1. Paint buildup
reason:
1.11 The flow of paint is slow. Since paint is a thixotropic fluid, there is a network structure and yield value. Yield value and viscosity are the two main factors that cause the accumulation of paint. The yield value of the coating is too high and the viscosity is too large, resulting in poor fluidity of the coating.
1.12 The flow marks produced by the coating during the flow process flow along the sand mold, and when it encounters the grooves, it accumulates, resulting in unclear edges and corners of the sand mold.
1.13 The inclination angle of the sand mold is not suitable, the flow rate is small, and the paint does not flow down, causing accumulation.
1.14 Due to insufficient pressure, the flow rate is slow, resulting in accumulation.
Take measures:
1.21 Considering the on-site operation, the Baume degree of the coating should be reduced. It has been proved by practice that the fluidity of the paint is the best when the Baume degree of the flow coating is between 22-26. Considering the factors of the coating itself, it is necessary to reduce the yield value and viscosity of the coating.
1.22 Remove the flow marks by blowing with an air duct or with a brush dipped in thinner.
1.23 Sand mold placement angle requirements: use the crane to hoist the sand mold to the top of the coating tank and form an angle of 75-90 degrees with the horizontal for flow coating, increase the cross-sectional area of the flow coating rod head and the hose, in order to increase the flow, generally used flow coating The rod head and the hose are 4 pipes. If the cross-sectional area is increased, 4 pipes and 6 pipes can be used respectively, or both can be used with 6 pipes at the same time.
1.24 Increasing the wind pressure can increase the flow rate. In order to obtain a suitable coating thickness, the flow rate of the coating from the flow coater is preferably 100-200mm/s, and the wind pressure is generally between 0.4×105Pa-0.6×105Pa. If it is too large It is easy to produce splashes.
2. The coating thickness is not enough
reason:
2.11 The paint flows directly without forming a sufficient coating thickness.
2.12 The coating penetrates into the molding sand, resulting in insufficient coating thickness.
2.13 There is a release agent on the surface of the sand mold, which reduces the permeability of the coating and directly affects the thickness of the coating.
Take measures:
2.21 Increase the viscosity of the coating (the maximum value is not more than 7s), thereby improving the coating and hanging properties and avoiding excessive flow of the coating.
2.22 Improve the compactness of the sand mold, which can effectively avoid excessive penetration of the coating. The compactness of the sand mold is suitable between 45% and 55%.
2.23 The mold release agent on the surface of the pattern can be fully dried before production. The parts of the sand mold partially stained with the mold release agent are ground off with fine sandpaper and then flow-coated.
3. Thickness requirements for wet coating thickness of furan resin sand casting iron castings:
Thin wall casting 0.15mm-0.30mm Medium casting 0.30mm-0.75mm Thick wall casting 0.75mm-1.00mm Extra thick casting 1.00mm-2.00mm
4. The coating surface peels off
During the assembly process, when the operator blows the floating sand in the cavity with an air duct, the surface of the coating layer will occasionally fall off.
reason:
4.11 Coating strength is low.
4.12 The paint layers are not sufficiently combined to form a whole.
Take measures:
4.21 The small amount of binder in the coating will easily lead to insufficient coating strength, so it is necessary to increase the proportion of binder in the coating.
4.22 Insufficient combustion of the paint will easily affect the bonding between layers. For castings above 3 tons, the surface of the coating is prone to peeling off. This problem can be solved as long as the ignition time is reasonably controlled. Generally, 3-5 seconds after the upper box flow coating is suitable for ignition, and 5-7 seconds after the lower box flow coating is the best ignition. it is good. Gas fire can also be used for baking, but the time cannot be too long, otherwise the coating will crack.
5. Casting sticky sand
The refractoriness of the coating is not enough, and the coating or sand mold is in contact with the high-temperature molten metal to cause a chemical reaction, which makes the surface of the casting form a substance that is extremely difficult to clean, usually called sticky sand, and the flow coating method also produces sticky sand.
Solution:
5.11 Change the composition of coating aggregate and improve the refractoriness of the coating, choose high alumina bauxite powder, zircon powder and other refractory fillers.
5.12 Increase the thickness of the coating, but the thickness cannot exceed the required maximum thickness of the coating. Too thick will cause casting defects such as coating skin.
