CN111604471B - Gypsum shell with low residual strength and preparation method thereof - Google Patents

Abstract

A gypsum shell with low residual strength and a preparation method thereof. The gypsum shell contains gelatin. The method comprises the following steps: uniformly mixing gypsum powder and filler; heating water, adding gelatin, and mixing to obtain transparent solution; adding mixed powder of gypsum powder and filler into the transparent solution to obtain slurry; pouring the slurry into a mold; after the slurry in the mold is hardened, the mold is dismantled and stands at room temperature to obtain a wet gypsum shell; and naturally drying and roasting the wet gypsum shell to obtain the gypsum shell with low residual strength. The gypsum shell has the advantages of low residual strength, easiness in cleaning, simple preparation method and high production efficiency.

Description

Gypsum shell with low residual strength and preparation method thereof

Technical Field

The present invention relates to the field of inorganic non-metal material, in particular, it relates to a gypsum type shell with low residual strength and its preparation method.

Background

The gypsum type precision casting process is a main process for forming nonferrous metals, and is the most widely used process in the current production. The most important factor determining the quality of the cast is the strength of the gypsum shell. Wherein, the residual strength is the strength of the shell after the casting of the poured alloy liquid is solidified. Aiming at the defects of high labor intensity, incomplete cleaning and the like of shell cleaning after pouring, the residual strength of the shell is properly reduced, and the method has important significance for accelerating the cleaning speed and improving the production efficiency and the economic benefit. However, at present, researchers at home and abroad pay more attention to how to improve the wet strength of the gypsum shell at normal temperature and the high-temperature strength after drying and roasting, and researches are fresh for reducing the residual strength of the shell and improving the mechanical properties after roasting.

Disclosure of Invention

The application provides a gypsum shell with low residual strength and a preparation method thereof.

A gypsum shell having low residual strength is provided, which contains gelatin.

In an embodiment of the present application, the raw materials for preparing the gypsum shell may include: gypsum powder, filler, gelatin and water.

In the embodiment of the present application, the addition amount of the gypsum powder may be 20 to 40 parts by weight, the addition amount of the filler may be 60 to 80 parts by weight, the addition amount of the water may be 40 to 50 parts by weight, and the addition amount of the gelatin may be 2.7 to 4.5 parts by weight, based on 100 parts by weight of the total addition amount of the gypsum powder and the filler.

In embodiments of the present application, the filler may be selected from any one or more of mullite, zircon and silica sand.

The present application also provides a method of preparing a low residual strength gypsum shell as described above, the method comprising:

uniformly mixing the gypsum powder and the filler;

heating water, adding gelatin, and mixing to obtain transparent solution;

adding mixed powder of gypsum powder and filler into the transparent solution to obtain slurry;

pouring the slurry into a mold;

after the slurry in the mold is hardened, the mold is dismantled and stands at room temperature to obtain a wet gypsum shell;

and naturally drying and roasting the wet gypsum shell to obtain the gypsum shell with low residual strength.

In embodiments of the present application, the water may be heated to 60-70 ℃.

In the embodiment of the present application, the temperature of the calcination may be 400-700 ℃, and the time may be 1-6 h.

According to the method, the gelatin is added into the gypsum shell, so that the residual strength of the gypsum shell is greatly reduced on the premise of ensuring that the normal-temperature wet strength and the high-temperature strength of the gypsum shell are unchanged or are reduced to a small extent, the gypsum shell has proper normal-temperature wet strength, cracks can be prevented from being generated in the process of carrying the gypsum shell, and the transportation of the gypsum shell is not influenced; meanwhile, the lower residual strength provides convenience for cleaning castings, and the production speed and the economic benefit are greatly improved. In addition, this application proposes for the first time to use residual strength as the index of evaluation gypsum shell performance, provides brand-new thinking for the development of gypsum shell, no longer limits to the normal atmospheric temperature wet strength and the high temperature strength of shell.

Additional features and advantages of the application will be set forth in the description which follows, and in part will be obvious from the description, or may be learned by the practice of the application. Other advantages of the application may be realized and attained by the instrumentalities and combinations particularly pointed out in the written description and claims hereof, as well as the appended drawings.

Drawings

The accompanying drawings are included to provide an understanding of the present disclosure and are incorporated in and constitute a part of this specification, illustrate embodiments of the disclosure and together with the examples serve to explain the principles of the disclosure and not to limit the disclosure.

FIG. 1 shows the results of a wet strength test at ambient temperature for wet gypsum shells prepared in the examples and comparative examples of the present application;

FIG. 2 shows the results of the residual strength test of the wet gypsum shells prepared in the examples of the present application and the comparative examples.

Detailed Description

To make the objects, technical solutions and advantages of the present application more apparent, embodiments of the present application will be described in detail below with reference to the accompanying drawings. It should be noted that the embodiments and features of the embodiments in the present application may be arbitrarily combined with each other without conflict.

The raw materials used in the following examples and comparative examples are all common commercial products in which the particle size of mullite powder is 200 mesh.

Examples 1 to 6 and comparative example 1

(1) The raw materials were weighed as in table 1:

TABLE 1

(2) Putting the weighed gypsum powder and mullite powder into a clean container, and fully stirring to uniformly mix the gypsum powder and the mullite powder (no obvious color difference exists after uniform mixing, and the color is consistent);

(3) heating the weighed distilled water to 65 ℃, adding the weighed gelatin into the heated distilled water for dissolving, obtaining transparent solution after the gelatin is dissolved and uniformly mixed, and storing for later use.

