US3630460A

US3630460A - Paper shredder

Info

Publication number: US3630460A
Authority: US
Inventors: Albert Goldhammer
Original assignee: Individual
Current assignee: Individual
Priority date: 1968-11-09
Filing date: 1969-10-20
Publication date: 1971-12-28
Anticipated expiration: 1988-12-28
Also published as: DE1808155A1

Abstract

A shredding apparatus for paper and the like is defined by a pair of spaced, parallel counterrotating rolls provided with spaced-apart, cylindrical and overlapping shredding discs. The discs do not come into contact, for friction-free operation of the shredder and have sharp corners and a high friction surface finish for engaging inserted paper. The paper is stretched and thereby torn or shredded as it is engaged by the discs and passes between the rolls.

Description

D United States Patent [111 3,630,460

[72] Inventor Albert Goldhammer l 56] ma m m s? PM UNITED STATES PATENTS My 221,744 11/1879 Sanford 241 /236 x [211 App]. No. 867,664

313,987 3/1885 Burckhardt. 241/236 X [22] Filed Oct, 20, 1969 2,236,969 4/1941 Flateboe 241/236 X [45] Patented Dec. 28, 1971 [32] pfiomy mm, 1968 3,190,573 6/1965 B ehn 241/236 [33] may 3,396,914 8/1968 L1ebman 241/236 X [3]] P 18 08 155.5 3,502,276 3/1970 Panning... 241/236 X 3 3,529,782 9/1970 Liebman 241/236 Primary Examiner- Donald G. Kelly Att0mey- Edward Brosler ABSTRACT: A shredding apparatus for paper and the like is l 54] PAPER SHREDDER defined b a pair of spaced, parallel counterrotating rolls pro- 8 Chi- 3 m vided with spaced-apart, cylindrical and overlapping Ill shredding discs. The discs do not come into contact, for fric- [52] US. 241/236 tion-free operation of the shredder and have sharp corners [51] Int. C 80% 4/08, and a high friction surface finish for engaging inserted paper.

B02c 4/30 The paper is stretched and thereby torn or shredded as it is en- [50] Field of Search 241/236 gaged by the discs and passes between the rolls.

Patented Dec. 28, 1971 3,630,460

INVENTORI- A 5537 60LOH/4MMER Attorney PAPER SHREDDER The present invention relates to a shredding apparatus for material such as paper and more particularly to a shredder provided with counter rotating rolls having opposing, counterrotating and overlapping annular rings.

Shredders having parallel shredding rolls fitted with overlapping, saw tooth-shaped external threads are known (British Pat. No. 1,002,799). The threads are fonned with outwardly arching side faces that terminate in relatively sharp but rounded ridges. The rolls are positioned so that the threads are disposed in the corresponding grooves of the opposite roll. Substantial clearance is maintained between the side faces of the overlapping roll threads. To facilitate the grasping of paper and its automatic transportation through the shredder the thread ridges have a coarse surface finish or are coated with a high-friction material.

In use, such shredders have exhibited a low capacity and function poorly. The saw tooth-shaped thread profile provides relatively small contact areas for the material to be shredded. This causes difiiculties since the material must be advanced by the rolls. The tear effect, that is the excessive stretching of the material as it passes through the space between the rolls, is relatively small even if the opposing threads overlap a substantial distance because the material is only torn at the thread ridges. However, even that tearing action is not always assured. If the inserted material comprises narrow strips, the strips can glide over the thread ridges and the material is merely crushed instead of torn or shredded, thus leading to no more than an intermittent shredding action.

Other known shredders comprise cutting devices which have a pair of parallel, counter rotating rolls. The rolls are provided with disc-shaped cutters that have sharp cutting edges in mutual engagement;

Such shredders can only operate when the cutting edges of the opposing disc cutters contact each other. The cutting edges must be sharp for a trouble-free operation. It is further necessary that the width of spaces between the disc cutters is closely controlled and equal to the thickness of the discs of the opposing roll entering such spaces.

Paper cutters of the above-outlined design require the highest precision in their manufacture and are therefore expensive. Such prior art paper cutters have another major shortcoming. The tight fit of the cutting discs, a must for their trouble-free operation, develops high friction in the area of the coacting, opposing cutting edges. Tests have shown that friction absorbs up to 50 percent of the output power of the drive motor so that the efiiciency of the shredder is quite low. Additionally, the cutting edges must be frequently sharpened to assure satisfactory operation of the shredder.

