Signs of abrasive wear
Abrasive wear is perhaps the most common type of wear in Twin Screw Extruders, it results in the erosion of both machined screw and barrel components. The sharp machined corners of screw and kneading elements appear rounded, smooth, and occasionally polished.
Typically, the part of a configuration most affected by wear is the last set of feed screws and first set of kneading elements. As abrasion progresses, the position of wear and the melting point will move further along the barrel. This reduces the effective length of the extruder that is used for mixing and will in turn reduce the achievable output.
The effects of abrasive wear
- To compensate for the reduction in output the operator may increase rpm which will result in accelerating the abrasive wear.
- The clearances between the screws and barrel will increase as the parts become worn, which reduces the self-wiping benefits of the twin screw design.
- Cleaning times are longer, and the extruder will require more purging material.
- There is also the possibility of melt stagnation in the worn area, which may result in the formation of cured “gel bits”.
- Fatigue failure is an additional risk when wear becomes extreme. The extruder shafts are unrestrained in the worn sections and may be subjected to strong bending forces and ultimately premature failure.
When does a part need replacing?
As a rule, parts need replacing when a reduction in output and/or quality can be observed. By checking inside of the extruder barrel on a monthly basis, wear can be assessed in the early stages and replacement parts can be ordered before any additional damage is caused.
XTS owners can easily perform this as a method of best practice, the clamshell barrel included in all our extruders provides quick and easy access to the screws & shafts. We can also supply wear gauges for all XTS extruders to make the process even simpler. For extruder owners with closed or fixed barrels such as those from Coperion, we can offer alternative methods of wear measurement.
If you have any questions regarding abrasive wear, wear measurement or any of the topics mentioned in this article, don’t hesitate to contact Xtrutech at sales@xtrutech.com