Working principle of coal centrifuge

Coal centrifuge is a kind of dehydration equipment that uses the centrifugal force generated by mechanical rotation to realize the separation of solid-liquid mixture. The slime passes through the material inlet and passes through the distribution cone to make the space between the screen basket and the spiral discharge rotor.

Coal centrifuge

Under the action of centrifugal force, water and small particles (centrifugal liquid) pass through the material layer, pass through the screen, flow into the water collection tank on the upper part of the machine base along the upper cover, and then are discharged from the machine through the drain pipes arranged on both sides of the machine base. Outside: The coal particles are kept inside the screen basket. Because there is a speed difference between the spiral discharge rotor and the screen basket, the spiral discharge rotor scrapes the coal particles from the screen and pushes them to the bottom of the screen basket, thereby reducing The dehydrated slime (dehydrated product) is discharged into the collecting hopper under the machine, and this dehydration process is continuously carried out.

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Working principle of linear vibrating screen

The linear vibrating screen uses the vibration motor as the source of vibration power, so that the material is thrown up on the screen while moving forward in a straight line. The material enters the inlet of the screening machine evenly from the feeder, and generates data through the multi-layer screen. The oversieve and undersieve of various specifications are discharged from their respective outlets. It has low energy consumption, high output, simple structure, easy maintenance, fully enclosed structure, no dust spillage, automatic discharge, and is more suitable for assembly line operations.

The linear vibrating screen is driven by dual vibration exciters. When the two vibration exciters are synchronized and rotated in opposite directions, the excitation force generated by the eccentric block cancels each other in the direction parallel to the axis of the motor, and in the direction perpendicular to the axis of the motor. Stacking is a resultant force, so the trajectory of the screen machine is a straight line. The two motor shafts have an inclination angle relative to the screen surface. Under the combined force of the exciting force and the material’s self-gravity, the materials are thrown up and jump forward on the screen surface for linear motion, so as to achieve the purpose of screening and grading the materials. It can be used to realize automated operations in the assembly line. It has the characteristics of low energy consumption, high efficiency, simple structure, easy maintenance, and a fully enclosed structure without dust spillage. The maximum sieving mesh is 400 meshes, which can screen out 7 kinds of materials with different particle sizes.

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Introduction to the performance of banana vibrating screen

The banana vibrating screen is a self-synchronizing heavy-duty equal-thickness screen. The screen box is similar to the shape of a banana. The screen beam adopts a box-shaped beam. The vibrator and the exciter are connected by an intermediate transmission shaft.
Banana vibrating screen is widely used in coal grading, desliming, dewatering, de-intermediation, and can also be used for screening in large-volume mining operations in mines. Compared with the traditional sieve of the same specification, the banana vibrating screen developed by our company has a larger processing capacity. Its processing capacity per unit area is 1.5~2 times that of the traditional one. It is a kind of vibrating screen with higher cost performance.

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Nucleic acid extraction kit

Recently, in Luoyang Aisen Biotechnology Co., Ltd., located in Bisheng Park, Luoyang National University Science and Technology Park, the newly commissioned automatic filling production line of viral nucleic acid extraction kits is busy. The staff are facing a batch of just off the assembly line. The kit is checked and accepted before leaving the factory. This type of product can efficiently and quickly complete the extraction of the new coronavirus.

At the beginning of January this year, with the help of departments at all levels in Luoyang City, Jianxi District and Science and Technology Park, Aisen Biotechnology moved to the new site while producing in batches. The new automatic production line was commissioned before the end of the month, and the production site was expanded to 1,500 square meters. , The production scale has also expanded from 20,000 to 200,000 a day. As of March 21, this year, Aisen Biotechnology has completed the order production of 2.2 million nucleic acid extraction kits. At present, the company’s products are not only meeting the domestic market demand, but also exported to Greece, Zimbabwe and other countries and regions.

