|
|
Home
|
|
Maverick now offers injection molding preventative maintenance packages to the plastics industry! Repair, troubleshooting, and installation of injection mold machines and peripheral equipment.
|
|
|
|
|
Offsets - What they are and why they matter |
|
|
Setting the laser up on the true center of the axis of rotation of the output shaft/thrust shaft (drive train) reveals errors both vertically or horizontally from the centerline at the feed chamber and the barrel input. This deviation is the called the offset.
Causes of offset error:
- Manufacturer alignment error due to not setting the feed chamber to the centerline of the axis of rotation.
- Feed chamber replacement without matching the feed chamber centerline to the thrust shaft centerline.
- Refurbishing feed chamber without matching the feed chamber centerline to the thrust shaft centerline.
The laser system will clearly show if there are any offsets in the vertical or horizontal axis, at the feed chamber and the barrel input.
Most offsets are relatively small, under .003, but we have experienced well above that, up to .030 in both the vertical and horizontal axis. Although we still find some of the newer extruders with more than .003, the higher offsets are found mainly in older extruders.
Offsets that differ between the feed chamber and the barrel input indicates a step either vertical or horizontal where the two surfaces meet. This causes the barrel input to wear down until the step is relieved, which will also be creating wear on the screw at the barrel input.
Most customers seem surprised when we show them the offsets we find at the feed chambers or the barrel input and want to know what can be done to correct this.
Feed chamber offset corrections:
Most feed chambers have flanges that bolt directly to the gearbox, which doesn't allow much adjustment, if any. We have been successful in some cases of removing .003 to .005 of the error in the older extruders. However, to correct the feed chamber offset problem would most likely require machining of the flange to adjust the centerline of the feed chamber to the centerline of the thrust bearing.
Barrel offset corrections: (barrel input)
The barrels have flanges that attach directly to the feed chamber. In addition, most barrels also have pilots that match to pilot guides on the feed chamber, which lessens the ability to adjust the input end of the barrel even more. While most pilot/pilot guides have up to .005 tolerance, there are some that are a tight fit, allowing no movement at all. Depending on the amount of tolerance in the pilot/pilot guide fit, it may be possible to adjust small amounts of offsets at the feed chamber/barrel input connection; but only if the flange bolts have enough tolerance to allow the adjustment as well.
Recommended offset solution:
First, if the offsets are opposite between the feed chamber and the barrel input, you will probably be able to feel a step where the barrel makes contact to the feed chamber. That should be the first adjustment you attempt to make to prevent wear as talked about above. If correction isn't possible, get it as close as possible.
We recommend aligning the barrel output to the offsets established at the barrel input as this will allow the barrel to be parallel to the centerline of the axis of rotation.
See the offset illustration for detailed view.
|
|
Last Updated ( Tuesday, 27 September 2005 )
|
|