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.

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.

Metal casting mold is one of the molds often used in cast aluminum plants. It is characterized by small casting tolerances, high efficiency, and beautiful surface of metal castings. Generally, after the acceptance, in order to maintain the performance state and the service life of the mold, the normal production and the quality of the product are ensured, and the production cost is reduced as much as possible, and regular inspection and maintenance are required.

First, preparation and inspection before casting

1. Wear protective equipment such as work clothes and safety shoes before you go to work.

2. Confirm the name of the casting and the metal casting mold number of the maintenance metal casting mold.

3. Find the casting sample and the two-mode aluminum casting of the metal casting mold, and inspect the faulty part of the metal casting mold aluminum casting.

4. According to the drawings and materials in the metal mold casting mold file, carry out the next step to confirm the required maintenance items, and develop a detailed maintenance plan.

5. Prepare the tools and accessories to be used, and do each step carefully and responsibly according to the maintenance plan.

Second, maintenance, grinding, assembly and cleaning of metal casting molds

1. After a period of production and use, a large amount of aluminum scraps and dirt accumulated on each movable part should be removed, and the parting surface, cavity, core, exhaust block and overflow trough should be more serious. During maintenance, the mold should be hung on the cleaning table with a cleaning tool such as a copper brush, a shovel, a rag, a brush, etc. to remove the aluminum slag products (aluminum, aluminum chips), oil stains, mold release residue or any other foreign matter on the mold. The dirt is removed. Be careful not to damage the cavity, core, etc. when cleaning.

2. When disassembling the mold, it should be noted that the combination of each component must have a relative number, which can be combined with the same number, and can not be misplaced. If the assembly is wrong, the phenomenon of flying aluminum will occur in the production, resulting in production failure.

3. Repair metal casting molds according to aluminum castings. Remove the residue in the cavity and save light in the cavity, the sticky aluminum on the core, and the collapse deformation. Repair the welds or changes in the meat to make it form and demould to prevent undercuts. Then check the slider, the guide rail and the position of the movable parts, and carry out effective mold repair and rectification.

4. Repair the mold parts that need to be replaced (such as cavity, ejector, cast pin, bolt, inclined guide post, slider and guide rail). If necessary, hand in the quality department inspection, and then replace the damaged parts after the inspection is correct, and assemble according to the installation identification code, beware of the wrong position and direction.

5. Cavity or core damage, can be modified as much as possible. If damage is required, replacement, repair or welding should be carried out as carefully as possible, and repair, replacement, excavation, and repair should be carried out under permitted conditions.

6. When assembling the disassembled mold parts, clean them before cleaning. Then apply rust prevention to the part of the mold (mold frame, cavity, insert, slider core, slider seat, splitter cone, barrel, cast pin, bead, wear block and exhaust block) The oil, as well as the guide pillar guide sleeve series and the moving parts such as the ejector rod and the reset rod, are rust-proof lubricating oil.

Third, the maintenance operation after the metal casting mold production operation

1. Regular cleaning and maintenance. In production and use, due to the uneven stress in the casting mold material under high temperature production, stress relief and tempering should be carried out to eliminate the internal stress generated during the production process. Prevent the casting mold from prolonging the production of high temperature conditions, and the material may be affected by deformation and fracture.

2. Tempering to do stress relief treatment. Maintenance is generally based on the size of the aluminum casting and the production batch size. When the mold is used in the production of 8 thousand molds to 10,000 molds, it is necessary to carry out secondary stress relief and tempering maintenance, and then carry out maintenance stress tempering treatment every 15,000 molds to 20,000 molds. Its service life.

3. When the mold is cracked or cracked, first check if there is any problem with the size. If there is no problem, first clean the surface residual aluminum residue product or any other foreign matter, and then use the abrasive cloth and oil stone thickness 150 particles to 400 particles for light treatment, and perform effective nitriding, ABP surface treatment or stress relief treatment, Improve product molding and surface quality. When there is a problem, the processing plan should be considered first, and the processing should be carried out after the processing is qualified.

4. Due to the wide variety of aluminum castings, the design structure of metal casting molds is complex and the conditions in production are different. Therefore, three points of stress relief processing, nitriding and ABP surface treatment are set as the maintenance basis.

5. The molds that have not been used for more than two months are cleaned and maintained by the staff. Open the mold and check the internal anti-rust effect. If there is any abnormality, it must be re-rustproofed. If you do not use it for a long time, you should apply butter to prevent rust and affect post-production. It must be cleaned and inspected before going to the machine.

Sand casting refers to a casting method for producing castings in a sand mold. Because the molding materials used in sand casting are cheap and easy to obtain, the castings are easy to manufacture, and can be adapted to the single-piece production, batch production and mass production of castings. For a long time, it has been the basic process in casting production.
Sand-type raw materials are foundry sand and sand binder.

