winding angle

[Tmoose]

We are thinking of making some part inhouse winding glass or carbon around a long stack of ~rectangular components then VPIing it.
We think we only need hoop strength so a circumferential wind ought to be OK.
I'd like to provide a few layers with some alternating angle to give us some bending strength too.

What is a reasonable angle to be able to produce manually or with simple equipment?

 

[MechanicalChef]

VPI - vacuum/pressure infiltration?

If so, I see this as being a problematic approach. I'm sure it's probably feasible with a round tool/part. But when you wind a rectangular part, even with generous corner radii, you'll see much greater fiber compaction over the corners, and not as much over the flat sections. Think of it as pressing a string against a table by pulling on the ends.

A fundamental of infusion is that resin will flow along the path of least resistence. So, since the corners will be much more compacted than the flat areas, flat areas will probably infuse, but the corners will be dry.

For your application, a resin bath or resin roller would get the resin on your fibers better.

http://www.mccleananderson.com/products/ResinBaths/resin_baths.htm

This page shows examples of the bath/rollers.

Regarding a winding angle to help with bending strength, from a stress point of view, you want the fibers oriented in the 0-direction as much as possible. Without pin-rings, you won't get this from winding. (And pin-rings are problematic as it is, but it depends on what you'll accept with your part) Anyway, how low you can go depends on part geometry. If you have a long thin part, you can concievably go as low as several degrees. Wider and shorter, not as much. You can get a feel for a stable wind simply by running a fiber around what you want to wrap. If you can create a stable fiber path by hand, then you're good.