RU2843191C1 - Parting compound composition for casting moulds - Google Patents

Abstract

FIELD: foundry production.

SUBSTANCE: parting compound for casting moulds, cores and ingot moulds contains the following components in wt.%: 2.4-19.6 of ethyl silicate, 11.5-29.5 of alcohol, 0.01-5.2 anti-sedimentation additive, balance is refractory filler. As alcohol, which is a solvent, providing fluidity, wettability, covering power and high drying rate, paint contains ethyl or methyl alcohol or isopropyl alcohol or a combination thereof. As an anti-sedimentation additive, the paint contains an additive based on phyllosilicates. Addition of alcohol together with phyllosilicate in the disclosed amount increases sedimentation resistance and covering power of the paint, increases its strength and reduces the probability of casting to the mould.

EFFECT: high sedimentation resistance and covering capacity of the paint, uniform thickness of the coating, no cracks after high-speed drying by direct fire or natural drying, as well as higher wear resistance of coating and absence of burn on metal casting.

1 cl, 1 dwg, 1 ex

Description

The invention relates to a technology for producing non-stick paint intended for foundry production as a protective coating for casting molds and cores, as well as molds used in the manufacture of castings from ferrous metals and alloys based on them.

One of the main problems of metal casting technologies in both even and non-ferrous metallurgy is the problem of casting sticking to the mold. Non-stick paints are produced on the basis of various refractory fillers, but the most refractory are fillers based on magnesium oxide. Due to the ability of magnesium oxide to hydrate, such paints cannot be produced on a water basis.

Magnesia anti-stick paints ensure the quality of the casting surface and maintain the integrity of casting molds and cores. At the same time, the number of casting defects is reduced and their appearance is improved. The paint forms a protective layer on the casting surface, which prevents interaction between the liquid metal and the mold material, which reduces the risk of damage. Also, the smoothness of the casting surface is improved by using anti-stick paints that fill in the unevenness of the casting mold. The paint helps reduce the adhesion between the casting and the mold, which facilitates the process of removing the finished casting. In addition, the cooling rate and, therefore, the structure of the casting can be regulated due to the thermal properties of the paint. This is especially important for obtaining the necessary mechanical properties of the castings.

The closest in the achieved result and technical essence is a non-stick paint for casting molds containing scrap of unfired periclase-carbon products as a refractory filler - the lining of steel-pouring ladles of converters [1]. The work indicates that scrap of unfired periclase-carbon products hydrates worse in an aqueous medium in comparison with metallurgical magnesite due to the fact that in scrap of unfired periclase-carbon products, particles of MgO and a solid carbon-containing substance (graphite) are firmly bound as a result of hardening and coking of the phenolic binder and are poorly wetted by water, which slows down the hydration processes. The authors claim that it is preferable to use organic solvents, such as isopropyl alcohol, as a dispersion medium. The compositions of the masses for obtaining non-stick paint are not given.

A composition of a non-stick heat-resistant paint is known [RU. author's certificate No. 2478019, B22C 3/00, published 27.03.2013] based on a filler, bentonite and water. The paint variant contains magnesite and chromite as a filler with the following content in wt. %: magnesite powder 20-35, chromite powder 45-55, bentonite 2.5-4.5, water is the rest. The quality of the casting surface is improved due to the increased heat resistance of the paint. A disadvantage of this paint composition is the hydration of magnesite (the authors most likely meant periclase MgO), which can cause an increase in its volume, entail a change in the properties of the paint, and deterioration in adhesion to the surface of the mold. In addition, hydration processes can lead to explosive release of water (steam) during metal pouring, resulting in the formation of cavities on the surface of the casting and burning of the metal to the casting surface.

If the authors actually introduce magnesite MgCO ₃ into the paint composition, then the said paint is subject to high gas formation during its use due to the decomposition of magnesite to periclase at a temperature of 550-650 °C.

The non-stick heat-insulating paint specified in the patent [RU. author's certificate No. 2453391, B22C 3/00, published 26.06.2012] contains a synthetic refractory filler, which is 39-42% titanium carbide, 7-9% sodium oxide, 5-7% aluminum oxide, 5-7% magnesium oxide and a varnish containing 3-5% polyvinyl alcohol powder and 97-95% water. The disadvantage of the composition is the use of pure oxides in the composition - expensive and scarce components.

In the composition of the non-stick paint for casting molds and cores [RU. author's certificate No. 1470417, B22C 3/00, published 07.04.1989], the following are used as a refractory filler: waste from the regeneration of electrocorundum from spent ceramic molds 45-52%, a binder - a solution of polyvinyl butyral 0.5-2.5% and ethyl silicate 4-8% in an organic solvent 35-40%, orthophosphoric acid as a catalyst for the hydrolysis of ethyl silicate 0.2-0.4% and a surfactant - polyethylene glycol ether 0.3-0.5%. The disadvantages of such a composition are that corundum-containing waste is used as a filler, which itself actively interacts with metal melts and forms a burn, and also that acetone is used as a solvent to dissolve polyvinyl butyral, which has a toxic effect on the human body and has a hazard class of 4. Drying the mold surface by direct exposure to fire is impossible.

The non-stick paint specified in the patent [RU. author's certificate No. 980922, B22C 3/00, published 15.12.1982] contains a refractory filler, which is 15-25% titanium carbonitride, 10-20% non-hydrolyzed ethyl silicate, a stabilizer based on 23-47% polyvinyl butyral varnish and acetone. The disadvantage of such paint is the use of an expensive and scarce filler and lower adhesive capacity of the paint due to the use of non-hydrolyzed ethyl silicate, which worsens the degree of adhesion of the paint to the surface of the mold and the strength of the resulting coating.

