Title:
Envelope making machine
United States Patent 2142143


Abstract:
The present invention relates generally to an envelope making machine and more particularly to the feeding mechanism for envelope blanks and the like of the type illustrated in my Patent 1,808,706. It concerns directly with a provision of a device for feeding blanks from the stack of blanks...



Inventors:
Abraham, Novick
Application Number:
US75646434A
Publication Date:
01/03/1939
Filing Date:
12/07/1934
Assignee:
SMITHE MACHINE CO INC F L
Primary Class:
Other Classes:
271/113
International Classes:
B65H3/28
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Description:

The present invention relates generally to an envelope making machine and more particularly to the feeding mechanism for envelope blanks and the like of the type illustrated in my Patent 1,808,706. It concerns directly with a provision of a device for feeding blanks from the stack of blanks so as to form a continuous band in which only the sealing flaps are exposed. Although applicable as a top feeder, the invention is particularly adapted for feeding the blanks from the bottom of the stack.

Many of the details of the feeding device are not shown herein and reference may be had for such details to the above mentioned patent. The principal object of the present invention is to provide a device of the type mentioned which will feed the blanks rapidly and accurately and which will be readily adjustable for different sizes of envelopes and envelope blanks.

Another object of the invention is to facilitate the feeding of window envelope blanks. It will be understood, however, that many features of the present invention are applicable to other types of envelopes and envelope blanks.

Further and more specific objects of the invention will be apparent to persons skilled in the art from the following specification.

The accompanying drawings illustrate one embodiment of my invention. It will be understood Showever, that various changes in the specific mechanism described may be made without departing from the spirit of my invention and certain parts of the structure disclosed may be employed without others.

:s Fig. 1 is a vertical view of an illustrative embodiment of the invention on line 1-I of Fig. 4.

Fig. 2 is a detail view taken on line 2-2 of Fig. 1.

Fig. 3 is a detail view showing the relation between the stack, stops, and the cooperating face of a separator disk taken on line 3-3 of Fig. 4.

Fig. 4 is a plan view of.the invention.

Fig. 5 is another plan view taken in the plane of the lowermost blank, this view eliminating some of the structural details for the purpose of clarity.

Fig. 6 is a vertical view of .a part of the device taken along the line 6-6 in Fig. 4.

Fig. 7 is a partial and enlarged view in the plane ,o of Fig. 1 for the purpose of more clearly illustrating the operation of the invention.

Fig. 8 is a similar enlarged detailed view of the parts cooperating to transfer the gummed blanks to a conveyor.

i55 Briefly the operation of the illustrative device is as follows: The forward end of the bottom blank is moved away from the stack by the operation of a sucker member common in the art, this affording an opportunity for a pair of separator disks upon which the weight of the pile partly rests, to start the separation of the bottom blank.

While this is taking place the sucker moves downward with the end of the blank for a short distance when the suction is cut off and a pair of presser members come into play and bring the end of the blank downward against a traveling conveyor. When this has occurred, traction between the blank and the conveyors is secured by means of a pair of rollers which move into place and press the blank thereupon, and since the separating disks have now accomplished their work, the withdrawal of the blank lengthwise of the stack is begun.

In the device constituting an embodiment of the present invention the stack of envelope blanks A rests upon a pair of cooperating separating disks 10 and II. Part of the weight of the stack is borne by a depending toe member or finger 12. Other similar toe members as shown in my prior patent may be employed if desired. The separating disks 10 and 1 are provided with means for adjusting the relative position of the disks. For this purpose and also for the purpose of rotating these disks, means for transmitting power to such disks are provided, the means being so designed and constructed that the disks may be moved to and from each other and retained in such adjusted position without interfering with the power transmitting means. The rotating drive shafts 13 pass through bearings 14 carried by arms 15 of the main frame 16. A pair of cooperating links 17 and 18 are interposed between the drive shaft 13 and the stud 19, which is affixed to the disk hub 20 by means of a set screw 21 or the like. The links 17 and 18 are pivoted to each other by means of the stud 22.

