MyKarta? Fiberglass resin VS Epoxy

AcridSaint said:
Hi Joe - I'm pondering this issue and I'm wondering if we're on the same page. The fiberlgass cloth that I've worked with in modeling is not sharp or pokey in any way. As a child and teenager I worked with it extensively without any gloves or even a respirator (not that I recommend this). From what I understand of G10, it's fiberglass cloth and melamine resin. Is the concern that when the fiberglass resin wears with use that you'll be left with stiff glass splinters on the handle?
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Acrid,
You get the woven cloth, chopped strand (common in boat building) and tissue. Chopped strand tends to be the one with thickest threads and will easily prick into your skin while handling. The 'tissue' is much finer and is made for surface finishing, and it tends to have a more fabricy texture which doesnt really prick you too much, if at all. That is probably what you used for modelling. If you have a fish tank, you will know that that glass wool for the filter doesnt prick you, even though it is essentially the same material.

I agree with Joe in that I wouldnt use glass in a handle that I was going to sand to shape.. Only if i was going to mould it to net final shape would I use glass.
 
Just thought that I would add that G-10 isn't made with melamine, I was wrong on that note. G-10 and 11 are epoxy resin based, G-9 and some others are melamine.
 
When using prepreg you have to heat cure the part, the epoxy doesnt become "sticky" and fluid until heated. I´ve learned you first lay the cloth (for CF that is) in 4 directions, so the part will be equally strong in each direction (if you dont it will warp), then vacuum out most of the air, then inside the autoclave where you first heat it and put positive atmospheric pressure on it, then negative, then positive again, this removes almost all internal bubbles, then you bake it. Im not 100% certain but almost. (maybe you could leave out the first positive and only go neg then pos) *edit: now when i think about it maybe they use several cycles*

A guy i used to work with told me this, he used to work with building the carbon fiber parts for fighter jets. The prepreg stuff is usually not really cosmetic, its just made for highest strenght not to be as cosmetic and beautiful as possible, the good thing about it is that its the best possible weightratio cf/epoxy from the start. (but for handles just weigh it up like already mentionend)

It has a shelf life of 3 years or so iirc, and when that time has passed they just throw it out, i think its the epoxy that dries out. It might be spossible to get some of the stuff they throw out if you know somebody.

i´ve done some "micarta" using polyester and cut up t-shirts etc, i used a 10ton press, i think it came out really good, but next time i would use maybe 5 tons instead. Down side of a hydraulic press is that it loses pressure after a while, so you need to clamp it any way (with really heavy duty claps).
 
M Wadel said:
When using prepreg you have to heat cure the part, the epoxy doesnt become "sticky" and fluid until heated.
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There is also prepreg which is refridgerated and starts curing when taken out of cool conditions, and doesnt required any autoclaving. Nonetheless, I think all prepreg is pretty $$$$$ anyway. I think the ambient curing prepreg actually has a shorter shelf life too.
 
It's not very often where I can provide info around here rather than ask for it, so I'd like to add something without stepping on any toes. By way of introduction, I've originally got an aviation background (AME) but I've been building boats for quite a while now, so I've worked with different resin systems.

The polyester and vinylester resins are really suited for production applications such as boat building. Polyester resins are the workhorse and are the base for most resin products like body fillers. Vinylesters are a higher cost, lower strength resin with a much better water resistance. Quality builders will spray a hull mold with gelcoat, then apply vinylester and 'veil' (a glass cloth product similar to Kleenex, described already) to strengthen the gelcoat and provide a moisture barrier and reduce cloth 'print-through'. The rest of the layup is done with poly resins an alternating layers of cloth and mat. Chopped strand is typically shot in with a gun to build layup density (hull thickness) cheaply. It doesn't really belong in a boat IMHO.

