US3030035A - Grinders - Google Patents

Description

April 17, 1962 w. P. GRUENDLER GRINDERS 4 Sheets-Sheet l Filed March 20, 1958 INVENTOR.

WILLIAM P. GRUENDLER FIG. 2

ATTY.

April 17, 1962 w. P. GRUENDLER 3,030,035

GRINDERS Filed March 20, 1958 4 Sheets-Sheet 2 III-Ill 2 FIG. 4 INVENTOR.

WILLIAM P. GRUENDLER ATT Y.

April 1962 w. P. GRUENDLER 3,030,035

GRINDERS Filed March 20, 1958 4 Sheets-Sheet 3 4 1' "7 7" 4 7 h. \l. M. \\\\\\\\\\\\X\\\\\\\\\ E eeeeeeeeeoeeeeeeeeeeee ooooooooooooowooooooooooooo ATTY.

A ril 17, 1962 w. P. GRUENDLER GRINDERS 4 Sheets-Sheet 4 Filed March 20, 1958 ited States Patent Ofilice spasms Patented Apr. 17, 1952 This invention relates in general to certain new and useful improvements in grinders, feed mills, and the like.

In grinding and pulverizing machines, such as feed mills, it is necessary to employ a screen having perforations of a size corresponding to the desired fineness to which the material is being ground. However, in the ordinary course of operation of a feed mill, it is frequently necessary to change the size of the screen since desired fineness of the ground material changes depending upon the nature of the material, and the use for which it is intended. Usually, the grinder must be completely shut down and partially disassembled in order to change screens and such procedure is both time-consuming and costly.

in connection with grinding and pulverizing relatively dry material in a feed mill, it frequently happens that there is a certain amount of leakage of dust from the grinder or mill housing past the screen therein. Such condition is annoying and unhealthy to Workers in the vicinity of the grinder, and, furthermore, since many of the materials being ground are combustible when in finely divided dustlike form, the presence of the dust represents something of a fire hazard.

It is, therefore, one of the objects of the present invention to provide a feed mill wherein the screen may be quickly and easily changed without shut-down of the machine.

It is also an object of the present invention to provide a feed mill of the type stated wherein the screen can be changed by remotely controlled power operated means.

It is an additional object of the present invention to provide a feed mill of the type stated which reduces the leakage of dust and other small particles from within the grinder housing to the atmosphere.

With the above and other objects in View, my invention resides in the novel features of form, construction, arrangement, and combination of parts presently described and pointed out in the claims.

In the accompanying drawings (four sheets)- 'FIG. 1 is a perspective view of a feed mill constructed in accordance with and embodying the present invention;

FIG. 2 is a side elevational view thereof, partly broken away and in section;

FIG. 3 is a top plan view thereof;

FIG. 4 is a sectional view taken along line 4-4 of FIG. 3;

FIGS. 5 and 6 are fragmentary sectional views taken along lines 5-5 and 66, respectively, of FIG. 2;

FIG. 7 is a fragmentary sectional view taken along lines 7-7 of FIG. 6;

FIG. 8 is an enlarged fragmentary sectional View of a portion of FIG. 2 and showing the cam bar and switch channel forming part of the present invention;

FIG. 9 is a fragmentary sectional view taken along line 9--h of FIG. 8;

FIG. 10 is a diagrammatic view of the screen-shifting control circuit forming part of the present invention; and

FIG. 11 is a diagrammatic view of a modified form of screen-driving mechanism.

Referring now in more detail and by reference characters to the drawings, which illustrate a practical embodiment of the present invention, A designates a feed mill comprising a series of spaced longitudinal channels 1, 2 which are welded to transverse channels 3, 4-, 5 in the provision of a box-like base frame 6. Bolted or otherwise rigidly mounted on the base frame 6 at one end thereof is a mill housing '7 comprising spaced parallel side walls 8, 9 joined by a polygonal top wall ill, a front wall 11, and a back wall 12, the latter being provided with a discharge opening 13.

