US3302893A - Disc mill - Google Patents

Description

Feb 7, F. R. FEDER AL DISC MILL Filed Feb. 18, 1964 5 Sheets-$heet l INVENTORS FRIEDHELM R. FEDER JOHN R. THOMAS w. E. WILLOUGHBY BY %W//M AT TORN Y.

Feb. 7, 1967 DISC MILL Filed Feb. 18, 1964 F. R. FEDER ETAL 3 Sheets-Sheet 2 V ATTOR Y.

DISC MILL Filed Feb. 18, 1964 3 Sheets-Sheet 5 F160 5.. 9 FIG 6. FIG. Z

CONTROLLER TIMER -70 n INVENTORS FRIEDHELM R. FEDER 5 .r- JOHN R. THOMAS BY 68 7 W. E. WILLOUGH ATTO NEY.

United States Patent 3,302,893 DISC MILL Friedhelm R. Feder, Westfield, N.J., John R. Thomas,

Elmhurst, Pa., and William E. Willoughby, Bernardsville, N.J., assignors to Wedco, Iuc., Garwood, N.J., a corporation of New Jersey Filed Feb. 18, 1964, Ser. No. 345,740 13 Claims. (Cl. 241-37) This invention relates to disc mills and more particularly to disc mills suitable for the working of plastics.

Disc mills for the size reduction and working of pulp and meal are very old. In recent years these mills have been used for size reduction of plastics. For example, plastics are readily available for primary reducers in a so-called pellet form, i.e. particle about minus fl p-minus inch, and for some uses of the plastic it is desired that it be provided in much finer form, e.g. powder form.

It has been observed that the known disc mills have disadvantages when utilized for working plastics. Thus, the plastics which are commonly treated are thermoplastic materials and a problem arises with respect to heat generation in that in the working of the material, the temperature is frequently raised to such a point that the material becomes plastic and the particles coalesce. This occurrence of course amounts to a gross interference with the processing and requires interruption of the operation of the mill for cleaning to free the working surfaces of the mill of adhering plastic material and to remove from the mill the glomerates of plastic which are formed upon the coalescence. In order to avoid the overheating of the plastics, it is common, when utilizing mills of known construction, to operate the mill at a throughput rate very substantially below what can be denominated the full capacity of the mill.

Accordingly, a principal object of the instant invention is to provide a disc mill construction particularly adapted to the processing of plastic materials, and which construction permits operation at near capacity of the machine. A further principal object of the invention is to provide a disc mill construction characterized in that upon overheating of the plastic material being worked, so that agglomeration of the material occurs, necessitating a shutdown and clean-up of the equipment, this work can be performed readily without the necessity of laying the equipment olf for a prolonged period.

The manner in which these and other objects are attained, will be apparent from the following description taken in connection with the accompanying drawings, wherein:

FIG. 1 is a side elevation, partially in section, showing an embodiment of apparatus according to the invention;

FIG. 2 is a cross-section view taken along line 22 in FIG. 1;

FIG. 3 is a cross-section view taken along line 33 in FIG. 2;

FIG. 4 is a cross-section view taken along line 4-4 in FIG. 1;

FIG. 5 is a front elevation view of one of the discs of a disc mill and is shown in FIG. 1;

FIG. 6 is an enlarged view of a portion of the apparatus shown in FIG. 1, more particularly, of the working faces of the discs shown in FIG. 1;

FIG. 7 is an enlarged view of a portion of a working face of a disc as is utilized in apparatus according to the invention;

FIG. 8 is a cross-section view taken along line 8-8 in FIG. 7; and

FIG. 9 is a schematic view of a control arrangement for the apparatus shown in FIG. 1.

In the drawings, like reference characters refer to corresponding parts.

According to the invention a disc mill includes a first disc and a second disc, and the discs are mounted in opposed relation, as is generally true for disc mills. A first shaft is provided and has the first disc mounted thereon, and this shaft extends axially outwardly from the disc mounted thereon. A second shaft is provided for the second disc, and the second shaft extends axially outwardly from its disc. The two shafts extend axially outwardly of the opposed discs in opposite directions. One of the disc-shaft pairs is mounted on a support and means are provided for moving this support relative to the other disc so that the supported disc can be moved toward and away from the other disc along a defined path. Fluid pressure means are provided for urging the movably supported disc toward the second disc, and spacer means are provided for limiting travel of the movable disc toward the stationary disc in response to urging of fluid pressure means, and, thereby, a suitable spacing of the discs for milling is obtained. Load sensing means are provided for sensing overload of the mill, and, further, overload relief means are provided. The overload relief means are connected to the load sensing means for response to the load sensing means, and are effective in response to control the fluid pressure means upon occurrence of overload to move the discs apart for relief of the overload and to then move the discs together to the milling spacing.

