Hello & Greetings Mr. Bond,

What is your rewind (winder) initial tension?

What is your rewind (winder) tension taper (the tension must decrease as the diameter of the finished roll increases)?

What type of plastic film are you winding? PET, PE, PP, etc.

What is the meaning of "PIB"?

I am an engineer with a coating/laminating company and may be able to help, provided the above questions are answered.

Mike

Plastic beading we use is polyethelene. The PIB I refered too is Poly butene which is used for creating a `stickyness' that sticks only to itself. The function of the film is pallet wrap for transporting of goods.

In regards to the winder, it is set to compensate for the increase/ decrease of film from the driven to the driver. It is fed through a number of winders and a banana roll to maintain consistant tension.

Very good, Mikerho-you mentioned tension taper. When winding a web the tension is a product of positive torque (overdriven winder with unwinder braked) or negative torque (constant-speed winder with braked unwinder).

To describe web tension we use the term "PLI" (pounds per linear inch) to describe the tension units. In other words, let's say the web is 10" wide and a winder is set to maintain 1 PLI. When the winding roll reaches 24" diameter this value of 10 will translate to a torque meaurement of 10 pounds/foot. (12" radius x 1 x 10). The winder must maintain this tension throughout the winding process so either the unwinder or winder (usually both) must change speed to maintain correct tension.

Does your machine use load cells to measure running tension and translate this to a signal that can be understood by the winder drive? I see that you mention a "banana roll" which I think we would call a bowed roll. Are the bearings of the bowed roll free turning? What is the "tack" of the bowed roll's rubber cover, and it this causing a tension increase? Bowed rolls can cause a lot of grief when they are stiff to turn, or too "tacky" for the web media.

Some media is much harder to wind than others, with the thinner products causing the most grief as they do not forgive upward tension shifts. I know how paper and nonwoven products behave, and image that the plastic you are winding is much the same save for one (1) characteristic-higher elasticity. This characteristic is acting as stored energy, and once it builds to a certain point it is crushing the core.

So, I would check to determine how the machine measures a pre-set tension value while it is running, and how it communicates this value to either the drive, the braking system, or both. If it is equipped with load cells, make sure they are calibrated and functional, and make sure the web path through the rolls is correct. Load cells can become "lazy" as their springs relax over time. If you have these, let me know and I can tell you an easy way to check and calibrate the control.

Best Regards,

Ing. Robert Forbus

Is this a centre driven winder, surface driven, or 2 drum winder?

On 2 drum winders with a rider roll, the initial loading of the rider roll can damage the cores, especially as the rider roll is initially lowered.

To reduce the wound in tension you would have to reduce the rider roll pressure, change the torque differential between the drums, and reduce the web tension (TNT = Tension, Nip, Torque).

Surface driven single drum winders have an advantage (disadvantage?) of eliminating the torque differential variable.

If reducing web tension still allows crushed cores you will need to go to a heavier walled core. The cores are available in various wall thicknesses, and hardness, along with steel tips, plastic inserts, keyed ends, etc. Your supplier should be able to help you.

You mention testing the cores. I would suggest a simple parallel plate arrangement with a controlled applied pressure while measuring the amount of deformation and ultimate failure point would be sufficient. (Basic stress strain type measurement.) Using a given test length of core you could determine a pressure / deflection and build your own table of merit for your core samples.