FR2500368A1 - HYDRAULIC PRESS FOR MOLDING SHEETS - Google Patents

Abstract

THE INVENTION CONCERNS SHEET MOLDING PRESSES. IT RELATES TO A PRESS HAVING TWO HALF-MOLDS 30, 31 WHOSE POSITIONS AND INCLINATIONS ARE ADJUSTED BY CYLINDERS WHICH MAINTAIN THE PARALLELISM OF THE TWO HALF-MOLDS 30, 31 DURING THEIR MOVEMENT AND DURING THE MOLDING. DISPLACEMENT DETECTORS AND FORCE DETECTORS ALLOW SUCH CONTROL. APPLICATION TO SHEET MOLDING PRESSES.

Description

2500W68

  The present invention relates to hydraulic presses

  hydraulics for molding various materials.

  U.S. Patent No. 4,076,080 discloses a compression-controlled compression molding method of speed and force, operated by servo controls. This patent

  represents a pressing device which is controlled

  canically and which is intended to move a pressing cylinder,

  but in the final closure of the mold, hydraulic cylinders

  hydraulics regulate the inclination of the mold so that

  parts of it remain parallel.

  U.S. Patent No. 3,531,830

  describes an apparatus for forming a molded object,

  taking a type of cam element to adjust the posi-

  stoppers which know the movement of the press

  to mold in its final molding operation.

  U.S. Patent No. 3,802,818 discloses a molding press which has retractable members

  in the corner which are controlled by hydraulic cylinders.

  In addition, U.S. Patent Nos. 2,722,174 and 3,543,344 disclose molding machines, and U.S. Patent No. 3,825,386 discloses

  slave controls hydraulic press.

  The assignee of this application has

  considerable work in the field of servo hydraulic controls, including the controls of various

  machines with rigid tables which must be

  held in a suitable position in relation to a plan of

  reference. For example, the United States Patent of

  No. 3,800,588 represents a slave control of

  designed to ensure the adjustment of a rigid structure with several degrees of freedom. U.S. Patent No. 3,918,298 discloses variants of this type

control.

  The assignee of this application also has patents concerning the hydrostatic bearings and the controls of such bearings. Such patents include patents from the United States of America

  No. 3,921,286 and 3,992,978. In addition, the United States Patent

  United States No. 3,994,540 discloses an external command

  height for hydrostatic bearing.

  In addition, U.S. Patent No. 3,908,429 discloses a deep-drawn aluminum cuvette hydraulic press for forming cans and U.S. Patent No. 4,063,453.

  describes a press frame construction that is re-

adjustable.

  Other features and advantages of the

  will become apparent from the following description,

  with reference to the accompanying drawings in which: FIG. 1 is a front elevation of a

  compression molding machine, according to a method of

  invention; Figure 2 is a side elevation of the press of Figure 1, with portions broken away and partly in block diagram form; Figure 3 is a plan view of the molding press of Figures 1 and 2; Figure 4 is a front elevation of the upper cross member shown in Figure 3; Figure 5 is a graph showing the variation of the deflection of a normal cross member supported by the ends in presses, and the cross member according to the invention; Figure 6 is a partial section showing

  the inside of a locking cylinder used with the

  verses shown in Figure 4, with portions in section and others torn off;

  FIG. 7 is a partial elevation

  sensing a clamp opening mechanism used with the cross member of the invention;

  FIG. 8 is a frontal elevation

  the bottom plate used with the press according to

  the invention, having portions in section and other parts

  part of the circuit being represented under

  synoptic diagram; Figure 9 is a partial plan view of the plate shown in Figure 8, with parts torn off;

  FIG. 10 is a timing diagram of FIG.

  presenting the sequence of operations of the various elements of the molding press during a pressing cycle; Figure 11 schematically represents a

  lower plateau and allows the understanding of the princi-

  controlled control die now holding a lower platen parallel to a reference, for example an upper half-mold, during a pressing operation; and FIG. 12 is a diagram of a control circuit used to obtain the timing diagram.

of Figure 10.

  A compression molding press, generally designated 15, is supported on a base 16 and conventionally comprises four vertical and smooth columns 17 which carry a top plate assembly 20. This set 20 is mounted so that it

  moves vertically along columns 17 (when

  it has been put in place) by means of a pair of single-effect lifting cylinders 22, one at each end of the machine, having lower ends connected to the base 16 and movable rods 24 connected with each other. way

  as indicated by reference 25 to the extremes

  opposing mites of the upper plate 20. A linear variable differential transducer 27 is coupled to the jack 22 so that it measures the displacement of the rods 24 allowing

a reaction.