The drive shaft 13 carries a sprocket wheel 23 at the upper end thereof, the same being preferably spaced from the link 17 by the sleeve 24. The stud 22 carries a cooperating sprocket wheel 25 which is driven from the sprocket wheel 23 by the sprocket chain 26. The stud 22 carries another sprocket wheel 27 which is connected to the sprocket 28 on stud 19 by the sprocket chain 29. The drive shaft 13 therefore transmits its power to the separator disk by means of these sprocket chains. These are shown in detail in Figs. 4 and 6 of the drawings. The frame 16 also carries the angular bracket plate 30 which carries on its lower face the guide plate 31 having an enlarged opening 33 to receive the stud 19 and its sleeve 32, the latter forming part of the link 18. The guide plate 31 is preferably made in two parts which are joined together by the screws 34 as shown to facilitate repair and replacement of parts. The frame member 16 also carries the transversely disposed suitably channelled guide 35 and is provided with the bolt 36 slidable therein and passing through a slot 37 in the link 18. It will now be understood that by means of these devices the stud I of either or both separator disks may be moved laterally within the opening 33 in the guide plate 3I and when brought to the desired position these are firmly bolted into position. The lateral distance between the separator disks 10 and II may thereby be adjusted within the limits provided by the opening 33 in the guide plate 31. During this adjustment operation the angle between the links 17 and 18 is varied and the operation of the sprocket wheels and sprocket chains for transmitting power from the drive shaft 13 to the stud 19 of the separator disks is not affected.

The separator disks in the present invention are provided with annular ribs 38 and grooves 39. By means of this form of disk the friction between the disk and the stack of envelopes is substantially reduced, thereby considerably facilitating the operation of the machine. In addition this alternate rib and groove structure of the operating face of the disk also serves to permit some of the vertical rod-like stops such as the stops 40 to project into such grooves and thereby positively preventing any movement of any of the blanks rearwardly during the operation of the machine.

The present device is also provided with adjustable stops both in front and in back of the stack of blanks. For this purpose each frame member 16 is provided with a rearwardly projecting channelled guide member 41 which carries the slidable arm 42 which in turn may be held in adjusted position by the wing nut 43. The arm 42 in its turn serves as a guide for the sleeve 44 which slides thereon and may also be held in an adjusted position thereon by means of the wing nut 45. The sleeve 44 is provided with an integral arm 46 which carries integrally therewith the rod-like stop 47 adapted to engage the rear face of the stack of blanks. The stop 47 preferably extends downwardly to a point somewhat above the operating face of the disk. The arm 46 also carries a cross member 48 which in turn supports at each end the slidable carriers 49 for the stops 40.

It will now be understood that by means of the device described immediately above the stops for the rear face of the stack are adjustable in several directions with the result that any size or Sshape of blank may be employed in this machine.

This feature of adjustability of the stops also cooperates with the adjustability of the disks to the same end.

Stops 49 which are similar to stops 47 are also disposed on the front face or faces of the stack.

These are carried by slotted carriers 50 which are adjustably supported on the angle brackets 30.

One feature of the present invention resides in providing means for guarding the leading edge 51 of the horn 52 on the separator disk from coming into contact with the blanks during the early portion of its passage between a partly separated blank and the stack. While this feature may be employed in the feeding of any type of blank, it has particular application in the feeding of window envelope blanks. With this type of feeding device known hitherto the leading edge of the separator disk frequently catches against the edge of the window in the blank and thereby damages the blank. The present feeding device is specifically designed to eliminate this difficulty. For this purpose the horn 52 of the disk is so designed that during the early portion of its travel between a partly separated blank and the stack the contact of the horn with the blanks is minimized and more particularly its contact with the window of the blank is such as to minimize the possibility of the horn catching against the edge of the window. In order to further re- a duce or eliminate such difficulties each disk Is provided with an oscillating pair of shovel-like members which straddle the disk and are operated to be interposed between a partly separated blank and the stack in such timely relation to the operation of the disk that they guard the leading edge of the horn from contact with the blanks during the early portion of the passage of the horn between the stack and its lowermost blank.

The shovel-like members are shown in Figs. 4 and 5 and are indicated by the reference characters 53 and 64, the first of these being disposed to travel over the disk and the second being disposed to travel ulider the disk. Each pair of members 53 and 64 Is carried by the arm 55 which is pivotally moudted on the bracket 30. These shovel-like members 53 and 54 are preferably spaced from the under side of the free end of the arm 55 by means of spacers 56 and 57. A pair of screws 58 qaid 59 serve to hold members 53 and 54 in position. The arm 55 is provided with curved slots 60 for each of the screws 59, whereby the members 53 and 54 may be adjusted with relation to each other and with relation to the arm 55. The operating link 61 serves to oscillate the shovel-like members 53 and 54 between the extreme positions shown in Figs. 4 and 5.

