US2844858A

US2844858A - Ceramic press

Info

Publication number: US2844858A
Application number: US521862A
Authority: US
Inventors: Assmann Otto
Original assignee: DORST Technologies GmbH and Co KG
Current assignee: DORST Technologies GmbH and Co KG
Priority date: 1954-07-13
Filing date: 1955-07-13
Publication date: 1958-07-29
Anticipated expiration: 1975-07-29

Description

0. ASSMANN "CERAMIC PRESS July 29, 1958 7 Sheets-Sheet 2 Filed' July 15, 1955 In venfvr y 9,1958. QKSSMANN. 2,844,858

" CERAMIC .PRESS Filed July 13, 1955 7 Sheets-Sheet s y In vznfor o. ASSMANN CERAMIC PRESS July 29, 1958 Filed July 13, 1955 '7 Sheets-Sheet 4 In Vera/or 0. ASSMANN CERAMIC PRESS July 29, 1958 Filed July 13, 1955' 7 Sheets-Sheet 5 .lnyznhor July 29, 1958 o. ASSMANN 2,844,858

CERAMIC PRESS Filed July 13, 1955 7 Sheets-Sheet 6 In van for y 1953 o. ASSMANN 2,844,858

8 CERAMIC PRESS Filed July 13, 1955 7 Sheets-Sheet 7 United States Patent 2,844,858 Patented July 29,1958

CERAMIC PRESS Otto Assmann, Selb, Bavaria, Germany, assignor to Dorst- Keramikmaschinen-Bau, Kochel, Upper Bavaria, Germany, a partnership Application July 13, 1955, Serial No. 521,862

Claimspriority, application Germany July 13, 1954 Claims. (CI. -93) The present invention relates to a press which is adapted for continuous operation for producing molded objects, for example, insulators and other parts of ceramic materials in a dry, pulverized state.

Although a variety of automatic presses are known for this purpose, most of them have the serious disadvantage that the pressing tools or dies thereof only permit the molding of objects of only one shape, and require a considerable length of time for exchanging the respective tools if an object of a difierent shape is to be molded, since the operating parts of the machine also have to be exchanged, adjusted, or modified so as to comply with the requirements of the new tools.

It is obvious that such operations decrease the efiiciency of the machine considerably and in many different respects, particularly also because they require very experienced workers to be done properly. Other automatic presses have already been proposed which do not require the operating parts of the machine to be exchanged when switching over from the production of one object to another, since the necessary changes in motion may be carried out by an adjustment of the periods of engagement of the machine parts which move the tools, and since the respective stroke length of the tools may be infinitely varied by a lever mechanism. Although such a machine has proved successful, its applicability is quite limited since the control of the tools which is thus obtained does, in many cases, not permit the production of articles which have been molded so as to comply with the highest standards.

These types of machines also have the disadvantage that the adjustments of the pressing tools or dies have to be carried out by a person of considerable experience and aptitude, since usually several adjustments have to be tried out before the individual tools and operating parts will be in the proper position so as to move correctly relative to eachother. The difficulties encountered in such adjustment Will be subsequently described, with reference to Fig. 1 which also illustrates the basic requirements which have to be fulfilled by an automatic dry-molding press which is universally adjustable.

The pressing tool consists of an upper die and a lower die. The upper die is mounted on the press ram of the machine, while the lower die is clamped on the stationary machine table and vertically below the upper die. The jacket of the lower die is vertically below the upper die. The jacket of the lower die is vertically adjustable and, since it is connected to the withdrawal bar of the machine, it carries out its own independent movements during the pressing operation.

