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US2946303A - Hydraulically operated presses - Google Patents

Hydraulically operated presses Download PDF

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Publication number
US2946303A
US2946303A US694042A US69404257A US2946303A US 2946303 A US2946303 A US 2946303A US 694042 A US694042 A US 694042A US 69404257 A US69404257 A US 69404257A US 2946303 A US2946303 A US 2946303A
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Prior art keywords
pressure
press
piston
cylinder
valve
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Expired - Lifetime
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US694042A
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English (en)
Inventor
Schmid Mathias
Current Assignee (The listed assignees may be inaccurate. Google has not performed a legal analysis and makes no representation or warranty as to the accuracy of the list.)
G Siempelkamp GmbH and Co KG
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G Siempelkamp GmbH and Co KG
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Application filed by G Siempelkamp GmbH and Co KG filed Critical G Siempelkamp GmbH and Co KG
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    • B—PERFORMING OPERATIONS; TRANSPORTING
    • B21—MECHANICAL METAL-WORKING WITHOUT ESSENTIALLY REMOVING MATERIAL; PUNCHING METAL
    • B21J—FORGING; HAMMERING; PRESSING METAL; RIVETING; FORGE FURNACES
    • B21J9/00—Forging presses
    • B21J9/10—Drives for forging presses
    • B21J9/12—Drives for forging presses operated by hydraulic or liquid pressure
    • B—PERFORMING OPERATIONS; TRANSPORTING
    • B30—PRESSES
    • B30B—PRESSES IN GENERAL
    • B30B15/00—Details of, or accessories for, presses; Auxiliary measures in connection with pressing
    • B30B15/16—Control arrangements for fluid-driven presses

