CN102366814B - A kind of preparation method of coating for metal mold used in aluminum alloy low pressure casting - Google Patents

Abstract

The invention discloses a method for preparing an aluminum alloy low-pressure casting metal mold coating. The coating prepared by the method comprises 35-45% mullite powder, 5-10% alumina powder, and 5.5-6.5% sodium base Bentonite, 2.0-2.5% polyvinyl alcohol, 0.8-1.0% sodium alginate, 3.5-4.0% silica sol, 0.8-1.0% sodium dodecylbenzenesulfonate, and the balance is water. The preparation method of the present invention has a wide range of raw materials , low cost, easy to prepare paint. The coating of the invention is used for aluminum alloy low-pressure casting metal molds, and the castings are easy to demould, and the castings have smooth surfaces without defects such as scarring and adhesion.

Description

A kind of preparation method of aluminum alloy low-pressure casting metal mold coating

technical field

The invention relates to the field of casting, in particular to the technical field of low-pressure casting aluminum alloys.

Background technique

There are many types of metal casting coatings, which are mainly distinguished by coating binders and high temperature resistant fillers. Commonly used binders include syrup, water glass, and polymer binders such as resins and polyvinyl alcohol. High temperature resistant fillers are black lead powder, spray carbon black, coke powder, high aluminum powder, etc. Commonly used syrup paint ingredients are: black lead powder > 30%, spray carbon black > 45%, syrup > 15%. After mixing these materials, put them in a rotary mixer, add an appropriate amount of water, and stir thoroughly for 1.5-2 hours. The paint density is required to be between 1.2-1.3g/cm ³ . Commonly used water glass binder coating components are: 80% carbon black, 20% water glass and an appropriate amount of water, with a density of 1.1-1.2g/cm ³ . Commonly used polyvinyl alcohol binder coating components are: 200 mesh or more high-alumina powder mixed with 300-400g polyvinyl alcohol and an appropriate amount of water. The advantage of using syrup as a binder is that metal molds are easy to clean when they are reused. The disadvantage is that the syrup is made of grain, and there are certain requirements for the temperature of the metal mold when used. If the temperature of the mold is too low, the paint cannot be applied, and the moisture in the paint is not easy to volatilize, which is easy to cause pore defects; the temperature of the mold is too high. , the syrup is easy to burn off, causing the coating to lose its cohesive properties, and the molten metal is easy to wash off the coating layer during pouring, which loses its protective effect on the metal mold, causing many small pinholes to appear on the surface of the casting, and sometimes produces a metal mold The phenomenon of sticking together with the molten metal of castings will lead to the scrapping of castings and molds in severe cases. The advantage of water glass paint is that it has high dry strength, and it will not deteriorate and burn when the metal mold temperature is high. The disadvantage is that it is difficult to clean up after use. The thickness of the coating can not be thick, only 0.3-0.5mm, otherwise it is easy to crack and peel off, so the service life of the mold is short. The advantage of polyvinyl alcohol coating is that it has high dry strength and can be mixed with various high-temperature resistant fillers. The thickness of the coating can be increased to 2-5mm. Under the high temperature of the molten metal, a carbonized bright film will be produced to make the surface of the casting smooth. The disadvantage is that the mixing time is long, and it must be stirred continuously during spraying to prevent the layering and precipitation of the coating, and the coating thickness is difficult to control uniformly.

In the prior art, in the low-pressure casting of aluminum alloy, the paint used for spraying on the surface of the metal cavity and the casting tool, the traditional domestic products mainly use zinc oxide, chalk powder, graphite powder and other powders as raw materials, and water glass is added in different proportions. It is prepared on-site with water, and sprayed after being evenly stirred. Practice has proved that the obvious defects of this technology are: ① It is troublesome and time-consuming to mix and prepare coatings; ② The cost of raw materials is high, which affects product benefits; Cause the cavity to stick and burn; ④The surface quality of the produced castings is not good.

Contents of the invention

In view of the deficiencies in the prior art, one of the objectives of the present invention is to provide a method for preparing a coating for aluminum alloy low pressure casting metal molds.