Curve 1 in Fig. 1 illustrates the course of movement of the press ram together with the upper die during the operation of the machine. This is a positive movement which is produced by a double jointed bell crank. Curves 2a and 3a show the course of the independent movements. of the lower die during a pressing operation Without finishing compression of the molded object, i. e.

without any so-called precompression. This move ment of the jacket of the lower die is produced by machine parts which are connected in a special manner and is composed of the two movements which are produced independently of each other according to

curves

2 and 3 relative to curves 2a and 3a. 7 7

According to Example 1, the lower die which is. filled with molding material is disposed in the filling position at the level x, where it remains until the press ram has been lowered according to curve 1* to the point a. which corresponds to the position a of the lower die. After the upper die has then penetrated into the lower die, both parts carry out the same movement until they reach the position b, i. e. the compressionpoint of the upper die according to curve 1 at the level x, or the position b, of the lower die according to curve 2 at the level x respectively, at which position they come to a short stop. At the beginning of the return movement of the press ram, the jacket of the lower die remains in the pressing position at the level x -until the molded object has been relieved of the pressure to suchan extent that it is able to swell sufiiciently. At the point c a further downward movement of the jacket of the lower die will start according to curve 3,,. This movement. releases the molded object from the mold of the lower die. Such lowering movement terminates at the point d 'atv the level x The molded object may then be removed from the lower die either by hand or mechanically before the jacket of the lower die begins its return movements. Thereafter, the lower die returns from the position d to the position 1, i. e. to the filling position, where the mold is again filled mechanically with molding material, whereupon the entire molding process is repeated.

The course of the molding movements accordingto Example 1 is, however, suitable only for molding operations without precompression, i. e. for molding of objects of simple shape and low height. Generally, however, and especially for high molded objects, a precomipression or premolding will be required since the object can be given a uniform density only in such a manner. In such premolding, the pressing operations are controlled in such a manner that the independent movement of the lower die jacket to the level x does not proceed together with'the press ram, but already prior to the time when the latter reaches its lowest position. The last compressing operation is thus carried out only by the press ram alone with the jacket of the lower die stopping at the level x The length of stroke of the premolding operation differs with each tool and must therefore'be infinitely variable on the machine from-a maximum of about 10 mm. to zero.

Example 2 illustrates the'course of the independent movement of the jacket of the lower die at the largest possible premolding operation. The jacket alreadyleaves the filling position at the position 0 which corresponds to the position 0 of the press ram, wherein the distance a of the press ramis equal to the distance of the lower die from such position plus the largest possible-premolding movement. When the upper die reaches the, position b at the jacket of the lower die will already be in the pressing position b where it remains until the position 0 is reached, so that the press ram carried out the supplementary or finishing compression of the molded object during its movement from the position b to the position b according to curve 1.

In view of the many diflerent shapes of the objects to be molded, not only the premolding but also the independent movements of the jacket of the lower die must be infinitely variable separately of each other according to curve 2 and curve 3 between their maximum. stroke and zero.

Examples 3 and 4 illustrate the independent movement of the jacket of the lower die with an arbitrary premolding and shortened pressing or withdrawal movements. The filling level of the lower die or the extent of the pressing movementthereof are shortened in accordance with a smaller height of the molded object to be formed. The curve shows that, independently of the extent of the pressing movement of the jacket of the lower die, it is necessary that the movements of the press ram and the jacket of the lower die be in absolute synchronism with each other up to the beginning of an arbitrary premolding operation.

Example 4 illustrates the shortening of the withdrawal movement of the jacket of the lower die according to curve 3, In this connection it is important that the pressing position of the jacket, i. e. the height x is always the same at any adjustment of the premolding operation, the pressing movement, and the withdrawal movement of any kind of dies. The distances of both the height x, as well as of the height x from the pressing position at the height x are therefore variable. If the extent of the pressing movement and of the withdrawal movement is zero, the height x, and x coincide with the pressing position x which means that the jacket of the lower die does not move, so that it will be considerably easier to mount the die. Also, both the upper and lower dies may then be accurately aligned, without danger to the tools while the machine is running.

