01
Introduction and application of single screw extruder
(1) Introduction of single screw extruder
Single screw extruder as the name implies, the extruder barrel body has a screw.Generally, the effective length is divided into three sections. The effective length of the three sections is determined according to the diameter of the screw, the pitch of the screw and the depth of the screw. Generally, the effective length of the three sections is divided into one third each.
Section 1: start from the last section of thread of the feed port, called the conveying section.Material here requires not plasticizing, but to preheat, squeezed, the old extrusion theory in the past that the material is loose, and later proved that the material here is actually a solid plug, that is to say, here is a solid after extrusion like a plug, so as long as the completion of the conveying task is its function.
The second section is called the compression section.This section of the screw body product from large gradually smaller, and the temperature to reach the degree of material plasticization, compression here (by conveying section three, here can be compressed to a, this is called the screw compression ratio – 3:1, some machines also have different), complete plasticization of the material into the third section.
The third paragraph: measurement section.Here the material maintains the plasticizing temperature, just like the metering pump accurate, quantitative transport of melt material, to supply the head, the temperature can not be lower than the plasticizing temperature, generally slightly higher.
(2) Single screw extruder application
Single screw extruder is mainly used for extrusion of pipe, sheet, plate and profile, and granulation of some modified materials.
(3) Single screw extruder maintenance
① Because the electrical control system has high requirements for environmental temperature and dustproof, the electrical system should be separated from the production site, and the installation of ventilation or ventilation fans, it is recommended to put the electric control cabinet in a simple room, keep the room clean and ventilated, so that the indoor temperature is not higher than 40℃.
(2) The single screw extruder is not allowed to run empty in order to avoid the screw and the machine simply rolling.The idle running of the host cannot exceed 100r/min.Start the main engine at a low speed first, check if there is any abnormal noise after starting the main engine, and then slowly increase the speed of the main engine to the allowable range of the process (it is better if it can be adjusted to the best state).When the new machine runs in, the current load should be 60-70%, and the current in normal use should not exceed 90%.Note: if any abnormal sound occurs during the operation of the extruder, stop immediately for inspection or repair.
(3) Start the oil pump first, and turn off the oil pump after shutdown;Water pump in the whole production process to maintain the working state, can not stop the operation of the pump, so as to avoid the barrel temperature rise lead to the barrel material decomposition and carbonization;Asbestos air cover of main motor fan should be cleaned frequently to avoid dust adhesion too much blocking air cover, resulting in insufficient heat dissipation of motor due to overheating and trip.
④ Clean the grime, tools and sundries on the surface of the unit in time.
⑤ Prevent metal or other debris from falling into the hopper, so as not to damage the screw and barrel.In order to prevent iron debris from entering the barrel, magnetizing parts or magnetic frame can be installed at the feeding mouth of the material into the barrel to prevent debris from falling into the material must be screened in advance.
⑥ Pay attention to the production environment is clean, do not make garbage impurities mixed with materials to plug the filter plate, affect product output, quality and increase the nose resistance.
The reducer should use the machine specification specified lubricating oil, and according to the specified oil level height to add oil, oil too little, lubrication is not enough, reduce the service life of parts;Too much oil, high fever, high energy consumption, easy deterioration of oil, also make lubrication failure, resulting in damage to parts.The oil leakage part of the reducer should be replaced in time to ensure the amount of lubricating oil.
02
Introduction and application of twin screw extruder
(1) Introduction of twin screw extruder
Twin-screw extruder includes the following multiple systems, the screw system mainly completes the plasticizing and conveying process of the material, which has a great influence on the performance and quality of the finished product.
Feeding system: including hopper, stirring motor, feeding motor.It can prevent material accumulation and facilitate its smooth entry into the feed port.
(2) External heating system: the main use of heating rod and cylinder for efficient heating of materials, promote plasticizing.
Cooling system: the use of heat transfer oil or water heat exchange system to reduce the fuselage heat, so as to effectively control the barrel temperature.
(4) hydraulic network change system: the use of replaceable filter to intercept impurities, improve the degree of plasticization, to ensure the quality of the output material uniformity and stability.
Vacuum system: water and other low molecular volatiles in the material.
⑥ Electric control system: responsible for monitoring and control of the main auxiliary system related equipment.
⑦ Screw system: the most important part of the extruder, can be divided into conveying section, melting section (exhaust), plasticizing section (vacuum mouth), discharge section.
(2) the segment of the twin screw extruder
The screw system of parallel twin screw extruder is generally divided into 4 sections: conveying section, melting section (exhaust port), plasticizing section (vacuum port), discharge section.
(1) Conveying section: function for conveying materials, prevent back.
(2) Melting section: this section through heat conduction and friction shear, so that the material is fully fused and mixed.
(3) Plasticizing section: further melting and mixing of each component of the material, with distribution and dispersion mixing function.
(4) discharging section: conveying and pressurizing, forming a certain pressure, making the material closer, and further mixing, to achieve the purpose of extrusion granulation.
