Invitation card

Dear Sir,Good day !

We hereby sincerely invite you and your company represeniatives to visit our booth at NEW CAST 2019 5th International Trade Fair for Castings Dusseldorf.

We’re the biggest mould manufacture and foundry in China,our main business are Lost Foam Mould, Moulding Line Mould(KW,HWS, GF,DISA), Cold Core Box Mould, Hot CoreBox Mould and Aluminum Alloy Castings.

It would be a great pleasure to meet you at the exhibition.We expect to establish long-term business relations with your company in future.

Dusseldorf Exhibition Center

Booth Number : 14A44-03

Date 25.06.-29.06.2019.

Invitation card

 

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Sand casting method, full solution of technical parameters

The sand molding process plays an important role in the casting production process, which directly affects the quality level, production cost, production efficiency and environmental pollution degree of the casting. The sand casting method can be divided into two categories: physical hardening modeling method and chemical modeling method.

The physical hardening modeling methods mainly include clay sand type, solid casting, V method modeling method, and freezing modeling method. Among them, clay sand type is divided into wet type, dry type and dry type. The solid shape and the V method are a binderless method (dry sand) and are formed by vacuum molding. The frozen molding method uses water as a binder.

The chemical modeling methods mainly include: water glass sand type, resin sand type and the like. They can be divided into three types: heat hardening, self hardening, and air hardening. Water glass is an inorganic binder and resin is an organic binder. When selecting a sand molding process, the following principles should be followed:

1. Should be able to guarantee the quality requirements of castings

At present, the widely used molding processes mainly include clay wet sand technology, CO2 blown hard water glass sand process, organic ester self-hard water glass sand process, and acid self-hardening furan resin sand process. In recent years, the hardening sand molding process of ester hardening phenolic resin has also been promoted and applied to a certain extent. The characteristics of these modeling processes, the impact on the quality of castings and the scope of application are as follows:

(1) Clay wet sand process

The advantages of the clay wet sand process are:

A. The raw materials used are cheap and the sources are abundant.

B. The shape is convenient, the sand type does not need to be dried, the casting production cycle is short, the efficiency is high, and it is easy to realize mass production.

C. The bentonite which has not been dehydrated in the recycled sand can be restored after mixing with water. The old sand has good recyclability and less investment in recycling equipment.

D. After a long-term application, a series of modeling equipment has been developed.

E. The dimensional accuracy of castings produced by general modeling is no less than that of chemical self-hardening sand. The high-precision modeling methods such as injection molding, air-punching and static pressure modeling can produce dimensional accuracy comparable to investment casting.

(2) CO2 blowing hardened water glass sand process

Ordinary CO2 blowing and hardening water glass sand process is the earliest rapid prototyping process in the field of water glass binder. Its main advantages are:

A. The device is simple, easy to operate and flexible to use.

B. the binder is non-toxic and tasteless, and the cost is low.

C. The sand type has high temperature repellent property and the shrinkage stress of the casting is small.

D. The binder system does not contain S, P, N, and there is no sulfur increase on the surface of the casting.

The CO2 blowing hardening water glass sand process has been widely used in the production of most steel castings at home and abroad, and is mainly used for the production of medium and small steel castings. However, the shortcomings of the CO2 blown hardened water glass sand process are also very obvious:

A. The sand type (core) has low strength and the water glass is added in a high amount.

B. large water content, easy to absorb moisture, poor hard penetration in winter.

C. The sand type (core) has poor collapsibility, the old sand is difficult to regenerate, and a large amount of old sand is discarded.

In the past, the problem of collapsibility and reuse of old sand was not well solved, which affected the expansion of water glass sand to a certain extent. In recent years, people have made breakthroughs in deepening the understanding of the basic composition of water glass and the essence of “aging” phenomenon and new hardening processes (such as vacuum-exchanged CO2 gas hardened water glass sand process), which are maintained in core sand. Under the condition of sufficient process strength, the high-quality natural silica sand with low content of mud can reduce the amount of water glass to 4.0%, so that the long-term existence of water-glass sand is poor, and the old sand can not be reused. Good solution. Water glass old sand recycling equipment has also matured, and water glass sand has developed a good momentum.