The present invention permits any of the adjustment to be carried out as indicated, for instance, in Examples 1 to 4, and thus completely fulfills all the requirements to be made upon an automatic dry-molding press which is universally applicable. The machine permits the adjustment of any kind of premolding operations or of the pressing and withdrawal movements to any length of stroke without requiring any exchange, adjustment or modification of the operating parts of the machine. It also permits the tools to be setup within the shortest possible time, without any appreciable interruption of the production, and by workers which have only been trained on the job and only possess a minor education. Corrections in movement because of a change in the molding material or for any other reason may be carried out without interruption of the pressing or molding operation while the machine continues to run. The molding movements which are always accurate for any course of movement of any type of molds not only assure a perfect quality of the molded object but also permit a quicker succession of the operations so that in connection with the relatively short setup times of the tools which may be obtained, it will be possible to increase the rate of production considerably.

The above-mentioned objects of the invention are principally attained by an infinitely variable adjustment of the premolding, molding, and withdrawal movements without change of the molding position of the respective jacket of the lower die relative to the machine itself.

Further objects, features, and advantages of the invention will be apparent from the following detailed description thereof which is to be read with particular reference to Fig. 1 as already described in principle and to the other accompanying drawings, wherein Fig. 1 shows a graphic illustration of the operating steps of an automatic dry-molding press according to the invention with four different working examples;

Fig. 2 shows diagrammatically one embodiment of the invention with a press ram and a withdrawal rod, and graphically illustrates the course of the movements of the upper die and the jacket of the lower die in accordance with Example 1 in Fig. 1;

Fig. 3 shows a horizontal cross section taken along line IVI V of Fig. 4 through the withdrawal rod mounted in the machine housing and the mechanism for producing and coupling the independent movements of the pressing tools according to Example 1 in Fig. 1;

Fig. 4 shows a vertical cross section through the mechanism as shown in Fig. 3;

Fig. 5 shows the design of the compensating bevel gear sector for carrying out the pressing or molding movement of the molding tool, with the pressing cam shown in displaced position, and in the position corresponding to the angle of rotation of the withdrawal cam shown in Fig. 6;

Fig. 6'shows the design and the position of the compensating bevel gear sector for carrying out the withdrawal movement of the molding tool by means of the withdrawal cam shown in displaced position without consideration of a premolding operation;

Fig. 7 shows the unchanged molding position of the operating parts as shown in Fig. 5 when the largest possible premolding movement has been set up;

Fig. 8 shows the operating parts shown in Fig. 6 when the largest possible premolding movement has been set up;

Fig. 9 shows partly in a side view and partly in a vertical cross section, the design and arrangement of the press ram and the withdrawal rod, as well as parts of the mechanism for producing and coupling the independent movements of the molding tool according to a modification of the invention; while Fig. 10 shows a rear view of the machine according to Fig. 9 with the molding and withdrawal cams which are driven in synchronism, and with the members for compensating the course of the independent movements of the molding tool.

Referring to the drawings, and first particularly to Fig. 2, the crankshaft 4 and the main shaft 5 are driven in synchronism in the direction shown by the arrows by means of the shaft 6 through a pinion 7 and the

intermediate gears

8 and 9, as well as the

gears

10 and 11. Crank 12 operates the double-jointed bell crank which is suspended on a pivot 13 and thus drives the upper die which is pivotally mounted on the double-jointed bell crank by a pin 14 and slidable in a vertical direction in a slide track of the upright of the machine so as to carry out a continuous reciprocating movement similar to operating curve 1 as graphically illustrated. The course of movement of the upper die 15 does not vary. The lower housing of the machine contains the elements necessary for producing the independent movements of the die. These movements are produced by cams which are laterally keyed on the main shaft 5, and are transmitted to the withdrawal rod 16 by means of a variable compensating gear. The lower die which is clamped on the table 18 is provided with a vertically slidable jacket which is bolted by means of a connecting rod to the mounting bridge 17 of the withdrawal rod 16 and carries out the movements as graphically illustrated by

curves

2 and 3. These independent movements of the die are of varying size and must be infinitely variable between their maximum size and zero without change of the pressing position of the die, i. e. of the height x when the extent of movement is shortened and an arbitrary premolding operation is set up.

