Method and apparatus for scrap removal from rotary dies

#The present invention relates generally to the field of rotary die cutting devices which are useful for manufacture of carton blanks and other workpieces from sheets or webs of material, and particularly to rotary die cutting machines used in high speed rotary cutting of a moving sheet or web of paper, paperboard, plastics and composite materials.

#As one example, rotary die cutting machines are used for the high speed mass production of paperboard carton blanks that are subsequently folded into the shape of carton or box containers. In rotary die cutting, the cutting operations can occur by either of two methods, the first being referred to in the trade as rotary pressure (“RP”) cutting and the second as the “crush cut” method. In the rotary pressure cutting method, the paperboard material from which the carton blanks are generated is advanced at high speed between two rotary die cutting cylinders. The cylinders are provided with cutting elements on them which cooperate to form cutting dies to cut the desired shape of the carton blank as the material advances between the cylinders. The cylinders rotate at the same speed so as to maintain registration of the co-acting cutting surfaces. Each rotation of the cylinders generates a discrete series of one or more cartons depending upon the size of the cartons, diameters of the cylinders, etc. In the crush cut method, one of the cylinders, the cutting cylinder, is provided with knife blades that perform the cutting operation and the other cylinder, known as the anvil cylinder, provides a smooth surface against which the knife blades operate.

#In both the above described processes there is necessarily generated a certain amount of scrap material. This material needs to be separated from the carton blanks and removed from the dies as each revolution of the cylinders generates a new series of carton blanks. There are various ways in which the scrap removal process is conventionally performed. In one method, the scrap material is initially retained on one of the die cylinders by stripping pins that hold the scrap pieces onto that cylinder as the carton blanks are advanced away. Thereafter, the scrap pieces are removed from the die cylinder by a stripping comb. Alternatively, scrap removal is accomplished separately from the cutting operation. In this method, the carton blank and scrap pieces are retained as contiguous pieces by leaving uncut during the cutting operation. The attached pieces are then carried to a stripping station. At the stripping station, the scrap material is removed from the carton blank by piercing the scrap portions with stripping pins carried on a rotating cylinder. As in the previous method, the scrap pieces are retained on the pins by the rotating cylinder until they are stripped off the pins by a stripping comb. A yet further alternative system employs a stripping station which removes the scrap pieces by rotatably registering male elements to “punch” the scrap from the moving web of pre-cut products.

#FIG. 1 schematically illustrates a typical example of a prior art rotary pressure type die cutting apparatus provided with conventional stripping pins and a stripping comb for scrap removal. For purposes of clarity, the cutting elements on the upper and lower dies are not shown.

#FIG. 2 is a fragmentary section view of the rotary die cutting system of FIG. 1, but further showing the cutting elements on the upper and lower dies.

#FIG. 3 is a fragmentary section view showing the lower die cutting cylinder rotated clockwise 90 degrees from the position shown in FIG. 2, at the position where the scrap removal step is performed.

#Referring now to the drawings in detail, and particularly FIGS. 1-3, there is shown a conventional rotary die cutting apparatus of a rotary pressure cutting type well known in the prior art generally designated at 10. The apparatus comprises a pair of upper and lower rotary dies 11 and 12, respectively, for cutting blanks 14 from a web 16 of sheet material passing between the dies. The upper and lower dies 11 and 12 are removably mounted to carrier cylinders, 17 and 18, respectively. The blanks 14 are generated by cutting the moving web 16 between co-acting edges of cutting elements 19 located on the upper and lower dies as the cylinders 17 and 18 are rotated in synchronicity in opposite directions of rotation by a suitable drive mechanism (not shown). Stripping pins 20 are mounted to the lower die 12 in those areas where scrap portions 22 are generated by the cutting process. Typically, the upper die 11 is provided with clearance holes 24 that register with each of the pins 20 as the pins reach the cutting position of the dies.

#Referring now to FIGS. 4 and 5, the stripping pins 20 typically are provided with a relatively sharp tip 21 adapted to pierce through the workpiece material, such as paperboard or plastic, and thereby retain the scrap portions as the blank portions advance through the space between the dies. In addition, the pins 20 may include a barb or undercut, such as at 23, to facilitate retention of the scrap portions thereon. A male threaded portion 25 allows the stripping pins to be screw mounted to the die inside tapped mounting holes.

#Referring again to FIG. 2, it can be seen that the tips of the stripping pins 20 extend above the top surfaces of the cutting elements 19. As the lower cylinder continues to rotate in a clockwise direction 90 degrees to the position shown in FIG. 3, scrap portions 22 retained on the lower die by stripping pins 20 will come into contact with teeth 28 of stripping comb 29. The pins 20 do not come into contact with the stripping comb because they pass through the spaces between the teeth 28.