  A bottom plate assembly 26 is carried by the base 16 as will be described hereinafter. A compression molding assembly is mounted between the lower plate 26 and the upper plate, and this assembly comprises an upper member 30 and a

  lower body 31 of molding. The upper organ or mold

  The lower mold is bolted to the top plate in a desired manner or is otherwise mounted on this plate, while the lower mold is supported on a plate of the lower plate, also by bolting if necessary.

  as described later in this specification.

  We first consider the set comprising the upper plate. As clearly represented on the

  FIGS. 3 and 4, the assembly 20 comprising the upper tray

  on a plate 35 in the form of a flat plate which

  is attached to an assembly 36 forming a cross-member on the

  which he climbed. The crossbar 26 is formed of several

  if plates or cheeks large and resistant

  shearing (four in the embodiment of

  presented), with reference 37 and which are in the form

  of generally rectangular shaped plates which are

  of each other and parallel to each other. In the central portion 40 of the crosspiece 36, a box-shaped section is formed by plate welding

  vertical members 41 forming tie rods between adjacent plates

  37 shear resistant. These plates 37

  a projection 42 at the lower edge and the plates 41 de-

  pass from the plane defined by the lower end of the projection 42 and join the upper edge of the plates 37. The lower edge of the projection 42 is in a

  plan distant from the plane of the lower edges of the parts la-

plates 37.

  The plate 35 bears against the edge

  the protrusion 42 of the plates 37 and is welded thereto. The outer portions of the plate 35 (those which are outside the projection and the vertical plates 41) are held by cheeks or squares

  suitable reinforcements which bear the

  pleated by the edges of the plate towards the central portion 40. The reinforcement cheeks have brackets 43 at the four corners of the plate 35, which are connected to the plates

  37 and, as shown, these cheeks

  are in the form of triangular

  placed obliquely in relation to the plane of the cheeks or

37.

  In addition, brackets or central reinforcing plates 44 in number are arranged between the two central plates. These 44 squares leave

  from the central part 40 in the lateral direction towards the ex-

  to the edges of the plate 35 and on each side

  of it. These brackets 44 also have a triangular shape

  and collect the forces from the edges of the plate 35 and directed to the central portion in form

of caisson of the crossbar.

  It is noted that this provision maintains the over-

  upper face of the plate, identified by the reference 35A, at a distance from the lower edges of the plates 37, except along the projections 42 which delimit the lower plane of the

  central section 40 formed by the vertical plates 41.

  Thus, the portions 35B of the outer edges, along the sides of the plate 35, and the portions 35C of the edges

  along the ends of the plate 35 are

  placed cantilevered with respect to the central section 40.

  The plates 43 and 44 transmit the bending forces near the outer edges of the plate 35 to the plates 41

  and so to the central portion 40 of the plates 37 re-

  shear-resistant, forming the top rail.

  This collection of forces increases a lot

  the deflection characteristics of the superstructure

  under the action of the molding forces, as de-

  written later in this memoir.

  The clamps of the upper cross member 36 are now considered. As indicated previously, the latter is movable along the columns 17 during the use of the lifting jacks 22 and these, as shown, are single-acting jacks. because the weight of the cross member causes their withdrawal when the fluid under pressure is not transmitted to the base of the cylinders. The lowering speed of the crosshead is regulated by simply adjusting the outgoing fluid flow

at the base of the cylinders 22.

  During molding operations, the work

  top pour and thus the top plate and the upper part 30 of the mold must be maintained

  in the clamping position when the cross member has been lowered

  after placing the molding material between

  the two mold parts. The device according to the invention

  tion employs clamping members which ensure not only the tight and tight clamping of the upper plate against the columns 17 but also which can

  slide sideways as you enter the trans-

  out of it so that the placement of long columns 17 is eliminated and that orifices or a very large vertical space is not necessary during the introduction and

  the removal of the columns themselves.

  The clamps are hydraulically controlled and operate in parallel for all the columns 17 on either side of the crossmember 36. The plates 37 of the cross member are spaced apart as indicated above, and each column with its clamp is arranged in the space between two of these plates. The clamping members comprise a slotted clamp 46. All these clamps are formed in elongated blocks of steel whose length is generally equal to the height of the plates 37. The clamps 46 are made with a bore 47

  allowing the passage of one of the columns.

  Sinnet anti-friction can be used as a coating of the bore 47. The tongs are slotted longitudinally and a slot 48 is disposed from the outer edge of the cartridge 46 containing the split tongs and opens

in the bore 47.

