the upper mold and the lower mold a second mold opening, two mold opening, and a three-layer mold structure. The mold, the lower mold, and the lower mold 2) are combined into a three-open mold structure of the motor casing, which realizes the perfect molding of the motor shell foam.

The new structure of the three-opening mold of the motor shell lost mold. The automatic feeding is realized by the automatic gun, which ensures that the heat sink of the motor shell foam pattern is full and has no defects; the side core pulling insert and the core pulling cylinder realize the automatic core pulling, the set hot steam through hole and the cooling water. The through hole realizes automatic heating and cooling, greatly improves the forming efficiency of the white mold, reduces the labor intensity and production cost of the worker, ensures the consistency of the white mold forming, has simple molding operation, good product consistency, high precision of the foam pattern, Good molding effect.

Detailed ways：

The working process of the three-opening structure of the motor casing is:

The first step is to hoist the motor shell mold between the four guide columns of the vertical molding machine, and fix the upper mold air chamber to the upper template (ie moving template) of the molding machine through the pressing plate, and press the lower mold air chamber through the pressing plate. Fixed on the lower die plate of the vertical forming machine (ie, the fixed die plate), turn on the vent pipe and the feed pipe of the automatic gun, turn on the vent pipe of the positioning cylinder and the core cylinder, and open the upper die chamber and the lower die. a hot steam pipe and a cooling water pipe of the air chamber;

Step 2: Debug the mold, adjust the opening and closing stroke of the vertical molding machine to the stroke suitable for the mold to open and take out the foam, and then press the mold tightly by the vertical molding machine to ensure smooth opening and closing of the mold without any stuck phenomenon; Material time, hot steam pressure, cooling time;

The third step: in the filling stage, when the mold is charged by the automatic gun, the upper mold chamber drives the upper core into the mold cavity after the side core insert is closed. At this time, between the upper mold and the lower mold Leave a gap of 6-8mm, and the upper core and the lower core are closely attached under the action of the spring force, which is equivalent to the mold cavity is 6-8mm larger, it is easier to fill the mold cavity, making use of The automatic gun fills the pre-expanded foam particles into the mold cavity by the negative pressure method, that is, the pre-opening feeding is realized, and after the feeding is finished, the upper mold and the lower mold are completely closed, in the process, the heat sink is partially The unfilled part is filled with the unfilled part when the vertical molding machine drives the upper mold downward to ensure that the foam particles are completely filled into the mold cavity, thereby ensuring the formation of the foam pattern heat sink; Pass hot steam, keep pressure, until the foam material is fully expanded, matured, blended, formed, turn off the steam valve, pass the cooling water, cool, set, open the drain valve, drain the cooling water, open the upper and lower molds first, complete Separation of core and motor shell foam The positioning cylinder drives the positioning plate to move downward, and moves the positioning boss to the lower side of the side core insert, and the core pulling cylinder drives the side core insert to disengage the heat sink of the motor shell foam and the side core insert, completing The release of the heat sink, the upper and lower molds are opened to the mold adjustment stroke, and the foam pattern is taken out from the lower mold to complete the mold opening action; when the mold is closed, the side core insert is closed first by the core cylinder, and the upper and lower molds are closed again. The positioning cylinder of the lower mold drives the positioning plate to complete the positioning limit of the opposite side core insert, ends the mold clamping, refills, and completes a molding process.

Note: The above mold structure Luoyang Liushi Mould Co., Ltd. has applied for a patent, counterfeiting will be investigated!

Invention patent number:

ZL 2012 1 0303995.X
ZL 2016 1 0057821.8
ZL 2016 1 0216915.5

Utility model patent number:

ZL 2012 2 0423206.1
ZL 2012 2 0423548.3
ZL 2012 2 0423999.7
ZL 2012 2 0423475.8
ZL 2016 2 0084122.8

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Special requirements for molten iron in lost foam casting

The quality of molten iron has a great influence on the lost cast iron parts. The influence of improper misalignment temperature on the defects of lost cast iron parts and the requirements of hot metal quality of different cast iron parts are analyzed. The measures and adjustment methods to prevent casting defects are analyzed. Lost Foam Casting Because the foaming mold (white mold) gasification consumes the heat of the molten iron, it is required to increase the temperature of the molten iron. Therefore, the iron collision smelting must be properly adjusted to obtain the same or better castings as the sand burning. organization.