Referring to the drawings, the device there shown includes a disc mill assembly 11 wherein the first disc 15 and the second disc 16 are contained in a casing 13 having a closure 14. The first disc 15 is fixedly mounted on shaft 17 for rotation therewith, and the second disc 16 is fixedly mounted on shaft 18 for rotation therewith. The shafts 17 and 18 extend axially outwardly in opposite directions from the opposed discs 15 and 16. The first disc 15 is made up of the support ring 19, disc spokes 20, and the disc working face 21 which is bolted to the support ring 19. The second ring 16 is made up of the support 22 and the working element 23, which is bolted to the support 22. A feed baffle 24 is secured to the closure 14 and terminates in the peripheral portion 25 which extends into the spokes 20. The feed baflle 24 serves to direct feed to the mill to between the discs, and this feed baflle construction is known in the art. A feed pipe 27 passes through the closure 14 and the baffle 24 and serves to direct feed to within the baffle, and the baffle, in turn, serves to direct the feed toward the discs. The feed flows from the space enclosed by the baflle 24 to between the spokes 20 and on to between the discs and is then exposed to the working action of the mill.

The shaft 18 on which the second disc 16 is mounted, is journaled in the journal blocks 28 and 2-9 and this shaft is provided with a drive wheel 30 which is connected to a motor 31 by belt 32. The motor 31 can be a variable speed motor. The journal blocks 28 and 29 are mounted on the frame 12, respectively, by supports 33 and 34, and the motor 31 is also secured to the frame 12 by the support 35. The shaft 18 is provided with a bore 36 which extends axially therethrough and communicates at the outer end with fluid conduit 37, and at the inner end with the annular slot 38. Radially outwardly extending tubes 39 communicate with the slot 38 at one end thereof, and, at the other end thereof, communicate with the outlets 40 which are disposed at spaced intervals about the working face 23 of the second disc 16. 'Fluid, gas or liquid, for cooling can be introduced into the bore 36 from the fluid conduit 37, and can pass from the bore 36 via the passageways 39 to the outlets 40, so that such fluid is introduced into the vicinity of the working of the material and cooling can thus be eflected by the fluid.

The shaft 17 on which the first disc is mounted extends through journal block 41 and journal block 42. A drive wheel 43 is mounted on the shaft and this drive wheel is connected with the motor 44 by drive belt 45. The motor 44 can be a variable speed motor. The journal block 41 is secured by bolting 46 to the disc assembly closure 14, and this journal block, as well as journal block 42 is mounted on the car 48 which, as is more fully described hereinafter, serves for carrying the parts mounted thereon. The motor 44 rests on bed plate 49, and this bed plate is supported by the uprights 50. The car 48 includes runner 51 which is slidably mounted on the track 53. Thus, by movement of the car over the track 53, the motor 44 and the shaft 17 together with the parts associated therewith including the first disc 15 and the closure 14 can be moved relative to the second disc 16 and the casing 13, and the parts associated with the second disc 16, including the shaft 13.

The means provided for moving the car can be best seen in FIG. 2, FIG. 3, and FIG. 4. Thus, mounted on the frame 12 is the track 53 having side extensions 54 which are bolted to the frame 12. The car includes runners 55 which are formed so as to be received in complementary manner by the track 53, and the runners 55 are slidably movable over the track 53. The frame 12, the track 53, and the runners 55 are provided, respectively, with cross-pieces 12a, 53a, and 55a. Mounted on the track cross members 53a is the cylinder piston assembly 56, by bolting 57, and this assembly includes the piston rod 58 which has mounted on the end thereof the flange 59. The flange 59 is secured to the cross member 55a of the car. The car can be moved over the track by operation of the piston-cylinder assembly.

