RU2295419C1 - Molds with use of investment patterns making method - Google Patents

Abstract

FIELD: manufacture of shell molds with use of investment patterns.

SUBSTANCE: method comprises steps of applying onto pattern front layer of suspension; slightly drying it; applying further inner layers of suspension; sprinkling said layers and drying them. Front and next layers are applied from suspension with next composition, mass %: aluminum boron phosphate, 16.00 - 20.00; water, 16.00 - 20.00; lignosulfonate (surface active matter), no more than 0.5; magnesium silicate powder, 3.5 - 5.0; pulverized refractory filler, the balance. Front layer is sprinkled with grog having fraction size no more than 0.2 mm; Further layers are sprinkled with grog having fraction size no more than 0.4 mm. Each layer is dried up for 30 - 40 min; pattern composition is melt and mold is subjected to high temperature drying at 300 - 350°C for 2 - 3 hours. Pulverized grog or pulverized synthetic corundum is used as refractory filler for front layer.

EFFECT: increased rate of making mold, improved knocking out capability of mold.

3 cl, 1 tbl, 2 ex

Description

The invention relates to foundry, in particular to a technology for the manufacture of molds for investment casting, and can be used for the manufacture of shell molds.

A known method for producing ceramic molds [Patent RU No. 2200643, A method for producing ceramic molds by investment casting using liquid glass as a binder, IPC В 22 С 9/04, В 22 С 1/02, publ. 03/03/2003]

The disadvantages of the method are the long manufacturing time, as well as the lower quality of the casting surface, the presence of a burn and the associated poor knockability of castings from the molds.

The closest to the essence of the claimed invention is a method of manufacturing molds for investment casting [Patent RU No. 2043825, Method for manufacturing molds for investment casting, IPC B 22 C 9/04, publ. September 20, 1995], including applying the face layer to the model, drying it, applying the subsequent inner layers from a suspension with an ethyl silicate binder, dusting and drying them, and applying the face layer from a suspension with an acidified aqueous solvent of the composition, wt.%: Water 15, 0-30.0, inorganic acid 1.0-3.0, surfactant of anionic or nonionic class 0.05-0.2, refractory filler, the rest, or from a suspension with an acidified aqueous-organic solvent composition, wt.% : a mixture of water and an organic solvent in the ratio 1: 1, 3: 1, 15.0-30.0, inorganic acid 1.0-3.0, the rest is refractory, the facing layer is dried for at least 5 minutes, followed by hardening with a suspension of the refractory filler and ethyl silicate binder .

The disadvantages of this method include the duration of mold manufacturing, the time for manufacturing a single layer from 1.5 to 2.5 hours, and for the manufacture of 4-5-layer shell molds, respectively, about 6-12.5 hours, as well as poor knockability associated with casting with high residual strength formed during firing of ceramics.

The objective of the invention is to reduce the manufacturing time of shell molds and improve knockability of forms.

To achieve the task in the proposed method for the manufacture of investment casting molds, including applying to the model the face layer of the suspension, drying it, applying the subsequent inner layers of the suspension, sprinkling and drying them, according to the invention, the front and subsequent layers are applied from the suspension composition, wt.%:

Aluminum phosphate 16.0-20.0 Water 16.0-20.0 Lignosulfonate (surfactant) no more 0.5 Magnesium Silicate Powder 3,5-5,0 Dusty refractory filler ost.,

the front layer is sprinkled with fireclay sand with a grain size of not more than 0.2 mm, and the subsequent layers are sprinkled with fireclay sand with a grain size of not more than 0.4 mm, then each layer is dried for 30-40 minutes, the model composition is melted and the mold is subjected to high-temperature drying 300- 350 ° C for 2-3 hours, as a refractory filler for the front layer using pulverized chamotte or pulverized electrocorundum.

The difference between the claimed solution and the known one is the introduction of the front and subsequent layers into the suspension, instead of an ethyl silicate binder, an aluminoborphosphate binder (TU 113-08-606-83) and magnesium silicate powder, which provide hardening of the shell-shaped layer for 25-30 minutes, as well as application high temperature drying instead of firing.

LST technical lignosulfonate (LST TU 13-0281036-029-94) was used as a surfactant.

The use of aluminum-containing refractory materials as fillers of the front and subsequent layers is due to the higher chemical activity of these materials when interacting with aluminoborophosphate binder at low temperatures.

For the manufacture of the front layer of molds, aluminum-containing dust-like fillers are used - dust-like chamotte or, for better casting, electrocorundum. Improving the quality of casting from the use of electrocorundum is expressed through a decrease in the wetting of the working part of the mold with metal, and therefore through a decrease in the roughness of the casting.

The use of chamotte as a sprinkling material is also due to its higher chemical interaction with a phosphate binder compared to quartz sand.

