Author Topic: A question for the experts (Read 673 times)

charlie · « **on:** March 27, 2011, 05:17:22 AM »

The colour of engine crankcases of commercial engines vary from the out of the die silvers to dark grey. (I am not considering the magnesium cases or anodising.) The cases with some sort of finish treatment have a matt surface and vary from light to dark grey. An example of the darker shade was the steel fin OS cases that Peter Chinn referred to as `Vapour blasted'. Does anyone know what the processes are, and why the colours vary? I am guessing that there might be some form of bead blasting involved, but do you know if there is there chemical treatment as well?
Thanks in advance

Marvin Denny · « **Reply #1 on:** March 27, 2011, 10:55:46 AM »

Well, I'm a long way from being an "expert", but I will try to give some insight.
The Black coating on the steel cylinder jobs--ia K&B torp and Steel fin fox 15 etc is Black Oxide The main purpose is as a rust prevenative. The same process is used on guns (gun blueing) Ti also dissipates heat a little better than bare or shiney steel surfaces.
For the matte finish on the aluminum surfaces, The sand blast texture is primarily cosmetic. The gillions of small pits caused by the blasting doea promote cooling some over the smooth surfaces. The blasting also removes surface flashing and other "not so nice looking" surface irregularities caused by the uneven cooling of the casting process. I call that cosmetic.
To coat or anodize aluminum requires additional processing steps that are costly so they are almost never done. Powder coating or painting of aluminum surfaces, in addition to cleaning, requires the application of a "chemical conversion coating" just before applying the paint or powder coating---- that is for good long lasting adhesion.

I hope thia gives you enough information

Bigiron

Steve Helmick · « **Reply #2 on:** March 29, 2011, 07:59:36 PM »

Big...I had two steel fin Fox .15's and while I haven't seen one in several decades, my lingering thought/opinion is that the cylinder fins were 'finished' by burning a coat of oil onto them. I believe this is also a gunsmithing technique, older and cruder than actual 'bluing'. The McCoy's, K&B's, and Max III's were black oxide, I think. But possibly gun blued.

Speaking of which...I once was involved with making a part for Boeing that was required to be "gun blued until black". Not "black oxide", but gun blued. An interesting prospect...none of the area's metal finishing specialists did gun bluing. None of the gunsmithing shops could provide the required 'certs'. Hmmm. I'm thinking that we got a gunsmith to do it, and hand write a note that told what he did and how he did it, temp, soak time, solution type, whatever, on his letterhead. Still seems goofy.

Steve

charlie · « **Reply #3 on:** March 29, 2011, 10:50:45 PM »

Thanks for the comments chaps, I am beginning to get a grasp on the techniques used.

Marvin Denny · « **Reply #4 on:** March 31, 2011, 11:59:56 AM »

Read up on Black oxide coatings and Gun bluing on wikipedia. As I said, they are synomonous.
I think that Fox mfg used the hot method and never used baked on oil. The fox engines got plenty of that just by running tons of castor(G)

Bigiron

Author Topic: A question for the experts (Read 673 times)

charlie

A question for the experts

Marvin Denny

Re: A question for the experts

Steve Helmick

Re: A question for the experts

charlie

Re: A question for the experts

Marvin Denny

Re: A question for the experts