RU2297301C1 - Shell molds and cores producing method - Google Patents

Abstract

FIELD: manufacture of shell molds and cores with use of heated fitting-out.

SUBSTANCE: method comprises steps of adding low boiling- temperature petroleum solvent in quantity 0.07 - 0.09 mass % into mixer for humidifying dry clad molding sand; feeding ready sand to heated fitting; solidifying it in said fitting and removing ready cores and molds out of fitting.

EFFECT: elimination of spreading of dry clad sand at making molds and cores, increased rate of solidification, prevention of occurring of rejected molds and cores.

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Description

The invention relates to foundry and can be used in the manufacture of shell cores and molds, hardening in a heated snap.

A known method of manufacturing shell rods and molds, including the preliminary preparation of a dry clad mixture, feeding it into a heated snap, forming and hardening the shell, removing the core or mold from the snap (N.A. Sokolov. Casting into shell molds. - M.: Mechanical Engineering. - 1969 p. 184).

The disadvantage of this method is the dispersion of the dry clad mixture in both horizontal and vertical directions when filling the tool in the case of applying the most common and simple method for producing rods and molds, namely, the sandblasting method with an open inflation system. To implement the method, protective covers or special inflatable devices are required that complicate the design of the equipment.

A known method of cold cladding, in which 0.3-0.4 wt.% A humectant (kerosene, engine oil, paraffin, liquid bakelite, furfural, etheroaldehyde fraction, alcohol) is introduced into the mixture. (N.D.Orlov, V.M. Chursin. Handbook of a caster. - M.: Mechanical engineering. - 1971, p. 237). However, the humidifier cannot eliminate the spread of the mixture when the air is open, since it is removed by blowing it with air before being fed into the equipment (the clad mixture is dried). Dried clad mixtures are prone to caking, their survivability is limited. Therefore, cold cladding is universally replaced by hot cladding.

Closest to the claimed method is a method of manufacturing shell rods and molds, including preparing a dry clad mixture, feeding into a heated tool, curing the mixture and removing the rods and molds from the tool (SU No. 1708490, B22C 5/04). To improve the physicochemical properties of the cured mixture, the dry clad mixture is moistened with water to a moisture content of 0.5-1.5% before being fed into heated equipment. According to the test results, the strength of the clad mixture when moistened with water increases both in hot and in cold conditions. However, an increase in the strength of the moistened mixture by 40% will not reduce the resin consumption by 1.5-2 times without compromising the quality of the rods and castings. Moisturizing the clad mixture with water reduces its curing rate, leads to an increase in the exposure time of the rods and molds in heated equipment until they acquire the necessary manipulative strength. A decrease in the cure rate leads to softening of the surface layers of the molds and cores and their creeping off from the vertical walls of the tooling, which causes peeling defects.

The invention is based on a technical problem, which consists in eliminating the dispersion of the dry clad mixture in the manufacture of molds and cores, increasing the curing rate by achieving the necessary "manipulative strength" in the shortest possible time and eliminating flaking defects while maintaining the final strength of the molds and cores.

This problem is solved by the fact that in the method of manufacturing shell rods and molds, including preparing a dry clad mixture, moistening it before feeding it into a heated tool, curing in a tool, removing rods and molds from a tool, according to the invention, the dry clad mixture is moistened with a low boiling oil solvent (nefras ) in an amount of 0.07-0.09 wt.%.

The petroleum solvent (nefras) provides a smooth and even surface of the rods and shapes, while when moistened with water, the surface of the rods and shapes is wavy and rough. This is because the water, evaporating at a constant temperature, creates a boiling effect near the walls of the equipment, as a result of which the surface of the molds and rods loosens, and an increased roughness of the castings appears. The oil solvent (nefras) evaporates in the temperature range, gradually and does not cause the boiling effect at the surface of the snap. Therefore, the surface of the rods and shapes is smooth. The amount of the proposed humidifier in the mixture is significantly less than water, which increases the speed of curing of the rods and molds and completely eliminates the rejection of delamination.