In the embodiments shown, the piston-cylinder assembly 56 is a hydraulic arrangement, and this assembly includes as well as the piston rod 58, the piston 60. Hydraulic fluid is maintained on each side of the piston 60 and is supplied to one side thereof by hydraulic fluid supply lines 61, while it is supplied at the other side thereof by hydraulic fluid supply line 62.

Referring to FIG. 1, by suitable operation of the piston-cylinder arrangement 56 shown in FIG. 2-FIG. 4, the car can be moved back and forth on the track 53 and thus the first disc 15 can be moved toward and away from the second disc .16, since the disc 15 is mounted on the car. An adjustable stop means 63 is secured to the track 53 and serves to limit the extent to which the car can travel to the right, as is shown in FIG. 1. Thus, the extent to which the first disc can be moved toward the second disc can be controlled by the stop means 63. This stop means is adjustable so that the spacing between the discs 15 and 16 can be controlled by manipulation of this stop means. A micrometer-type adjusting means can be provided so that the spacing of the disc plates can be selected in units of 0.001 inch. Outfitted with a stop means, such as stop 63, the device can be operated in the manner that the piston-cylinder arrangement normally urges the first disc 15 toward the second disc 16 and so that the runner 5.1 of the car is normally in abutting relation with the stop means 63. Further, means can be provided so that in the event of an overload on the machine as may occur when the feed rate becomes excessive, the piston-cylinder arrangement can be actuated so that the car moves to the left (as shown in FIG. 1), whereupon the first disc 15 moves away from the second disc 16 so as to relieve the overload. Upon relief of the overload, the piston-cylinder arrangement can be actuated to return the car to its normal position with the runner 51 abutting with the stop means 63. Desirably, the means for occasioning the movement of the first disc 15 away from the second disc 16 upon the occurrence of overload, is provided so that upon such operation the device goes through a cycle wherein the first disc moves away from the second disc 16 and then returns to its normal work position, all automatically.

A further feature of the disc mill according to the invention, is that the mill can be conveniently opened up to provide access to the inside thereof. Thus, the device can be constructed so that when it is desired to open the mill to expose the working surfaces of the disc, the usual overload control means can be disconnected, and the piston-cylinder arrangement 56 can then be actuated to move the discs apart a distance such that they are exposed for working. Thus, to service the discs, the car on the track 53 can be moved to the extent that the closure 14 of the disc mill assembly is removed from the casing 13 and the first disc 15 is moved to without the casing 13.

In the normal running operation wherein provision is made for relieving overload, the closure 14 does not move to the extent that the disc mill assembly is opened. An overlap is provided so that the closure .14 may move an amount appropriate to relieve the overload while at the same time the casing is not opened. Thus, the casing 13 is provided with the angle iron seat 64 and the closure 14 is provided with the extension 65, and the extension 65 is slidable in the seat 64 and is closefitting therein, so that as the closure 14 moves back and forth in the relief of overload, the extension 65 slides back and forth in the seat 64, but is always in engagement therewith.

