Coating accumulation



the reason:      

1. The flow of the coating is slow. Since the coating is a thixotropic fluid, there is a network structure and yield value, and the yield value and viscosity are the two main factors that cause the coating to accumulate. The yield value of the coating is too high, and the viscosity is too large, resulting in poor fluidity of the coating.

2. The flow marks generated by the paint during the flow process flow along the sand pattern, and the grooves are generated when the grooves are formed, resulting in unclear edge angles of the sand.

3. The sand angle is not suitable.

4. The flow rate is small, and the paint does not flow to cause accumulation.

5. The flow rate is slow due to insufficient pressure, causing accumulation.



Take measures:      

1. From the field operation, it is necessary to reduce the wave beauty of the coating. It has been proved by practice that when the flow coating material is between 22 and 26, the fluidity of the coating is the best. The coating yield value and viscosity should be reduced in consideration of the coating itself.

2. Use a duct to blow or use a brush to remove the flow marks.

3. Sand type placement angle requirements: Use the crane to hang the sand pattern above the paint tank and flow at a 75-90 degree angle.

4. Increase the cross-sectional area of the flow-coated head and hose to increase the flow rate. The commonly used flow-coated head and hose are 4 points. If the cross-sectional area is increased, you can use 4 and 6 tubes respectively or both. All use 6 points.

5. Increasing the wind pressure can increase the flow rate. In order to obtain a suitable coating thickness, the speed of the paint flowing out from the flow coater is preferably 100-200 mm/s, and the wind pressure is generally between 0.4×105 Pa and 0.6×105 Pa. Large is prone to splashes.



Not enough coating thickness



the reason:      

1. The paint flows directly without forming a sufficient coating thickness.

2. The coating is completely infiltrated into the molding sand, resulting in insufficient coating thickness.

3. The sand surface has a release agent, which reduces the permeability of the coating and directly affects the thickness of the coating.



Take measures:      

1. Increase the viscosity of the coating (maximum of 7 s) to improve the coating and avoid excessive drooling of the coating.

2. Improve the sand compaction, which can effectively avoid excessive penetration of the coating. The sand compaction is suitable between 45% and 55%. The surface release agent can be fully dried before production.

3. The part of the sand type partially coated with the release agent is ground with fine sandpaper and then flow coated.



Cast iron sand-type wet coating thickness requirements:

Thin wall castings 0.15mm-0.30mm

Medium casting 0.30mm-0.75mm

Thick wall castings 0.75mm-1.00mm

Extra-thick casting 1.00mm-2.00mm



Coating surface peeling off



During the assembly process, when the operator blows the sand in the cavity with the air duct, the surface of the paint layer occasionally falls off.

the reason:

1. The coating strength is low.

2. The coating layer and the layer are not fully combined to form a whole.



Take measures:

1. The small amount of binder in the coating tends to cause insufficient coating strength, so increase the proportion of binder in the coating.

2. The coating does not burn sufficiently causing the bond between the layers to be easily affected. For castings with more than 3 tons, the surface of the coating is prone to fall off. As long as the ignition time is properly controlled, this problem can be solved. Generally, the ignition is preferably 3-5 seconds after the flow of the tank, and the ignition is 5-7 seconds after the flow of the lower tank. it is good. Gas fire baking can also be used, but the time should not be too long, otherwise the coating will crack.



Casting sand



The paint has insufficient refractoriness, and the coating or sand type reacts with the high-temperature metal liquid to form a chemical reaction, which makes the surface of the casting form a material that is extremely difficult to clean. It is usually called sticky sand, and the flow coating method also produces sand sticking.

Take measures:

1. Change the composition of the coating aggregate and improve the refractoriness of the coating. Select high-alumina bauxite powder, zircon powder and other refractory fillers.

2. Increase the thickness of the coating, but the thickness should not exceed the maximum required for the thickness of the coating. Too thick will result in casting defects such as paint coating.

3. Improve the wave beauty of the flow coating, the maximum is not more than 28, otherwise the fluidity will decrease.

4. Some castings have local overheating phenomenon, and the flow coating is very easy to stick sand. Before the flow coating, the paint with high refractoriness is applied at the hot joint position, which can effectively prevent sticking sand.



Serious flow marks



the reason:

The paint has poor fluidity and high viscosity. When the paint flows downward, it can not drip, resulting in serious flow marks. When the paint flows out, the pressure is too large. The distance between the flow coating head and the cavity surface is too close, and the coating liquid forms an impact on the coating surface. There are signs of unevenness; the flow rate of the paint is small, the flow is unstable, and flow marks are formed on the surface of the cavity.