The method is as follows. Dry clad mixture is fed into the hopper above the mixers of core machines, for example, automatic machines of model 4701 of the Pavlograd plant “LITMASH”, or automatic machines of model KSVE 12 of GIZAG (Germany).

In the mixers, 0.07-0.09 wt.% Nefras is introduced into the dry mixture, mixed for 30-60 seconds, fed to the hopper of the core machine and the mixture is blown into the heated equipment.

The effectiveness of the proposed solution is confirmed by examples of specific performance. When testing used a mixture of hot cladding of the following composition (wt.%):

Sand quartz grade 1 K 0202 GOST 2138-91 96.0 Novolac phenol-formaldehyde resin brand SF-015 3,5 Aqueous 33% urotropine solution 0.35 Calcium stearate 0.15

Dry clad mixture was loaded into laboratory runners of model 017 of the Usman foundry equipment, nephras grade S-50/170 GOST 26377-84 was introduced into the mixture, mixed for 60 seconds. It was established that for humidification it is necessary to use nefras of the gasoline fraction with a product boiling point of not more than 200 degrees Celsius. High boiling fractions are impractical to use, since they reduce the curing speed of molds and cores and require an increased concentration in the mixture.

The optimal duration of mixing the mixture with nephras was determined visually by achieving a uniform distribution of the humidifier.

Samples — “eights” 12.5 mm thick — were made from the moistened mixture in a laboratory setup of model 4735 of the BELNIILIT design; the curing time of the samples in the equipment was varied from 30 to 60 seconds in order to determine the optimal handling strength. The snap temperature remained constant at 270 degrees Celsius.

The tensile strength in the hot state was determined (8 seconds after removal of the samples from the snap) and the final strength of the samples cooled after removal from the snap to room temperature. The test results are shown in the table.

Table No. Humidifier, its content, wt.% The tensile strength of the samples in tension, MPa after holding in snap at 270 ° C, for, sec Hot condition Cold condition thirty 45 60 90 90 one Without humidifier no 0.12 0.6 0.9 2,3 2 Water - 1.0 no 0.15 0.3 0.95 2.2 3 Nefras - 0.05 0.1 0.5 0.8 1.4 2,3 four Nefras - 0.07 0.35 0.7 1,0 1.8 2,37 5 Nefras - 0.09 0.37 0.79 1,11 1.87 2.45 6 Nefras - 0.1 0.3 0.68 0.9 1.79 2.43

Based on the recommendations that the “hot” or manipulative strength required to remove the bar or mold from the tool without deformation should be at least 0.2 MPa (Reference “Molding materials and mold technology”, under the general editorship of S.С Zhukovsky. 1993 - p.120), the most preferred are options for moistening the clad mixture with nephras in the amount of 0.07-0.09 wt.%, Since in these cases the manipulative strength is achieved after 30 seconds of exposure of the samples in a snap ( lines 4 and 5 tables). When moistened with nefras in an amount less than 0.07% and more than 0.09%, the manipulative strength of the samples decreases. The final strength of the samples with nefras is higher than the final strength of the samples moistened with water (column 6 of the table). The surface of the samples made from a mixture moistened with water, as a result of its intense boiling, is wavy and rough. In samples and rods made from a mixture moistened with nephras, the surface is smooth and even, because Nefras evaporates gradually, and the amount of moisturizing fluid is much less than water.

Thus, the proposed method completely eliminates the spread of the mixture outside the workplace, provides dense, uniform shell rods and shapes without surface defects. The cores are cured in a snap in a relatively short period of time. The method completely eliminates the marriage of rods and molds for peeling shells, improves the cleanliness of the surface of the castings.

Claims (1)

A method of manufacturing shell rods and molds, including preparing a dry clad mixture, moistening it before feeding it into a heated tool, curing in a tool, removing rods and molds from a tool, characterized in that the dry clad mixture is moistened with a low boiling oil solvent in an amount of 0.07 - 0 , 09 wt.%.