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DMS Seals: Classification and Application of PTFE

DMS Seals: Classification and Application of PTFE

2022-11-29

There are many kinds of materials for sealing rings and sealing parts. 

Today, DMS Sealing will introduce one of the materials of sealing rings to you.


PTFE resin is mostly powder or dispersion.


PTFE powder resin is a white, odorless, tasteless, non-toxic powder. When processed into products, it becomes a transparent or opaque white material, waxy and non-hydrophilic, smooth and non-sticky, and looks like polyethylene. Its density is as high as 2.14g/m3, which is the heaviest among plastics.


There are three main categories of PTFE: suspension resin, dispersion resin and concentrated dispersion. In my country, the suspension method resin accounts for about 66.81%, and the dispersion method resin accounts for 31.19%.


4.1 Application of Suspension Method PTFE


Suspension method PTFE is mainly used in the manufacture of sealing rings, gaskets, etc. for the machinery industry, as well as pumps, valves, pipe fittings, and equipment linings for chemical equipment, as well as electrical insulating parts, films, etc.


Suspension method PTFE is generally divided into the following three categories:


(1) Micropowder:


The average particle diameter is 20-35 μm, which can be used for compression molding.


(2) Granulation material:


It has good powder fluidity and high apparent density. Coarse particles (particle size about 300μm) are used for automatic compression molding and hydraulic molding, and can also be used for general compression molding.


(3) Pre-sintered material:


It can be processed into thinner and thinner products by plunger method. Such as rods with a diameter of 5-50mm, pipes with a wall thickness of 3-25mm, etc.


In addition, the suspension method PTFE can also be processed into ultra-fine particle size powder with a fineness below 10 μm. DLX-6000 of Mitsui DuPont Fluorine Chemicals Company and L-168, L-169, L-170, L-171 of Asahi Glass Company are such products. Their main use is as a dry powder lubricant. At present, with the continuous improvement and improvement of performance, this kind of resin is expanding its application range day by day.


4.2 Application of dispersion method PTFE


Dispersion method PTFE is mainly used in the manufacture of corrosion-resistant, high-temperature-resistant, high-dielectric wires and cables. In the chemical industry, it is mainly used to make threaded sealing raw material belts, pipeline linings, etc.


(1) High compression ratio powder:


It is extruded under the condition that the compression ratio is greater than 2500:1. It is suitable for processing into thin-walled thin tubes and wire insulation sheaths with a diameter of less than 2mm and a wall thickness of 0.2-0.5mm.


(2) Medium compression ratio powder:


Extruded under the condition of compression ratio greater than 400:1, it is suitable for processing into medium-sized thin-walled tubes with a diameter of 2-15mm and a wall thickness of 0.5mm or more.


(3) Low compression ratio powder:


Extruded under the condition that the compression ratio is less than 300:1, it is suitable for processing into thicker pipes and thick rods with a diameter of more than 5mm for making sealing raw material belts.


4.3 Application of PTFE Concentrated Dispersion


PTFE concentrated dispersion is mainly used as anti-stick coating and impregnated glass cloth, asbestos, etc. in food, textile, printing and dyeing, papermaking and other industries.


In addition, it can also be used for glass fiber and porous materials.


4.4 Overview of classification of PTFE products


(1) PTFE tubing: it can produce miniature thin-walled capillary tubes, push tubes, plunger extrusion tubes, etc. At present, the maximum diameter of the domestic plunger extrusion pipe is 320mm, and the length is 4-6m.


(2) PTFE plate: The maximum area of the molded plate can reach 1.2×1.2m2. Turning plate: turning with isobaric forming blank, the plate width can reach 2m, and using molded blank, plate width is 1.5m.


(3) PTFE rods: various general-purpose rods can be produced. The length of molded bar can reach 1.5m, that of isobaric molding can reach 2m, and that of plunger extrusion method can reach 4-6m.


(4) PTFE film: PTFE film has oriented film, non-oriented film and semi-oriented film. At present, the widest domestic film can reach 600mm.


(5) PTFE-impregnated glass cloth: PTFE-impregnated glass cloth is limited by the base material (glass cloth) and equipment. At present, only products with a width of 1.5m can be produced. At the same time, PTFE-impregnated glass cloth that can be bonded can also be produced.


