The most prone problems of paint and corresponding measures

the reason:

1.

2.

3.

4.

5.

Take measures:

1.

2.

3.

4.

5.

2.

the reason:

1.

2.

3.

Take measures:

1.
Increase the viscosity of the paint (the maximum value does not exceed 7 s), thereby improving the coatability and avoiding excessive flow of the paint
.

2.
Improve the compactness of the sand mold, which can effectively avoid the excessive penetration of the paint.
The compactness of the sand mold is between 45% and 55%.

3.
The mold surface can be produced after the mold release agent is fully dried, and the part of the sand mold that is partially stained with the mold release agent is polished off with fine sandpaper and then flow-coated
.

4.
Requirements for the thickness of the wet coating on the sand mould of iron castings:

Thin wall castings 0.
15mm-0.
30mm

Medium-sized castings 0.
30mm-0.
75mm

Thick wall castings 0.
75mm-1.
00mm

Extra thick castings 1.
00mm-2.
00mm

3.
The coating surface comes off

During the assembly process, when the operator uses the air duct to blow the floating sand in the cavity, the surface of the coating layer will occasionally fall off
.

the reason:

1.
The coating strength is low
.

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

Take measures:

1.
The small amount of binder in the coating will easily lead to insufficient coating strength, so the proportion of binder in the coating should be increased
.

2.
The paint is not fully burned, resulting in the easy-to-influence layer-to-layer bonding
.
For castings of more than 3 tons, the coating surface is prone to fall off.
As long as the ignition time is reasonably controlled, this problem can be solved.
Generally, 3-5 seconds after the upper box flow coating is appropriate, and the lower box is the most ignited 5-7 seconds after the flow coating.
Good
.
The gas fired baking method can also be used, but the time cannot be too long, otherwise the coating will crack
.

Four.
Casting sticky sand

The coating has insufficient refractoriness, and the coating or sand mold contacts the high-temperature molten metal to cause a chemical reaction, which makes the surface of the casting form an extremely difficult to clean substance, usually called sand sticking.
The flow coating method also produces sand sticking
.

Solution:

1.
Change the composition of the paint aggregates and improve the refractoriness of the paint.
Choose high alumina bauxite powder, zircon powder and other refractory fillers
.

2.
Increase the thickness of the coating, but the thickness cannot exceed the maximum required by the coating thickness.
Excessive thickness will cause casting defects such as coating skin
.

3.
Increase the Baume degree of the flow coating coating, the highest is not more than 28, otherwise the fluidity will be reduced
.

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

Five.
Severe flow marks

the reason:

The paint has poor fluidity and high viscosity.
The paint cannot drip when it flows downwards, resulting in serious flow marks; when the paint flows out, the pressure is too high, and the distance between the flow coating rod and the cavity surface is too close, and the coating liquid will impact the coating surface , There are uneven marks; the flow of paint is small, the flow is unstable, and flow marks will be formed on the surface of the cavity
.

solution:

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

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

3.
Increase the distance between the flow-coated rod head and the surface of the cavity, generally 18-25mm is appropriate
.

4.
Use fan-shaped flow to coat the club head
.

Six.
Stacked

Overlay is the superimposed texture produced by two or more flow coatings from top to bottom or from left to right during flow coating on the surface of the cavity
.

cause:

It is mainly caused by high sand mold temperature, high paint viscosity, low flow coating flow, and multiple flow coatings
.

solution:

1.
The temperature of the sand mold that has just been flowed by the sand mixer is high.
Do not flow it immediately, and cool it by air according to the specific situation
.

2.
Reduce the Baume degree of the paint and improve the fluidity
.

3.
Increase the flow rate and avoid multiple flow coating
.
The flow rate can be controlled reasonably by making different specifications of the flow coater.
When selecting the pump, the head and flow rate should be slightly higher, and the pressure of the liquid flow is high.
The flow can be controlled by the control switch, etc.
, to achieve the required flow.
Application pressure and flow rate
.

Seven.
Paint splash

Paint splash is the splash of paint droplets on the smooth coating surface
.

cause:

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

solution:

1.
Reduce the outlet pressure of flow coating
.
The thickness, length, surface roughness, and outflow position of the pipeline 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 no less than 0.
4×105Pa
.

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

8.
Sand raking on the surface of the sand mold

Commonly known as "puffing", the surface of the sand mold often suffers from the phenomenon of sand pick-up when the mold is used for a long time or the shape is unstable.
After flow coating, the surface of the sand mold is not flat enough and dented, which greatly affects the appearance quality
.

solution:

Method 1.
After repairing the part of the sand mold with paint paste, flow coating is carried out.
The disadvantage of this method is that it takes a longer time after flow coating, otherwise the parts repaired with paint paste will blisters
.

Method 2.
After flow coating, use paint paste to repair the sand-scraping part, then use thinner to smooth the paint paste, and finally ignite
.
This method is currently widely used, saves manpower, and makes up for the deficiencies caused by tooling and pre-operation
.

Nine.
Uneven coating

During flow coating, sand molds are often prone to thin coatings and thick coatings
.
When the rotor speed of the viscometer is fixed, the apparent viscosity of the coating decreases with the increase of the shearing time, and can reach a constant value for a long time.
If it is turned into a static state, its apparent viscosity increases with the standing time The gradual rise, this is the thixotropy of the coating [2]
.
The thixotropy of the coating is too strong, which is conducive to leveling, but it is easy to cause excessive flow and make the coating appear thin on the top and thick on the bottom
.
Poor fluidity and small inclination angle will also cause uneven coating thickness
.
For water-based zircon powder coatings, the thixotropy rate M=9%-12% is better
.

in conclusion

(1) The flow coating process is nearly ten times more efficient than the original brush coating process, which is very suitable for production line assembly
.

(2) The casting mold after flow coating operation has smooth surface, uniform coating thickness, compactness and clear outline
.
After casting, the surface of the casting is smooth and clean, the surface roughness can reach Ra25um or more, and the dimensional accuracy of the casting is high, reaching CT9 level or more in GB 6414-1999 "Dimensional Tolerance of Castings and Machining Allowance"
.

(3) Since the flow coating is uniform, the flowed coating can be recycled
.
According to on-site measurements, the use of flow coating technology can save about 25% of the original paint
.

(4) After many experiments, it is found that when the Baume degree of the flow coating paint is between 22-26, the fluidity of the paint is the best, the coating thickness is appropriate, and the casting defects are the least
.

(5) Reduce the pollution of the working environment, and use flow coating to completely solve the air pollution of paint dust
.