Definitions

  • Hydraulically operated presses particularly extrusion presses or drop-forge presses are, in most cases up to now, driven directly by air-cushioned high-pressure water accumulators.
  • it is difiicult to accomplish the forming and relieving operation of a press within short time intervals as is often necessary or at least desirable in order to attain the proper speed for the forming process which speed depends, on the type of material to be formed or on other reasons.
  • the forming of hot titanium sheets becomes difiicult if done in presses employing a rubber pad or cushion as a counter die and in which the time for forming and relieving is of relatively long duration inasmuch as the rubber pad is unable to withstand the application of high temperatures over a relatively long period of time as it will heat up to a point where the rubber is damaged or destroyed.
  • the present invention relates to hydraulically operated presses, particularly extrusion presses or drop-forge presses employing rubber pads which are operated, for instance, by means of an air cushioned highpressure accumulator.
  • the invention resides therein that a high-pressure transformer is arranged between the high-pressure accumulator and the press by which the actual forming process is accomplished after the press has been initially closed.
  • This pressure transformer is operatively adjustable in various ways so that its: operation is advantageously suitable for the forming process. It-is advantageous to also arrange a low-pressure trans.-v former between the high-pressure accumulator and the press for efiecting the initial closing operation thereof.
  • a further essential advantage of the present arrangement resides therein that, contrary to hydraulic presses which are directly driven by high-pressure accumulators, considerable energy is saved, as will be explained in more detail later on.
  • the working pressure in the press may be increased markedly whereby the power actuating parts may be made smaller and, as a result thereof, the space required becomes less than for arrangements wherein the press is actuated directly from an accumulator.
  • the lowpressure transformer includes a small high-pressure piston combined with a lowpressure piston of the size corresponding to the weight of the parts that must be moved .in initially closing the press. It is especially advantageous, as mentioned above, to control the pressure in the high-pressure transformer during the forming process in such a way that it coincides with the pressure characteristic actually required for the forming operation. A further saving on energy is thereby possible, inasmuch as the pressure rise thus coincides with that actually desired in the press during the forming operation whereby the expended energy is limited to the absolute required amount.
  • the high-pressure transformer itself consists, in itssimplest form, of driving and driven pistons whereby, through transmission of forces from the driving piston which is supplied by the high-pressure accumulator to the driven piston, the pressure transformation and control thereof is accomplished.
  • the movement of the driving pistons is perpendicular to that of thedriven pistons and the pistons are directly interconnected with each other by connecting rods so that, in the simplest manner, the rise in pressure at the driven pistons coincides with the pressure characteristic desired in the press.
  • the pressure rise in the highpressure transformer is; limited by a' pressure-limit valve.
  • This pressure-limit valve may beconnected to the driving pistons, respectively, to their cylinders.
  • the high-pressure transformer is constructed in such a way that it operates at the same time as acontrol of the press pressure during the unloading of thepress as, for instance, in such a way that the two driving pistons of the high-pressure transformer are arranged coaxially intwo. cylinders and that these two pistons are connected with each other by a rigid piston rod while the connecting rods of the driven pistons, which are attached thereto, move in a direction substantially perpendicular to the movement of the driving pistons.
  • the driven pistons at the beginning of their movement, produce only a small hydraulic pressure while at the dead center position of the connecting rods they theoretically produce an infinitely large hydraulic pressure whereby thedelivery of these driven'pistons in relation to the travel of the driving pistons is in the inverse ratio to the pressure they produce.
  • the hydraulic pressure in such a pressure transformer increases along a similar characteristic as isdesirable in drop-forges and particularly extrusion presses with rubber pads.
  • a further advantage in the operation of the present hydraulic press resides thereinthat it is possible to have 4 porates a conventional solid die 2 and a rubber cushion 3 that acts as a counter die.
  • the pressing or forming operation of the workpiece S is accomplished with a conventional press piston or ram 4 and the general structure of the press itself, being also of conventional design, does not need to be described in detail.
  • a conventional accumulator 5 with a working liquid, such as water, is provided for the hydraulic operation of the press.
  • the water in the accumulator 5 is kept under pressure in a conventional manner by compressed air.
  • the Water is supplied to this accumulator 5 by a pump through the pump discharge line 21.
  • This line 21 includes a check valve 22, an automatic shut-01f valve 23,
  • the high-pressure transformer operate with oil, whereas, the driving pistons of the pressure transformer and the high-pressure accumulator can be operated with water.
  • an object of the present invention is to provide a hydraulically operated press in which the time two control valves 2% and 2%.
  • a line 30 leads to the cylinder space 32 of a low pressure transformer 31 which includes a differential piston 33 comprising a smaller high pressure piston 33a and a larger low pressure piston 33b.
  • Another object of the present invention resides in the relativelysmall size of the force transmitting parts as well as the high etficiency of the working cycle.