Figs. 3 and 4, respectively show horizontal and vertical cross sections through the machine housing and illustrate the design and arrangement of the parts which produce and couple the necessary independent movements of the die.

The compensating lever 19, the bevel gear sector 20, and the bevel gear sector 21 are rotatably mounted on the main shaft 5 of the machine. A bevel gear 23 which is rotatably mounted on the journal 22 of the compensating lever 19 is in mesh with the bevel gear sectors and 21. A shoe 26 which is mounted on a projecting pin of a slide 25, which is adjustable by a spindle 24 engages in aradially extending track on the bevel gear sector 20. Slide 25 is movable in a slide track in lever 27. Both parts thus form an adjustable crank, which has a radius of zero when the axis x.; of the slide pin coincides with the axis x of the journal 28. This journal 28 is mounted on a stationary part of the machine housing and is rigidly secured to a crank arm 29 which transmits a pivotal move-- ment of constant angle and uniform motion to lever 27 which is produced by means of a roller 30 which is mounted on a pin 31 and rolls along a withdrawal cam 32. By changing the radius of the crank arm formed of the slide 25 and lever 27 it is possible arbitrarily to adjust the angle of the pivotal movement transmitted by shoe 26 to the bevel gear sector 20.

The stroke produced by the pressing or molding cam 33 which is likewise k'eyed on main shaft 5 is transmitted by the roller 36 which is mounted on a pin 34 on the crank arm 35, through a journal 37 to the spur gear sector 38 which transmits an invariable pivotal-movement to a spur gear sector 39 and thus to the bevel gear sector 21 which is bolted thereto. The bevel gear sectors and 21 are held under tension by springs 40 so that the

rollers

30 and 36 are held in constant engagement with the withdrawal cam 32 and the pressing cam 33, respectively. in Figs. 3 and 4, compensating lever 19 is disposed horizontally and thus likewise the bevel gear sector 20. In. this position it is possible to shift the shoe 26 of slide in its slide track by turning spindle 24 wthout thereby pivoting the bevel gear sector 20. The slide track of shoe 26' and that of lever 27 are therefore parallel to each other. In the pressing position, cam 41 which is rigidly secured to bevel gear sector 20 is disposed in a vertical position, as shown in Fig. 4, and rests against a pin 42'of the mechanism for adjusting the pre-molding operation in such a manner that the operating parts for producing the independent movements of the die will not be afiected bysuch adjustments. As shown in Fig. 3, withdrawal rod 16 is pivotally mounted on compensating lever 19 by means of a pin 43 and a shoe 44 so that the pivotal movement of the compensating lever is freely converted into a vertical movement of the withdrawal rod 16. If themain shaft 5 which is driven by gear 11 turns in the direction indicated by the arrow, roller rolls along the withdrawal cam 32, as shown particularly in Fig. 6, whereby such motion is transmitted through crank arm 29 to the bevel gear sector 20 to pivot the same in accordance with the radius to which the crank has been adjusted by means of the shoe 26. If the bevel gear sector 21 is at rest at this phase of the operation, bevel gear 23 rotates between the two gear sectors and pivots the-compensating lever 19 about half of the pivotal angle of bevel gear segment 20 and in the same direction. After supporting lever 45 has been mechanically disengaged, compensating lever 19 then transmits a lowering or withdrawal movement to rod 16 in accordance with the graphical illustration of curve 3 in Fig. 1, the returning movement then being carried out by the tension springs 40.

The movement of supporting lever 45 is controlled by a.

cam 46 through the roller 47, the arm 48, and the shaft 49 which is mounted on the housing of the machine. When in its locking position, supporting lever 45 protects the compensating gear from excessive loads from the pressure of the upper die in the event that the two parts.

of the die are not properly aligned with each other.