  The lateral surfaces of the clamps 46 are flat surfaces which slide in the space between two plates 37. It may be noted that each of the clamps 46 has three transverse holes (aligned with the slot 48) spaced vertically and intended to house rods 52 which are connected so that they can

  be controlled by locking actuators

  transom lage. The rods 52 are arranged over the entire width of the crossbar and thus pass through the

  four plates 37 (holes allowing play to

  obviously this passage) and in the two clamps 46, at both ends of the cross. Each stem

  52 is attached to a suitable collar 53 for

  box the efforts and placed outside one

plates 37.

  The rod 52 has its other end fixed to

  a moving block 54 of hydraulic cylinder placed outside the

  plate 37, on the opposite outer side of the crossmember. As shown in Figure 6, the actuating blocks 54 have annular orifices 55 formed therein. These orifices 55 have an annular configuration

  or toroldale. An annular piston 56 is housed in the opening

  each orifice 55 and is fixed to the outer plate

  dull 37, on this side of the transom. An annular piston

surround each of the rods 52.

  Each of the slots 48 is associated with one or more actuators providing the release

  or the expansion of the clip as indicated by the

  60 (see Figure 6). These members 60 have a piston 58 and a cylinder 59, each of which is arranged on one of the faces of the slot 48. Each clamp 46 usually has such release members. Hydraulic fluid is transmitted to the cylinders 59 so that they tend to open the slot 48 and thus release the clamp of the column 17 by enlarging the bore 47. The operating members of the clamps are controlled in parallel and the organs release also work in parallel. A control valve can be used for these actuators because when one of the games is in operation, the other

must be released.

  It should be noted that spacer tubes 61 are placed on the rods 52, between the two central plates 37 so that they prevent a deflection

  excess of these plates when ordering the clamps.

  When pressurized hydraulic fluid reaches the cylinder 55, the rods 52 are energized

  and react via the pistons 56 con-

  the outer face of the plate 37 which is on this side of the crossbar, the collar 53 reacts to the tension of the rods 52 by exerting a force on the crossbar so that the tension load of the rods tends to pull all the end portions of the plates towards each other by tightly tightening the crosspiece on the columns 17 by compression of the clamps 46. The spacer tubes 61 prevent the two inner plates

  37 to collapse towards each other. A block 25 represented

  shown in Figure 3 allows the attachment of the rod

24 of the cylinder 22.

  According to a characteristic of the tongs of the in-

  vention, the cylinders 54 and the rods 52 can be pulled. The cylinders 54 are screwed onto the rods or the rods can be released from the collars 53 and pulled

  longitudinally outward. During this operation

  tion, the clips 46 of the cross-member can slide

  laterally from the ends of the cross member (after removal of the retaining bolts 57). The plates 37 form slots which are open towards the end of the crosspiece. The columns 17 and the clamps can pivot laterally as shown in broken lines

  in Figure 4, when setting up or removing

  the column of the transom. The columns 17 can be bolted to the base 16 so that they can

  rotate during installation and removal.

  The crossbar is properly supported during its installation. However, very

  height of removal of columns 17 vertically

  wedge the housing holes of the columns 17 when removing and maintaining the transom are not necessary. As shown in FIG. 7, a stop band 62 can limit the opening of the clamps 46. The band is in two parts 62A and 62B which are held one on the other by bolts. The gripper has 62C-lined orifices at its ends, and 62D studs are

  placed on the clamp 46 on both sides of the slot 48.

  The studs pass through the holes of the band and the ends

  Mouths cooperate with the studs by preventing excessive spacing of the clamp. The two parts 62A and 62B may have a shim 62E allowing adjustment

of the opening.

  The mounting of the plate 35 on the crossbar, as

  represented, allows a new distribution of

  the tray during use, in a manner

  advantageous for the operation of a molding press.

  We have been trying for a long time to make a plate and a very rigid crossbar so that the sag is

  under the action of molding forces, with

  the same amount of steel and the same weight as in a conventional support mechanism. A rigid central section of machined plates is disposed about half of the span and ends between the two sets of columns, and the outer ends of the plates 37 are laterally flexible enough that these plates have an infinite resistance to fatigue under the action of clamping forces. This achievement is extremely effective. The deflection characteristics are shown in FIG. 5 in the case of a conventional cross member which is simply clamped at its ends and which supports any tray or structure

  in a uniform way between its ends.

