Stop Excessive Wear Caused by Misalignment! Correct Extruder Alignment Practices to Know

Is extruder alignment important? Absolutely! The larger and longer the extruder, the more important it becomes.

Misaligned extrusion can lead to excessive wear of the screw and barrel. The barrel’s attempt to accommodate the bending motion of the screw during each rotation may cause other adverse effects, such as screw breakage, equipment vibration, additional drive load, and, in extreme cases, even "dragging the entire production line."

In this case, there is a height difference between the two machine barrels, which should actually be cleaned and aligned using optical instruments for range measurement. The current alignment status is shown in the attached figure.

Due to misalignment and improper design of the two brackets, the screw was bent into an "S" shape. Forcing the rotating screw to align with the bent barrel will result in enormous pressure between the screw threads and the barrel.

In this situation, the screw thread wear exceeds 0.055 inches, and the barrel wear also exceeds 0.015 inches. In the area of "most severe wear" before the screw breaks, even if the strength of the threaded element is ignored, a radial force of more than 155,000 pounds is required to bend the screw beyond this figure. Meanwhile, the pressure from the drive components merely forces the screw into the barrel, resulting in adhesive wear that continuously tears the metal alloys from both surfaces. Ultimately, this continuous and increasing bending exceeds the fatigue strength of the screw, leading to screw fracture.

The correct procedure is to place the optical or laser alignment mirror inside the drive sleeve and align it with the fixed centerline by rotating the drive sleeve. Then, by adjusting the barrel's bracket or feed port mounting surface, align the barrel and feed port with the centerline.

Taking a single-screw extruder as an example

An important point is that the barrel must be able to expand freely through the supports when heated, without becoming deformed. The barrel should not be locked in place by supports that completely surround it, so that it does not slide easily when expanding. The support points need to be made of non-corrosive materials, such as brass, to prevent corrosion from “freezing” the supports.

It is equally important that the entire barrel stand must be sturdy enough to maintain its position and not topple over as the barrel expands. I believe this is a major weakness in many extruder designs.

4. Since heat waves cause light to bend, barrel alignment must be performed when cooled, whether for optical alignment or laser alignment. When the barrel is heated, it does not necessarily maintain the same position as when cooled, so some additional checks should be carried out after the initial heating to ensure the alignment is flawless.

This can be done by placing a dial gauge at a 90° angle on the discharge flange to check whether there is significant deflection of the barrel when heat is applied. Some factors that may cause this deflection include:Malfunctioning brackets, heating imbalance caused by half of the heater being burned out, half of the heater surrounding the vent, or weak barrel structure.

The larger and longer the extruder, the more important alignment becomes. For larger or longer extruders, there is rarely a base with sufficient rigidity to maintain the manufacturer's alignment.

There are quite a number of skilled extruder calibration technicians who can use appropriate equipment and techniques, but some provide incomplete or even incorrect services. It is best to inquire carefully with them before proceeding.

If you encounter screw breakage, excessive wear of the screw/barrel, barrel swing, or heater creep,In the long run, starting with a properly aligned extruder can save you a lot of money and downtime.