The foundry sand has enamel sand, zircon sand, chromite ore, corundum sand and the like.

The binder is used to make the sand mold and the core made of the shaped sand have a certain strength, and the loose sand particles are joined together. There are clays, drying oils, semi-drying oils, water-soluble silicates or phosphates and various synthetic resins.

1. Clay wet sand type: The main binder of clay is made of clay and appropriate amount of water. After being made into sand type, it is directly combined and poured in a wet state. The strength of the wet sand depends on the clay slurry in which the clay and water are mixed in a certain ratio. The amount of clay and moisture are important process factors for the wet type of clay.


(1) Clay is rich in resources and cheap.

(2) Most of the used clay wet sand can be recycled after proper sand treatment.

(3) The cycle for manufacturing the mold is short and the work efficiency is high.

(4) The mixed molding sand can be used for a long time.

(5) After sand compaction, it can still withstand a small amount of deformation without damage, which is very advantageous for both drafting and lower core.


(1) Applying a thick clay slurry to the surface of the sand during sand mixing requires high-power sand mixing equipment with a smashing effect, otherwise it is impossible to obtain a good quality sand.

(2) Since the sand is well mixed, it has a relatively high strength. The molding sand is not easy to flow during the molding, and it is difficult to compact. The manual molding is both laborious and requires a certain skill. When the machine is used, the equipment is complicated and huge.

(3) The rigidity of the mold is not high, and the dimensional accuracy of the casting is poor.

(4) Castings are prone to defects such as sand washing, sand inclusion, and porosity.

2. The mold used for sand casting is generally composed of an outer sand type and a core. In order to improve the surface quality of the casting, a layer of paint is often applied to the sand and core surfaces. The main components of the coating are powdery materials and binders with high refractoriness, high chemical stability, and a carrier (water or other solvent) and various additives for ease of application.

3. Clay dry sand type: The wet moisture of the molding sand used to make this sand type is slightly higher than that of the wet type. After the sand mold is prepared, the surface of the cavity should be coated with a refractory paint, and then dried in an oven. After it is cooled, it can be combined and cast.

Disadvantages: It takes a long time to dry the clay sand type, which consumes a lot of fuel, and the sand type is easily deformed during the drying process, which affects the accuracy of the casting. Clay dry sand types are commonly used in the manufacture of steel castings and larger cast iron parts.

4. Chemically hardened sand type: The sand used for this type of sand is called chemically hardened sand. The binder is generally a substance which can undergo molecular polymerization under the action of a hardener to form a three-dimensional structure, and various synthetic resins and water glass are commonly used.

There are basically three ways of chemical hardening.

(1) Self-hard

Both the binder and the hardener are added during the sand mixing. After being made into a sand mold or a core, the binder reacts under the action of the hardener to cause the sand mold or the core to harden by itself. The self-hardening method is mainly used for styling, but it is also used to manufacture larger cores or to produce cores with a small batch size.

(2) Aerosol hardening

Add binder and other auxiliary additives during sand mixing without first adding hardener. After molding or core-making, a gaseous hardener is blown or blown into the gaseous carrier to atomize the liquid hardener, which is dispersed in the sand or core, resulting in sand hardening. Aerosol hardening is mainly used for core making and sometimes for small sand types.

(3) Heat hardening

A binder and a latent hardener which does not function at normal temperature are added during sand mixing. After the sand or core is made, it is heated, at which time the latent hardener reacts with certain components of the binder to form an effective hardener that hardens the binder, thereby hardening the sand or core. The heat hardening method is mainly used for core making except for the production of a small thin shell sand type.

Sand casting is one of the casting processes, and the mold used for sand casting is generally composed of an outer sand type and a core. Because the molding materials used in sand casting are cheap and easy to obtain, the castings are easy to manufacture, and can be adapted to the single-piece production, batch production and mass production of castings. For a long time, it has been the basic process in casting production. At present, internationally, in all casting production, 60 to 70% of castings are produced in sand, and about 70% of them are produced using clay sand.

The sand casting process is a casting method in which sand is used as a main molding material to prepare a mold. Sand casting is the most traditional casting method. Due to the characteristics of sand casting (not limited by the shape, size and alloy type, short production cycle and low cost), sand casting is still the most widely used casting method in casting production, especially single or small. Batch casting.

