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Glass weave style numbers, 120, 7781, etc.

Glass weave style numbers, 120, 7781, etc.

Glass weave style numbers, 120, 7781, etc.

Is there a reasonably authoritative source? There's a few snippets (e.g., Thayercraft.com have a bit of background although the descriptions are sometimes a bit odd) but surely these codes are agreed by cloth manufacurers (sometimes called converters)? Is there an AMS or ASTM standard for such things? If there's a standard do the numbers indicate the fiber material and any sizing as well as details about the weave style? Maybe my googling phraseology is just off.

RE: Glass weave style numbers, 120, 7781, etc.

I don't know how the style codes are set but competitive weavers do use the same codes for common fabrics. Sizing formulation is proprietary to each company. Some sizings were developed by companies like Dow and sold to the weavers. So different weavers can supply volan or Z-6040 finishes. But there will be minor differences.

These handbooks describe the different weave styles.


RE: Glass weave style numbers, 120, 7781, etc.

Thanks. I'd never spotted the Hexcel one. Those specs are very useful and have some AMS and MIL spec references. The issue seems a bit standardized but not very. Glass fabric seems more supported than most. They seem to use some of the same style numbers for Kevlar. We're probably lucky they're willing to tell us as much as they do about the sizes.

They seem happy to standardize the end count in each direction and the amount of twist along with fibre size. Is there any measure of the tightness of the weave?

RE: Glass weave style numbers, 120, 7781, etc.

I'm not sure what you mean by tightness of the weave. The thread TEX or denier and the pick-count determines the areal fiber weight and thickness of the fabric. Twisted threads will tend not to spread as much as untwisted so you may get a thicker fabric with twisted threads, keeping the AFW constant. Packing density of fibers (fiber volume) will also depend of weave style. Plain weave has a lower packing density than satin weaves. All fibers can also be "bulked-up" by entangling or crimping the filaments so they cannot pack tightly. Pillow stuffing is the ultimate of bulked fiber. Simply passing carbon fabric over rollers will cause slight bulking each time. Some carbon fibers are intentionally bulked-up for weaving so that they will soak-up more resin in the solution prepreg process.

RE: Glass weave style numbers, 120, 7781, etc.

Thanks for the info. What I had in mind for 'tightness' was the attached sort of thing. I'm not too sure of the most widely used methods of controlling thickness and fiber areal weight. I've seen some examples of very open weaving so the tows were quite widely spaced. I wasn't sure how that sort of thing was controlled. I take it that the bulking up you described has the effect of introducing sligihtly greater spacing between fibres in the tow so reducing areal weight of each tow a bit.

RE: Glass weave style numbers, 120, 7781, etc.

I don't know entirely the origins of the fiberglass fabric style nomenclature. MIL-C-9084 (now superseded by AMS-C-9084) defined many weave styles, itemized by typical MIL classifications (Type/Class), and identified (for reference) the commercial designations. The commercial designations were flag noted: "Commercial designations are nominal weights per square yard are shown for information only and are not requirements. Commercial designations for a given type may vary with different suppliers." Beyond that, I don't know how style numbers are decided and/or whether they're correlated with other manufacturers in the fiberglass weaving industry or the AMS-C-9084 folks. Good question though...I'd like to know more about it as well...

Regarding the weave tightness (I've always called it weave openness, but there's no industry accepted term that I'm aware of) I don't know of any common metric. I've seen obscure things like air permeability reported from time to time, but it's certainly not common and permeability would be a function of more than weave openness (e.g. areal weight). For me, the measurement has been experiential...seeing and using...samples...swatch books, etc. Of course, advice and insight from the manufacturer is always helpful. (just to make sure we're talking about the same thing...I use the term openness in describing the visual differences between the weaves in the attached photo)

RE: Glass weave style numbers, 120, 7781, etc.

Bulking does not affect AFW, only thickness the fabric. There is more air space between the filaments in the tows or yarns. Same concept as taking a box of toothpicks and shaking them up in a jar. They will not pack back together and thus take up more volume.

Openness is probably the most appropriate term for what you describe. Most of the highly open weaves are leno weaves. Pairs if warp yarns are crossed over each other after every pick so they essentially pinch the fill yarns to hold them in place. Style 1659, which is pictured in jotunn's link is a common leno weave that is used in drywall joint tape. Binders are also to glue the yarns in place.

One useful test for openness of carbon is to fold some fabric over on itself at a 45 degree angle and counting how many pinholes of light you see per unit area.

RE: Glass weave style numbers, 120, 7781, etc.

I haven't been at this as long as some, but I haven't seen a weave openness spec on carbon or glass fabrics. I've seen fabric openness defined by % of light that passes through the fabric (on curtains for example), but have yet to find an equivalent in structural fabrics for CFRP/GFRP. Likely that this info if given would be deemed unreliable because processing effects can change results?

Similarly interested in origins of the Glass fabric designations, which seem to be much better defined than carbon fabrics. As Noted the Mil-C-9084 spec which was originally from the 60's (?) specified several glass fabrics according to warp/fill, yarn construction, and areal weight. Interestingly (to me), what would now be a 7781 fabric was listed with a commercial designation of 181-75DE in an old version of the spec, so somewhere in the last 50 years the accepted commercial designation has changed.


Quote (Jotunn)

"Commercial designations are nominal weights per square yard...
reads as Commercial designations and nominal weights in my copy, so I don't think that's the origin of the commercial designations.

RE: Glass weave style numbers, 120, 7781, etc.

Quote (MartinShane)

reads as Commercial designations and nominal weights in my copy, so I don't think that's the origin of the commercial designations.

Reads the same in mine...good catch...thanks. Sometimes the fingers work faster than the brain...

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