Cutting – Processes
Reexamination Certificate
2000-01-07
2001-06-19
Rachuba, M. (Department: 3724)
Cutting
Processes
C083S349000, C083S508300, C083S674000
Reexamination Certificate
active
06247389
ABSTRACT:
FIELD OF THE INVENTION
This invention concerns a rotary cutting head for cutting polymer, especially polymer strands and the like, and a process for cutting polymer using this head.
TECHNICAL BACKGROUND
Polymers are abundant and important items of commerce, being useful in a myriad of applications. During handling, processing or reclamation of polymers it is often necessary to cut the polymers into smaller pieces of various sizes and/or configurations. For instance, when thermoplastics are produced they are often cut into pellets or granules of relatively small size so they can be easily fed to a forming machine such as an injection molding machine or an extruder.
Cutters for polymers are available in many forms. In one common form a rotary head containing knives approximately parallel to the axis of rotation is used to cut polymer against a bed knife as the polymer is being fed into the cutter head. Such a cutter is pictured schematically in FIG.
2
. In these cutters the knives are such that they cut by a slicing action, with a narrow leading cutting edge slicing through the polymer. While cutters of this type have been popular for many years, they have certain drawbacks. Among these is cutter knife breakage and/or wear, especially when hard and/or abrasive polymers are being cut. It is believed that when knives with sharp acute cutting angles are used, the small amount of metal at the cutting edge makes that edge relatively weak and prone to breakage and/or relatively fast wear. When breakage or excessive wear occurs, the cut quality is adversely affected, and the cutter must be shut down to resharpen or replace the worn or broken blades. This downtime is expensive in both actual maintenance costs and lost production time, and a polymer cutting apparatus which can cut at high speed with good cut quality, while at the same time requiring less downtime, would be advantageous.
SUMMARY OF THE INVENTION
This invention involves a rotary cutter head having an axis of rotation, comprising, one or more knives, each knife having a cutting edge on a circumferential periphery of said rotary cutter head, each knife having a knife angle of about +10° to about −15°, and a cutting edge angle of 70° or more, and provided that no point on a cutting face of said knife is further from said axis of rotation of said rotary cutter head than said cutting edge.
Also described herein is a rotary cutter for cutting polymer, comprising, a bed knife, a rotary cutter head, and a means for advancing polymer into said rotary cutter head, and wherein said rotary cutter head has an axis of rotation and one or more knives, each knife having a cutting edge on a circumferential periphery of said rotary cutter head, each knife having a knife angle of about +10° to about −15°, and a cutting edge angle of 70° or more, and provided that no point on a cutting face of said knife is further from said axis of rotation of said rotary cutter head than said cutting edge.
This invention also concerns a process for cutting polymer with a rotary cutter, wherein the improvement comprises, using a rotary cutter head which has an axis of rotation and one or more knives, each knife having a cutting edge on a circumferential periphery of said rotary head, each knife having a knife angle of about +10° to about −15°, and a cutting edge angle of 70° or more, and provided that no point on a cutting face of said knife is further from said axis of rotation of said rotary head than said cutting edge.
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Samuels Michael Robert
Waggoner Marion Glen
E. I. Du Pont de Nemours and Company
Magee Thomas H.
Rachuba M.
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