This article included below is from the web site <http://www.sweetcomposites.com/Fabric.html>. ?These guys weave and finish composite fabrics to sell. ?What I read here is that our discussion has some terminology issues. ?Sizing is a coating for the yarn so they can weave the fabric, but is cleaned away once the weaving is completed. ?Silane is most likely what our fabrics are coated with which does enhance the bonding of the resin to the cloth. ?Note, the key word here is that it enhances the BONDING, now the wetting out of the cloth. ?
The work I am currently doing is being done with 8 year old cloth. ?However, it should be noted that none of it is structural, so minor losses in bonding won't matter. ?For that matter, the plane isn't going to fall out of the sky if the current work falls off in flight, so I am still comfortable working with this material. ?However, based on what I am reading here, if I was building a new structural component such as a horizontal stab or elevator, I would buy new material to work with. ?Thank you Sid for bringing this to our attention. -Jeff Scott Los Alamos, NM Fiberglass Finishes When fiberglass cloth comes off the loom it is said to be ?in the greige? [pronounced grey]. In order to be compatible with resin systems it must first be heat cleaned to remove oils and sizing needed for weaving and then treated in a chemical bath, called ?finishing.? Finishing formulations are proprietary recipes that enhance bonding with the type of resin to be used. One of the earliest fomulations that is still in use is called Volan, which employs compounds of chromium. We do not recommend the use of Volan finishes because of the chromium content. Chromium is a toxic heavy metal that is considered a strategic material by the military and much of it is imported from Africa. Potential problems are evident! It also imparts a green cast to the fiberglass and the resulting laminate is generally rather grey and dirty looking. Silane finishes produce a clearer laminate and avoid the chrome problems. Our preferred silane finish from BGF is called 497A. It was developed for critical aerospace applications and is compatible with epoxy, vinylester, and polyester resins. We occasionally have fabrics with 627 finish, also a general-purpose silane. Our fabrics that are made by Hexcel-Schwebel have a CS-767 finish, which we believe to be comparable to the BGF finishes. Very occasionally we will have some material that is finished specifically for one resin system, usually epoxy. In those instances we are careful to assure that a potential buyer is using the correct resin before making a sale. Fiberglass finishes are degraded by environmental conditions such as moisture or even humidity and they deteriorate to some degree just with time. The 497A finish has especially good longevity, which is one of the reasons we prefer it. While deterioration begins as soon as finishing is completed, there is no significant loss of physical properties over the first year or two, provided the fabric has been wrapped in plastic and protected from high heat and humidity. I would be careful about using fiberglass more than three years old and would probably not use it after five years for any critical application without running some tests first. > ----- Original Message ----- > From: smwood > Sent: 03/27/13 10:45 AM > To: krnet at list.krnet.org > Subject: Re: KR> Glass cloth shelf life > > The glass in fiberglass cloth does not have a shelf life. The glass is > inorganic. The sizing coating on the glass strands is an organic compound > and has a definite shelf life. > I use to teach this fiber glass stuff for the EAA Sport Air Workshops and > still do at AirVenture. > > Sid Wood > Tri-gear KR-2 N6242 > Mechanicsville, MD, USA > > ----------------------------------------------------------- > > Sid said - Fiber glass cloth has a sizing coating on each strand to help > > the epoxy > > resin to bond to the glass. The shelf life for most fiber glass sizing is > > five years. After that time the wetting out with the resin becomes more > > difficult and will result in a weaker structure. The older the cloth the > > worse the situation will be. > > > > I posted this question to the group some time ago and was told that there > > is > > no end shelf life on fiber glass cloth. Would someone in the industry, (If > > there is someone in the group), please check in and clear this up. > > > > Patrick Driscoll > > Saint Paul, MN > > patrick36 at usfamily.net > > www.pensbypat.com > > If you can read this, Thank a teacher > > If you are reading this in English, thank a veteran > > > > > > > > _______________________________________________ > Search the KRnet Archives at http://tugantek.com/archmailv2-kr/search. > To UNsubscribe from KRnet, send a message to KRnet-leave at list.krnet.org > please see other KRnet info at http://www.krnet.org/info.html > see http://list.krnet.org/mailman/listinfo/krnet_list.krnet.org to change > options
