Archive for the ‘Converting Tips’ Category

Understanding Lay-on Rollers and Web Tension to Achieve Superior Reel Quality when Slitting & Rewinding!!

Thursday, September 16th, 2010

by Peter Kelly Managing Director…

On my previous expose regarding reel tension on Slitting machines I purposely described how tension only in the web and how it is adjusted affects reel quality. However there is another important principle involved in the reel winding process, which for most materials is integral in achieving the highest quality reels, this being Lay-on/Pressure rollers.

Most Centre Wind Slitting Machines have lay-on rollers and all Centre Surface Slitting Machines have the capability to apply pressure to the outside diameter of the rewinding reel. There are two principle benefits to having reels being continuously pressed by a roller while winding.

a) As surface speed increases dependent on material types and surface finishes, air becomes encapsulated between each winding layer to an increasing degree the faster material travels. This causes the material to float creating a poor reel edge profile and if severe will cause telescoping. If the materials are robust, then significant increase in tension can mitigate this effect, but for most materials, this is not an option. Applying a certain controlled amount of pressure by a roller on the surface of the reel forces the air out from each layer producing a more compact harder reel. The second effect is the pressure applied by the roller at the point of contact forces the molecules in the material to touch and consequently grip producing book end quality reel sides.

b) The second advantage is that as a consequence of pressing the material layers together the actual tension required to produce a good quality reel can be reduced. This having beneficial effects on tension sensitive materials and low co-efficient surface finishes and a net gain in motor power reduction.

Understanding Web Tension to Achieve Superior Reel Quality when Slitting & Rewinding

Friday, August 20th, 2010

by Peter Kelly Managing Director…

The control of web tension in slit reels from the core to the maximum reel diameter is fundamental to achieve quality slit reels. In my experience companies the world over do not know what tension values they use to run their various materials. Slitting machines old or new will have settings that have been gained through trial and error and the intervention of operator experience to achieve an acceptable reel quality.

However, to understand the principles that are taking place will help to determine how important tension values and control is when slitting and rewinding. Two distinct rewinding methods used today are Centre and Centre Surface both having rewind shafts driving the core producing the tension that need a control to take account of the build up ratio. A simple example would be that material being wound onto a 100mm OD core with a finished reel diameter of 600mm would need to increase the energy producing the tension by six times to achieve constant tension throughout the reel. To consider the effects on the materials is to understand that each wrap is transmitting tension to all the layers above in the same way as winding a clock spring. The worst case being that the material attached to the core would be transmitting six times the tension when the reel is 600mm diameter.

In reality constant tension is rarely applied in this scenario as these varying tensions can have destructive effects on the character of the materials, quality of reel and crushing of cores.

Another aspect of reel quality and winding technique, Taper Tension is to be understood that the starting tension at core is to reduce by a selected percentage at the periphery as the reel diameter increases. The energy producing the tension will increase as the diameter rises, but not to the same degree as constant tension. This selected higher or lower degree of taper satisfies most materials with the classic signs of not enough taper being displayed on the reel sides as ‘starring’ or material flattening from the core outwards, too much taper results in the reels becoming soft, telescoping and unstable for handling.

For winding very difficult materials that have very low co-efficiency of friction such as silicone coated products, a linear taper tension is not precise enough to ensure the tension applied at each layer will prevent material adhesion breakaway. The next level of control is to employ ‘zoned taper tension’, this allows for varying degrees of taper covering the diameter range. Certain materials benefit from applying a parabolic tension profile as the reel increases in diameter, this is a calculated curve applied throughout the diameter build up. Due to the fact that characteristics of materials vary enormously, an initial judgement on the tension control type and settings should be made by an experienced individual. Trial runs should be made and the resulting reels analysed for quality and stability of the reel, along with any affect to the integrity of the material and log the results.

Changes to the tension values and profiles should be made singularly and recorded, ultimately leading to optimum values and settings for repeat quality performance.