Introduction to Polytetrafluoroethylene (PTFE) Molding Technology
2020-03-20
PTFE primarily utilizes the most common molding techniques, including compression, hydraulic pressing, extrusion, calendering, and coating, as well as bonding, welding, and winding. The first five methods involve directly processing PTFE resin into finished products, while the latter three use PTFE plastic sheets or tapes to create a variety of items. In addition to these, there are also forming methods such as roll pressing and thermal molding. Below is a brief introduction to each of these molding techniques:
01 Molding Method
Mold pressing typically uses suspension resin, but when producing thin sheets thinner than 1.5 mm, dispersion resin is employed instead. The process involves the following steps: resin—screening (suspension resin is crushed and loosened, then passed through a 20-mesh sieve)—pressing machine (PTFE powder loaded into a mold is compacted under a pressure of 20–235 MPa)—sintering (the molded part is sintered in a furnace at a temperature of 370°C–380°C)—final molding (after cooling and shaping either inside the mold or in a free state, the material takes the desired form, such as plates, rods, tubes, gaskets, and packing products).
02 Hydraulic Method
The hydraulic method, also known as the isobaric method or rubber-bag method, is a specialized technique used to produce PTFE products. It involves applying hydraulic pressure to a rubber bag, which then forces the PTFE resin to expand uniformly into the mold, compacting it before sintering into the final product. The process typically proceeds as follows: Place the rubber bag inside the outer mold, connect it to a water pump, and slowly fill it with tap water until the bag inflates into a cylindrical shape. Next, evenly distribute the PTFE resin between the bag and the outer mold, close the mold, and continue pumping water to gradually increase the pressure—reaching 12–13 MPa—and hold this pressure for 30 minutes before releasing the water. Finally, reduce the pressure, remove the mold, sinter the material, and allow it to cool, resulting in a smooth, high-quality preform ready for further processing.
03 Push-Pull Method
Push molding, also known as paste extrusion molding, involves mixing a dispersed resin screened through 20-30 mesh with an organic liquid (such as toluene, petroleum ether, or solvent oil) to create a paste-like mixture at a ratio of 1:5. This mixture is then pre-compressed into thick-walled cylindrical blanks, which are placed inside the barrel of a push-molding machine. The material is heated, and a plunger is used to push it into shape. After drying, the molded parts are sintered at a temperature range of 360–380°C, followed by cooling to produce robust and durable products such as push-molded tubes and rods.
04 Extrusion Method
Extrusion molding can be divided into two types: screw extrusion and plunger extrusion. After the pre-sintered resin, which has been crushed and screened, is added to the barrel, it is compacted and conveyed into the extruder either by the rotation of a screw or the reciprocating motion of a plunger. At a temperature range of 360–400°C, the material is continuously extruded, sintered, and then cooled to produce various tubular and rod-shaped products.
05 Spray Coating Method
The spraying method includes two processes: one involves sintering a film formed after PTFE emulsion is sprayed, and the other uses direct plasma spraying of PTFE resin powder to create a film.
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