Rebling has used many grades of polycarbonate for demanding, close tolerance, plastic injection molding applications. Polycarbonate is an amorphous thermoplastic formed by the mixture of Bisphenol A and Carbonic acid. Being an amorphous material, it is available in a wide range of opaque, translucent and transparent colors, lending to its use in applications such as lighting fixtures and optical lenses. For exact color matching requirements of this plastic injection molding material, the wall thickness of the part will influence the shade and color density, with thicker cross sections being darker. Rebling has molded polycarbonate parts for aircraft, telecommunications, electronics and appliance applications. We routinely mold grades ranging from general purpose unfilled grades to glass fiber reinforced grades in concentrations from 10 to 40 percent. Rebling is also experienced at plastic injection molding FDA approved grades, flame retardant grades, internally lubricated grades and UV resistant grades that withstand outdoor applications or where UV radiation is a concern.
Rebling can maintain precise dimensional control when plastic injection molding Polycarbonate because of its predictable uniform mold shrinkage. Glass filled grades exhibit mold shrinkage typically around .3%. Polycarbonate is not considered a good bearing material, but when formulated with an internal lubricant such as PTFE, it has been successfully used in bearing applications.
Properties of Polycarbonate plastic
General purpose grades of polycarbonate used in plastic injection molding typically exhibit Heat Deflection Temperatures of 270°F at 264 psi. Adding glass fiber reinforcement will increase the Heat Deflection Temperature by 25°F; increase rigidity but lower impact strength, an important property of polycarbonate in many applications. The coefficient of thermal expansion for unfilled grade is 3.75 x 10-5 in/in/°F dropping to 1.49 x 10-5 in/in/°F for a 20 % glass filled grade. As with all amorphous thermoplastics used in plastic injection molding, the mechanical properties of polycarbonate such as tensile strength, flexural strength and flexural modulus decrease steadily with increasing temperature, while the impact strength drops dramatically as temperatures approach 0°F.
The chemical resistance of this high impact material, as with all plastic injection molding materials, is an important design consideration. In general, it is stable in organic and mineral acids, but will decompose in strong alkaline solutions, aromatic and chlorinated hydrocarbons. Stress crazing is another consideration when Polycarbonate is used in a high stress, moist hot water environment.
Secondary Operations for Polycarbonate plastic parts
Polycarbonate can be readily machined and Rebling is able to provide a full range of secondary machining operations, such as turning, drilling, tapping and grinding, as well as ultrasonic insertion, ultrasonic welding, pad printing and assembly. When designing parts that are to be fastened, it is recommended that self-tapping vs. thread forming screws be used. For repeated assembly and disassembly, threaded metal inserts should be used. Ultrasonically installed insert is preferred over a molded-in insert as the knurls on a molded-in insert can cause notch effects on the plastic, reducing its strength.