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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.

R&D background：

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

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

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

Process requirements：

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

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

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

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

4. The grounding mark is placed in four orientations.

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

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

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

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

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

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

Mold design：

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

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

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

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

According to the mold assembly diagram:

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

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

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

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

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

Detailed ways：

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

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

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

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

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

Invention patent number:

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

Utility model patent number:

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

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

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

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

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

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

1. 2 Main features of high quality lost foam die

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

1.3 How to get high quality lost mode die

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

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

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

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

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

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

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

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

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

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

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

4.1 Performance analysis of domestic pre-expander

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

5. Germany Teubert lost mode special pre-expansion hunger

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

Main performance characteristics:

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

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

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

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

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

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

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

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

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

With the rapid development of the automobile industry, the production and use of large-scale stamping parts has increased sharply, and the demand for medium and large-sized molds has also increased significantly. In recent years, a large number of researches and practices have shown that the yield strength of nodular cast iron is higher than that of ordinary steel. The matrix structure is the same as that of steel. The spherically distributed graphite is not easy to generate stress concentration. In addition, ductile iron can be immersed in lubricating oil, and the graphite in the structure has self-lubricating. The effect can effectively reduce the friction in stretching. In theory, the heat treatment process that can be applied to steel is basically applicable to ductile iron. Therefore, the microstructure of the ductile iron can be changed by appropriate heat treatment to improve its performance. The ductile iron material is the preferred material to replace the alloy mold steel, and the high-strength gray cast iron material can also replace part of the carbon steel.

The FM method is a solid self-hardening sand casting method, which is different from the dry sand binderless vacuum molding method. It has many years of production history and mature experience in China. In the production of cast iron parts, furan resin is usually used to fill the mold to cover the vaporized foam mold. After the mold is hardened, the molten iron is poured into the cavity, and the foam mold is burned out in the sand mold to form a casting. This method eliminates the process of demoulding, tumbling, lower core and boxing in general sand casting, which improves the overall dimensional accuracy of the casting, reduces the labor intensity and shortens the production cycle, and is suitable for casting large and medium single piece cast iron molds. method.

How to choose the right coating in the real casting process is a crucial step. In the past, in the process of coating configuration, the different materials and particle size distribution of the aggregates were adjusted according to the requirements of the castings to obtain the technical indexes of different refractoriness, coating strength, sintering performance and gas permeability of the coating. Considering the different mold casting size and wall thickness, the different characteristics of the paste-like solidification of ductile iron and the layered solidification of gray iron, the most suitable coatings often need to be customized. This method is difficult to achieve under the current commercial conditions of coatings. To this end, I have tested the use of two or more different types of coatings, in the use of the site according to the needs of the composite configuration of the process to meet the needs of the field. This not only takes into account the commodification, standardization, but also meets the individual needs.

1, paint selection and performance testing

According to the general requirements of cast iron lost molds, we chose two coatings as the basic coating. One is a graphite alumina-based paint specially used for cast iron parts (hereinafter referred to as E5), and the other is a high-refractory, high-breathing paint (hereinafter referred to as E2) with a brown corundum base as the main aggregate, as a follow-up test. And tested the base paint.

1.1, refractoriness
Refractoriness, also known as refractory degree, refers to the temperature at which a material reaches a certain degree of softening under high temperature. It is an important technical index for evaluating refractory materials. The degree of refractoriness is not a physical constant of a substance, but a technical index whose height is determined by the chemical composition of the material, the degree of dispersion, the proportion of the liquid phase in it, and the viscosity of the liquid phase.

The meaning of refractoriness is different from the melting point. The melting point is the temperature at which the liquid phase and the solid phase of the crystal are in equilibrium. The degree of refractoriness is the temperature at which a multiphase body reaches a certain degree of softening. For most common refractory materials, they are heterogeneous heterogeneous materials, without a certain melting point, and the liquid phase to complete melting is a gradual process. In a fairly wide range of high temperatures, the solid and liquid phases coexist. Therefore, the characteristics of softening and melting of such materials at high temperatures can only be measured in terms of refractoriness.

The test standard for refractoriness is in accordance with GB/T 7322-2007 refractory test method for refractory materials. The test principle is to plant the test cone of refractory material on the frustum together with the standard temperature measuring cone of known refractoriness under the specified conditions. The degree of refractoriness of the test cone is expressed by heating and comparing the bending of the test cone with the standard temperature measuring cone.

The test parameters are: rated temperature 1800 °C, heating rate 0-20 °C / min, cone table rotation speed 3r / min, control mode is microcomputer automatic measurement and control.

It has been found through experiments that the refractoriness of the coating E5 is 1550 ° C, and the refractoriness of the E 2 is 1680 ° C. The refractoriness of the coatings of the two materials is greater than the general pouring temperature of the cast iron parts. Considering that the actual wall thickness and the thermal joint of the casting have different requirements on the refractoriness of the coating, the two coatings can be compounded according to the actual use requirements of the casting, and the ideal state has been achieved.

