CN109365739B

CN109365739B - Precoated sand for medium-thickness stainless steel castings

Info

Publication number: CN109365739B
Application number: CN201811504394.9A
Authority: CN
Inventors: 单艳军; 李青春; 杨晓平; 武晓峰; 赵作福
Original assignee: Kezuo Houqi Xingda Sand Industry Co ltd
Current assignee: Kezuo Houqi Xingda Sand Industry Co ltd
Priority date: 2018-12-10
Filing date: 2018-12-10
Publication date: 2021-07-23
Anticipated expiration: 2038-12-10
Also published as: CN109365739A

Abstract

The precoated sand for the stainless steel casting with the medium thickness comprises, by weight, 50-55 parts of Baozhu sand, 30-35 parts of Hainan sand, 8-15 parts of white corundum, 2-5 parts of iron sand, 1.6-2.0 parts of binder phenolic resin, 15-20% of curing agent urotropine and 4-8% of lubricant calcium stearate. The invention has simple process, convenient operation, easy realization and no pollution. Is suitable for pouring stainless steel castings with the temperature of more than 1650 ℃. The obtained stainless steel casting has clear outline and accurate size, the surface roughness reaches the level of investment casting, and the stainless steel casting can be processed without mechanical processing or only by a small amount.

Description

Precoated sand for medium-thickness stainless steel castings

Technical Field

The invention belongs to the technical field of casting, relates to precoated sand, and particularly relates to precoated sand for casting a medium-thickness stainless steel casting with the thickness of 10-40 mm and the size of 800 mm.

Background

The traditional stainless steel casting process uses investment casting. The investment casting process has the advantages of high production cost, complex procedures, long production period, low efficiency, more manual operations and low yield. With the continuous rising of the prices of raw and auxiliary materials and labor force and the annual increase of the national requirements on environmental protection, it is inevitable to find a casting process which is low in cost, environment-friendly, convenient and practical to replace an investment casting process. Compared with investment casting, the precoated sand shell mold has the advantages of low casting production cost, simple and convenient shell manufacturing, short production period, high efficiency, high per capita yield, high yield and qualification rate, good production environment, low labor intensity and good process adaptability, the size precision of the casting can reach CT7-CT8 level, and the surface roughness Ra value of the casting is 6.3-12.5.

The shell mold casting is suitable for producing castings with large batch, high requirement on dimensional accuracy and complex shapes. However, any casting process has its applicability. The traditional precoated sand shell mold casting is only applied to materials such as cast steel, cast iron, cast copper, cast aluminum and the like. For stainless steel castings, the casting temperature is required to be about 1650 ℃, the casting temperature is high, the high-temperature strength of phenolic resin in a conventional precoated sand shell mold can only be maintained for a short time of about 25 seconds, the content of the phenolic resin is up to more than 2.0 percent, and the gas evolution is large, so that the stainless steel castings are produced by adopting a common precoated sand shell mold casting process, and particularly the thicker castings have the defects of sand sticking on the surface, rough surface, air holes, heat cracking and the like. In order to make the surface quality of the casting reach the level of investment casting, a method of spraying zircon powder and other coatings on the surface of the shell mold is adopted, but the dimensional accuracy of the casting is influenced. Therefore, until now, people cannot prepare stainless steel castings with medium thickness by adopting a precoated sand shell type casting mode.

Disclosure of Invention

The invention aims to solve the technical problem of providing the precoated sand for the stainless steel casting with medium thickness, which is suitable for pouring the stainless steel casting with the pouring temperature of more than 1650 ℃. The obtained stainless steel casting has clear outline and accurate size, the surface roughness reaches the level of investment casting, and the stainless steel casting can be processed without mechanical processing or only by a small amount.

The technical scheme of the invention is as follows:

the precoated sand for the stainless steel casting with the medium thickness comprises, by weight, 50-55 parts of Baozhu sand, 30-35 parts of Hainan sand, 8-15 parts of white corundum, 2-5 parts of iron sand and 1.6-2.0 parts of binder phenolic resin, wherein the addition amount of a curing agent urotropine is 15-20% of the mass percentage of the phenolic resin, and the addition amount of a lubricant calcium stearate is 4-8% of the mass percentage of the phenolic resin.