  • Still another object of the present invention resides there nthat the forming and relieving process may be accomplished extremely fast by the inventive action of thehigh-pressure transformer, becausea reversal of the fluid flow to the driving piston of the transformer is not required during the two above-mentioned processes.
  • Figure 2 is a diagram showing the pressure course in the high pressure transformer and press cylinder during one complete press cycle
  • Figure 4 is a cross-sectional view through the lowpres sure transformer of a modified construction
  • Figure 5 is a cross-sectional view through the highpressure transformer.
  • Figure 6 is a cross-sectional view through a modified various views to designate like parts,the extrusion or drop-forge press which, as illustrated in Figure 1, incor-
  • a second line 34 branches off the high pressure line 21 leading to operating control valve assemblies 35 and 36, each of which includes two valves 35a, 35b and 36a, 36b, respectively.
  • Lines 37 and 38 lead from the valve assemblies 35 and 36 to cylinder spaces 39 and 4th of a high pressure transformer 41.
  • driving actuator pistons 39a and 4011 are slidably arranged and are rigidly connected with each other.
  • the check valve assembly 44 in '7 turn is connected to a cylinder space 45a in the pressure limit valve 46 through line 45.
  • the pressure limit valve 46 comprises a cylinder space 49 and a difierential piston valve 47 slidably arranged in the cylinder spaces 45a and 49 and is spring loaded by a spring 43.
  • the control valves 2%, 35b and 36a are connected through line 51 to the water reservoir 27.
  • a second line 58 is connected to line 53 behind the check valve 54 and leads to an operating control valve 59 and from there connects to the intake of a check valve 60.
  • the discharge side of the valve 60 is connected to line 53 ahead of the check valve 54 through line 61 while the intake side thereof is connected to the oil reservoir 64 through line 65.
  • the high pressure transformer 41 further comprises two driven pistons 66 and 67, the center line of which is preferably disposed perpendicularly to the center line of the driving pistons 39a and 40a and which are slidably arranged in cylinders 66a and 67a.
  • the driven pistons 66 and 67 are operatively connected to the driving piston assembly 39a, 40a, by connecting rods 68a and 68b at joint a. From the cylinder spaces '66:: and 67a of the high pressure transmitter 41, lines 69 lead to line 56.
  • thev specific pressure exerted on the ram 4 is con-. siderably smallerthan that in the high pressure accumulator 5; that. is, the pressure in the cylinder 4a is reduced in the ratios of the areas of pistons 33b to 33a.
  • the piston in the press cylinder 4a must only be of a magnitude suificient to raise the moving weights of the press 1 during initial closing of the press.
  • the speed of the upward movement of the diflerential piston 33 which also determines the speed, of the upward movement of the ram 4 during the initial closing operation of the press may be adjusted to any desired value by adjusting the flow area through the check valve assembly 54, as, for instance, by limiting the lift of the check valve or by other means.
  • valves 35a and 36b are opened and pressure fluid from the accumulator 5 is applied to the cylinder space 3 9 of the high pressure transformer 41.
  • the piston assembly 39a, 46a is moved to the left.
  • working fluid that is, water remaining in the cylinder space 40, is discharged through the open valve 36b and 1ine51-to the water reservoir 27.
  • valve 29a In order to further open the press to remove the finished workpiece 8 therefrom, valve 29a is closed, and valves 29b and 59 are opened.
  • the operation of valve 29b permits the water in the cylinder space 32 to escape through line 51 into the water reservoir 27 and opening of the valve 53, on the other hand, establishes communication between the cylinder spaces 4a and 52 through line 58, control valve 59, check valve 60 and line 61.
  • the differential piston 33 in thelow pressure transformer 31 moves downwardly by its own weight or by spring means drawing oil out of the press cylinder 4a whereby the press piston 4 together with thedie 2 are also allowed to move downwardly to thereby open the press to its initial starting position.
  • the speed of the downward movement of the differential piston 33 which also determines the speed of the downward movement of the ram 4 during the opening operation of'the press may be adjusted to any desired degree by corresponding dimensioning of the flow passages through the valves 59 and 60 as, for instance, by limiting the effective lift of these valves or other means.
  • the distance a'.a represents the initial closing movement of the press piston, whilev the distance c-.c' representsopening of the press to its initial starting position.
  • the pressure in the press cylinder 4a during the initial closing of the press rises very slightly, as shown in the diagram, While during the forming operation the pressure rises rather rapidly attaining theoretical infinity at position b.
  • the pressure limit valve 46 provides an assurance that the driving piston assembly 39a, 40a does not become stuck at a point between a, and b due to excessive resistance to movement produced, in the cylinders 66a and 67a of the driven pistons 66 and 67.
  • valves 36a and 35b are opened which produces a movement of the driving piston assembly 39a, 40a from a position c back to the original position a.
  • a line 113 leads from cylinder 1111 to the cylinder space 114 of the low-pressure transformer 115.
  • the construction and functioning of the low-pressure transformer 115 is similar to that described in connection with Figure 1 except that a spring 116 is provided which tends to force the differential piston assembly 11 7 downwardly at all times.
  • a line 120 branches off line 113 and is con-. nected to the cylinder 106 of the automatic reverse valve 104 and a second line 118 connects line 113 with an operating control valve 119.
