[kxkraze]

A quick update on my chromate research:

I have been having good success with the blue and yellow chromate method that I posted earlier. One remaining problem that I would encounter from time-to-time was that if I had a post-chromate, post-rinse water bead (in a threaded hole of a bracket for example), when that water bead rolled down the bracket, it would sometimes leave wash marks on the yellow chromate.

I called Caswell and found out the manufacturer of the blue and yellow chromate. I then called the manufacturer and talked to one of their techies for a while. They had the following information to offer:

1) Use sulferic acid (1% in dist. water) as a pre-chromate dip, followed by a double rinse in dist. water. They recommeded this over nitric acid even. The purpose of this dip is to remove organic residues that might exist from the plating solution. Failure to perform a pre-chromate dip will eventually contaminate the chromate as organics build up. There are tools to test for chromate contamination but signs include a yellowish tint in the blue chromate and a lack of color in the yellow chromate.

2) Following chromate, double rinse in dist. water. Dry in cool to luke-warm air first to remove excessive water. Use hot air (approx. 150 deg. F) after all water droplets are gone. The reason that he gave not to go straight to hot air is because if a water droplet is heated and then runs down the object, the hot water droplet can cause an unwanted blemish.

3) Allow to air cure for 48 hours before any handling of any sort.

4) For the ultimate in corrosion protection and durability, follow the 48 hour cure time with a hydrogen embrittlement removal by placing them in an oven (toaster oven, etc.) at 375 ~ 400 Deg. F. for 2~3 hours.

Anyway, I just thought I would share the information that I received today. I have not tried any of this yet but I plan to this weekend. I will post back later with the results.

BTW -- due to the posts on this forum regarding sulferic vs. nitric acid, I questioned him about this several times - up to the point where I sensed he was getting annoyed. He said that they not only sell the chemicals but also have a plating plant in which they use their chemicals for large contracts. Hey said they use a 1% sulferic dip exclusively for all of their pre-chromate dips. He said nitric will work but sulferic is better.