At present, Aisen Biotech has passed ISO9001 and ISO13485 quality system certification. Its main products magnetic bead method nucleic acid extraction kit, 32-channel automatic nucleic acid extraction instrument and 96-channel automatic nucleic acid extraction instrument have been registered in China for a class of medical records In addition, the above products have also obtained the EU CE certification and the US FDA certification.

Source: Luoyang University Science and Technology Park

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Characteristics of vibrating screen

Today I will share with you a topic about the vibrating screen. Vibrating screen is a device specially designed for screening materials in quarries. It can also be used for product classification in coal preparation, mineral processing, building materials, electric power and chemical industries. The screen machine has the characteristics of advanced structure, strong excitation force, low vibration and noise, easy maintenance, sturdiness and durability. Vibrating screens can be divided into light vibrating screens and heavy vibrating screens. Generally, light vibrating screens are used to screen food, medicine, etc.; heavy-duty vibrating screens are generally used to screen ore and used together with crushers.

Features of the device:
1. Large processing capacity and high screening efficiency.
2. The vibrator adopts bearing thin oil lubrication and an external block eccentric structure. It has the characteristics of large excitation force, low bearing load, low temperature and low noise. (Bearing temperature rise is less than 35°).
3. The overall disassembly and assembly of the vibrator is convenient for maintenance and replacement, which greatly shortens the maintenance period. (It only takes 1 to 2 hours to replace the vibrator).
4. The side plate of the screen adopts the whole plate cold work, no welding, high strength and long service life. The cross beam and the side plate are connected by torsion shear high-strength bolts, no welding, and the cross beam is easy to replace.
5. The screen machine adopts rubber spring to reduce vibration. Compared with metal spring, it has the advantages of low noise, long life, smooth cross-vibration zone, and small dynamic load on each fulcrum of the screen machine.
6. The connection between the motor and the vibration exciter adopts a flexible coupling, which has the advantages of long service life and small impact on the motor.

If you want to know more, you can visit Vibrating screen manufacturer。

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Application of ceramic casting sand in casting process

The lost foam casting process is suitable for a large number of castings that have intricate structural features and are difficult to produce by other methods. From the actual situation of developed countries, such as the United States and several European countries that have lost foam process operations, this view is true. Lost foam process has been successfully used to produce aluminum alloy engine blocks and has been mass-produced in the United States for automobiles and ships. This casting method has given a demonstration to the world’s foundry industry, proving the advantages of the lost foam process.

In China, the development of lost foam technology shows the advantages of this process from different aspects. And has been mostly applied to cast iron and cast steel products. It has been used to investing in the production of various parts, from relatively simple to parts with relatively complex features. In addition, it is also suitable for different production operations including mass production, loose parts, and even prototypes.

In order to ensure that the lost foam raw sand has sufficient fluidity to fill the complex deep cavity parts of the foam pattern, plus a thick coating layer has a certain mechanical strength to prevent box collapse, therefore the lost foam casting requires roundness Be good enough. In addition, during the casting of lost foam casting, a large amount of gas or liquid pyrolysis products will be generated along with the cracking and burning of the foam pattern. Therefore, the sand must have sufficient air permeability to prevent the residue from overflowing.

Since the ceramic casting sand is close to a spherical shape, it has good fluidity and high air permeability. It can fill slender holes, angled parts of castings and complex inner cavity parts, and it is easier to compact. Material, which guarantees its wide application in cast iron and cast steel (including high manganese steel, etc.).

The use of ceramic casting sand has the advantages of high fire resistance, good fluidity and high air permeability, and is used for lost foam casting, which can increase the yield of castings, reduce costs, and improve the working environment.

Physical and chemical properties of ceramic foundry sand

Grain shape spherical Coefficient of expansion (20~1000℃)6×10-6/℃
Colour Black-brown Al2O3 65-85%
Refractory temperature ≥ 1800 ℃ Fe2O3 ≤5%
Bulk Specific Gravity 1.95 -2.05g /cm3 SiO2 8~22%
True density 3.4g /cm3 TiO2 3~4.5%
Thermal conductivity (1200 ℃)5.27W/M·K PH value 7~8
Granularity 6 ~ 320 mesh (φ0.053 ~ 3.36mm) /
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What are the classifications of the lost foam casting process?

