CN1243050A - Metal type heat-insulation coating - Google Patents

Abstract

The present invention relates to a metal heat insulating coating which comprises (wt%) mica powder 45-65%, diatomite 15-25%, Leituoshi 5-10%, colloidal silica 10-20% and sodium salt aqueous solution 5-10%. The raw materials are ground into paste or pulp by adding water, and the paste or the pulp possesses excellent suspension and coating property, and can be matched with primer coating and surface layer heat-insulating coating, it possesses the obvious action of regulating casting cooling speed and raising the effect of riser padding, its lubricating property is good, adhesive strength is high, service life is long, it is convenient for pulling core and forming casting, and the aluminium alloy casting surface roughness can be up to Ra 3.2-12.5 micrometer.

Description

Metal Type Insulation Coating

The present invention is a divisional application of the title "metal type series paint", application number 94104236.7, application date 940423 invention patent application.

The invention belongs to the component selection of the surface coating of the casting mold in the casting molding process, and provides the thermal insulation coating used in the series of semi-permanent coatings for metal molds.

Metal molds belong to the special casting process in the field of casting and are widely used in the production of aluminum castings. This process requires that there is a coating between the metal mold wall and the surface of the casting to protect the metal mold, adjust the solidification speed of the casting, and facilitate the release of the casting. Commercial series of coatings, such as the Dycote series of coatings developed by Foseco, have been widely used in metal casting and low-pressure casting of aluminum castings in Britain, the United States, France and other countries, but their formulations have not been publicly reported. In China, since there is no series of commercial coatings with excellent performance, each manufacturer prepares them for their own use. At present, there are three main types of coatings used for production: 1. Asbestos powder thermal insulation coatings are generally used in brushing processes, although there are better ones. 2. Zinc oxide coating is generally used in spraying process, because of its formula The interaction between zinc oxide and water glass results in poor suspension of the coating, easy deterioration and failure, short storage period, short working life, and poor lubricity. For metal molds with complex shapes or embedded with deep iron cores, open core pulling Difficulty; 3. Graphite powder-water coating is mostly used in dipping process. The coating has poor adhesion, low strength and poor durability. For cast aluminum parts with low requirements, the above-mentioned coatings can still meet the requirements, but it is obviously insufficient for special parts with high requirements. Overcoming the shortcomings of the above-mentioned coatings has become a factory to further improve the quality and output of metal castings, and to expand its production capacity. The main technical key of the application range.

The purpose of the present invention is to overcome the shortcomings of existing metal mold coatings, to prepare metal mold coatings with good suspending properties, applicability and durability, etc., and to require the coating to protect metal molds and regulate casting solidification. It is superior to existing coatings in terms of speed and ease of core pulling, etc., and has good performance.

In order to achieve the above goals, three basic coatings are required to be used together, namely, primer coating, thermal insulation coating and surface thermal conductivity coating. The present invention adopts special non-metallic materials and formulations, and provides thermal insulation coating formulations by weight percentage: 45-65% of mica powder, 15-25% of diatomite, 5-10% of rectorite, and 10-20% of silica sol , 5-10% sodium salt solution, the above-mentioned raw materials are added with water and rolled into paste or slurry.

When rolling into a slurry, the silica sol can be alkaline silica sol with a pH value of 9-11, the sodium salt solution is a saturated Na ₃ PO ₄ aqueous solution, the mica powder particle size is 50-20 μm, and the diatomite particle size is 50-20 μm. 28μm, when the raw material is put into the colloid mill or ball mill for grinding, the amount of water added can control the viscosity of the paint between 15 and 25 seconds (measured by N-6 viscosity cup), which is suitable as a thermal insulation paint for cavity insulation.

When rolled into a paste, the silica sol can be acidic silica sol with a pH value of 2 to 4, the sodium salt sol can be water glass with a modulus of 2.5 to 3.0, the particle size of the mica powder is 100 to 63 μm, diatomaceous earth The particle size is 80-50μm. The raw materials are prepared by a mixer or a rolling machine. The amount of water added makes the paint a paste, which is suitable for riser thermal insulation paint.

The combination of thermal insulation coating, primer coating and surface thermal conductivity coating can achieve overall optimization.

