G10 Glass Epoxy Tube

Glass-epoxy tube is woven fiberglass cloth and epoxy resin wound on a mandrel and cured, giving a rigid insulating tube that machines and turns like the sheet. It is supplied to NEMA G-10 and MIL-I-24768/2 Type GEE. Read the tube numbers rather than the sheet numbers, because they differ in both directions. Published properties for rolled tube are compressive strength 42,500 psi by ASTM D695 and tensile strength 39,500 psi by ASTM D638, both lower than the equivalent sheet figures, while the temperature index is 200C electrical and 200C mechanical, which is higher than the 130 and 140C published for G-10 sheet. That index is a NEMA LI-6 recommendation rather than a maximum operating temperature.

Electrically it is close to the sheet but not identical: relative permittivity about 4.4 and dissipation factor 0.024 to 0.034 at 1 MHz, against 4.8 and 0.020 for sheet. Hardness is Rockwell M110. The grade is UL 94 HB and is NOT flame retardant; FR-4 tube is the same construction with a flame retardant in the resin and is the one to specify if you need a rating.

One thing worth asking about if the application is structural. Rolled convolute tube and filament-wound tube are different products with different numbers, and denser does not mean stronger in every direction. Filament-wound runs 2.0 specific gravity against 1.80 for rolled and it is strongly directional - on the same datasheet its axial compressive strength is 29,200 psi while its radial compressive strength is 82,400 psi, so axially it is actually weaker than rolled tube's 42,500 psi. The two are not interchangeable on a loaded part. Tell us what the tube has to do and we will confirm the construction on the lot.

On size: tube is listed and sold bore first, because the bore is the dimension the tube is formed to and the outside is where the stock-removal tolerance lands. Rolled tube runs up to about 48 inches long, with some small diameters limited to 18 or 36 inches. The outside is centreless ground as standard from 0.156 to 9.000 inches, lathe turned from 9.001 to 24.000 inches, and above 24 inches it is supplied as wound with no outside finishing offered. It is used for insulating sleeves and bushings, standoffs and spacers, coil and bobbin forms, terminal and conductor insulation, transformer and switchgear components, and machined structural insulators. 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.