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Design Requirements and Influencing Factors of Precision Castings

Released on Mar. 01, 2020

China butterfly valve manufacturer in china shares with you: the method of casting liquid metal into a casting cavity suitable for the shape of the part, and cooling and solidifying to obtain the part or blank is called casting. The casting obtained by casting is called casting.

Casting structure design: In order to ensure its working performance and mechanical performance requirements, taking into account the requirements of the casting process and alloy casting properties on the casting structure, whether the structural design of the casting is reasonable or not, it has a great impact on quality. Production efficiency and casting costs.

What is a precision casting and what are its design requirements?

The main problems and design requirements of the design, the layout of the parts inside the box, and the relationship between the parts outside the box and the parts outside the box should be considered first in the design. For example, the shape and size of the box should be determined by the lathe according to the requirements of the two minarets. In addition, the following issues should be considered:

(1) Meet the requirements of strength and stiffness. It is an important issue to meet the strength of the box with a large force, but for most box parts, the main index for evaluating its performance is stiffness, because the stiffness of the box part not only affects the normal work of the transmission part, And affect its performance. Durability of parts. Includes automatic selection of castings.

(2) Heat dissipation and thermal deformation. The frictional heating of the parts inside the box changes the viscosity of the lubricant and affects the lubrication performance. The increase in temperature causes thermal deformation of the box, especially thermal deformation and thermal stress with uneven temperature distribution, which has a great impact on the accuracy and strength of the box.

(3) The structural design is reasonable. For example, the fulcrum arrangement, the reinforcement arrangement, the location of the openings, and the design of the connection structure are all conducive to improving the strength and stiffness of the box.

(4) Good technology. Including blank manufacturing, machining and heat treatment, assembly adjustment, installation and fixing, lifting and transportation, maintenance and repair.

(5) Good appearance and small quality.

Identity that affects the dimensional accuracy of compact castings: Under normal circumstances, the dimensional accuracy of compact castings is affected by multiple factors such as the layout of the casting, the material of the casting, the mold, the shell, the firing, and the casting. At any point in the process, there are differences in setting and manipulation Licheng transformed the shortening rate of castings, which caused errors in the dimensional accuracy of castings and requirements. The following are the identities that can contribute to the dimensional accuracy disadvantages of compact castings:

(1) Influence of casting layout: a. Thickness of casting wall, large shortening rate, thin casting wall, small shortening rate. b. The free shortening rate is large, and the obstacle shortening rate is small.

Steel Castings

Steel Castings

What are the factors that affect the dimensional accuracy of steel castings?

(2) Influence of casting material: a. The higher the carbon content in the material, the smaller the wire shortening rate, and the lower the carbon content, the greater the wire shortening rate. b. Forging reduction rate of common materials is as follows: casting reduction rate K = (LM-LJ) / LJ × 100%, LM is cavity size, LJ is casting size. K is affected by the following identities: wax mold K1, casting layout K2, alloy variety K3, and pouring temperature K4.

(3) The influence of mold making on the shortening rate of the casting line: a. The effect of wax injection temperature, wax injection pressure, and holding time on the size of the investment mold is the temperature of the wax injection, followed by the injection wax pressure, and the holding pressure at After the investment molding of the tube is formed, the effect on the final size of the investment mold is small. b. The linear shortening rate of wax (mold) is about 0.9-1.1%. c. When the investment pattern is registered, the shortening will occur further. The shortened value is about 10% of the total shortened amount, but after 12 hours of registration, the basic size of the investment pattern does not change. d. The radial shortening rate of the wax mold is only 30-40% of the target shortening rate of the length target. The effect of the waxing temperature on the free shortening rate is far greater than the effect of the blocked shortening rate (the better waxing temperature is 57-59). ℃, the higher the temperature, the greater the shortening).

(4) Impact of shell materials: Zircon sand, zircon powder, Shangdian sand, Shangdian powder are used. Because of its small shrinkage coefficient, it is only 4.6 × 10-6 / ℃, which can be ignored.

(5) Effect of roasting of the shell: Because the shrinkage coefficient of the shell is small, when the shell temperature is 1150 ° C, it is only 0.053%, so it can be neglected. (6) The influence of casting temperature: the higher the pouring temperature, the larger the shortening rate, the lower the pouring temperature, and the smaller the shortening rate, so the pouring temperature should be appropriate.

(5) Effect of roasting of the shell: Because the shrinkage coefficient of the shell is small, when the shell temperature is 1150 ° C, it is only 0.053%, so it can be neglected. (6) The influence of casting temperature: the higher the pouring temperature, the larger the shortening rate, the lower the pouring temperature, and the smaller the shortening rate, so the pouring temperature should be appropriate.

When the shell mold sintering of the precision casting is formally carried out, the delaminated wax shell mold is pushed by the shell mold to the sintering furnace, and the shell mold is taken out to check whether there is any break or crack. Next, place it neatly on the shell mold cart. Start the main power of the sintering furnace, open the furnace door, and clean the furnace with a broom and air gun. Use the shell mold fork to carefully lift the shell mold in turn, and slowly put it into the furnace. Note that during the insertion process, the shell mold must not touch the bottom or the wall of the furnace to prevent it from breaking. Set the sintering temperature according to the product type and technical requirements, generally 1000 ~ 1200 ℃. Start the sintering oil pump, the oil pressure is about 105 ~ 2.0kg / m2. Use a torch to ignite in the combustion nozzle. After the ignition is successful, the flame will be stabilized and the furnace will be preheated. When the hearth of a furnace is preheated to above 600 ° C, the shell is heated up, the furnace door is closed, and the oil quantity and air pressure are adjusted again to enable it to burn completely.


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