G10/FR4 Glass Epoxy Tube

Flame-retardant glass-epoxy tube is the same wound construction as G-10 tube with a flame retardant in the resin, supplied to NEMA FR-4 and MIL-I-24768/27 Type GEE-F. It is the tube to specify where an insulating sleeve, standoff or coil form has to carry a flammability rating.

On strength we would rather tell you what is not published than quote a number nobody measured. No maker we buy from publishes compressive or tensile strength for FR-4 rolled tube. The 42,500 psi compressive and 39,500 psi tensile figures you will see quoted around the trade belong to G-10 rolled tube, not an FR-4 one. What is safe to say is that rolled tube strength sits well below the sheet figures for the same grade. If you are sizing a loaded part, ask us and we will get data for the actual construction before you commit.

The electrical and thermal picture is better documented. The temperature index is 130 to 140C, the dielectric constant 4.4 to 5.0 and the dissipation factor 0.014 to 0.032 at 1 MHz, with volume resistivity around 3 x 10^15 ohm-cm. On flammability, FR-4 is defined as the flame-retardant grade and the US makers we buy from publish UL 94 V-0; ratings on imported stock are not always documented to the same standard, so ask us for the certificate if the rating is a requirement. Heating this grade above 300C decomposes the flame-retardant package and releases hydrogen bromide, which the non-FR grades cannot do.

As with G-10 tube, rolled convolute and filament-wound constructions are different products and are not interchangeable on a loaded part. Rolled tube is listed and sold bore first, because the bore is the dimension it is formed to. It runs up to about 48 inches long, with the outside centreless ground as standard to 9 inches, lathe turned to 24 inches and supplied as wound above that. It goes into insulating sleeves and bushings, standoffs and spacers, coil and bobbin forms, terminal and conductor insulation, switchgear and motor control components, and battery and EV module insulation. 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.