BENEFITS
- Lower installation torque.
- High pull-out force.
- Greater margin of safety installation torque and pull-out force.
- High cut resistance in the joined material.
- Minimizes flow resistance of the thermoplastic material.
- Designed to minimize stresses on the thermoplastic material.
- Highly resistant to vibration and loosening.
- Ability to use smaller bosses.
DESIGN GUIDE
Preparing the bore
When choosing a self-tapping screw, it is important to get the widest possible margin of safety between installation torque and pull-out force. Of course, the shape of the screw, the characteristics of the material, the molding process, the dimensions of the hole, and the installation speed are all factors that have an impact on the decision. In our Technology Center, we have specialized equipment that enables us to assess all these factors, which enables you to select the best screws for the application at hand.
Therefore, we highly recommend conducted pre-production tests and include a widening at the upper edge of the hole. This is important for the following reasons:
- Prevents damage at the boss head;
- Facilitates alignment of the screw in the boss;
- Facilitates repeat installations of the screw;
- Provides an outlet for the extruded material towards the screw head and allows for flush finishes.
N.B. If the design of the mold or the application in an existing boss does not allow for this type of design, we recommend you contact PSM CELADA Fasteners for assistance.
INSTALLATION
ASSEMBLY INFO
To get the best performance out of a self-tapping screw, numerous factors need to be taken into account to avoid problems during production or in operation. To determine the optimal clamping force, you first need to know:
- Tightening torque needed for the first tapping.
- Torque needed to bring the screw head into contact with the component to be joined.
- Clamping force that breaks the joint.
These figures should be determined using specialized equipment that simulates production conditions, because manual testing does not include the effects of the friction generated by high-speed installation. PSM CELADA Fasteners’ technology center is equipped to conduct these tests for you. The precision and repeatability of the torque of the installation tool may vary and must always be taken into account when specifying the recommended tightening torque.
RECOMMENDED SPEEDS FOR INSTALLATION TOOLS
Installation speed is important because speeds that are too high can destroy the material in which the screw is being installed. We recommend a maximum speed of 600 RPMs.
The following is a formula that can be used to determine the optimal torque of the installation tool (Nm):
Ta = Ti + 0.3 (Tp – Ti)
Tm: assembly torque.
Ti: installation torque or torque to cut plastic.
Tp: pull-out torque from the plastic boss.
This formula allows for an ample margin of safety in the mechanical resistance of the joint.
