Threaded Fasteners for plastic - Infastech

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FasTening & assembly soluTions For PlasTic aPPlciaTions Plastics continue to open up a world of design opportunities, yet present some unique fastening problems. Whether you’re fastening plastic to plastic or plastic to another material, Infastech offers a wide selection of high- performance fasteners engineered to meet the requirements of your application. selecTing The righT FasTener With thousands of different polymers available today, there can be no absolute guidelines to follow when fastening these materials. Laboratory testing of fasteners in the subject material is the only way to determine if acceptable performance levels can be achieved. For maximum performance, a fastener should be selected early in the design process. Infastech applications engineers are available to help you every step of the way, from selection and testing to boss design. Why use sPecial FasTeners For PlasTics? Each type of plastic has its own set of performance issues, such as ductility, thermal expansion and clamp retention. Selecting a fastener that can best match these requirements is critical to the overall performance of an application. Type B, type AB and other standard fasteners, with wide flank angles and shallow threads, were designed for use in sheet metal and can not meet the dynamic requirements of plastics. oPTimal PerFormance Fasteners specially designed for plastics can optimize performance in specific types of materials. By selecting the proper fastener, you may obtain: • Higher strip-out torque values • Increased resistance to loosening • Higher pull-out values reduced in-Place cosTs Proper fastener selection may allow the use of thinner bosses and eliminate the need for supplementary locking devices. This can reduce in-place costs through: • Reduced material usage • Reduced cycling times • Elimination of inserts and adhesives • Streamlined assembly
Standard Fastener Typical Boss Design for Standard Screw Fasteners For Pl astic vs. standard scre ws Special Fastener for Plastics Typical Boss Design for Fastener for Plastics MØ 1 MØ2 mØ1 Standard Fastener R 1 R 2 30° 15° 60° S CM 1 mØ 1 CM 1 FRAD 1 60° CM 2 CM 2 mØ 2 Standard Fastener FRAD 2 30° 30° – 48° mØ 2 2 /3S Special Fastener for Plastics Special Fastener for Plastic FRAD = 0.500R FRAD = 0.259R narroW Thread ProFiles maximize PerFormance Type B, type AB and other standard fasteners have a wide thread profile (also called flank angle) of 60°. Special fasteners for plastics have special thread profiles to meet the needs of these unique materials. These narrower thread profiles, ranging from 30° to 48°, reduce radial stress and expansion. This in turn maximizes fastener performance. Because radial stress is reduced, special fasteners for plastics allow the use of smaller bosses than standard screws, as shown at left. Using smaller bosses can reduce your overall costs through decreased material usage and molding cycle times. increased resisTance To Pull-ouT In the illustrations at left, CM represents the area subjected to shear when an axial load is applied. Because the special fastener for plastics has a smaller minor diameter (mø) and a higher thread profile, it contains a larger volume of material (CM) and has a larger axial shear area. This greater area of thread engagement means the special fastener for plastics is more resistant to pull-out. loWered radial sTress PrevenTs boss damage Radial force (FRAD) is an undesirable force since it creates outward stress and can damage the boss. Although the same volume of material is displaced between the 60° thread and the 30° thread, the radial force generated by the 30° thread is approximately one-half that of the 60° thread. In the photo at right, the plastic boss with a 60° thread fastener shows radial stress and subsequent damage. The plastic boss with a special fastener for plastics shows reduced radial stress. Standard Fastener Special Fastener for Plastics 5
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