Mounted in the side walls 8, 9 somewhat centrally thereof are spaced aligned bearings 14, 15 for journaling a shaft 16 which projects outwardly from the side walls 3, 9. Within the housing 6 the shaft 16 has a plurality of axially spaced discs 17 mounted thereon, and extending through the discs 17 are hammer rods 13 for securing a plurality of hammers 19. The hammers 19 extend radially outwardly of the hammer rods 18 so that as the hammers 19 rotate with the shafts 16 they will pass in closely contiguous relationship with a grinder plate 26 mounted on the front wall 11 interiorly of the housing 7. Rigidlymounted on the base frame 6 in spaced relation to the side wall 8 is a motor mount 2f for supporting a large electric motor 22 having a drive shaft 23 which is connected to the shaft 16 by means of a coupling 24.

Mounted on the front wall 11 and projecting forwardly and upwardly therefrom is a hopper 25 provided with a rotatable shaft 26 having a plurality of feeder arms 27 projecting radially outwardly therefrom. The shaft 26 is provided on one end with a large pulley 23 which is aligned with a small pulley, 29 mounted on the feed mill shaft 16, and trained around the pulleys 28, 29 is a drive belt 3'0. Also rotatably mounted in the hopper 25 is a.

second shaft 31 similarly provided with a plurality of feeder arms 32 and having a gear 33 operatively mounted on one end thereof which meshes with a gear 34- mounted on the shaft 26.

Bolted to the back wall 12 around the discharge opening 13 is a duct 35 which is, in turn, connected to the in take of a fan 36 driven by a motor 37. The fan 36 is also provided with a vertical discharge pipe 38.

Formed in the side walls 8, 9 are aligned arcuate slots 39, 4% for receiving a foraminous screen 41 comprising a plurality of perforated sections 4-2, 43, d4, 45 which are joined together by mounting chanels 46. The perforations in the sections 4-2, 43, 54, 45, respectively, are, preferably, of different sizes and each section 42, 43, 44, 45 is approximately the same width as that of the housing 7. While the screen 41 in the persent embodiment of the invention is illustrated as having four sections, it should be understood that a greater or lesser number of sections of graduated size may be used. Welded or otherwise rigidly secured to the back side of the screen 41 by means of narrow plate-like flanges 47 is a plurality of spaced parallel rods 48 which are shiftable in slide-forming pipes 49 mounted in and extending between the side walls d, 9. The pipes 49 also extend a short distance outwardly of the side walls 8, 9 and are, furthermore, positioned radially outwardly of the slots 39, 4t) and are provided with longitudinally extending slots 50 for receiving the flanges 47 as best seen in FIGS. 6 and 7. Bolted to the exterior faces of the side walls 8, 9 adjacent the slots 39, 46 are arcuate mounting plates 51, 52, 53, 54 each provided with flanges 55, 56, 57, 58 which are spaced from the side Walls 3, 9, and snugly confined between the flanges 55, 56, 57, 58 and side walls 8, 9, are fibrous or rubber-like arcuate sealing strips 59, ea, 61, 62, the latter edgewise abutting the screen ll on each side thereof and thereby reduce the leakage of dust from within the housing 7 when the feed mill A is in operation.

Welded to the bottom of the screen 41 at each end thereof are downwardly projecting flanges 63, 64 for journaling rollers 65, 66, the latter riding on rails 67, 68 mounted on the base frame 6. Also mounted on the lower position- indicator lamp 124, 125, 126, 127.

edgedf the screen 41 is a rack 69 which meshes with a spur gear 70, the latter being driven through a worm wheel 71 and worm 72 which is, in turn, driven by a small electric screen-driving motor 73 having poles r, s, and being spaced outwardly from the side Wall 8. Secured to the lower edge of the rack 69 is a cam bar 74 provided adjacent one end with a cam 75 and cut-away 76. Welded or otherwise rigidly secured to the rail 68 is a channel 77, the upper end of which is providedwith a U-shaped switch channel 78 having four single pole, single throw microswitches 79, 80, 81, 82 mounted therein, and four single pole, double throw microswitches83, 84, 85, 86 mounted opposite the switches 79, 80, 81, 82. One pole of each switch 83, 84, 85, 86 is normally closed. Fur thermore, the successive spacing of the microswitches' along the switch channel 78 is preferably equal to the width of one of the sections 42, 43, 44, 45. The cam bar 74 rides in the switch channel 78 so'as to selectively actuate the microswitches 79, 80, 81, 82, 83, 84, 85, 86, as best seen in FIGS. 8 and 9, and for purposes presently more fully appearing.

