This screw combines aspects of a “Hi-Lo” screw with a unique thread profile that includes small “steps” around the profile as shown in the image below. This geometry works with the cold flowing (creep) properties of plastic to increase the removal torque, which in turn, improves the security of the connection.Īnother option for high vibration environments is the BosScrew. Plastite screwĪs we can see, this means the screw threads will almost appear as if they’re triangular instead of circular. This screw improves on the standard plastic screw with a tri-lobular shape as shown in the drawing below. The first type of screw we’ll look at in this category is known as a plastite screw. This will result in increased cost, but it will likely improve the quality and durability of the product enough to outweigh any cost increase. If a product is required to operate in a high vibration environment, a specialty fastener will be a good option.
Standard duty screws will not always work in dynamic situations. These screws may be chosen when a designer is constrained by wall thickness, driving torque, or needs improved pullout resistance. On the other hand, the “Lo” threads help reduce driving torque. The “Hi” threads help to improve the pullout resistance and stripping torque, much like a standard screw for plastic. We can see that half of the threads have a larger major diameter than the other half, hence the Hi-Lo name. The screw shown below is known as a Hi-Lo fastener. In addition to thread profile changes, some manufacturers have taken the screw design even further to improve on various factors.
Difference in thread profile for screws designs for plastics When it comes to using a metal screw in a plastic boss, the failure point will almost always be the plastic, so these thread profile changes are important. This difference in geometry is to reduce radial stresses in bosses and increase the pull-out strength of the fastener. Standard Duty Plastic ScrewsĪlmost all screws that are designed for plastics have a narrower thread profile, a coarse thread pitch, and a larger difference between the major and minor diameters when compared to similarly sized screws for metals. Let’s go through some examples of screw fastener designs that are specifically engineered for plastics. But the design intricacies for screwing into different materials are broad. The basic design of a screw fastener is well known-an inclined plane wrapped around a metal dowel. Screw fasteners are among the most common non-permanent fastening methods for assemblies, ranging from automobiles to plastic housings for consumer electronics. These requirements can be driven by factors such as cost, quality, manufacturability, and plastic assembly techniques, as well as technical factors that impact performance, such as corrosion resistance, material compatibility, and conductivity. The approach for choosing the right fastening option should be based on product requirements. This guide will help you choose the best, most cost-effective fastening methods for your plastic product design with all the technological advances that 2022 has brought to the industry.
In this article, we’re going to dive in a bit deeper with a more comprehensive guide to all the options available for plastic fastening assemblies, including:
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Fictiv’s guide to fasteners for 3D printed parts includes an overview of threaded inserts, self-threading screws, how to design threads, captured hex nuts, and cutting threads with a tap.
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