The shovel-like members 53 and 54 are preferably made of sheet metal. The lower one 54 has a forwardly curved engaging end so that it engages the separated blank with the correspondingly curved face, and the upper member 53 has a round corner also to minimize any possible harm to the blank during its travel. In order to relieve the separator disk of a part of the load of the stack of blanks during the separating operation a lifting device 62 Is provided which operates to lift the rear of the stack during such operation as shown in Fig. 7. The structure and operation of the lifter 62 will be understood by referring to Fg. 1. The lifting device comprises a parallel motion device and includes a pair of parallel rock shafts 63 each having downwardly depending rocking arms 64 which are joined by pivot links 65 as shown. Each rock shaft 63 also has fixed thereon, and movable therewith, bracket 66 which is pivoted at its other end to one end of the bar 67. The sleeve 68 is slidably adjustable on the bar 67 and carries the roller 69, which may therefore be adjusted to a position below the rear portion of the stack.

The rock shafts 63 are operated by the lever 70 which is pivoted to the link 70a fixedly carried by one of the rock shafts 63. This lifter device is normally in the position shown in Fig. 1 and is not in contact with the stack. When the leading edge of the horn I5 of the disk enters the stack the lever 70 comes into operation to operate the lifting device to the position shown in Fig. 7 and returns to its normal position as soon as the horn projects partly beyond the rear of the stack, at which time the separated blank is withdrawn from the stack.

The specific manner of cooperation of the different operating elements will be more clearly understood from the following description of the operation of the present feed mechanism: The feeding of the blank is initiated by the action of a sucker 71 which has a compound motion to T7 and fro, as well as up and down, the mechanism for accomplishing these movements being shown in Patent No. 1,808,706 and is here merely indicated by the lever 7 la. The first step in the cycle of operation Is best shown in Fig. 4 of the drawings where the sucker 71 is shown in engagement with the lower face of the lowermost blank in this stack. The sucker then moves downwardly a short distance and thereby separates the forward portion of the lowermost blank from the stack. The suction is then cut off and the upper face of the blank is engaged by a pair of daggers 73 which move the end of the blank against the conveyer 74. Simultaneous with the operation of the daggers 73 the shovel-like members 53 and 54 also start their forward movement and are preferably slightly in advance of the daggers. As soon as the daggers are down over the leading edge of the blank the rollers 75 start forward. At the same time the lifter 62 comes into operation so that when the daggers have reached the lowermost position the lifter 62 has reached its uppermost position and.slightly lifts the rear of the stack. At the same time the sucker 71 has been withdrawn to its rearmost position. It will be seen therefore that before the leading edges of the horns 52 enter the space between the stack and the partly separated blank, the cooperating parts are substantially, in the Position shown in Fig. 5. These operations have all taken place and been completed immediately before the horn reaches the position B shown in dotted lines in Fig. 5. As the separator disk continues to rotate the horn 52 soon passes between ,ý the shovels 53 and 54 and reaches the position C, having completed the separation of the blank from the stack. The lifter 62 will then have released the stack and is in its downward movement. The blank has now become separated from the stack and is being carried off by the conveyer 74, the traction being supplied by the pressure of the rollers 75. When the horn 52 reaches the position indicated by the dotted line D in Fig. 5 the daggers 73 start back to the inoperative position so as to permit the repeated operation of the sucker 71. When the horn reaches the position indicated by the dotted line E the shovels start back to their normal positions, and approximately at the same time the sucker 71 ay also starts forward for the purpose of initiating the separation of the next succeeding blank.

When the horn reaches the position F the rollers 75 start back so as to permit the lowering of the next succeeding blank and then the cycle of 5 operations is repeated.