A control arrangement suitable for facilitating operation of the mill as is described above is set forth schematically in FIG. 9. Each side of the piston 60 of the piston-cylinder arrangement 56 is filled with hydraulic fluid, and the corresponding fluid bodies are maintained under suitable pressure by auxiliary cylinders 75 and 76 which communicate, respectively, with the two sides of the piston 60, via lines 77 and 78. The auxiliary cylinders, in turn, are maintained under pressure by the air cylinders 73 and 74 which are communicated with the air accumulator 67 and the air compressor 66 by, respectively, air lines 69 and 70, and the manifold line 68. A pressure differential across the piston 60 is maintained so that in normal operation the first disc member 15 is urged toward engagement with the second disc member 16 and so that the runner 51 of the car is urged into abutting relation with the stop means 63. To provide the desired cyclic operation for relief of overload, means are provided for sensing the overload, and in the embodiment illustrated, this detection is provided by ammeter 87, in the lines 89, to the motor 44. Upon the occurrence of overload, current will increase. The ammeter will sense the increase in current, and is connected by line 91 to the controller 93 so that upon the occurrence of an overload, the ammeter will actuate the controller. The controller can include a sensitivity means, for example a time delay, so that operation thereof is dependent on the overload existing for more than say about to 15 seconds, commonly about 3 seconds. Power is introduced into the controller via line 99 and the controller is connected to solenoid valves 71 and 72 in, respectively, lines 69 and 70 by, respectively, power lines 97 and 96. Further, operation of the controller 93 in response to overload occasions activation of the timer 95 which serves to provide the desired timing for the cycle. Thus, each of the valves 71 and 72 is a two-way, three-position valve. In one position, each of these valves communicates the inlet and outlet side of the air line with which it is connected, and in its other position it communicates the low pressure side of its air line with the atmosphere to release air from the low pressure side (the piston-cylinder arrangement 56 side). As illustrated in the drawing, upon occurrence of overload, the piston rod 58 initially moves to the left to occasion separation of the discs, and following such movement, the piston rod moves to the right to bring the discs back to the working position. Upon the occurrence of overload, excessive current is taken by both of the motors 44 and 31 and this is sensed by the ammeter 87 in the power line of the motor 44. Thereupon the controller 93 is actuated so that the valve 72 is moved to communicate the high pressure side of line 70 with the low pressure side thereof, i.e. to communicate the compressor 66 with the air cylinder 74. Air pressure then effects an increase of hydraulic pressure in the system made up of the line 78 and the hydraulic fluid on the right hand side of piston 60, as shown in FIG. 9. At the same time, the controller 93 effects the operation of the valve 71 so that the low pressure side of line 69 is communicated with the atmosphere. Under such conditions, the piston 60 is moved to the left occasioning the separation of the discs. During this operation, the timer 95 is itself in operation and automatically occasions reversal of the operation of the valves 71 and 72, so that after a short time interval, the positions of these valves are reversed so that the piston 60 is moved towards the right (as shown in FIG. 9) whereupon the car on the track 53 is moved to the right (as is shown in FIGURE 1) to bring the discs back to their working position. At this point in the cycle, the runner 51 of the car is in abutting relation with the stop means 63 and the desired spacing is provided. The timer can be set so that the discs are separated about 7 at maximum opening. Purging results and thus overload is relieved.

The invention further provides for the separating of the discs to the extent that the internals of the disc assembly are exposed for servicing. This separating of the discs can be accomplished by operation of the pistoncylinder arrangement 56. Thus, the power line 91 interconnecting the controller 93 with the ammeter 87, is provided with a switch 92, and the line interconnecting the controller 93 with the timer 95 is provided with a switch 94. These switches are normally closed, but can be opened to permit separating of the discs for facilitating servicing of the device. Upon opening of the switches, the switch 99 which interconnects the controller 93 with the manual operating panel 101 can be closed. The manual operating panel 101 can then be used as a control center for manually selecting the positioning of the valve 71 and 72 to manipulate these valves so as to provide suitable pressure to the piston-cylinder arrangement 56, whereby the desired actuation of the piston 60 can be made so as to effect the separation and subsequent bringing together of the discs.

The control arrangement further provides for the maintaining of selected pressures on each side of the piston 60. Thus, the pressure sensing instruments 81 and 82, powered respectively by lines 03and 84, are connected to the respective sides of the piston 60. Power lines 85 and 86 connect the pressure sensing instruments 81 and 82, respectively, with the power lines 96 and 97 of the solenoid valves 72 and 71. The pressure instruments 81 and 82 are each operative over a selected narrow pressure range to occasion prcssurizing of the cylinder as is desired to maintain the selected pressure on each side of the piston 60. The power lines 85 and 86 which interconnect the pressure instruments 81 and 82 with the appropriate valves pass through the switch 100. Switch 100 is actuated by the flanges 59 on the piston rod 58 so that the circuit through lines 85 and 86 is closed when the car is in the normal working position on the tracks 53, but is open when the car is moved to the left (FIG. 1). Thus, when the piston-cylinder arrangement is in operation to relieve an overload, the switch 100 will be opened and the controls for the overload will be effective to control operation and the pressure instruments 81 and 82 will be ineffective to control operation.

The valves 71 and 72 are biased to the position wherein the pressure supply system made up of the compressor 66 and the accumulator 67 is isolated from the air cylinders 73 and 74 so that when the various control devices are not operating, the piston-cylinder arrangement is isolated from the air supply system.

