RU2226445C1 - Filler for burning-inhibiting coatings - Google Patents

Abstract

FIELD: foundry, namely manufacture of burning-inhibiting coatings for casting molds and cores. SUBSTANCE: slag formed at remelting secondary aluminum alloys is used as filler for coating compositions. Said slag contains metallic aluminum in quantity 3.4 - 23.2 mass% and silica in quantity 6.85 mass%. Due to presence of Al₂O₃ and SiO₂, having high refractoriness, thermal burning on castings is reduced. Metallic aluminum in the result of contact with melt forms additional quantity of Al₂O₃. Use of flux components provides formation at high temperature of activated gas phase in the form of chlorine-, fluorine- and hydrogen-containing ions and radicals. When metallic aluminum, slag and iron from melt metal react with said gas phase chlorides are formed. Said chlorides form "crust" preventing realization of chemical reactions between casting and mold. EFFECT: enhanced quality of castings due to complex action of slag. 2 tbl

Description

The invention relates to the field of foundry, and in particular to compositions of non-stick coatings for foundry molds and cores in the manufacture of castings from ferrous alloys.

A known composition for producing a non-stick coating on foundry molds and cores, containing as a refractory filler a waste of water-air granulation of carbon slag ferrochrome slag (AS USSR No. 13233206, B 22 C 3/00, 1987).

However, this composition has the following disadvantages: it is used only for cast iron castings, surface cleanliness is achieved only by increasing the strength properties of the coating, i.e. the occurrence of only a mechanical burnout is eliminated.

Known filler and binder for non-stick coatings, which is a waste product of etching aluminum alloys with alkali (AS USSR No. 1357116, 22 C 3/00, 1987).

However, the raw material base for the manufacture of filler can be expanded. In addition, the high viscosity of 42-43 s coatings can cause unevenness when applied to a mold or core. In addition, when using this filler in non-stick coatings, the stick is eliminated only due to the formation of aluminum oxide (thermal and mechanical) and the action of the gas layer (mechanical).

These shortcomings are addressed by the proposed solution.

The problem to be solved is the expansion of the raw material base due to the disposal of waste generated during the remelting of aluminum alloys, a comprehensive effect on the formation of burns, as well as cost reduction.

The technical result is an improvement in hiding power by reducing viscosity.

This technical result is achieved through the use of slag formed during the remelting of secondary aluminum alloys as a filler for non-stick coatings of molds and cores.

This material can be used both in pure form or in combination with known fillers in aqueous and self-drying coatings.

The use of slag formed during the remelting of aluminum alloys as a filler of non-stick coatings makes it possible to obtain castings with a clean surface. 2 tab.

Used slag formed during the remelting of secondary aluminum alloys (aluminum slag) has the following average chemical composition,%:

Al ₂ O ₃ 30.3

SiO ₂ 6.85

MgO 3.08

CaO 1.28

CuO 0.32

Fe ₂ O ₃ 1,2

TIO ₂ 0.5

The content of aluminum metal in the slag ranges from 3.4 to 23.2%.

In addition, the compounds Si, Mg, Ca, Cu, Cr, Fe, Ti, Zn, Mn, Ni, Co, V, Mo, Sr, Pb, Ag, Sn, Ga, Be, Y, Zr, Li, Ba.

Aluminum slag is a mechanical mixture of these elements with a true density of 2990 kg / m ³ and a specific surface area of 40.33 m ² / kg.

The compositions of non-stick coatings use aluminum slag with a particle size of less than 0.063 mm, previously ground and dried. The choice of just such a fraction of aluminum slag is not accidental, since it is it that provides coatings in the form of a homogeneous suspension with optimal properties for the selected ratios of the components. With a change in the percentage ratio of components in the coating composition, it becomes possible to use the entire range of the fractional composition of aluminum slag. In this case, the resulting coating can be both in the form of paint, and in the form of a paste.

The prerequisites for the use of aluminum slag as a filler of non-stick coatings is the presence in its composition Al ₂ O ₃ with high refractoriness, a relatively constant chemical composition; sufficiently stable grain composition, providing the necessary fine and dusty fraction up to 30% by weight of the material; metallic aluminum, which is part of aluminum slag; non-wettable by liquid melt.

In addition, this material has an intense gas evolution in contact with molten iron and steel and significantly changes its mass during calcination.

The use of aluminum-slag coatings of foundry molds and cores for steel and iron casting has a complex effect on the prevention of burnout.

Reducing the thermal burnout is achieved by the presence of Al ₂ O ₃ and SiO ₂ in the composition of the aluminum slag, which have high refractoriness.