  We now consider the decline in

  the crossing. Figure 5 shows the curve curves

  a conventionally supported cross member as indicated by reference numeral 63, and it is noted that the maximum deflection occurs in the middle of the plate, and that the sag decreases towards the clamps mounted on the columns. However, under the action of charges as indicated by the arrows 64 in FIG.

  bending of the cross-member shown on the

  FIGS. 3 and 4 show the reference numeral 65 in FIG. 5. It will be noted that, with respect to the reference axis bearing the reference 66, the bending of the plate 35 in the center is practically the same as in a cross member supported by classic way. At the outer edges of the

  plateau, the deflection with respect to the reference axis

  The rence increases again because the outer edge of the tray 35 is supported by plates or brackets.

  and instead of plates 37. The decline in

  in relation to the reference axis does not decrease

  compared to a classic crossbar, but the distortion

  or the deflection with respect to an optimum flat surface decreases significantly. The deformation of the mold is reduced, according to a feature avantagaevs.c

  in compression molding operations.

  The deflection with respect to a surface

  planar plane, in the case of a cross-beam of typ-, class-

  it is supported at its outer ends and formed with the same weight or the same quantity of steel, is much greater than that of the cross member according to the invention which

has several plates.

  We now consider the control of the work

  pours. FIG. 2 represents, in simplified form, a control circuit for the jacks 22. The circuit has a slave control and comprises a programmed control element 67 which provides the programmed global control, and a servo-controlled control element 67 provides the adjustment of a servo -vanne 68 which can be of the three-way type, according to the program, whereas a signal transmitted by the line

  27A by the differential transducer 27 indicates the posi-

  crossing. In the case of the single-acting cylinders 22, the servovalve connects the base ends of the cylinders 22 to the pressurized fluid reservoir by parallel pipes 68A, or connects these lines to the purge so that the cross-member drops below the action of its own weight, depending on the flow allowed by the cylinders. The programmed controller co-ordinates the displacements to the molding operations which are also controlled by hydraulic jacks which operate by slave control. If necessary, the indention of the jacks 22 can be prevented by check valves.

pilot control restraint.

  The cylinders 55 of the blocks 54 are controlled by a distributor 60A and the clamping forces are removed before and during the movement of the crossbar, and the operating members 60 are controlled when the blocks 54 are released. The 60A distributor

  can be used to control the six servo actuators

  rage in parallel and eight release cylinders, in parallel. The clamping and release actuators are single acting cylinders. The distributor 60A can be controlled by a direct electrical signal

transmitted by a line 70.

  We now consider the set comprising the lower plate. This assembly 26 comprises a thick structure or plate supported with respect to the base 16. The latter is a structure sufficiently

  robust so that it can absorb forces encountered

  during a molding operation. The lower plateau

  is used for mounting the lower half mold

  31 and this arrangement is such that during the cycle of movement

  When the cross member has been locked in the molding position, the lower plate rises under the action of a regulated force exerted by the hydraulic cylinders at

slave control.

  Figures 8 and 9 representenj, in partly schematic form, the assembly comprising the lower plate. The assembly 26 is mounted on a surface or upper part of the base 16 and has a plate 72 which has a support member of the lower mold half 31. The molding or compression force is applied using cylinders 75 each comprising an outer casing 76 forming a cylinder attached to the base 16, and a piston

  77. The latter has a peripheral flange or

  nular 78 which forms a partially spherical surface or a short cylindrical surface leaving sufficient clearance for the piston 77 can tilt relative to the circular side wall of the cavity 79, a limited angle of a few degrees. A sealing ring is mounted in a groove formed on the annular flange so that the piston is sealed. The plate 72 is supported by a support plate 81

  hydrostatic, from which it can be separated in the direction

  tical. The plate 72 has shallow cavities at its lower face, for accommodating slats or tapered studs such that 82, when the plate 81 is supported on the plate 72 and supports it, the two parts can not not to slide relative to each other. When the studs are moved vertically however, the plate 72 can move relative to the plate 81. An elastomeric seal ring 83 is mounted in a groove of each piston 77 and defines

  an annular space at the bottom face of the plate 81.

  A passage 84 opens out of the cavity 79 of each jack

  in the space defined by the sealing ring 83.

  When the cylinders are under pressure, the oil under pressure

  sion assures the support of the plate 81 on a hydrostatic bearing. The diameter of the ring 83 is chosen at a value less than the effective diameter of the piston 77 so that the operation is suitable. The pressure in the hydrostatic bearing is the same as in cavity 79, and the hydrostatic bearings (there are four

  jacks 75 as shown each having a bearing)

  put the easy movement of the tray 72 and the

  81 to the proper positions of the half-molds even when the molding force is applied. The support pressure in the region of the bearing delimited by the rings 83 is a function of the molding force and thus the

force collected by the plate 72.

  The plate 72 can thus move on hydrostatic bearings (within limits that can be determined mechanically by bearing blocks) along the Y axis (as indicated by the arrow Y of FIG. 9) and along the X axis (marked by the arrow X in Figure 9) (ie from one side to the other), and it can also move in yaw, that is to say by rotation around the central axis of the piston 77. This arrow is located

to the left of Figure 9.

