The PT® SCREW is a direct screw fastener for use in thermoplastics. The key design aspects include a profiled thread root to assist plastic flow, a 30° flank angle to reduce boss bursting forces and an 8° pitch angle which combine to give low installation torques with high stripping torques. For those applications not requiring the high levels of thread re-use and high clamping torque, (properties associated with threaded inserts) PT® screw offers an economical solution to plastics assembly and has distinct advantages over other direct screw fixings.
Advantages
- Reduced installation torque.
- High stripping torque.
- Greater safety margin between installation torque and stripping torque.
- High parent material shear strength.
- Minimises material flow resistance.
- Designed to reduce stress within the thermoplastic to an absolute minimum.
- High resistance to vibration and relaxation
- Allows for smaller bosses.
Advantages
When choosing a direct screw fixing, one of the major criteria is to obtain the maximum margin between driving torque and stripping torque. Screw design, material characteristics, moulding practice, hole size and installation speed all have an influence.
The specialised equipment necessary to measure the effect of these factors is available at P.S.M’s Technology Centre.
This allows customers to obtain the best design possible. Pre-production testing is therefore strongly recommended. Please note the inclusion of a counterbore – this is important for the following reasons:
- Prevents damage to the top of the boss
- Helps alignment of the screw in the boss
- Assists in repeated assemblies of the screw
- Acts as a relief for any material extruded to the head of the screw and allows flush finishes.
N.B. If moulded tool design or application into an existing boss renders the recommended boss design impractical, please contact P.S.M for specific advice.
8° OPTIMUM PITCH ANGLE
- Lowest installation torque/highest stripping
- Maximum resistance to vibration loosening and material relaxation in the component
PROFILED THREAD ROOT
- Improved plastic flow reduces stress, providing long term reliability
- Greater surface area contact between screw thread and plastic, to give a high shear and stripping torque
- Lower installation torques
30° COMBINED FLANK ANGLE
- Lowest installation torque/highest stripping
- Greater thread penetration into the plastic material, permitting enhanced clamping torque.
- Reduced centre of pressure, producing lower installation torque.
Resolution of Resultant Forces for the Same Volume Displacement
F Rad 1 = 0.500R
F Axl 1 = 0.867R
F Rad 2 = 0.259R
F Axl 2 = 0.966R
DESIGN RECOMMENDATION
* Where materials are known to be sensitive to environmental stress cracking, ageing tests should be carried out as recommended by the material manufacturer.
TORX PLUS®,TORX® and AUTOSERT® are registered trademarks of Camcar Division of Textron Inc.
STANDARD RECESS STYLES
Other shown on available optional recesses features are page.
MATERIAL
Through Hardened & Tempered Steel
STANDARD FINISHES
Zinc Plate and Clear Passivation (Z) Zinc Plate and Chromate (ZC)
Zinc Plate and Black Chromate (ZBC) Stainless Steel (SS)
Stainless Steel 316 (S6)
OTHER FINISHES
-Available to order.