The control circuit for operating the motor 73 is shown in FIG. 10 and includes a' source of direct current 87 having a positive pole in and a negative pole n. The circuit also includes two double pole, single throw 'relays 88, 89 having'contacts 90, 91, 92, 93, two double pole, double throw relays 94, 95 having contacts 96, 97, 98, 99, 100,

101, 102, 103a'nd four push- button switches 104, 105, 106,107 provided with holding ' coils 108, 109, 110, 111. Each push- button switch 104, 105, 106, 107 corresponds to one of the screen sections 42, 43, 44, 45'as does each relay88, 89, 94, 95, each microswitch 79, 80, 81, new each microswitch 83, 84, 85, 86 so that four parallel circuitsare formed for controlling the motor 73. Connected in series with the relays 88, 89, 94, 95 and push button switches 104, 105, 166, 107'arefou'r doub1e throw cut- out relays 112, 113, 114, 115, each of which has one normally open set of contacts 116, 117, 118,119, in series" with the relay coils 120, 121, 122, 123, respectively, and also in series with one pair of normally-closed contacts of each of the other cut-out relays 112, 113, 114,115. The'microswitches 79, 80, 81, 82 are each connected in series with the source of current 87 and a corresponding It ,will be apparent that the various relays 88, 89, 94, 95, 108, 109, 110,111 and position indicator lamps 124, 125, 126, 127 maybe'housed in a suitable control box at a point remote from the feed mill A and connected by electric cables to the motor 73 and sWitches79, 80, 81, 82, 83, 84, 85, 86.

In FIG. 10 the screen 41 is shown in the second position, that is, with the section 43 disposed within the housing 7 as""shown' in 'dotted lines in FIG. 4." Thus'material fed into the hopper 25 will be pulverized and when ground to the proper size will be sucked through the screen-section 43 by the fan 36 and discharged through the pipe 38. In the control circuit, the microswitch 81 will be closed by the cam 75,; thereby illuminating the position indicator lamp 126. The push button switch 105 will be open since no current is flowing through the'holding coil 109 and the microswitch 85 will be in the neutral position since it is opposite the cut-away 76. Similarly the contacts 96, 97, 98, 99 will all be open since no current is flowing through either coil in the relay 94.

If, during the operation of the feed mill A, it is desired to position the screen-section 45 within the housing 7, the push-button switch 107 is depressed causing current to flow through the relay contacts 92, 93, the holding coil 111 and motor 73 which begins to rotate and shift the screen 41. The pole s of the motor 73 will become positive and the pole 2' will become negative. Current also flows through the relay coil 120 closing the normally open contacts 116 and opening the three normally closed contacts on the relay 112. As the screen 41 shifts, the cam bar 74 will move along the switch channel 78. As soon as the cam 75 "moves past the microswitch 81 the lamp 126 will shut off and when the cut away 76 moves past the microswitch 85, the latter will close energizing the upper coil in the relay 94 and close the contacts 96, 97. Then as the cut-out 76 passes over the microswitch 84 the closed contacts will be broken shutting oii current from the energized coil in the relay 95, thereby opening the contacts 1'82, 103. As soon as the cut away 76 moves past the microswitch 84 the other set of contactstherein will become closed, energizing the other coil in the relay 95, thereby closing the contacts'100, 101. When the cutout 7 6 reaches the microswitch 83 the closed contacts will be opened de-energizing the holding coil ofrelay 89 and cutout holding coil 111 of the push button switch 107 thus cutting off current to the motor 73 and stopping same. The screen section 45 will then be in operative position within the housing 7 and the microswitch 79 will be closed illuminating the position indicator light 124.