To achieve the above object, the technical scheme adopted in the present invention is as follows:

A method for preparing an aluminum alloy low-pressure casting metal mold coating, comprising the steps of:

1) The composition of the paint is, by mass fraction: 35-45% mullite powder, 5-10% alumina powder, 5.5-6.5% sodium bentonite, 2.0-2.5% polyvinyl alcohol, 0.8-1.0% alginic acid Sodium, 3.5-4.0% silica sol, 0.8-1.0% sodium dodecylbenzenesulfonate, the balance is water, and the ingredients are weighed according to the above components;

2) First add 200-280 mesh sodium bentonite, 200-280 mesh mullite powder, and 200-280 mesh alumina powder into the wheel mill according to the above ratio, and dry mix for 15-25 minutes;

3) Then add sodium alginate, sodium dodecylbenzenesulfonate, polyvinyl alcohol and water in sequence according to the above ratio, and mix and grind for 180-240min;

4) Then add silica sol and mix for 30-40 minutes according to the above ratio;

5) Finally, sieve the mixed and milled paint through an 80-100 mesh sieve to remove impurities.

200-280 mesh alumina powder and 200-280 mesh alumina powder are selected as the main refractory aggregate of the coating of the present invention, and mullite powder is used as the main refractory aggregate, so that the surface of the low-pressure cast aluminum parts is smooth and clean, without scarring and adhesion and other defects. In addition to mullite, 5-10% alumina powder is added to the refractory aggregate of the paint in order to improve the high temperature resistance of the paint, which can ensure that the paint has better high temperature strength and good flow coating performance.

The paint of the invention uses sodium bentonite, polyvinyl alcohol and sodium alginate as suspending agent, and the suspending agent is used to prevent the precipitation of refractory aggregate. Adding sodium alginate to the paint can significantly improve the suspension of the paint. The raw materials for polyvinyl alcohol are petroleum and natural gas, which have a wide range of sources, and are non-toxic and tasteless. Adding them to paints can improve the suspension performance of paints. When they are used together with sodium-based bentonite and sodium alginate, they can obtain higher sedimentation stability. Quick drying and good brushability.

The viscosity of silica sol is small, and the powder-to-liquid ratio of the coating can be greatly increased, so that the surface strength and hardness of the coating can be improved, so as to obtain a high-quality and smooth casting surface. In addition, the silica sol coating has good stability, and can obtain strength by natural drying. Silica sol is also non-toxic, non-corrosive, non-flammable and explosive, and the coating prepared with it has no pollution to the environment and is safe for people. Adding 3.5-4.0% silica sol in the paint of the invention as a binder can make the paint have good high-temperature bonding strength.

In order for the paint to be well attached to the surface of the metal mold, it is required to have a certain wetting ability on the surface of the metal mold, and an appropriate amount of surfactant is added to reduce the surface tension of the paint or the contact between the paint and the metal mold material. Interfacial tension, 0.8-1.0% sodium dodecylbenzenesulfonate is added to the coating of the present invention. After it dissolves in water, it will be ionized into negatively charged alkylbenzenesulfonate and positively charged sodium particles. One end of the positively charged It is attracted and aligned with the metal mold, which reduces the interfacial tension between the metal mold and the coating, and improves the combination effect of the coating and the mold.

The beneficial effect of the method for preparing coating of the present invention is:

1. The method of the present invention has wide sources of raw materials, low cost, and simple operation for preparing coatings.

2. The paint of the present invention only needs to be painted on the metal mold with a temperature of 300-330°C, and then dried. It does not need frequent heating of the mold cavity and spraying during use, and is easy to use.

3. The coating of the present invention is used for aluminum alloy low-pressure casting metal molds, and the castings are easy to demould, and the surface of the castings is smooth and free of defects such as scarring and adhesion.

detailed description

Embodiment one

A method for preparing an aluminum alloy low-pressure casting metal mold coating, comprising the steps of:

1) The composition of the paint is, in terms of mass fraction: 35% mullite powder, 10% alumina powder, 5.5% sodium bentonite, 2.5% polyvinyl alcohol, 0.8% sodium alginate, 4.0% silica sol, 0.8% ten Sodium dialkylbenzene sulfonate, the balance is water, and the ingredients are weighed according to the above components;

2) First add 200-280 mesh sodium bentonite, 200-280 mesh mullite powder, and 200-280 mesh alumina powder into the wheel mill according to the above ratio, and dry mix for 15 minutes;

3) Then add sodium alginate, sodium dodecylbenzenesulfonate, polyvinyl alcohol and water in sequence according to the above ratio, and mix and grind for 240 minutes;

4) Then add silica sol and mix for 30 minutes according to the above ratio;

5) Finally, sieve the mixed and milled paint through a 100-mesh sieve to remove impurities.