The blanks released from the stack are carried away successively by the conveyor 74 which is so disposed that it receives the separated portion of the blank by the action of the daggers 73 and the CO rollers 75. The conveyor is carried around a large drum 76 and the idler pulleys 77. Due to the action of the pair of roller members 75 cooperating with the belt 74, the blank held between them is conveyed from the bottom of the stack, the arrangement being such that when this action takes place the separator disks 10 and I I will have completely severed the blank from the stack. It will be understood that the action of the feeding members described is such that a ,0 fresh blank will be presented to the conveyor 74 when the preceding blank has been conveyed a distance equal only to the desired width of the gum on the sealing flap whereby a band of overlapping blanks is produced. For the further iT transportation of the overlapping band of blanks formed, a conveyor 18 is provided which extends around a portion of the periphery of the drum 17 and above the conveyor 74 and passes over idler pulleys 79. In this manner the band of blanks is conveyed between bands 74 and 18 to a large 6 drum 80. Upon traversing the drum 80, the blanks are gummed by means of the gum box 81.

After passing the gumming apparatus and also guide rolls 82 the blanks pass to a mechanism by means of which the blanks are individually gripped by means of grippers 83 carried by a chain 84. By means of this arrangement the gripped blanks are passed through a drying way and are delivered in timed relation to the operating cycle of the machine to mechanism which individualize, gum and fold the blanks into finished envelopes.

The chain 84 moves slightly faster than the surface speed of the drum 80, consequently each blank is moved slightly from the immediately succeeding blank before it is gripped by the clip or grippers 83. This is done for the purpose of preventing the blanks from sticking to each other during the drying operation. A sucker 85 is employed to assist in transferring the blanks to the chain and to prevent collision of one edge of the window aperture in the blank being transferred with the opposite edge of the window opening in the next succeeding blank. The sucker is adjustably mounted on the parallel motion device 86 and is designed to operate upon the leading edge of each blank and on the ungummed face thereof. The parallel motion device oscillates the sucker 85 between the position shown in Figs. 1 and 8 and during its motion from the position shown in Fig. 1 to that shown in Fig. 8, suction is applied and the blank with which it is in engagement is thereby moved slightly in advance of the next blank. At the point shown in Fig. 8 suction is cut off and the blank falls on top of the chains 84, there being a pair of such parallel chains.

The chains travel in part each in a channel bar 87 which has mounted at its upper end a small spring 89a which coacts with the dagger 89 to hold the blank before it is gripped by the clip or gripper 83. Each link 88 of the chain carries a clip or gripper 83 at its forward end which cooperates with the link next in advance to grip the blank. The daggers 89 are carried by the arms 90 of rock shaft 91 and are oscillated between the positions shown in Figs. 1 and 8. In the position shown in Fig. 1 the daggers 89 serve to hold up the blank which is being acted upon by the sucker 85. As soon as the sucker has moved to the position shown in Fig. 8 the dagger 89 is moved to the position shown therein, thus permitting the blank to drop on to the chains and so that the daggers may readily engage behind the side flaps of the next succeeding blank to assist in transferring it to the drier chains 84. The horns of the separator disks have been particularly designed for operation upon window envelope blanks. The apex of the horn first strikes the solid part of the stack and as it proceeds into the stack to complete the separation of the blank the outer receding edge of the horn has a shearing action on the edge of the window and the possibility of damage to such edge is eliminated.

Another feature of the present feeding device 70 is that the separated blank drops entirely free and clear of the stack due to the timely lowering of the lifter 62. The forward travel of the blank is not interferred with by the weight of the stack or any part of it. The free dropping of the sep- 76 arated blank also prevents hooking of the outgoing blank with the next blank in the pack.

No claim is made herein for the devices for transferring the blanks from the drum to the chain with the gum areas spaced from one another for the reason that such devices are disclosed and claimed in my pending application Serial No. 202,393 filed April 16, 1938, for Blank transferring device, which is a division of the present application.

I claim: 1. In a device for feeding envelope blanks, a support for holding a stack of blanks comprising a pair of rotatable separator disks, each of said disks having a series of circular grooves on its operative face to reduce frictional contact between the disk and the stack.

2. In a device for feeding envelope blanks, a support for holding a stack of blanks comprising a pair of rotatable separator disks, and means for adjusting the distance between the axes of rotation of said disks.

3. In a device for feeding envelope blanks, a support for holding a stack of blanks comprising a pair of rotatable separator disks, each of said disks having a series of circular grooves on its operative face to reduce frictional contact between the disk and the stack, and vertically disposed rod like stops against the rear of the stack, the lower ends of said stops projecting into the grooves of the disks.

