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United States Patent 3,790,093
McIntyre February 5, 1974



A granulator for synthetic plastic and other material such as cans made of thin steel or aluminum in which, instead of one screen to permit the exit from the machine of material cut to size, a second screen is also provided, the second screen being mounted adjacent the inlet side of the cutting element of the granulator and at the bottom of a vertical chute for feeding materials to the granulator.

Inventors: McIntyre; John W. (Attleboro, MA)
Assignee: Cumberland Engineering Company, Inc. (Pawtucket, RI)
Appl. No.: 05/200,130
Filed: November 18, 1971

Current U.S. Class: 241/73 ; 241/241; 241/81
Current International Class: B02C 18/14 (20060101); B02C 18/06 (20060101); B02C 23/00 (20060101); B02C 23/16 (20060101); B02c 018/06 (); B02c 013/13 ()
Field of Search: 241/24,73,77,81,84,86,88,88.2,88.3,89.3,241

References Cited

U.S. Patent Documents
2343270 March 1944 Agnew
2922585 January 1960 Searfoss
3630458 December 1971 Smiley
3561685 February 1971 Feder
3419223 December 1968 Morin
2509242 May 1950 Miller
1666797 April 1928 Snyder
Foreign Patent Documents
558,654 Jun., 1958 CA
1,073,924 Jan., 1960 DT
Primary Examiner: Kelly; Donald G.
Attorney, Agent or Firm: Davis; Albert P. Norton; Burnett


1. Apparatus for cutting material into small particles comprising, a chute having a first portion including an inlet for receiving said material for passage through said chute and a second portion offset from said first portion, said second portion being situated in a plane below said first portion whereby said material is conducted by gravity from said first portion to said second portion, rotor means in said second portion, means for driving said rotor means, said rotor means carrying a plurality of rotor knives, at least first and second bed knives secured in said second portion in spaced apart locations for cutting engagement with said rotor knives as said rotor means is driven, a first screen positioned in the path of the material moving from said inlet to said second portion, said first screen having openings of predetermined size therein, material conducted through said chute and having a dimension smaller than the openings in said first screen passing through said screen prior to entry into said second portion, the material not falling through said first screen passing over said screen and being cut by the action of said rotor knives and said first bed knife, and a second screen having openings of predetermined size therein disposed between said first bed knife and said second bed knife, said material passing between said rotor knives and said first bed knife and having a dimension smaller than the openings in said

2. Apparatus as set forth in claim 1 wherein said openings of said first

3. Apparatus as set forth in claim 1 wherein said rotor means when rotated acts to convey material not falling through said second screen to said

4. Apparatus as set forth in claim 1 wherein said first bed knife is located below the axis of said rotor means, and said second bed knife is located between 135.degree. and 180.degree. away from the first bed knife

5. Apparatus as set forth in claim 1 including an opening below the rotor means and the first and second screens in position to receive material

6. Apparatus as set forth in claim 1 wherein said chute has a substantially vertically extending section, said second portion being disposed substantially horizontally from said vertically extending section, and said first screen forming a surface of curvature connecting said

7. Apparatus as set forth in claim 1 including means for adjusting said bed

8. Apparatus as set forth in claim 4 wherein said second screen spans substantially the entire distance between said first and second bed knives.


In the synthetic plastic molding business, particularly where thermoplastics are used, scrap material resulting after the molding operation is recycled by first cutting it into small pieces and then it is fed into extruders for further molding operations. To prepare the scrap material for such recycling, it is fed through machines called granulators which cut the material into small pieces of particulate size. Such machines are generally provided with two stationary bed knives positioned around the cutting circle of a rotary cutting knife (generally plural bladed). The material to be cut up is fed into the machine where it is cut by the first bed knife. Between the first and second bed knife there is provided a screen which will pass material which has been cut small enough to meet the customer's requirements. A material which is not cut small enough to pass through the screen is moved by the rotor to the second bed knife, where it is again cut further by the rotor knives. After being cut by the second knife, the cut material is then conveyed by the rotary action of the rotary cutting knives over the top of the rotor to the first bed knife, where it is cut again. It then moves to the screen lying between the two bed knives.

This action continues until all of the material has been cut fine enough to pass through the screen.

Several problems are connected with the use of such machines as follows:

One of the problems is that some of the material which otherwise would be small enough to go through the screen gets carried around and is cut again by the second bed knife and then again to the first bed knife before it has a change to go through the intermediate screen again. As a result, some of the material which is so cut and cut again will be in the form of fine powder which is objectionable, since it may cause difficulty in the remolding operation. Also, the fine dust may create an industrial dirtiness which should be avoided.

Another problem is that machines which will take the scrap resulting from molding of large bulky objects of necessity need to have rather large entrance throats in order to feed such bulky scrap pieces to the cutting knives of the granulator. In order to provide such large throats, generally not more than three knives are used, and preferably two, with the result that the output of the machine in terms of pounds per hour or minutes is necessarily not as large as could be desired.