  • a return line 121 connects valve 119 with the water reservoir 27.
  • a second line 126 leads from cylinder 111 of the automatic reverse valve 104 to a four-way valve 127, and lines 128 and 129 connect the four-way valve 127 with the cylinder spaces 139 and 140, respectively, of the high pressure transformer 141.
  • the four-way valve 127 is also connected with line 121 through line 130.
  • Line 126 and consequently cylinder 111 are further in communication with cylinder 132 of a pressure limit valve 133, wherein a piston 134 is slidably arranged in the cylinder 132 and is urged to one side thereof by a spring 136.
  • a valve piston 135 is slidably arranged in a cylinder 137 which is separate from cylinder 132.
  • the piston valve '135 divides the cylinder 137 into two cylinder spaces 122 and 123.
  • a piston rod 138 connects piston 134 with piston valve 135.
  • the cylinder space 152 of the low-pressuretransformer is in communication with the press cylinder 4a through line 53 including a check valve 54 similar to the arrangement shown in Figure 1.
  • a by-pass line 124 around the check valve 54 includes an operating control valve v14 2.
  • the control valves 102, 119 and 142 are operatively connected together by a connecting rod 143 so that they may be operated simultaneously.
  • a line 143 in communication with the cylinder spaces 166a and 167a of the high-pressure transformer 141 is connected to line 53 between the check valve 54 and press-cylinder space 4a.
  • a line 144, which includes a check valve 145 connects line 143 with the oilresenvoir 64.
  • Cylinder space 123 is in direct communication with the oil reservoir 64 while line 1143 is also" connected to cylinder137 of the pressure limit :valve 133.
  • the pump 20 draws water from the reservoir 27 and matic reverse valve 104 through line 103 and from there into cylinder space 114 of the low-pressure transformer 115 through line 113, moving the piston 133a upwardly.
  • the piston 133b which is rigidly connected to the piston 133a through a piston rod 116 compresses the oil in the cylinder 152 to a pressure equal to the accumulator pressure reduced in the ratio of the piston area 1331) to 133a.
  • the oil in the cylinder space 152 is pushed through line 53 and the check valve 54 into the press cylinder 4a of the press 1 and moves the'press plunger or ram 4 upwardly.
  • the die 2, Figure 1, with the working piece 8 resting thereon, is :also moved upwardly until the workpiece 8 contacts the rubber pad or counter die 3. When this occurs,the pressure in the cylinder chambers 4a, 152 and 114 begins to rise.
  • the four-way valve 127 allows the flow of water into the cylinder space 139 and forces the plunger 139a to the left whereby the water remaining in the cylinder chamber 140-is forced through line 129, the four-way valve 127, line to the water reservoir27.
  • the driven pistons 166 and 167 which are operatively connected with the driving pistons 139a and 140a through connecting rods 168a and 16811, are moved outwardly.
  • the oil in the cylinder spaces 166a and l167t1 is delivered through lines 163, 143, 53 into the press cylinder 4a of the press 1.
  • the check valve 54 prevents the oil from cylinders 166a and 167a from flowing back into the cylinder chamber 152 of low-pressure transformer 115.
  • the press piston 4 of the press 1 moves toward its maximum outer position, the pressure in lines 143 and 126 increases rapidly as indicated in the pressure diagram, Figure 2.
  • valves 102, 119, 142 which are operatively connected with each other by connecting rod 143, are turned 90 either manually or mechanically by a moving part of the high-pressure transformer by which action the operating control valve 102 is closed and the valves 1 19 and 142 are opened. Communication between the automatic reverse valve104 and the high-pressure accumulator 5 is thereby disrupted.
  • the press cylinder 4a is connected with the cylinder chamber 152 of the low pressure transformer 115 by by-passing the check valve 54" through lines 124 and control valve 142.
  • the four-way valve 127 is rotated by- 90 whereby the connections to the cylinder chambers 139 and 140 of the high-pressure transformer 141 are interchanged so that the piston assembly 139a, 140a moves from the left to right if pressure fluid from the accumulator 5 is received.
  • the control valves 102, 11 9; 142 are turned into the original position, as shown in Figure 3, through rod 143 whereby the new working cycle commences.
  • FIG. 4 represents a lowpressure transformer modified from that shown in Figure 3 in that a spring 216 is arranged within the cylinder space 252 for forcing the piston assembly downwardly when the pressure in the cylinder-space 214 is reduced.
  • Figure 5 is an enlarged view of the high-pressure transformer indicating the connectinglines thereto by numerals as they appear in Figures 1 and 3.
  • Figure 6' is a modified construction of the automatic reverse valve 104 shown in Figure 3.
  • piston 205 in Figure 3 is rigidly con nected with the piston "alves 199 and 110 by a connecting rod 112
  • piston 205 according to the embodiment of Figure 6 is resiliently connected to the piston valve assembly 209, 210 in the following manner:
  • the piston 205 is in resilient engagement with a snapring 270 by Way of a connecting rod 271 having a shoulder 272 at its end and being guided in a bore 273 thereof.
  • Springs 274 and 275 on each side of the shoulder 272 retain the shoulder 272 in an approximately central position. of bore 273.
  • Two V-shaped grooves 276 and, 277 are provided on the circumference, of the snap ring. 270 and the snap ring is held in position by a spring loaded ball 27S engaging one of the grooves.
