Blade thickness
Because material is displaced rather than removed in rotary knife cutting, think of the blade as a wedge. The thicker the blade, the greater the displacement. This displacement can cause fracture in rigid profiles and tubing, which is often observed as a whitening on all or a portion of the cut. You can reduce this fracturing by reducing the thickness of the blade. (This effect can also be minimized by heating the profile or tube. However, if heat is used to enhance cut quality, the bush- ings must be supportive enough to minimize distortion.)
If the cutting blade is too thin, it may actually deflect within the bushing bore. This can lead to "S" shaped cuts or prema- ture blade breakage.
Optimizing blade speed
Flexible extrudates generally require a very fast blade speed with a slicing action for best results. This is due to the fact that even minimal interruption can cause a blade jam on a product that has little or no internal strength.
On the other hand, rigid extrudates may require different blade speeds to obtain the desired cut quality. What's needed for a particular application depends on blade style, internal heat, and blade thickness. Speeds as slow as 300 rpm may be required if a curved blade is used with little or no heat.
Improving cut quality by adding heat to certain materials
All rigid extrudates can have their cut quality improved by the addition of heat. A few of the most common materials and the respective temperatures are listed below:
Rigid PVC | |
Styrene ABS | |
Polypropylene |
It is important to remember that as the temperature approaches the glassification zone, the degree of support offered by the bushing becomes more important.
CUTTER BLADE
SELECTION
AND USE
UGE059/1003 | CUTTER BLADE SELECTION AND USE | APPENDIX |