It is the general purpose of this invention to provide a cutting machine for synthetic plastic and other materials which solves the above two problems in an expeditious and economical way.

Therefore, among the several objects and advantages of the invention may be noted the following:

One object of the invention is the provision of cutting means for cutting plastic scrap which provides a wide throat for the introduction of large bulky pieces of scrap into the cutting mechanism.

Another object of the invention is the provision of apparatus of the above kind, in which the output of the machine is in the order of 50 percent more than the output of conventional machines of similar size on the market.

Still another object of the invention is the provision of machines of the above kinds, in which means are provided for the minimizing of particulate material which is finer than desired by the user.

Yet another object of the invention is the provision of machines of any of the above kinds, which are easy to make, use standard components for the most part, and which reliably and sufficiently perform their required operation.

Still another object of the invention is the provision of machines of the above kinds which run cooler and safer than conventional machines.

Other objects and advantages will be in part obvious and in part pointed out hereinafter.

The invention accordingly comprises the elements and combinations of elements, features of construction, and arrangements of parts which will be exemplified in the structures hereinafter described and the scope of the application of which will be indicated in the appended claims.

The invention will be described as applied to the cutting of plastics, but it will be understood that it can be applied to the cutting of other materials.

In the accompanying drawings, in which one of the various possible embodiments of the invention is illustrated:

FIG. 1 is an illustration showing generally and somewhat schematically the entire machine; and

FIG. 2 is an end elevation of a portion of the machine in schematic form given to show the critical parts of the invention.

In the drawings, for the purposes of clarity in showing the important features of the invention, conventional parts of the machine have been eliminated. Also, throughout the drawing, like parts will be designated by like reference numerals, and known details and elements will be described only to the extent required for conveying an understanding of the invention.

Referring now to FIG. 1, there is shown a cutting machine, oftentimes called a granulator, of this invention, the machine generally comprising a base 2 having an opening 4 for receiving a hopper 5 to collect cut particles. The cutting portion 6 of the machine is mounted on the base and is driven by the motor 8 in conventional manner. A vertical feed chute 10 is mounted on top of the granulator for feeding materials thereinto by gravity.

Referring now to FIG. 2, the critical features of the invention are shown. Chute 10 is shown leading to the granulator mechanism itself. The latter comprises a rotor 12 mounted on conventional bearings and adapted to be driven by the motor 8, the bearings, pulley and motor not being shown in this drawing. On the rotor 12 are mounted the fly knives 14 and 16 which are fastened thereto in the usual manner, for example, by means of the bolts 18. Since the construction of the rotary knife system is well known in the art, no further description will be given here. It will be noted that the cutting edge of the rotary knives traverses the usual circle indicated by dot and dash line 20.

Fastened securely to the granulator framework 22 is a support member 24, and fastened to the side of the chute (or preferably to the frame of the machine) firmly is another support member 26. Also fastened to the granulator frame is a third support member 28. Supports 24 and 28 must be rigid and strong because they support bed knives as described below.

Fastened rigidly but adjustably to the support 28 by means of the usual bolts 30 is a first adjustable bed knife 32. Fastened rigidly but adjustably to the support 24 by means of the bolts 34 is the second bed knife 36. In the case of the bed knife 32, the bolts 30 draw a clamping member 38 down against the bed knife so as to clamp the latter securely to the support 28. Similarly, in the case of the bed knife 36, the bolts 34 draw the clamping member 40 tightly against the bed knife so as to clamp the latter securely against the support 24. Bed knife 32 is generally below the axis of the rotor 12, and bed knife 36 is positioned between 135.degree. and 180.degree. away from the knife 32 around the cutting circle 20.

A first screen 42 provided with the openings 44 of a predetermined size is fastened by means of the outwardly turned edges 45 of the screens and bolts 46 to the supports 26 and 28. It will be understood that the screen 42 extends the full length of the rotor 12, the fly knives 14 and the bed knives 32 and 36.

It will also be noted that the screen 42 is adjacent the bed knife 32 but to one side thereof, and in addition is located in general at the bottom portion of the chute 10.

The clamp 38 is provided with a slot 48 extending its full length, and welded or otherwise fastened to the inner front edge of the slot is a rod or abutment 50 which partially closes this entrance. If desired, of course, the clamping means 38 could be milled from solid material so that the narrowed slot entrance could be provided integrally.

At suitable places in clamp 38 are provided holes 52 which are aligned with the bolts 30 in order to provide access to these bolts.

A second screen 56 having holes 58 of predetermined size is mounted between the supports 24 and 28 as follows:

The screen has outwardly turned edges 60 and 62. The edge 60 is inserted in the slot 48 and then when the screen is turned upwardly (as viewed) to bring the turned edge 62 against the clamp 40, this will rotate the edge 60 so that it is firmly engaged by the entrance-narrowing abutment or rod 50. Edge 62 is secured against the face of the clamp 40 by means of the bolts 64.

Preferably the holes 44 in screen 42 and holes 58 in screen 56 will be the same size.

