SU750318A1 - Method of determining khock-out ability of moulding and rod mixtures using specimens - Google Patents

Description

I

The invention relates to the field of determining the properties of molding and core sands used in foundries. Embossability is understood to mean the degree of difficulty in removing rods or mold parts from a cooled casting.

The main conditions for approximate reproduction of the laboratory conditions of ablation to real, in which the rods in the castings are located at the moment of knockout, are the composition of the mixture, the temperature of heating the rod, the duration of the constriction at different temperatures, the magnitude of the volume compression at the metal shrinkage, the cooling rate of the rod.

Known methods of knockability are divided by process samples and standard samples.

In order to reproduce the actual conditions of the mold in the tested mixture, a technological sample is used, i.e. casting a simplified design, to a greater or lesser extent, modeling some group of castings. To change the warm-up temperature

The test mixture made technological samples of various sizes or of the same size, filling the test rod with alloys with different pouring temperatures, for example, cast iron, copper and light alloys with pouring temperatures of 1350, 1150 and 720 ° C, respectively. As a criterion for estimating the labor intensity of knocking a rod, the number of blows on a casting required for spilling a rod is usually used. Since until now there are no standard knockout devices, it is impossible to compare the results obtained by different researchers, since it is very difficult to create the same knockout conditions for experienced rods without standard instruments. In addition, it is impossible to objectively determine the time of the end of the knockout due to the formation of a hot crust of various thicknesses.

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By standard samples, a quantitative assessment of knockability combines methods in which 1C knocks out for a value. And the work of knockout spent on the squabble, punching of a heat-treated and cooled specimen with a special copra, or residual strength of heated and cooled standard cylindrical specimens 1 is taken. punching a specimen at a special (TsNIITMASH method) allows obtaining reproducible quantitative results, but does not eliminate the disadvantages inherent in methods of limitability in standard samples, since prototypes during cooling of Denmark and at the time of testing are not in compression, for example biaxial compression, which leads to a significant difference in the stress state of the mixture during the knockout process in the actual casting and in the process of destruction of the subject sample; Punching the center of the sample with a special brisk reflects the actual process of removing the cores from the castings using jackhammers and does not reflect the entire processes of the cores' destruction during embossing on the vibrating gratings, since in these cases the impact on the mixture in the form of vibration or shock is not carried out directly, but through the walls of the casting or flask. It is also known that experiments are carried out using planning of experiment 2. The closest to the described invention to the technical essence and the achieved result is the method for determining knockability of molding and core mixtures, which means that the standard cylindrical sample of the hardened mixture is heated, cooled and destroyed in conditions of biaxial compression, after which the residual strength of the specimen is determined during compression testing 3. Obviously, the compression test of the specimen does not reflect the There are a lot of processes for the destruction of rods when being knocked out on vibravdone grids. The purpose of the invention is to approximate the test conditions to the process of destruction of real rods when embossing on vibrating grates. The goal is achieved by producing a sample in a heat-resistant thin-walled sleeve, subjecting them to a joint heat treatment followed by vibration, applying a shock load alternately to the diametrically opposite sides of the sleeve at half the height of the sample and perpendicular to the sample axis, fixing the time to remove the sample from sleeves. The ability to determine the operation of knockout after knockout time follows from the formula: A.k-N-t. And - the work spent on knocking; N is the power of the equipment on which the knockout is carried out; fc is the time required for knockout; k is a constant value for this type of testing device. When knocking out samples on a stationary device driven by a constant-power motor, the work of knocking is proportional to the time of knocking out and the time of knocking can serve as a measure of knockability. It is advisable to carry out vibration destruction of samples on a special device mounted rigidly to the moving part of a standard device for determining the grain composition of model 026 sands instead of a set of sieves. The frequency of shocks is determined by the oscillation frequency of the moving part of the model 026 device and is equal to 10 Hz. The blows to the sleeve are directed radially, perpendicular to the axis of the sample and are carried out alternately from diametrically opposite sides of the sleeve at a distance of 15 mm from the base. The impact force on the liner is equal to 2.6 N. During the experiments, liners 50 mm high were used, in which a sample 30 mm high from the base was formed with three strokes of a standard copra. The proposed method can be standardized in terms of exposure time in the furnace, heating temperature, cooling time, but for the purpose of optimizing the composition of the core mixtures, the heat treatment modes should be selected taking into account the heating temperature of the real rod, which depends not only on the grade of alloy used and pouring temperature, but also on the wall thickness of the casting and on the cooling time of the casting until the moment of knockout. The method of determining knock-out is carried out in relation to sandy-clay mixtures for straps of shaped castings of sanitary fittings (castings are made by pouring metal into metal molds). This solves the problem of finding the composition of a sandy-clay core mixture with minimal knockability. The variable factors in research are Xf, the amount of clay introduced into the mixture; X 2 moisture content of the mixture; the amount of refreshing sand; sample heating temperature. The effect of the remaining factors on knockability in these experiments was not studied. They were fixed at certain levels and did not change during the whole experiment 2. In order to determine the duration of exposure of the test samples in the muffle to reproduce the temperature of heating of real rods with the help of built-in thermocouples, measurements were taken of the dynamics of the temperature change of a mixture of real rods and experimental X samples. Measurements showed that 4 minutes after the metal was poured to obtain the casting to be studied or the sample was placed in a muffle heated to 800 ° C, the rod was heated the same way, reaching 225 ° C. Time 7503 5

Table 1 86 of the exposure in the muffle (4 min) and the temperature of heating of the test rod (225 ° C) are taken in the middle of the interval of variation according to the fourth factor. In the process of the experiment on matrix 2, 34 experiments were implemented, i.e. Matrix experiments were duplicated. The levels of factors and intervals of variation are presented in table. one.

Clay content

in mixture,%

Humidity mixture, 9

The amount of refreshment sand,%

Warm-up temperature, ° C Samples for determining knockability are formed by three. blows of standard copra in special thin-walled (wall thickness 3 mm) sleeves made on heat-resistant steel. The made samples were heated in a muffle furnace for 3 or 5 minutes and, after being removed from the furnace, were cooled in air for 3 minutes. Knockability is estimated by the time of complete destruction and removal of the tested mixture from

9

3

12 6.5

five

1.5

20 300

15,225

Claims (1)

1. Medvedev Ya. I., Valisovsky I. V. Tech-Science, 1976. Nologic trials of molding mattern-3. USSR Author's Certificate N 351126, fishing M., Mechanical Engineering, 1973, p. 204-210.cl. B 22 C 1/00, G 01 N 3/32, 1970.