Molding is a common process to produce semi-finish parts, or basic shapes. This process is adapted to all materials, including high performance plastics. Even PTFE is easily molded, even if this particular fluoropolymer requires its own equipments.
Molded parts with specific tools for quality and performance
Molding of high performance plastic is an essential step to produce basic shapes, semi-finished or finished parts (after machining for example). Plastic or compound is compressed and heated in mold of desired shapes. PTFE molding process is slightly different, as the part is heated after compression (see below).
For high performance polymers, with high melting temperature, dedicated tools are needed, and strong know-how in cooling behavior and cristallinity is required to design the materials for its use. Indeed, in the same polymer family, different grades will show drastically modified properties, hence use cases.
Cost constraints of high performance polymers are also at stake in the molding process. The right mold design and molding process parameters allow limited or even no scrap to reach tolerances on final parts. This is highly critical as high performance polymers are quite expensive compared to engineering plastics.
Usually, molding process is preferred to extrusion when highly cohesive parts for demanding applications. Such applications can be linked for example to crack reduction, permeability, or flexlife. In some cases, a post-treatment, for example curing, can also be a complementary solution, to achieve even better performances. For example, X850 is a molded PCTFE to reduce crack compared to extruded PCTFE, and X860 is a post-treated PCTFE to reduce even further the risk of cracks.
PTFE molded parts require an impacting extra step
PTFE is a really specific thermoplastics, as it shows ultra high viscosity above melting point. Thus PTFE can’t be directly melted.
PTFE requires then specific processes. It is first shaped with presintered forms : PTFE powder is first compressed to the desired shape, in the corresponding mold, then left to dwelling. Only after these steps, the presintered form is sintered in oven above PTFE melting point. Strong knowledge of PTFE grades or compounds, and calculation of presintered form during this step are essential to produce state of the art parts, at a competitive price. Molds and sintering processes are designed to diminish or even delete machining for fine tolerances.
For enhanced performance, different molding technologies are available. The most common molding process of PTFE is based on axial molding, where molding pressure is applied on ends of the mould. For more complex parts and better properties, one solution is isostatic molding, where the mold is fitted in a chamber fitted with fluid. When pressure is applied to the chamber, it is equally applied on all the surface of the mold, thus allowing uniform properties.
Such know-how in the particular transformation steps, developed at 3P for more than 50 years of PTFE transformation, is also a strong asset in molding solutions for the other high performance plastics, including the 3P’s Xytrex® range.