Lost foam casting is a method of casting a refractory bonded paint, drying it and then performing dry sand molding, vibrating tightly, and then pouring the molten metal to heat the gasification to disappear, thereby obtaining a metal part having the same shape as the pattern. Lost foam casting is a new technology with no margin and precise forming. It does not need to take the mold and use the binderless dry sand to reduce the pollution. It is considered as the green casting technology.

Lost foam casting classification

The castings processed by lost foam casting have high dimensional accuracy, uniformity, clean environment and no pollution; low labor intensity, less labor, less technicians; less equipment investment. The processing for small and medium-sized enterprises reduces costs, improves the economics of the company, and understanding its process classification can help companies better choose the casting process.

1. Pressure lost foam casting technology

The pressure lost foam casting technology is a new casting technology combining the lost foam casting technology and the pressure solidification crystallization technology. It is in the pressure irrigation with a sand box. After pouring the molten metal to vaporize the foam, the pressure irrigation is quickly sealed. A casting method in which a certain pressure of gas is introduced to solidify and crystallize the molten metal under pressure. This casting technology is characterized by significantly reducing casting defects such as shrinkage, shrinkage, and porosity in the casting, increasing the density of the casting and improving the mechanical properties of the casting.

2. Vacuum low pressure lost foam casting technology

Vacuum low pressure lost foam casting technology is a new casting technology developed by combining negative pressure lost foam casting method and low pressure anti-gravity casting method. The characteristics of vacuum low pressure lost foam casting technology are: combining the technical advantages of low pressure casting and vacuum lost foam casting, the filling process is completed under controlled pressure, which greatly improves the casting filling ability of the alloy; compared with die casting, the equipment The investment is small, the casting cost is low, and the casting can be heat-treated and strengthened. Compared with the sand casting, the casting has high precision, small surface roughness, high productivity and good performance; under the action of anti-gravity, the sprue becomes the supplementary shortening channel and the pouring temperature. The loss is small, the liquid alloy is filled and solidified under the controllable pressure, the casting system of the alloy casting is simple and effective, the yield is high, and the structure is compact; the vacuum low pressure lost foam casting has a low pouring temperature and is suitable for various colored alloys.

3. Vibration lost foam casting technology

The vibration lost foam casting technology applies vibration of a certain frequency and amplitude during the lost foam casting process, so that the casting solidifies under the action of the vibration field. Since the solidification process of the lost foam casting is applied to the metal solution for a certain period of time, the vibration force makes the liquid The relative motion between the phase and the solid phase causes the dendrites to break, and the crystal core in the liquid phase is increased, so that the final solidification structure of the casting is refined, the feeding is improved, and the mechanical properties are improved. The technology utilizes the ready-made compact vibrating table in lost foam casting, and the mechanical vibration generated by the vibrating motor causes the molten metal to nucleate under dynamic excitation to achieve the purpose of refining the structure, and is an easy operation, low cost and no environment. The method of pollution.

4. Semi-solid lost foam casting technology

Semi-solid lost foam casting technology is a new casting technology that combines lost foam casting technology with semi-solid technology. Because the process is characterized by controlling the relative proportion of liquid-solid phase, it is also called transformation control semi-solid forming. This technology can increase the density of castings, reduce segregation, improve dimensional accuracy and casting performance.

