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Soft PVC pipe knowledge

Soft PVC pipe

Soft PVC pipe is made of PVC resin by adding a large amount of plasticizer, a certain amount of stabilizer and other additives, and then extruded. Soft PVC pipe has excellent chemical stability, excellent electrical insulation properties and good flexibility and coloring. This kind of pipe material is commonly used to replace rubber pipes, used to transport liquids and corrosive media, and also used as cable sleeves and wire insulation.
Chinese name soft PVC pipe material pvc resin, plasticizer, stabilizer characteristics chemical stability, electrical insulation, flexibility suitable for transporting liquids and corrosive media
table of Contents
1 Raw materials and formula
2 Product standards
3 Classification
4 Production process
5 Process flow
6 Equipment and features
Raw materials and formula editing
Generally, SG-2 ~ SG-4 (namely XS-2 or XS-3) and other loose medium viscosity PVC resins are used. Because the loose resin is easier to plasticize than the compact resin, the medium viscosity resin can not only maintain better physical and mechanical properties of the product, but also have better fluidity during molding. The typical formula of soft PVC pipe is shown in the table.

Product Standards
The soft PVC pipe adopts GB / T 13527. 1-92 (liquid transportation) or GB / T13527.2-92 (for wire insulation). Medical soft PVC tubing implements the national standard GB 10010-88.
classification
Soft PVC pipe is also called PVC hose. It is a kind of engineering or civilian hose formed by processing PVC resin as raw material. It can be divided into PVC steel wire reinforced hose and PVC fiber according to the material used for reinforcement. Reinforced hoses (since most fiber reinforced materials are polyester, they become PVC polyester reinforced hoses), PVC plastic reinforced hoses (that is, PVC resin reinforced hoses, plastic reinforced hoses). Due to the different arrangement of the reinforcing materials in it, there are PVC steel wire spiral reinforced hose, PVC fiber spiral reinforced hose, PVC resin spiral reinforced hose (bead tendon), PVC steel wire mesh reinforced hose, PVC fiber mesh Reinforced hose and composite reinforced hose, such as PVC steel fiber composite reinforced hose. It can also be divided into conventional PVC hoses and PVC anti-static hoses, PVC insulated pipes, PVC anti-wear hoses, PVC high-pressure hoses, PVC high-temperature hoses, PVC low-temperature hoses, etc. PVC fire hose. In addition, it can be called PVC fluid pipe according to the medium it conveys, and can be divided into several categories, such as PVC air hose, PVC gas hose, PVC oxygen hose, PVC acetylene hose and so on. It can also be divided into PVC single pipe or PVC double pipe according to the different arrangement forms. PVC double pipe is mostly used for gas welding and gas cutting, such as PVC oxygen acetylene double pipe. In addition, it can be divided into PVC transparent hose, PVC color tube, and Hose tube (household PVC tube) according to whether it is transparent, appearance color, and commonly used places.
In addition to the better reinforcement effect, the PVC hose with mesh reinforcement can also avoid twisting, so it is also called PVC anti-twist hose or PVC anti-twist mesh reinforced pipe.
Production Process
Synthetic hose with green soft PVC inside and white hard PVC outside
Synthetic hose with green soft PVC inside and white hard PVC outside
The production process of soft PVC and hard PVC is slightly different. Because the most plasticizer of NPC is added to the formulation of soft products, kneading plasticization is an important part in the production of soft PVC pipes. During the kneading process of soft PVC, in order to make the resin swelled by the plasticizer and make the kneading material evenly dispersed, it is necessary to pay attention to the order of addition. When adding a certain amount of filler (such as CaCO3), the resin and plasticizer should be mixed first. If the resin and the filler are mixed first, and then the plasticizer is added; because the particle structure of the filler is generally more loose than the resin, when both are present, the plasticizer first penetrates into the filler particles, and The resin cannot be fully swelled. Kneading generally uses "Z" type kneading machine, jacket heating, vapor pressure is about 0.24 ~ 0.39MPa. Knead for 50 ~ 60min. After kneading, it should be turned frequently to prevent the resin from overheating and decomposing itself. After the kneading material is pelletized, it is sent to the extruder to extrude the pipe. The extrusion temperature can be slightly lower than the temperature of the extruded PVC pipe.
Process flow
(1) The extruder chooses SJ65-B, the head chooses straight-through type, the head compression is larger: 2.5: 1; the length to diameter ratio is: L / D value is 25: 1; the screw groove is equidistant. Equal depth.
Recycled soft PVC has a low melt viscosity and good fluidity, so the compression ratio of the machine head is controlled at 10-20, the length of the straight part of the mouth membrane is about 10-20 times the wall thickness of the hose, and the size of the core membrane is comparable to the inside , The outer diameter is expanded by 10% to 20%. After extruding the PVC hose, it needs to be stretched to reach the required pipe diameter. The cooling method uses spray cooling water to cool, and the spraying position is 20-40mm away from the machine head.
(2) The temperature control range of each section of the extruder when extruding PVC hose:
Feeding section: 100 ° C-120 ° C; compression section: 120 ° C-140 ° C; homogenization metering section: 140 ° C-160 ° C; shunt: 140 ° C-160 ° C; mouthpiece: 160 ° C-180 ° C.
(3) Selection of screw speed:
Due to the good melt fluidity and easy plasticization of regenerated soft PVC, the screw speed is faster than that of hard PVC. Generally, the screw speed of an extruder with a screw diameter of 65 mm is (30 ± 10) r / min. Because the vent hole is connected to the outside air, no compressed air is used in the processing, and it will not cause adhesion and the diameter of the pipe is not round.
(4) Control of traction speed
During the production of recycled PVC hose, there is no need to pass compressed air into the pipe, nor cooling and shaping, so that the traction force is reduced accordingly, the traction speed must be strictly controlled to ensure the wall thickness of the pipe and the outer diameter of the recycled PVC hose.

Equipment and features
The screw is equidistant and unequal depth gradient type, the length to diameter ratio L / D is 20 ~ 25, and the compression ratio is 3-4. The main parameters of the machine head are basically the same as the hard PVC. The diverter expansion angle α is greater than 60 °. The head compression ratio is 10 ~ 20. The length of the straight part of the mandrel and die is 10 times the wall thickness. The size of the die mouth and core die should be 10% to 30% larger than the inner diameter and outer diameter of the pipe (to achieve the desired size by traction).

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