Advantages and disadvantages of sand casting process


1. Clay is rich in resources and cheap. Most of the used clay wet sand can be recycled after proper sand treatment;

2. The cycle for manufacturing the mold is short and the work efficiency is high;

3. Mixed sand can be used for a long time;

4. Adaptability is very wide. Small pieces, large pieces, simple pieces, complicated parts, single pieces, large quantities can be used;


1. Because each sand mold can only be cast-times, the mold is damaged after obtaining the casting, and must be reshaped, so the production efficiency of sand casting is low;

2. The rigidity of the molding machine mold is not high, and the dimensional accuracy of the casting is poor;

3. Castings are prone to defects such as sand washing, sand inclusion, and porosity.

Sand casting process

The basic process of the traditional sand casting process has the following steps: sand mixing, molding, core making, molding, pouring, falling sand, grinding processing, inspection and other steps.

1. In the sand mixing stage, the sand and core sand are prepared for the modeling. Generally, the sand mixer is used to put the old figure and the appropriate amount of clay to stir.

2. Mold stage, according to the parts drawings to make molds and core boxes, generally single pieces can be used to produce plastic molds or metal molds (commonly known as iron molds or steel molds) using wood molds, mass production, large-scale castings can be used to make models. Nowadays, the molds are basically made of engraving machines, so the production cycle is greatly shortened, and the molding generally takes 2 to 10 days.

3. The shape (core) stage: including the shape (formed cavity with casting sand to form the casting), core making (forming the internal shape of the casting), the mold to put the core into the cavity, the upper and lower sand box is good) . Modeling is a key link in casting.

4. The melting stage: according to the required metal components with chemical components, choose the appropriate melting furnace to melt the alloy material, forming a grid of liquid metal liquid (including qualified components, temperature qualified). Smelting generally uses a cupola or an electric furnace (due to environmental protection requirements, the cupola is now basically banned, and the electric furnace is basically used).

5. Pouring stage: the molten iron melted in the electric furnace is injected into the finished type with a ladle. The pouring of molten iron requires attention to the speed of pouring, so that molten iron fills the entire cavity. In addition, pouring molten iron is dangerous and needs to be safe!

6. Cleaning stage: After the pouring, after the molten metal solidifies, take the hammer to remove the gate and shake off the sand of the casting, and then use the sand blasting machine to spray sand, so that the surface of the casting will appear very clean! The casting blank is not strict. After inspection, it can be shipped out.

7. Casting processing: For some castings with special requirements or some castings that cannot meet the requirements, simple processing may be required. Generally, the grinding wheel or the sander is used for processing and polishing, and the burrs are removed to make the castings smoother.

8. Casting inspection: Generally, in the process of cleaning or processing, unqualified ones have been found out. However, some castings have individual requirements and need to be checked again. For example, some castings require a central hole to be inserted into a 5 cm shaft, so you need to wear a 5 cm shaft for a try.

After the above eight steps, the castings are basically formed, but for the castings that require precision, machining is still required.

Molds are various molds and tools used in industrial production for injection molding, blow molding, extrusion, die casting or forging, smelting, stamping, etc. to obtain the desired products. In short, a mold is a tool for making a shaped article, and the tool is composed of various parts, and different molds are composed of different parts. Next, let’s take a look at the mold design and production process!

First, manufacturing preparation

Prepare the molds to be made, whether it is materials or technicians, you need to be well prepared.

Second, feasibility analysis

Feasibility analysis of the products of the designed molds, taking the automobile parts as an example, firstly, the assembly drawings of each component are analyzed by the design software, that is, the set of drawings mentioned in our work, to ensure that the drawings of the products are correct before the mold design. On the other hand, you can familiarize yourself with the importance of each component in the entire car to determine the key size, which is very beneficial in the mold design. The specific set of drawings still needs to be designed by yourself.

Third, the structure

After the product analysis, the product to be analyzed, what kind of mold structure is used for the product, and the product is sorted, the content of each process is determined, and the product is developed by using the design software. To expand forward, for example, a product requires five processes, and the stamping is completed from the product drawing to the fourth, third, second, and first projects, and a graphic is copied and then the previous project is executed. The work of starting the work of the five projects is completed, and then the detailed work is carried out. Note that this step is very important and needs to be very careful. If this step is completed well, it will save a lot of time in drawing the mold diagram. After the stamping content of each project is determined, including in the forming mold, the inner and outer lines of the thickness of the product material are retained to determine the size of the convex and concave molds. The method for product unfolding is not described here, and will be in the product unfolding method. Specific introduction.

Fourth, preparation materials

According to the product development drawing, the template size is determined in the drawings, including the fixed plate, the unloading plate, the convex and concave mold, the insert, etc., pay attention to directly preparing the material in the product development drawing, which is of great benefit to the drawing mold drawing. I have seen that many mold designers directly calculate the product development drawings by hand. This method is too inefficient, draw the template size directly on the drawing, and express it in the form of a group diagram. The preparation of the material is completed, and on the other hand, a lot of work is saved in the work of the various parts of the mold, because in the work of drawing each component, it is only necessary to add the positioning, the pin, the guide post and the screw hole in the preparation drawing.

