G11 Glass Epoxy Rod

High-temperature glass-epoxy rod is machining stock for insulating pins, studs, standoffs and spacers that have to hold load while hot. The resin system is the one used for G-11 sheet, and the property that justifies it is hot strength: on that sheet material, flexural strength measured at 150C is published at 30,000 psi as the NEMA required minimum and 40,000 psi as one maker's typical. At room temperature expect 70,000 to 80,000 psi lengthwise flexural, compressive strength around 70,000 to 72,500 psi and tensile strength 37,000 to 43,000 psi, with a dielectric constant of 4.5 to 5.0 and a dissipation factor of 0.014 to 0.022 at 1 MHz.

Read this before you put it on a drawing, because the standards do not cover it the way they cover sheet. NEMA LI-1 and MIL-I-24768 do not recognise a high-temperature epoxy-glass convolute rolled tube form - one major maker says so in terms - and we are not aware of a NEMA or MIL rod form in this resin system either, though no maker states that as plainly for rod as for tube. Separately, no specification sets requirements for sheet-ground rod in any grade. So this rod is sold as high-temperature epoxy glass and carries no NEMA G-11 and no MIL-I-24768/3 Type GEB claim of its own. G-11 sheet does carry both. If your drawing calls out NEMA G-11 rod, it is worth a conversation before you order.

The temperature figures are published two ways and the difference matters. The UL 746B temperature index for this resin system is 170C electrical and 180C mechanical, which is a short-term index, while makers describe 155C as the figure the material holds for decades. Treat 155C as the design figure for long continuous service. On flammability, one maker publishes UL 94 HB for G-11 and describes it as not flame retardant while another publishes V-0 at 0.250 inch and thicker, so do not assume either from the grade name - tell us if you need a rating and we will confirm it on the lot.

It is turned and milled into motor and generator hardware, hot insulating standoffs and studs, transformer components, down-hole and aerospace parts, and any non-conductive pin or spacer with a thermal duty. Natural stock is light green.

Machining and handling. The glass abrades tooling, so carbide is the floor and diamond-coated or PCD cutters are what hold tolerance in production; run high spindle speeds with secure workholding and design in generous internal radii, because small tools wear out fast against glass. Threaded holes are normally milled rather than tapped and external threads turned or thread-milled, since the plies can delaminate. The laminate has no hazards as shipped, but cutting it releases a fine dust, and the epoxy resin in that dust is classified as a skin and respiratory sensitiser - use local exhaust, a dust respirator, eye protection and gloves, and work to your own site's exposure limit, because published limits for glass dust differ by jurisdiction and by whether total or respirable dust is measured. It comes off as powder rather than chips, so vacuum it up rather than blowing it airborne. These are our shop notes, not a manufacturer specification.