HVOF Coating Calender Roll issues. Suggestion needed
02-10-2021, 12:54 PM, (This post was last modified: 07-13-2021, 10:06 AM by tobjung.)
Shy  HVOF Coating Calender Roll issues. Suggestion needed
Greeting from Venture Engineering Thailand.

I would like to ask for some helps on Calender roll-WC17Co HVOF Coating. I have to admit that this was my first time spraying this kind of roll. 

The issue is after the roll was operated for 3 days, as you can see from the picture, there are some marks on the surface distributed all over the roll (like the coating bounce off). 
Moreover, there are cracks appear on the coating surface. (We did PT and it was fine before delivery). 
Now we have to re-coat it but we still have no idea what are these problems are coming from (especially, marks on the surface).

Pictures and Videos

Here are the coating details

  1. HVOF coating (JP-5000)
  2. WC17Co powder (particle size 15-45um and 15-53um)
  3. We did HVOF coating for 400um in thickness
  4. We sprayed 15-45um powder for 200 microns and the rest were 15-53um powders (we ran out of 15-45um powders so we had to use substituted powder)
  5. The operator changed feed rate back and forth throughout the operation
  6. Using slide way instead of handheld (but the gun was vibrated quite hard as you can see from the video)
  7. Temperature control on roll surface was 100 C
  8. Time interval of each ignition was 1-2 hours (as the cooling water was really hot, we had to wait)
  9. Grind to 200 microns with roughness of 0.1 Ra

Here are the working environment (see picture)
  1. This is the Queen Calender roll
  2. In the middle of King and Middle roll
  3. It is working with doctor blade
  4. The roll is in contact with chemical compound
Any suggestion would be helpful
02-10-2021, 02:03 PM,
RE: HVOF Coating Calender Roll issues. Suggestion needed
Why was the operator changing the feed rate? I would expect that to give less than optimum results. When you resumed spraying did you reheat the roll first? Why spray to 400 microns only to grind half of it off? That is a lot of wasted powder, more time to grind and could leave more stress in the coating.
04-29-2021, 03:34 PM,
RE: HVOF Coating Calender Roll issues. Suggestion needed
Dear Tobjung,

I know I'm a bit late but I cannot see all the videos and pictures.

Where you able to solve the problem?
07-13-2021, 10:12 AM,
RE: HVOF Coating Calender Roll issues. Suggestion needed
(04-29-2021, 03:34 PM)JeroenB Wrote: Dear Tobjung,

I know I'm a bit late but I cannot see all the videos and pictures.

Where you able to solve the problem?

Thanks for the reply. Here is the link Pictures. Also, I updated the post with new link already.
Current situation: we cannot identify the problem yet. I discussed with the lab already but they told me they can't do anything if we cannot pull out a small piece of coating from the roll. (Must be from around the defected area). We tried to take the coating out using various tools but not successful as the coating is very dense and adhere very well to the substrate or nearby coating. Unfortunately, we cannot use a chisel to take it off as the customer said it would be too risky to the substrate.
07-24-2021, 08:53 AM,
RE: HVOF Coating Calender Roll issues. Suggestion needed
Now I suspect that oils or chemical agent embedded in the roll surface was the problem as we didn't degrease the roll prior to HVOF Coating

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