Coating shrinkage
06-23-2010, 04:57 AM,
#1
Coating shrinkage
Dear Forum,
We sprayed pump sleeves with Diamalloy 2002 with HVOF to diameter 100.2 and the following day found some sleeves having 100.15 only. First measurement was made with (calibrated) micrometer when the part was hot(100'C) with confirmation by 2nd person. During grinding process found untouched area where the thickness was less.Is this due to coating/part shrinkage, too small allowance or measurement error. Happened 2 times on different parts. Max part temperature during the spray is 150'C.

Kindly advise.
Guna
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06-23-2010, 11:53 AM,
#2
RE: Coating shrinkage
Hello Guna,
The coating/part will shrink so will be less than hot measured thickness. If you spray a little thicker to allow for this then you don't have to allow part to fully cool for an absolute measurement. Middle areas can be slightly thinner and need more to clean up. You should try to verify overall thickness and differences even with hot measuring to ensure adequate/acceptable finished dimension everywhere.
Len Wood
METAL MONSTER LTD
BIGGER BETTER FASTER MORE!
Ph: +64 9 4730705
Fax: +64 9 4730706
Email:: len@metal-monster.com
www.metal-monster.com
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06-23-2010, 12:26 PM,
#3
RE: Coating shrinkage
(06-23-2010, 11:53 AM)LEN WOOD Wrote: Hello Guna,
The coating/part will shrink so will be less than hot measured thickness. If you spray a little thicker to allow for this then you don't have to allow part to fully cool for an absolute measurement. Middle areas can be slightly thinner and need more to clean up. You should try to verify overall thickness and differences even with hot measuring to ensure adequate/acceptable finished dimension everywhere.

This is where science meets art in my opinion. So many variables involved and points to consider and confuse the situation further:
  • Base Material of the sleeve, remember the thermal expansion of SS is relatively large
  • Wall thickness of sleeve
  • Thickness of coating
  • Lenght of part and area coated
  • Material used
  • Cooling method during coating

I agree the coating shrunk and the part shrunk as well. Do not forget to check the ID also, otherwise your customer in the field will have serious complaints when the part does not fit on shaft.

Please let us know how it goes by making the coating thicker
Stephen James Booth
www.ipsteknokraft.com
www.teknokraft.com
Indonesia WhatsApp +6281905603262

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06-23-2010, 03:29 PM,
#4
RE: Coating shrinkage
Hi Guna and all

Quote:This is where science meets art in my opinion.
Smile

Measure dimensions when hot and again when at ambient. Add the difference to the coating thickness when measuring hot along with machining allowance to compensate - sorry, obvious Smile. If its a one off, estimate expansion and add a little extra Smile You can always remove excess, not so easy add more coating.
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06-24-2010, 02:49 AM,
#5
RE: Coating shrinkage
Hi experts,
Thank you very much for the replies. We did the the job again but this time as advised by you all we coated additional 0.1~0.15mm for the 'shrink' and it worked well at finishing priocess. I will extend my observation as Stephen mentioned. Is all HVOF powder materials will show similar trend or Diamalloy 2002 which is Nickel Base Fusible Alloy type? Can we assume x% of shrink as expected in torch fused coatings?

Regards
Guna
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06-28-2010, 02:37 PM,
#6
RE: Coating shrinkage
Hello Guna

Quote:Is all HVOF powder materials will show similar trend or Diamalloy 2002 which is Nickel Base Fusible Alloy type? Can we assume x% of shrink as expected in torch fused coatings?

All thermal spray coatings (cold process only) will show similar trend as this is mainly due to coefficient of expansion of part as a whole, which in most cases the substrate will be the major factor.

Fused coatings are quite different, as the coating is radically changed during high temperature post processing. The coating shrinks due to densification and dimensions may change due to fluid/plastic flow via gravity or surface tension effects.
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