Epoxies are a completely different animal, not generally used in conjunction with the above. Epoxy will (mechanically) bond to cured poly, but not the other way around. Additionally, chopped glass products (strand, mat) contain binders which are dissolved by styrene, so are ineffective with epoxy. Another important difference is that the structural components in an epoxy formulation are shared between the resin and hardener, preventing customization of the ratios by the end user. Poly resins use a catalyst simply to initialize the exotherm that begins the cure cycle, so different ratios can be used (within limits) to change pot life and cure times. Epoxy works far better with wood and has a water resistance nearing 100%, but this last point is the subject of recent study.

Prepregs, because of their cost, are typically used with high end epoxy layups . While I was in tech school, we had the prepregs that were stored cool and curing was started by allowing to warm to room temperature. I haven't used others, but it stands to reason that oven-curing prepregs would also work, albeit perhaps resulting in a lower ultimate strength (heat is an epoxy's weakness).

I don't have as much experience with Micarta and Bakelite, which are phenolic resin products (think billiard balls) which does indeed require heat and pressure. I have made tool handles in the past using epoxy and cloth and the end product is pretty effective. After the final sanding, I brushed on a final coat of liquid epoxy to seal it and AFAIK they're still going strong.

A final thought is about amine blush, the waxy byproduct of curing epoxy. It is water-soluble, so a scotchbrite pad and fresh clean water will easily remove it, where sanding will heat it and drive it into the layup, reducing the surface area of subsequent mechanical bonds. I've been told on the quiet by a sales rep that, despite manufacturers' claims, there's really no such thing as a true no-blush epoxy. Any chemists in the house ?

Apologies for the length of the post - it started as a single paragraph but I thought these points were important to make, even though they pertain more to boats than knives. My question for those making their own handle laminates: what have you folks found best for tinting epoxies ? Apparently acrylic (poster) paints are chemically compatible, but I haven't tried it myself.
 
Aramid is a type of nylon, and afaik epoxy does not stick well to it. You could probably use other resins.
 
The problem with kevlar in a layup is that, quite right, the epoxy encapsulates the fibers rather than saturating them. When you sand it, kevlar scales would be 'fuzzy'. In layups, it's generally sandwiched between layers of graphite or glass cloth to allow sanding.
 
Deadeyelefty,

Thanks that was great, you mind dropping me an email I would like to chat with you more about this.
 
M Wadel said:
Aramid is a type of nylon, and afaik epoxy does not stick well to it. You could probably use other resins.
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Kevlar is made into epoxy prepreg frequently for certain aerospace applications. I believe you could make an epoxy micarta using it.
I'll defer to DeadeyeLefty on fuzziness or sanding the result. I've made Kevlar prepreg, but I haven't made laminates out of Kevlar. Lots of graphite and some fiberglass, but not Kevlar.

There are certain advantages to prepreg over wet layup.
1) prepreg has a more uniform fiber to resin ratio. This gives more uniform structural properties. Important for engineers designing aircraft etc, but I think not for knifemakers.

2) Prepreg is faster and easier to layup. And it's a lot less messy. This is especially good if you are doing high production rates.

3) Prepreg lets you produce layups using resins that are not flowable at room temp. (I've made experimental wet layups using such resins. Trust me, pouring hot resin is a pain in the tail.) When prepreg is made, resins are typically thinned with acetone and the cloth is run through it. Then you run the stuff through an oven (very Carefully!) to drive off the acetone. That leaves you with resin and fabric. (Spent a while as the site chemist at a prepreg plant.)

The disadvantage to prepreg is that it's expensive. (After all, you're paying folks to run acetone through an oven.) Most prepregs are heat cured because it gives you a longer working time before it sets up. But there are a few room temp cure systems available.