Take measures:

1. When flowing, use a large flow rate to flow quickly from top to bottom. Do not stay on the sand surface for a long time.

2. Improve the fluidity leveling of the coating and reduce the viscosity.

3. Increase the distance between the flow coating head and the cavity surface. The general distance is 18-25mm.

4. Use a fan-shaped flow coating head.



Lamination



The laminate is a superimposed texture that is produced when the flow is applied to the surface of the cavity, two or more times from top to bottom or from left to right.

the reason:

Mainly due to high sand temperature, high viscosity of paint, small flow rate, and multiple flow coatings.



Take measures:

1. The sand mold has just finished flowing, and the temperature of the sand is high. Do not spray immediately, and air cooling according to the specific conditions.

2. Reduce the viscosity of the coating and improve the fluidity.

3. Increase the flow rate and avoid multiple flow coatings. By making different flow coating machines to control the flow rate reasonably, when selecting the pump, the head and flow rate should be slightly higher, the flow pressure is large, and the flow can be controlled by the discharge of the control switch to achieve the required flow. Apply pressure and flow rate.



Paint splash



The paint splash is a smooth coating surface that splashes on the paint drops.

the reason:

This kind of defect is mainly caused by excessive pressure at the outlet of the flow coating.



Take measures:

1. Reduce the flow rate of the flow coating. The thickness, length, surface roughness, and outflow position of the pipe through which the paint flows will have a great influence on the pressure of the flow coating. The outflow pressure P of the paint must be not less than 0.4×105 Pa.

2. Do not spray the flow coating head and cavity surface vertically to avoid splashing paint.



Sand surface sand



Commonly known as "drawing hair", sand mold surface sanding phenomenon often occurs when the mold is used for a long time or the mold is unstable. After the flow coating, the flatness of the sand surface is insufficient, and the depression causes great influence on the appearance quality.

Take measures:

Method 1. The sand-type sand-sanding part is repaired with the coating paste and then flow-coated. The disadvantage of this method is that it needs to be placed for a long time after the flow coating, otherwise the parts repaired with the coating paste will foam.

Method 2. After the flow coating, the surface of the sand is repaired with a coating paste, and then the paint paste is flattened with a diluent, and finally ignited. This method is currently widely used, saving manpower and making up for the deficiencies caused by tooling and pre-order operations.



Uneven coating



Sand patterns are often prone to thin and thick coatings during flow coating. When the viscosity of the viscometer rotor is fixed, the apparent viscosity of the coating decreases with the increase of the shearing time, and a constant value can be achieved for a long time. If it is turned into a standing state, its apparent viscosity increases with the standing time. And gradually picking up, this is the thixotropy of the paint. The thixotropy of the coating is too strong, which is good for leveling, but it is easy to cause excessive flow and make the coating appear thin and thick. Poor fluidity and small angle of inclination can also cause uneven coating thickness. For water-based zircon powder coatings, the thixotropy rate is M=9%-12%.



Poor adhesion to the substrate, falling paint



During the coating and spraying process, due to the poor adhesion between the substrate and the paint, the paint fading problem often occurs, resulting in high product defect rate, which seriously damages the quality and production cycle.

Take measures:

Nowadays, the general method is to use an adhesion promoter, which is a special treatment agent that can improve the adhesion between the coating and the substrate. It has a special functional group and can effectively combine with the polar group on the surface of the material to produce high. Adhesive adhesion between the layers provides a good primer.



to sum up

1. The flow coating process is nearly ten times more efficient than the original brushing process, which is very suitable for production line flow operations.

2. The mold after flow coating operation, the surface is smooth, the coating thickness is uniform, compact and clear. After casting, the surface of the casting is smooth, the surface roughness can reach above Ra25um, and the casting dimensional accuracy is high, reaching the CT9 level above GB 6414-1999 "Molding dimensional tolerance and machining allowance".

3. Due to the uniform coating of the flow coating, the paint flowing down can be recycled. According to the on-site measurement, the flow coating process can save about 25% of the coating.

4. After many experiments, it was found that when the flow coating was between 22 and 26, the flowability of the coating was the best, the coating thickness was suitable, and the casting defects were the least.

5. Reduce the pollution of the working environment, using flow coating to completely solve the air pollution of paint dust.

6. The adhesion of the coating to the substrate can be quickly solved by the adhesion promoter.