1. The primer coating is matched with the thermal insulation coating of the cavity and the thermal conductivity coating of the surface layer to improve the durability of the composite coating and make it semi-permanent. Considering the thermophysical properties of the coating, the primer has semi-thermal conductivity, the heat-insulating coating for cavity insulation has heat-insulating effect, and the heat-conducting coating for the surface layer has both heat-conducting and lubricating functions, so the thermal-insulating coating for cavity insulation is coated on the primer coating. Then apply the surface layer of heat-conducting paint to form a heat-insulating composite coating; and directly coat the surface layer of heat-conducting paint on the primer to form a heat-conducting composite coating. By adopting the above-mentioned paint and composite coating process, the composite coating has good thermophysical properties and release properties, and is also durable or semi-permanent.

2. The thermal insulation coating for the riser and the thermal insulation coating for the cavity are matched with the heat-conducting coating for the surface layer to regulate the solidification of the casting.

Although the riser thermal insulation coating and the cavity thermal insulation coating use the same type of thermal insulation aggregate, the former should be made into paste and the aggregate particle size is relatively coarse, which is easy to brush thick without flowing, while the latter should be made into paste and aggregate The fine particle size is easy to spray, low viscosity and good suspension, which can meet the requirements of different parts and different degrees of heat insulation. According to the special requirements of the coating for different parts of the casting, coatings with different thermal conductivity, coating thickness and surface roughness are used to achieve the purpose of controlling the cooling speed of the casting. For example, at the riser, apply a thicker riser thermal insulation coating to improve the filling and feeding capacity, and spray a thinner surface layer of heat-conducting coating at the thick mold cavity of the iron core or casting to eliminate local Shrinkage porosity to obtain dense castings.

The thermal insulation coating of the present invention has good suspending property and applicability; used in conjunction with the primer coating and the surface layer heat-conducting coating, it has the obvious effect of adjusting the cooling speed of the casting and improving the feeding effect of the riser, and has good lubricity. It is convenient for core pulling and casting out; high adhesion strength, long service life, and semi-permanent. The surface roughness of aluminum alloy castings produced by this series of coatings can reach Ra3.2～12.5μm, which is two levels higher than that of conventional zinc oxide coatings, and its main performance indicators have reached the performance indicators of similar coatings from the internationally advanced British Foseco company: Heat transfer coefficient W/m ² ·C ⁰ Coating strength N/mm ² Suspension Gas volumeml/g Cavity thermal insulation coating ＜400(coating 0.15mm) >3.2 >90% <20 Riser insulation coating ＜160 (coating 0.65mm) >2.5 paste <20 When conducting production verification, the actual formula of the coating is: thermal insulation coating for cavity insulation

Mica powder (50～28μm) 50%

Diatomaceous earth (50～28μm) 20%

Rectorite 5%

Alkaline silica sol (PH=10) 15%

Na ₃ NO ₄ saturated aqueous solution 10%

Appropriate amount of water

The viscosity of the paint is 16 sec, timed using a No. 4 flow cup. Riser insulation coating

Mica powder (100～63μm) 50%

Diatomaceous earth (80～50μm) 25%

Acidic silica sol (PH=2) 15%

Rectorite 5%

Water glass (modulus 2.8) 10%

Appropriate amount of water

paint in paste form

Claims (3)

1. A metal type thermal insulation coating, characterized in that the formula of the coating is: 45-65% of mica powder, 15-25% of diatomite, 5-10% of rectorite, 10-20% of silica sol , 5-10% sodium salt solution, the above-mentioned raw materials are added with water and rolled into paste or slurry. 2. The metal thermal insulation coating as claimed in claim 1, characterized in that the silica sol is alkaline silica sol with a pH value of 9 to 11, the sodium salt aqueous solution is Na _PO saturated _aqueous solution, and the particle size of mica powder is 50 to 11. 20 μm, diatomite particle size 50-28 μm, when the raw materials are put into the colloid mill or ball mill for grinding, the amount of water added can control the viscosity of the coating between 15-25 seconds. 3. The metal type thermal insulation coating as claimed in claim 1, characterized in that said silica sol is acidic silica sol with a pH value of 2 to 4, said aqueous solution of sodium salt is water glass with a modulus of 2.5 to 3.0, and said mica The particle size of the powder is 100-63 μm, and the particle size of diatomite is 80-50 μm. The raw materials are prepared by a mixer or a rolling machine, and the amount of water added makes the paint a paste.