(3) Organic ester self-hardening water glass sand process

Organic ester self-hard water glass sand is widely used in cast steel and has certain applications in cast iron. The main advantages of this hardening process are:

A. The molding sand has a high strength, and the amount of water glass added can be as low as 2.5-3.5%.

B. Sand type (core) has good collapsibility, and the old sand dry regeneration rate is ≥80%.

C. The sand type has good thermoplasticity and low gas generation, which can overcome the defects such as cracks and pores which are prone to occur when the furan resin sand is used to produce steel castings. The quality and dimensional accuracy of the castings are comparable to those of the resin sand.

D. The production cost is the lowest and the working conditions are good in all self-hardening sand processes.

The hardening process still has the following disadvantages: the core sand hardening speed is slow, the brittleness is large, and the fluidity is poor.

(4) Acid self-hardening furan resin sand process

Acid self-hardening furan resin sand and organic ester self-hardening water glass sand are typical representatives of organic binder chemical self-hardening sand and inorganic binder chemical self-hardening sand. The common features of chemical self-hardening sand process are:

A. After the sand type hardens, the mold sand does not need high wet strength, the sand has good fluidity, the sand type has high strength, the deformation is small, the tooling is simplified, the shape is simple, the sand type does not need to be dried, and the dimensional accuracy of the casting is significantly improved, which can reach CT8~ Level 10, casting defects are also less.

B. Chemically hardened sand generally uses a liquid self-hardening binder. Therefore, it requires high quality of the original sand to minimize the amount of binder added.

C. Since the hardening of the binder is an irreversible chemical reaction, it cannot be re-used as simply as clay sand. When used in large quantities, a relatively complete old sand regeneration system must be used.

D, the model structure and surface quality requirements are higher, in order to demould.

The self-hardening sand process is mainly suitable for small batch or batch production of large-scale castings, and there is no competition or substitution relationship with the clay wet sand technology.

The acid self-hardening furan resin sand process is a self-hardening sand process which is widely used in cast iron, and its outstanding advantage is that the sand type (core) has good collapsibility and the old sand regeneration has high recycling rate.

The furan resin used in the foundry production needs to be modified with urea-formaldehyde and applied to the non-ferrous alloy, gray cast iron, ductile iron and cast steel according to the nitrogen content of the modified resin.

The disadvantages of the acid self-hardening furan resin process are:

A. The N, S, P and other gases generated after the pyrolysis of the resin binder and the curing agent may cause severe osmosis of the surface of the ductile iron casting and the steel casting, causing defects such as pores and cracks.

B. Sand type has high thermal expansion rate, large thermal stress, poor high temperature retreat, large shrinkage stress of castings, and cracks and burrs in castings.

C. The resin binder is expensive, and the furan ring produced after decomposition is very harmful to human health.

(5) ester hardening phenolic resin self-hardening sand

The ester hardening phenolic resin self-hardening sand process was developed by Bolton Company of the United Kingdom and is called a-set process. It was patented in 1981 and has been widely used in Europe in 1984. It was first used in cast steel production and has been expanded to Cast iron and non-ferrous alloy castings.

The phenolic resin has a strong basicity and a pH of from 1 to 13.5. The resin contains organic solvent, low flash point, flammable, and soluble in water. The shelf life is short. It can be stored for 6 months at 20 °C, 2-3 months at 30 °C, and only 1- at 40 °C. 2 months.

The hardener of such self-hardening sand is an organic ester, which can be selected according to the requirements of the curing speed. The amount of hardener is about 20~30% (mass fraction) of the resin, and the amount of phenolic resin added is 1.5~2.5% of the original sand. The sand mixing process is the same as the acid self-hardening furan resin. The sand temperature is usually controlled at 20~30%, the type (core) sand can be used for 5~30min, and the demolding time is 15~60min.

The main features of ester hardening phenolic resin self-hardening sand are:

A. Only partial reaction occurs under the action of hardener. The mold or core has a certain thermoplasticity after hardening. After pouring the metal, there is a short process of complete hardening due to heat. This is also the difference from the acid self-hardening furan resin sand. Therefore, the mold (core) made by this process is not very strong after hardening, and the compressive strength is only 2 to 4 MPa, but the dimensional stability and thermal stability of the mold are further hardened due to the initial stage of casting. All are good, the castings produced have high dimensional accuracy and good surface quality.

