RU2314891C1 - Mold making method for casting with use of investment patterns - Google Patents

Abstract

FIELD: casting processes and equipment, possibly manufacture of castings of refractory, alloyed and stainless alloys.

SUBSTANCE: method comprises steps of applying layer by layer onto investment pattern suspension on base of refractory material with ethyl silicate layer adding to suspension graphite in quantity 2 - 4% of mass refractory material; at molding prepared mold in flask with quartz sand adding to it carburizing agent in quantity 4 - 6% of mass of quartz sand.

EFFECT: improved quality of outer layer of ready cast pieces, lowered number of rejected castings due to making high-strength and geometrically regular molds.

Description

The invention relates to the field of foundry and can be used in complex molds for castings, especially from heat-resistant, alloyed and stainless alloys.

The well-known "Method for the manufacture of foundry ceramic molds" (patent RU No. 2177856, IPC В 22 С 9/04, 01/10/2002) obtained by investment casting, including applying to the investment casting model of at least two layers of a suspension on an ethyl silicate binder, subsequent application of at least two layers obtained on a liquid-glass binder, drying each layer, drowning in water, while in the last layer of the suspension on ethyl silicate binder, sodium fluoride is introduced in an amount of 0.1-0.3 wt.%.

The disadvantage of this method is the low mold strength, as a result of which the integrity of the mold is violated when pouring metal, which leads to a high percentage of marriage.

The well-known "Method of manufacturing multilayer combined molds for investment casting" (AS No. 1129014, MKI B 22 C 9/04, publ. Bull. No. 46 dated 12/15/84,), including the sequential application of the model layers of suspension on ethyl silicate the binder and the layers obtained on a liquid-glass binder, sprinkling with a refractory material of each layer, drying simultaneously the paired layers obtained on the said binders, while after sprinkling each layer obtained on a suspension on an ethyl silicate binder, drying is carried out, and then a layer of water liquid glass solution with a density of 1.1-1.35 g / cm ³ .

The disadvantages of this method are the low mold strength and a large number of shells formed on the surface of products from heat-resistant and high-alloy materials, which are obtained from molds made by this method.

The closest in technical essence and the achieved result is “A method of manufacturing a multilayer shell mold according to investment casting” (AS No. 1136883, MKI V 22 C 9/04, publ. Bull. No. 4 dated 01/30/85), including sequential application of the suspension layer layers on the ethyl silicate binder and the layers obtained on the liquid-glass binder onto the block of investment models, sprinkling with refractory material of each layer, drying the layers, while granular slag from the production of ferroalloy is used as refining material with a grain size of 0.5-6.0 mm and a magnesium oxide content of 35.0-49.0 wt.%, the first layer being sprinkled with granular slag from the production of ferroalloys with a grain size of 0.5-0.7 mm, the second layer with slag grit size 0.7-1.1 mm, and the third and fourth layers - slag grit 1.3-6 mm.

The disadvantages of this method are the high complexity of the manufacture of the mold and a large number of shells formed on the surface of the products, which are obtained from the molds due to burning and decarburization of the upper layer of the castings made by this method.

The technical task of the invention is the creation of a cost-effective method of manufacturing molds for investment casting, with which would be obtained strong and geometrically correct forms to obtain high-quality products (castings) with a small amount of marriage, caused by the violation of their geometry and uneven temperature distribution when receiving castings , as well as the presence of a large number of shells on the surface, leading to the need for rough cleaning of castings.

The technical problem is solved by the method of manufacturing investment casting molds, including layer-by-layer application of a suspension on the basis of a refractory material with an ethyl silicate binder to the investment casting, subsequent coating of each layer with quartz sand and further molding of the obtained mold in a flask.

New is that in the suspension, starting from the third layer, 2-4% of silver graphite, by weight of the refractory material, is added, and when molded into quartz sand, which is filled into the flask, 4-6% of the carburizer of the mass of quartz sand is preliminarily added.

