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Re: [ATM] making carbon tubes
a step that should not be overlooked and was not mentioned yet in this
thread is applying mold release first.
another thing is the details of how to wrap the carbon unidirectional tow on
the Aluminum tube . For small jobs (or rush, or lazy) I just tape the carbon
tow end to the Al tube and then wrap relatively tight . When I reach the
other end, tape there too then cut the tow.
I then tape the unidirectional pieces (that I had precut to tube length
before starting to laminate) all at one end of the tube . I stretch them by
hand for small tubes and tape the other end to the tube . Then similarly for
the outer spiral layer .
If it's a larger tube I drill some holes close to the mandrel ends and
insert some pins there (might need lots of these pins, because they must be
spaced about 2 tow widths apart) . Then I just tension the longitudinal tow
from one pin to the other mandrel end along the mandrel, wrap it along a pin
at that end then place the tow back along the mandrel to the next pin etc .
A kind of zigzag that keeps the longitudinal tow in tension .
The mandrel can be a 2 part separating in the middle , if the tube is long
it's easier to pull out the halves than a whole mandrel.
I oven cure the thing, and by oven I mean a simple cardboard contraption
with a thermostat and a couple of ceramic heaters , but that's good enough .
After the curing is over, I pull the whole thing out of the cardboard
box/oven (which is made to shape for each tube , just leave a few inches in
each direction from tube walls to cardboard , use again tape to hold things
together , nothing fancy ). Immediately, without wasting time, I pour some
cold water and ice from a bucket into the mandrel Al tube . The Al shrinks
but don't expect miracles . Mold release must be there , applied correctly ,
your tube must be free of defects like variable diameter , dents etc. If
that's not possible, there are methods in which the mandrel material (not
aluminum) is corroded away or dissolved after curing . Alternatively, the
mold release can be more radical, more layers etc.
best regards,
matt tudor
p.s. the tow must be stretched carefully if you want not to get wrinkles .
Just loosely wrapping won't work .
A simple jig to prepreg the carbon tow with the epoxy before laminating
works best. I use slow curing epoxy (at room temperature, but faster once in
the oven) and that lets me work at my own pace and not rush . For larger
jobs I cut all the carbon material first, perhaps do a dry run to see what
doesn't fit, prepreg them , store in the refrigerator on some wax paper ,
and take the prepreg out when required .
Also, you don't need to pull a very high vacuum , the part has no core , no
large voids , no rigid insertions to be flexed by the vacuum (like some
plywood cores or veneers that were a nightmare to torture into shape) .
The slower curing epoxy and moderate vacuum accomplishes a good fiber to
resin ratio , no need for anything excessive .
If this is way too complex, there are even simpler ways which don't require
vacuum , just wrapping with tape to squeeze the epoxy out .
-----Original Message-----
From: Peter <peter@kitgear.com>
To: atm@atmlist.net <atm@atmlist.net>; shane@dreamscopes.com
<shane@dreamscopes.com>
Date: Wednesday, February 01, 2006 6:43 PM
Subject: Re: [ATM] making carbon tubes
>Hi,
>
>I have this book and it does not explain the detailed method very well.
>
>I tried to make a composite tube on a mandrel and it also wrinkled once
>vacuum bagged. I recall watching the process and I observed that the vacuum
>created high points (wrinkles or channels) where the epoxy existed more
>readily from the cloth causing the outer layer to slide - hence the
wrinkle.
>My inner layers stayed put and made for a very nice inner surface finish.
>
>Cord, the other problem I had was removing the CF tubing off the mandrel.
>The vacuum applied so much pressure that I had trouble removing it.
>
>Shane, perhaps you would consider sharing some of you experience in this
>area? Much appreciated!
>
>Peter
>
>-----Original Message-----
>From: atm-bounces@atmlist.net [mailto:atm-bounces@atmlist.net]On Behalf
>Of James P Crombie
>Sent: February 1, 2006 10:49 AM
>To: atm@atmlist.net
>Subject: Re: [ATM] making carbon tubes
>
>
>If the tow is wound tight the the vacuum bagging will not affect it.
>The main reason to vacuum bag it it to remove the excess resin from the
>fibres and to help the fabric conform to the mold or substrate. The
>resin should pass through the peel ply (release fabric) into the
>breather material. With your previous efforts with fabric, if it was
>not in tight contact with the alum tube then when the vacuum was applied
>it may have moved and resulted in the wrinkes you got.