B. Because it does not contain N, P, S, it is especially suitable for the production of steel castings and ductile iron castings.

C, there will be no burr defects. Other self-hardening resin molds exhibit cracks at the mold/metal interface during casting and solidification. While the ester-hardened phenolic resin self-hardening sand has a short-term thermoplastic stage in the surface layer during the casting and solidification process to avoid cracking, a smooth casting with no burr defects can be obtained.

D. Alkaline phenolic resin has wide adaptability to raw sand, and is not only suitable for silica sand, but also suitable for special sand such as magnesia, forsterite sand and chromite ore with high acid value.

2. Should be compatible with the production batch

In mass production, priority should be given to mechanized, automated clay wet sand molding production lines and resin sand core production lines. For small castings of clay wet sand casting, it is possible to adopt a boxless high-pressure molding production line with horizontal splitting or vertical splitting. The production efficiency is high and the floor space is small. For medium parts (greater than 10kg), various high-pressure boxes are available. Modeling production line, pneumatic molding line to meet the requirements of fast, high-precision modeling production line. The old-fashioned shock-type or shock-pressure molding machine has low production line productivity, high labor intensity, high noise, and is not suitable for mass production. It should be phased out.

In medium-volume production, it is possible to consider the application of resin self-hardening sand, CO2 blowing hardened water glass sand, vacuum displacement blown hardened water glass sand molding and core making.

Manual styling is still an important method when producing single-piece small batches. Manual modeling can adapt to a variety of complex requirements, more flexible, does not require a lot of process equipment, can be applied to resin self-hardening sand type, CO2 blowing hardened water glass sand type, vacuum replacement blowing hardened water glass sand type, organic ester water glass self-hardening sand type , clay dry type and cement sand type. For heavy-duty castings produced in one piece, the pit-forming method is low in cost and quick in production.

The multi-box shape and the box-boxing method are suitable for mass production or long-term production of styling products. Although the initial investment of molds and sand boxes is high, it can be compensated for from saving man-hours and improving product quality.

3. Should adapt to the company’s own conditions

The production conditions (including equipment, site, staff quality, etc.), production habits, and accumulated experience of different enterprises are different. It is necessary to consider what modeling method is suitable according to these conditions. The best is applicable. At present, various technologies are competing for development. Each technology has its own advantages, and it also has certain limitations and scope of application. Advanced, high-tech processes are not necessarily applicable. According to the company’s own conditions, it is necessary to make practical choices by selecting technically applicable and economically reasonable processes and focusing on the combination of technology and economy.

For example, when producing castings such as large machine bed, the core forming method can be used, and the mold and the sand box are not made, and the core is assembled in the pit; while the other factory adopts the sand box modeling method to make the appearance.

4. To balance the quality and cost of castings

The quality of the castings obtained by various casting processes is different, the initial investment and production efficiency are also inconsistent, and the final economic benefits are also different. Therefore, to be more, faster, better, and more economical, we should take into account all aspects. Cost estimates should be made for the chosen casting method to ensure both economic efficiency and casting quality.

5. Pay attention to the environmental protection characteristics of the modeling process

Foundry production has always been known for its serious environmental pollution. Its pollution form is mainly caused by air pollution and waste slag pollution caused by steel melting and modeling materials. Among them, air pollution and waste residue pollution caused by modeling materials are the most serious.

According to statistics, it takes about 1t of new sand to produce 1t castings, and about 1t of old sand is discarded. At present, China produces about 28 million tons of castings a year, and the annual amount of old sand discharged is about 28 million tons. This not only accounts for a large amount of natural resources, but also causes serious environmental pollution. In order to reduce the amount of old sand emissions, it is necessary to use the casting process with high old sand recycling rate, clay wet sand and resin sand.

However, the clay wet sand has large dust pollution and black pollution of coal powder. The harmful gas generated by the combustion and decomposition of coal powder during the pouring process also causes serious air pollution; while the air in the resin sand production site is free of many organic substances. Exhaust gas (SO2, formaldehyde, benzene, methyl, etc.) will produce a lot of harmful gases after pouring, which is very harmful to human health. The water glass sand is composed of silica sand, inorganic water glass binder, etc., and uses CO2 gas or organic ester (such as ethylene glycol diacetate) as a curing agent, and the production environment is friendly, and no harmful gas is generated. Compared with clay sand and resin sand, the water glass sand process is the most suitable core making process for green clean casting production.