  • a hydraulically operated press particularly for forming materials at elevated temperatures comprising a relatively stationary part and relatively movable part, hydraulic means including pressure supply means operatively connected with said press for initially closing said press during a first stage of operation and including piston means displaceable from an initial position for supplying high-pressure to the press and thereafter toward said initial position for releasing the application of said highpressure to the press, a movable actuator means connected to the piston means and movable continuously in one direction for displacing said piston means both from and toward said initial position for thereupon further actuating said relatively movable part relatively rapidly in the closing direction to form said material and for thereafter moving said relatively movable part in the opposite direction during a second stage of operation.
  • a hydraulically operated press particularly for forming materials at elevated'temperatures comprising a relatively stationary part and a relatively movable part, hydraulic means including first piston means and pressure supply means operatively connected with said press for initially closing said press during a first stage of operation, high-pressure transformer means operatively connected with said pressure supplymeans and said press including second piston means displaceable froman initial position for supplying high-pressure to the press and thereafter toward said initial position for releasing the application of said high-pressure to the press, a movable actuator means connected to the second piston means and movable continuously in one direction for displacing said second piston means both. from and toward said initial position for further actuation of said relatively movable part at a relatively rapid rate in the closing direction to form said material and for thereafter moving said relatively movable part in the opposite direction during a second stage of operation.
  • a hydraulically operated press particularly for forming materials at elevated temperatures comprising a relatively stationary part and a relatively movable part, bydraulic means. including pressure supply means, lowpressure transformer means including first piston means operatively connected with said supply means and said press for initially closing said press during the first stage of operation, and high-pressure transformer means operatively connected with said pressure supply means and said press including second piston means displaoeable from an initial position for supplying high-pressure to the press and thereafter toward said initial position for releasing the application of said high pressure to the press, a movable actuator means connected to the second piston means and movable continuously in one direction for displacing said second piston means both from and toward said initial position for further actuation of said relatively movable part at a relatively rapid rate in the closing direction to form said material and for thereafter moving said relatively movable part in the opposite direction during a second stage of operation.
  • control means for automatically bringing said high-pressure transformer into operation after completion of said first stage of operation, said control means being responsive to the rise in pressure in said press at the end of said initial closing operation.
  • control means for automatically bringing said high-pressure transformer into operation after completion of said first stage of operation, said control means being responsive to the prevailing pressure in said lowpressure transformer at the end of said initial closing operation.
  • control valves are included in said pressure transmitter.
  • said low-pressure transformer includes a high-pressure piston having a relatively small diameter and a low-pressure piston of a relatively large size, the ratio of said diameters being such that the pressure produced by said lowpressure piston is capable of moving said relatively movable part during said initial closing of said press.
  • said high-pressure transformer includes at least one driving actuator piston and at least one driven piston, pressure transformation being accomplished by transmission of power from said driving piston to said driven piston.
  • said high-pressure transformer includes two driving pistons slidably arranged in coaxial cylinders and connected with each other by a rigid piston rod, two driven pistons the movement of which is in a perpendicular direction of that for said driving pistons, connecting rods pivotally connecting said driving and said driven pistons with each other, said connecting rods being disposed sub: stantially perpendicular to the direction of movement of said driving pistons.
  • connection of said second piston means to said actuator means comprises a linkage providing an increased mechanical advantage in transmitting the forces from said actuator means to said piston means during movement of said actuator means near the position thereof corresponding to the position of the press being fully closed.
  • a hydraulically operated press particularly an extrusion press or drop-forge press for forming materials
  • hydraulic means including pressure supply means, a high-pressure transformer means operatively connected with said pressure supply means and said press including at least one driving piston and at least one driven piston, said driving piston being directly connected with sm'd driven piston by means of a connecting rod, the movement of one of said pistons being at an angle to the movement of the other of said pistons, pressure transmission being accomplished by transmission of power from said driving piston to said driven piston for actuation of said relatively moveable part at a relatively rapid rate in the closing direction to form said material and for thereafter moving said relatively moveable part in the opposite direction.
  • a hydraulically operated press particularly an extrusion press or drop-forge press for forming materials
  • hydraulic means including pressure supply means, low-pressure transformer means operatively con-' -mission 'being accomplished by transmission of power from said driving piston to said driven piston for further actuation of said relatively moveable part at a relatively rapid rate in the closing direction to form said material and for thereafter moving said relatively moveable part in the opposite direction during a second stage of operation.

