Twin-screw extruder is a commonly used equipment for modified plastics manufacturers, today introduced some small details that can improve the performance of twin-screw extruder.This article describes the skills, including equipment modification, equipment maintenance and operation of the three aspects.
Equipment modification
1, In the feed section and the second paragraph of the flange between the insulation pad
Most of the feeding section of the barrel is water-cooled, and the flange is locked with the second barrel (heated), so that the heat can be continuously transmitted from the barrel with the higher temperature to the cold barrel. As a result, the second barrel can not Typically, the operator sets a temperature of 180 ° C in the second section of the barrel, but the actual stability typically does not exceed 135 ° C due to the loss of heat from the feed section.
The simplest solution is to add 1-2 1mm thick insulation pads between the feed section and the second barrel flange and replace the thermal pads for several years because of the aging of the thermal pads Degradation and shrinkage tendency.
2, Extruder cooling system replaced by high-pressure cooling system
It is well known that turbulence in pumps can lead to more wall heat exchange than laminar flow turbulence in high pressure transmission has a high degree of lateral momentum exchange that breaks through the boundary layer.As a result of violent fluid movements, A much larger heat exchange between fluids. The extruder cooling circuit typically provides a pressure of 20-60 psi. To achieve turbulence it is best to achieve a pressure of 120 PSI. Almost all of the cooling system components of the extruder (hoses and valves ) Must be upgraded to 150PSI, in order to meet the safety factor of 120PSI. After the completion of the transformation process, the cooling system can discharge a lot of heat in time.
3, Use the appropriate modification to increase the amount of feed
Side feeds are commonly used to feed fillers into twin-screw extruders. Many processors require very high levels of packing, which tend to have very low packing densities.The final fill level is governed by:
1, the volume of side feeding material feeding capacity and the extruder screw capacity of the main feed. Volumetric feeding capacity depends on the free volume of the side feeders and the main screw, as well as the speed of the two screws.
If a material can flow into the drum without being dragged by the main screw during testing, this material can be fed very well.If the side feeder is connected directly to the main screw, the aid screw Acceptable material levels will be limited so that the host screw preferably has a long pitch thread element that extends 2D-4D downstream of the side feed opening This will allow the melt to quickly pass through the side feed opening to maximize the packing The main screw is fed in. If the host screw design causes any side feed to be fed into the material, it will severely limit the amount of feed.
2, allowing the exhaust gas from the extruder discharge capacity. The purpose of venting is to allow easy escape of air while also protecting the packing from substantial escaping from the vent. The best configuration is to vent the vent up exhaust upstream of the side feed port. The upper part of the feeder opens with a small half-slit vent.
3, there are some other factors to consider:
(1) feeder blanking height
Ideally, the feed screw should be mounted as close as possible to the top of the side feed spout to reduce the blanking height.If a fluffy material is flowing from the air, it may become filled with air so that it Fallen density is greatly reduced after falling.
(2) feeder mixing type
Make sure that the agitator in the filler feeder does not fluidize the packing Many blender manufacturers have designed special mixers for stuffing feed, which, together with the fillers, introduce air into the extruder.One open top Of the chute hopper helps exhaust.If your chute feed hopper has a solid lid with a round tube and is flexible with the feeder, then you need to design a vent.
(3) hopper chute should be grounded anti-static
Some materials are static due to friction and cause the powder to hang on the wall of the hopper, causing the powder to cake. A simple solution is to ground the hopper chute.
(4) compressed air blasting device
Something special is often required if the cake remains in place. A hopper shaker can be used but it takes up space and an alternative is to install a blasting unit with an air nozzle mounted in place on the chute in Bake it before blowing it up.
Equipment maintenance
1, Rinse cooling water with acid
The water-cooled extruder barrel is essentially a heat exchanger that, like all heat exchangers, tends to foul and deteriorate. Many operators note that the cooling performance of a new extruder is better than using three, four Years of the extruder much better.Old machine has a layer of scale attached to the surface of the waterway, affecting heat transfer efficiency.Using a certain concentration of acid cleaning barrel can be cleaned of scale, to maintain a good tube heat transfer.
