PEEK (polyetheretherketone) is a linear aromatic semi-crystalline thermoplastic that maintains a multitude of desirable properties at high temperatures, including excellent mechanical strength and dimensional stability, wear resistance, chemical resistance, electrical performance and hydrolytic stability.

Because PEEK can be injection molded only up to thicknesses of approximately 15-20 mm (0.059-0.079”), large-section PEEK components, especially large-diameter rods, thick-walled tubes or thick sheets, must be compression-molded.  Also, compared to injection molding, compression molding allows slower cooling, which leads to higher crystallinity and can improve performance.  The main disadvantage of compression molding PEEK is that the cycle time is typically several hours or longer.

Generally, compression-molded PEEK parts are more crystalline, giving them higher modulus and tensile strength than PEEK parts processed by injection molding.  However, compression-molded PEEK parts have lower ductility and are harder and brittle.

By adding milled glass or carbon fibers, graphite, PTFE, titanium dioxide or silicon oxide nanoparticles or other fillers, certain PEEK properties such as the abrasion resistance, coefficient of friction and surface hardness can be improved.

PEEK / VICTREX® Properties

• Excellent strength, stiffness and dimensional stability in high-temperature and harsh environments
• Excellent long-term creep and fatigue properties
• High abrasion and cut-through resistance plus a low coefficient of friction yields excellent wear resistance
• Low tendency to form stress cracks
• Easy to process and lightweight compared to titanium, steel and aluminum
• Low coefficient of friction and high wear resistance
• Low outgassing, low particle generation and inherent purity yield reduced contamination
• Low levels of ionic extractables
• Naturally flame retardant, carries a V-0 flammability rating
• Extremely low smoke and toxic gas emissions when exposed to flame
• Chemically resistant and insoluble in common solvents, including acids oils and salts
• Low moisture absorption plus resistance to steam, water and brine with low permeability means good hydrolysis resistance
• Chemical and water resistance similar to that of PPS but at higher continuous operating temperatures, up to 250 °C (482 °F)
• Electrical properties are maintained over a wide frequency and temperature range
• Fully recyclable, yielding environmental and regulatory benefits
• FDA compliant

PEEK / VICTREX® Applications

Compression-molded PEEK is used to manufacture parts that are designed to replace metal parts, improve performance and reduce overall costs for demanding oilfield, electronics, transportation and medical applications.

PEEK is used to produce large seal rings and other parts for the oil & gas industry.

PEEK is often used to make medical implants.

Compression-molded PEEK / VICTREX® Parts

• Fittings
• Valves
• Valve Plates
• Seals
• Gaskets
• Gears
• Medical implants

PEEK / VICTREX® Compression Molding Process

Use fine powder grades to achieve the best-performing compression molded parts.  The lack of shear forces in compression molding makes it less suited for molding pellets, which would result in grain boundaries between compressed pellets that would reduce mechanical performance similar to weld lines.  Using pellets would also make it more difficult to achieve equivalently high packing density, which could lead to voids in the molded part.

To prevent moisture from causing bubbles, the PEEK powder should be dried for 3 hours at 150 °C or overnight at 120 °C.  PEEK materials must be kept clean and free of cross-contamination.

Thoroughly clean the mold components.  To avoid the formation of black spots during molding, the internal surfaces of the mold must be spotless.

Coat the molding surfaces with mold release and allow it to dry.

Fill the tool with powder, place the seal ring on top and apply approximately 5,000 psi (350 bar) of pressure to pack the powder.  Keep adding powder and repacking until the mold is filled with the required amount of powder.

Set the heaters for the mold and the platens to the required temperature, typically about 752 °F (400 °C) and heat the PEEK resin as fast as possible while applying a low cavity pressure of about 290 psi (20 bar).

After the system reaches the temperature that was set, hold the temperature and pressure constant for a length of time, which depends on the size of the molding, to establish homogeneity in the melt.

Increase the pressure to a high setting and switch off the heaters.  Allow the system to cool down naturally to room temperature.  To prevent stresses, cool at a slow, controlled rate of 40 °C per hour or less.  Starting at about 140-150 °C, the part can be demolded.

Post-processing thermal treatment (annealing) is used to relieve stresses in the material.