Fluoroplastic molding
Fluoroplastic molding can be processed plate, rod, sleeve, tape, sealing ring, diaphragm and parts with metal inserts.
Compression molding is divided into three steps: pre-molding, sintering and cooling. Pre-forming is the PTFE powder uniformly added to the mold, pressurized at room temperature into a dense preform (i.e., blank); sintering is the preform is heated above the melting point, cooling is from the sintering temperature down to room temperature process.
Some fluoroplastics are pressurized above the melting point temperature, this molding die, called the hot press mold, the corresponding PTFE mold is called cold press mold.
When molding, attention should be paid to the compression ratio (a Yin PTFE 4-6) and molding shrinkage (generally PTFE 2.6-4.5%) on the impact of products.
Raw materials are best used in the suspension method of polymerization resin, particle size of 20-500 microns of loose fine powder is best. Pressing process must be "deflated", pre-molding pressure of 17-35 MPa, holding time according to the thickness of the blank, such as 100 mm thick blanks, should be held for 15 minutes.
Sintering should be noted: the heating rate can be used 20-120 ℃ / hour, the larger the product, the slower the rate of heating, suspension method of resin sintering temperature is higher, 370-380 ℃, and dispersed method of resin sintering temperature is lower, 360-370 ℃, the sintering temperature is high, the shrinkage rate and porosity increases, the sintering time should be controlled appropriately.
Cooling, the general situation with a slow cooling, speed of 15-25 ℃ / hour, in special circumstances, such as a few thickness of less than 5 mm sheet or push molding of thin-walled tube, only with rapid cooling.
Sometimes the products are annealed at a temperature of 100-120 ℃ for 4-6 hours.
Fluoroplastic roll forming
PTFE diaphragm is roll forming, roll forming can be divided into one-way rolling and multi-directional rolling two kinds of processes, after rolling, PTFE diaphragm from the original opaque self-color, into translucent crystal color.
One-way rolling is to reheat the transparent film, quickly through the calender of the two same rotating rollers for processing. The calendering multiplier is controlled in the range of 1.5-2.5 and the typical roller speed is 20 rpm.
Multi-directional rolling is a molding processing method in which the sintered and quenched film sheet is placed on the calender and calendered in multiple directions to gradually reduce the film thickness. Where the calendering ratio is 2-2.5 range. The temperature of the roller should be controlled at 150-200°C, and the steam pressure is in the range of 0.5-0.9 MPa for steam heating. The calendering ratio is an important parameter, too large and too small for the products are not good. Sometimes it is necessary to repeat a number of rolling, in order to press a good product.
Fluoroplastics injection molding
PFA (tetrafluoroethylene and perfluoroalkyl vinyl ether **** polymer), that is, fusible PTFE, can be injected. Its processing temperature is wide, up to 425 ° C, its decomposition temperature of 450 ° C or more, the general control of the processing temperature range of 330-410 ° C. The temperature is the highest temperature, and the decomposition temperature of 450 ° C or more.
PFA's hygroscopicity is very small, 0.03%, so do not have to dry, before injection, inserts should be preheated to 140 ℃ or so, the injection barrel of three temperatures: 200-210, 300-310, 350-410 ℃,, the nozzle temperature is slightly lower than the barrel temperature is the highest temperature, the mold temperature of 140-230 ℃, the injection pressure of 40-90 MPa, injection speed should be a little slower, holding time should not be The injection speed should be a little slower, and the pressure holding time should not be too long. Cooling time is 40-150 seconds.
Fluoroplastics secondary processing technology
By the processing characteristics of fluoroplastics, so that some products are difficult to a molding, but also must be processed through the secondary process in order to get the finished product can be used. Secondary processing techniques are: cutting, welding, lining, blowing and so on.
Cutting: similar to the metal cutting methods, equipment such as lathes, drilling machines, planers. Note that before cutting, the blank body must be left for 24 hours before proceeding.
Welding: hot compression welding and hot air welding rod welding two kinds. Hot compression welding, to be in a special clamp, heated to more than 327 ℃, and at the same time pressurized in order to weld.
Hot air welding rod welding is the use of PFA to defend the rod, heating and pressurization through the PFA and connect the two pieces together.
Lining: generally with polytetrafluoroethylene and polyperfluoroethylene propylene (written F4 and F46) plastic lined with ferrous metal pipe and pipe fittings, can be used for chemical corrosion-resistant materials.
Blow-up: products for the bellows and heat-shrinkable tube, heat-shrinkable film, etc.. Also divided into continuous blowing and intermittent blowing.
For example, F46 heat shrinkable tube billet using water-cooled vacuum shaping method of preparation, pipe stretch ratio of 3-7, molten cone length control in 10-20 mm, blowing mold temperature 80-160 ℃, blowing pressure of 0.1-0.2 MPa, hauling line speed of 80-500 mm / min. Others are blowing F4 spiral pipe.
such as PTFE machine tool guide soft belt: PTFE fine granular material with suspension method, mashed, 20 mesh sieve, bronze powder or aluminum powder particle size of 200 mesh, for 100 mm high blank holding pressure for 5 minutes, the middle of the bleeder three times, the sintering temperature rate of 50-60 ℃ / hour, at 320 ℃ when the insulation for 1 hour, cooling down to 150 ℃ when out of the furnace. Before turning the blank, it should be preheated to 80 ℃ and held for one hour before proceeding. Soft tape should be treated with sodium naphthalene, of which 51 grams of naphthalene, 100 ml of tetrahydrofuran, appropriate amount of sodium metal, soft tape less than 1 mm thick in sodium naphthalene treatment solution for 1-3 minutes, and then rinsed with hot water at 90 ℃.
such as PTFE can be **** mixed into polyphenylene, polyimide, poly parabens, while filled with graphite, molybdenum disulfide, bronze powder can be applied in the hydraulic gate, fluorine plastic 46 can be used in the corrosion-resistant ball valves, its molding temperature 320-350 ℃, molding pressure 3-30 MPa, stereotypes insulation temperature of 120-150 ℃.
And glass fiber reinforced PTFE pipe as a steel pipe lining, can solve the problem of pipeline corrosion, the process is as follows:
PTFE resin → pounding and sieving → but the pressure molding → sintering and shaping → tube cylindrical turning → detection → surface activation treatment → glass fiber reinforced plastic → mounting flange → package flange → curing → flange head turning → stripping the mandrel → mounting gaskets → flanging → finished products
Such as polyvinylidene fluoride sealing ring: add 1 part of acid-absorbing agent, mixed ball mill for 24 hours, in the template temperature of 195-250 ℃ press, Xu Xu pressure to 2.5-3.5 MPa, the middle of the bleed 1-2 times, the mold temperature rises to 180-190 ℃ when the rapid move to the cold press at 14 MPa pressure cooling, 50 ℃ when taken out, trimming burr, and then into the 130 ℃ oven, heat treatment for 24 hours, can be inspected and packaged. Can be inspected and packaged.
And fluorine plastic varieties developed as: fluorine-containing epoxy resin (used in optical communication systems), perfluoroelastomer (used in semi-conducting rest equipment), thermoplastic fluorine elastomers (used in medical care, cable coatings), perfluorinated polyethers (used in high and low temperature resistant grease). There is also polyfluoroethylene solvent-free processing, only 9 parts of lubricants, 4 parts of heat stabilizers, 2 parts of other additives can be added to the molding process.