  In addition, the tray 72 may have a number of

  pitch, that is to say a rotation about an axis arranged from front to back and parallel to the plane of the upper face of the plate, this movement being marked by the

  arrow in the middle of Figure 8. The

  water has a movement along the roll axis, that is,

  transversely, passing through the central plane of the

  plateau 72, and this roll is marked by the arrows

  placed on the right and left of Figure 2.

  The control of X, Y and yaw movements (three

  degrees of freedom) is provided by inclined blocks of

  The molding members have interlocking blocks which allow suitable cooperation of the molds, giving suitable thicknesses to the walls of the moldings. These bearing blocks are identified by the reference 90 and they are housed in complementary guides 91 formed on the other mold part. As shown, the blocks can be attached to the upper mold section 30

  and guides can be formed in the lower section

  but, in any case, guidance is provided by four blocks as shown. Half-molds can not

  turning around a vertical axis (yaw) and

  Investments along the X and Y axes are limited. These movements

  ments, after final guidance in place, are prevented.

  Four power cylinders are placed on

  the lower face of the lower plate and, as

  previously mentioned, they are single-acting cylinders that bear against the lower plate and push

  the lower mold half against the upper half-mold

  when the cross member has been locked in a suitable position. It is important that the elastic return is extremely low so that the half-molds are

  separated without breaking the room. Four cylinders of separation

  ration or demolding are used, one at each corner. These demolding cylinders are also single-acting and they tend to spread the lower half-mold of the upper half-mold and at the same time they

  must set back the cylinders 77 of the cylinders 75.

  This movement is effected over a relatively short distance, simply to cause spacing, and it tends to minimize the possibility of deterioration of the molded part when the elastic forces applied along the path of the forces

is weak. The separation of the demolding cylinders corre-

  pond to a very short column of hydraulic fluid and

  allows a reaction against a rigid structure directly-

  associated with the pliers, or against another structure

* Fixed suitable.

  As indicated more specifically in FIG. 8 and with reference to FIG. 9, the lower support is

  represented in the position in which he was

  pushed down so that the half-molds shown generally in Figure 8, are separated. A demolding cylinder 95 is mounted at each corner of the press

  and all these cylinders are arranged outside the co-

  corresponding cylinders 17. The demolding cylinders have

  an outer casing 96 which has an internal cylinder chamber

  dre, and a piston 97 mounted by their opening and having a

  maneuvering end protruding from the orifice. The extré-

  mity 99 of the piston 97 has a position such that it bears against a reaction member 100 of the frame. This member 100 is mounted at each corner of the room. As shown in FIG. 2, each of these members can be clamped on the corresponding column 17 and a vertical leg 101 is fixed to the horizontal member 100 so

  that the forces are returned to the base 16 by reaction.

  Some elastic return is possible. The size of the members 100 and 101 can be chosen so that the

  deformation keeps a desired value.

  The individual demolding cylinders 95 are controlled by the same servo valve as the main molding cylinder corresponding to the corner of the press. In other words, the two cylinders work together in a manner quite similar to a double-acting cylinder and, when the cylinder 75 is under pressure, the cylinder 95 is connected to the purge by the same servo valve, at each corner of the press. Similarly, when the jack 95 is under pressure, the jack 75 of this

  corner is connected to the purge and can come back.

  In a variant, instead of the members 100 of the frame, mechanical stops 105 as shown may be aligned on suitable pads 106 placed on the underside of the plate 35, near the outer corners, so that the demolding force is directly applied between the lower plate and the upper plates. The stops are of mechanical type and are intended to stop the upper rail. The press may comprise four stops 105, one at each corner, on the jack

  95. The stops 105 may have a length

  adjustable range and may for example include sections

  different lengths that can be mounted in combination so that they give the desired height

depends on the height of the mold.

  It should be noted that the cylinders 95 are suitably guided over a limited distance in the vertical direction relative to the stops 100. The internal piston has a stop such that the rod can not be driven out.

  boot maker. The guides are not represented anymore

  cisely. They can have any desired shape allowing the box 96 to move vertically without being chased. Each of the cylinders 95 is connected to a support guide block 107 against which it is supported so that the separation forces exerted by the jacks 95 on the plate 72 or the support are supported and simultaneously so that the plate 72 or the support can be moved horizontally alternately when the mold parts are to be changed or maintained. The blocks 107 are shown in plan in FIG. 9, one being placed near each column 17. The blocks 107 have a relatively small length in the Y direction as indicated by the arrow Y in FIG. 9. The blocks 107 each have a side rail 108 to the inner face, with a lip 108A facing upwards. The rail 108 is

  realized so that it fits in a throat or lunge slot

  complementary longitudinal groove 110 made along the sides of the plate 72, and this groove 110 is disposed in the

  fore-and-aft Y direction along the entire length of the

  teau. Note that the groove 110 has a surface delimited by a locking lip 112, this surface cooperating with the lip 108. A lower surface of the slot cooperates with the rail 108 which supports it. In addition, the lower corner 107A of block 107 bears against

the side of the board.