A prime objective of the present invention is to provide a shredder having a high efficiency so that its capacity is substantially greater than prior art shredders having a like power input.

A further objective of the invention is to provide a shredder which securely grasps inserted material between its counter rotating rolls and which positively shreds the material into narrow strips.

The shredder of this invention has a pair of parallel rolls mounting spaced-apart, cylindrical shredding discs of a square or rectangular cross section. The discs have sharp corners and a thickness that is at the most one-tenth smaller than the axial spacing or gap-between adjacent discs of the opposing roll. The discs extend into that gap a distance about equal to the thickness of the discs.

The shredder of the present invention has the advantage that it stretches inserted material to a much greater extent than prior art shredders having a like overlap of the cutting discs or threads. For example, the previously discussed prior art shredders provided with a saw tooth-shaped thread profile stretch the material to about 1.5 times the thread overlap. In contrast thereto, the shredding rolls of the present invention stretch the material to three times the overlap of the shredding discs.

Additionally, the tear effect is substantially enhanced by the fact that the material is simultaneously grasped by four sharp corners at each effective disc pair of the rolls. Consequently, slidable movements of the inserted material in an axial or the feed through direction of the shredder are prevented by the multiple contact points between the material and the shredding discs. To further enhance the engagement of the material by the shredding discs, the cylindrical outer surfaces of the latter preferably have a coarse surface finish to increase their coefficient of friction.

A further advantage of the present shredder over prior art shredders results from the simultaneous engagement of the inserted material by sharp disc comers and the coarse exterior surfaces of the shredding discs. The transportation of the inserted material in the feed direction and through the shredding rolls is thereby substantially enhanced. This in turn increases the capacity of the shredder while its use is simplified. It is presently preferred to form the exterior cylindrical surfaces of the shredding discs with axially oriented, relatively coarse grinding or tool marks.

This has a twofold advantage. First, it results in an excellent engagement of the inserted material by the shredding discs and, secondly, it causes sharper shredding disc corners to thereby increase the tear efficiency of the shredder significantly. It is further advantageous to surface harden the discs by a process such as nitride hardening to reduce their wear.

For highest shredding efficiency and capacity of the shredding apparatus of the invention, it is best to rotate the rolls at a rate providing a shredding disc surface speed of between about 1.1 m. (meter) to about 1.75 m. per second.

At the indicated operating speed of the shredder rolls a good feed rate of the inserted material and an excellent tear efficiency is obtained. The shredder exhibits optimum operating characteristics when the feedthrough speed and intake acceleration of the inserted material have the values obtained from the above-indicated shredding disc speeds. Furthermore, if paper is being shredded at the above speeds it is dynamically torn where it inhibits reduced strength, as compared to the papers static strength, to thus reduce the power requirement of the shredder.

In contrast to the above-referred-to prior art paper-cutting device, the shredder of the present invention has a much greater efficiency. In the present shredder the shredding discs do not come into contact, as is the case with that prior art device Energy dissipation due to a frictional engagement of the shredding discs is thus eliminated and virtually the total power input is available for the actual shredding of the inserted material.

The invention is further described in connection with the accompanying drawings and the therein illustrated embodiments from which additional features and advantages of the invention are apparent.

FIG. 1 is a fragmentary plan view of a pair of parallel shredding rolls constructed in accordance with the present invention;

FIG. 2 is a fragmentary view similar to FIG. 1 and illustrates another embodiment of the invention; and

FIG. 3 is an elevational view, in section, and is taken on line A-B of FIG. 1.

Referring to FIG. 1, the first illustrated embodiment of the shredder of the present invention comprises a pair of parallel,

nonidentical rolls

1 and 2. The rolls have cores 3 and 4, respectively, from which a plurality of

discs

5 and 6, respectively, extend. The axial spacing a2 between adjacent discs 6 of roll 2 equals the thickness d2 of the discs. The axial spacing a2 between adjacent discs 5 of roll 1, on the other hand, exceeds the thickness of opposing discs 6 of roll 2 so that the thickness dl of discs 5 is less than the thickness d2 of discs 6.

This arrangement of the discs and rolls enables the discs to overlap each other. Discs 5 of roll I extend into gaps 7 defined by discs 6 of roll 2. Likewise, discs 6 of roll 2 extend into gaps 8 defined by discs 5 of roll 1. The magnitude of the overlap corresponds to about the thickness d2 of discs 6 of roll 2.