5. Lost shell casting technology

The lost shell casting technology is a new casting method combining investment casting technology and lost foam casting. The method is to apply a plurality of layers of refractory material to the surface of the foam molding which is made of a foaming mold and has the same shape as the part, and after hardening and drying, the foamed plastic pattern is burned and disappeared to form a shell, and is fired. And then casting, to obtain a new precision casting method for higher dimensional precision castings. It has the characteristics of large size and high precision in the lost foam casting, and has the advantages of crust precision and strength in investment casting. Compared with ordinary investment casting, it is characterized by low cost of foam plastic molding, convenient combination of pattern bonding, easy disappearance of gasification, overcoming the problem of melt deformation caused by easy softening of investment casting mold, and can be produced. Large size of various alloy complex castings.

6. Lost foam suspension casting technology

The lost foam suspension casting technology is a new practical casting technology that combines the lost foam casting process with suspension casting. The technical process is that after the molten metal is poured into the mold, the foam plastic pattern is vaporized, and the suspending agent is mixed in the riser model (or the suspending agent is placed at a specific position of the pattern, or the suspending agent is foamed together with the EPS. Physicochemical reaction with molten metal to improve the overall (or partial) structural properties of the casting.

Due to the low cost, high precision, flexible design, clean and environmental protection, and suitable for complex castings, the lost foam casting technology meets the general trend of casting technology development in the new century and has broad development prospects.

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Analysis of lost foam casting process of aluminum alloy

Lost foam casting has strong vitality because of its quick and good green environmental protection characteristics. Especially in recent years, the development momentum has the potential to break the bamboo. The lost foam casting process has precise casting shape and almost no allowance, which is in line with the lightweight and precise casting. The development trend of complexity and complexity. However, the lost foam casting process covers many disciplines such as mechanics, chemical engineering, metallurgy, casting, and computer. It is a complex process technology that combines knowledge and application technology. Due to the use of dry sand molding, the change of objective conditions such as the actual gasification wall negative pressure greatly simplifies the production process, shortens the process flow, greatly facilitates production, improves productivity, improves the labor environment, and reduces labor. Strength, its advantages are obvious.

The lost foam casting is very special, the dry shape does not have any adhesive, and the real and casting system does not need to be taken out, which greatly improves the design freedom of the casting and improves the surface finish and dimensional accuracy of the casting.

1. Process analysis of lost foam casting aluminum

In the filling process, in the filling process, under the strong heat radiation of the high temperature molten metal, an irregular gap layer is formed between the liquid metal front and the foam pattern. Taking the bottom note as an example, the front edge of the molten metal is pushed forward in a “concave” shape, and the corresponding foam pattern end is zigzag or finger-type retracted. The solid slag and the liquid phase foam which are not completely cleared at the forefront of the alloy flow in the direction of escape of the gas. The gas exists in a small molecule state and is easily excluded by the negative pressure, and the solid impurities are blocked on the inner wall of the coating. That is, the surface of the casting forms a surface slag pit, which is the main reason why the lost foam casting has a smaller internal slag hole and the outer slag hole protrudes: the liquid phase foam is also discharged at the metal-coating interface, and is partially coated. Adsorption, partial secondary vaporization, and secondary vaporization of the gas mostly overflow, and a small amount of intrusive metal forms surface pores. The riser of the casting is generally designed at the top, and it is a dark riser. It cannot obtain high-temperature metal by means of refilling. The aggregated metal is all metal after being cooled by vaporization and heat absorption, the shrinking effect is not good, and the shrinkage ratio is increased. . The pores, slag holes, shrinkage holes, and carbon defects have similarities in the process control of many lost modes, and they are not contradictory. Therefore, the vanishing die pores are the main line here, and the prevention measures are explained together.

(1) Definition of pores: During the solidification process, the bubbles trapped in the metal form pores in the casting, which are called pores.

(2) The pores are divided into intrusive pores, wrapped pores, precipitated pores, endogenous reaction pores, and exogenous reaction pores.