  The block 107 which forms a demolding block can be fixed to the casing 96 of the jack 95 in any desired manner, for example with bolts which can hold the two elements together, or they can even be formed

in one piece.

  When the cylinders 95 are controlled, the pressure

  sion disappears from the cavity 79 of the cylinder 75, and the fluid

  hydraulic pressure reaches the inner casing 96.

  When the mold is to be opened, four servo-valves one by 95 demolding ram, are controlled so that the cavity 79 of the associated jack 75 is connected to the purge and pressurized fluid enters the chambers of the bootmakers 96 by driving the latter downwards since the pistons 97 are in abutment against the members and, via the stops 105 and 106, against the upper plate 35. Guiding blocks 107 are then driven down and the complementary surfaces of these blocks and the plate 72 cause a downward thrust on the plate 72 at the four corners so that the jacks 75 come back and the two parts

of mold separate.

  As described hereinafter, the control of the molding operation is ensured by a

  programmed controller and transducers detected

  both the displacements are used for the formation of reaction signals allowing the control of the slave cylinders. When the crosspiece and the upper plate are set back, four displacement measuring transducers 140 placed between the plate 72 and the base 16 allow control by reaction of the position of the plate, determined by the jacks 75 and 95 which are supported by on both sides of the tray 72. The appliance

  comprises at least three transducers 140 and, as a re-

  presented, four transducers give information on the height and orientation of the plateau compared

to a horizontal plane.

  The final reaction necessary for the control during molding is obtained by means of four transducers detecting the displacements, in the form of variable linear differential transducers 120 which are fixed to the lower half-mold 31, at each of the four corners of the

  mold. The transducers 120 have 121 ends

  resiliently strung and intended to cooperate with small tabs 122 fixed to the upper half-mold 30. The transducers 120 are put into the control circuit when the cross member is locked in its lower position and the transducers 140 are used when

the cross is raised.

  When the half-molds recede as indicated so that the bearing blocks 90 are no longer retained in the guides 91 since the mold part release forces can be unbalanced in the horizontal direction, it is possible

  that the plate 72 has a significant misalignment.

  Thus, it is desirable that a mechanism

  venable ensures the positioning of the lower

  that it is moved back, that is, lowered.

  Several hydraulic cylinders 115 are intended to limit this displacement of the lower plate 72 and the support plate 81. The cylinders 115 have a cylinder and an internal piston connected to a rod 116. The rods

  have narrowed ends 116A and a truncated shoulder

  conical connecting the end to the body of the stem. This body of the rod 116 is housed without play in a short sleeve 117 attached to the lower part of the plate 81. The cylinders are placed between the cylinders 75 and they therefore occupy four locations close to each of the edges of the

  plate 81, approximately halfway along the corresponding edge.

laying of the plate.

  The rods 116 also have a flange 118 whose dimension is such that it abuts against the sleeve 117, the plate 81 and the plate 72 and supports them when the plate has been set back, in the position shown in FIG. 8. The shaft 116 is part of the piston rod and the inner piston is mounted in the housing 119 which defines a chamber for receiving pressurized hydraulic fluid from a valve

  at a suitable pressure so that it

  a fixed stop preventing the plate from moving downwards beyond the position shown in FIG. 8; the stop cylinders 115 prevent the descent

  despite the forces exerted by the release cylinders 95.

  In other words, unless the hydraulic fluid under pressure is expelled from the casing 119, the lower plate 72 can not come back beyond the

  position shown generally in Figure 8.

  The rods 116 and in particular their main cylindrical body, ensure a positioning of the

  support plate 81 with respect to the hydrostatic bearings

  ticks, and the jack 75 and, although the slot 110 presents

  a certain clearance with respect to the rail 108, the lower support

  72 and the lower half-mold 31 remain

  aligned when the upper half-mold and the

cross 20 are set back.

  Thus, it is noted that the rigid plate 72 is directly supported by the cylinders 75 which apply the molding force to the plate 72 via the hydrostatic support plate 81. In addition, the cylinders

  demoulders delimit a short application path.

  charge between the upper half-mold 30 and the lower half-mold via the rigid cross-member, vertical columns 17 and reaction members 100 so that the half-molds are separated with low elastic return, fact that the single-acting cylinders 75 and 95 of the same corner are controlled by a servo-valve simplifies the operation and

reduce the cost.

