How to improve the blending performance of twin screw extruder? (2)

Views: 1     Author: Site Editor     Publish Time: 2022-05-04      Origin: Site

There are many methods for improving the performance of twin-screw compounding extruders, which are well known to operators and plant engineers. However, many of these methods do not appear in the device manual. Paying attention to small details can go a long way in increasing extruder performance.


5. Switch to synthetic gear oil

Gearbox is the heart of twin screw extruder. If it goes down, it's expensive and time consuming to repair. At this point, one thing we can do is to avoid gearbox problems: switch to synthetic gear oil. Synthetic oils are a huge step forward in lubrication:

---More slippery, resulting in less friction;

---Gears, bearings and seals will last longer;

---Gear running temperature is lower and quieter;

---Synthetic oil does not lose viscosity due to machine shearing;

---It maintains high viscosity at high temperature;

---Improve the overall gear efficiency


6. Clean the machine often

Purge is a simple and extensive method for removing material from extruders and dies, avoiding time-consuming dismantling for cleaning. There are many materials available for cleaning. There are not only commercial cleaning products, but also our own special cleaning products. These materials are often divided into two categories: chemical cleaners and mechanical friction cleaners. Many cleaners have both chemical and abrasive functions. Chemical cleaners attack plastic residue like a solvent. Many chemical cleaners also incorporate a foaming function that requires a 5-minute "soak" in the barrel to exert a chemical effect.

The principle of mechanical friction cleaning is to rub and wash away residual material from the metal surface, using friction and shear. Processors do a lot of trial and error to find the right cleaning materials and methods. There is no "magic" material that works for all materials. Commercial cleaning materials are generally more expensive than homemade cleaning materials. However, if you get the job done faster with less commercial cleaning material, the actual cost may be less.

Processors need to clean materials cheaply and efficiently. For example, many operators in the Midwest of the United States use corn fed to cattle because it is readily available and has a good cleaning effect on the machine.

Here are two effective homemade cleaning agents:

---1# mixture: 50% HDPE + 50% diatomaceous earth

---2# mixture: HDPE + water + decontamination powder. The HDPE was fed into the screw at the usual rate at the melt temperature. The decontamination powder is stirred into a slurry with water in a bucket, and the slurry is slowly added from the main feeding port. These slurries impact, rub, and clean the screw due to foaming.


7. Effectively switch colors and materials

People who squeeze out always want to run the machine longer. But in reality, due to customer demand, we often need to keep switching, making 80 pounds of product A, then 200 pounds of product B, and so on.

It was important to find a way to reduce operator workload and problems:

---If possible, schedule production in the order of reducing cleaning. That means going from light to dark. On the contrary, you only have to disassemble.

---Write out the process of cleaning or dismantling that produces each product, which helps operators plan their time and eliminate their arguments about how much headstock will be produced.

---The batch of products should correspond to the size of the machine. This seems self-evident. But many processors were unplanned, producing 500-pound orders with 75 model, resulting in 300 pounds of scrap.

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

--- Study the sequence in which raw materials and finished products flow into and out of the operation site. Arranged so that the operator spends less effort moving the transport.


8. Heating and cooling

Those who run the extruder like to keep the extruder heated all the time. However, if the extruder is heated to its maximum temperature and then left idle for several hours, the polymer will stick to the screw and barrel. Once adhered, these polymeric materials will continue to degrade and char. Cleaners can't remove these materials. To make matters worse, once the machine produces the product, black spots will periodically run out of the screw and barrel, contaminating the product and causing customer complaints.

The best way to handle heating is to plan when you actually want to operate the extruder and start heating, as long as the temperature is fully in place and the barrel is charged. There are also better shutdown cooling routines to avoid black spot problems. It is good practice to fill the extruder with an inert polymer, such as HDPE, as much as possible to seal the gaps in the machine before shutting down. HDPE drives away oxygen and coats metal surfaces, greatly reducing the oxidation and formation of carbon.

After the extruder is "sealed", it is best to quench the extruder rather than leave it in the air for 18 hours. The so-called quenching is to set all the temperatures to zero and let the cooling water valves all open. Turn on the cooling water pump, which will allow the cooling water to pass through all parts of the cylinder, and the temperature will drop rapidly. Rapid cooling will not give the polymer a chance to degrade and char.


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