As shown in Fig. 4, compensating lever 19' is maintained in the pressing position by the threaded socket 50. If the withdrawal rod 16 with the die thereon is to be moved into the filling position, this is done by turning a crank on the bevel gear shaft 52 and thus turning spindle 51. An accurate adjustment from zero to the maximum filling level may be obtained by means of a Vernier scale, the socket being supported by a guide bolt 53.v Compensating lever 19 may thus pivot, the pivotal movement thereof being produced by spring 40 acting on the bevel gear sector 20, so that the latter will roll along the bevel gear 23. The arrangement of the bevel gear thus adjusts itself in accordance with the adjustment of the filling level. When the main shaft 5 of the machine turns, the press ram-which isdriven in synchronism with the compensating gear is lowered until the upper die entersinto In the pressing position of the machine, as shown- 6 the mold of the-lower die. In such angular position of mainsshaft 5; roller 36 will roll alongthe'pressing cam 33 to-move'the withdrawal rod 16 positively and against the action of springs 40- into'the pressing position in accordance with curve 2 of Fig; 1.

Fig. 5 shows the bevel gear sector 21 which is acted upon byspring40, in anangular position of main shaft 5 of approximately 255 corresponding to the abscissa shown in Fig. 1-, while Fig. 6- shows the position of bevel gear sector 20 with cam 41 in the same angular position of main shaft 5. Shoe 26 in the slide track of bevel gear sector 20 is shown as being set to half of its full stroke. Through the action of springs40,

rollers

36 and 30 engage the withdrawal cam 33 and the pressing cam 32, respec-.

tively. In this angular position of main shaft 5, the press ram and withdrawal rod 16 will move uniformly and in the same direction. After a further rotary movement of main shaft 5, the compressing operation will be completed when it arrives in the position 0. The pressing cam 33 rotates up to the angular position without exerting a stroke. Within the range of 255 to 0, withdrawal rod 16 remains withoutmovement in the pressing position and does not begin the withdrawal movement until cam 32 is in the angular position of 10. The Withdrawal height x according to the curves shown in Fig. 1 will be attained when cam 33 has reached the angular position of 75. The distance between the pressing position and withdrawal end' position is dependent upon the respective adjustment of the radius of the crank arm formed of the slide 25 and the lever 27. The descending parts of the cam up to the angular position of return the withdrawal bar to the filling position of the die at the level x, according tothe curves shown in Fig. 1. Between the angular posit-ions of 120 and roller 36 abuts against cam 33 only if the maximum pressing stroke according to curve 2 in Fig. 1 has been set up. In all other cases, roller 36 will-be clear of cam 33 and remain in a position corresponding tothe respective pressure stroke level as adjusted.

Fig. 6 clearly illustrates the gate mechanism! in bevel gear sector 20. The shoe 26 only rests with its upper surface on the slide'track. Tension springs 40 and roller 30 which engages with cam 32 maintain the gate mechanism in a horizontal position so that shoe 26- may be shifted within the distance of y to y; without pivoting of the bevel gear sector 20. The-lower surface of shoe 26 does not engage the gate which means that bevel gear sector 20 may be pivoted upwardly to 'a' certain extent without hindrance. Lever 27 is providedat the end position of shoe 26 on the line y, with a cam 54 which in the pressing position shown in Fig. 6 rests on an anvil 55 forming a part of sector 20. Cams 54 and anvil 55 serve in connection with other elements for setting up an arbitrary premolding operation.

As may be seen from the above description it is therefore possible to vary the pressing and withdrawal movements uniformly and in the same direction as the movements of the press ram.

For adjusting the premolding operation, a special set-up device and a further auxiliary cam, the so-called premolding cam, are provided on the main withdrawal cam 32. Fig. 4 illustrates the set-up device for the premolding operation in a cross section. A main socket 56 is secured by a pin in an aperture of the machine housing. A threaded socket 57 with the stop pin 42 thereon is slidably mounted in the main socket 56 and acted upon by-a compression spring 58. By turning a threaded spindle 59, socket 57 may be shifted axially up to a stop 60 on spindle 59. Spring 58 is of a strength so that if sufiiciently tensioned it will overcome the strength of tension springs 41).