Embodiment two

A method for preparing an aluminum alloy low-pressure casting metal mold coating, comprising the steps of:

1) The composition of the coating is, by mass fraction: 45% mullite powder, 5% alumina powder, 6.5% sodium bentonite, 2.0% polyvinyl alcohol, 1.0% sodium alginate, 3.5% silica sol, 1.0% ten Sodium dialkylbenzene sulfonate, the balance is water, and the ingredients are weighed according to the above components;

2) First add 200-280 mesh sodium bentonite, 200-280 mesh mullite powder, and 200-280 mesh alumina powder into the wheel mill according to the above ratio, and dry mix for 25 minutes;

3) Then add sodium alginate, sodium dodecylbenzenesulfonate, polyvinyl alcohol and water in sequence according to the above ratio, and mix and grind for 180 minutes;

4) Then according to the above ratio, add silica sol and mix for 40 minutes;

5) Finally, sieve the mixed and milled paint through an 80-mesh sieve to remove impurities.

Embodiment Three

A method for preparing an aluminum alloy low-pressure casting metal mold coating, comprising the steps of:

1) The composition of the paint is, in terms of mass fraction: 40% mullite powder, 8% alumina powder, 6% sodium bentonite, 2.3% polyvinyl alcohol, 0.9% sodium alginate, 3.8% silica sol, 0.9% ten Sodium dialkylbenzene sulfonate, the balance is water, and the ingredients are weighed according to the above components;

2) First add 200-280 mesh sodium bentonite, 200-280 mesh mullite powder, and 200-280 mesh alumina powder into the wheel mill according to the above ratio, and dry mix for 20 minutes;

3) Then add sodium alginate, sodium dodecylbenzenesulfonate, polyvinyl alcohol and water in sequence according to the above ratio, and mix and grind for 210 minutes;

4) Then add silica sol according to the above ratio and mix and grind for 35 minutes;

5) Finally, sieve the mixed and milled paint through a 90-mesh sieve to remove impurities.

The applicant declares that the present invention illustrates the detailed process equipment and process flow of the present invention through the above-mentioned examples, but the present invention is not limited to the above-mentioned detailed process equipment and process flow, that is, it does not mean that the present invention must rely on the above-mentioned detailed process equipment and process flow process can be implemented. Those skilled in the art should understand that any improvement of the present invention, the equivalent replacement of each raw material of the product of the present invention, the addition of auxiliary components, the selection of specific methods, etc., all fall within the scope of protection and disclosure of the present invention.

Claims (1)

1. a preparation method for aluminum alloy low pressure casting metal mold coating, is characterized in that, comprises the steps: 1) The composition of the paint is, by mass fraction: 40-45% mullite powder, 8-10% alumina powder, 5.5-6.5% sodium bentonite, 2.0-2.5% polyvinyl alcohol, 0.8-1.0% alginic acid Sodium, 3.5-4.0% silica sol, 0.8-1.0% sodium dodecylbenzenesulfonate, the balance is water, and the ingredients are weighed according to the above components; 2) First add 200-280 mesh sodium bentonite, 200-280 mesh mullite powder, and 200-280 mesh alumina powder into the wheel mill according to the above ratio, and dry mix for 15-25 minutes; 3) Then add sodium alginate, sodium dodecylbenzenesulfonate, polyvinyl alcohol and water in sequence according to the above ratio, and mix and grind for 180-240min; 4) Then add silica sol and mix for 30-40 minutes according to the above ratio; 5) Finally, sieve the mixed and milled paint through an 80-100 mesh sieve to remove impurities.