Metco 16C-NS fusing problem

[Sprayman12]

Hello
We are using Metco 16C-NS for shafts and sleeves. Now we have a huge problem after fusing. The surface cracked after fusing. Nothing was changed in our process. We have a furnace for fusing. Not vacuum oven. Temperature is 1030 Celsius in oven. What is recommendation for fusing temperature ?

[Vadim Verlotski]

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

[Sprayman12]

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.

[loriol]

Hi Sprayman12

If you do not change anything, spray parameters, kind of gas, gas provider, the only thing can be changed is powder, and I had many problems with different lot of powder doing plungers for glass applications, and as well as we used a special automatic system to spray and fuse, and every time we change lot of powder or gas bottles, it was necessary to do a new parameters settings, so the problem could be powder size distribution, or some change in the process gas.
Remember that for the fuse and spray process, it is necessary a very slow cooling.
Regards
Luis

[Met.Eng.]

Hello
We are using Metco 16C-NS for shafts and sleeves. Now we have a huge problem after fusing. The surface cracked after fusing. Nothing was changed in our process. We have a furnace for fusing. Not vacuum oven. Temperature is 1030 Celsius in oven. What is recommendation for fusing temperature ?

in addition
1-Please be carefull to clean the Al2O3 blasting dust on your coating surface. Couse some oxide lyer occure on the surface if you dont cleand these dust. İf you wanna get more quality boanding you have to use STEEL grit
2-How about your pre-heating tem? try this may be u can get more free stress on your surface: Pre-heat the surfece tem at 200-250 C with more acetylene flame, after than spray 200 micron 16C-NS and than heating tem. at nearly 700 C , and finally spray final coating lyer. (Note : if you want more bonding you can up the 200 mic coating temperature at fuse & semi fuse degeree)
3-Take a look sleeve hardness, you know if the hardness over 45 HRC some crack will be occure. (+ stress effect)

Regards