Fifth, draw drawings

After the preparation is completed, the mold drawing can be fully entered, and a copy can be made in the preparation drawing to draw the components, such as adding screw holes, guide post holes, positioning holes, etc., and in the punching die. The hole for each hole needs to be cut by the wire. In the forming die, the forming gap of the upper and lower molds must not be forgotten, so the mold drawing of one product after the completion of these work is almost completed 80%, and the process of drawing the mold drawing is also completed. Need to pay attention to: each process, refers to the production, such as the fitter scribing, wire cutting, etc. to the different processing steps have a complete production of the layer, which has great benefits for wire cutting and drawing management, such as color distinction, etc., size The labeling is also a very important job, but also a troublesome job, because it is too time consuming.

Sixth, proofreading

After the above drawings are completed, the drawings cannot be issued. It is also necessary to proofread the mold drawings, assemble all the accessories, make different layers for each different mold plate, and use the same reference as the guide post holes to perform the mold. Analyze the analysis and insert the product development drawings into the group diagrams to ensure that the hole positions of the template are consistent and the gap between the upper and lower molds of the bending position is correct.

Seven, production

During the production process, pay attention to check the glue position and check whether the glue position is uniform. If it is uneven, it will cause shrinkage and affect the appearance.

Eight, open the mold direction

Determine the parting surface and the draft angle

1. The parting surface selects the value projected in the mold opening direction and is as simple as possible.

2. Touching the position: Try to touch the back mold as much as possible. If you want to touch the front mold, it is easy to walk the front, affect the appearance, and use the plane contact.

3. Pillow: Pillow 5-8 mm, and then flat with the large part, the plastic part is pulled 3 degrees, the back is pulled 3 degrees or avoiding the air.

4. Insert the position: use the side work, pull 3 degrees, generally do inserts.

The above is the entire content of the mold design and manufacturing process. In general, the mold design and production process is mainly preparation preparation, production feasibility analysis and production design structure, preparation of production materials, drawing production drawings, and then in detail Proofreading, to ensure that the production is started after the error is correct, it is also necessary to pay attention to the direction of demoulding when demolding.

With the rise of lost foam casting, how to reduce the cost of castings, increase the yield and improve the quality is a problem. To solve such problems, the key is in the choice of sand type. Usually, in order to reduce the cost of sand, people will choose cheap quartz sand. However, due to the disadvantages of low refractoriness, poor gas permeability and poor fluidity, such sand has many casting defects during the casting process, such as: sand, pores. These defects are obvious in alloy steel casting. In addition, this kind of sand will generate a lot of dust in the subsequent treatment, which makes the environment of the production workshop very bad, the amount of waste sand increases, the sand is reduced, the sand recycling rate is low, and it is not durable. Therefore, from a comprehensive perspective, the cost of sand increases.

Nowadays, a new type of sand for lost foam casting has been widely concerned by the foundry industry and is known as the new sand “ceramic foundry sand” for green products. The major factors affecting the quality of castings and the excellent properties of ceramic foundry sand are summarized below.

1. Liquidity

Since the ceramic foundry sand is a spherical particle, its fluidity is very good, it is easy to compact when it is molded, and it can maintain good gas permeability, while quartz sand and forsterite sand are both polygonal sand, and the fluidity is poor. Originally, forsterite sand was used as the filling sand. Due to the poor fluidity of the polygonal sand, defects such as rat tail and scarring occurred many times. This phenomenon has been significantly improved after the use of ceramic foundry sand, improving the yield by 5%. Practice has proved that the fluidity of ceramic foundry sand is better than the existing various types of sand.

2. Refractoriness

The ceramic foundry sand is made of high-quality aluminum bauxite from Shanxi and is made by melting in a high-temperature electric furnace. Ceramic foundry sand is a spherical particle, the main component is aluminum oxide (Al2O3), its refractoriness can reach 1900 °C. The main component of quartz sand is silica (SiO2), which has a refractoriness of less than 1700 ° C. Quartz sand will have various crystals at different temperatures, which will reduce the refractoriness of the sand again during the casting process.

Practice has proved that the use of ceramic casting sand can significantly reduce mechanical and chemical sand, greatly reduce the labor intensity of sand cleaning, and is not easy to produce sand, sand, porosity and other defects. For example, the high-manganese steel castings produced by Jilin Innovation Lost Foam Equipment Co., Ltd., before the use of ceramic foundry sand, the sand-sanding and sand-sanding phenomenon is very serious, and each time it takes a lot of manpower and material resources to clean and polish the surface of the casting. It not only increases the production cost of the casting, but also causes the surface quality of the casting to be unattractive. This type of casting defect has been eliminated after the use of ceramic foundry sand. To this end, the cost savings are 6%. The ceramic refining sand is comparable to chromite ore and is now widely used in the casting of raw chromite ore.

