Manufacturing and tribological properties of sandwich materials with chemically bonded PTFE-PA 66 and PA 66/GF

The sandwich molding process for the production of multi-component shaped parts is gaining increasing importance. With this procedure different materials, such as functional and construction materials, can be combined to form composite construction parts with good load-bearing characteristics.The investigations were performed with a pure PA 66 and 4 different modified PTFE-PA 66 compounds with a PA 66 injection type matrix. The virgin PA 66 granulate was processed without extrusion directly by injection molding under usual processing conditions of PA 66 materials without changes of the technical parameters as compound material and as skin material of the sandwich molded specimen. Compound materials were processed with irradiated PTFE micropowder by reactive extrusion to form chemically bonded PTFE-PA 66 compounds with 20 wt% of irradiated PTFE Zonyl® MP 1100 (DuPont) or Zonyl® MP 1200 (DuPont). These compound materials were also used as skin materials for sandwich molding. The compound material was reinforced with 10 vol.% bronze powder or by aramide short fibers.The tribological investigations were performed as load increment tests using a ring-on-disk test machine. The pressure was increased in each step after a testing time of tB  =  2 h. For the sliding speed of vlowvlow  =  0.01 m/s the pressure increment was Δp = 2 MPa and for the higher sliding speed of vhighvhigh = 0.65 m/s Δp = 0.5 MPa. The tests were carried out at room temperature.The investigations of sandwich compounds with chemically bonded PTFE-PA 66 surface material and glass-fiber reinforced core at different pressures and sliding speeds under unlubricated condition show a decrease of the specific wear rate k in comparison to compact material of the same composition more than the half. The investigation of the morphology of sandwich specimen cross-sections resulted in the fact that with sandwich molding a characteristic property gradient in the function layer is developed which leads to an optimal adjustment of the friction partners during the running-in process. The glass-fiber reinforced core gives a sufficient stiffness effect of the part even at higher pressures. On the other hand the addition of bronze powder as filler or aramide fibers as reinforcement material in compound PTFE-PA 66 materials results in compounds with high mechanical strength and low wear.