CS223385B1 - Shaping mixture for making the foundry moulds and cores - Google Patents

Description

The invention relates to a molding composition for the production of foundry molds and cores, in particular for the production of precision castings of aluminum alloys using a permanent model, processed from fine and coarse foundry binders bonded with a binder and a process for their production.

Up to now, precision aluminum alloy castings have been produced using a permanent model in plaster and ceramic molds. Gypsum molds can be used for metal casting only in compliance with special technological procedures during their production. The molds have to be heat treated for 16 to 72 hours with often complicated thermal cycles and using special equipment. In ceramic molds, it is necessary to heat-treat these molds from the known molding compositions at high temperatures in order to obtain the necessary properties. For mixtures bonded with ethyl silicate at temperatures of 800 to 900 ° C and for mixtures bonded with refractory clays even at temperatures above 1000 ° C. This is highly disadvantageous for production in modern high-performance foundry operations.

The purpose of the invention is to provide such a molding composition and a method for producing foundry molds and cores for the production of precision aluminum alloy castings using a permanent model without the need for annealing prior to casting.

The present invention provides a molding composition comprising 70 to 83% non-quartz and quartz sands, consisting of 60% fine quartz or quartz sand with a grain size of up to 0.06 mm and 40% coarse quartz sand with a grain size of 0.1 to 0 3 mm and two binders consisting of 15 to 25% hydrolysed ethyl silicate containing 14% S1O2 and 2 to 6% of a solution of phenol-formaldehyde or phenolic resin in an alcohol content of 20 to 30% / o dry matter, supplemented with 0.08 to 0.12 % cyclohexylamine or 2 to 3% magnesite. In the present invention, a method for producing foundry molds and cores from molding compositions is advantageous, in which all the constituents of the molding composition are mixed quickly and thoroughly and filled without delay into molding frames or cores equipped with a suitable separator and after 5 minutes of dwelling a portion of the molding compound with a ruler and 6 to 15 minutes after the molding frame or core is filled with the molding compound, the mold or core is disassembled, ignited and allowed to burn on a flat non-combustible support.

Advantageous in the molding compositions for the production of the molds and cores according to the invention is that, taking advantage of all advantages identical to the ceramic molds produced by the prior art method from the known molding compositions, casting without high temperature annealing is possible. This leads to significant energy savings, shortening of working time and lowering of investment and production space requirements. The phenol-formaldehyde resin not only improves the mechanical properties of the molds and cores, so as to allow non-annealing casting, but simultaneously with the binder, which burns on casting, decreases the strength of the mixture after casting, thereby improving and facilitating the cleanability of castings. The molding composition for the production of molds and cores according to the invention allows the production of precision castings of aluminum alloys with excellent surface quality.

Examples of the composition of the molding compositions are applications of the invention and are also indicated by the processing procedure.

As a first example, it is a molding compound of the following composition:

15.0% hydrolysed ethyl silicate containing 14% SiO2

45.0% zircon sand with grain size up to 0.06 mm

33.0% molochite having a grain size of 0.2 to 0.3 millimeter

4.0% phenol-formaldehyde resin 2.9% alcohol

0.1% cyclohexylamine

The molding composition according to the second example has the following composition:

17.0% hydrolysed ethyl silicate containing 14% SiO2

43.0% zircon sand with grain size up to 0.06 mm

(1) burnout

2. moisture after burning out

3. Compressive strength after curing for 15 minutes

4. Compressive strength after burnout

5. milling abrasion at 3 revolutions

6. Workability after mixing the ingredients

30.0% foundry sand with grain size 0.1 to 0.3 min

6.0% phenol-formaldehyde resin

3.9% alcohol

0.1% cyclohexylamine

As a third example, a molding composition of the following composition is given:

16.0% hydrolysed ethyl silicate containing 14% S1O2

42.0% zircon sand with grain size up to 0.06 mm

29.0% molochite having a grain size of 0.2 to 0.3 millimeter

2.0% powdered phenol resin 10.4% alcohol

0.1% cyclohexylamine 0.5% hexanetriol

All components of the molding mixture are mixed quickly and perfectly to avoid unnecessary aeration and without a time delay the molding mixture is immediately filled into prepared molding frames or core boxes. These flasks or cores must be provided with a suitable separator, for example a solution of petrolatum in gasoline. After filling the molding frame or core with the molding mixture, the excess part of it is cut off after about 5 minutes, and after 6 to 15 minutes after filling the mold, the mixture gels, disassembles on a flat non-flammable mat, ignites and burns. The combustion products must be exhausted. After the burnout, the mold or core is ready for casting. The basic properties of the molding compound are limited by the following values:

up to 80 Sij 0

0.40 to 0.60 MPa 0.50 to 0.80 MPa 1.8 to 3.0 MPa 0.5 to 1.5 mm 40 to 70 seconds

Claims (1)

Ρ Ř Ε D Μ Ε Τ A molding composition for the production of foundry molds and cores, in particular for the production of precision castings of aluminum alloys using a permanent model, processed from fine and coarse foundry ores bonded with binder, characterized in that it consists of 70 to 83% non-quartz and quartz sands. 60% of fine non - quartz or quartz sand of grain size up to VYNALEZU 0,06 mm and 40% of coarse quartz sand with a grain size of 0.1 to 0.3 mm and two binders consisting of 15 to 25% hydrolysed ethyl silicate containing 14% SiO2 and 2 to 6% phenol-formaldehyde or phenolic solution resin in alcohol containing 20-30% solids, supplemented with 0.08 to 0.12% cyclohexylamine or 2 to 3% magnesite.