The difference in the thickness of discs 5 and the axial spacing a2 between discs 6 of roll 2, and the difference in the thickness d1 and the axial spacing a1 between discs 5 result in an axial spacing or

narrow gaps

9 and 10 between

adjacent discs

5 and 6 in the disc overlap region generally identified with e. There is thus no contact between

discs

5 and 6 of

rolls

1 and 2 and, during operation of the shredder, no energy losses from friction between the discs are encountered.

The thickness of

gaps

9 and 10 is between 0.05 mm. (millimeters) and about 0.25 mm. Discs 6 of roll 2 have a thickness of about 5 to 6 millimeters.

As best seen in FIG. 3,

discs

5 and 6 have a cylindrical configuration. Cylindrical surfaces II and 12 and annular faces 13, 14 and I5, 16, respectively, of

discs

5 and 6 further define sharp circular edges 17, I8 and 19, 20, respectively.

The cylindrical surfaces 11 and 12 of

discs

5 and 6 are coarsely machined. The coarse surface finish is preferably obtained from tool or grinding marks which extend in an axial direction to increase the coefficient of friction of

cylindrical surfaces

11 and 12. T reduce the danger of damage to the finish of disc surfaces 11 through 16 and particularly to sharp edges 17 through 20 from accidental contact with hard foreign objects the surfaces of the discs are surface hardened.

The diameters of cores 3 and 4 and of discs and 6 are identical. The diameters and the spacing of the axes of

rolls

1 and 2 is selected so that the distance between the exterior rolls surfaces equals the overlap e plus 2s.

Passageways

21 and 22 of equal widths s remain between

discs

5 and 6 and cores 4 and 3, respectively.

In the embodiment illustrated in FIG. 1 the thicknesses d1 and d2 of

discs

5 and 6 and the axial spacings a1 and a2 between

adjacent discs

5 and 6 differ. Referring now to FIG. 2, in another preferred embodiment of the invention, rolls 1 and 2' are provided with discs 5' and 6, respectively, which have equal thicknesses d. The axial spacings between

discs

5 and 6 are also equal. In this embodiment of the invention the thickness d of

discs

5 and 6 is between 0.1 mm. and about 0.5 mm. less than the spacing a between adjacent discs 5 and 6'. Narrow axial gap 9 and therefore exist between adjacent discs 5' and 6' in the overlap region of the discs and direct contact between discs 5' and 6' of rolls 1' and 2 is prevented.

In the embodiment of the shredder illustrated in FIG. 1

rolls

1 and 2 are nonidentical since the disc thicknesses d1 and d2 and the axial disc spacings a1 and a2 of

discs

5 and 6 differ. In the embodiment illustrated in FIG. 2, however, rolls 1 and 2 are identical. For practical considerations the embodiment illustrated in FIG. 2 is therefore presently preferred.

Discs 5' and 6 are also cylindrical. The discs also include exterior

cylindrical surfaces

11 and 12 and sharp comers l7, l8 and 19, 20. The cylindrical surfaces 11 and 12 are provided with a coarse surface finish and discs 5' and 6 are surface hardened as previously described.

In operation rolls 1 and 2 or 1 and 2' are driven in opposing directions as indicated by

arrows

23 and 24 at a rate so that the cylindrical surfaces of

discs

5, 6 or 5', 6', have a speed of between about 1.1 and about 1.75 meters per second. Materials, e.g. paper to be shredded, is inserted from above between the rolls in the direction of arrow 25.

Referring now to FIG. 3, corners 17, 18 (or cylindrical surface 11) of

discs

5 or 5 and comers 19, (or cylindrical surface 12) of discs 6 or 6' intersect at point 26 at an acute angle. The magnitude of that angle has a significant influence on the effectiveness with which rolls 1 and 2 or 1' and 2' pull in the material inserted in the direction of arrow 25. The effectiveness increases with a decrease of the angle defined by

exterior surfaces

11 and 12 of

discs

5, 6 or 5, 6'. The magnitude of the angle is a function of both the overlap e and the diameter of discs 5,6or5,6.

