Tips for Improving Twin Screw Extruder Performance

Twin screw extruders are commonly used equipment for modified plastics manufacturers. Today, we will introduce some small details that can improve the performance of twin screw extruders. The skills introduced in this article include three aspects: equipment modification, equipment maintenance, and operating specifications.

Equipment Modification of Twin Screw Extruder

1. Add heat insulation gasket between the feeding section and the flange of the second section

The feeding section of the extruder barrel is mostly water-cooled, and is locked with the second section of the barrel (heated) by a flange, and the heat can be continuously conducted from the high temperature barrel to the cold barrel. As a result, the second-stage cylinder cannot maintain sufficient temperature. Usually, the operator sets a temperature of 180°C in the second section of the barrel, but due to the heat loss in the feeding section, the actual stability usually does not exceed 135°C.

The simplest solution is to add 1-2 1mm thick insulation gaskets between the feeding section and the flange of the second section of the cylinder. And replace the insulation gasket every few years, because the insulation gasket tends to degrade and shrink.

2. Replace the plastic extruder cooling system with a high-pressure cooling system

We all know that turbulent flow in a pump can cause more heat exchange on the tube wall than laminar flow. Turbulence in high-pressure transmission has a high degree of lateral momentum exchange, which breaks the boundary layer. As a result, the violent fluid movement causes a much greater heat exchange between the tube wall and the fluid. The plastic screw extruder cooling circulation system generally provides a pressure of 20-60 psi. To achieve turbulent flow, it is best to achieve a pressure of 120 PSI. Almost all cooling system components (hoses and valves) of the polymer extruder must be upgraded to 150PSI to meet the safety factor of 120PSI. After the transformation is completed, the cooling system can discharge a large amount of heat in time during processing.

3. Use appropriate modifications to increase the feed volume

Side feed is usually used to feed the filler into the twin screw extruder machine. Many processors need to make very high filling levels of fillers, which often have a very low bulk density. The final filling volume is restricted by the following factors:

(1) The volume feeding capacity of side feeding and the volume feeding capacity of the main screw of the extruder machine.

The volumetric feeding capacity depends on the free volume of the side feeder and the main screw, and the speed of these two screws.

If a material can flow into the storage drum without the resistance of the main screw during the test, the feeding speed of this material can be very good. If the side feeder is connected directly next to the main screw, the amount of material that the additive screw can accept will be limited. Therefore, the main engine screw should have a long-pitch threaded element, extending 2D-4D length downstream of the side feed port. This will allow the melt to quickly pass through the side feeding port so that the filler is eaten by the main screw to the maximum extent. If the screw design of the main engine causes any accumulation of side-feeding materials, it will severely limit the amount of filler fed.

(2) Exhaust capacity that allows gas to be discharged from the twin screw plastic extruder.

The purpose of the exhaust is to make the air easy to escape, and at the same time to protect the packing from escaping in large quantities from the exhaust port. The best configuration is to open an upward exhaust port upstream of the side feed port. Sometimes, a small half slit is opened in the upper part of the side feeder for exhaust.

(3) There are some other factors to consider:

1. Blanking height of the compounding extruder feeder

Ideally, the feeding screw should be installed as close as possible to the top of the side feeding port to reduce the height of the material. If a kind of fluffy material flows through the air, it may become full of air, which greatly reduces its false density after falling.

2. Mixing type of compounding extruder feeder

Make sure that the agitator in the filler feeder does not fluidize the filler. Many mixer manufacturers have designed special mixers for filler feeding. The accumulator will introduce air into the compounding extruder along with the filler. A chute hopper with an open-top helps exhaust air. If your chute feeding hopper has a solid lid and a round tube and is flexibly connected to the feeder, then you need to design an exhaust port.

3. The hopper chute should be grounded to prevent static electricity

Some materials cause the powder to hang on the wall of the hopper due to static electricity due to friction, resulting in the powder cake. A simple solution is to ground the hopper chute.

4. Compressed air blaster

If the cake continues to exist, some special measures are often needed. A hopper vibrator can be used, but it takes up space and needs to be installed. An alternative is to install a blaster with an air nozzle, install it in the proper position of the chute, and blow it through before the cake grows.