The use of chamotte with a grain size of not more than 0.2 mm as a backing material for the front layer made it possible to obtain a better front layer, since larger sands during punching of the suspension increase the roughness of the working surface of the molds and, consequently, of castings.

The use of fireclay sand to sprinkle subsequent layers larger than a grain of 0.4 mm negatively affects the strength of the molds, since the specific surface of the fireclay participating in the chemical reaction with a phosphate binder decreases.

When using chamotte filler, the thickness of the applied layer increases by about 1.5-2 times, which reduces the number of layers, and consequently, the manufacturing time of the molds.

Since the suspension hardens at room temperature (it is possible to accelerate the hardening process by heat treatment of molds, the temperature is not higher than 50 ° C), there is no need for additional chemical curing of the layers as in the traditional manufacture of molds on ethyl silicate binder (curing in ammonia vapor) or liquid glass (curing in aqueous solution of ammonium sulfate).

High-temperature drying (300-350, maximum 500 ° C) instead of firing is explained by the absence of the need for high temperatures, since in a mold made from a suspension on a phosphate binder at these temperatures, there is practically no water, and the mold has the necessary strength. In addition, such drying does not contribute to the sintering process in phosphate form, which reduces the residual strength and contributes to its easier destruction and knockout casting. High-temperature drying gives the phosphate form the necessary strength for casting and, at the same time, good knockability, it also significantly reduces the energy consumption (compared to firing) for processing the mold before pouring.

The forms obtained using a suspension on a phosphate binder have a lower coefficient of thermal expansion in contrast to a suspension on an ethyl silicate binder, where the modification transformations of SiO _{2 are} accompanied by significant changes in volume, and the polymorphic transformations AlPO _{4 of the} crystallochemical analog of SiO _{2 are} less significant.

Examples of specific performance of the method of manufacturing molds.

Example 1. On the block of models made from the model composition PS 50-50, a face layer was applied from a suspension of the composition, wt.%: Aluminoborophosphate 19.0, water 19.0, lignosulfonate 0.5, magnesium silicate powder 5.0, pulverized chamotte rest. Sprinkle with fireclay sand with a grain size of not more than 02 mm.

After 30-40 minutes, two more coating layers of a suspension of the same composition were applied to the front layer, sprinkled with chamotte sand with a grain size of not more than 04 mm, dried for 30-40 minutes, the model composition was smelted in an oven and dried at 350 ° C for 2 -3 hours.

Example 2. On the block of models was applied the front layer from a suspension of the composition, wt.%: Aluminoborophosphate 17.0, water 17.0, lignosulfonate 0.5, magnesium silicate powder 5.0, dusty electrocorundum the rest. Sprinkling with chamotte sand grit 02, drying 30-40 min.

Then two layers were applied analogously to example 2.

After smelting the model composition and drying, the mold samples were tested to determine the tensile strength under static bending according to the method of GOST 4648-71. The results of strength tests and the time of their manufacture are shown in table 1.

The production time of the mold and its preparation for pouring is about 4 hours. The residual strength of the obtained forms below the prototype, which will greatly facilitate knocking out of the mold. Thus, the application of the proposed method for manufacturing molds by investment casting will allow for a milder mode of mold processing, which will facilitate knockout of molds and reduce the time of the technological cycle from the manufacture of foundry molds to the production of castings in it up to one working day.

Table 1 Example prototype one 2 Mold making time 7 h 40 min 2 h 2 h Residual strength (knockability), kgf / cm ² , 51 35.1 32 The temperature of the heat treatment of the forms, ° C 800-900 300-350 300-350 Processing time, h 5 2 2 The time from the beginning of the manufacture of the mold to fill 12 h 40 min 4 h 4 h

Claims (3)

1. A method of manufacturing molds according to investment casting, including applying to the model the face layer of the suspension, drying it, applying the subsequent inner layers of the suspension, sprinkling and drying them, characterized in that the face and subsequent layers are applied from the suspension of the composition, wt.%: Aluminum phosphate 16.0-20.0 Water 16.0-20.0 Lignosulfonate (surfactant) No more than 0.5 Magnesium Silicate Powder 3,5-5,0 Dusty refractory filler Rest the front layer is sprinkled with fireclay sand with a grain size of not more than 0.2 mm, and the subsequent layers are sprinkled with fireclay sand with a grain of no more than 0.4 mm, then each layer is dried for 30-40 minutes, the model composition is melted and the mold is subjected to high-temperature drying 300- 350 ° C for 2-3 hours 2. The method according to claim 1, characterized in that as a refractory filler for the front layer using pulverized fireclay. 3. The method according to claim 1, characterized in that as a refractory filler for the front layer using pulverized electrocorundum.