5 Common Slitting Mistakes

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25 March 2013 - 19:51, by , in Converting 101, FAQ/Troubleshooting, Comments off

Converting a roll of material can be a challenging task if you or an operator is running a new machine or material for the first time. If you are having trouble yielding the results you are looking for, the lack of results can feel even more daunting when your latest project consists of hundreds of master rolls that you need to slit quickly. Whether you are working with wovens, non-wovens, foils, films, laminates, or what have you, there are common mistakes or issues that you may run into if you aren’t getting the cut quality or rewind roll quality that you are looking for. Here is a small list of 5 common issues that you could be experiencing and potential solutions. If you are experiencing any of the issues below, hopefully we can guide you in the right direction.

1) Your rewind rolls are loose or just not as tight as the master roll.

This is a common issue we hear from our customers and we have seen it first hand in our converting department on new material runs and in the middle of larger runs. There are ways to remedy and to prevent this. REMEMBER: For first time materials, it can take a few roll runs to get the machine settings “dialed in” to get the best possible finished slit roll. Sometimes the easiest solution is just a matter of adjusting your tension settings before slitting but here are a few things to keep an eye out for.

First, check your diameter sensors: 95% of our machines are built with automatic tensioning controls that will read the diameter of the unwind and rewind rolls and automatically increase or decrease the torque or tension as the unwind roll unwinds and the slit rolls rewind. If you are operating on a machine that has an automatic tension system, check to see that the diameter sensor is positioned directly over or under your unwind roll and one of the slit rolls.

Slitter Rewinder with Inspection Lighting - 1

Adjust your tension settings: If you see that the sensors are properly positioned and are accurately reading the diameters of the rolls in question, try to adjust the tension settings in between rolls. In some cases, adjusting the tension settings during the run may have adverse effects and cause rolls to “pop” or fall over.

Air in the unwind shaft: There can be a lot of things running through an operator’s mind during a run and it absolutely true that missing one small detail can cost you a lot of time, energy, and material. It is recommended that you get in the routine of checking and making sure that that your air shaft has air in it and is properly holding the unwind roll before moving to the next step in the machine threading process.

2) The material is wrinkling as it runs across the cutting blades.

Loose/Poorly Wound Rolls
Loose/Poorly Wound Rolls

Check your unwind tension. Again, the majority of time, this is due to a tension issue. There are several things that could be causing this but the most common culprit is incorrectly set unwind tension. Having adequate tension as the material passes through the blades will decrease the likeliness of having the material fold or bunch up at any point within the webpath. When material that is loose runs through the blades, you risk having folded material cross the blades and resulting in jagged edges or a “lightening bolt” effect. Other possibilities are as follows…

Master Roll is skewed: One reason could be that the material on the rewind shaft is skewed (one side of the roll is closer to the blades than the other). If you have a rewind module with adjustable skewing controls, check to see that the roll is centered and even across the length of the shaft. If the roll is skewed, one side of the roll would feel tight and the other side would feel comparatively loose.

Check the air in the unwind shaft: Another quick thing to check is if the roll itself is moving left or right as it is being unwound or if it is unwinding while the shaft is sitting idle. Not properly filling the unwind air shaft can make the roll move left and right over the shaft. As the material moves, it can create slack in the material and begin to slit improperly. You or the operator will see this on the rewind side during the run. When the roll moves left or right, the trim or scrap rolls will become larger or smaller during the run.

Edge guide has “maxed out”: Not all master rolls are created equal. Some come in straight and flush from the core to the top layer of the material and some have more of a “cone” shape. If the roll you have started with is coned, it may be coned beyond the available unwind correction movement (left to right) capability. Basically, the edge guide can’t keep the material straight anymore and has done all it can do. If you are working with master rolls that are coned, it may be a good idea attempt a reroll first if necessary in order to straighten the rolls out. If your rolls are consistently coned beyond the correction range or capabilities of your unwind edge guide, it may be a good idea to evaluate a new unwind stand or an edge guide that has a wider range of movement.

Slitter-Rewinder-with-Inspection-Lighting-16

3) Seeing poor quality slit rolls

Blade pressure: Sometimes you may have everything in-line and operating smoothly but seeing that your cuts are fraying or your blades are simply not cutting. in this case, check to see that there is enough air pressure applied to the blades. Not enough pressure on the blades can create a less than satisfactory cut but on the flipside, too much pressure can make the bearings seize up, begin to wear down the blades and/or begin to scratch the surface of the anvil shaft. It is essential to find the least possible blade pressure that provides a satisfactory cut in order to prevent wear on your anvil shafts, blades, or blade holders.

Loose/Poorly Wound Rolls
Loose/Poorly Wound Rolls

Improper Slit Method: There are several slit methods available but they don’t always produce the same cut quality. More common methods of cutting are razor, score and shear. You can also get into some more costly and complex methods of slitting such as standard hot-knife, round blade hot-knife, ultrasonic, and even laser slitting. Depending on the material, you may yield better cuts using for example films do great using a razor slitting method. Some films can tend to have tiny “hairs” when slitting using a score blade. The cut quality is up to your end product, manufacturing environment, manufacturing process, and ultimately, your customer. We have access to all cutting methods at Pinnacle Converting Equipment.  Most of the time, a small sample of material is all we would need to evaluate your material. If you are interested in seeing how different slitting methods may affect your cut quality, connect with us to conduct a slit trial.

4) Material isn't re-rolling directly onto the core.

Some of our more custom machines have features to assist in preventing this but just in case you do not have assisted or automatic core placement features, this may be helpful. This is a common occurrence that can happen on machines that do not have any core placement features but can usually be fine tuned after the first roll is complete. If the material isn’t winding directly onto the core that you have set up on your machine, you may have made a mistake in positioning the core on the shaft. An easy method to fix this on future runs is to simply place a mark on the shaft along side of where the material is winding. Note: if you use this method to fine tune your core positioning, make sure to make the mark on the same side of each slit roll (i.e. make all marks on the left of the slit rolls or all on the right side of the slit rolls).

5) Material isn't properly slitting near the middle of the roll:

Anvil shafts are one of the strongest pieces of metal on your machine but they do have some slight malleability. Depending on the length of the anvil, the amount of air pressure the blades are set to, blade diameters, number of blades you are using to slit, and your slit widths, the anvil shaft can actually bend. This is mainly a concern for score blade slitting. If there are a lot of score blades positioned to cut, once they are activated, the amount of pressure across the anvil shaft can bend the shaft in the middle making the blades in the middle reach farther to the material and sometimes come up short. One way to avoid this to to start slitting with new blades that are all the same diameter. If you start out with blades that are all the same diameter, you can rule out that there are any differences in the blades. Secondly, try adding a little more air pressure to the blades if there is room to do so indicated by your blade pressure gauge. Lastly, you may have to cut the roll in half first and run 2 rolls instead of one. If you have to attempt this method, make sure to deactivate the blades that you aren’t using to alleviate some of the pressure on the shaft. If these solutions don’t work, your project may require an anvil shaft that is larger in diameter.

Adhesive Tape Duplex Slitter Rewinder-8

These are just a few common things that you might be running into while getting used to your slitting machine and procedure. There can be a lot of factors that could cause issues in slitting. This article may not describe the exact issues or problems that you are having but hopefully can help guide you in the right direction. If the issues listed here aren’t what you are experiencing and if you still have issues during slitting, feel free to call us at 704-376-3855 and we’ll ask the right questions to help you get the quality cuts that you need.

About author:
Pinnacle Converting Equipment of Charlotte, NC has been designing and building slitting machines, sheeting machines, and custom converting equipment since 1995.

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