The reduction of mechanical burning is achieved by the use of aluminum slag of a fine and dusty fraction, the non-wettability of aluminum slag by a liquid melt. When in contact with the melt, aluminum metal deoxidizes it, forming Al ₂ O ₃ , which is part of an insoluble oxide film that creates obstacles to the penetration of the melt into the pores of the moldable mixture. The gas layer formed as a result of thermal degradation of the coating plays the role of a “gas shutter” or a heat-insulating gas cushion, which interferes with the penetration of the first hot melt streams into the pores of the mold. In addition, the gas layer at the initial stages of pouring the metal into the mold together with the casting crust counteracts the pressure of the molten liquid on the working surface of the mold.

The presence in the slag of the coating flux components used in the remelting of secondary aluminum alloys (mainly KCl, NaCl, Na ₃ AlF ₆ , KBF ₄ ), as well as the high hygroscopicity of the slag contribute to the formation of active components in the form of chlorine at high temperatures in the gas phase emitted by the coating -, fluorine - and hydrogen-containing ions and radicals, resulting in the so-called "activation of the gas phase". The activated gas phase in the zone of advancement of the temperature front creates the conditions for the reaction of the molten metal and the coating with it. The result of this reaction is the formation on the surface of the casting crust, and then the casting of a special layer containing, first of all, iron and aluminum chlorides and representing an easily removable "shell", which also performs a protective function and prevents the gas from moving into the casting.

An aqueous non-stick coating is applied to the surface of the mold or rod, and is dried. Self-drying coating is applied to the warm surface of the mold or core.

Aluminum-slag filler can be used in combination with other fillers, for example, in the production of iron castings in combination with carbon-containing fillers.

The use of aluminum slag as a filler in non-stick coatings leads to the absence of a stick.

Examples of the preparation of coatings with aluminum-slag filler. The coating compositions are given in table. 1, and their properties are in table. 2.

Example 1

Water-based non-stick coating based on aluminum slag for painting molds and cores for small and medium steel castings. The coating composition includes: aluminum-slag filler, clay suspension with a density of 1.3-1.5 g / cm ³ , technical lignosulfonate with a density of 1.25-1.27 g / cm ³ , water. The coating is prepared by mechanical mixing of the components. Water is poured into the container with aluminum-slag filler, everything is thoroughly mixed. Then a clay suspension and lignosulfonate are added. The paint is mixed until smooth for 15-20 minutes.

Example 2

Self-drying paint based on aluminum slag for painting molds and cores for small and medium steel castings. The coating composition includes: aluminum-slag filler, polyvinyl butyral and ether-aldehyde fraction, acetone. The coating is prepared by mechanical mixing of the components. Acetone is added to a container with a pre-prepared composition: polyvinyl butyral powder and an ether-aldehyde fraction, mixing is performed until a homogeneous mass is formed. Then an aluminum-slag filler is introduced. The paint is mixed for 20 minutes.

Example 3

Water-based non-stick coating based on aluminum-slag filler with the addition of carbon-containing fillers for painting molds and cores for small and medium iron castings. The coating composition includes: aluminum-slag filler, crystalline graphite (silver), crystalline carbon graphite (black), clay suspension with a density of 1.3-1.5 g / cm ³ , technical lignosulfonate with a density of 1.25-1.27 g / cm ³ , water. The coating is prepared by mechanical mixing of the components. Black graphite, silver graphite and aluminum-slag filler are mixed in the tank. Then water is added and everything is thoroughly mixed. After this, a clay suspension and lignosulfonate are added. The paint is mixed until smooth for 15-20 minutes.

Example 4

Self-drying coating based on aluminum-slag filler with the addition of carbon-containing fillers for painting molds and cores for small and medium iron castings. The coating composition includes: aluminum-slag filler, silver graphite, black graphite, polyvinyl butyral and ether-aldehyde fraction, acetone. The coating is prepared by mechanical mixing of the components. Acetone is added to a container with a pre-prepared composition: polyvinyl butyral powder and an ether-aldehyde fraction, mixing is performed until a homogeneous mass is formed. Then a mixture is introduced, consisting of an aluminum-slag filler, black and silver graphite. The paint is mixed for 20 minutes.

Conclusion. The proposed filler of non-stick coatings for painting molds and rods for steel casting provides a surface quality of castings comparable to the quality of castings obtained in molds with coatings based on marshallite, electrocorundum, distene sillimanite and zircon concentrate (at a significantly higher cost of the latter), for cast iron casting achieves a reduction in defect by surface defects of ~ 15%.

Claims (1)

The use of slag formed during the remelting of secondary aluminum alloys containing metallic aluminum in an amount of 3.4-23.2 wt.% And silicon oxide in an amount of 6.85 wt.% By average composition as a filler for non-stick coatings of molds and cores.