> There are several books availabel on vacuum bagging for hobbist,
>mainly for model aircraft types.
>
>I found this on a google search
>http://www.jamestowndistributors.com/product;part;14778;process;search;ID;,
F
>iberglass,Vacuum.Bagging.Supplies
>
>Cord Scholz wrote:
>
>>Hi Matt,
>>why would a spiral layer of tow not wrinkle when vacuum bagged?
>>
>>Best,
>>Cord
>>
>>
>>-----Original Message-----
>>From: matt [mailto:electro_optic@bellsouth.net]
>>Sent: Wednesday, February 01, 2006 4:41 AM
>>To: Cord Scholz; atm@atmlist.net
>>Subject: Re: [ATM] making carbon tubes
>>
>>A cheap and simple way to make tubes is not out of fabric but out of
>>unidirectional carbon tow.
>>Need to wrap the mandrel in a spiral layer of tow, then apply a second
>layer
>>of longitudinal unidirectional tow uniformly distributed around the
>mandrel,
>>then wrap it all in a top spiral layer of tow.
>>Advantages are no seams to deal with, can be vacuum bagged and oven
>>postcured, and tow is the cheapest type of carbon per weight available.
>>Also, you decide how much you need in the longitudinal direction and how
>>much strength in the hoop, rather than use some woven cloth or biaxial at
a
>>preset ratio. The whole tube is going to have a continuous fiber structure
>>rather than a bunch of cuts .This will result in the lowest weight to
>>strength ratio , so this is no tradeoff, you get it both strongest and
>>cheapest at the same time .
>>
>>
>>best regards,
>>matt
>>
>>-----Original Message-----
>>From: RodShea <RodShea@comcast.net>
>>To: Cord Scholz <cord@astro-image.com>; atm@atmlist.net <atm@atmlist.net>
>>Date: Tuesday, January 31, 2006 9:50 PM
>>Subject: Re: [ATM] making carbon tubes
>>
>>
>>
>>
>>>Cord,
>>>
>>>>From what I can tell, tubing is often made by wrapping the
>>>mandrel-composite-(?bleeder+?breather+release ply) with heat shrink
>>>tape, instead of vacuum bagging it. This might give you better control
>>>of the fabric. I have not done this, but it seems reasonable. I would
>>>also have thought it would work better to cut unidirectional CF to
>>>exact width, equal to diameter, for each ply, or to do all the layers
>>>of uni as one piece, rolled around the mandrel. I'm guessing the
>>>wrinkles come from excess width material, meaning > diameter, that
>>>becomes a problem when the vacuum decreases the effective diameter of
>>>the mandrel plus whatever thickness of cloth is under the ply that
>>>
>>>
>>wrinkles?
>>
>>
>>>Rod Shea
>>>
>>>----- Original Message -----
>>>From: "Cord Scholz" <cord@astro-image.com>
>>>To: <atm@atmlist.net>
>>>Sent: Tuesday, January 31, 2006 9:01 AM
>>>Subject: [ATM] making carbon tubes
>>>
>>>
>>>
>>>
>>>>Hi all,
>>>>I'm trying to make a carbon tube using an aluminum tube as a positive
>>>>mandrel. Does anyone know ho to prevent the carbon cloth from
>>>>wrinkling
>>>>
>>>>
>>in
>>
>>
>>>>the vacuum bag? In my first attempt I used several cloth pieces that
>>>>were about 1" longer than the circumference of the tube and moved the
>>>>seam
>>>>
>>>>
>>from
>>
>>
>>>>layer to layer a few inches, the result were several nasty wrinkles
>>>>in
>>>>
>>>>
>>the
>>
>>
>>>>cf part.
>>>>I know that there must be a way to do this with a positive mandrel
>>>>
>>>>
>>because
>>
>>
>>>>I
>>>>have a sandwich tube that was made this way but I don't how it was
>>>>done exactly.
>>>>
>>>>Cord Scholz
>>>>www.astro-image.com
>>>>
>>>>
>>>>
>>>>_______________________________________________
>>>>ATM mailing list http://www.atmlist.net/
>>>>
>>>>
>>>>
>>>_______________________________________________
>>>ATM mailing list http://www.atmlist.net/
>>>
>>>
>>
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>>
>>
>>
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