3. Breathability

The permeability of the sand depends mainly on the size of the sand, the particle size distribution, the type of the grain and the type of binder. In the pouring process, if the permeability of the molding sand is poor, a large amount of gas generated by the internal heat due to high temperature cannot be immediately discharged, so that a bonfire phenomenon occurs, and defects such as pores, cold separation, and insufficient pouring are generated in the casting, and even scrapped.

Both quartz sand and magnesium olive sand are polygonal sands, which have poor gas permeability, while ceramic foundry sands are spherical particles with uniform particle size distribution and good gas permeability, which can avoid such casting defects. In the production of high-manganese wear-resistant steel castings, quartz sand and forsterite sand have been used successively, but the fruit is not ideal. Due to the poor gas permeability of the two sands, the molten bubble gas is not discharged, and a large number of knots are formed on the surface of the casting. Oh, and a large amount of gas generated by high-temperature heating during pouring cannot be discharged, resulting in defects such as porosity, crusting, and insufficient pouring, or the use of ceramic casting sand to solve this problem, and the yield is improved by 7%.

4. Thermal expansion coefficient

During the high-temperature casting process of castings, the thermal expansion of the molding sand will cause a slight change in the size of the molding sand, which in turn affects the accuracy of the casting size. The thermal expansion coefficient of the molding sand is too large, which may cause casting defects such as sand inclusion, crusting, and rat tail. The ceramic casting sand has a small coefficient of thermal expansion, and there is almost no expansion phenomenon during the casting process, which greatly improves the precision of the casting, and its performance is comparable to that of zircon sand. Henan Xinxiang has many manufacturers producing vibration equipment. There are many small holes in the wall panel. Due to its precision and refractoriness, zircon sand is used as casting sand. Ceramic casting sand is now used, and the cost of molding sand is reduced by 70%.

5. Reuse performance

Because quartz sand is polygonal sand, the strength is low, and the sand is easily broken during the modeling and sand treatment process. Not only will it generate a lot of dust, pollute the production environment, but also generate a lot of waste sand, which will make the sand not durable. According to statistics, The amount of waste sand cleared per pouring is about 5%. The ceramic foundry sand is spherical sand, which has high strength and is not easy to be broken. It can greatly reduce the amount of dust in the production workshop, reduce the labor intensity and production cost of the sand treatment workers, reduce the amount of waste sand, and increase the quantity of recycled sand. Thereby greatly reducing the amount of sand loss. According to statistics, the annual loss of ceramic foundry sand is below 5%. Therefore, the high cost caused by the high price of the ceramic foundry sand is directly offset, and the production cost is greatly reduced. According to the calculation of the manufacturer using the sand, the cost of the secondary increase can be recovered within 8-10 months.


Through the application of the lost foam and solid casting, the paper sprue tube does not produce an endothermic reaction or a gasification and cooling of the foaming runner at the beginning of the molten metal casting like the ceramic tube.

Because of its good thermal insulation performance, the paper sprue tube reduces the heat transfer of the molten metal to the pipe wall, so that keeping the molten metal without cooling is equivalent to increasing the temperature at which the molten metal enters the mold, and the temperature of the molten metal is relatively stable, prompting the molten metal. Filling is fast and smooth. The molten metal has sufficient time to replenish, which is beneficial to equalization and solidification.

The advantages of a paper sprue tube are as follows:

(1) Light weight, good toughness, easy to cut, easy to install, easy to connect with foam plastic runner.

(2) Good high temperature strength, high refractoriness and strong anti-scour ability. The paper sprue tube adopts socket connection, and the filter mesh is used together to filter the slag and impurities after pouring the molten metal into the runner, effectively preventing and Eliminate the occurrence of slag inclusion defects.

(3) Does not have any effect with the molten metal, maintains the original performance of the molten metal, and has no carburization problem for the casting. Use paper sprue tube, sprue cup and sprue superheat zone, sprue and sprue joint, no foam or paint layer, will not cause sand washing, sand inclusion and sand into the casting White spot (dot) defects. The paper sprue tube has high refractoriness, reducing and avoiding the formation of carbon deposits and wrinkle defects.

(4) Compared with the foam-coated sprue, the paper uses a hollow hollow sprue tube, and the initial casting does not burn the foam material, which reduces the incidence of the reverse reaction caused by the pyrolysis and gasification reaction of the foam material during pouring. Effectively reduce the heat loss of the runner metal liquid, and prevent the occurrence of problems such as sudden and small, broken flow during the casting process due to back spray.

(5) After pouring with a paper runner, there is little hard solid waste, which is easy to peel off after high temperature.

