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Registered in England & Wales Company number 3275391
V.A.T Registration number GB 684 1384 17
Specialist Fasteners for Sheet Metal
+44 (0) 1302 836010
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Thermoplastics Curing Process Thermoplastic pellets soften and become more fluid as additional heat is applied. The curing process is completely reversible as no chemical bonding takes place. This characteristic allows thermoplastics to be recycled without affecting the materials physical properties. Features There are multiple thermoplastic resins that offer various benefits, but most materials commonly offer high strength, shrink resistance and easy bendability. Pros Highly recyclable Aesthetically superior finishes High impact resistance Remoulding/reshaping capabilities Chemical resistant Hard crystalline or rubbery surface options Eco-friendly manufacturing Cons Generally more expensive than thermoset Can melt if heated Example of commonly used thermoplastics ABS PVC Nylon Polycarbonate Thermoplastics can be further broken down into two categories, amorphous and semi-crystalline polymers. Amorphous polymers have a random molecular structure and do not have a sharp melting point, gradually melting as temperature rises.  ABS and PVC are common examples of amorphous thermoplastics. Semi-crystalline polymers have an ordered molecular structure and do not soften as the temperature rises, having a defined and narrow melting point. This melting point is generally above that of the upper range of amorphous thermoplastics. PET and PEEK are common semi- crystalline plastics. Amorphous polymers: Polymethyl methacrylate (PMMA), Acrylic, Polystyrene (PS),  Polycarbonate (PC), Polysulfone (PS), PVC, ABS Semi-crystalline polymers: Acetal (POM), Polyethelyne (PE),  Polypropylene (PP), Polybutylene terephtalate (PBT), Polyethylene terephthalate (PET),  Polyetheretherketone (PEEK) Nylon (PA) can be amorphous or semi-crystalline depending on the blending.
Thermoset Curing Process Thermoset plastics contain polymers that cross-link together during the curing process to form an irreversible chemical bond. The cross-linking process eliminates the risk of the product remelting when heat is applied, making thermoset plastics ideal for high- heat applications. Features Thermoset plastics significantly improve the materials mechanical properties, providing enhanced chemical resistance, heat resistance and structural integrity. Pros More resistant to high temperature than thermoplastics Highly flexible design Thick to thin wall capabilities Excellent aesthetic appearance High levels of dimensional stability cost effective Cons Cannot be recycled More difficult to surface finish Cannot be remoulded or reshaped Example of commonly used thermoset plastics Phenolic (Bakelite) Epoxies Urea and polyester resins Ultrasonic/Heat Inserts are not suitable for these plastics. Thermoset plastics require the use of Mould- In, Press-In or Expansion Inserts.
THERMOPLASTICS VS THERMOSET PLASTICS While thermoplastics and thermoset plastics may sound similar, they actually have very different properties and applications. Thermoplastics can be remelted back into a liquid, whereas thermoset plastics always remain in a permanent solid state once cured.
Thermoset (Phenolic) Plastics Electrical Junction Box
Thermoset (Phenolic) Plastic Electrical Junction Boxes
Semi-Crystalline Polymer Structure
Amorphous polymer structure
Semi-crystalline polymer structure
POST-MOULD INSERT USAGE GUIDELINES Holes Moulded holes are preferable to drilled holes. The strong, denser surface of a moulded hole increases the performance of the insert. Core pins should be large enough to allow for shrinkage. Unless specified the hole taper should not exceed a 1˚ inclusive angle. Hole Size It is highly important that holes are the correct size. Oversized holes decrease performance, while undersized   holes induce stresses and have the potential for crack formation in the plastic. Undersized holes may also result in flash at the hole edge. Recommended hole sizes should be reviewed if fillers are used. If the filler content is equal to or greater than 15%, it is suggested to increase the hole 0.08mm and if the content is equal to or greater than 35%, the suggested hole increase is 0.15mm. For anything in between an interpolated size increase should be calculated. Hole Depth As a general rule, it is recommended that hole depth for post-moulded inserts be the insert length plus a minimum of 2 thread pitches. Expansion inserts require full screw thread engagement plus 2 full threads protruding from the bottom of the insert to ensure correct function. It is important to ensure that the screw doesn’t bottom out as this would result in jack-out. Boss Diameter / Wall Thickness Boss diameter / wall thickness can affect insert performance. As a general rule, the optimum wall thickness or boss diameter is 2 to 3 times the Insert diameter. The larger the insert diameter, the larger the required wall thickness / boss diameter. The wall thickness must be enough to avoid bulging during installation and for boss diameters to be strong enough for the recommended assembly screw installation torque. Poor knit lines will cause failures and reduced Insert performance. Post-moulded inserts that are cold-pressed into the hole require larger boss diameters and/or wall thickness to withstand the greater stresses induced during installation. Installing the Inserts while the plastic is still warm from the moulding process generally eliminates this need. Counterbores Counterbores are not recommended for any Insert type except for Headed Inserts. Counterbores can be used with Headed Inserts so that the top of the Insert will be flush with the surface of the plastic after installation. The diameter of the counterbore should be 0.5mm to 1.3mm larger than the head diameter of the Insert. The minimum depth of the counterbore should be specified as the thickness of the head. For non-headed Inserts or Headed Inserts installed into a counterbored hole, the top of the installed Insert should be flush with the surface of the plastic part with a recommended maximum protrusion from the surface of 0.13mm. Clearance Hole It is important that the diameter of the clearance hole in the mating component is the correct size, as the Insert and not the plastic must carry the load. The hole in the mating component must be larger than the outside diameter of the assembly screw but smaller than the pilot or face diameter of the Insert. This prevents jack-out. If a larger hole in the mating component is required for alignment purposes, a headed Insert should be considered. Inserts should be installed flush (or no more than 0.13mm above the hole). If the mating component is plastic, the use of a compression limiter should be considered to maintain the preload of the threaded joint. In order for the compression limiter to work properly, it should abut the Insert so that the Insert, and not the plastic, carries the load.
CORRECT Insert Pilot  Mating Hole  INCORRECT Compression Limiter Hole in mating part must be smaller than the insert pilot diameter to prevent the insert from pulling through the assembly (Jack-Out). A compression limiter is highly recommended when the mating component is plastic to maintain the pre-load of the threaded joint.