As the most popular plastic compounding machine, a twin screw extruder has dominant advantages compared to a single screw extruder. But a twin screw extruder is also a machine which still has some problems during the operation wherever you buy this twin screw extruder.
Here are some common problems which almost all twin screw extruders might have during the operation.
Twin Screw Extruder Common Problems And Solutions
1. Extruder Overload
In this case, the operator or maintenance manager should check the extruder step by step to eliminate the reasons that caused this over-load alarm. That will feedback via the extruder ampere. If the ampere exceeds the maximum ampere of the motor. The extruder will alarm and stop immediately to protect the extruder parts from breaking.
1.1 Feeding rate
Too much material feeding should be one of the reasons cause extruder is overloaded. The extruder feeding volume is fixed since the Do/Di is fixed. This DO/DI decide the maximum volume that the extruder can eat.
Solution: Slow the feeder speed to allow a bit less materials intake.
1.2. Screw elements wearing out
After a long time of operation of the twin screw extruder, the screw elements might be worn out due to the friction with the material in the long term. That will weaker the extruder eating capacity. When the feeding rate keeps the same, the extruder is quite easily to be overloaded.
Solution: Take out the screw from the extruder, check the wear-out screw elements and change them.
1.3. Hard materials/metals falling into the extruder
This happens from time to time due to the wrong operation. That metal might be from the materials or even a screw nut/bolt close to the feeding throat falling into the extruder. That makes the extruder load significantly increase in a second.
Solution: Take the screw out from the twin screw extruder, check the screw, and remove the hard materials or metals. Also, check the inside of the barrel if there is some hard material or metal residue, clean the barrel before putting the screw back into the extruder. If some screw elements are seriously damaged, you need to change them.
Furtherly, check the aliment of the shaft, when the hard material or metal gets into the extruder, the shaft, the screw load will significantly increase to a higher level. Sometimes the safety clutch will disconnect when the load overtake the allowed torque. That easily gets the screw elements cracking and twisting the shaft. This checking is a must if this happens.
1.4. Extruder heater fault
When some of the heaters of the twin screw extruder do not work properly. That means the extruder zones are not heated. So the material could not be melted in those zones. That will cause an increase in the extruder ampere. Thus it will make the extruder alarm overloaded.
Solution: Check the heaters from the temperature controller and solid state relay to check the exact zones in which the heaters are not working. Change the heaters.
2. Raw Material Components Are Not Well Mixed And Dispersed
Some customer will encounter such problem on the new extruder. They run the extruder for many different formulations and materials, finding out that some of the formulations are not applicable on the new extruder. Such as that the mixing and dispersion of materials are not qualified, the materials are burnt in the extruder, etc.
There are several reasons for this.
2.1. Screw configurations
The extruder supplier will deliver the extruder with one original screw configuration which is customized for a specific formulation when come into the purchase. But as a universal extruder, the twin screw extruder is enabled to process many other different materials and formulations. So some customers don’t have too much experience with the extruder principle. They run the extruder for other formulations without changing the screw configuration.
Solution: Need to change the screw configurations based the specific formulations or materials. If you don’t know how to redesign the screw configuration, you can turn to your extruder supplier for some valuable advice.
2.2. Temperature setting
In different formulations, the temperature setting will be different.
Solution: Change the temperature based on the physical data of different polymer and additives. Meanwhile customer should also consider the shearing heat of the screw in order to avoid the over heating for the melt which might damage the
melt. For some heat sensitive materials, need to less heating and shearing heat,
Also need to make sure the cooling system works well to keep the melt cooled sufficiently.
Conclusions
There might be some more specific problems for different extruder with different specifications during the operation of the twin screw extruders.
Meanwhile, different educated operator makes difference on operation of twin screw extruder as well as the maintenance abilities.
From the twin screw extruder manufacturer side, they have to get enough knowledge on the polymer compounding by twin screw, furtherly they should know the end users’ various applications on the twin screw extruder. Those factors should be considered from the proposal discussion to the design of the twin screw extruders. What’s more, extruder supplier should give enough valuable support to customer to help them make the best quality products on the twin screw extruders.