Paper sprue tube effect

According to the situation of a foundry enterprise, replacing the ceramic tube runner with a paper sprue tube, the same pattern can reduce the cutting and binding time, which can save 2/3 time; because the paper sprue tube itself is very light, The labor intensity of the operator is greatly reduced. The sprue splicing assembly task that originally required 2 to 3 people can be completed. Now it can be completed by one person under normal conditions, and the effect and efficiency are better than the original ceramic sprue tube. Paper sprue tubes are easy to cut, unlike ceramic sprue tubes, which require a special cutting machine. Originally used ceramic sprue tube cutting, noise, dust, and labor.

The paper sprue tube of the same specification is about 1/10 of the quality of the ceramic sprue tube. The texture is light and lightweight, and the handling and use are labor-saving. The former male worker can now be qualified and the labor intensity is greatly reduced. After using the paper sprue tube, the hand saw can be cut freely according to the length of use, and the dust is small, and there is almost no noise. The production workshop environment has been greatly improved.
It can be seen from the production site that after the use, due to the socket connection and the tight interface, the risk of the molding sand entering the mold during the molding is eliminated, so that the sand inclusion defect is reduced, the scrap rate of the foundry is significantly reduced, and the economic benefit is obviously improved.


The raw material of the paper sprue tube is made of waste paper and special materials. It is non-burning, light weight and degradable. It realizes the reuse of resources and reduces environmental pollution. It is supported by the national environmental protection policy. The paper sprue pipe has various specifications such as straight pipe, elbow pipe, equal-diameter tee, variable-diameter tee, and variable-diameter straight-through. The lower end of the pouring cup can be customized with a tight seamless interface, and adopts a stop form; generally, the common sprue tubes are mainly round.

At present, the price of paper sprue tubes is relatively high, causing users to hesitate and influencing the use of casting enterprises. Therefore, improving quality and reducing costs are new issues faced by paper sprue pipe manufacturing enterprises. It is believed that with the continuous advancement of technologies such as industrialization and automation, the widespread use of paper sprue pipes in the foundry industry will become a reality.

Paper sprue tubes have many advantages over paper sprue tubes compared to (solid) sprues, sprues, and ceramic sprue tubes that have been widely used in plastic foam sheets, resulting in solid casting of resin sand. The casting system of castings such as large machine bed is simplified, the whole process of production is simplified, the casting defects are obviously reduced, and the high-quality castings are cast in a short production cycle, which brings significant economic benefits to the enterprise.

The solid sand casting process has its unique advantages. There is no drafting angle and there is no model parting surface. It can not only save the cost of making wooden models for the production of single or small batches of machine bed, base and other castings. Moreover, it has the advantages of good surface quality, high dimensional accuracy and small processing allowance; it can also save the core making and drying process; it saves the cumbersome process such as the hanging core and the card core of the molding process, and the operation is more convenient; especially It shortens the production cycle and significantly improves the production efficiency, so it is favored by the machine tool casting industry.

1. Characteristics and problems of machine tool castings

Large machine bed, column, base and box castings are usually made of HT200 ~ HT350. They generally have a complicated internal cavity structure, and the wall thickness is usually 12 ~ 30 mm. The traditional sand casting process (such as resin sand molding) requires more cores to form the inner cavity of the casting. There are some disadvantages:

(1) because the batch size of such castings is not too large, different model specifications require different wood molds. More cores require more core shell molds, which increases the cost and manufacturing cycle of the mold, and also increases the difficulty of mold management;

(2) Since the inner cavity is formed by combining a plurality of cores, the difficulty in controlling the dimensional accuracy of the casting is increased;

(3) The gap between the cores will enter the molten iron, forming flash edges and winged wings, and the grinding and cleaning work of the castings will increase the difficulty and difficulty.

In order to overcome the shortcomings of the above-mentioned traditional sand casting production, the resin sand foam solid casting process has been widely used in the production of large machine tool castings, but the foam solid casting also has some unfavorable characteristics, the most typical of which are three:

(1) Casting requires the formation of high-temperature molten iron to dissolve solid materials (such as EPS), which requires a large amount of heat, and therefore requires a higher pouring temperature;

(2) The pyrolysis material will generate a large amount of gas and residue, and the risk of forming pores and slag inclusions on the casting is high;

(3) A large amount of harmful gases containing benzene and toluene and black smoke are emitted during the pouring process, and environmental protection problems need to be solved. If the casting system is also made of a solid material such as EPS, the damage is even greater because the molten iron is first passed through the casting system.

The use of ceramic tube material as a casting system can effectively overcome the above shortcomings, but the ceramic tube casting system also has shortcomings:

(1) Ceramic tubes are hard, brittle, difficult to cut, and also heavy, and a slightly complicated casting system is difficult to assemble;

(2) The ceramic tube is sintered from the material of the sputum, and the pouring process is eroded by the erosion of the high-temperature molten iron, and there is a risk of falling into the cavity to form inclusion defects;

(3) The ceramic tube fragments after casting sand falling into the sand will be mixed into the sand recycling and regeneration system, which increases the difficulty and cost of recycling and recycling of the sand.