It should be noted that since the relay contacts 90, 91, 96, 97, 100, 101 are now closed, actuation of the pushbutton switches 104, 105, 106 will deliver current to the motor 73 with proper polarity so that the motor 73 will rotate in a direction opposite to that previously described because the polarity of the current applied to the motor 73 is determined by which pairs of contacts are closed in the relays 94, 95, and the closing of the contactsin the relays 94, 95, are in turn, controlled by the microswitches 84, 85. Thus, wheneither the screen section 44 or 45 is in position in thehousing 7, the contacts 96, 9,7 in the relay 94 are closed and subsequent closing of the pushbutton switch will deliver current to the motor in such polarity 'as to cause the screen 41 to shift to the left, reference being'made to FIG. 4, and position the screen section 43 within the housing 7. On the other hand if the section 42 is in the housing, the contacts98, 99'will be closed, and upon closing of the push-button switch 105:, the current polarity will be reversedand cause the motor 73 to rotate in the opposite direction and shift the screen to the right, thus moving the section 43 to operative position within the housing 7. it will, therefore, be apparentthat the relays 94, 95 control the direction of rotation of themotor 73 when push- buttons 105, 106 are depressed and, therefore, permit the intermediate screen sections 43, 44 to be positioned within the housing 7 notwithstanding that they may initially be located on either side of the housing 7. I

It should also be noted that when the push-button switch 102 was closed, as previously described, the relay coil opens the three normally closed contacts in the relay 112 which provides a break in the circuits of the remaining push-button switches. Thus, if after the switch 102 is depressed and before the screen has stopped moving, one of the other push-button switches is depressed, no current will be delivered to the motor 73 or to the holding coil, and, consequently, short circuits in the control system are eliminated due to accidental closing of more than one push-button switch.

If it is then desired to position the screen section 42 within the housing 7, starting from the position Where the section 43 is in the housing, the push-button switch 104 is depressed causing current to flow through the relay contacts 90, 91, the holding coil 108 and the motor 73, which will rotate and shift the screen 41. The relay contacts 102, 103, 92, 93, will be closed. It is to be noted that the contacts 90, 91, are included in the circuitry so that the pole s of the motor 73 will always be negative when the cam bar 74 is positioned over any of mic- roswitches 83, 84, 85, if the push-button 104 is depressed. As the micro-switches 83, 84, are normally closed, current will then flow through the relay coil 123 closing the normally open contact 119 and opening the normally closed contacts on the relay 115. When the screen 41 shifts, the cam bar 75 will move to the left, reference being made to FIG. 10, allowing the micro-switch 85 to close, in turn closing the relay contacts 98, 99. As the cut-away 76 passes over the micro-switch 86 the closed contacts will be broken de-energizing the coil in the relay 83 and breaking the contacts 90, 91, and thereby cutting out the holding coil 198 of re push-button 1114. Current supplied to the motor 73 will be cut off and the motor 73 will then stop as the screen section 42 is positioned within the housing 7. As the switch 82 will be closed, the indicator light 127 will be illuminated.

The operation of positioning the screen section 44 in the housing 7 is similar to the previously described operation concerning screen section 42 and screen section 45. Again, assuming that the screen section 43 is positioned in the housing 7, the push-button 1116 is depressed causing current to flow through relay contacts 192, 193, holding coil 110, and motor 73 shifting the screen. It is to be noted that since the contacts 192, 183, are closed the polarity of the motor 73 will be such that the pole s is positive and the pole r, negative, causing the motor to shift the cam bar 74 to the right, reference being made to FIG. 10. As the cam bar 75 moves past the micro-switch 35, it Will cause and the cut-away 76 will pass over the micro-switch 84. The contacts of the micro-switch 84 will be broken and shut off current from the core in the relay 95, opening contacts 192, 103, thus de-energizing the holding coil of relay 95, cutting out the holding coil 116, and thereby cut oif current to the motor 73. The cam bar 75 will cause the lower contacts of the micro-switch 85 to close as it passes, thereby closing the contacts 96, 97, on the relay 94. It can be seen that if the pushbutton 1115 is depressed the pole r of the motor 73 will be positive and the pole s will be negative causing the cam bar 74 to move to the left. As the micro-switch 30 will be closed when the cut-away 76 passes over, the indicator light 125 will illuminate.