(6) Expanded PTFE rib sealing tape: PTFE rib sealing tape has a thickness of 0.075-0.1mm and a width of 13, 22, 26, 52mm and other specifications. Many domestic units can produce and export in large quantities.


(7) Biaxially stretched PTFE microporous membrane and its composite materials: PTFE microporous membrane can be used as a filter material for the filtration of ultra-pure reagents, with a pore size of 0.1-1 μm; it can also be combined with fabrics to make advanced waterproof and moisture-permeable Clothing fabrics and high temperature resistant filter materials. Composite material width up to 2m.


(8) Expanded PTFE sealing tape, packing, and stuffing rod: used as sealing material for chemical anticorrosion, etc., the service temperature is -218~320℃; among them, the thickness of the sealing tape is 0.5~5mm, and the maximum width is 80mm. The diameter of the filler rod is 1-25 mm.


(9) Polytetrafluoroethylene fiber: fabrics made of PTFE fibers are used as filter materials abroad, and samples of PTFE fibers and fabrics are available in China.


(10) Filled and modified polytetrafluoroethylene products: In order to improve the creep characteristics and wear resistance of PTFE, PTFE is filled and modified. The main materials are graphite, carbon black, molybdenum disulfide, glass fiber, carbon fiber, polyester Phenylsulfide, etc.


(11) PTFE bellows and reinforced tubes: bellows and fiber or steel wire braided reinforced hoses made of secondary processing, with high and low temperature resistance, pressure resistance, corrosion resistance, non-stick and long service life, etc. features. Hose connections for hydraulic, pneumatic, vapor delivery, etc.


(12) Fluorine-containing plastic coatings and coatings:


1. Fluorine-containing plastic coatings: Fluorine-containing plastic coatings have many characteristics of fluorine-containing plastics, mainly including anti-stick coatings, anti-corrosion coatings, hidden sound, noise reduction, hydrophobic and oleophobic coatings. Widely used in aerospace, aviation, papermaking, petrochemical, light industrial machinery, medical and health, food machinery, ships, etc.


2. Fluorine-containing plastic non-electroplating coating: PTFE particles are plated on the surface of the metal substrate during the nickel-plating process by electroless plating. The thickness of the coating is 5-25 μm, and the surface hardness (HV); the untreated one is 150- 250; 300-400 after heat treatment. The coating does not fall off, does not peel off, has self-lubricating properties, and the friction coefficient is below 0.25.


4.5 Application fields of PTFE


Teflon is the heaviest of the plastics. It has a series of unique properties such as wide temperature range (-250~260°C), good chemical stability, excellent dielectric properties, self-lubrication and anti-sticking properties, so it has a wide range of applications.


It can be used as an anti-corrosion material in the chemical industry, and can be used to manufacture various anti-corrosion parts, such as pipes, valves, pumps and pipe fittings. In terms of chemical equipment, it can be used to make linings and coatings for reactors, distillation towers and anti-corrosion equipment.


Mechanically, it can be used as self-lubricating bearings, piston rings, oil seals and sealing rings, etc. Self-lubrication can reduce wear and heat of parts, and reduce power consumption.


In terms of electronic appliances, it is mainly used to manufacture various wires and cables, battery electrodes, battery separators, printed circuit boards, etc.


Among medical materials, it can be used as a material for various medical devices and artificial organs by virtue of its heat-resistant, water-resistant, and non-toxic properties. The former includes sterile filters, beakers, and artificial cardiopulmonary devices, while the latter includes artificial blood vessels, hearts, and esophagus.


Compared with other plastics, PTFE has the characteristics of chemical corrosion resistance, and it has been widely used as sealing material and filling material.


PTFE is used as an engineering plastic and can be made into PTFE tubes, rods, strips, plates, films, etc. It is generally used in corrosion-resistant pipes, containers, pumps, valves and radar, high-frequency communication equipment, radio equipment, etc. with high performance requirements. The dispersion liquid can be used as an insulating impregnating liquid for various materials and as an anti-corrosion coating on the surface of metal, glass, and pottery, etc. Various PTFE rings, PTFE gaskets, PTFE packings, etc. are widely used in various types of anti-corrosion pipeline flange sealing. In addition, it can also be used for spinning, polytetrafluoroethylene fiber - fluorine (foreign trade name is Teflon).


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