(4) Adding the mixed powder of the gypsum powder and the mullite powder obtained in the step (2) into the transparent solution obtained in the step (3), and stirring at the speed of 250r/min for 2min to ensure that the mixed slurry is uniformly stirred until no precipitate exists;

(5) pouring the slurry obtained in the step (4) into a mold, so that the slurry is filled in an inner cavity of the mold, and in the pouring process, firstly dropping the slurry from the lowest part (namely the upper surface of the bottom plate) in the mold, firstly pouring slowly in a thin stream and then pouring quickly in a large stream, so as to prevent air from being involved into the slurry due to the fact that the pouring is fast first, so that the air holes in the gypsum shell are increased, and the accuracy of performance test is influenced;

(6) scraping the upper surface of the mold, hardening the slurry for 1h, then removing the mold, and standing at room temperature for 24h to obtain a wet gypsum shell;

(7) putting the wet gypsum shell into an XD-1400S type high-temperature box-type resistance furnace (the distance between adjacent gypsum shells is kept to be 5-10mm, and the distance between the adjacent gypsum shells and a heating element or a furnace door of the resistance furnace is 40-50mm), heating the resistance furnace to 700 ℃ at the heating rate of 4 ℃/min, then preserving heat for 1h to roast the gypsum shell, and then stopping heating to cool the gypsum shell to room temperature along with the furnace to obtain the gypsum shell with low residual strength.

Performance testing

The wet gypsum shells obtained in step (6) of examples 1 to 6 and comparative example 1 were subjected to a test for wet strength at room temperature by a three-point bending method according to the test method specified in the test methods for investment casting shell properties (HB 5352.1-2004), wherein the amount of gelatin added was expressed in terms of the mass of gelatin relative to the total mass of the gypsum powder and the filler. The test results are shown in fig. 1.

As can be seen from FIG. 1, when the addition amount of the gelatin is in the range of 0-3.6% of the total addition amount of the gypsum powder and the filler, the normal-temperature wet strength of the gypsum shell basically tends to decrease with the increase of the addition amount of the gelatin, but the decrease is not large; when the addition amount of the gelatin is within the range of 3.6-5.4% of the total addition amount of the gypsum powder and the filler, the normal-temperature wet strength of the gypsum shell is rapidly reduced along with the increase of the addition amount of the gelatin, which shows that the excessive addition amount of the gelatin can bring adverse effects on the normal-temperature wet strength of the gypsum shell. According to the requirement that the wet strength of the gypsum shell is more than or equal to 1Mpa, the addition amount of the gelatin is more suitable within the range of 0-4.5 percent of the total addition amount of the gypsum powder and the filler.

The gypsum shells obtained in step (7) of examples 1 to 6 and comparative example 1 were subjected to a test for residual strength by a three-point bending method according to the test method specified in the test methods for investment casting Shell Performance (HB 5352.1-2004), and the test results are shown in FIG. 2.

As can be seen from FIG. 2, when the gelatin is added in an amount ranging from 0 to 2.7% of the total amount of the gypsum powder and the filler, the residual strength of the gypsum shell does not substantially change with the increase in the amount of the gelatin added; when the addition amount of the gelatin is within the range of 2.7-3.6% of the total addition amount of the gypsum powder and the filler, the residual strength of the gypsum shell is rapidly reduced along with the increase of the addition amount of the gelatin; when the gelatin is added in an amount ranging from 3.6% to 5.4% of the total amount of the gypsum powder and the filler, the residual strength of the gypsum shell does not substantially change with the increase in the amount of the gelatin added.

Moreover, tests show that the above rule is met when the total adding amount of the gypsum powder and the filler is 100 parts by weight, the adding amount of the gypsum powder is 20-40 parts by weight, and the adding amount of the filler is 60-80 parts by weight.

Therefore, considering the room temperature wet strength and the residual strength of the gypsum shell, it is preferable that the gelatin is added in an amount within a range of 2.7 to 4.5% of the total amount of the gypsum powder and the filler.

In addition, the high temperature strength of the gypsum shell prepared in comparative example 1 was about 0.392MPa, and the high temperature strength of the gypsum shells prepared in the examples of the present application was less than 0.4MPa, indicating that the addition of gelatin had little effect on the high temperature strength of the gypsum shell, and the high temperature strength of the gypsum shells prepared in the examples of the present application satisfied the use requirements.

Although the embodiments disclosed in the present application are described above, the descriptions are only for the convenience of understanding the present application, and are not intended to limit the present application. It will be understood by those skilled in the art that various changes in form and details may be made therein without departing from the spirit and scope of the disclosure as defined by the appended claims.

Claims (4)

1. A gypsum shell having low residual strength, comprising gelatin, wherein the gypsum shell is prepared from: the gypsum powder comprises 20-40 parts by weight of gypsum powder, 60-80 parts by weight of filler, 40-50 parts by weight of water and 2.7-4.5 parts by weight of gelatin, wherein the filler is selected from any one or more of mullite, zircon and silica sand.

2. The method for preparing a gypsum mold shell having low residual strength according to claim 1, wherein the method comprises:

uniformly mixing gypsum powder and filler;

heating water, adding gelatin, and mixing to obtain transparent solution;

adding mixed powder of gypsum powder and filler into the transparent solution to obtain slurry;

pouring the slurry into a mold;

after the slurry in the mold is hardened, the mold is dismantled and stands at room temperature to obtain a wet gypsum shell;

and naturally drying and roasting the wet gypsum shell to obtain the gypsum shell with low residual strength.

3. The method of claim 2, wherein the water is heated to 60-70 ℃.

4. The method as claimed in claim 2, wherein the calcination temperature is 400-700 ℃ and the calcination time is 1-6 h.

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