Prepping cast iron.

[Stytooner]

Hi all again. Thanks to Caswell for the great Forum and its Members for such good feedback. It seems I am rarely able to contribute. I have done quite a bit of PCing in the short time I've had my Caswell system. I love it and get great results 98% of the time. I have coated at least 500 parts and only a handful had any defects.
My question this time is with some cast iron that I just powder coated. It is a tail stock for a metal lathe. I may have screwed up when I used the iron phosphate as a primer for the cast iron. I seem to be getting a lot of very easy chipping. I let the part stay in the oven 5 minutes longer than normal at 400 degrees. Then I let the part cool slowly. It probably weighs about 3 pounds or so. Maybe a little more.
I did not sandblast, but I did used a wire wheel and a sander and grinder. The part was not real smooth. I have had good adhesion with smoother surfaces. I do have a sandblaster now and will blast the PC back off to try again.
Do ya'll think it could have been the IP primer? Should I just blast with glass beads and PC again? What would I clean up with after blasting?
Thanks in advance for ya'lls help.

[bzer1]

Asking questions is contributing. You remind those that know, and inform those that don't. It sounds to me like maybe you may be a little bit under cured. I use IP on all iron/steel, and have never had a problem. I would blast it and do the entire process again. You might want to keep a close eye on the part temp in several locations. Thicker areas will not heat as quickly and could be under curing. Remember that almost all powders are 100% overcure. What kind of IP are you using? You might want to check the PH to make sure it's correct, and that there are not too many suspended particles.

[Stytooner]

The IP is some that I bought from here. It works great on steel. I may need to make a new batch of it though. I have had that batch sitting for a couple of weeks in a covered sealed container. I mixed 1/4 of the bottle to 1 gallon of water. On the steel I have done, the coloring kinda looks like those cobalt drill bits. Blue to gold or yellow coloring. I may also have left the part in there too long. This coupled with the possible under cure should solve the problem. Here is a pic or two.

[bzer1]

IP sitting for a couple weeks in a close container sould not be a problem. I would test the ph and dilute or enhance accordingly. (I hate to waste good material). A ph kit is very cheap and you can pick one up at any wal-mart. Does your set up require heating of the IP? The coloring you described sounds good to me, but look for streaking or way off color bands on the surface. That is an indication of a ph problem. After you IP the part bake it for about 10-15 mins at around 250-300 to be sure that all the IP is dry and the surface conversion is complete. Beyond that I'd say an extra 20 mins in the oven should solve your problem. Let us know how you make out.