Most plastic extruder manufacturers in the plastics extrusion industry are aware of the need for anti-seize extruder lubricants. There are several different extruder lubricants types: copper-based, molybdenum, lithium, etc. For things like plastic extruder screws and threaded components, any type can be used is fine. But for extruder spline shafts, the choice of anti-seize is even more critical.
Tengda extruder threaded components are assembled to spline extrusion shafts with very tight clearance tolerances, but low viscosity polymers tend to creep down between adjacent twin screw extruder components and into that clearance. With time and heat, the degraded polymer forms high-strength adhesives like epoxy resins. They can be very difficult to remove from the extruder shaft if the extruder screw remains in the extruder and is not periodically disassembled. This is why the choice of extrusion anti-seize is so important.
Many types of screw extruder anti-seize lubricants are acceptable for short periods of time, but after prolonged use at high temperatures, they degrade to a fine plastic extruder machine powder. This makes them a poor choice for tengda extruder spline shafts, and when you are ready to remove a plastic extruder screw after months or years, you need a higher level of pellet extruder anti-seize effectiveness.
Blow cleaning is widely used as an easy way to remove material from extruders and dies and avoid time-consuming stripping cleaning. There are several types of materials that can be used for cleaning extruder, and these materials typically fall into two categories: chemical cleaners and mechanical abrasive cleaners, many combining chemical and abrasive action.
Extruder chemical cleaners work by attacking the plastic residue like a solvent. Many extrusions chemical cleaners also have a foaming effect and need to be "soaked" in a cartridge for five minutes to take effect chemically.
Extruder mechanical abrasive cleaning works by using friction and shear to flush and scrub material from metal surfaces.
Plastic extruder processors have conducted numerous iterations to find the right cleaning materials and techniqu es. But there is no one screw extruder "magic" cleaning material that works for all materials. However, if you can use less material in the commercial extruder cleaning, or get the extruder cleaning jobs done faster, the total cost may actually be lower. So Plastic extruder processors will try a variety of materials through extruders to find inexpensive and effective cleaning materials.
For example, in the Midwest, many plastic extruder operators use cattle feed corn because it is readily available and cleans quite well on the pellet extruder machine. Here are two effective homemade removers.
Mix #1: 50% HDPE (or another high viscosity resin) + 50% diatomaceous earth (DE)
DE is finely ground tiny fossilized shells of marine life. It is readily available at garden supply stores. DE looks like a fine powder, but the particles have very sharp edges that create a scrubbing effect. Running sheet and film extrusion can use this cleaner because it can sometimes remove die lines, thus saving lengthy extruder die removal time.
Mix #2: HDPE or other tacky resin mixed with kitchen cleaner and water.
Mix a water slurry and three or four cans of kitchen cleaner in a bucket. Extruder feed HDPE at normal purge rate and temperature and slowly pour the slurry into the main inlet. The water in the slurry will flash to steam and combine with the abrasive in the kitchen cleaner for a very good cleaning effect. (Safety Precaution: Warn any nearby extruder operators that steam may escape through the extruder opening. Do not look directly into the extruder die or vents unless wearing a full polycarbonate face shield and long-sleeved shirt.)
The most important thing is to cleaning extruder frequently. The goal is to prevent old material from "baking" on the extruder metal surface. Once this happens, cleaning usually cannot remove the material and extruder manual peel cleaning will be the only remedy.
One mistake that many extruder processors make is to run the cleaning at a fixed extruder screw speed only. It is much more effective to vary the speed during the plastic extruder process, from low to medium to high, running at each speed for about 30 seconds. This will create a different shear rate on the metal surface and help remove the old material from the barrel wall.
Color or material changeovers often create problems, and plastic extruder co-minglers want to always produce the same product consistently over time. But in the real world, twin screw extruder customer demands mean frequent changeovers to produce 80 pounds of Product A, then 200 pounds of Product B, and so on. Therefore, it is important to perform changeovers in a way that minimizes pellet extruder machine operator workload and errors by.
1. Understand how important extruder cleanliness is to the next product to be run. Any extrusion shop has anecdotes of people blowing for 16 hours to avoid pulling screws to brush them off. The point is, if you know the next product needs to be thoroughly brushed, don't waste time and materials trying to clean extrusion without taking it apart.