4. In a device for feeding envelope blanks, a support for holding a stack of blanks comprising a pair of rotatable separator disks, each of said disks having a series of circular grooves on its operative face to reduce frictional contact between the disk and the stack, vertically disposed stops against the rear of the stack, the lower ends of said stops projecting into the grooves of the disks, and means for adjusting the position of said stops.

5. In a device for feeding envelope blanks, a support for holding a stack of blanks comprising a pair of rotatable separator disks, each of said disks having a series of circular grooves on its operative face to reduce frictional contact between the disk and the stack, and stops against the stack to hold the blanks in the stack, some of these stops having their lower ends extending into the grooves in the stack.

6. In a device for feeding envelope blanks, a support for holding a stack of blanks comprising a pair of rotatable separator disks, each of said disks having a series of circular grooves on its . operative face to reduce frictional contact between the disk and the stack, and stops against the stack to hold the blanks In the stack, some of the stops being free of the disks and other stops extending Into the grooves of the disks.

CI 7. In a device for feeding envelope blanks, a support for holding a stack of blanks comprising a pair of rotatable separator disks, each of said disks having a series of circular grooves on its operative face to reduce frictional contact beStween the disk and the stack, stops against the stack to hold the blanks in the stack, some of the stops being free of the disks, other stops extending into the grooves of the disks, and means for adjusting the position of said stops.

8. In a device for feeding envelope blanks from a stack of blanks, in combination, means for initiating the separation of the outside blank, and means for completing the separation of the blank from said stack independently of the foryi ward feed of the blank, said last named means comprising a pair of rotating separator disks and a pair of oscillating shovel-like elements cooperating with each disk to guard the same against contact with the blank and stack during the early portion of its passage therethrough. 9. In a device for feeding window envelope blanks from a stack of blanks, in combination, means for separating the forward portion of the outside blank from the stack and means for completing the separation of the blank from said stack independently of the forward feed of the blank, said last named means comprising a pair of rotating separator disks, said disks each having a suitably shaped horn to enter between the outside blank and the stack after the separation was initiated by the first named means, and oscillating shovel-like elements cooperating with each disk to guard the leading edge of the horn from engagement with the blank and stack during the passage of the horn past the window. 10. In a device for feeding envelope blanks from a stack of blanks, in combination, means for separating the forward portion of the outside blank from the stack and means for completing the separation of the blank from said stack independently of the forward feed of the blank, said last named means comprising a pair of rotating separator disks, said disks also serving as supports for the stack and each having a suitably shaped horn to enter between the outside blank and the stack after the separation was initiated by the first named means, and oscillating shovel-like elements cooperating with each disk to guard the leading edge of the horn from engagement with the blank during the early portion of the passage of the horn between the blank and the stack.

11. In a device for feeding envelope blanks from a stack of blanks, in combination, means for separating the forward portion of the outside blank from the stack and means for completing the separation of the blank from said stack independently of the forward feed of the blank, said last named means comprising a pair of rotating separator disks, said disks also serving as sup- 4 ports for the stack and each having a suitably shaped horn to enter between the outside blank and the stack after the separation was initiated by the first named means, and a pair of oscillating shovel-like elements straddling each disk and cooperating therewith to guard the leading edge of the horn from engagement with the blank during the early portion of the passage of the horn between the blank and the stack.

12. In a device for feeding envelope blanks from a stack of blanks, in combination, means for separating the forward portion of the outside blank from the stack and means for completing the separation of the blank from said stack independently of the forward feed of the blank, said a, last named means comprising a pair of rotating separator disks, said disks also serving as supports for the stack and each having a suitably shaped horn to enter between the outside blank and the stack after the separation was initiated by the first named means, and a pair of oscillating shovel-like elements straddling each disk and operable to enter the space between the separated forward portion of the blank and the stack in advance of such entry by the horn of the disk, TO and thereby guarding the leading edge of the horn from engagement with the blank during the early portion of the passage of the horn between the blank and the stack.

13. In a device for feeding envelope blanks yI from a stack of blanks, in combination, means for separating the forward portion of the outside blank from the stack and means for completing the separation of the blank from said stack independently of the forward feed of the blank, said last named means comprising a pair of rotating separator disks, said disks also serving as supports for the stack and each having a suitably shaped horn to enter between the outside blank and the stack after the separation was initiated by the first named means, and a pair of oscillating shovel-like elements straddling each disk and operable to enter the space between the separated forward portion of the blank and the stack in ad-, vance of such entry by the horn of the disk, and thereby guarding the leading edge of the horn from engagement with the blank during the early portion of the passage of the horn between the blank and the stack, and lifting device normally free of engagement with the stack to lift the rear of the stack and reduce the load on the disks during the separating operation.

