SU833349A1 - Mixture for producing casting form - Google Patents

Description

(54) MIXTURE FOR THE MANUFACTURE OF CASTING FORMS

The invention relates to foundry, in particular, to mixtures for manufacturing and casting molds, and can be used both in single and mass production of castings. Blends are known that contain various carbon-containing additives in their composition in order to increase the technical properties of the mixture and reduce the tendency to form tehimine and burn. The most common nonstick additive is ground coal fl. To improve the physicomechanical and technological properties of the mixtures, oil bitumen combined with mineral oil is introduced into their composition. However, the use of petroleum bitumen reduces the strength of the forms in the moisture condensation zone. as well as increased gas pollution in the workshop, i.e. deteriorating working conditions. In order to increase the efficiency of the collapse of the binder and reduce its consumption, GZ fuel oil is added to the mixture. In addition to the disadvantages listed above, the use of fuel oil increases the viscosity of the mixture, which makes it unsuitable for forming under high specific pressure, and also increases the fire hazard in the workshop due to the sedimentation of products condensation of evolved gases in ventilation systems. Known mixtures containing in its composition instead of coal petroleum coke 4. This additive reduces the cost of the mixture, but does not improve the quality or the surface of the casting, because it does not increase the yield of shiny carbon compared to coal. A sandy-clayey mixture is known, containing as additives 6070% of a solution of gassioleum resin in white spirit (CKf-H binder) and starchite 5. This mixture is characterized by a rather high content of ground coal in the mixture, which significantly worsens the conditions labor, in addition, due to the presence of SKT-11 increases - the viscosity of the mixture makes it unsuitable for molding under high specific pressure; in order to achieve high technological properties, it is necessary to additionally add starch into the mixture.

The closest to the proposed technical essence and the achieved result is a mixture for the manufacture of casting molds, containing refractory filler, ground coal, bentonite, soda ash, water and an additive based on brown coal processing products, namely coal tar. Brown coal tar is a liquid product of high-temperature processing of brown coal without air access, with a thermal decomposition starting temperature of 130 ° C and brilliant carbon yield of up to 30% Gb1.

However, it is desirable to further improve the properties of this known mixture, in particular, physicomechanical, as well as improve its ability to resist the formation of a burn and wear it when making castings from ferrous alloys.

The purpose of the invention is to improve the physico-mechanical properties of the sand-beitonitovoy mixture and reduce its tendency to the formation of calcinus and burnt

This goal is achieved by the fact that the mixture for the manufacture of casting molds, including refractory filler, ground coal, bentonite, soda ash, water and an additive based on brown coal processing products, contains brown coal as a supplement in the following ratio of ingredients, wt.% :. Coal

ground 0,5-2,0

Bentonite 4-10.

Calcium

soda0,12-0,30

Water 2.2-4.5

Brown coal

resin0,2-1,0

Fireproof-,

fillerEverything else

A lignite resin is a product of extraction with organic solvents from brown coal during the production of lignite waxes; it is a solid product consisting of terpenes and polyterpenes with a carbon chain structure. The temperature of its initial decomposition is 240 ° C, and the yield of bright carbon is no less than 40%.

The high plastic properties of this resin, which appear in the critical interval of formation of coaxia, cause its high efficiency in preventing surface defects of cast iron type castings. The increased yield of bright carbon compared with tar provides high nonstick properties of the molding sand.

The use of a lignite resin does not lead to an increase in the viscosity of the mixture, which makes it suitable for use in mixtures for forming under high specific pressure.

The content of the coal-tar resin in the mixture below the lower limit (0.2%) does not ensure the output of a sufficient amount of bright carbon and does not reduce the high thermal stresses resulting from the expansion of the mixtures when the metal is poured.

Increasing the content of the coal tar resin in the mixture above the upper limit (1.0%) significantly increases the yield of shiny carbon, and therefore there is a risk of defects in folding castings.

It is advisable to grind the lignite resin in its original lumpy form together with lumpy bentonite in crushers, followed by domolo in a ball mill.

The molded mixture is prepared by loading a refractory filler, ground coal, a complex powder additive from bentonite and coal tar, soda ash and water into the mixing runners and mixing them for 10 minutes, after which the mixture is ready for use.

In tab. 1 shows the compositions proposed and known mixtures.

In tab. 2 shows the comparative properties of the proposed and known mixtures.

From tab. 2, it is seen that by incorporating the sandy-bentonite mixture of a brown coal tar into the composition, the technological properties are improved, in particular, the increase in compressive strength in the raw state and shear strength.

The increased non-stick properties of the proposed mixture provide a high yield of shiny carbon.

Significantly reduced danger. occurrences of snillage, as the proposed mixture has high strength in the zone of moisture condensation and relatively low thermal stresses.

Optimum properties are provided by composition 3, in which the above advantages are most pronounced.

All production castings obtained in molds made from the mixtures according to the invention have a free, burned and burnished surface.

Thus, the molding mixture offered provides molds with improved physicomechanical characteristics and with a reduced tendency to form tehimine and burns in the production of castings from ferrous alloys.

90.59 90.19 89.79 91.29 89.79

Compressive strength

raw, kgf / cm 1,5 1,6

Gas permeability

unit 160 160 160

Flowability by

73 75 Fisher,%

Humidity,%, with

seals 45% 2.4 2.3 2.2

72 78

0.45 0.50 0.52

0.55 0.058 0.60

0.28 0.44 0.60. 8.0 7.5 6.7

Table 1

table 2

78

80

70

85 0.44 0.50.

0.04

0.055

-. t 0,30

0.50 10.2

7.5

Claims (6)

1. Foundry, 1976, I 8, p.26. 2. Authors certificate of the USSR 383509, cl. In 22 of 1/00, 1970. 3. USSR author's certificate number 372014, cl. In 22 C 1/00, 1969. 4. Foundry production, 1972, No. 9, p.39-40. 5. USSR author's certificate number 564084, cl. B 22 C 1/02, 1974. 6. The patent of the Federal Republic of Germany 1458104, KL.31 6 1/02, published. 1970.