What is a casting? Sand Mold, Metal Casting Defects
Deshengrui Machinery Introducing various metal casting defects. These are the common sand casting defects on the surface and inside of cast iron and cast steel parts.
1. Blowhole and Pinhole
This is a kind of cavities defect, which is also divided into pinhole and subsurface blowhole. Pinhole is very tiny hole, some could be seen on the surface. Subsurface blowhole only can be seen after machining or grinding.
The most of subsurface blowholes could be found after machining or grinding. If the surface is flat, Deshengrui Machinery could inspect them by ultrasonic flaw detector.
2. Sand Burning Defect
This defect includes chemical burn-on, and metal penetration. Normally, you could see extra metal materials at the corner positions. This is caused by the poor sand. The metal has penetrated into sand molds.
3. Sand Inclusion and Slag Inclusion
These defects are also called as scab or blacking scab. They are inclusion defects. Looks like there are slag inside of metal castings.
4. Sand Hole Defect
Sand hole is a type of typical shrinkage cavity defect. You could see the empty holes after sand blasting or machining process. The sand dropped from sand molds, rolling into the liquid metal, then caused sand holes.
It is the problem of sand mold, or the flow speed of the metal is too high, so could be solved by foundries.
5. Cold lap Defect
It is also called as cold shut. It is a crack with round edges. Cold lap is because of low melting temperature or poor gating system. This is not just surface defect. Normally, this position may cause air leakage, moreover, the material quality at this position will be very poor, so may be fragile.
6. Flash, Fin and Burrs
Joint flash is also called as casting fin, which is a thin projection out of surface of metal castings. Joint flash should be removed during cleaning and grinding process.
Sharp fins and burrs are similar problems as the flash. Actually, large flash is a casting problem, the foundry should improve it by modifying the patterns, but small fins and burrs are not casting defects, foundries just need to grind and remove them.
7. Misrun defect
This is a kind of incomplete casting defect, which causes the casting uncompleted. The edge of defect is round and smooth.
8. Porosity Shrinkage Defect
Shrinkage defects include dispersed shrinkage, micro-shrinkage and porosity. For large porosity on the surface, you could see them easily, but for small dispersed shrinkage, you may see them after machining. The following photo is showing the porosity shrinkage. The metal density is very poor, many small holes could be seen after machining.
9. Shrinkage Cavities Defect
These are also called as shrinkage holes, which is a type of serious shrinkage defect, you can see these holes easily on the rough surface of the metal castings. Foundries could improve their gating and venting system, then could solve these shrinkage problems.
10. Shrinkage Depression
This defect is also a type of shrinkage defect, which looks like depressed region on the surface of metal castings. This defect is not serious as shrinkage cavity, but still cause poor surface quality and may have some inside defects, so foundries should try their best to solve or improve it.
11. Elephant Skin Defect
It is a type of surface defect, which cause irregular or wrinkle shapes surfaces. This defect is caused by the poor metal temperature melted, or poor sand molds.
12. Veins Defect
It is also called as rat tail, which looks like many small water flow traces on the surface of metal castings. Sometimes, it is because of the low metal temprature melted, or unreasonable gating and venting system.
13. Rough Surface
Coarse surface is also a kind of surface defect. Normal rough surfaces can not be judged as defects, but too rough and uneven in surface will be a defect.
14. Mismatch and Shift Defect
This mold defect is because of the shifting molding flashes. It will cause the dislocation at the parting line. Near the parting line, the left side may be several milimeters lower or higher than another side. The parting line is not defect, but if the left side has different height as the right side, it will be one casting defect. If there is no special requirement, mismatch smaller than 1mm is allowable. No any mismatch is impossible for sand casting process.
However, if the mismatch has affected the function of the castings, then the foundries have to control it, grind it or machine it to meet the requirement.
15. Mechanical DamageThis is not casting defect, but it is a real casting quality problem you may meet.
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