1. Increase the pouring temperature

After the molten iron is introduced into the cavity, the casting white mold (EPS, STMMA) with the lifting system must first be gasified, decomposed and cracked. For this reason, the temperature of the sewing is generally 30-50″C higher than that of the sand casting. The squash iron piece is even increased to 80 ° C. The ductile iron temperature range is: 1380-1 480 . C. Gray cast iron is 1 360- 1 420″ C, alloy cast iron (anchor white iron) is 1 380- 1450 .C. Increasing the heat of the scratching temperature should be just consumed by burning the white touch. After that, the temperature of the molten iron should be lowered to the temperature of the sand casting, so that the qualified castings can be guaranteed. Therefore, in the actual production process, the process must be based on the unit. Conditions such as equipment find the appropriate tip temperature.

(1) Defects caused by excessive pouring temperature

a. sticky sand
Excessive shovel temperature is likely to cause chemical sticking and mechanical sticking.
Chemical grit: The sand in the sand contains fine sand, dust, especially quartz sand, which is easy to react with the iron smelt to produce chemical grit. It is extremely difficult to clean $ mechanical sand: excessive iron temperature The white paint layer peels off, cracks, softens and ruptures, the molten iron passes through cracks, cracks in the gaps, and the speed of the threading is fast, the temperature of the molten iron is high, and the degree of sticking sand is more serious. The most prone to occur is the bottom or side of the casting and the hot joint zone. The sand is not easy to be compacted, especially at the corners. The joints of the string castings are easy to form mechanical sand with mechanical mixing of the iron and the sand.

b. Back spray
The gasification mode EPS (or STMMA) pattern casts a fierce pyrolysis reaction under the action of excessively high temperature iron.
75 – 1 64 ‘C : Thermal deformation, high elastic state, the mold begins to soften and expand and deform. The air and foaming agent in the cell begin to escape, the volume shrinks, and the cell loses its viscous flow. Polystyrene steroid
164 – 316″C : Melting, the molecular weight of the flow state is unchanged g
316 – 576 “C: depolymerization, gasification state, when the weight begins to change, the long-chain polymer breaks into a short-chain low-molecular polymer, and the gasification reaction begins, producing a polyethylene monomer and its Small molecular weight derivatives constitute a vaporous product;
567-700″C: cracking, gasification combustion, precipitation gas increased significantly, low molecular weight polymer cracked into a small amount of hydrogen (0.6%), C02, CO small molecular weight saturated, unsaturated hydrocarbon g
700-1350’C: Extremely cracked, gasified and burned, and the decomposition of low molecular weight polymer is gradually completed. At the same time as the production of a large number of small molecular hydrocarbons, hydrogen and solid carbon are decomposed; the hydrogen content is precipitated at 1 350 ‘C. Up to 32%; in the presence of aerobic conditions with the presence of free carbon and flames
150- 1SS0 ‘C: Rapid cracking, combustion gasification, rapid cracking of low molecular weight polymer, precipitation of hydrogen up to 48%; at the same time the combustion process is more intense, and a large amount of free carbon and a flame generated by volatile gases are precipitated. If the pouring temperature is too high, the decomposition and cracking will be rapid, and the amount of gas will increase sharply. If the vacuum pump is too late to suck and discharge, the gas will not be able to escape, which will cause back-spraying, which may cause injury and cause accidents.

c. stomata
It can be seen from the above that the white mold is decomposed and cracked by the heat of the molten iron, and a large amount of gas is generated. When the temperature is too high, the well is rushed to generate gas, and the gas dispersion expands into the cavity, and the sand type cannot be discharged in time to enter the molten iron. Stomata, which is large and numerous (cluster) and is accompanied by carbon black. Too high pouring temperature, excessive heat burning sand type makes the cavity, sand type produces more gas, and can not be discharged from the mold and iron in time, it will produce pores.
Injecting ductile iron, using white mold STMMA (EPMMA), its gas generation is larger than EPS, more, more concentrated – the time zone is very cracked, more attention should be paid to the sharp generation of pores and timely exhaust (adjustment) Vacuum pump suction speed, control of iron flow and speed). In addition, the amount of gas generated by the decomposition of the white mold is large, rapid, rapid, the exhaust speed of the mold is not enough, the vacuum pump suction, the speed is insufficient, the gas impact mold, resulting in mold anger, the collapse of the casting can not be a good product . It can also cause other defects in lost foam casting: nodule, shrinkage, shrinkage, hot slag hole, etc.

