ShopPTFE Processing Techniques – Key Differences Among Turning, Mould Pressing, and Extrusion
Sep
Polytetrafluorethylene (PTFE) exhibits extremely poor melt fluidity, making it unsuitable for conventional hot melt injection molding processes. The three main categories of mainstream moulding processes in the industry are as follows: turning, mould pressing and extrusion moulding. There are significant differences among the three types of processes in terms of raw materials, production logic, product precision, physical performance, production capacity and cost, and suitable working conditions. The following section outlines a detailed overview of the distinctions among the three processes through the combination of production practices and application scenarios.
- PTFE turning process
PTFE turning is a secondary mechanical processing technology. It should be noted that this process does not directly result in the formation of powder materials. Firstly, solid PTFE rods, tubes and plates are manufactured using the moulding and sintering processes. The subsequent mechanical processes, including cutting, trimming, grooving and drilling, are performed using CNC or conventional lathes, ensuring precise and consistent results. The excess blank is then removed to obtain the finished products. This processing is a pure mechanical subtraction processing mode.
- Advantages
The primary benefit of this processing is its ability to achieve exceptional dimensional accuracy, control over finished product tolerance and an excellent surface finish. It is capable of processing complex and irregular structures, including special-shaped sealing parts, ultra-thin gaskets, micro sealing rings and precision insulating accessories. The structure is not restricted by moulds and there is no limit to the customization and sampling options. At the same time, the internal structure of the processed product is uniform and there is no stress residue.
- Disadvantages
The raw material loss rate is high, the processing time is long, and the production capacity is extremely low, which means it cannot meet the requirements of large-batch production. The production cost for large plates and standard straight tubes is comparatively high, with cost efficiency only achieving with ultra-thin, special-shaped small parts and ultra-precision products. It is therefore not recommended to process conventional, general-purpose parts in this manner. The turning processing is compatible with scientific research accessories, precision instrument sealing, non-standard gaskets for semiconductors, and small-batch customized components.
- PTFE mould pressing
Compression molding represents the most classic and widely used molding process for PTFE, belonging to an integrated sintering molding process. The precise weight of the pure PTFE suspension resin powder is determined according to the established proportion, and it is then meticulously deposited into the customized closed steel mould, where it is pre-formed by static high pressure at room temperature. Following removal from the mold, the blank is subjected to a high-temperature sintering furnace for constant-temperature crystallization and sintering. After cooling, it is directly formed into a finished product without undergoing secondary cutting processing.
- Advantages
This process relies on mold shaping, featuring extremely high material density, compact structure without delamination, and extremely low internal porosity. The processed product demonstrates robust performance in three core physical properties: compressive strength, creep resistance and sealing stability. It also boasts good resistance to high pressure, strong corrosive media, and long-term exposure to high and low temperature alternating environments. The moulding pressing process is well-suited for the production of PTFE gaskets, flange gaskets, sealing rings, thick plates, blocks, and specially shaped, non-standard molded components. The utilization rate of raw materials is high, with no cutting waste.
- Disadvantages
The limitations of the process are significantly constrained by the mold. The cycle for creating molds is long and the cost of designing a custom mold for irregular parts is high. In addition, complex hollowed structures and ultra-thin-walled parts are difficult to demold and form. The production process involves dual processes of pressing and sintering, resulting in a relatively long production cycle for a single batch. The cost-effectiveness of mass production with standard molds is optimal, while the cost of customizing non-standard small parts is relatively high.
- PTFE Extrusion moulding
PTFE extrusion is categorized into two primary methods: plunger extrusion and screw extrusion. It belongs to a continuous assembly line forming process. PTFE dispersion resin is used as the core raw material, combined with additives for mixing. Long tubular and rod-shaped blank are continuously extruded through high-pressure axial push of extrusion equipment. Following segmentation, the blank is uniformly sintered at high temperature in order to achieve the desired shape. This is the only PTFE process that is capable of automation and continuous production.
- Advantages
This process exhibits ultra-fast mass production, automated assembly line operations, no restrictions on single sets of molds, and continuous production of ultra-long PTFE rods, straight tubes, capillary tubes, long welding rods and other linear products. The process offers the advantages of flexible cutting and fast production speed, while also ensuring the lowest cost for large-scale mass production. The extrusion molding process is perfectly suited to large-scale supply of standardized long strip-type PTFE products.
- Disadvantages
The main disadvantage of this process is that it is unable to produce block-shaped, thick-walled, and irregular non-standard parts. Extrusion processed products have a slightly lower radial density and a greater number of internal trace pores when compared to mould-pressed products. They also have lower high-pressure resistance, creep resistance and corrosion resistance. Extrusion processing of PTFE products results in relatively low dimensional accuracy, a wide tolerance range and an ordinary surface finishing, which makes it challenging to produce precision sealing parts. Therefore, extruded materials are not permitted in high-purity corrosion and high-pressure sealing conditions.
The three types of processes are distinguished by variations in the grades of raw materials, the shrinkage rate of finished products, the potential for subsequent processing, and the service life. In the event of high-pressure corrosion conditions, extrusion moulding should not be used as an alternative to mould pressing. In the case of precision non-standard parts, extrusion molding is not recommended. Achieving cost and service life balance necessitates precise alignment of the process according to application.