Sheet in PEI 3000x620 mm amber

PEI GF50 is polyetherimide with 50 percent glass fiber. The content is high enough to move the material out of the engineering plastics and into a range where tensile strength and stiffness come close to light metal levels in certain load cases. The sheet is made for parts that have to hold their shape and carry load under heat, where a lower filler content is not enough. It is often the borderline between plastic and aluminum that decides the choice.

Technically PEI GF50 shares its core properties with the other PEI grades. The density is about 1.27 g per cubic centimeter. Continuous service temperature is 170 degrees and the material stays usable down to minus 50 degrees. UL 94 V0 meets the stricter fire requirements in rail vehicles, aviation and process industry. The high glass fiber content lowers thermal expansion sharply compared with unfilled PEI and reduces creep under longer load stress, and that is the difference from GF30. Water absorption is low, around 0.5 percent, and does not affect the dimensions noticeably in a humid environment.

The natural color is brown and comes from the resin and the composition of the glass fiber. The tone is even through the thickness and varies slightly between production batches, which is normal for such a highly filled grade. The brown shade is at the same time a good visual marker for telling GF50 apart from GF30 and unfilled PEI on the shop floor. The surface turns matte after milling and takes engraving well.

The sheet is used for load-bearing, dimensionally stable parts in demanding environments. That can mean support plates and fixtures in soldering and wave soldering ovens, breaker components and base plates in electrical cabinets that run hot, wear strips in conveyor systems close to the temperature limit of the material, and structural parts in test equipment and air traffic control cabins. The material is also interesting where a metal part has to be replaced with something lighter and insulating without losing dimensional stability under heat. In semiconductor and vacuum manufacturing GF50 shows up in fixtures where low outgassing is combined with high stiffness.

Machining calls for some thought. The high glass fiber content wears heavily on tooling, so sharp carbide or diamond-tipped inserts are in practice a requirement in larger runs. Moderate cutting speeds, generous chip evacuation and clean cooling give the best result. Drill larger holes in steps and clear them often. Do not use acetone, methylene chloride or other aromatic solvents on loaded parts, PEI is stress sensitive to exactly those. Count on shorter tool life and plan for tool changes and checks in longer production runs.

The sheet is supplied in fixed dimensions and a number of thicknesses. Pick a thickness close to the finished size to keep machining time down, and leave margin for a light face milling of the surface if needed. In larger volumes the cutting layout usually affects the material cost more than you would think, since the raw material price is high. For single parts it is simplest to start from the next larger stocked thickness. Store the sheets flat, dry and with interleaves if they are stacked, which avoids both pressure marks and moisture pickup before machining.

PEI GF50 is overkill in many situations where GF30 does the job well, but exactly the right choice when stiffness and dimensional stability at temperature is the most important criterion and you do not want to step up in price to PEEK or PEKEKK. For simpler parts where machinability and price matter more, a lower filler content or unfilled PEI is enough. The difference from GF30 shows most clearly in long load cycles and in applications where thermal expansion is a real problem.

In designs against metal, PEI GF50 sits close to aluminum in thermal expansion, which is one of the reasons the grade often turns up in hybrid constructions with metal fastenings. When press fitting insert bushings the material keeps its grip without creeping over time, as long as hole and bushing are dimensioned with margin for the glass fiber content. For screwed joints a moderate tightening torque is recommended, since point load in a highly filled grade more easily gives local cracks. Bonding works with polar epoxy systems after surface activation. For critical screwed joints metal threaded inserts are preferred, since they spread the load over a larger area in the material and reduce the risk of creep at operating temperature.

Wondering whether GF30 or GF50 is the right choice for your part? Get in touch, we will go through load and operating environment together.

In the long 3000x620 mm format the PEI sheet gives material for milled parts where heat and electrical insulation are required. Amber colored all the way through.