The use of paper materials instead of ceramic materials to make casting casting systems has many advantages and is a development trend. Firstly, the paper material is light and thin, easy to cut, and can be assembled into a complicated casting system. Secondly, the paper casting system is carbonized by high-temperature iron combustion, and the residual is small, and the risk of forming inclusion slag is extremely small; The mixing of ceramic runner tube residues into old sand creates problems that are difficult to clean and reclaim.

2. Application of paper sprue tube in solid casting of resin sand

The casting system of solid sand casting is the same as that of traditional sand casting. It consists of a pouring cup (gate basin), a sprue, a sprue, and a gate. The function of the molten iron is also fast. Smoothly attract people. For large and medium-sized machine tool castings, stepped or medium-sized injections are used to make the flow of molten iron as smooth as possible, and the filling is smooth and fast.

The number of sprues for medium and large machine tool castings can be set to two or more, and some large and extra large castings even need to place 4 to 6 sprues. A sprue basin shall be placed on the sprue to store a certain amount of molten iron. When the pouring is not interrupted, the molten iron can flow into the mold under normal pressure, which can effectively prevent back spray and bonfire from the sprue during pouring. .

The sprue uses a paper sprue tube and two or more sprues can use the same larger sprue basin. When using it, it should be noted that the paper sprue tube needs the sand type to provide support force, and the compactness of the molding sand should be suitable, but the sprue tube should not be damaged too much. The casting filling process is a high-temperature metal liquid casting cavity. The pouring pipe is subjected to the gravity flushing of the molten metal, and also has to withstand the tension of the high-temperature molten metal to the sprue pipe wall; the pouring system is in the high-temperature collecting zone, and all the entering the cavity The molten metal has to pass by. In particular, the use of large-tonnage castings requires that the outer wall of the “paper sprue tube” have a constant supporting force to ensure that the entire filling process is not destroyed.

The sprue and sprue tubes of the paper sprue tube can be connected as a whole, and the size and length of the caliber are determined by the casting system process of the casting. The connection method of the paper sprue tube is a socket interface, which is very convenient, and the length of the sprue tube can be cut by hand saw. The paper sprue tube and fittings are simple and flexible to assemble.

3. The link (assembly) method

(1) Socket (embedded). Insert the lower end of the hollow tube into the socket. It is best to apply a small amount of adhesive to the outer wall before insertion so that the connection between the two is better.

(2) Nesting (stop type). The bottom of the gate cup, the hollow tube of the paper sprue has an inner diameter of the outer diameter of the foam plastic white mold (which can be 0.5 mm larger, the foam plastic mold can be shrunk), and one end of the hollow tube is inserted into one end of the circular diameter of the foam plastic white mold ( Can not be painted in the nesting section).

(3) Bonding (section adhesive). When installing the paper sprue tube before the casting, in order to prevent the distortion and finally put it on the glass plate, according to the total amount of molten iron used in the casting + pouring system, including flow direction, flow selection sprue tube diameter, diameter reduction, turning, three The pipe, pipe and pipe used are all connected by sockets to ensure that the paper sprue pipe is firmly connected. In this way, it is possible to effectively prevent the occurrence of sand inclusion defects due to inadvertent operation during molding. If the two sections of the sprue of the paper sprue hollow tube are flat, the cross-section of the outer wall and the inner wall of the two-end tube and the cross section of the sprue must be adhered with adhesive glue, and wrapped with glass cloth or tape paper. can.

(4) Bonding plus refractory mud strips. The pouring cup and the hollow tube are not integrated, and the sprue is leaked out of the top surface of the sand box by 3~5 mm, and the hollow tube is tightly packed with a foam block to prevent debris. Place a circle of refractory mud strips around the box, place the sprue cups on top and join them with refractory mud strips at the joints (such as sealing mud strips), or the bottom surface of the sprue cups and the top surface of the sprue hollow tubes Adhesive with adhesive, the outer ring is brushed with refractory mud.

(5) Other bonding. According to the size and shape of the gate cup and the sprue, the hollow sprue can be modified according to the above method.

The body of the lost foam mold is made of forged aluminum or cast aluminum. It is used in alternating hot and cold water environments. Different maintenance methods are required depending on the mold structure.

First, the maintenance of manual disassembly mold

Before using the mold, check the following items.