For purposes of illustration in order to describe the operation of positioning screen section 43 in the housing 7 it can be assumed that the screen section 45 is within the housing 7. The push-button 195 is depressed causing current to flow through the closed contact 97, the holding coil109, and the motor 73 that will rotate and shift the screen section 43 and cam bar 74 to the left. Since the contacts as, 97 are closed, the pole r of the motor 73 will be positive and the pole s Will be negative. As the cam bar moves past the micro-switch 79 the lamp 124 will shut 011 and when the cut-away 76 moves past the micro-switch 83, the latter will close, energizing the coil in the relay 89 closing the contacts 92, 93. As the cutaway 75 passes over micro-switch 35, the closed contacts will break and thereby shut 011 current from the energized coil in the relay 94, and opening contacts 96, 97. The holding coil of relay 94 will be de-energized and cut out holding coil 1119 of the push-button switch 195. The screen section 43 will then be in operative position Within the housing 7 and as micro-switch 81 is closed the indicatorlight 126 will be illuminated.

It is also possible to provide a modified form of driving system for the screen 41 as shown diagrammatically in FIG. 11 in which the opposite ends of the screen 41 have a pair of eyelets 128, 129 for anchoring the opposite ends of a cable 130. The cable 139 passes through cable guides 131, 132 and is also trained around pulleys 133, 134, 135, 136. The cable guides 131, 132 and pulleys 133, 134, 135', 136 may be mounted on suitable building columns 137, 138 so that the cable 130 may extend upwardly to a building floor F the latter being above the floor F on which the base frame 6 is mounted. The cable 139 extends upwardly of the floor F and is wrapped around a drum 139 which is rotatably mounted in a supporting stand 140, resting on the floor F. The drum 139 is provided with a crank 141 and also with a flange 142 having four notches 143, 144, 145, 146 spaced 90 degrees apart and corresponding to one of the screen sections 42, 43, 44, 45. Provided for releasable locking engagement with any one of the notches 143, 144, 145, 146 is a spring biased pin 147. Thus, when it is desired to shift the screen 41, the pin 147 is released from the notch in which it is engaged and the crank 141 actuated to rotate the drum 139 in either direction and thereby position the appropriate screen section 42, 43, 44, 45 within the housing 7. When the desired screen section is in position the notch corresponding thereto will be aligned with the spring biased pin 147 which is then released so as to snap into said notch and lock the screen-section in position.

In connection with the screen-driving system shown in FIG. 11, it will be apparent that the drum 139 may be mounted at locations remote from the housing 7 other than the floor and the cable 139, pulleys 133, 134, 135, 136, and cable guides 131, 132 appropriately positioned so that the cable is trained around the drum 139 in the manner previously described. Thus, the drum 139 may be one the same floor as the housing 7, or in fact, the drum may be mounted at any point remote from the housing 7 depending upon the requirements of the particular installation of the feed mill A.

It should be understood that changes and modifications in the form, construction, arrangement, and combination of the several parts of the grinder may be made and substituted for those herein shown and described without departing from the nature and principle of my invention.

Having thus described my invention, what I claim and desire to secure by Letters Patent is:

l. A grinder comprising an arcuate screen, a housing having a pair of spaced walls provided with aligned arcuate slots conforming in shape to the cross-sectional shape of the screen, a plurality of tube members extend ing axially across the housing at annularly spaced intervals along the slots in diametrically spaced relation to the screen, said tube members also extending between said walls adjacent said slots and projecting axially beyond the walls on opposite sides of the housing, and a screen projecting through said slots and having a plurality of perforated sections adapted for selective disposition within said housing, said screen also being provided with a plurality of rods slidable in said tube members.

2. A grinder comprising an arcnate screen, a housing having a pair of spaced walls provided with aligned aperture slots conforming in shape to the cross-sectional shape of the screen, a plurality of tube members extending axially across the housing at annularly spaced intervals along the slots in diametrically spaced relation to the screen, said tube members also extending between said.

walls adjacent said slots and projecting axially outwardly beyond the walls, and an arcuate screen projecting through said slots and having a plurality of perforated sections adapted for selective disposition within said housing, said screen also being provided with a plurality of rods slidable in said tube members.