Fig. 6 shows the threaded socket 57 as being set back to its end position by means of spindle 59. A pin 60' which is slidable in a slot in main socket 56 prevents socket 57 from being turned when spindle 59 is turned.

In the end position, stop pin 42 rests without pressure against earn 41 of the bevel gear sector 20. The compressing operation of the machine is in such a case carried out without premolding. If a premolding operation is required, spindle 59 is turned by means of a crank until the desired degree of premolding is indicated on a Vernier scale or any other suitable indicating device. The premolding operation may be set up during any phase of the operation of the machine without interrupting its continuous movement.

Fig. 8 shows the setup of the machine for a maximum premolding operation. After the force of tension spring 40 has been overcome by means of socket 57 together with the force of compression spring 58, cam 41 has been pivoted about an angle x whereby the bevel gear sector 20 has been turned likewise. Since cam 54 rests on anvil 55 ofbevel gear sector 20, such pivotal movement will also be transmitted to lever 27 and arm 29. Thus, roller 30 will no longer engage the path of the withdrawal cam 32 but remain at a distance therefrom corresponding to the pivotal angle x until it contacts the track of the premolding cam 61, for example, in the angular position of 255 as illustrated in Fig. 8. Because of the pivoting of bevel gear sector 20, bevel gear 23 rolls along the two bevel gear sectors which, in turn, changes the position of the operating parts. Since the compensating lever 19 is temporarily locked in the pressing position by the threaded socket 50 and the action of springs 40, as shown in Fig. 4, bevel gear sector 21 will carry out a pivotal movement in the opposite direction so that, as shown in Fig. 7, rollers 36 on the arm 35 will assume a different position relative to the path of movement of pressing cam 33. During this time, as shown in Fig. 8, shoe 26 is unsupported in the gate. The adjustment of the premolding does not affect the pressure path of curve 2 in Fig. 1 since this is only dependent upon the adjustment of the threaded socket 50. As shown in Figs. 7 and 8, the premolding step is carried out during the operating phase between the angular positions of 195 and 255 of main shaft 5 of the machine and with uniform and unidirectional movements of the press ram and the withdrawal rod. Until this time, roller 30 remained along the cam path x without exerting any stroke. In the angular position of 255, however, it engages with the premolding cam 61 and forces the bevel gear sector 20 against the action of spring 58 to carry out a reverse pivotal movement corresponding to the positive movement of bevel gear sector 21. In the pressing position, i. e. in the an-' gular position of of main shaft of the machine, the two pivotal movements of the bevel gear sectors which compensate each other are terminated. The roller 30 engages at point x again with the basic circular path of cam 32. which means that the die is in the pressing position at the level x of Fig. 1. During the reverse pivotal movement of the bevel gear sectors, bevel gear 23 rolls along the teeth of the sectors without thereby pivoting the compensating lever which in the angular position of 255 of the main shaft is already disposed in the position of rest, i. e. in the pressing position, since because of the premolding step it had already assumed a lower starting point in accordance with the adjustment of the premolding. Between the angular positions of 0 and roller will be moved positively without stroke along withdrawal cam 32 and premolding cam 61. The withdrawal movement does not begin until roller 30 has passed beyond the 10 position, and it continues up to the angular position of 75 of main shaft 5. Then follows the reversal of the die to the filling position, i. e. the angular position of 75 of main shaft 5. Then follows the reversal of the die to the filling position, i. e. the angular position of 120 of main shaft 5. By shifting the threaded socket 57 from the end position x to the stop at the front end of main socket 56, any premolding distances from a maximum premolding to zero may be ad- 8 justed infinitely. The infinite variation of the pressing, withdrawing, and premolding movements without requiring any exchange or modification of the operating parts of the machine, as obtained according to the present invention, is not dependent upon the particular elements of the embodiment as above-describedand may be carried out by other means, for example, by those of a second preferred embodiment of the invention which will now be described.