(2) Defects caused by low temperature of the scratching

Wrinkled skin

The main influence is that the pouring temperature is too low and the heat is insufficient. The decomposition, cracking and pores cannot be completed. The white mold pyrolysis is not complete, the gas phase product is reduced, and the liquid phase and solid phase product increase are more conducive to the appearance of wrinkled carbon deposits. The temperature of the iron liquid is lower than 1420 – 1480 ‘C, which is more likely to produce wrinkles, carbon deposits and carbon black for thin-walled iron castings. Cold insulation (for fire), heavy leather, pouring white mold is heated and decomposed, to absorb a large amount of heat, too low pouring temperature provides insufficient heat to decompose the white mold, so it is necessary to absorb heat from the iron shovel, so that the iron shovel The temperature is too low (often appearing in the wall thickness of the casting, the distance is long); the gas produced increases to prevent the filling of the molten iron, which in turn reduces the fluidity of the molten iron, thus causing cold separation, heavy skin, and pouring. When the two streams of molten iron are filled with the top of the casting type, the temperature of the iron shovel has been lowered to a lower level and cannot be fused. When the casting is started, the cold separation is likely to occur when the temperature of the casting is lower. When the pouring temperature is low, a thin iron shell (film) is formed near the casting surface, and after the subsequent iron filling, there is not enough heat to melt the film (shell), and a heavy skin defect occurs. In addition, the temperature of the pouring is too low, and the molten iron in the cavity does not have sufficient heat, so that impurities, slags, and wastes in the fast liquid cannot be raised to the top surface in a timely manner, thereby forming defects such as inclusions and slag inclusions.

2, adjust the iron liquid

Although there are differences in the heat capacity (specific heat) of different types of dry sand, the cooling rate of the mold is slower than that of sand casting. For gray cast iron, there is less tendency to white mouth. For cast iron, dry sand casting The rigidity of the type is not as good as that of the metal type (or the type of sand-covered metal). When casting the white cast iron of the anchor, the surface of the casting is not as good as the hard shell of the casting formed by the metal type, so the iron shovel or corresponding measures should be adjusted.

For lost foam casting, in order to increase the temperature of the threading, it is generally smelted by induction furnace or cupola-induction furnace.
(1) Gray cast iron
a. Cast iron parts mainly based on toughness, iron liquid plus inoculation treatment of 75% Si-Fe, or adding a small amount of aluminum, aluminum, copper for microalloying.
b. When the mechanical properties of stiffness and strength are the main requirements, reduce the carbon content, increase the amount of spheroids, and micro-synthesis of Cr and Mo to promote the increase of the amount of spheroids.
(2) Ductile iron
Smelting in an induction furnace increases the temperature of the molten iron. It is necessary to use ductile iron and spheroidizing agent suitable for induction furnace melting.
(3) Anchor anti-wear cast iron
Due to the slow cooling rate of the lost foam casting, the structure and properties of the white iron are changed and refined by the heavy rare earths; copper, front dart, silver iron microalloying
Good matrix structure performance; if the wear resistance is insufficient, adjust the size, shape and distribution of the matrix carbide to change (by adding Ming, button, sensitive, sputum, etc.).
Castings of various cast irons are affected by the slow cooling rate of the lost foam casting, which can be adjusted by the corresponding measures mentioned above.

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How to obtain a uniform density of lost foam pre-expanded beads

The density of the lost foam pre-expanded beads determines the density and degree of fusion of the various parts of the die, and the quality of the die determines the quality of the casting. The main factors affecting the density of the pre-expanded beads of the lost foam are the quality of the raw materials and the performance of the pre-foaming machine. The use of raw materials that meet the requirements of the lost foam process and the high-performance pre-expanding machine for the lost foam can achieve the same density disappearance. Mold pre-expanded beads.