Equipment Maintenance of Twin Screw Extruder

1. Flush the cooling water channel with acid

The water Cooling Strand Pelletizer barrel is a heat exchanger. Like all heat exchangers, the water channel is prone to fouling and deterioration. Many operators have noticed that the cooling performance of a new compounding twin screw extruder is much better than that of a three or four-year extruder machine. The old extruder has a layer of scale attached to the inner surface of the water channel, which affects the heat transfer efficiency. Using a certain concentration of acid to clean the barrel can clean up the scale and maintain the good heat transfer effect of the barrel.

2. Use synthetic gear oil

The gearbox is the heart of the double screw extruder. Therefore, we need to prevent gearbox problems, and use synthetic gear oil to better protect the gears.

Advantages of synthetic gear oil:

1. More slippery, resulting in less friction;

2. Gears, bearings, and seals will last longer;

3. The gear running temperature is lower and quieter;

4. Synthetic oil does not lose viscosity due to machine shear;

5. It maintains a higher viscosity at high temperatures.

3. Clean the twin screw extruder regularly

The purpose of the cleaning co-rotating extruders and counter rotating extruders is to remove the residual materials in the extruder and die, which avoids time-consuming disassembly and cleaning. Cleaning materials are often divided into two categories: chemical cleaning agents and mechanical friction cleaning agents. Many cleaning agents have both chemical and frictional functions. Chemical cleaning agents will react with plastic residues to remove them from the mechanical surface.

The principle of mechanical friction cleaning is to rub and wash away residual material from the metal surface, using friction and shearing methods. The processor can find suitable cleaning materials and methods through many trials.

Here are two more effective cleaning agents:

1. Mixture: 50% HDPE+50% diatomite

2. Mixture: HDPE+water+decontamination powder.

The HDPE is fed into the screw at the usual speed at the melting temperature. Stir the decontamination powder with water in a bucket to form a slurry, and slowly add the slurry from the main feed port. These slurries impact, rub, and clean the screw due to foaming.

Operating Specifications of Twin Screw Extruder

1. The correct way to switch colors and materials

People who squeeze out always want to drive the extruder machine longer. But in reality, due to customer demand, we often need to switch continuously, producing 80 kg of product A, and then 200 kg of product B, and so on.

1. It seems self-evident that the batch of products should correspond to the size of the plastic extruder. But many processors had no plans to produce 500 pounds of orders on the 75 extruder machine, resulting in 300 pounds of waste.

2. Write down procedures for cleaning or disassembling each product produced. This helps operators plan time and eliminates their disputes about how much headstock will be produced.

3. Help the operator to place clean operating tools around the plastic extruders. If the material is changed frequently, set up a workbench around the extruder to prepare everything needed.

4. Study the flow of raw materials and finished products into and out of the operation site. It is arranged so that the operator spends less energy on the mobile transportation.

5. Clear the requirements of the next product on the cleanliness of the plastic screw extruder. If you know that the next product requires a thorough manual cleaning machine, then don't waste time and materials to confuse the machine.

6. If possible, schedule production in the order of reducing the number of cleaning twin screw extruder machines. This means going from light to dark. On the contrary, you have to disassemble the machine multiple times.

2. The correct way to start and stop the extruder

Common operation methods:

Operators are used to leaving the polymer extruder machine on when they arrive at the factory in the morning, but they go to work on other things. Allow the extruder to heat to full scale and leave it idle for several hours. Doing so will cause the polymer to adhere to the screw and barrel, and then these polymer materials will continue to degrade and char. The cleaning machine cannot remove these materials. What's worse is that once the machine produces products, black spots will periodically run out of the screw and barrel, contaminating the product, and causing customer complaints.

The correct boot method:

Plan when you want to operate the screw extruder, and then start heating, as long as the temperature reaches a predetermined value, and then the barrel is filled.

The correct shutdown method:

Before shutting down, fill the twin screw extruder with inert polymers (such as HDPE) to seal the gaps of the machine. HDPE drives off oxygen and coats the metal surface, greatly reducing the formation of carbon oxides. After the extruder machine has been "sealed", it is better to chill the extruder rather than leave it in the air for 18 hours. The so-called rapid cooling is to set all temperatures to zero and open all cooling water valves. Turn on the cooling water pump to let the cooling water pass through all the cylinder parts to quickly cool down. The rapid cooling will avoid polymer degradation and carbonization.

Do you now know how to better display the real performance of the extruder? Chuangbo is a professional twin screw extruder manufacturer and supplier in China. We can provide customers with different extruders with excellent performance, such as masterbatch extruder, PVC compounding, thermoplastic elastermor, reaction extrusion line, devolatilization extruder, pelletizing system, etc.