The closest in composition Author's Certificate [SU. aut. svid. № 733847, B22C 3/00, published 15.05.1980] describes a self-drying anti-stick paint for foundry cores and molds, intended for use in foundry production. The main components of this paint include a hydrolyzed solution of ethyl silicate with 3-12% silicon dioxide and 0.5-1.5% acetic acid in an amount of 39.5-49.5 wt. %, polyvinyl butyral adhesive 1.2-1.8 wt. %, the rest is refractory filler. A disadvantage of the paint is the presence of polyvinyl butyral in the composition, which contributes to cracking and peeling of the coating when pouring large steel castings with a long pouring time (more than 60 seconds). Cracking and peeling can lead to the formation of surface defects (squeezes) on castings, which negatively affects their quality. Another disadvantage is the presence of silicon oxide, which reduces the non-stick properties of the paint, since it easily interacts with iron-based melts to form fayalite. In addition, fast drying modes using direct fire are not applicable to such paint.

The problem solved by the invention is the creation of a composition and technology for the production of non-stick paint for casting molds with improved properties: high sedimentation resistance, increased mechanical strength, improved heat resistance, high drying speed, including by direct fire.

This problem is solved by introducing alcohol into the paint composition, which is pre-mixed with ethyl silicate and an additive based on phyllosilicates in a given proportion, and with constant stirring, a magnesia refractory filler is introduced.

The result is high sedimentation resistance, good covering power and uniform coating thickness, no cracks after high-speed drying by direct fire or natural drying, as well as abrasion resistance, no burning on the metal casting.

This technical result is achieved by using the following paint composition.

Various types of alcohol can be used as a solvent that ensures fluidity, wettability and covering ability of paint, as well as high drying speed due to the possibility of igniting the paint: ethyl, methyl, isopropyl, in the amount of 11.5-29.5 wt. %. The amount of alcohol depends on the technology of applying paint in each specific production. With an alcohol content of less than 11.5%, the viscosity of the paint increases, the thickness of the applied coating increases, and an uneven coating of the mold is formed. In addition, the drying time of the paint increases.

When the alcohol content exceeds 29.5%, paint begins to settle. This reduces the density of the paint, which increases the likelihood of burning due to the application of a thin layer of coating.

Ethyl silicate is used as an adhesive, its content is 2.4-19.6 wt.%. With a lower content of ethyl silicate (less than 2.4%), the degree of adhesion of paint to the surface of the form decreases, with a content of more than 19.6%, the drying rate decreases, and when applying a second layer of paint, a defective surface is formed due to the destruction of the first layer.

As an anti-sedimentation additive, additives based on phyllosilicates are used in the amount of 0.01-5.2%. When using an additive of less than 0.01 wt.%, the sedimentation stability of the paint is lost, the paint settles and exfoliates. With a higher content of the additive (more than 5.2 wt.%), the degree of adhesion of the paint to the surface of the mold decreases, and shell formation is observed when it burns out.

A magnesium-containing component with a particle size of less than 200 μm obtained from recycling periclase, periclase-spinel, periclase-chromite, periclase-carbon refractory products, periclase ceramics, fused periclase, sintered periclase, caustic periclase in the remaining amount after the introduction of ethyl silicate, antisedimentation additive, and alcohol was used as a refractory filler.

Examples

The compositions of the masses for obtaining non-stick paints are presented in Table 1.

The paint is prepared in the following way: alcohol is mixed with ethyl silicate and a phyllosilicate-based additive in a given proportion and the filler is introduced with constant stirring.

The paint was applied by spraying, dipping, pouring, and brushing. The method of applying the paint depends on the relative viscosity (Table 1).

After the coating was applied to the product, it was set on fire to reduce drying time and obtain a more durable layer.

After drying, the following paint properties were determined: sedimentation resistance, abrasion resistance, viscosity, covering power in accordance with GOST 10772-78, the presence of burning and heat resistance. The heat resistance of the coating was determined by the presence of cracks and paint rebound after rapid drying, carried out by setting fire to the form. The properties of the coatings are given in Table 1.

Table 1 shows that the exclusion of polyvinyl butyral from the paint composition and the introduction of alcohol together with phyllosilicate in an amount of 0.01-5.2% increases the sedimentation resistance and covering ability of the paint, increases its strength and reduces the likelihood of the casting burning to the mold.

Non-stick paint for casting moulds, obtained from magnesium-containing filler 62-70%, hydrolyzed ethyl silicate (2.4-19.6%), alcohol (isopropyl, methyl, ethyl) (11.5-29.5%), additives based on phyllosilicates (0.01-5.2%), characterized by: absence of sedimentation and characterized by rapid drying when exposed to direct fire, absence of gas evolution during its combustion, eliminating the formation of gas cavities.

Claims (2)

Anti-stick paint for casting moulds, cores and ingot moulds, containing ethyl silicate and a refractory filler, characterized in that it additionally contains ethyl, or methyl, or isopropyl alcohol, or a combination thereof, as well as an anti-sedimentation additive based on phyllosilicate, in the following ratio of components, wt. %: ethyl silicate 2.4-19.6 alcohol 11.5-29.5 anti-sedimentation additive 0.01-5.2 refractory filler rest