2. If possible, plan to run extruder machine in decreasing order of cleanliness requirements. For example, this means going from lighter to darker colors. That way, you should only face one difficult transition when going from dark to light.
3. Develop written removal or stripping extrusion procedures to regulate the flow of the changeover. This helps extrusion operators plan their time and avoids later discussions about how many pounds of product must be scrapped because the plastic extruder operator did not clean the machine properly.
4. Select the right size extruder for the size of output required. This may seem obvious, but many extruder processors do not plan for the correct extruder machine run and end up running 500 lb batches on a 75 mm extruder, generating 300 lb of scrap while keeping it running properly.
5. Help the extruder operator by keeping the necessary tools, cleaning supplies, screens, templates, etc. near the extruder. If frequent changeovers are required, set up a workstation so that the extruder operator has everything he needs close by.
6. Study the flow of raw material and final product in and out of the process area. Try to schedule it to reduce extruder operator workload. The less extruder operators have to move material tubes and adjust conveying equipment, the more extruder operators can focus on maximizing run time.
Extrusion workers tend to keep the machine hot all the time. Extrusion operators usually turn on the heating zone the moment they enter the plant at 7:00 AM. If you really want to start the extruder at 8:00 AM, there is nothing wrong with that. However, people are often distracted by maintenance work and the extruder sits idle, heating up to full operating temperature for hours at a time.
This is a bad practice because it allows the polymer to bake onto the screw and barrel. Once baked, the material will continue to degrade and carbonize, making cleaning difficult to remove this material. Worse yet, when the extruder runs the product, black spots will periodically flake off the screw and barrel, contaminating the product and causing customer complaints.
The best way to handle preheating is to plan for when you really want to start running the extruder. Then, as soon as you allow for full preheat plus sufficient soak time, you can start heating extruder machine.
There is also a preferred shutdown/cooling extruder procedure to avoid black spot problems. Before shutting down the extruder, it is a good idea to "seal" the machine by maximally filling the extruder and die head with some inert polymer, such as HDPE, which displaces oxygen and covers the metal surfaces to greatly reduce oxidation and carbon formation.
After the extruder is "sealed", it is best to allow the machine to cool quickly rather than allowing it to cool over the next 18 hours due to exposure to ambient air. Emergency cooling extruders involves turning all temperature settings down to zero to force the cooling solenoid valve to open. With the cooling extruder pump running, this forces cold water to flow through all barrel sections, resulting in a rapid drop in temperature. Rapid cooling extruder does not give the polymer a chance to degrade and carbonize.
Most extruder operators tend to be like old pilots, preferring to fly by feel. Many extruder operators have a keen instinct for knowing when a process is running properly and when it's not. But as products become more complex and processing windows tighten, it is desirable to have some kind of quantitative way to assess how the machine is running.
A common example is when an extruder operators is convinced that the material is a little different. The plastic extruder production line will run very differently. If the material supplier is contacted, it may say that its QC records show that the material is the same as it has always been. Without some real numbers, how do you prove to the material supplier and yourself that the material is indeed different?
Specific throughput (kg/hr ÷ rpm = kg/hr/rpm) is proportional to fill level. Fill level is very useful, especially when records of many different products have been kept for some time, because it can help you predict how best to run new products. It can also help you plan plastic pellet extruder machine man-hours, as products that require low fill levels take longer to run a certain batch. Finally, fill level helps to scale up (or down) runs on different size extruders.
This must be calculated in two steps.
Kw (applied) = kW (motor rating) x % torque x running rpm x 0.97 max rpm.
Specific Energy = kW (applied) ÷ kg/hr
Specific energy defines the extruder power consumed per kg of material processed and the extruder mechanical work performed. Again, it is useful to keep track of this number for a specific product over time. Extruder operators will know which products are "energy consumers" and which are not. This will help in planning the operation of new products and estimating the production capacity of any given line.
Specific energy can also help identify problems. If the product always runs at a specific energy of about 0.25kW/kg/hr, and if one day it only runs at 0.16kW/kg/hr, if all else is equal, this would be reason to suspect that the material is different.
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