Carbon Steel surface prep for Carbon Fiber Composite
Carbon Steel surface prep for Carbon Fiber Composite
(OP)
Hi all,
I am facing a problem with ensuring that a multi layer carbon fiber composite properly bonds to a carbon steel surface (one side only) and it stays bonded while going through termal cycles going as low as -25F to 150F. I would also like to avoid any cathodic corrosion between the steel and the carbon fiber while rataining a high heat transfer rate through the bond.
What mechanical/chemical surface prep should be done, and do I have to use a special adhesive as the bonding layer or can I just use the epoxy used as the matrix?
Thanks,
M
I am facing a problem with ensuring that a multi layer carbon fiber composite properly bonds to a carbon steel surface (one side only) and it stays bonded while going through termal cycles going as low as -25F to 150F. I would also like to avoid any cathodic corrosion between the steel and the carbon fiber while rataining a high heat transfer rate through the bond.
What mechanical/chemical surface prep should be done, and do I have to use a special adhesive as the bonding layer or can I just use the epoxy used as the matrix?
Thanks,
M





RE: Carbon Steel surface prep for Carbon Fiber Composite
You can cure directly to steel but in most cases the stresses are such that an adhesive layer should be used. The streses caused by thermal expansion difference can be very great and may be beyond the ability of any adhesive. If the parts are large and there will be large strain differences between the parts it might require using a low modulus adhesive like silicone or urethane and very thick glue line, like 1/8".
As for electrical isolation of the parts, spacers can be included in the glue line. For thin glue lines spunbonded polyester like Remay is used. For thicker glue lines Open weave fabrics or glass beads in the glue are used.
RE: Carbon Steel surface prep for Carbon Fiber Composite
> If the parts are large and there will be large strain
> differences between the parts
The part is a steel rod of .56" diameter surrounded by a carbon fiber sleeve which cycles through a range of -20F to +200F. While it heats up the carbon fiber should contract with a thermal expansion near 0 or just slighly negative so I don't foresee the problem there. What concerns me is the -20F end of the operational range where steel should contract faster/more than the carbon fiber sleeve.
> An adhesive is designed to carry load across large area
> interfaces and stresses in bondlines are often non-uniform
I am still unsure whether the adhesive may be a way to go. Will the adhesives mentioned adversely effect thermal transfer? It is a thin layer of adhesive for sure but one never knows...
> As for electrical isolation of the parts, spacers can be
> included in the glue line
This all sounds very complicated and probably beyond my manufacturing capacity. Is there no way to coat the steel first with something, e.g. blue it. I've also been suggested to use stainless steel which should not have the same problem, is this true? I could use a layer of fiberglass between the carbon and the steel but I am worried about that approach compromizing the good heat transfer that I am looking for
RE: Carbon Steel surface prep for Carbon Fiber Composite
You can put a rough surface on the steel interface to get a strong mechanical lock with the rod. You can eliminate any corrosion issues by coating the outside surfaces of the steel and composite and keeping thing dry. Steel will rust without contact with carbon if it isn't coated or kept dry. Carbon contact will only accelerate the problem, and only if there is a complete electrical path through electrolyte from carbon to steel.
In another post I believe it was you who asked about improving through thickness thermal conductivity. You might consider twisting the carbon fiber tows. Axial conductivity of carbon fiber is much greater than radial conuctivity. Twisting the fiber will mean that axial heat flow will cause heat to flow though the ply thickness as well. Twist also makes the fiber easier to wrap around a rod. Twisted fibers "rope-up" under tension, however.
RE: Carbon Steel surface prep for Carbon Fiber Composite
I was trying to keep the issues in separate posts for future searchers of the forum who may not be interested in the compound problem...
> You can put a rough surface on the steel interface to get a
> strong mechanical lock with the rod.
Will sand/bead blasting do it? ... then, I am thinking of skipping the whole adhesive idea and just going epoxy all the way
RE: Carbon Steel surface prep for Carbon Fiber Composite