2. Analysis of the causes of the porosity defects in the lost aluminum mold

The reasons for the occurrence of air holes in lost foam casting are as follows:

(1) Foam model gasification decomposition to generate a large amount of gas and residue can not eliminate the mold in time;

(2) Dehydration of aluminum water is poor, and the pouring process is unreasonable to cause slag holes;

(3) The pouring system is unreasonable;

(4) The pouring temperature is unreasonable;

(5) The location of the sprue is unreasonable;

(6) The permeability of the coating is poor or the negative pressure is unreasonable, and the permeability of the filling sand is poor;

(7) The pouring speed is too slow, fail to fill the pouring cup, expose the sprue, entrap the air, inhale the slag, and form the carrying hole and the slag hole;

(8) The capacity of the gate cup is too small, and the molten metal forms a vortex, which invades the air to generate pores;

(9) The joint between the sprue cup and the sprue and the gating system is not well sealed;

(10) The particle size of the sand is too fine, the dust content is too high, and the gas permeability is poor. The vapor can not remove the coating in time to form pores or wrinkles.

3. Process measures to control porosity defects

(1) selecting suitable model materials;

(2) the use of the gating system and the insulated riser;

(3) Improve the gas permeability of the coating, and the quality of the lost foam coating is critical. In the case of mass production, the gas permeability of the paint is regularly checked, and the particle size of the aggregate is adjusted in time. Since the binder and suspending agent of the coating contain organic matter, the summer and autumn seasons should pay special attention to the fermentation mildew of the coating. The qualified castings cannot be separated from the best coating, and the quality of the coating is not light;

(4) The pouring temperature should be suitable;

(5) Control of dehydrogenation and slag removal time of aluminum water;

(6) Reasonable pouring position;

(7) Reasonable casting process and negative pressure.

4. Production principle and process flow

The method is made into a foam molding model according to the EPS process, and the special coating is applied. After drying, it is placed in a special sand box, filled with dry sand, three-dimensional vibration is tight, pouring under vacuum, the model gasification disappears, and the metal replacement model The casting is the same as the foam molding mold, and after condensing, the vacuum is released, and the casting is taken out from the loose sand for the next cycle.

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What is casting?

Casting is a process in which a metal is smelted into a liquid that meets certain requirements and poured into a mold, and cooled, solidified, and cleaned to obtain a casting having a predetermined shape, size, and performance. Casting blanks are near-formed to achieve machining-free or small-scale processing, reducing costs and reducing time to some extent. Casting is one of the fundamental processes in the modern manufacturing industry.

There are many kinds of castings. According to the modeling method, it is customarily divided into: ordinary sand casting, including wet sand type, dry sand type and chemical hardening sand type; according to modeling materials, it can be divided into special castings with natural mineral sand as the main modeling material (such as Investment casting, clay casting, shell casting, negative pressure casting, solid casting, ceramic casting, etc.) and special casting with metal as the main casting material (such as metal casting, pressure casting, continuous casting, Low pressure casting, centrifugal casting, etc.)

According to the forming process, it can be divided into gravity casting: sand casting, permanent mold casting, pouring molten metal into the cavity by gravity; pressure casting: low pressure casting, high pressure casting. The molten metal is instantaneously pressed into the casting cavity by an additional pressure.

The casting process usually includes:

(1) Preparation of molds, molds can be divided into sand type, metal type, ceramic type, mud type, graphite type, etc. according to the materials used, which can be divided into disposable type, semi-permanent type and permanent type according to the number of times of use. Advantages and disadvantages are the main factors affecting the quality of castings;

(2) Melting and casting of cast metal, the cast metal mainly consists of cast iron, cast steel and cast non-ferrous alloy;

(3) Casting treatment and inspection. The casting treatment includes removing foreign objects on the surface of the core and casting, cutting out the riser, burrs and burrs, and heat treatment, shaping, anti-rust treatment and roughing.

The casting process can be divided into three basic parts, namely casting metal preparation, mold preparation and casting processing. Cast metal refers to the metal material used for casting castings in casting production. It is an alloy composed mainly of a metal element and added with other metal or non-metal elements. It is customarily called cast alloy, mainly cast iron. Cast steel and cast non-ferrous alloys.