Further, the precoated sand manufacturing process comprises the following steps: uniformly mixing Baozhu sand, Hainan sand, white corundum and iron sand serving as raw sand, preserving heat at 200 ℃ for 15-20 min, adding phenolic resin when the temperature of the raw sand is reduced to 125-135 ℃, stirring for 90-100 seconds, adding urotropine and calcium stearate, stirring, cooling, crushing, and screening to obtain the precoated sand for the stainless steel casting with medium thickness.

Furthermore, the Baozhu sand, Hainan sand, white corundum and iron sand are used as raw sand, the granularity of the raw sand is 70-140 meshes, and the proportion of the raw sand is shown in Table 1.

Further, the addition amount of the urotropine is 17-20% of the mass percentage of the phenolic resin.

Furthermore, the precoated sand has the performances of high strength, high temperature resistance and low gas evolution, can be used for casting stainless steel castings with the thickness of 10-40 mm and the size of 800mm, is suitable for casting stainless steel castings with the pouring temperature of more than 1650 ℃, and has the surface quality of the castings reaching the level of investment casting.

The invention has the beneficial effects that:

the invention has simple process, convenient operation, easy realization and no pollution. Alkaline or neutral substances are selected as raw sand of the precoated sand, and products suitable for oxidizing stainless steel liquid are taken as alkaline substances. The Baozhu sand and the white corundum are neutral, have high refractoriness and are suitable for pouring the raw sand for stainless steel parts. The addition of the iron sand can promote the formation of an iron oxide film with enough thickness, so that the bonded sand layer is easy to peel off from the surface of the casting, thereby avoiding the formation of chemical bonded sand. Although the Hainan sand is acidic, the Hainan sand has high purity and the addition amount is reasonably controlled, so that the surface quality of a casting is not influenced, and the cost is reduced. The precoated sand is suitable for pouring a stainless steel casting with the temperature of more than 1650 ℃, the obtained stainless steel casting has clear outline and accurate size, the surface roughness reaches the level of investment casting, and the precoated sand can be processed without machining or in a small amount.

Drawings

FIG. 1 is a comparison of the surface quality of the precoated sand shell casting (corresponding to example 1) and investment cast stainless steel castings of the present invention.

Detailed Description

Example 1

Weighing the following raw materials: 50kg of Baozhu sand, 30kg of Hainan sand, 15kg of white corundum, 5kg of iron sand, 1.8kg of phenolic resin, 0.306kg of urotropine and 0.144kg of calcium stearate; the Baozhu sand, Hainan sand, white corundum and iron sand are used as raw sand, and the granularity of the raw sand is 70/140 meshes; the ratios are shown in Table 1;

TABLE 1

Number of meshes	70 mesh	100 mesh	120 mesh	140 mesh
					In proportion wt%	22.7	52.8	20.2	4.3

Uniformly mixing Baozhu sand, Hainan sand, white corundum and iron sand serving as raw sand, preserving heat at 200 ℃ for 15min, adding phenolic resin when the temperature of the raw sand is reduced to 135 ℃, stirring for 90 seconds, adding urotropine and calcium stearate, stirring, cooling, crushing, and screening to obtain the precoated sand for the stainless steel casting with medium thickness.

FIG. 1 is a comparison of the surface quality of coated sand shell and investment cast stainless steel castings. The thickness of the cast product cast by the precoated sand shell type casting method is 40mm, and the thickness of the cast product cast by the investment casting method is 20 mm. The figures illustrate that, although the precoated sand shell cast castings are thicker than the investment cast castings, the surface quality of the two is close.

Example 2

Weighing the following raw materials: 50kg of Baozhu sand, 35kg of Hainan sand, 12kg of white corundum, 3kg of iron sand, 1.6kg of phenolic resin, 0.304kg of urotropine and 0.096kg of calcium stearate; the Baozhu sand, Hainan sand, white corundum and iron sand are used as raw sand, and the granularity of the raw sand is 70/140 meshes; the ratios are shown in Table 1;

uniformly mixing Baozhu sand, Hainan sand, white corundum and iron sand serving as raw sand, preserving heat at 200 ℃ for 20min, adding phenolic resin when the temperature of the raw sand is reduced to 125 ℃, stirring for 100 seconds, adding urotropine and calcium stearate, stirring, cooling, crushing, and screening to obtain the precoated sand for the stainless steel casting with medium thickness. The precoated sand has the performances of high strength, high temperature resistance and low gas evolution, can cast stainless steel castings with the thickness of 10mm-40mm and the size of 800mm, is suitable for stainless steel castings with the pouring temperature of more than 1650 ℃, and the surface quality of the castings reaches the level of investment casting.

