Some questions for you lovely people - making a part worthy of selling.

General Composites Discussions Composites Talk
#1

Sorry for the fairly long list. Any help is much appreciated :slight_smile:

  1. I’m going to be making some simple rectangle shapes, so plan on laying the carbon down on a sheet of glass. Will just waxing and polishing the glass give the part a very good finish?
    Would it be possible to get a matt finish by laying carbon on glass?

  2. Will this vacuum pump be ok for the short term production? http://www.ecfibreglasssupplies.co.uk/p-1903-vacuum-pump.aspx
    Or is it possible to use an air compressor with ventuuri? If so, would this option be more future proof (for larger scale items)?

  3. Is it ok to lay down UD fabric on top of itself or should there be a layer of woven carbon fabric between UD layers?

  4. Which grade of sandpaper should I use to rough up the carbon so I can bond 2 carbon pieces together?

That is all I can think of at the minute.

Thanks in advance,

Kyle.

#2
  1. I’m going to be making some simple rectangle shapes, so plan on laying the carbon down on a sheet of glass. Will just waxing and polishing the glass give the part a very good finish?
    Would it be possible to get a matt finish by laying carbon on glass?
    The surface of the part will duplicate the surface of the mold/form/glass. If the release surface is glossy then the part will be glossy. No need to polish the glass. Just apply some proper mold release wax.
  1. Will this vacuum pump be ok for the short term production? http://www.ecfibreglasssupplies.co.u…cuum-pump.aspx
    Or is it possible to use an air compressor with ventuuri? If so, would this option be more future proof (for larger scale items)?
    That pump is probably just fine…although I’ve never used it.
  1. Is it ok to lay down UD fabric on top of itself or should there be a layer of woven carbon fabric between UD layers?

It really depends on the demands of the structure. In general, you want to align fibers with the forces involved. If you need the panel to handle forces in multiple directions then you need fibers in multiple directions. Many structures are built with only UD fiber formats. It’s sometimes easier though to use 1 or 2 layers of woven rather than four layers of UD.

  1. Which grade of sandpaper should I use to rough up the carbon so I can bond 2 carbon pieces together?

I use 40 grit and then clean the bonding surfaces with acetone.

#3
  1. Is it ok to lay down UD fabric on top of itself or should there be a layer of woven carbon fabric between UD layers?

As a rule of thumb, you don’t want to have more than 1800gsm of carbon in one direction in one block. If you put a layer of cloth between blocks of 1800gsm you should be fine.

The reason behind this is as the blocks get thicker you increase the chances of a rolling failure, where the fibres roll apart. Think about a stack of pipes, once the stack gets too high the bottom ones will roll away allowing the upper ones to fail into the gaps. The resin will hold the fibres together but only to a point.

#4

There are several possibilities. I use a tempered glass sheet in our lab. I really like a semi permanent release on it, which lasts for ages. (I use Ferrokote FS10). It is a combination of sealer and release. Some manufacturers, like Zyvax, have matte sealers.
Another option is tp spray PVA (mist coat) on the glass (could even be done on semi perm) to temporarily make it a matte surface.
A third option is to use melamine board. Some have a small texture, which, although not matte, creates a more matte finish. Also more scratch resistant. (basicly you only scratch the tops, not the valleys)

  1. Will this vacuum pump be ok for the short term production? http://www.ecfibreglasssupplies.co.uk/p-1903-vacuum-pump.aspx
    Or is it possible to use an air compressor with ventuuri? If so, would this option be more future proof (for larger scale items)?

Yes, basicly OK. I would like to see a lossless regulator with it, as these pumps create a very deep vacuum, and could potentially even boil off ingredients of epoxy. However, even with polyester I did succesful infusions with them. If you use MTI hose, there is no need for regulators.
These pumps do smoke, keep that in mind. Have extra oil ready, and do not use them inside if you do not have to. The better your vacuum, the less smoke.

  1. Is it ok to lay down UD fabric on top of itself or should there be a layer of woven carbon fabric between UD layers?

Lots have been said already. As for layers in between: avoid 90-direction orientation, especially if the UD is in compression. use ±45 instead.

  1. Which grade of sandpaper should I use to rough up the carbon so I can bond 2 carbon pieces together?

Depends on the glue used. Grit 40 usually is OK, although MMA glues can do with much less surface preparation.

That is all I can think of at the minute.

Thanks in advance,

Kyle.

Hope to have been of any help.

#5

Excellent! Thanks very much folks! Much appreciated.

#6

With you saying about how that vacuum pump will smoke, I think I may go the air compressor route and use a venturi - http://www.airtechonline.com/Airtechstore/product.asp?Dept_ID=7&ProductID=20
Unless you advise against this as it’s not the best idea?

That way I can have a vacuum and have an aircompressor for use with other accessories (air sander, air blower for drying bikes etc…)

#7

Use an air compressor with reasonable capacity. Compressed air is not the most economical route, but it can work. You do not get the deep vacuum of the pump however. In terms of purchase price a small pump or a venturi do not differ much.
I do not like the noise of a compressor, which is why I would tend to choose for a pump.

#8

Personally I would go with the purpose built pump. I have the pump in the picture, or very similar. It works great, burns a little oil when pulling vac but it is no problem. Keep some spare oil on hand, but I’m pretty happy with it. The smoking is negligible actually. If you are worried about the oil vapour contaminating the laminate (which i am not really) you could use a longer hose, with the pump further away or in another room even.

Reason for all this, is the ultimate achievable vacuum with the venturi is probably not as high as with the pump, plus i think the venturi puts a lot of stress on the compressor. Although i am not sure, as i read this somewhere on the forum, but I can imagine it does.

cheers

#9

.kyle,

I would agree with Herman on this one… you’ll get into deeper vacuum with a pump and the noise level is A LOT more manageable than the venturi method, not to mention the price is going to be about the same. A running vac pump is A LOT quieter than a running compressor.

-C

#10

Thanks for the replies. Venturi idea scrapped. Purpose built pump back on the ‘to buy’ list.