. The press ram 66 of the machine shown in Fig. 9 is driven by a crank 62. A worm 63 on the countershaft 64 drives a worm wheel 65 and a pinion 79, and thusalso the cams for producing the pressing and withdrawing movements of the machine. The movements of the press ram and the independent movements of the die are thus coupled positively and in synchronisrn with each other. Press ram 66 is designed as a slide and is vertically movable in the slide track of the upright of the machine. A shaft 67 which is mounted on a stationary part of the machine housing pivotally supports a beam 68 which is connected through a shaft 69 and a shoe 70 thereon with the withdrawal rod 71 of the machine, thus carrying the same. The other end of beam 68 carries a compensating rod which is pivotally mounted thereon by means of a shaft 72. The adjustment of the filling level of the die corresponds to that described relative to the first embodiment of the invention, for which purpose the threaded socket 73 may be adjusted through a spindle 74 by means of a set of bevel gears which may be turned at 75 by means of a crank. The lower end of the withdrawal rod 71 forms a piston which passes through a cover 76 into a cylinder 77 which is supplied with a suitable pressure medium through a pipe 78 so as to force the withdrawal rod 71 in an upward direction. This modification of the invention illustrates that the draw spring 40 may be replaced by other means which produce the same effect, for example, by a hydraulic lift. Such hydraulic operation has the advantage that the entire withdrawal operation may be carried out with adjustable and constant pressure.

The rear of the machine, as shown in Fig. 10, carries the elements for producing, coupling and varying the independent movements of the die. The cams which are jointly driven in a clockwise direction by a pinion 79 are rotatably mounted on shafts 80 and 31. Two

further shafts

82 and 83 carry the bell cranks 84 and 85, respectively. A roller 86 on bell crank 84 rolls along the pressing cams 87. Bell crank with a roller 89 engaging the withdrawal cam 88 is provided with a sector-shaped arm, the center of which, in the position as shown in Fig. 10, is disposed Within the longitudinal axis of a pin 90. The angular sector 85 is designed as a circular slide track along which a block 91 may be moved in a circular direction about pin 90. Block 91 is provided with a handle end may be secured in a fixed position on the sector 85. Block 91 carries a shaft 92 on which a draw bar 93 is pivotally mounted, the bifurcated end of which is connected through pin with a three-armed lever 95 which is mounted on a shaft 94. The oblong hole in draw bar '93 permits the premolding to be set up, and thus carries out the function of the gate on the bevel gear sector 20 according to the first embodiment. The bell cranks 84 and 85 are connected with each other by a chain 96 which extends over a chain gear 97 which is mounted on beam 68 by means of an axle pin 98, a bifurcated member 99 and a draw bar 100.

In place of the premolding adjustment by means of a compression spring, as shown in the first embodiment of the invention, the present modification thereof provides hydraulic adjusting means. For this purpose, a cylinder 101 with a piston 102 therein is mounted on the machine housing. A pressure medium may be supplied to cylinder 101 through a pipe 103. Cylinder 101 is generally held under pressure, with piston 102 being in the position as shown in Fig. 10. In such a case, the machine operates without premolding. The premolding operation is set by hand by means of a hand wheel 104a and by unscrewing of setscrew 104. The action of hydraulic piston 102 is such that, through the leverage of the mechanism, a turning of hand wheel 104a will not adjust the position of piston 102, but of the piston-shaped withdrawal rod 71 in cylinder 77. Such adjustment raises the threearmed lever 95 which is connected to chain 96, thereby pulling the same to rotate chain gear 97 and to draw bar 100 upwardly. Such movement is .then transmitted to beam 68 and thus to withdrawal rod 71. At the same time, roller 105 which engages with the cam on the bell crank 85 moves the roller 89 away from the path of the withdrawal cam 88 by an amount corresponding to the respective premolding adjustment. Similar to the premolding operation of the machine between the angular positions of 255 and of main shaft 5, according to the first embodiment of the invention, setscrew 104 will then force back the piston 102 along the distance of the premolding movement when roller 89 is positively moved back against the withdrawal cam 88 by the premolding cam 106. The individual movements of the die are the same as those in the first embodiment and therefore do not need to be discussed again.