Example 3

Weighing the following raw materials: 45kg of Baozhu sand, 38kg of Hainan sand, 3kg of white corundum, 4kg of iron sand, 1.7kg of phenolic resin, 0.34kg of urotropine and 0.068kg of calcium stearate; the Baozhu sand, Hainan sand, white corundum and iron sand are used as raw sand, and the granularity of the raw sand is 70/140 meshes; the ratios are shown in Table 1;

uniformly mixing Baozhu sand, Hainan sand, white corundum and iron sand serving as raw sand, preserving heat at 200 ℃ for 18min, adding phenolic resin when the temperature of the raw sand is reduced to 130 ℃, stirring for 95 seconds, adding urotropine and calcium stearate, stirring, cooling, crushing, and screening to obtain the precoated sand for the stainless steel casting with medium thickness. The precoated sand has the performances of high strength, high temperature resistance and low gas evolution, can cast stainless steel castings with the thickness of 10mm-40mm and the size of 800mm, is suitable for stainless steel castings with the pouring temperature of more than 1650 ℃, and the surface quality of the castings reaches the level of investment casting.

Comparative example 1

The precoated sand comprises, by weight, 60kg of jewel sand, 35kg of Hainan sand, 5kg of iron sand, 1.8kg of phenolic resin, 0.306kg of urotropine and 0.144kg of calcium stearate; the Baozhu sand, Hainan sand and iron sand are used as raw sand, and the granularity of the raw sand is 70/140 meshes; the ratios are shown in Table 1; the manufacturing process is the same as example 1.

Comparative example 2

The precoated sand comprises, by weight, 95kg of Hainan sand, 5kg of iron sand, 1.8kg of phenolic resin, 0.306kg of urotropine and 0.144kg of calcium stearate; the Hainan sand and the iron sand are used as raw sand, and the granularity of the raw sand is 70/140 meshes; the ratios are shown in Table 1; the manufacturing process is the same as example 1.

Comparative example 3

The precoated sand comprises 90kg of Hainan sand, 5kg of white corundum, 5kg of iron sand, 1.8kg of phenolic resin, 0.306kg of urotropine and 0.144kg of calcium stearate according to the weight ratio; the Hainan sand, the white corundum and the iron sand are used as raw sand, and the granularity of the raw sand is 70/140 meshes; the ratios are shown in Table 1; the manufacturing process is the same as example 1.

Table 1 shows the performance parameters of the precoated sand according to the present invention in example 1, example 2, and example 3, and in comparative example 1, comparative example 2, and comparative example 3. As can be seen from table 1, the gas evolution of the precoated sand described in the examples was lower than that of the comparative precoated sand, and the room-temperature tensile strength was high.

TABLE 1

	Resin amount%/g	Gas evolution volume mL/g	Tensile strength at room temperature MPa
				Comparative example 1	1.8	11.70	3.46
Comparative example 2	1.8	12.84	3.15
				Comparative example 3	1.8	13.10	3.43
Example 1	1.8	10.12	4.67
				Example 2	1.7	10.06	3.76
Example 3	1.6	9.56	3.61

The above description is only exemplary of the present invention and is not intended to limit the present invention, and various modifications and changes may be made by those skilled in the art. Any modification, equivalent replacement, or improvement made within the spirit and principle of the present invention should be included in the protection scope of the present invention.

Claims

1. The utility model provides a medium thickness stainless steel foundry goods is with tectorial membrane sand, characterized by:

the composite material comprises, by weight, 50-55 parts of Baozhu sand, 30-35 parts of Hainan sand, 8-15 parts of white corundum and 2-5 parts of iron sand, wherein the granularity of the iron sand is 70-140 meshes;

1.6-2.0 parts of binder phenolic resin, 15-20% of curing agent urotropine and 4-8% of lubricant calcium stearate;

the precoated sand can be used for casting a stainless steel casting with the thickness of 10-40 mm and the size of 800mm, is suitable for casting a stainless steel casting with the pouring temperature of more than 1650 ℃, and ensures that the surface quality of the casting reaches the level of investment casting.