14. In a device for feeding envelope blanks from a stack of blanks, in combination, means for separating the forward portion of the outside blank from the stack and means for completing the separation of the blank from said stack independently of the forward feed of the blank, said last named means comprising a pair of rotating separator disks, said disks also serving as supports for the stack and each having a suitably shaped horn to enter between the outside blank and the stack after the separation was initiated by the first named means, and a pair of oscillating shovel-like elements straddling each disk and operable to enter the space between the separated forward portion of the blank and the stack in advance of such entry by the horn of the disk, and thereby guarding the leading edge of the horn from engagement with the blank during the early portion of the passage of the horn between the blank and the stack, and a lifting device normally free of engagement with the stack and operable by a parallel motion device to lift the rear of the stack and reduce the load on the disks during the separating operation.

15. In a device for feeding envelope blanks from a stack of blanks, in combination, means for separating the forward portion of the ouside blank from the stack and means for completing the separation of the blank from said stack independently of the forward feed of the blank, said last named means comprising a pair of rotating separator disks, said disks also serving as supports for the stack and each having a suitably shaped horn to enter between the outside blank and the stack after the separation was initiated by the first named means, and a pair of oscillating shovel-like elements straddling each disk and operable to enter the space between the separated forward portion of the blank and the stack in advance of such entry by the horn of the disk, and thereby guarding the leading edge of the horn from engagement with the blank during the early portion of the passage of the horn between the blank and the stack, and a lifting device normally free of engagement with the stack and operable by a parallel motion device to lift the rear of the stack and reduce the load on the disks during the separating operation, said device comprising a roller for engaging the stack and means for adjusting the position of the roller relative the stack.

16. In a device for feeding envelope blanks from a stack of blanks, in combination, means for initiating the separation of the outside blank and means for completing the separation of the blank from said stack, said last named means comprising a pair of rotating separator disks and means to increase the gap between the partly separated blank and the stack to guard the disks against contact with the blank during the early portion of its passage through the stack. 17. In a device for feeding envelope blanks from a stack of blanks, in combination, means for initiating the separation of the outside blank and means for completing the separation of the blank from said stack, said last named means comprising a pair of rotating separator disks and means cooperating with each disk to guard the disks against contact with the blank during the early portion of its passage through the stack.

18. In a device for feeding envelope blanks from a stack of blanks, in combination, means for separating the forward portion of the outside blank from the stack and means for completing the separation of the blank from said stack independently of the forward feed of the blank, said last named means comprising a pair of rotating separator disks, and a lifting device normally free of engagement with the stack and operable to lift the rear of the stack and reduce the load on the disks during the separating operation. 80 19. In a device for feeding envelope blanks from a stack of blanks, in combination, means for separating the forward portion of the outside blank from the stack and means for completing the separation of the blank from said stack independently of the forward feed of the blank, said last named means comprising a pair of rotating separator disks, said disks also serving as supports for the stack and each having a suitably shaped horn to enter between the outside blank and the stack after the separation was initiated by the first named means, means operable to enter the space between the separated forward portion of the blank and the stack in advance of such entry by the horn of the disk thereby guarding the leading edge of the horn from engagement with the blank during the early portion of the passage of the horn between the blank and the stack, and a lifting device normally free of engagement with the stack and operable to lift the rear of the stack during the separating operation, and to release 50 the blank for unimpeded movement after completion of the separation.

20. In a device for feeding envelope blanks, a supporting element for holding a stack of blanks, comprising a rotatable separator disc5 having a substantial portion of its operative supporting face occupied by a series of circular ribs alternating with circular grooves and adapted to afford an extensively subdivided supporting structure having a relatively low frictional coefficient.

21. In a device for feeding envelope blanks, a supporting element for holding a stack of blanks at spaced apart regions thereof, comprising a pair of rotatable separator discs, each of said discs having a substantial area of its operative supporting face occu'pied by a series of circular ribs alternating with circular grooves and adapted to afford an extensively subdivided supporting structure having a relatively low frictional co-efficient. 70 ABRAHAM NOVICK.