CS218325B1 - Mass for ceramic cores - Google Patents

Abstract

The invention relates to a material for ceramic cores for precision metal casting, removable from the casting by the action of alkaline solutions or the melt of these solutions. The invention addresses the composition and structure of the material for ceramic cores. The essence of the material is that it consists of 82 to 92 parts by weight of ground fused quartz and 8 to 18 parts by weight of aluminum oxide with an α-corundum content of more than 95 percent.

Description

BACKGROUND OF THE INVENTION 1. Field of the Invention The present invention relates to a mass for precision cored metal casting based on ground fused quartz containing 8 to 18% by weight alumina.

The use of cores or cores is known in precision casting of metals. They are made of pulverulent materials with a major proportion of quartz sand, natural clays and organic additives. For precise cavities in castings of smaller dimensions and more complex in shape, cores made of ceramic technology are used with possible machining to required dimensions and shapes of cores. Materials with natural quartz, molochite, corundum and zirconium dioxide are used for these cores. Their disadvantage is the shrinkage, which does not guarantee a high form accuracy, and in the case of materials with natural quartz, modification conversions with a volume change take place. The mechanical strength and surface quality of the cores of these materials is not sufficient.

The deficiencies of the prior art are eliminated by the ceramic core mass according to the invention, which comprises 82 to 92% by weight of ground fused silica and 8 to 18% by weight of alumina containing α-corundum in an amount above 95%.

An advantage of the invention is that the mass has low shrinkage, even in injection molding. Another advantage is the minimal distortion by firing, even at the points of maximum core weakening. These properties ensure that the precise geometrical shapes of the cores are maintained. Another advantage is the low thermal expansion (CE20 to 1000 ° C = 1.3 to 1,5.10 ~ θ K ^_1) and the associated high resistance to abrupt temperature changes. The mass of the cores is easily removed from the castings by the action of alkaline lye solutions or in the melting of these lyes.

The invention will be explained in more detail on the basis of examples of the inventive composition.

EXAMPLE 1% by weight of ground fused quartz with a maximum zirconium size of 0.2 mm,% by weight of alumina. Purity, calcined at 1380 to 1400 ^° C and having an α-AhO 3 content of 97% by weight, was ground dry with 1% by weight oleic acid at a milling ratio of 1: 6 for 5 hours. The specific surface area of the powder mass was 1.50 m ^{2 by} grinding. • g ' ¹ ·

By incorporating an additive of 8% polyvinyl alcohol solution in an amount of 10 wt. and granulating to obtain a mixture for pressing flat shapes of ceramic cores.

The firing of the cores was at 1250 ° C.

The cores had the following characteristics:

Bulk density: 1.45.10 ³ kg.m ^-3

Absorbency (w / w): 24%

Mechanical flexural strength: 16 'MPa

Example 2% by weight of ground fused quartz with a maximum grain size of 0.1 mm,% by weight of mineralized alumina with an α-AlaOs content of 96% by weight was ground under dryness with the addition of 1% by weight of oleic acid at a milling ratio of 1: 4. 2 hours, after which a specific surface area of 1.38 m ² was reached for the powder mass. g ^-1 . The ground powder mass was heat treated with a thermoplastic paraffin binder for casting slurry containing 16 wt% paraffin and 0.3 wt% beeswax in the region. above 65 ° C liquid. Since they were cores of complex shapes, such as the cores for hollow turbine blades of aircraft engines, they produced with low-pressure spray casting a pressure of 0.4 to 0.6 MPa into metal molds.

Removal of the binder was performed in the charge alumina mode when a temperature rise of 10 ^C C / h up to a temperature of 220 ° C.

The firing of the cores was at 1280 ± 10 ° C.

Kernels had Features:

Bulk density: 1.54.10 ³ kg. m ^-3

Water absorption: 22.2%

Mechanical bending strength: 16.5 MPa

Surface roughness Ra: 1.8 to 2.2 μτη

Example 3% by weight of ground fused silica, max. Grain size 0.1 mm,% by weight of special alumina for ceramics, α-ΐ2θ3 content 98% by weight was dry ground with 1% by weight oleic acid at a grinding ratio of 1: 5 The specific surface area of the ground powder mass was 1.8 m ² . g ^-1 .

The ground powder mass was worked up with a carboxymethylcellulose slurry, wherein the binder dry matter content was 4% by weight, in a plastic dough from which, after vacuuming, cores of circular cross-section were drawn.

The cores after free drying were dried in an oven at 120 ° C.

The firing of the cores was at a temperature of 1250 ° C.

The cores had the following characteristics:

Bulk density: 1,63.10 ³ kg. m ³

Water absorption (weight) 20%

Mechanical bending strength 17 MPa

The mass has proven suitable for the preparation of cores of various types, including the most demanding in shape for precision casting.

Claims (1)

SUBJECT Compound for precious metal casting based on ground fused quartz, containing 8 to 18% alumina by weight, characterized in that it contains 82 to 92% by weight of ground fused quartz and 8 to 18% by weight of alumina containing an alumina content in excess of 95%.