process, such as det gun, or plasma spray? and Meaning that a

flange or other raised portion

is what

is crucial?

Royce

Royce, The Electrofusion process used by Kawasaki is done by heating the

raw surfaced but

otherwise finished barrel to "a specific temperature" then a wire of the

desired plating materials

is placed in the cylinder. (I believe tungsten was typical) A HUGE

current and voltage is applied

to the wire causing it to literally explode. The atmosphere in the

application chamber, (either

oxygen or vacuum or other gas), then controls the final product applied

to the walls. As explained

to me the prep of the aluminum surface is very important. When anything

is applied to aluminum

controlling oxides is difficult. The EF process blasted the coating

material into the surface

creating a great bond. The reason I believe the process is not used on

plate surfaces is waste and

uniformity. You can explode the wire above a flat surface but the area

closest to the wire gets

the heaviest coating. Often several applications are needed to build up

a thick enough coating. A

bore is obviously the best setup for this process. I am trying to find

out if the Mazda material

can be plasma sprayed or sputtered on. Paul mentioned the problem with

coating aluminum, as it

starts getting soft at fairly low temps. Nowhere near melting of course

but softening. This

surface change makes it possible for the coating to work loose. The

other problem is that the

coatings we normally apply, normally have a vastly different coefficient

of linear expansion than

the base aluminum. This is the crucial area I mentioned earlier. Anodize

is an example of this.

The aluminum oxide expands less quickly than the aluminum it is

generated from. In the case of

ceramic coatings like plasma spraying the difference is pronounced. The

CLE for aluminum is 10

to-5 units per deg F. For ceramics it can be ten times higher. This

causes surface stress on every

thermal cycle. If the bond to the surface is strong enough...no problem.

If not then cracking and

flaking. This problem is on every coated surface. Corners or raised

flanges just make things more

difficult since a corner can concentrate stresses. Bill Jepson

Bill,
That's beautiful - couldn't have put it better myself even if I knew all
that stuff, which of course now I do.
George (down under)

 
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