1.2, gas permeability
There are many factors that affect the permeability of the coating. In the case of selecting the same bonding system and the same coating thickness, the change in the type and composition of the refractory aggregate in the coating has an important influence on the gas permeability. It was verified by making three kinds of representative different aggregates into test samples and measuring the gas permeability of the samples. The test method adopts the coating of the current common metal mesh sheet, and after drying, the gas permeability data is measured in the sand permeability tester.

The larger the particle size of the powder, the higher the gas permeability. This is because as the particle size of the powder becomes larger, the gap between the powders becomes larger, and the gas permeability of the coating naturally increases. And among the three aggregates of brown fused alumina, zirconium powder and bauxite, brown corundum has the best gas permeability. When the average particle size is 0.038mm, the permeability of brown corundum is better than that of the other two aggregates of 0.075mm. When the particle size of the three aggregates reaches 0.075mm, the permeability of brown corundum reaches the highest. It is twice as much as the other two aggregates. It can be seen from the results that the aggregate structure of the brown corundum can improve the gas permeability of the coating.

The structure of the corundum powder is an irregular polygonal crystal, and the powder has a large hardness, and this property easily forms voids between the powders. Moreover, the brown fused alumina has small thermal expansion and uniformity, so that the volume under high temperature is stable and cracked, and the size of the gas permeable pores is not changed, so that the gas permeability of the coating is higher than that of other powders.

Through the gas permeability test of aggregates, we should choose brown fused alumina as the main aggregate to make coating E2 to meet the high gas permeability requirements of customers. However, the one-sided improvement of gas permeability is at the expense of reducing the surface quality of the coating. In order to ensure the gas permeability and also the surface quality of the coating, we have chosen E5 coating made of bauxite as the main aggregate. The two coatings are used in combination according to actual needs.

2, the use of paint

For the production of cast iron parts, graphite is an ideal choice for refractory aggregates. Graphite is easy to produce a reducing atmosphere at the mold interface, inert to iron oxide, and produces a joint between the mold and the casting interface at high temperatures. A bright carbon film that is not wetted by metals and metal oxides, allowing the sand layer to be easily peeled off. Finally, the surface of the casting is smooth, and the graphite has good thermal stability and a small expansion coefficient. The coating can withstand extreme temperature changes at high temperatures without cracking.

According to the experience of our comprehensive majority of customers. Unless the special complicated parts are used, the castings can be directly selected from the E5 type below 3 tons, which can basically meet the requirements of refractoriness and gas permeability; the casting ratio of the castings in the range of 3 to 10 tons of E5 and E2 is 6: 5, that is, 6kgE5 and 5kgE2 are used in combination; if the casting is more than 10 tons, the mixing ratio of paint E5 and E2 is generally required to be 3:10. Of course, it can also be adjusted according to the actual process of the customer when using it on site.

2.1 brushing
In some smaller companies, the brushing process is generally used in view of the site and turnover. Brushing method, as its name suggests, is mainly done by hand through the brush. Relatively speaking, the technical requirements of the coating method for the coating are not as strict as the spraying method and the dip coating method, but since it is mainly done manually, for the operation The technical and experience requirements are relatively high. The biggest disadvantage of the brushing method is the high labor intensity and low production efficiency. Almost all work is done manually.

When using the brushing process, the general control of the composite paint is between 90 and 100, and the paint is applied with 2 to 3 layers. It is important to note that since it is hand-painted, it is inevitable that there are more or less in some places, so it is necessary to prevent a large amount of paint from accumulating in corners and deep pits. Figure 4 shows the mold casting used for manual brushing.

For most large-scale companies, the flow coating process is generally recommended. At this time, the Baume degree of the composite coating is generally controlled between 65 and 70, and the coating is applied to 2 to 3 layers. Since the paint at this time is relatively thin, after the flow coating is completed, the excess paint will naturally flow away when the model is turned over, and there is no accumulation in some places as in the case of brushing. Figure 5 is a view of the case where the mold casting is flow coated.

3, field application practice

3.1 automotive stamping die castings
A large-scale foundry enterprise in Anhui uses furan resin sand as a mold, and uses a lost foam casting process to mass produce automobile stamping die cast iron parts. The coating process is to apply a composite coating with a weight ratio of 6:5 (E5:E2) on the pattern. The coating has a Baume degree of 68, the coating flow is applied twice, the total thickness of the coating is about 0.8 mm, and the pattern after drying is shown in Fig. 6. The casting material is HT300, the casting temperature is 1390 °C, the casting weight is 7.5 tons, the casting result is shown in Figure 7. After the casting is cleaned, the surface is smooth and the size is accurate.

3.2 Large machine tool castings
A foundry enterprise in Jiangsu Province also uses a furan resin sand lost foam process to produce large machine tool castings. The coatings are brushed, the Baume degree is controlled at around 90, and the weight ratio of the coating is 3:10 (E5:E2). The coating is twice, the coating thickness is about 1mm, the pattern after brushing the composite coating is shown in Figure 8; the casting material is HT250, the casting weight is 13.2 tons, and the casting temperature is 1450 °C.