  The plate 72 forms a support which can roll, and is made in such a way that it can be removed by rolling towards the support rails during the change of the half-molds and the maintenance of the support or the molds.

the appropriate cés.

  As shown in Figures 8 and 2, the base 16 supports two rails and parallel and remote tracks which are placed outside the cylinders 75 and are directed forward of the press, for a desired distance. The tray 72, as shown, has wheel housings 126 mounted at the front and rear and the wheels such as 127 are just above the rails 125. At the front end, the wheels are mounted on a transverse tree 128

  which is housed in the housings, on bearings suitable for

  The shaft 128 is driven by a hydraulic motor 130 via a gear or chain transmission, in a conventional manner. The wheels 127 of the front of the support or the plate 72 are selectively driven by control of a distributor

  suitable for powering the motor 130.

  The housings 126 on the rear side of the tray 72 simply contain crazy wheels that are mounted

  on trees that can spin into housings.

  As shown in FIG. 8, in the normal stopped position of the plate 72 and the plate 81, the wheels 127 are at a distance from the upper faces of the channels 125. However, when the plate 72 must be removed, the fluid of the housings 119 of the cylinders 115 is no longer under pressure so that the pistons and the pins 116 fixed thereto can return to the housings by lowering the collar 118 and allowing the plate to lower when the main cylinder 75 is compressed, until the wheels 127 are in contact with the rails 125. The weight of the plate 72 lowers it, and the blocks

107 also descend at this moment.

  A stop collar 135 is attached to each of the columns 17, just below the corresponding block 107, this collar being of a split type which can be clamped around the corresponding column 17 and which has ears projecting outwards on a noticeable length, as shown in FIGS. 8 and 9. When the lugs are tightened, they form an inclined surface as shown in FIG. 8. This inclined surface has a position such that it can be in contact with the underside of the corresponding block 107 and can cause a

  pivoting of the block during its descent. This phenomenon

  then a slight tilting of the rail 108 in the groove so that the contact surfaces 111, 107A and the lips 108A and 112 are released. The blocks 107 are supported on the upper face 136 and the plate 72 is released from the rails 108 so that it can move outwardly along the tracks or rails 125. When the motor 130 is powered, the tray and the half-mold 31 attached thereto may move to a position in

  which mold can be maintained or changed.

  It should also be noted that the support plate 81 is of sufficient weight to cause the pistons 77 to move inwardly and thus free up space.

  between the upper face of the plate 81 and the underside

  upper tray 72 so that the axes 82 which have a small dimension, clear the lower face of the plate when it is removed by rolling. The plate 81 remains in position so that the hydrostatic bearings formed are not deteriorated and in particular the seals 83 are not subjected to scraping forces and

there is no oil leak.

  When the tray 72 is to be replaced, it must simply be brought into rolling position, the rails 108 being in the grooves. Pins or positioning pins 116 are controlled by transmission

  pressurized fluid to the sheaths 119 so that the

  81 be raised. The axes and complementary housing 82 are then locked so that the plate 72 has a

suitable position.

  When the half-molds are moved together

  from the position shown in Figure 8, the

  chons 117 provide an upward traction aligning the narrow portion 116A of the axes 116, and the support or plate 72 is then free to align properly when the blocks 90 enter the guides 91. Some floating along the X and Y axes is allowed so that the support blocks ensure the final alignment, well

  that the axes 116 maintain the initial alignment of the mold.

  The servo-valve controls of the cylinders 75 and

  are such that the control member 67 regulates the

  the running time of the press and adjusts when the crosshead is moved and tightened and when

  the cylinders 75 must be ordered so that the half

  mussels are close together. The signal of the communication organ

  programmed control which locks the jacks 54 of the clamps on the cross member, at the suitable location as detected by the transducers 27, on the cylinders 22, is also transmitted to a member 150 of degree of freedom control. The control member 150 of degree of freedom

  is that which maintains the proper orientation of the

  lower water 72 relative to the upper half-mold and which adjusts the closing movement. This member 150 follows a program which can be created in any case known for a controlled command and which receives a reaction of the sensors 140 until the transom

be tight.

  The signal which controls the clamps of the cross-member also controls an electronic mode switch which switches the feedback to the sensors 120. The reaction to the force of the jacks 75 is also used for the adjustment of the force during operation. molding operation, and differential pressure transducers 151 give such a reaction to the force of each cylinder 75 and its associated demolding jack 95. A separate servo valve 152 is associated with the cylinders of each corner of the plate 72 and there are therefore four servo-valves which each receive a control signal

of the organ 150.