Metal smelting is not only a simple melting process, but also a refining process that allows the metal to be poured into the mold to meet the expected requirements in terms of temperature, chemical composition and purity. For this reason, various inspection tests for the purpose of controlling quality are carried out during the smelting process, and the liquid metal can be allowed to be poured after reaching various specified indexes. Sometimes, in order to achieve higher requirements, the molten metal is treated outside the furnace after being discharged, such as desulfurization, vacuum degassing, refining outside the furnace, gestation or deterioration treatment. Commonly used equipment for smelting metals are cupola, electric arc furnace, induction furnace, electric resistance furnace, reverberatory furnace and the like.

Process flow introduction

With the advancement of technology and the booming of the foundry industry, different casting methods have different mold preparation contents. Taking the most widely used sand casting as an example, the mold preparation includes two major tasks: modeling material preparation and modeling core making. Sand casting, various raw materials used for molding core, such as foundry sand, sand binder and other auxiliary materials, as well as molding sand, core sand, paint, etc., which are formulated by them, are collectively referred to as modeling materials. The task of preparing materials is to follow castings. The requirements, the nature of the metal, the selection of the appropriate raw sand, binder and auxiliary materials, and then they are mixed into a certain type of molding sand and core sand in a certain proportion. Commonly used sand mixing equipment are a roller-type sand mixer, a counter-flow sand mixer and a blade grooved sand mixer. The latter is designed for mixed chemical self-hardening sand, continuous mixing and fast speed.

The shape core is based on the requirements of the casting process, based on the determination of the modeling method and the preparation of the molding material.

The accuracy of the casting and the economics of the entire production process depend mainly on this process. In many modern foundry workshops, the styling core is mechanized or automated. Commonly used sand-type styling equipments include high, medium and low pressure molding machines, sand blasting machines, boxless injection molding machines, core shooting machines, cold and hot core boxes.

After the castings are removed from the cast-cooled mold, there are gates, risers, metal burrs, drapes and mold lines. The sand-cast castings are also adhered to the sand and must be cleaned. Equipment for performing such work includes a sander, a shot blasting machine, a pouring riser, and the like. The sand falling of sand castings is a process with poor working conditions. Therefore, when selecting the modeling method, it should be considered to create convenient conditions for the falling sand cleaning. Some castings are subject to special post-processing requirements such as heat treatment, shaping, anti-rust treatment, roughing, etc.

Industry characteristics

Casting is a relatively economical method of forming blanks, which is more economical for parts with complex shapes. Such as the cylinder block and cylinder head of a car engine, ship propellers and fine art. Some hard-to-cut parts, such as nickel-base alloy parts of gas turbines, cannot be formed without casting.

In addition, the size and weight of the cast parts are wide, and the metal types are almost unlimited. The parts have general mechanical properties, and also have comprehensive properties such as wear resistance, corrosion resistance and shock absorption. Other metal forming methods such as forging , rolling, welding, punching, etc. can not be done. Therefore, the number of blank parts produced by the casting method in the machine manufacturing industry is still the largest in terms of quantity and tonnage.

Materials commonly used in foundry production are various metals, coke, wood, plastics, gas and liquid fuels, modeling materials, and the like. The equipment required is a variety of furnaces for metallurgy, various sand mixers for sand mixing, various molding machines for core making, core machines, sand falling machines for cleaning castings, and shot blasting. Machine and so on. There are also machines and equipment for special casting and many transportation and material handling equipment.

Casting production has different characteristics from other processes, mainly due to its wide adaptability, the need for materials and equipment, and pollution of the environment. Casting produces dust, harmful gases and noise that pollute the environment. It is more serious than other mechanical manufacturing processes and requires measures to control it.

For casting and mechanical structural design engineers, heat treatment is a very meaningful and highly valuable method for improving the quality of materials. Heat treatment can change or affect the structure and properties of cast iron while achieving higher strength. , hardness, and improve its resistance to abrasion and so on.