(3) Conveying elements
Type is divided into: large lead and small lead.
The use effect of lead: the more lead, the increase of screw extrusion, the shorter the residence time of the material, the weaker the mixing capacity of the material.
(3) the usual use of small lead: combination gradually reduced, used for conveying section, melting section, plasticizing section, to boost, improve melting;Improve the homogenization degree of mixture and stability of conveying capacity.
(4) Shear element
① Direction classification: forward and reverse.Positive, promote material flow and realize its function;Reverse, also known as reverse rotation, has a backflow effect on the conveying of materials, prolong the residence time of materials, enhance the plasticizing ability, improve the mixing effect.
(2) Angle classification: generally 30°, 45 °, 60 °, 90 ° points.
③ Effect and effect: in the forward direction, the staggered Angle is increased, the conveying capacity is reduced, the residence time is prolonged, and the plasticizing degree is improved.For dispersion, the larger the Angle, the more obvious the effect;Dispersion mixing is generally best at an Angle of 45°, followed by 30°, and worst at 60°.
④ The effect of the number of heads
In the forward direction, the smaller the number of heads, the greater the extrusion capacity, the greater the torque, the better the mixing effect, but the less shear action;
In reverse, the less the number of heads, the smaller the extrusion capacity, the better the mixing effect.
03
Single twin screw extruder difference
Next, from the price, operability, screw and other aspects of specific understanding of the two extruders in the end what is the difference.
The picture
(1) The price of single screw extruder is lower
Single screw extruder has simple structure and low price.
Twin screw structure complex, high price.Twin screw extruder is about 1 times more expensive than single screw extruder.Individual will be higher, specific because of manufacturer, model and different.
(2) single screw formula is simple
For operations, the difference is actually not that great.But the single screw extruder process, formula is relatively simple, and the twin screw extruder process, process, formula will be more complex.
(3) Twin screw can be freely combined screw
Twin screw thread can be combined thread according to the material and the mood of the operator.Single screw is more rigid, can not combine screw.
(4) Twin screw efficiency is higher
Twin screw extruder output is large, extrusion speed is fast, low energy consumption per unit output, and the single screw is poor.The efficiency of twin-screw extruder is mostly about 1 times that of single screw extruder.Specific according to manufacturer, model and decide.
(5) the twin screw mixing plasticizing ability is strong
In simple terms, the single screw is suitable for polymer plasticizing extrusion, suitable for particle material extrusion processing, such as: molding, blowing film, injection molding, etc., the use of a wide range of materials;
Twin-screw extruder has good mixing and plasticizing ability and is suitable for modification of plastics.And the twin screw extruder can make two colors.
(6) The single screw is easy to maintain
In terms of maintenance, the single screw will be more simple than the twin screw, because the structure of the single screw is relatively simple, easy to repair.
(7) Transport mechanism
The conveying of single screw extruder mainly depends on the friction force between the material and the barrel. The opposite direction twin screw extruder is forward conveying and has the effect of forcing the material forward. Moreover, the opposite direction twin screw extruder also produces shear effect on the material at the meshing place of the two screws.(For opposite twin screw extruder)
(8) Velocity field
The velocity distribution in single screw extruders is relatively clear and easy to describe, while in opposite twin screw extruders it is quite complex and difficult to describe.This is mainly because the screw has meshing zone. The complex flow in the meshing zone has many advantages such as full mixing, uniform heat transfer, strong melting capacity and good exhaust performance, but it is difficult to accurately analyze the flow state in the meshing zone.(For opposite twin screw extruder)
(9) Application examples
Application examples of twin screw extruder:Glass fiber reinforced, anti-fuel granulation (such as PA6, PA66, PET, PBT, PP, PC enhanced flame retardant, etc.), high filling material granulation (such as PE, PP fill 75% CaCO3), heat sensitive material granulation (such as PVC, XLPE cable material), thick masterbatch (such as fill 50% toner),Antistatic masterbatch, low alloy, coloring, filling blending granulation, cable materials granulation, such as sheath materials, insulation materials, described.properties tube material granulation, such as used for hot water crosslinking masterbatch), thermosetting plastic mixing extruder, such as phenolic resin, epoxy resin and powder coating), hot melt adhesive, PU reactive extrusion granulation (such as EVA hot melt adhesive, polyurethane),K resin, SBS devolatilization granulation, etc.
Single screw extruder application examples: suitable for PP-R pipe, PE gas pipe, PEX crosslinking pipe, aluminum-plastic composite pipe, ABS pipe, PVC pipe, HDPE silicon core pipe and various co-extruded composite pipe;Suitable for extrusion of PVC, PET, PS, PP, PC profiles and plates, other kinds of plastic extrusion such as wire, rod, etc.Adjusting the speed of the extruder and changing the structure of the extruder screw can be used to produce PVC, polyolefin and other plastic profiles.
