PVC resin is a polar amorphous polymer with poor thermal stability and is difficult to process. It cannot be used directly and must be modified and mixed.
Cowin’s PVC Compound Machine
PVC Compound Machine Technical Specifications：
|Model||Screw diameter (mm)||Screw speed (rpm/min)||Motor power (Kw)||Output (Kg/h)|
The molecular weight of industrial PVC is generally in the range of 50000 ~ 110000, with great polydispersity. The molecular weight increases with the decrease of polymerization temperature. There is no fixed melting point. It begins to soften at 80 ~ 85 ℃, changes to a viscoelastic state at 130 ℃, and changes to a viscous flow state at 160 ~ 180 ℃.
PVC granulation generally uses a two-stage machine. The upper stage adopts a twin-screw extruder, and the lower stage adopts a single screw extruder.
The temperature control system of the PVC compound machine can strictly control the material temperature according to the process requirements of customers, and the screw speed can be adjusted. The upper stage twin-screw extruder provides blending modification conditions for PVC raw materials, and the lower stage single screw extruder provides cooling time for PVC. After the air-cooling die face hot granulation auxiliary machine is used for granulation, the PVC pellets have good mechanical properties, high tensile strength and impact strength, and high-quality dielectric properties.
Generally, a high-speed mixer is required for mixing, and then it is cooled by the low-speed mixer. Then the raw materials are sent to the extruder, plasticized and mixed by the co rotating twin-screw extruder (L/D=28~36), and then cooled by a single screw at low temperature for pressure building extrusion. The length diameter ratio can be selected according to the needs of the formula.
Specially Extruder for PVC Compounding： Two Stage Extruder
Upper Stage Extruder – Twin Screw Extruder
- The deceleration and torque distribution parts are integrated into one, with a compact structure.
- Needle roller bearing, the radial bearing of bearing deceleration torque distribution system.
- The gears are made of high-quality alloy materials, and the precision is manufactured according to iso1328-1995 cylindrical gear precision. All gears are carburized and hardened. The special gear grinding software is used to trim the gear profile to ensure the gear strength, uniform load in the tooth direction, high strength, low noise and low vibration.
- The screw is of a building block structure.
- Material of mandrel: 40CrNiMoA, the threaded element and mandrel are connected by involute; High strength, large bearing load, convenient disassembly and assembly.
- The threaded element is made of high-quality high-speed tool steel W6Mo5Cr4V2, which is subject to high-temperature vacuum quenching heat treatment.
- Overall hardness: hrc60-64.
- The screw head and cap are connected by a reverse tooth connection to ensure that the connection is firm.
- Material: 45#steel as the matrix and the ∞ inner hole adopts high-quality double alloy bushing.
- The first section of the barrel is a feeding barrel, the sixth section is a natural exhaust barrel, the ninth section is a vacuum barrel, and the rest are closed barrels.
- The barrel is cooled by soft water.
- The inner hexagon high-strength bolts are used to connect the barrels.
- Heating section: the feeding area is not heated, and other areas use high-quality cast aluminum heaters.
Lower Stage Extruder – Single Screw Extruder
Reduction gearbox: the high-precision gear transmission device with a hard tooth surface and thrust seat designed with a single screw rubber and plastic extruder is adopted. The design adopts various technical specifications specified in JB/T8853-2001 cylindrical gear reducer. The output shaft is made of high-strength 42CrMo, and other gears and shaft parts are made of high-strength 20CrMnTi material; Gears are processed by carburizing, quenching and gear grinding process, with high precision and hardness. The gear accuracy is gb10095-88, grade 6, and the tooth surface hardness is HRC-54 ~ 62. The thrust bearing is equipped at the front end of the hollow output shaft to bear the axial thrust when the screw works. The whole machine has a small volume, high bearing capacity, stable transmission, low noise and high efficiency. When the oil level is lower than the oil level indicator, please add medium load industrial gear oil L-CKC220 or L-CKC320 (the oil products shall be purchased by the customer).
- The material is 38CrMoAlA nitriding treatment, nitriding hv950-1050, depth 0.6-0.75mm, brittleness not greater than grade II, and the screw surface is plated with hard chromium.
- The screw core is cooled by water.
- The material is 38CrMoAlA nitriding treatment, nitriding hv950-1050, depth 0.6-0.75mm, and brittleness not greater than grade II.
- The screw barrel is cooled by water.
- The barrel is slotted and the copper pipe is coiled to supply cooling water.
- The screw barrel is provided with a protective cover made of stainless steel.
- Heating section: high quality cast aluminum heater.
- The machine head is heated by a mold heater.
Air-cooling die face hot granulation auxiliary machine
- Air cooled die surface hot granulator: 4-stage motor, one set of hot cutting knives, one motor coupling, and 4 blades for hot cutting.
- Speed regulation control: variable frequency speed regulation is adopted.
- Pelletizing Hood: opposite blowing type, made of stainless steel. One piece. Push pull structure. With braking device. There is enough space for the heat shield to be separated from the machine head. Easy operation. The opposite blowing hot air hood is integrated with the bed.
- Primary cyclone: φ 800mm, stainless steel. One piece. Use φ 160mm stainless steel pipe connection.
- Secondary cyclone: φ 800mm, stainless steel. One piece. Use φ 130mm stainless steel pipe connection.
- Lengthened vibrating screen: one. Motor: special motor for vibration. The vibration quantity can be adjusted: two sets of motor power. The vibrating screen adopts three layers to separate materials. Large hole diameter φ 8mm, hole diameter φ 2.5mm, stainless steel.
- Air blown Silo: one set. One 1m3 silo is made of stainless steel. Use φ 130mm stainless steel pipe connection.
