Special black paint for a carburetor ???

[Paps]

Original rough and finish machining of these carb bodies should have removed almost all traces of the original stresses associated with the castings. Cooling processes of rough castings are a means to remove intense stresses for machining purposes along with maintaining strengths. Engineering of these castings are determined by final finished values, thus the processes of stress removal is applied. I am no metalurgist but I have worked the material, from plain Jane simple composites such as iron and mild steels, to exotics, such as silver, titanium, hastoloy, all coppers, tool steels, aluminums, etc., over my years, and I have learned a feel for it. Whether I machined welded materials ot parent materials, I learned to feel the existing stresses left in them. It would be hell to skin cut a finish surface, only to distort other finished surfaces do to remaining stresses left in the material due to origin of it's formation. Cotton's pictorials show material loss of memory due to operational temperature stresses. Just my thoughts coming from more than 30 years of hands on tool and die making along with certified machinists documentations. Paps

[swall]

Cotten--this is what I found out about zinc alloy die castings.They start to melt at 730F, but the creep behavior begins as low as 200F. At that point the tensile strength of the metal drops to 3500 psi from 11,000 psi at room temp. It was recommended that high stress (high loading) be avoided above 250F. 150F was considered the safe level.Jeeze--we've got plastics better than that now! Now, as to the original question about paint baking--even though 150F was cited as a safe limit per the zinc data, keep in mind that if you bake an item at a higher temperature and it doesn't have any applied stresses on it , it won't creep/distort if it is properly supported. This also brings up a possible point on any machining for a rebuild--if you stress relieved the casting, prior to machining, at the max expected service temperature, it would warp as much as it was going to and your machining corrections could then be expected to be stable. I used VHT engine enamel (good for 550F) for the cylinders on my Chief and VHT claims "solvent resistance" with a 200F bake. Might be a good choice for black carb paint.200F should not warp these zinc castings any worse than they already are. Obviously, zinc alloy castings are not what you would want to use for any engine part. But back then, they didn't have a lot of choices.

[KNUCK]

What have I started?

I painted with VHT high temp engine paint ,550 degree. The next day I baked it at only 200 degrees, just to be safe. Looks great. I put the carb back together today and will start up the Chief for the first time this week. We learned alot about paint and carb material. We should put this in a book.

I am always amazed at the intelligence of the club members !!

[T. Cotten]

Bakeing potmetal

Although it would seem that being put into service would be a quick bake in itself, I got out the Toastmaster and calibrated it for 200F.

Then I baked for an hour two "long-bowls" that had been sprayed with VHT epoxy the day before.

uh oh.

Even where blemishes had been polished prior to painting, the metal "bloomed" into tiny zits. Remaining knarfs and blemishes became sharpened and exaggerated,
even after the dried paint was removed!

Only after sanding and a second coat and bake could a satifactory finish be achieved.
Apparently these vintage castings need to be 'relieved' before anything else is done to them. And there is no certainty that they will stay that way.

Two '40 "beanpot bowls", which are not die-cast, and of a lighter alloy, showed no ill effects from baking.

...Cotten