The method is implemented as follows (for example, a specific implementation).

First, hydrolysis of ethyl silicate-32, TU 6-02-895-78 is prepared. Then, based on hydrolyzed ethyl silicate-32 and refractory material (marshalite grade A, GOST 9077-82), a suspension is made. Part of the suspension (up to 3/4 parts) is selected and 2-4% of silver graphite GOST 5279-74 is added from the mass of marshalite from the suspension (the higher the melting point, the higher the percentage). For castings from alloys 20X13 and 12X18H9T, 3% silver graphite is added to the suspension. The silo sand grade BC-020-1 GOST 22551-77 is poured into the hopper with a dispenser.

In the manufacture of ceramic molds, the first two layers are made by sequentially placing the model block in suspension and in a dispenser with a hopper for sprinkling with quartz sand, which are dried in an ammonia cabinet. Next, starting from the third layer, the model block for each layer is sequentially placed in a suspension with silver graphite and in a dispenser with a hopper, followed by drying. For castings from alloys 20X13 and 12X18H9T, 7 layers are made.

Then carry out a reflux in hot water, followed by drying in air for 24 hours. The presence of silver graphite from the third layer forms micropores in them, due to which a better and stronger bond with quartz sand occurs, and moisture is evenly distributed over the layer during drying, eliminating warping and cracking in the mold.

Then model blocks are formed into flasks, where group 04 quartz sand is used as a filler, mixed with 4-6% of GOST 2407-83 carburizer based on the mass of quartz sand (the higher the melt temperature, the higher the percentage of carburizer in quartz sand). For castings from 20X13 and 12X18H9T alloys, quartz sand with 4% carburizer was used.

Next, the model blocks molded in the flask are calcined at a temperature of 900 ° C, kept at 900 ° C for 4 hours at a heating rate of 100 ° / h. Then pour molten metal.

The presence of a carburizing agent in the quartz sand of the flask and silver graphite in the mold layers increases their heat capacity, which allows a more even distribution of the temperature effect on the smelted product (casting), which eliminates the temperature distortions of the resulting castings. Moreover, the presence, starting from the third layer, of silver graphite allows intensive gas removal from the surface layers of the castings and does not allow particle detachment from the first two layers (experimentally determined), which leads to a significant improvement in the quality of castings, especially from heat-resistant, alloyed and stainless alloys .

When using multilayer forms obtained by other methods using a suspension based on a refractory material with an ethyl silicate binder or a liquid glass binder, 100% castings were obtained, the surfaces of which were 90% coated with shells up to 0.5 mm deep and deviation from linear geometric dimensions to 1, 5% of the set, which required making molds with a “margin”, taking into account preliminary roughing, peeling processing of castings to bring into line with the given parameters the surface cleanliness and geometrically sizes. After applying the molds made by the proposed method, castings were obtained with a deviation from linear geometric dimensions of not more than 0.35% and with a surface cleanliness corresponding to a cleanliness of at least R _z 320, which made it possible to produce molds with lower tolerances and, as a result, save on materials used in the manufacture of the mold and in obtaining the casting itself (which are expensive, especially heat-resistant and stainless alloys), on technological operations (the absence of the first roughing operation) and on materials, t to how to receive the same number of castings, as in similar methods, require less melt.

Using the proposed method for manufacturing investment casting molds allows to save molds and castings on technological operations and materials by obtaining a solid geometrically regular shape and uniform temperature distribution when producing castings, as well as a better outer surface of the obtained castings.

Claims (1)

A method of manufacturing investment casting molds, including layer-by-layer deposition of a suspension based on a refractory material with an ethyl silicate binder on a lost wax model, subsequent sprinkling of each layer with quartz sand and molding of the obtained mold in a flask, characterized in that the suspension is introduced from the third layer into 2-4% of silver graphite by weight of the refractory material, and when molded into quartz sand, filled into the flask, 4-6% of the carburizer of the mass of quartz sand is introduced.