Precautions for Processing PVC Plastic Pellets
PVC can be said to be a common material in the plastic industry. It can be seen everywhere in people’s life. The skirting line beside the room wall, the switch face box on the wall, the pipe on the top of the toilet, and the plastic floor stepping on the floor are all made of PVC. PVC is the abbreviation of PVC. It is a polymer polymerized by vinyl chloride monomer with peroxide, azo compound and other initiators, or by a free radical polymerization reaction mechanism under the action of light and heat. Because of its low price and stable performance, it is widely used in various industries. The following points shall be paid attention to when processing PVC plastic pellets:
- The processing temperature of PVC should not be too high. Generally, the processing environment of injection grade materials is about 160-170 ° C, and that of extruded materials is 160-190 ° C. beyond this temperature, PVC materials are prone to coke or material decomposition.
- It is recommended to use PVC special screw for processing PVC plastic pellets. PVC has certain corrosivity due to the characteristics of the material. In order to prolong the service life of your screw, it is recommended to use a special grade.
- The fluidity of PVC materials is worse than that of other materials. At this time, we generally recommend that users change the injection hole diameter to more than 3-5mm before processing, especially for larger products, which is more convenient for complete product molding.
- Pay attention to the temperature change of the fuselage at any time. When touching the strip with clean hands, it should be heated immediately. Until the strip touches the hand, it is normal.
- When the reducer bearing is burned or accompanied by noise, it shall be repaired in time and refuelled.
- When the bearings at both ends of the main bearing chamber of the plastic granulator are hot or noisy, it is necessary to stop the machine for maintenance and add butter. During normal operation, grease the bearing chamber every 5-6 days.
- Pay attention to finding out the operation law of the machine; For example, if the machine temperature is high or low and the speed is fast or slow, it can be handled in time according to the situation.
- When the fuselage is unstable, pay attention to check whether the fitting clearance of the coupling is too tight, and loosen it in time.
Customer Location: China
Machine Model: CHT65B & CSE150 Two-stage Extruder Pelletizing Unit
Time: September 7, 2020
What is PVC Compound？
Polyvinyl chloride (PVC) is a polymer polymerized by vinyl chloride monomer (VCM) with peroxide, azo compound and other initiators or under the action of light and heat according to the free radical polymerization mechanism. Vinyl chloride homopolymer and vinyl chloride copolymer are collectively referred to as vinyl chloride resin.
The stability of PVC to light and heat is poor. When it is above 100 ℃ or exposed to the sun for a long time, it will decompose to produce hydrogen chloride, and further Autocatalytic Decomposition will cause discoloration. The physical and mechanical properties will also decline rapidly. In practical applications, stabilizers must be added to improve heat and light stability.
PVC used to be the world’s largest general-purpose plastic with a wide range of applications. It is widely used in building materials, industrial products, daily necessities, floor leather, floor tiles, artificial leather, pipes, wires and cables, packaging films, bottles, foaming materials, sealing materials, fibers, etc.
What is PVC Extrusion Granulation?
The granulation process is the production process of making granular plastic from polymer resin and various additives through metering, clutching, plasticization and granulation. Plastic pellets are semi-finished products of the plastic molding and processing industry, as well as raw materials for extrusion, injection molding, hollow blow molding, foaming and other molding and processing.
PVC granulation generally uses a two-stage machine. The upper stage adopts a twin-screw extruder, and the lower stage adopts a single screw extruder. The main working mode of PVC granulator is wet granulation of pellets. Through a certain amount of water or steam, the basic waste will be fully chemically reacted after being humidified in the cylinder. Under certain liquid phase conditions, with the help of the rotating movement of the barrel, the material pellets will be extruded and agglomerated into balls.
PVC resin is a polar amorphous polymer, density: 1.38 g/cm³. Glass transition temperature: 87 ℃, so it has poor thermal stability and is difficult to process. It can not be used directly. It can only be used after modification and mixing and adding relevant additives and fillers.
However, the properties and requirements of the prepared PVC materials are different due to the different types and fractions of additives and fillers. We usually call it the PVC formula. Strictly speaking, it is PVC modified formula, and PVC can only be used after modification. This category is often classified as polymer-modified materials. The modification of polymer materials mainly focuses on the high-performance of general plastics, the transformation from single component materials to multi-component materials (alloys, blends, composites), the functionalization of materials, and the optimization of performance and price. The main modification methods are chemical modification, filling modification, reinforcement modification, blending modification and nanocomposite modification.
PVC generally needs to be modified and granulated first. The basic principle of modification is to endow materials with functions or improve some properties through additives.
After the pellets are prepared by screw extruder, the plasticization will be more sufficient and the processing will be easier, especially for injection molded products. A screw extruder is one of the most important pieces of equipment for plastic forming and processing. It carries out solid conveying, compaction, melting, shearing, mixing and extrusion of plastics through external power transmission and heat transfer of external heating elements. Screw extruder plays an important role in both plasticizing and granulating machinery and forming and processing machinery.
Production Process of PVC Compounds
PVC can be used for PVC doors and windows, PVC pipes, PVC films, PVC plates, soft PVC, PVC packaging materials, PVC wallboards and floors, PVC coated products, PVC foam products, PVC transparent sheets, etc. PVC can only be used after modification. Therefore, PVC-modified granulation is a very important step in the use of PVC.
PVC modified granulation process
high-speed mixer–screw feeder–twin-screw metering feeder–twin-screw extruder — connector–single screw extruder–integrated hydraulic plate automatic screen changer–air-cooling die face hot granulation auxiliary machine–primary cyclone separator–air-cooled vibrating screen–secondary cyclone separator–air blown silo.