Self-tapping screws develop their own threads as they penetrate into and below the surface of a material. Screws used to drill into plastic require a uniquely designed profile to ensure the structural integrity of the assembly is not damaged. Tapping screws designed for use with steel may induce residual stresses in plastic that diminish the material’s structural soundness. At ITW Shakeproof Industrial, we are your source for the best self-tapping screws for plastic, including thread forming and thread cutting self-tapping screws.
Plastic screws provide enhanced flexibility and enable quick assembly of components using a smaller number of fasteners. These screws provide a cost-effective method of joining plastic to metal or plastic to plastic, and also allow easy assemble and disassembly.
Self-tapping screws used for plastic material applications are organized into two general categories. These are thread forming and thread cutting. Choosing the best self-tapping screw between these two categories depends on the type of plastic into which you are fastening. These are thermoplastic and thermoset.
Thread Cutting Screws
Thread cutting self-tapping screws are designed to operate effectively in thermoset material. These screws feature a sharp cutting edge that cuts through plastic when the screw is drilled into a pilot hole, creating a threaded joint. Thread cutting screws also include a smaller flank angle. This decreases the torque to install while increasing surface area, resulting in a greater pullout force. The result is lower internal stresses than are present with thread forming screws, making thread cutting screws ideal for stiffer plastic that has a higher flexural modulus.
For a successful thread cutting screw installation into plastic, the proper depth and pilot hole diameter must be used. The depth of the hole must be deeper than the length of the screw engagement to provide space for the displaced material to move. Thread cutting self-tapping screws are susceptible to thread stripping during the process of disassembly.
Thread Forming Screws
Thread forming screws are more effective with thermoplastic materials than thermoset materials. These screws do not generate waste during installation. The displaced plastic which creates the thread moves back into the thread root, providing a tight, secure fit. Taptite self-tapping screws are a type of thread forming screw that pushes the material back around the screw during elastic recovery.
A pilot hole is required when installing thread forming screws into plastic. They don’t have a pointed tip. Due to the displaced plastic flowing around the screw threads, the thread profile angle and thread engagement (overlapping amount) are vital.
Since thread forming screws produce high internal stresses from the deformation of material, rather than its removal, they are only suitable in soft polymers with a lower flexural modulus.
For information about the selection of thread cutting and thread forming screws, including Taptite self-tapping screws, we offer for plastic material applications, call us today at 920.261.2652 or reach us through our contact form.