Prior to operation, of course, the bed knives 32 and 36 are adjusted to be in cutting relationship with respect to the cutting edges of the knives 14 and 16. Since such cutting engagement is conventional, it will not be further described here.

The material to be cut is fed by gravity to the cutting mechanism in the direction indicated by the arrows 70 and it will be noted that because screen 42 (the first screen) is adjacent the entrance of the granulator proper, any particles which are already of a size tO pass through the openings 44 will do so, and without being further cut will fall in the direction of the arrows 70 and through the usual opening 73 provided below the granulator and into the hopper 5.

The material which does not pass through the openings 44 then enters the first cutting means which comprises the combination of bed knife 32 and the rotor knives 14 and 16. The material is then cut by this first cutting means, and a portion theereof will be small enough to pass through the openings 58 of screen 56 to emerge therefrom in the direction indicated by arrows 74 and thus fall downwardly into the hopper 5. Any material which does not pass through the openings 58 will be moved by the rotation of rotor 12 and the knives 14 and 16 to the throat at the entrance of the second cutting means comprising the rotary knives 14, 16 and the bed knife 36. The oversized material will then be cut by this second cutting means, and having been cut will then be conveyed by the rotation of the rotor over to the throat of the first cutting means (14, 32). As it is so conveyed, material thus cut which is small enough to pass through the openings 44 in screen 42 will do so and fall into hopper 5. Material which is still too large to pass through screen 42 will then be cut again by the first cutting means, and portions small enough to pass through opening 58 will do so as in the first case. This cycle is repeated until all of the material has been cut small enough to pass through the openings of the screens.

It will be noted that material which is cut by the second cutting means (14, 16, 36) is beyond the point that it can go through the screen openings 58 prior to its being re-cut by cutting means 14, 16, 32. Ordinarily, in the conventional granulator, this material which is already small enough to pass through screen 56, Will be moved against the cutting edges of knives 14, 16 and 32, with further cutting so that they are re-cut to a needlessly small size. Furthermore, the necessity in the conventional granulator of having to go through the cutting knives again slows up the output of the machine and requires more power to drive the machine.

In the instant invention, a large proportion of such material which has gone beyond the screen 58 but is then cut to the right size by the knives 14, 16 36 will pass through screen 42 and thus escape further cutting.

As a result of this construction, the output of a machine of a given size is unexpectedly increased approximately 50 percent. In order to establish this, the following test figures are given. In Test I, general purpose polystyrene tape cartridge cases were granulated into (a) a standard single screen machine and (b) the two-screen machine of this invention. The screen holes of the screens used in the standard granulator and in the granulator of this invention were 5/16 of an inch in diameter. Each machine was fed for two minutes and then allowed to clean out for 30 seconds. The results are as follows:

Test I

Machine Output Standard single screen 13 lbs. of material Machine of this invention 19 lbs. of material

Machine of this invention also produced a cleaner cut, that is, a cut with lesS "fines" therein.

In Test II, modified polystyrene runners were granulated in the same machines as Test I, except that in this test an identical weight of material was fed to each machine and the machine was allowed to run until all the material had gone through the screens and into the hopper. The time for this was measured. The results were as follows:

Test II

Machine Standard single screen 75 minutes to exhaust all material Machine of this invention 45 minutes to exhaust all material

Again, the machine of this invention produced cleaner cut material.

Thus, from the tests, it will be observed that in each of the tests approximately 50 percent increase in the output of the machine was provided by this invention as compared to a standard single screen machine.

If desired by the user, there could be more fly knives than the two shown. In general, not more than five such fly knives should be used, and the number will depend upon the size of the scrap being charged into the machine. For very large bulky pieces, two knives are preferred, whereas for smaller pieces a large number of knives can be used.

The hole size in the screens will depend upon the user's requirements as to a final product. In conventional practice, the hole sizes generally lie within the range of 1/4 inch to 3/8 inches. The hole size does not play a part in this invention.

The machine of this invention is operated no differently than is a conventional machine. The rotor speed is the same as in the case of the single screen machine.

In the above cases, the rotor 12 and its fly knives were approximately 12 inches long, and the cuttIng circle 20 was approximately 11 inches in diameter. The bed knives 32 and 36 were, of course, the same length as the knives 14 and 16 (that is, 12 inches approximately). The speed of operating the machine during the above tests was 600 r.p.m.

In view of the above it will be seen that the several objects of the invention are achieved and other advantageous results attained.

It is to be understood that the invention is not limited in its application to the details of construction and arrangement of parts illustrated in the accompanying drawings, since the invention is capable of other embodiments and of being practiced or carried out in various ways. Also, it is to be understood that the phraseology or terminology employed herein is for the purpose of description and not of limitation.

As many changes could be made in the above constructions without departing from the scope of the invention, it is intended that all matter contained in the above description or shown in the accompanying drawings, shall be interpreted as illustrative and not in a limiting sense, and it is also intended that the appended claims shall cover all such equivalent variations as come within the true spirit and scope of the invention.

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