Due to different purposes, there are many types of heat treatment, which can be mainly divided into two categories. The first type is the tissue structure, which does not change or should not change through heat treatment. The second is the change of basic organizational structure. By. The first heat treatment procedure is mainly used to eliminate internal stresses which are caused by different cooling conditions and conditions during the casting process. The structure, strength and other mechanical properties are not significantly changed by heat treatment. For the second type of heat treatment, al-Qaeda has undergone significant changes and can be broadly divided into five categories:

(1) Softening annealing: The purpose is mainly to decompose the carbide, lower the hardness thereof, and improve the processing property. For the spherical stone-milled cast iron, the purpose is to obtain a ferrite structure having a high fertility.

(2) Normalization treatment: It is mainly used to improve or to obtain a uniform distribution of mechanical properties of a cast iron-completed cast product.

(3) Quenching: Mainly to obtain higher hardness or wear strength, and at the same time to a very high surface wear resistance.

(4) Surface hardening treatment: mainly to obtain a surface hardened layer, and at the same time obtain a very high surface wear resistance.

(5) Precipitation hardening treatment: mainly in order to obtain high strength, the elongation does not change drastically.

Industry Trends

The trend in the development of foundry products is to require castings with better overall performance, higher precision, less margin and a smoother surface. In addition, the requirements for energy conservation and the voice of society to restore the natural environment are also increasing. To meet these requirements, new casting alloys will be developed, and new smelting processes and new equipment will emerge.

As the degree of mechanization automation in foundry production continues to increase, more will be developed towards flexible production to expand the adaptability to different batches and varieties. New technologies for energy conservation and raw materials will be given priority. New processes and new equipment with little or no pollution will be the first priority. Quality control technology will have new aspects in the detection, non-destructive testing and stress measurement of various processes. development of.

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What are the defects and solutions for mold heat treatment?

A mold is a variety of molds and tools for obtaining a desired product by injection molding, blow molding, extrusion, die casting or forging, smelting, stamping, and the like. Simply put, it is a tool for making shaped articles. It can make a variety of different items and some parts, and the mold has the title of “mother of industry”. Although it is very powerful, the mold will still appear during the production process. Some problems, especially in the heat treatment stage, are prone to defects, so what are the defects in mold heat treatment, and how to solve it?

1. Soft spots appear on the surface of the mold

After the heat treatment of the mold, there are soft spots on the surface. This situation will affect the wear resistance of the mold and reduce the service life of the mold. The main reason for this is that 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.

For this case, we can solve the problem by removing the scale and rust before the heat treatment of the mold, and properly protecting the surface of the mold during quenching and heating. It should be heated in a vacuum electric furnace, a salt bath furnace and a protective atmosphere furnace. When quenching and heating, select a suitable cooling medium. For long-term use, the cooling medium should be filtered frequently, or replaced regularly. Shading can prevent the occurrence of soft spots.

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, band and chain carbides, which will cause the mold to be cracked after quenching, resulting in scrapping of the mold. This situation is generally due to the presence of severe carbide segregation in the original structure of the mold 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.

In this case, 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 quench crack

The cracking of the mold after quenching is a 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. The reason for this is due to the presence of 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.

At this time, the intrinsic quality of the mold raw materials should be strictly controlled, the forging and spheroidizing annealing processes should be improved, the mesh, ribbon and chain carbides should be eliminated, and the uniformity of the spheroidized structure can be improved. 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. The microstructure of the mold after quenching

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. The reason for this is that the mold steel is confused, and the actual steel quenching temperature is much lower than the quenching temperature of the required mold material. 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.

The solution is to strictly inspect the steel before it is put into storage, so as 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.

The above is the whole content of the mold heat treatment defects and solutions. In general, the above defects can be caused because there is no treatment before the production, and there is serious carbide segregation in the original structure of the mold steel material. The forging process is not good, and there is a possibility that the mold steel is confused. The actual steel quenching temperature is much lower than the quenching temperature of the required mold material.

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