The above-described prior art paper-cutting devices can be provided with a relatively small overlap e that may have a minimum which equals the thickness of the inserted material. However, shredders of the type disclosed herein require an overlap e which is substantially greater than the permissable minimum for such prior art cutting devices. The greater overlap is necessary because the overlap determines the extent to which the inserted material is stretched and, therefore, it determines the effectiveness with which the paper is torn. Since paper shredders are generally relatively small office appliances, the increase of overlap e through an increase in the diameter of

discs

5, 6 or 5, 6' is limited by overall size considerations. Determination of the greatest possible overlap e for maximum shredding effectiveness, and determination of the minimum angle between exterior

cylindrical surfaces

11 and 12 at their intersection 26 for maximum pull-in effectiveness therefore require an optimization of these two parameters.

It has been established that best results are obtained when overlap e is between about one-seventh to one-tenth the

diameter ofdiscs

5, 6 or 5', 6'.

The coarse, high-friction surfaces 11 and 12 of

discs

5, 6 or 5', 6 grasp inserted material at intersection 26 and thereafter pull it through between

rolls

1 and 2.

Sharp corners

17, 18 and 19, 20, respectively, of

discs

5, 6 or S, 6' prevent movement in the axial direction of the rolls of paper being pulled through the shredder. At the same time the inserted material, say paper, is stretched to a multiple of its possible elastic elongation by an amount equal to overlap e so that it is tomor shredded.

In contrast to prior art cutting devices of the type discussed above, there is no friction between the moving components of the shredder of the present invention with the exception of negligible friction in the bearings (not shown) of

rolls

1, 2 or 1', 2. This enables the use of almost the full input power for the shredding of the inserted material to give the shredder an excellent efficiency. Trouble-free operation of the shredder is assured by

construction discs

5, 6 or 5', or 6 and by determining the extent of overlap e as described in the preceding paragraphs.

Iclaim:

1. Apparatus for shredding tearable material comprising a pair of shredding rolls, each including a plurality of axially spaced ribs forming troughs therebetween, with ribs of each roll meshing with ribs of the other roll in axial spaced relationship thereto and with each of said ribs having a sharp edge at each side, whereby to grip said tearable material when passing between said rolls as said ribs pull said tearable material into said troughs to effect tearing of such material along said sharp edges.

2. Apparatusin accordance with claim 1, characterized by each of said ribs having substantially parallel side surfaces and substantially cylindrical surface connecting with said side surfaces in sharp edges.

3. Apparatus in accordance with claim 2, characterized by the substantially cylindrical surface of each of said ribs having axially directed markings therein, whereby to increase the grip of said ribs on tearable material passing between said rolls, while said ribs pull said tearable material into said troughs to effect tearing along said sharp edges.

4. Apparatus in accordance with claim 2, characterized by a spacing between each of said ribs and the proximate walls of its associated trough being of the order of 0.050.25 mm.

5. Apparatus in accordance with claim 4, characterized by each of said ribs on its cylindrical surface, having axially directed markings therein, whereby to increase the grip of said ribs on tearable material passing between said rolls, while said ribs pull said tearable material into said troughs to effect tearing along said sharp edges.

6. Apparatus in accordance with claim 3, characterized by means for rotating said rolls in opposite directions and at like speeds.

7. Apparatus in accordance with claim 6, characterized by I the speed on the cylindrical surfaces of said ribs being of the order of 1.1- l .75 meters per second.

8. Apparatus in accordance with claim 3 characterized by a spacing between each of said ribs and the proximate walls of its associated trough being of the order of 0.05-l.75mm., and

means for rotating said rolls in opposite directions with a speed on the cylindrical surfaces of said ribs of the order of 1.1-1.75 meters per second.

Claims

2. Apparatus in accordance with claim 1, characterized by each of said ribs having substantially parallel side surfaces and substantially cylindrical surface connecting with said side surfaces in sharp edges.

4. Apparatus in accordance with claim 2, characterized by a spacing between each of said ribs and the proximate walls of its associated trough being of the order of 0.05-0.25 mm.

7. Apparatus in accordance with claim 6, characterized by the speed on the cylindrical surfaces of said ribs being of the order of 1.1-1.75 meters per second.

8. Apparatus in accordance with claim 3 characterized by a spacing between each of said ribs and the proximate walls of its associated trough being of the order of 0.05-1.75mm., and means for rotating said rolls in opposite directions with a speed on the cylindrical surfaces of said ribs of the order of 1.1-1.75 meters per second.