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  • Engineering & Computer Science (AREA)
  • Mechanical Engineering (AREA)
  • Press Drives And Press Lines (AREA)
  • Forging (AREA)
US694042A 1957-02-01 1957-11-01 Hydraulically operated presses Expired - Lifetime US2946303A (en)

Applications Claiming Priority (1)

Application Number Priority Date Filing Date Title
DES52180A DE1145018B (de) 1957-02-01 1957-02-01 Schnellarbeitende hydraulische Presse, insbesondere Schmiedepresse oder Ziehpresse

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US2946303A true US2946303A (en) 1960-07-26

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US694042A Expired - Lifetime US2946303A (en) 1957-02-01 1957-11-01 Hydraulically operated presses

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Cited By (2)

* Cited by examiner, † Cited by third party
Publication number Priority date Publication date Assignee Title
US3208255A (en) * 1961-07-07 1965-09-28 Siemens Elektrogeraete Gmbh Method and apparatus for hydraulic deep-drawing of sheet material
US5568766A (en) * 1993-09-02 1996-10-29 Maschinenfabrik Mueller-Weingarten Ag Method for controlling the drive for a hydraulic press having a plurality of operating phases

Families Citing this family (1)

* Cited by examiner, † Cited by third party
Publication number Priority date Publication date Assignee Title
DE1500374B1 (de) * 1965-04-14 1969-09-04 Eumuco Ag Fuer Maschb Hydraulischer Antrieb fuer Arbeitsmaschinen

Citations (6)

* Cited by examiner, † Cited by third party
Publication number Priority date Publication date Assignee Title
US1888990A (en) * 1929-08-16 1932-11-29 Economy Fuse And Mfg Co Automatically controlled hydraulic press intensifier
US2200998A (en) * 1937-06-03 1940-05-14 Farrel Birmingham Co Inc Hydraulic press
US2239339A (en) * 1937-02-22 1941-04-22 Firm Henschel Flugzeug Werke A Pressing apparatus
US2403912A (en) * 1944-01-17 1946-07-16 Link Engineering Co Press operating device
US2573993A (en) * 1948-07-10 1951-11-06 American Steel Foundries Hydraulic pneumatic system for actuating pressure
US2737138A (en) * 1955-01-06 1956-03-06 Rohr Aircraft Corp Drop hammer

Family Cites Families (4)

* Cited by examiner, † Cited by third party
Publication number Priority date Publication date Assignee Title
DE261719C (de) *
DE47229C (de) * W. LORENZ in Karlsruhe i. B Presse, bestehend aus dem Kniehebelmechanismus des Patentes 38701 in Verbindung mit einer Pumpe
DE329510C (de) * 1919-05-27 1920-11-22 Eugen Maier Hydraulischer Druckuebersetzer fuer Pressen
US1927085A (en) * 1929-08-05 1933-09-19 Baldwin Southwark Corp Hydraulic apparatus

Patent Citations (6)

* Cited by examiner, † Cited by third party
Publication number Priority date Publication date Assignee Title
US1888990A (en) * 1929-08-16 1932-11-29 Economy Fuse And Mfg Co Automatically controlled hydraulic press intensifier
US2239339A (en) * 1937-02-22 1941-04-22 Firm Henschel Flugzeug Werke A Pressing apparatus
US2200998A (en) * 1937-06-03 1940-05-14 Farrel Birmingham Co Inc Hydraulic press
US2403912A (en) * 1944-01-17 1946-07-16 Link Engineering Co Press operating device
US2573993A (en) * 1948-07-10 1951-11-06 American Steel Foundries Hydraulic pneumatic system for actuating pressure
US2737138A (en) * 1955-01-06 1956-03-06 Rohr Aircraft Corp Drop hammer

Cited By (2)

* Cited by examiner, † Cited by third party
Publication number Priority date Publication date Assignee Title
US3208255A (en) * 1961-07-07 1965-09-28 Siemens Elektrogeraete Gmbh Method and apparatus for hydraulic deep-drawing of sheet material
US5568766A (en) * 1993-09-02 1996-10-29 Maschinenfabrik Mueller-Weingarten Ag Method for controlling the drive for a hydraulic press having a plurality of operating phases

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Publication number Publication date
DE1145018B (de) 1963-03-07

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