Blushing: These days I work as a materials engineer, but my degree is in chemistry, and I spent a fair amount of time as an epoxy resin chemist formulating paints, adhesives, and a couple of composite resins. I've always considered the "blush" to be a reaction of very reactive amines with CO2 (they form a compound called a carbamate), although dampness does play a part. The more reactive the amine curing agent, the more likely you are to see blushing. My advice would be not to cure a room temp epoxy at less than 75°F. Lower RH is better too. The rate of the epoxy reaction slows down as the temperature drops. It drops faster than that of the amine-CO2 reaction. You want the amine to react with the epoxy rather than the CO2 in the atmosphere. Best advice, though is not to use a super-fast curing epoxy. The super-fast ones use more reactive amines that will be more likely to react with the CO2. Your sales rep was kind of telling the truth. Darn near any amine will react with CO2 given the proper conditions. But some are more likely to than others under normal conditions.
 
A thought on kevlar though: as RHankins mentioned in post #3, one could mold the kevlar into a scale. Maybe make wood scales and use them to make a female mold, then lay up the epoxy and kevlar inside. When pulled, the part should need little finishing. As the kevlar would be completely encapsulated in epoxy, I can't really see an advantage to it though, given the high cost.

knarfeng, it never occurred to me that a heat-cured prepreg resin would have to be thicker, but that makes total sense. A common 'trick' is to warm up resin when used with wood to reduce the viscosity and allow it to penetrate better. It stands to reason that trait would have to be allowed for when 'cooking' the resin. Thanks for the great info on blush, I will have to remember that because I was ignorant of the mechanics of the blush reaction. I concur with you on the temperature recommendation. The rule of thumb in the industry is 77 degrees for poly resins and 72 for epoxies. Is there any value in excluding co2 from the cure ? I'm thinking maybe a nitrogen bath (nitrogen is common in aviation).....

On vacuum bagging, I've done flat panels at home using a shop vac, vapor barrier, tuck tape, and some of those plastic spacers that keep the top of a pizza box from touching the pizza. To be honest, the benefits weren't worth the hassle. Again, as knarfeng mentioned, its value is in deriving the most strength from a minimum amount of resin (and therefore weight). Another advantage of prepreg is that it helps to eliminate human error on the shop floor. My hand layups will have a slightly different resin-to-fiber ratio than someone else's or than one I did a while ago. Not a good thing in.....say....a tail rotor repair !
 
DeadeyeLefty said:
Is there any value in excluding co2 from the cure ? I'm thinking maybe a nitrogen bath (nitrogen is common in aviation).....
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Never tried it, but I would think so. The initial reaction is CO2 with N-H in the amine curing agent. Moisture then soaks up into the carbamate forming the blush. If the CO2 is excluded, the intial reaction would not be able to occur.
 
I'm not a knife maker, but I've built several wood and fiberglass kayaks using epoxy resin. One thing to bear in mind with epoxy is that there are a number of brands and formulations out there. They range from fairly thin to fairly thick, some with a fair amount of blush and some with little or no blush, some that cure clear and some that cure with a bit of a tint, and a wide range of curing times. I've never worked with polyester or vinylester resins so I don't know much about them, but epoxy is pretty easy to work with in a home or workshop environment.
 
butcher_block said:
yep its all about makeing something cool
that you cant get any place
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Sorry to bring up an old thread, but I have GOT to know how those pieces are made. The red and black for example, is it just red and black materal that is wadded up before being put into the press (after being soaked with resin)?

I understand how to make the basic (x amount of layers, laid flat and pressed) but I'd really like to know how to get the other designs!
 
I've made about 10 pieces with Kevlar... it is fuzzy, like several other materials, but worse! Natural fibers, glass, carbon, finish out fine.
 
GrizzlyBear said:
Sorry to bring up an old thread, but I have GOT to know how those pieces are made. The red and black for example, is it just red and black materal that is wadded up before being put into the press (after being soaked with resin)?

I understand how to make the basic (x amount of layers, laid flat and pressed) but I'd really like to know how to get the other designs!
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That camo pattern looking one is awesome. I remember someone doing a tutorial where they twisted the layers before pressing but you are right that looks like they smushed it up somehow. I just got my resin the other day and am looking for a pair of jeans to "recycle" and would love to know how that pattern was achieved.

Anyone????
 
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