2, Use synthetic gear oil
The gearbox is the heart of a twin-screw extruder, so we want to prevent gearbox problems and use synthetic gear oils to better protect the gear.
Synthetic gear oil Advantages:
1. More creamy, resulting in less friction;
2. Gears, bearings and seals will be more durable;
3. Gear running lower temperature, more quiet;
4. Synthetic oil does not lose viscosity due to machine shearing;
It maintains high viscosity at high temperatures.
3, Clean the machine frequently
The purpose of the cleaning machine is to remove the material remaining in the extruder and the die, which avoids the time-consuming disassembly of the cleaning machine The material is often divided into two categories: chemical cleaners and mechanical friction cleaners Many cleaners have both chemical And friction function Chemical cleaning agents react with plastic residues to disengage them from mechanical surfaces.
The principle of mechanical friction cleaning is the friction and scouring of the residual material from the metal surface, using the friction and shear method, and the processor can find suitable cleaning materials and methods through multiple tests. There is no cleaning material for all materials There are cleaning effects. Processors need to clean materials cheaply and effectively.
For example, many operators in the Midwest use maize as a material for cleaning machines because of its ease of use and good cleaning of the machine.
Here are two more effective cleaning agents:
1, Mixture: 50% HDPE + 50% diatomaceous earth
2, the mixture: HDPE + water + decontamination powder. HDPE at the usual speed at the melting temperature by adding screw. The decontamination water in the bucket with stirring into a slurry from the main feed port slowly added to the slurry because these foaming The impact, friction, cleaning the screw.
Code of practice
1, The right way to switch colors and materials
People who tend to squeeze out want to run the machine for longer, but in reality, we often need to switch between producing 80 kg of product A, and then 200 kg of product B, due to customer needs.
1. It seems self-evident that the batch size of the product corresponds to the size of the machine, but many processors are scheduling unscheduled production of a 500 pound list on a 75 machine, resulting in 300 pounds of scrap
2, Write out the procedures for clearing or disassembling each product, which helps operators plan their time and dispel their arguments about how much crankshaft material will be produced.
3, to help operators, the cleaning operation tools placed around the extruder, if frequent refueling, then engage in a table around the extruder, the things you need are ready.
4. Investigate the order in which raw materials and finished products flow in and out of the operation site, and arrange for the operator to spend less effort on moving the conveyance.
5, clear the next product on the machine cleanliness requirements.If you know the next product requires a thorough manual cleaning machine, then do not waste time and materials to fool the machine.
6, if possible, in accordance with the order to reduce the Qing scheduling in. This means that to do from the light-colored dark, on the contrary, you have to repeatedly disassemble.
2, Extruder boot and shutdown the correct way
Common mode of operation:
The operator is used to going to the factory in the morning to put the extruder on, but to do other things, heating the extruder to full capacity for several hours, which will allow the polymer to adhere to the screw and barrel, and then Polymer materials will continue to degrade and carbonize. The machine can not remove these materials. Even worse, once the machine produces the product, black spots will periodically run out of the screw and barrel and contaminate the product, causing customers to complain.
The right way to boot:
Plan when you really want to operate the extruder, and then start heating as long as the temperature reaches a predetermined value and then charge the barrel.
The correct method of shutdown:
Prior to shutdown, the extruder was filled with inert polymer (such as HDPE) to seal the gap to the maximum. HDPE drove away the oxygen and coated the metal surface, greatly reducing the formation of carbon oxides. After the machine is 'sealed', it is best to quench the extruder rather than letting it cool in the air for 18 hours. The so-called chill is to set all temperatures to zero and turn on all cooling water valves. Cooling water passes through all of the barrel sections for rapid cooling, and rapid cooling will prevent polymer degradation and charring.