Chemraz is Greene Tweed's perfluoroelastomer brand. Compounds are numbered rather than named, and several are direct cross-references to Kalrez grades. This page lists every Chemraz compound covered on MLC -
6 of them - with maximum continuous temperature, low-temperature limit and hardness side by
side, so you can pick a grade without opening each datasheet in turn.
FFKM (perfluoroelastomer, ISO 1629 designation FFKM) is the most chemically resistant elastomer
family in general use. It costs many times what FKM does, so it is specified where a Viton seal will
not survive: aggressive amines, hot steam, strong bases, oxidising plasma, or a mixed-chemistry
process where nobody wants to qualify a different seal for each stage. Grade choice within a brand is
mostly a trade between temperature ceiling, chemical breadth and hardness.
Chemraz compounds compared
| Compound | Max continuous | Min temp | Hardness |
Colour | Family |
|---|
| Chemraz 505 | 230°C | -34°C | 75 Shore A | Black | Cold-flexible FFKM (lowest min temp in Chemraz line) |
| Chemraz 526 | 327°C | -10°C | 75 Shore A | Off-White | Semiconductor-grade FFKM |
| Chemraz 555 | 240°C | -20°C | 75 Shore A | Black | General-purpose chemical-grade FFKM |
| Chemraz 615 | 324°C | -10°C | 75 Shore A | Black | Thermal-grade FFKM, slightly higher temp ceiling than Kalrez 4079 |
| Chemraz 633 | 327°C | 0°C | 90 Shore A | Black | Hard FFKM for high-pressure |
| Chemraz 696 | 327°C | 0°C | 90 Shore A | Black | RGD-resistant high-pressure FFKM |
Every compound above links to its full specification, size availability and UK supply options.
Manufacturer: Greene Tweed.
Cross-referencing Chemraz to another brand
FFKM grades are not interchangeable by number, and no cross-reference is exact - two compounds can
share a hardness and a temperature rating and still behave differently in your specific media. Treat
any equivalent as a starting point for qualification, not a drop-in. These head-to-head pages set out
where each pair actually differs against Kalrez, Simriz, Perlast:
Choosing a grade
Start with the lowest temperature ceiling that covers your process, not the highest available. The
broad-resistance grades near the top of a range carry a price premium and often a lower
low-temperature limit, so specifying the flagship compound for a 150C duty costs money and can make
cold-start sealing worse. Confirm the low-temperature figure in the table above against the coldest
condition the seal sees, including shutdown and cleaning cycles, rather than the running temperature
alone.