Loss-mode pre-expanded beads of uniform density are the basis for the production of high quality molds. As the first process of lost foam casting, the pre-issue t-package is the most important part of lost foam casting.

1. The importance of the quality of the lost mode die

1. 1 The importance of the quality of the lost mode die
As one of the most advanced casting processes in the world, lost foam casting can achieve precision casting precision.

The lost foam casting line consists of three parts: self-region, yellow zone and black zone. From the pre-fabrication of raw materials to the casting of castings, after a series of production processes, there are many factors that affect the quality of the chess pieces. Kind. According to the statistical analysis of the defects of the lost foam casting, 70% of the casting defects are caused by the poor quality of the die. Once the die is manufactured, its quality is difficult to adjust in the subsequent process. The quality of the die determines the quality of the lost die casting. The high quality die is the primary prerequisite and guarantee for the production of high quality castings.

1. 2 Main features of high quality lost foam die

1) The die is evenly filled and the density of each part is consistent.
2) The consistency of the beads is consistent
3) The surface of the die is smooth and flat
4) Accurate die only inch

1.3 How to get high quality lost mode die

1) Use suitable materials that meet the lost foam production process.
2) Using a high-performance foaming pre-expansion machine to obtain pre-expanded beads of uniform density, thus ensuring uniform density and uniformity of the die.
3) Using a high-performance automatic mold and mold for the lost-foam mold, the scientific mold forming process is designed to ensure that the parts of the mold are evenly filled, and the precise size and perfect bead fusion degree are obtained.

2. Effect of pre-expanded bead density on die and casting

2.1 Effect on density, fusion and surface finish of the die
The pre-expanded beads have the same density and uniform particle size, and the density of each part of the produced die is uniform, the degree of fusion is uniform, especially the surface finish is high, the casting defects can be reduced, and the quality and surface finish of the casting can be improved.

2.2 Influence on castings of multiple pieces
In the lost foam production process, more than 85% of the models need to be sliced ​​and then bonded into a complete model. Generally, the die is divided into 2-3 pieces, and the complex one needs to be divided into 4- 5 pieces. If the density of the pre-expanded beads is inconsistent when the sheets are formed, the density of each part of the mold after bonding may be deviated. The density deviation of each sheet exceeds 0.6 g / liter, which will cause scratch casting defects. The density deviation of each part of the model is large. When the temperature and speed of the casting are the same, the burning speed, combustion decomposition and gas generation of the model are constantly changing. It is easy to bonfire (back spray) during casting, and the casting is easy to cause wrinkles ( Defects such as carbon deposits, pores, oversize and deformation.

3. Analysis of the influence of the quality of raw materials on the density of pre-expanded beads

3.1 Quality of raw materials
At present, there are no EPS materials for the lost molds in China, and most of the lost foam companies use EPS materials for packaging. Compared with the EPS material used in the lost mold of Styrochem, the stability of the raw material is slightly worse.

3. 1. 1 Feng Li Trail
The particle size consistency of the domestic EPS raw materials is poor, and the particle size fluctuation of the beads after pre-expansion is large, which will affect the degree of fusion and surface roughness of the various parts of the die, and reduce the quality of the casting.

3. 1. 2 amylose content
The content of pentamidine is an important factor affecting the quality of pre-expansion of beads. The content of pentamidine in EPS is most suitable for pre-expansion at 5.9%-6.5%. The content of pentamidine in the EPS is inconsistent, and it is necessary to constantly adjust the parameters of the pre-foaming machine to stabilize the density during pre-carrying. There are many factors affecting the change of the content of pentane, such as: the fluctuation of the content of pentamidine in the domestic EPS itself is large. The volatilization of the amylose v. caused by the change of the temperature during storage and transportation of the raw material manufacturer. The pentylene is volatilized.

After the same batch of EPS raw materials arrived at the factory for 7 days, 3 bags were randomly selected for testing. The content of pentamidine in the 3 bags of raw materials was inconsistent (9%, 7.8%, 7.3%, respectively), and the results of 14 days, 21 days… 54 days later It shows that in the same batch of EPS raw materials, the content of pentamidine and the rate of volatilization of amylose are also different. Therefore, it is difficult to produce a high-quality die using a material having a large particle diameter error and an inconsistent EP material.

