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Help required in Spec Interpreation and possibly more...

Help required in Spec Interpreation and possibly more...

Help required in Spec Interpreation and possibly more...

I may need some help in spec interpretation and possibly more from experts here. Although this question concerns more of manufacturing and materials sourcing, I did not where else to post this.

I (we) have a spec for a communication antenna dish/mirror which needs to fabricated using composites. So far have received only the main drawing with very limited info about materials etc.

The main dish needs to be fabricated from UP-GF2x (ex UP GF25). From my prelim research, I found out that UP stands for Unsat Polyester and GF is Glass Fibers and 2x indicates the percentage of the fibers.

I have attached a spec sheet of a product from one of the suppliers.

Have a few questions. I am coming from a place of little understanding and before we reach out to get further details, just wanted to get more understanding of the basics involved.

1. The quantity '2x' indicates Fibers content by weight in the prepegs correct? Not the final fiber content of the laminate? Am I on the right track?
2. Most of my Google searches point out to SMC (Sheet Moulding Compound) data sheets. From what I could understand, these SMC sheets are woven prepegs (?) and they can be moulded per desired shape in a Compression Moulding Machine.
3. Lastly, the actual quantity of the Fiber per spec should be in low 20s. In my searches, the lowest commercial product has around 25% GF. Is a lower number available commercially?

- VN

RE: Help required in Spec Interpreation and possibly more...

Are you designing the antenna?
Or are you fabricating the antenna from someone else's design?
Or something else?

Where did the antenna spec come from?

Are the "material suppliers" called out in the spec?

20% fiber volume sounds really low. Unless this is a requirement for antenna performance. And typically prepreg and laminate fiber content are the same, unless resin is bled out during cure.

RE: Help required in Spec Interpreation and possibly more...

The antenna design is coming off from a client. We will be trying to get it fabricated. The antenna spec was mentioned in a technical communication from the client.

Is fibre content by weight different from volume? The spec sheet I have attached in my first post states that GF 25% by weight. The antenna will be a ground based structure and will be reinforced internally by a metallic mesh. We did not do the design and hence cannot speak for the some of the choices.

>> And typically prepreg and laminate fiber content are the same, unless resin is bled out during cure.

Thanks for the above. A very crucial piece of info I was looking for!

RE: Help required in Spec Interpreation and possibly more...

yes, fiber content by weight is different than by volume, since the density of the fiber and resin are different.

hopefully the client specified the exact materials and processes to use in fabrication.

RE: Help required in Spec Interpreation and possibly more...

Having built satellite antennas in the past, the metallic mesh is actually the reflecting surface for the antenna, Most of the ones I built were back in the 1970s , the layup at that time was Gelcoat over a male mold then , one layer of chop from a chopper gun , then the mesh , and two more layers of chop followed by a spray on polyester enamel. The glass to resin content was very similar to your spec.

You are judged not by what you know, but by what you can do.

RE: Help required in Spec Interpreation and possibly more...

Re Q. 2, most SMCs are short fiber reinforced rather than cloth (usually fibers are less than a mm long, but some are 'long short' fibers, several mm long) and the properties are pretty much isotropic, at least in 2 dimensions. The example you supply can be injection molded which will give a significant amount of orthotropy (longer fibers are straightened out more on injection than shorter ones). Most SMCs have low strength and stiffness compared with continuous fiber reinforced composites, even with similar fiber contents, and a fiber content in the 20s% is pretty low. A modulus of 12000 MPa is low. A strength of 62 MPa isn't that much more than the basic resin.

Re Q. 4,, less than 20% short glass fibers won't give much increase on the basic resin properties at all. Is there a problem with the glass for some reason?

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