Polyimide; Tecasint® and Vespel®

Ensinger’s Tecasint® family and DuPont’s Vespel® family of high-performance polyimide resins out perform most engineering thermoplastics in thermally aggressive bearing and seal applications. With or without lubrication these materials function over a wide range of temperatures and stresses while retaining outstanding creep strength, abrasion resistance, and compressive strength. Their superior thermal resistance allows them to carry loads at temperatures beyond the reach of most plastic materials and do so while exhibiting extremely low creep.

The extraordinary properties of Tecasint® and Vespel® make them the optimal choice for thermally aggressive applications in the automotive, off-road vehicle, jet engine and semiconductor manufacturing sectors. Polyimides do not become brittle, even at -400° F and have continuous service temperatures approaching 600° F.  Close tolerance machining can be achieved with standard metal-working equipment with experience, however special techniques are employed to achieve extremely close tolerances and surface finishes less than 10 rms. Typical applications include sleeve and flanged bearings, rotary seal rings, wafer guides and carriers, insulators, valve seats, gaskets and thrust washers.

Grades

Bearing Grade Polyimides most commonly used as bearing and wear components are;

Tecasint® 2021, Vespel® SP-21, where 15% graphite by weight is added to the base resin for increased wear resistance and reduced friction in applications such as bearings, thrust washes, bushings, seal rings, slide blocks and other wear surfaces. These have the highest mechanical properties of the graphite-filled grades.

Tecasint® 2031, Vespel® SP-22, where 40% graphite by weight is added to the base resin for enhanced resistance to wear and friction and good dimensional and oxidative stability. These have the lowest coefficient of thermal expansion of the graphite-filled grades.

Vespel® SP-211, where 10% Teflon (PTFE) and 15% graphite by weight are added to the base resin for the lowest coefficient of friction over a wide range of operating conditions. Vespel® SP-211 has excellent wear resistance up to 300° F.

Vespel® SP-3, where 15% molybdenum disulfide by weight is added to the base resin for bearing and wear components in vacuum and moisture-free environments.

Tecasint® is a registered trademark of Ensinger, Vespel® is a registered trademark of E.I. Dupont

Specifications for Tecasint® 2031 and Vespel® SP-22 (40% Graphite Filled Polyimide) Test Value Units
Specific Gravity, 73°F D792  .0596 Lb/in.3
Tensile Strength @ Yield, 73°F D638  9430 psi
Tensile Modulus of Elasticity, 73°F D638 psi
Tensile Elongation (at break), 73°F D638  2.2 %
Flexural Strength, 73°F D790  12700 psi
Flexural Modulus of Elasticity D790  755.2 ksi
Shear Strength, 73°F D732 psi
Compressive Strength – Ultimate  16,300 psi
Compressive Strength at 2% Deformation D695  6,000 psi
Compressive Strength at 10% Deformation D695  16,300 psi
Deformation Under Load %
Compressive Modulus of Elasticity, 73°F D695  294  ksi
Compressive Strength ⊥ to Laminate (Modulus) psi
Compressive Strength ⊥ to Laminate (Yield) psi
Compressive Strength ⊥ to Laminate (Ultimate) psi
Hardness, Durometer (Shore “D” scale) D2240  84
Hardness, Rockwell (Scale as noted) D785 Rockwell M
Izod Impact, Notched @ 73°F D256 Type A  1.57 ft.lbs/in. of notch
Coefficient of Friction (Dry vs Steel) Static PTM55007  .27
Coefficient of Friction (Dry vs Steel) Dynamic PTM55007  .2
Maximum Static Bearing Load (P) PTM55007  6,000 psi
Maximum Unlubricated No Load Bearing Velocity (V) PTM55007  1,000 ft/minute
Maximum Limiting PV (Unlubricated) PTM55007  300,000 psi x ft/min.
Wear Factor “K” x 10-10 PTM55010 Cubic in.-min/ft.lbs.hr
Sand Wheel Wear/Abrasion Test UHMW=100
Minimum Mating Surface Hardness Rockwell (Brinnell)
Coefficient of Linear Thermal Expansion E-831(TMA)  1.67 in/in/°F x 10-5
Coefficient of Thermal Expansion // to Laminates E-831(TMA)  1.67 in/in/°F x 10-5
Coefficient of Thermal Expansion Perpendicular to Laminates E-831(TMA)  1.67 in/in/°F x 10-5
Softening Point °F
Heat Deflection Temperature 264 psi D648  613 °F
Embrittlement Temperature  <400 °F Min.
Continuous Service Temperature in Air  572 °F Max.
Short Term Service Temperature  600 °F Max.
Tg-Glass Transition (Amorphous) D3418  698 °F
Melting Point (Crystalline Peak) D3418  N/A °F
Thermal Conductivity F433  12.0 BTU-in/(hr/ft2°F)
Dielectric Strength Short Term D149 Volts/mil
Volume Resistivity D257  1012-1013 ohm/cm
Surface Resistivity D257 ohm/cm
Dielectric Constant, 106 Hz D150
Dissipation Factor, 106 Hz D150
Flammability @ 3.1mm(1/8 in.) UL94 UL94  V-0
Arc Resistance seconds
Water Absorption, Immersion 24 Hours D570 (2)  1.2 %
Water Absorption, Immersion Saturation D570 (2)  2.1 %
Machinability Rating  5 1=easy, 10=difficult
Rod Diameter Availability (Call for Availability) 1   3 inches
Sheet Thickness Availability (Call for Availability) .25   2 inches
Characteristics / Attributes Superior Temperature & Chemical Resistance, Highest PV Rating, Excellent Bearing and Wear Properties, High Cost