4 Conclusion

For the use of the lost foam process for large mold cast iron parts, the choice and rational use of the paint is particularly critical. Through the research in this paper and the experience of similar factories, we can draw the following conclusions:

1) By selecting the composite use of two different properties of the lost foam coating, the field can be flexibly adjusted according to the process requirements, and the most suitable use effect has been achieved;
2) The refractoriness and permeability of the coating are important indicators for measuring the performance of the lost foam coating;
3) The use of graphite as a refractory aggregate for cast iron parts is an ideal choice, considering its refractoriness can be added as part of the refractory material;
4) The structure of brown corundum powder is irregular polygonal crystal, and the hardness of the powder is also large. This property is easy to form voids between the powders, so that the permeability of the coating is high;
5) The coating process can significantly improve the working efficiency by using the flow coating process, and the uniformity of the coating can be better ensured.

The production of aluminum alloy castings by the lost foam process has become an unstoppable trend. Cylinder top cover, new energy vehicle gearbox, heavy truck gearbox, etc., have gradually realized mass production in China, especially the mass production of 12-speed truck gearboxes. It marks the arrival of a new era of China’s lost foam aluminum alloy casting. The successful development of the 0.12 gearbox gearbox’s lost-mould mold has laid the foundation for its mass production.

The basic structural shape of the gearbox, the product is a cavity structure, the outer part is full of reinforcing ribs, and the middle partition plate technical requirements: wall thickness 8 mm, casting material ZL101A, white mold material: EPS, castings must not have sand holes, pores, shrinkage , cracks and other defects, non-machined surface should be smooth and smooth, surface shot peening; castings using T6 solution heat treatment plus full artificial aging, casting hardness of 90-100HB castings dimensions: 589X589X404 (unit: mm), weight: 48.9 kg .

12-speed truck gearbox lost foam process casting difficulties:

1. The material is aluminum alloy, the casting temperature is 720-750 °C, the casting temperature is low, and the white mold is not easy to be gasified and liquefied.
2. The shape has many reinforcing ribs, the spacing of the reinforcing ribs is small, and it is easy to stick sand.
3, the internal partition and ribs more than oil holes, rib thickness 9.7mm, hole size: 30X27 (unit: mm), the ribs are easy to tear when forming.
4. The product is open on both sides, the internal cavity, the white mold is difficult to demould, and the anti-deformation measures should be taken during casting.
5. The shape of the box body is multi-shaped, and there are many side core inserts when the white mold is formed.
6. The coaxiality of the three bearing holes of the intermediate partition and the end face must be guaranteed.
7. The 4 sides of the box are closed, and it needs to be formed by two pieces of bonding.

In order to solve the above problems, it is necessary to introduce a lost foam mold structure of a 12-speed truck gearbox. The mold process should be consistent with the molding equipment of the foundry, conform to the lost foam casting production line of the foundry, and the complete set of lost molds of the foundry manufacturer. The production process is combined, and the mold structure adopts the following technical solutions:

Firstly determine the segmentation scheme, the structural analysis of the gearbox body, combined with the molding machine, the vibrating table, the coating, the bonding process, etc. of the casting manufacturer, the gearbox body should consider the white mold automatic molding process and the automatic bonding in the white zone section. Process. This process should focus on:

First: the white mold segmentation helps to automatically release the mold. The white mold adopts the cylinder automatic ejection mechanism during molding. The cylinder acts on the ejector rod and the stripper plate, so that the white mold is evenly forced to automatically push out 25mm, white mold and convex. The mold body is automatically separated, and the white mold is not deformed during the demolding process and is not displaced. Forming is stable.

Second: the white mold segmentation helps the automatic core pulling, and the inner and outer shape of the box determines its multi-side core pulling mechanism. After the piece is divided, all the side core inserts can be cylinder-assisted, so that the white mold is formed. The appearance quality is good, the efficiency is high, and it is not deformed.

Third: the white mold segmentation helps the automatic filling, and the white mold after the segmentation can effectively use the φ30mm straight-through automatic gun, which is dense in packing and uniform in density, and improves the filling speed of the white mold.

Fourth: the white mold segmentation helps to auto-heat and cool. When the white mold is formed, it can adopt automatic heating and spray cooling for a large area, so that the white mold is mature and the surface is smooth.

Fifth: The white mold segmentation helps the robot to operate. After the white mold is automatically ejected 25mm, the robot uses the suction cup to take out the white mold, and the white mold reserves enough position to place the suction cup.
Sixth: The white mold segment helps to automatically bond, the split surface is straight, no groove or inverted buckle, easy to use with automatic glue glue, easy to bond.

(Luoyang Liu’s Mould Co., Ltd. Liu Zhonghua, Zhang Guangbo)