(09-30-2014, 10:51 AM)Vadim Verlotski Wrote: Hello Spayman12,
There may be several reasons for the appearance of cracks in the coating at melting (furnaces with protective atmosphere):
1. Defects sandblasting or spraying (cracks appear when heated),
2. Changes in the composition of the powder (bad charge),
3. The increased oxygen content in the protective atmosphere (gas leak),
4. Too high temperature in the furnace (thermocouple failure or controller).
The most likely reason - the poor quality of the surface prior to the spraying due a problems with sandblasting.
To determine the exact cause like more information and photos of coatings.
Regard
Vadim
Hello ,
Please check my comments :
1. Defects sandblasting or spraying (cracks appear when heated),- we have used aluminium oxide several year, no problems. Guns are checked and flowmeters are calibrated.
2. Changes in the composition of the powder (bad charge),- maybe this powder is faulty? we will examine composition
3. The increased oxygen content in the protective atmosphere (gas leak), We are using regular gas oven, not vacuum
4. Too high temperature in the furnace (thermocouple failure or controller). The oven calibrated one day ago and the difference is only 5 degree inside oven. 16C-NS dataheet says that fusing temperature is approx. 996 Cels. Maybe we have to high temperature? we have tryied 1030, 1040 and 1050 Celsius. Always the surface will crackle. Check photos.