4. Analysis of the effect of foaming machine performance on the density of pre-expanded beads

After long-term application, domestic lost foam enterprises have realized the importance of bead pre-expansion and die-forming in lost foam casting.

4.1 Performance analysis of domestic pre-expander

1) Steam pressure control is inaccurate, the degree of drying of the beads is inconsistent, and the curing time cannot be accurately controlled. The pre-expanded beads have a density fluctuation of 1.3 – 2.4 g.
2) The accuracy of the feed weighing is low, the weighing deviation is 8 – 9%, so that each time
The weight of the beads entering the pre-expansion chamber varies, and at the same vapor pressure and pre-expansion time, the higher the feed, the higher the density, and the lower the feed, the lower the density.
3) No density detection and feedback control device, manual adjustment of pre-fire gun parameters based on manual experience.
4) Sometimes pre-expanded beads are agglomerated to form a dead material.
5) The beads remaining in the pre-expansion chamber after each pre-expansion cannot be removed. When the content of pentamidine in these beads volatilizes to a lower level, a dead material is formed, and the dead material cannot be in the molding machine. Perform secondary foaming. When the dead material is mixed into the next batch of pre-expanded beads and transported to the molding machine to form the die, they will shrink, resulting in inconsistent bead density and degree of fusion inside the die, and formation of holes in the surface of the die. , causing scratch casting defects, causing loose casting and slag holes.

5. Germany Teubert lost mode special pre-expansion hunger

Germany Teubert intermittent foaming mold pre-foaming machine, fully automatic pre-foaming production, the operator only needs to input the target density of the beads into the control computer, the system will automatically adjust the parameters and control the density.

Main performance characteristics:

1) Fully automatic production, suitable for EPS and copolymer pre-expansion, foam chamber temperature can be adjusted from 70 °C -13O”C, steam chamber can be adjusted at any time, steam pressure control accuracy O.Olbar The density fluctuation after pre-expansion of domestic beads is: 1:0.3 g, the density fluctuation after pre-expansion of imported beads is: 1:1 g

2) Proprietary density control device, fully automatic detection of the density of pre-expanded beads per beat, and feedback to the PLC to adjust various parameters, full-closed detection and adjustment parameters, reducing external factors on the pre-foaming machine Interference ensures the accuracy of density control.

3) Automatic weighing and adjusting the weight of the beads entering the pre-expansion chamber each time, the feeding weighing accuracy is high, and the weighing deviation is less than 2%.

4) The proprietary pre-foaming chamber design facilitates the cleaning of residual beads and avoids the mixing of dead materials into the next batch of pre-expansion operations, ensuring the quality of the die and castings.

5) The fluidized drying bed with adjustable temperature ensures the uniform drying degree of the beads and better controls the curing time.

6. How to get the density – honey i Xiao lost mold pre-package rough recommendations

6.1 Selection of raw materials
It is preferred to select the special materials for the lost foam with uniform particle size and stable pentane content; or to meet the requirements of the lost foam process, select raw materials with smaller particle size and relatively stable pentamidine content, and reduce the raw material to the die and casting. The impact of quality.

6. 2 Storage of raw materials
When the raw materials are shipped from the factory, they are packed and transported in a sealed container. When the raw materials arrive at the factory, they are stored in a special constant temperature storage room. The temperature of the storage chamber is stabilized at 15″C -20 .C, which is as slow as possible. The volatilization rate keeps the content of pentamidine stable.

6.3 Selection of pre-foaming machine
The performance of the domestic pre-foaming machine is not good, but the price is straight, the imported pre-foaming machine has superior performance, but it is expensive. The performance of the pre-explosive gun is an important factor affecting the uniform density of pre-expanded beads. Try to use a high-performance lost-mode special pre-emphasis machine to obtain stable high-quality pre-expanded beads. After selecting the right raw materials and the pre-emphasis machine for the lost foam, the pre-expanded beads with uniform density can be obtained, which makes it possible to produce high-quality molds and lays a foundation for the production of high-quality castings.

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