5.13 Improve the Baume degree of the flow coating coating, the highest is not more than 28, otherwise the fluidity will be reduced.
5.14 Some castings have local overheating phenomenon, and flow coating is very easy to stick to sand. Before flow coating, apply a coating with high refractoriness at the hot spot position, which can effectively prevent sand sticking.
6. Serious flow marks
reason:
The paint has poor fluidity and high viscosity, and the paint cannot drip when it flows down, resulting in serious flow marks. When the paint flows out, the pressure is too large, the distance between the flow coating rod head and the surface of the cavity is too close, and the paint liquid has an impact on the surface of the coating. There are uneven traces, the paint flow is small, the flow is unstable, and flow marks will be formed on the surface of the cavity.
solution:
6.11 When flow coating, use a large flow to quickly flow from top to bottom, and do not stay on the surface of the sand mold for a long time.
6.12 Improve the fluidity and leveling of the coating and reduce the viscosity.
6.13 Increase the distance between the flow coating rod head and the surface of the cavity, and the general distance is 18-25mm.
6.14 adopts fan-shaped flow coating rod head.
7. Laminate
Lamination is the superimposed texture produced when flow coating the cavity surface two or more times from top to bottom or left to right.
cause:
It is mainly caused by high sand mold temperature, high paint viscosity, small flow coating flow and multiple flow coating.
solution:
7.1 If the temperature of the sand mold that has just been flowed by the sand mixer is high, do not flow coating immediately, and air cooling according to the specific situation.
7.2 Reduce the Baume degree of the coating and improve the fluidity.
7.3 Increase the flow and avoid multiple flow coating. By making flow coaters of different specifications to reasonably control the flow, when selecting a pump, the lift and flow rate should be slightly higher, and the liquid flow pressure is large. The liquid flow can be controlled by the control switch, etc. Application pressure and flow rate.
8. Sand surface scouring
Commonly known as "pulling", the mold surface is often plucked if the mold is used for a long time or the mold is unstable.
solution:
8.1 After repairing the sanding part of the sand mold with paint paste, flow coating is carried out. The disadvantage of this method is that it needs to be placed for a longer time after flow coating, otherwise the repaired part with paint paste will foam.
8.2 After flow coating, use paint paste to repair the sanded parts, then use thinner to brush 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-sequence operations.
9. Uneven coating
When flow coating, the sand mold is often prone to the situation that the coating is thin on the top and thick on the bottom. When the rotational speed of the viscometer rotor 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. and gradually pick up, this is the thixotropy of the coating. The thixotropy of the coating is too strong, which is conducive to leveling, but it is easy to cause excessive flow, which makes the coating appear thinner at the top and thicker at 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.
10. Summary
10.1 The efficiency of the flow coating process is nearly ten times higher than that of the original brush coating process, which is very suitable for the assembly line operation.
10.2 The casting mold after flow coating operation has smooth surface, uniform coating thickness, dense and clear outline. After casting, the surface of the casting is smooth, the surface roughness can reach Ra25um or more, and the dimensional accuracy of the casting is high, reaching the CT9 level or above in GB 6414-1999 "Casting Dimensional Tolerance and Machining Allowance".
10.3 Due to the uniform coating of the flow coating, the flowed down coating can be recycled. According to the on-site measurement, the use of the flow coating process can save about 25% of the paint compared to the original.
10.4 After many experiments, it was found that when the Baume degree of the flow coating coating is between 22-26, the fluidity of the coating is the best, the coating thickness is suitable, and the casting defects are the least.
10.5 Reduce the pollution of the working environment, and use flow coating to completely solve the air pollution caused by paint dust.
Qingdao Sanzhuji Equipment Manufacturing Co., Ltd. specializes in the production of Green Sand Molding Line,Self-hardening sand molding line,foundry machines,Sand molding machine,Sand casting equipment,sand mixer,GS high efficiency rotary mixer,Resin sand mixer,no-bake resin sand mixer,Jolt squeeze molding machine/Jolt-squeezing moulding machines,Multi- Piston Moulding Machine/Hydraulic multi-piston moulding machine,sand casting molding machine,sand reclamation equipment，foundry molding machine,flaskless moulding machine,shot blasting machine,dust collector,according to the amount of old sand recovered Carry out plan customization, and provide sand reclamation equipment installation, commissioning, and training. Welcome guests to visit the factory.
