Fabrication Techniques for Fluoropolymers

It is sometimes necessary to bond the fluoro-polymer parts to themselves or to other materials. Of course these polymers are known for their nonstick properties and must be rendered adherable. Machining and treatment for adhesion are two examples of finishing techniques routinely applied to fluo-ropolymer parts. This chapter describes a number of techniques commonly used to finish parts made from fluoropolymers. 

Dimensions of PTFE parts should be measured at a specified temperature due to the large dimensional change (1.3%) that takes place between 0°C and 100°C.[ 1 

Other than poor thermal conductivity, fluoropolymers have much higher coefficients of linear thermal expansion than metals. This means that any type of heat buildup will cause significant expansion of the part, resulting in overcuts or undercuts, thus deviating from the desired part design. 

PTFE stock shapes may require extensive machining to produce complex shapes. Coolants should be applied to remove heat if the surface speed of the tool exceeds 150 m/min. At higher speeds, low feeds are helpful in reducing heat generation. Surface speeds between 60 and 150 m/min are satisfactory for fme-fmish turning. At these speeds, feed should be run between 0.05 and 0.25 mm per revolution. At higher speeds than 150 m/min, feed must be dropped to a lower value. 1 1 

Other considerations include material support, especially when turning long thin stocks due to the flexibility of PTFE. Another issue is the characteristics of machined resin, which tends to be continuous and 

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Failure of parts, irrespective of plastic t5 e, is an inevitable fact of the operation of chemical plants. Fluoropolymers are no exception in spite of their excellent chemical, thermal, and mechanical properties. These plastics form the processing surfaces of equipment where they are exposed to the most aggressive and corrosive chemicals. The repeated exposure of fluoroplastics to these chemicals, in addition to other factors, can affect the integrity and surface quality of the parts. The chapters dealing with properties and part fabrication techniques of fluoropolymers should be consulted extensively. An understanding of the limitations of fluoropolymers and flaws created by fabrication methods is required for successful failure analysis of parts. 

Part Two describes the fabrication techniques for various fluoropolymers. They include perfluoroalkoxy polymer (PFA), fluorinated ethylene-propylene polymer (FEP), polyvinylidene fluoride (PVDF), ethylene-tetrafluoroethylene copolymer (ETFE), ethylene-chlo-rotrifluoroethylene copolymer (ECTFE), and polyvinyl fluoride (PVF). Major fabrication techniques including injection molding, extrusion, compression... 

The brief description of the commercially important fluoropolymers indicates the techniques by which they can be fabricated. Generally, the processing method is dependent on the rheology of the fiuoropoly-mer in question. Table 3.6 summarizes the structure-rheology-fabrication technique characteristics of various copolymers. Melt viscosity values represent a wide range of shear rate for melt processible polymers in Table 3.6. Volume One focuses on fluoropolymers which are processed by non-melt methods.The present volume is devoted to the melt processible fluoropolymers. 

Simplicity and promise of low cost—Fuel cells are extremely simple. They are made in layers of repetitive components, and they have no moving parts. Because of this, they have the potential to be mass produced at a cost comparable to that of existing energy conversion technologies or even lower. To date, the fuel cells are still expensive for either automotive or stationary power generation, primarily because of use of expensive materials, such as sulfonated fluoropolymers used as proton exchanged membrane, and noble metals, such as platinum or ruthenium, used as catalysts. Mass production techniques must still be developed for fabrication of fuel cell components and for the stack and system assembly. 

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