Every Tuesday at 1PM Eastern time (11AM Mountain time), About.com and Fibre Glast co-host a composite chat session. If you have questions about composite manufacturing, this is a good place to ask them. General discussions about composites are also welcome.
The chat room is located at http://composite.about.com/mpchat.htm.
2 November 1999
- Barry
- There was a posting on my forum earlier today which has some good manufacturing questions.
- Barry
- I'm going to paste it in so we can discuss it...
- Doug
- go ahead.....
- (Andy)
- I could use a little help with a project. I am developing a high performance snowmobile hood to sell as an aftermarket part. For now it is a vacuum bagged, epoxy, hand lay-up part. The lay-up schedule is one layer of 8 OZ carbon/kevlar, 1 MM coremat where required for stiffness, and then a layer of 6 OZ glass cloth.
- Barry
- Coremat consists of microspheres held together by a styrene-soluble binder. It feels like a paper towel, and is used as a sandwich core.
- (Andy)
- The carbon/kevlar shows through the hood in a couple of areas to give the "carbon fiber look". Before starting the lay-up, I put down a surface coat of duratec sanding primer on the areas of the hood that are painted. On the areas that the cloth will show through I saturate a surfacing veil and let it cure to a tack before proceeding with the rest of the lay-up.
- (Andy)
- Most elements are coming together nicely (The prototypes I have built look great and weigh about half of a stock hood.) but a few things could be better.
- (Andy)
- 1. The surfacing veil is very difficult to use with the epoxy. Without styrene, the binders in the veil do not break down so it is not very conformable. The veil only works on areas without a compound curvature. Is there a veil that will break down in epoxy? Alternatively, is there a clear epoxy that will break down the regular veil? Maybe there is a better, completely different way to achieve the "carbon look"? My neighbor has a kevlar Mad River canoe with a clear exterior tha
- (Andy)
- 2. No matter how hard I work at it there are always a few air bubbles in the veil. I could live with it, but the engineer in me wants it perfect. Any tips?
- (Andy)
- 3. I need to paint the hoods. The majority of each hood will get color. The portion that the cloth shows through should get a clear coat to protect the epoxy from UV. Anyone have suggestions on a base coat/clear coat paint system that looks great where both parts will work with epoxy and duratec primer (polyester based)?
- Marilyn
- Although there are some mats that will break down in epoxy, I am not aware of any veils with an epoxy soluable binder.
- Barry
- I don't work much with veils, but I also don't know of any that break down.
- Marilyn
- As far as it goes, the reason people usually use veils is to improve sanding. If he wants the graphite to show through, I would recommend discontinuing the use of the veil altogether.
- Barry
- Agreed...I've made graphite tooling on foam plugs which probably have the look he's after. We used an epoxy-compatible gel coat on the tool surface. But the cosmetic side will have to be against the tool to get a really good finish.
- Barry
- A mat might work, though, if it's thin enough. What weights or densities are available?
- Marilyn
- Mats typically come in 3/4 oz, 1 oz and 1-1/2 oz. We stock 3/4 and 1-1/2 but we quit trying to maintain only the ones that are soluable in both poly and epoxy. There wasn't enough demand.
- Barry
- You now stock just the epoxy-soluble mats?
- Marilyn
- No, we just stock mats that only work in poly. We can get the other though. The problem is that for us, and for the major distributors, it turned out to be pretty low demand. Before it came out, everybody wanted it but when it was available, nobody seemed to care.
- Marilyn
- I don't think there is a better way to get a good cosmetic finish than in-mold.
- Barry
- Looking at his third point, he wants a clear coat over the fabric. That would be solved by getting rid of the veil cloth and using a gel-coat against the tool.
- Barry
- It's also hard to tell from the posting if he's using a male or a female tool.
- Doug
- # 2, I wonder how he is preparing the layup before applying the vacuum bagging....your part will only be as good as the work on the front end. Vacuum bagging will only help with a quality layup, otherwise you're just making lightweight low quality workmanship.
- Doug
- I've been pretty successful rolling out the air before applying the vacuum bag and thereby avoiding the problems he seems to be encountering
- Barry
- Even with a tight veil or mat?
- Barry
- We often have trouble with trapped air in tightly-woven glass fabrics. We use stippled rollers to release the bubbles, but that works because it can open up the weave a bit.
- Doug
- We also use several different sytle rollers and squeegees to work the air out. Generally, it's more a matter of patience working it through than not being able to get the air out.
- Barry
- It also helps to carefully place the mat or fabric, sort of rolling it down and "pushing" the air out as you go.
- Doug
- Yes, and working in smaller areas at a time when reasonable. It allows you to concentrate on getting one area complete instead of trying to work a large area before your resin kicks off.