3. A grinder comprising an arcuate screen, a housing having a pair of spaced walls provided with aligned arcuate slots conforming in shape to the cross-sectional shape of the screen, a plurality of tube members extending axially across the housing at annularly spaced intervals along the slots in diametrically spaced relation to the screen, said tube members also extending between said walls adjacent said slots and opening at their ends exteriorly of the walls, said tube members being split along their lengths, a screen projecting through said slots and having a plurality of perforated sections adapted for selective disposition within said housing, a plurality of rods slidable in said tubes, and a web connecting each rod to the screen, each web projecting through the tube member at the split therein.

4. A grinder comprising an arcuate screen, a housing having a pair of spaced walls provided with aligned arcuate slots conforming in shape to the cross-sectional shape of the screen, a plurality of tube members extending axially across the housing at annularly spaced intervals along the slots in diametrically spaced relation to the screen, said tube members also extending between said walls adjacent said slots and opening at their ends exteriorly of the walls, said tube members being split along-their lengths, a screenprojec'ti'rig through said slots and h'avin'g a plurality of perforated sections adapted for s'electivedisposition within said housing, a plurality of rods slidable in said tubes, at web connecting each rod tothe screen, each web'projecting. through the tube memher at the split therein, and power-operated means for driving said screen alongsaid tube members.

A' grinder comprising an arcuate screen, a housing having av pair of spaced walls provided, with aligned areuate slots conforming in shape to the cross-sectional shape of the screen, a plurality of tube members extending axially across the housing" at annularly spaced intervals along the slots in diametrically spaced relationto thescreen, said tube members also extending between said walls adjacent said slots andopening at their ends exteriorly of the walls, said tube members being split along their lengths in the provision of an inwardly opening lnegthwise extending guide-way, a screen projecting through said slots and having a plurality of perforated sections adapted'for selective disposition within said housing, a plurality of rods slidabie in said tubes, a web connecting each rod to the screen, each Web projecting through theguide-way of the tube member with which it is'asso'ciated,'and sealing .means mounted on said walls and disposed over the slots, M I

;6. A grinder comprisinga housing having a pair of spaced'wallshpr'ovided with aligned arcuate slots, a plurality of axially slottedutubes extending through the hcusing between saidlslots, said tubes being spaced from each other at intervals' along the periphery" of the slots ap'd opening at, their ends: exteriorly of the housing, an, arcuzltescreenslidable said slots and having a plurality,

ofiaxially' extending support members .having acrosssectional, shape conforming to the interior cross-sectional shape of the tubes andbei n'g slidably mounted'therein,

said screen'haviriga plurality of axially spacedperforated sections, poweroperated means; mechanically connected to said screen for shifting said screen in said slots, a pushbutton switch electrically connected to each section, and

a relay'switchelectrically connected to said push-button switch and being 'pr'ovidedwith a holding coil for hold ing said pushebutton switch in actuatedposition, said relay switch, in turn, being connected to said power-operated means foractuating the power-operated means and cansing the latter to automatically position any one of the sections within the housing upon closing of the switch related thereto. H I

7L In a' grinder comprising a housing having a pair of spaced wallsprovidedwith aligned slots, a screen slidable in said aligned slots and having a plurality of perforated sections; electric motor-operated meanstfor shifting said screen in said slots, ,control means operatively associated'with the electric motor-operatedvmeans to selectiv'ely dispose any -one offsaid sections Within the ,housing','said'control means including an element rigidly mounteded onand extending axially along the screen, said elementhavin'g a pr'otuberant shoulder disposed at a'selected point along its length, a'plurality of switches l ocate'dalo'ng the p'ath'of movement of said protuberance for actuationthjereby depending upon the position and movement of the protuberance, each of said switches being associated uniquely with one of the perforated sections of the screen and being so located along the path of movement of 'tlie'screenfas to be shifted into circuitopen position when the particular perforated section with which it is associatedis positionedwithin. the grinder housing,'arid a manually operable circuit-closer associated with each of said switches and being in series with said switch and the electric motor so that a circuit can be completed to the electric motor by manual operation of the circuit-closer whenever the switch with which it is associated is in closed position.