For adjusting the withdrawal movements it is necessary to shift block 91 along the sector of bell crank 85. If the axis of shaft 92 coincides with the axis of shaft 83, the withdrawal movement will be equal to zero. In this position it is likewise possible to set up any desired premolding movement.

Although my invention has been illustrated and described with reference to the preferred embodiments thereof, I wish to have it understood that it is in no way limited to the details of such embodiments or to the specific examples as described, but is capable of numerous modifications within the scope of the appended claims and depending primarily upon the respective demands to be made upon the various operating elements of the machine.

Having thus fully disclosed my invention, what I claim 1. A press having exchangeable dies for molding objects of dry pulverized ceramic materials which comprises in combination a press ram, means to drive said press ram, a shaft connected to be driven by said driving means, two cams shaped to cause separate movements for producing the motions of the die and driven by said shaft, a withdrawal rod, means for adjusting said movements independently of each other and a continuously adjustable differential gear to transmit the cam motions to the said withdrawal rod, the said last recited gear comprising a compensating lever rotatably mounted on the main shaft of the machine, a bevel gear mounted at one end of said compensating lever, a pair of bevel gear sectors mounted so as to be pivotable about said main 10 shaft and in mesh with said bevel gear, the other end of said compensating lever carrying said withdrawal rod, and means for adjusting the amplitude of the pivotal movements of said two bevel gear sectors from zero to a maximum value.

2. A press as defined in claim 1, wherein the infinitely variable adjustment of the pressing distances is obtained by an adjustment of the length of a crank which is adapted to pivot said compensating lever.

3. A press as defined in claim 1, wherein the infinitely variable adjustment of the withdrawl movements of said withdrawal rod is produced by varying the position of said compensating lever under spring action and by adjusting the vertical position of a threaded member pressing upon the free end of said compensating lever through a threaded spindle by turning a bevel gear pinion connected to said member.

4. A press as defined in claim 1, wherein the infinitely variable adjustment of the premolding movements is produced by varying the position of said compensating lever and the withdrawal rod thereon by pivoting a cam on one of said bevel gear sectors, whereby, through the engagement of a cam with an anvil on said bevel gear sector, the lever engaging the withdrawal cam pivots downwardly a distance in accordance with the distance of the premolding movement as adjusted, and lifts the roller on said lever from engagement with said withdrawal cam.

5. A press as defined in claim 4, wherein a premolding cam is provided on the cam shaft and extending on said withdrawal cam along a certain distance of the rotary movement of said main shaft, said premolding cam because of the engagement of the cam on said anvil being adapted to pivot the bevel gear sector with the cam thereon downwardly against the action of a compression spring of the adjusting means for the premolding operation, and thus carrying out a movement opposed to the movement of the bevel gear sector thereof, whereby the bevel gear pinion rolls along between these bevel gear sectors without affecting the compensating lever which is already in the angular position of 255 because of the premolding as adjusted, to carry out any further movement.

References Cited in the file of this patent UNITED STATES PATENTS 298,646 Whittaker May 13, 1884 312,066 Balson Feb. 10', 1885 389,334 Smith et al Sept. 11, 1888 685,536 Stanley Oct. 29, 1901 2,449,515 Seelig Sept. 14, 1948 2,499,980 Stokes Mar. 7, 1950 2,682,080 Saalfrank June 29, 1954 FOREIGN PATENTS 324,259 Great Britain Jan. 23, 1930