A further feature of the mill of the invention is the manner in which the discs are constructed. Thus, the discs each have a toothed area disposed in an annulus adjacent the outer periphery thereof, and the toothed portions of the two discs are opposed to each other for working of the material to be milled. The space between the discs inwardly of the toothed areas is open and free for movement of material introduced between the discs to the toothed areas. That is, radially extending paddles or the like, as are commonly used in disc mills to move material to the periphery of the discs and to themselves effect a size reduction, are not utilized and the space between the discs is left free for travel of the material to the working surface by gravity, air currents, and centrifugal force. Further, the toothed areas are inclined toward each other and the toothed area of one of the discs terminates radially inwardly of the toothed area of the other of the discs.

As can be seen in FIG. 1, the second disc 16 is made up of a supporting member 22 which can be a solid casting, and the ring member 21 which bears the working surface of the disc, this working surface being like the corresponding part of the other disc, shortly to be described.

The disc 15 is made up of a supporting member 19 and the spokes 20, and the working ring 21. See FIG. 5. Further, a hub 103 is provided. The spokes 20 provide the intermediate spaces 104 which permit passage of material through the disc 15 to between the two discs. The working surface 21 is made up of a toothed area disposed in an annulus adjacent the outer periphery of the disc, and, as can be best seen in FIG. 6, the annular toothed area of one of the discs terminates radially inwardly of the toothed area of the other of the discs. Such construction obviates the necessity for maintaining close tolerance insofar as the outer edges of the working surfaces are concerned. The configuration of the working teeth can be seen in FIG. 7 and FIG. 8. Thus, the working surface 21 of the disc 15 is made up of the radially extending teeth 105 as is shown in FIG. 8. The working surface of the other disc is of like configuration.

Example and differing in diameter by about /2. Two 50 horse-- power 1750 rpm. motors can be used. The motor can be connected so that peripheral disc speeds of up to about 25,000 feet per minute (relative peripheral speed, about 50,000 feet per minute) are obtained. In operation a vacuum can be drawn on the equipment to facilitate'removal of the milled material. A vacuum reducing the pressure on the downstream side of the discs by 20 inches of water can be used. This can be provided by applying suction to the discharge line 10 (FIG. 1) for the milled material.

A bore 9 can be provided in the closure 14 to provide air for sweeping the material from the mill and of course some air is drawn through the mill with the feed. A vibrating feeder (not shown) can be used to feed the material to be milled through feed line 22. The motors are preferably variable speed motors and throughput can be as follows. For milling low or medium density polyethylene to reduce pellets of size Ma to A" to about 20 to 200 mesh, at a disc r.p.m. of 2200-3000 the throughput can be about 1500 to 250 pounds per hour. The throughput at the r.p.m. employed can be very close, say to within a fraction of a percent, preferably less than about 0.1% of overload throughput, since the machine automatically relieves overload without substantial interference with operation. The normal spacing of the discs (spacing during normal running condition) can be about .001-.090". Operation described here is without use of coolant as can be introduced through shaft 18. Conventional recycle procedures can be used to return oversize material to the mill. Thermoplastics other than polyethylene can be worked and non-thermoplastics can also be worked.

While the invention has been described in reference to particular embodiments thereof, these embodiments are merely representative, and do not define the limits of the invention.

What is claimed is:

1. A disc mill comprising:

(a) a first disc and a second disc, said discs being mounted in opposed relation, a first shaft having said first disc mounted thereon and extending axially outwardly from the opposed discs, a second shaft having said second disc mounted thereon and extending axially outwardly of the opposed discs in a direction opposite to the direction in which the first shaft extends,

(b) means for driving each of said shafts to rotate the discs in opposite directions,

(c) a support for said first shaft and its disc and means for moving said support relative to the second disc for axially directed movement of the first shaft and its disc away and toward the second disc along a defined path,

(d) fluid pressure means for urging the movably supported disc toward the second disc,

(e) spacer means for limiting travel of the first disc toward the second disc in response to said urging of the fluid pressure means and to provide the discs spaced for milling,

(f) load sensing means for sensing overload of the mill, and overload relief means connected to the load sensing means for response to the load sensing means and effective in response to control said fluid pressure means upon occurrence of overload to move the discs apart for relief of the overload and then move the discs together to the milling spacing.