8. A grinder comprising a housing having a pair of spaced walls provided with aligned ,arcuate slots, a plurality of axially slotted tubes'extending through the housing between said slots, said tubes being spaced from each other at intervals along the periphery of the slots, an arcuate screen slidable in said slots and having a plurality of axially extending support members having a cross-sectional shape conforming to the interior cross sectional shape of the tubes and being slidably mounted therein, said screen having a plurality of axially spaced perforated sections, power-operated means mechanically connected to said screen for shifting said screen in said 10. A grinder comprising a housing having a pair ofv spaced walls provided with aligned arcuate slots, a plu-= slots,.and electrical control means electrically connected to said power-operated means, said control means including a plurality ofselector switches electrically conre cted -to the power-operated means for actuating said power-operated means and causing the latter to position any preselected section within the housing.

9 A grinder comprising a housing having a pair-of spaced walls provided with aligned arcuate slots, a plurality of axially slotted tubes extending through thehousing between said slots, said tubes being spacedfrom each other at intervals along the periphery of the slots, an ar-,

cuate screen slidable in said slots and having a plurality of axially extending support members having-a crosssectionalshape conforming to the interior cross-sectional shape of the tubes andbeing slidably mounted therein, said screen having a plurality of axially spaced perforated means and causing the latter to position any preselected section within the housing.

rality of axially slotted tubes. extending through the housingbetween said slots, said tubes being spaced from,

each other at intervals along the periphery of the slots and opening at their ends exteriorly of the housing, an arcuate screen slidable insaid slots and having a pl-urality of axially. extending, support members having a cross-sectional shape conforming to the interior crosssectional shape of the tubes and being slidably mounted therein, said screen havinga plurality of axially spacedperforated sections,powerroperated means mechanically connected to said screen for shifting said screen in said slots,

and electrical control means electricallyconnected to said power-operated means, said control means mechani cally related to each section including a switch electrically connected to thepower-operated means for actuating the powenoperated means and causing the latter to automatically position any one of the sections within the housing upon closing of the switch related thereto.

11. A grinder comprising ahousing havinga pair of spaced walls provided with alignedarcuate slots, a plurality of axially slotted tubes extending through the hous ing between said slots, said tubes being spaced from each. other at uniformly spaced intervalsalong the peripheryv of. theslots and openingiat their ends exteriorly of the housing, an arcuate .screen slidable in said slots and mechanically connected to said screen for shifting said screen in said slots, electrical control means electrically.

connected to said power-operated means, said control means mechanically related to each sectionand including a switch electrically connected to the. power-operated means for actuating the power-operated means and causing the latter to automatically position any one of the sections within the housing upon closing'of the switch related thereto, and position-indicator means responsive to movement of said screen for signaling which of said sections is within said housing.

12. A grinder comprising a housing having a pair of spaced walls provided with aligned arcuate slots, a plurality of axially slotted tubes extending through the housing between said slots, said tubes being spaced from each other at intervals along the periphery of the slots and opening at their ends exteriorly of the housing, a plurality of slide-forming members extending between said walls adjacent said slots, and a screen projecting through said slots, said screen having a plurality of outwardly extending narrow flanges rigidly attached thereto and a plurality of axially extending support members integrally formed on said flanges, said support members having a 10 cross-sectional shape conforming to the interior crosssectional shape of the tubes and being slidably mounted therein, said screen having a plurality of axially spaced perforated sections adapted for selective disposition Within said housing.

References Cited in the file of this patent UNITED STATES PATENTS 10 2,227,090 Hughes Dec. 31, 1940 2,258,537 Calkins Oct. 7, 1941 2,661,159 Thomas Dec. 1, 1953 2,669,396 Nickle Feb. 16, 1954 2,732,137 Fisher Jan. 24, 1956

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