1. Whether the filling port is smooth;

2. Whether the locking screw can be locked;

3. Whether the insert block is in place;

4. Whether the air plug hole is blocked;

5. Whether the upper and lower molds can be tight;

6, whether the mold has cracks;

7. Whether the surface of the mold cavity is heavily abrasive;

8. Whether the water pressure gauge and the air pressure gauge are normal;

9. Is the pipeline valve normal;

10. Is the water pH of the water user appropriate;

11. Is the autoclave normal.

Through the above inspection content to determine the maintenance of manual molds to achieve the following four aspects:

1. Try to use the standard gun of the mold factory, use stainless steel round bar, can not block the gun hole due to rusting of other materials or block the air plug hole due to rust, and use stainless steel bolts for locking screws. Replace it as soon as possible to ensure that the mold can be locked at each opening and closing to prevent flashing of the material during molding.

2. The mold is matured by hot steam, and then cooled by cold water. Inevitably, the outer surface of the mold is covered with scale such as calcium carbonate, which affects the hot and cold exchange of the mold, the molding quality, and more serious blockage of the gas plug hole, so that the hot steam can not Arriving at the surface of the mold cavity, and overhauling the mold, replacing the gas plug, which requires the mold to be descaled and maintained around the week. The descaling is to put the mold in a weak acid environment to soften the scale and then knock it off. The material determines that the mold can not stay in a weak acid environment for a long time, and it is easy to corrode the surface of the cavity. Descaling is a big challenge for the maintenance of the lost mold. Our company now finds that the solution can easily remove the scale of the mold without corroding the mold. Cavity surface. The water quality is often checked so that the mold water environment is in a weak alkaline environment, and it is not easy to cause the mold to generate scale.

3. Because the foam also has a certain corrosive effect and wear on the surface of the mold cavity, this requires a special cover mold on the surface of the mold, which is resistant to acid and alkali, high temperature and can ensure the smooth and easy mold release of the mold surface, and can also be used with the mold. The material has a good affinity, and the surface of the mold cavity is not easy to fall off. The mold of our company adopts the special fluorocarbon coating technology, covering 0.02mm thick fluorocarbon film on the surface of the mold to meet the requirements of the mold. Performance requirements.

4. Manual molds need to be disassembled and handled by hand during use. Pay attention to the lightness during use and try to extend their service life. Inspections before use of autoclaves, pipes, etc. can also avoid some hidden dangers of the mold during molding.

Second, the maintenance of ordinary lost molds

Ordinary machine molds are used on the molding machine, and the maintenance method is similar to that of the manual mold. The following are the following aspects:

1. Before the mold is installed, check the upper and lower templates of the molding machine to ensure clean and flat. If it is not used for a long time, first remove it and clean it, and check the pipeline valve to ensure that the joint points are airtight and non-wetting. Ventilation and water flow are smooth and controllable.

2. Before installing the mold, check whether the individual inserts and core blocks of the mold are assembled in place to ensure that the mold will not escape to the mold air chamber during the filling process.

3. Before the mold is installed, the sealing strips of the upper and lower air chambers of the mold and the forming surface of the forming machine and the separating surface of the mold are installed to ensure that the forming effect of the foam pattern is not affected by the air leakage during the molding process.

4. When installing the machine, ensure that the mold is positioned and fixed on the molding machine, and the method of four-sided positioning is adopted to make the force uniform.

5. During the molding operation, the mold is first opened and closed to ensure that the upper and lower molds are semi-stable.

6. For those who have manual core pulling, the mold should be used according to the operation process. It is first to open the mold and then draw the core, or to draw the core and then open the mold. First, understand the sequence and ensure that the mold will not be crushed due to operational errors. Or scrapped, the inserts and live blocks taken out by the core are placed reasonably, and the underlying foam protection inserts and the live blocks are not bumped. For moving parts, it can be lubricated without affecting foam molding.

7. The surface of the mold cavity is coated with fluorocarbon. It is not possible to scratch the surface of the mold with sharp objects, which affects the foam forming fruit.

8. After the mold is used for 2 weeks, the scale treatment is carried out, and the molding machine template is rustproofed.

Third, the maintenance of automatic lost mold

The use of the automatic lost mold mold mainly involves the service life of the cylinder and the use environment. In addition to the above, the maintenance and maintenance of the cylinder is the maintenance of the cylinder.

1. Before the mold is installed, simulate the opening and closing of each cylinder to ensure smooth and smooth movement of the core block and the stripper, and the stroke is appropriate.

2. For the external cylinder, after understanding the sequence of the core-opening mold, it is only necessary to apply oil lubrication frequently to ensure that there is no hair jam between the sliding sleeve and the copper sleeve.

3. For the internal cylinder, because it is used in the environment where the hot steam and the cooling water circulate back and forth, the heat-resistant cylinder is used, and it is replaced regularly according to the difference of the water quality. Under normal circumstances, the batch is changed for 2 months, and the model is guaranteed when replacing. The journey is consistent.