2. Disc mill according to claim 1, said fluid pressure means consisting essentially of a hydraulic piston-cylinder assembly, means for applying hydraulic pressure to each side of the piston, said overload relief means in control of the fluid pressure means, varying the pressure on each side of the piston to provide said movement for relief of overload and return to milling spacing.

3. Disc mill according to claim 1, said means for driving the first disc comprising a motor, said motor being mounted on said support for movement therewith.

4. Disc mill according to claim ll, said means for driving the shafts including at least one motor.

5. Disc mill according to claim 4, said load sensing means consisting essentially of an ammeter for sensing current to said motor.

6. Disc mill according to claim 1, said support being movable along said defined path a distance effective to separate the discs to expose them for servicing.

7. Disc mill according to claim 1, a casing for the discs and a closure for said casing, one of the closure and casing being mounted for movement with said first disc, the

other of the closure and casing being mounted in an axially fixed position, an overlap fit between the closure and casing sufficient to prevent opening of the casing upon movement as aforesaid for relief of overload, said support being movable along said defined path to remove said closure, opening said casing and moving said first disc to without the casing to open the casing and separate the discs to expose them for servicing.

8. Disc mill according to claim 7, said fluid pressure means consisting essentially of a piston-cylinder assembly, means for applying fluid pressure to each side of the piston, said overload relief means in control of the fluid pressure means varying the pressure on each side of the piston to provide said movement for relief of overload and return to milling spacing, means for disconnecting the load sensing means and the fluid pressure means, and means for actuating the fluid pressure means when disconnected from the load sensing means to separate said discs to expose them for servicing as aforesaid.

9. Disc mill according to claim 8, said fluid pressure means being a hydraulic fluid pressure means.

10. Disc mill according to claim 1, the spacer means being adjustable to permit selection of milling spacing.

11. Disc mill according to claim 3, said means for driving said second disc comprising a motor fixedly mounted with respect to the second disc.

12. Disc mill according to claim 1, the discs each having a toothed area disposed in an annulus adjacent the outer periphery thereof, the toothed portion of the two discs being opposed to each other for working of the material to be milled, the space between the discs inwardly of the toothed areas being open for free movement of material introduced between the discs to the toothed areas.

13. Disc mill according to claim 12, the toothed areas being inclined toward each other, the toothed area of one of the discs terminating radially inwardly of the toothed area of the other of the discs.

References Cited by the Examiner UNITED STATES PATENTS 2,216,611 10/1940 Dimm 241-256 X 2,887,277 5/1959 Sakata 241-37 2,971,704 2/1961 Johansson 241-37 3,040,996 6/ 1962 Ginaven 241-251 3,129,898 4/1964 Michel 241-256 3,207,450 9/1965 Horstman 241-251 3,212,721 10/1965 Asplund 241-37 FOREIGN PATENTS 946,390 1/1964 Sprout.

ROBERT C. RIORDON, Primary Examiner.

D. KELLY, Assistant Examiner.

Claims (1)

1. A DISC MILL COMPRISING: (A) A FIRST DISC AND A SECOND DISC, SAID DISCS BEING MOUNTED IN OPPOSED RELATION, A FIRST SHAFT HAVING SAID FIRST DISC MOUNTED THEREON AND EXTENDING AXIALLY OUTWARDLY FROM THE OPPOSED DISCS, A SECOND SHAFT HAVING SAID SECOND DISC MOUNTED THEREON AND EXTENDING AXIALLY OUTWARDLY OF THE OPPOSED DISCS IN A DIRECTION OPPOSITE TO THE DIRECTION IN WHICH THE FIRST SHAFT EXTENDS, (B) MEANS FOR DRIVING EACH OF SAID SHAFTS TO ROTATE THE DISCS IN OPPOSITE DIRECTIONS, (C) A SUPPORT FOR SAID FIRST SHAFT AND ITS DISC AND MEANS FOR MOVING SAID SUPPORT RELATIVE TO THE SECOND DISC FOR AXIALLY DIRECTED MOVEMENT OF THE FIRST SHAFT AND ITS DISC AWAY AND TOWARD THE SECOND DISC ALONG A DEFINED PATH, (D) FLUID PRESSURE MEANS FOR URGING THE MOVABLY SUPPORTED DISC TOWARD THE SECOND DISC,

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