6. In conclusion

There are many kinds of products to be cast, and the process of modeling is also ever-changing. We must have a scientific attitude when choosing the production process of our products. We must proceed from the actual situation and make comprehensive considerations according to the material, structural characteristics and quality requirements of the castings.

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Casting mold parts take advantage of the forging process

Blanks of lost foam casting mold parts are generally formed by forging, and the purpose of forging is to obtain a certain geometric shape, so as to save raw materials, save processing time and reduce cost.

First. Forging temperature

The initial recrystallization temperature of steel is about 727 ° C, but 800 ° C is generally used as the dividing line. Above 800 ° C is hot forging; between 300 and 800 ° C is called warm forging or semi-hot forging, forging at room temperature. It is called cold forging.

Forgings used in most industries are hot forging, warm forging and cold forging are mainly used for forging of parts such as automobiles and general machinery. Warm forging and cold forging can effectively save material.

Second. Forging category

1.Free forging

Refers to a method of processing a forging that uses a simple universal tool or an external force directly applied to the blank between the upper and lower anvil of the forging equipment to deform the blank to obtain the desired geometry and internal quality. Forgings produced by the free forging method are called free forgings.

Free forging is mainly for the production of forgings with small quantities, and forgings are processed by forging equipment such as forging hammers and hydraulic machines to obtain qualified forgings. The basic processes of free forging include upsetting, lengthening, punching, cutting, bending, twisting, misalignment and forging. Free forging is a hot forging method.

2. Die forging

Die forging is divided into open die forging and closed die forging. The metal blank is subjected to compression deformation in a forging die having a certain shape to obtain a forged piece, and the die forging is generally used for producing a part having a small weight and a large batch size. Die forging can be divided into hot forging, warm forging and cold forging. Warm forging and cold forging are the future development directions of die forging, and also represent the level of forging technology.

3. Grinding ring

Rolling ring refers to the production of ring-shaped parts of different diameters by special equipment grinding machine, and also used to produce wheel-shaped parts such as automobile wheels and train wheels.

4. Special forging

Special forging includes roll forging, cross wedge rolling, radial forging, liquid die forging, etc. These methods are more suitable for the production of parts with special shapes. For example, roll forging can be used as an effective preforming process to significantly reduce subsequent forming pressures; cross wedge rolling can produce steel balls, drive shafts, etc.; radial forging can produce large forgings such as barrels and step shafts.

Third. Forgings advantages

Compared with castings, metals can improve their microstructure and mechanical properties after forging. After the hot-formed deformation of the cast structure by the forging method, the original coarse dendrites and columnar grains become the equiaxed recrystallized structure with fine grains and uniform size due to the deformation and recrystallization of the metal, so that the original segregation in the steel ingot Compaction and welding of loose, stomata, slag inclusion, etc., the structure becomes more compact, improving the plasticity and mechanical properties of the metal. The mechanical properties of castings are lower than those of forgings of the same material.

In addition, the forging process can ensure the continuity of the metal fiber structure, so that the fiber structure of the forging is consistent with the shape of the forging, and the metal streamline is complete, which can ensure the good mechanical properties and long service life of the part. Forgings produced by precision die forging, cold extrusion, and warm extrusion are unmatched by castings.

A forging is an object to which a metal is pressed to shape a desired shape or a suitable compressive force by plastic deformation. This force is typically achieved by using a hammer or pressure. The forging process creates a refined grain structure and improves the physical properties of the metal. In the practical use of components, a correct design enables the particles to flow in the direction of the main pressure.

Through forging, the material structure can be fine, the carbide distribution and the streamline distribution are reasonable, the heat treatment performance is improved, and the service life of the mold is improved.

Faced with the main working parts of the mold, especially those parts requiring high heat treatment quality and long service life, such as the convex and concave molds of the die, the forging die, the plastic die, and the cavity of the die-casting die, in addition to the requirement to obtain a certain geometry. The main purpose is to improve the performance of raw materials by forging, in addition to shape, saving raw materials and reducing processing time. Therefore, the mold parts, especially the main working parts, must be forged before processing, and the mold can serve the public for a long time.

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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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