We recently did a PM on a Customer with 9 stretch wrappers. After performing an assessment on all the machines, we realized some of the pre-stretch rollers needed to be replaced. You may be wondering what pre-stretch rollers are. Pre-stretch rollers are located in the carriage of a stretch wrapper. The main job of pre-stretch rollers is to “stretch the film.” Film is elongated using a pre-stretch carriage on a wrapper. The film gets pulled between the rollers and is stretched prior to being applied to the load.
Why is this important?
Film that is stretched properly will hold the load more securely, be more cost effective, and lead to a more productive plant because properly maintained pre-stretch tends to minimize film breaks when wrapping skids. As you can see, there are a variety of reasons why you would want to replace your pre-stretch rollers.
What are some signs that your rollers need to be replaced (in order of amount of occurrences):
- The rollers contain debris, cuts, and rough edges.
- The rollers are smooth. Similar to a car tire, after much use the tread or grooves tend to smooth out
- The roller shafts are worn where they spin in their top and bottom bearings.
What are the common causes for having to replace your rollers?
When the film gets stuck around the rollers (see our article on how a PM can help with this problem), machine operators tend to cut the film on the pre-stretch rollers using a razor blade. What the machine operators don’t realize is as they are cutting film from the rollers, often times they end up cutting the roller as well. If your pre-stretch rollers have cuts or gaps on the surface, it will puncture holes into the film as the film is pulled tightly across the rollers. Once film is punctured, it tends to zipper causing a film break.
You should replace your rollers if they are worn smooth. The rubber on the rollers should be soft but still, have ridges. The ridges are a special pattern that can be proprietary to the machine manufacturer. The purpose of the ridges are to grab the film to stretch it. If the pre-stretch rollers are worn or smoothed out, the rollers machine can’t grip the film properly. Instead of being stretched, the film slides across the rollers causing friction and heat. When film slides across pre-stretch rollers, the risk of film breaks is dramatically increased. Film that slips off the rollers doesn’t achieve 70% of ultimate stretch thus producing an un-secure load. In addition, if your film is not stretching enough you can expect to use more film per pallet which is not cost effective.
Why is this a problem?
When pre-stretch rollers are cut, damaged or worn operators will notice the film breaks more frequently. When this happens the most common response from machine operators is to reduce the force-to-load by dialing it back on the control panel or in the touchscreen. However, reducing the force to load doesn’t actually solve the problem since the origin of the issue is the rollers. Reducing the force-to-load eventually presents a bigger problem, because often times, the loads don’t have enough holding force to say together. After a thorough assessment, our Best Packaging technicians were able to replace the rollers and bring all the wrappers back to good working condition. Since the customer chose to repair vs. buy new equipment, they ended up spending less money than they would have on just one machine.
If you experience issues with your stretch wrapper or your loads, check your pre-stretch rollers, and if you suspect your rollers are due for a swap, it’s best not to delay. Give us a call at (888) 930-BEST.