  Servo valves regulate the flow of fluid from a pressurized reserve to a purge,

  in a classic way. The signal reaching each servo

  valve 152 is taken from the position detection and the determination of the proper displacement of each of the cylinders 75 so that the support 72 does not deviate from the parallelism with the upper mold half 30. The adjustment thus made is thus connected to the system multi-axis adjustment described in US Pat. No. 3,800,588. It should be noted that the reaction control

  displacement from the transducers 140 is used.

  only until the transducers 120 are turned on, and an electronic switch provides switching of the controller so that the feedback signals of the transducers 120 are automatically detected when the clamps block the transom at the location. molding, the half-mold 30

of the lower mold half 31.

  As indicated above, when the mold closes, the blocks 90 adjust the yaw movements and along the X and Y axes. In this way, control or restraint is ensured with 3 degrees of freedom. The cylinders 75 are precisely controlled so that they control the pitch, roll and vertical displacements of the plate 72, ensuring the parallelism

half-mussels.

  Three jacks and three displacement transducers

  at least are required between the base and the tray so that they are held parallel to the mold

  superior. Figures 11 and 12 correspond to the application

  general cation and the control of the degrees of freedom of the plateau considered for illustrative purposes. In FIG. 11, the plate 72 is shown schematically and, for example, the parallelism must be maintained with respect to the upper half-mold in pitch as indicated by the curved arrow, about an axis 155 (the same as represented on FIG. Figure 8, around which the pitch must be set) and the roll around an axis 156 is also set. Cylinders of equal dimensions A1 and A2 are placed on either side of the axis 156 at the same distance from this axis for simplification spokes, and a third cylinder A3 having a surface double that of the cylinders Ai and A2 is placed at the other end of the plate and is centered on the axis 156 so that the aforementioned operations can be performed properly in the general case. Thus, the adjustment of the roll around the axis 156 is determined by the displacement of the cylinders A1 and A2 relative to each other. The cylinder A3 is placed at the same distance from the axis 155 as the cylinders A1 and A2, in a simple case, and the relative vertical position of the cylinder A3 with respect to the cylinders A1 and A2 determines the pitch position. Displacements are detected by sensors X1, X2 and X3 which correspond to the sensors 120 in this case (or to the sensors 140 insofar as they provide the control). The displacement signals correspond to the vertical positions of the corresponding cylinders A1, A2

  and A3. In addition, different pressure transducers

  may be used for the determination of the

  force applied by each of the cylinders, and they are

  broken by the references F1, F2 and F3. These sensors or force sensors can also be used for the control of the force balance, as described in

  United States Patent Specification No. 3,800,588.

  Transducers X1 and X2 are equally

  on both sides of axis 156 and are

  same distances from the axis 155 as the X3 sensor.

  The control 67 shown in FIG. 12 creates a control signal shown in FIG. 10 for controlling the mold, this signal being schematically represented by reference numeral 160. The control signal is transmitted to an addition junction 161 forming part of FIG.

  the degree of freedom control member 150.

  Signals received from displacement transducers

  are shown in Figure 12 (X1, X2 and X3) and

  It may be noted that in the setting of movements, a

  average displacement is transmitted to the 161

  addition by an averaging circuit 162.

  A mode electronic switch 163 is triggered to transmit a medium force signal from the transducers F1, F2 and F3 to the addition junction, through the line 164, during the force adjustment, as shown in FIG. The displacement signal

  medium or the medium strength signal reaches the junction

  161, and the addition signals then form an error signal transmitted by a line 166 and which allows the control of the main error signal for the servo-valves after passing through a suitable amplifier 165. Compensation signals are necessary to that the mold parts remain parallel during rapid operation, and the pitch compensation is achieved by use of the displacement signals from the transducers and by proper weighting of these signals by suitable amplifiers.

  division or by a signal processing circuit 170.

  The signals of the transducers X1 and X2 are divided by four while the signal of the transducer X3 is halved as it constitutes the only transducer at this end of the plate 72. When using four transducers of displacement as indicated on In FIG. 8, there is a fourth signal X4, and each of the signals is then divided by four in the processing circuit. The signals of the transducers Xi and X2

  arrive at additional inputs of an amplifica-

  addition, and the transducer signal X3 par-

  it comes to the negative input of this same amplifier so that the signals form an average transmitted to an addition junction 172. The average signal is added to a signal transmitted by line 173 and representing a signal

  pitch (this signal is zero in the pa-

  rallele), and it is amplified in an amplifier 174. This signal is then transmitted by a line 175 which reaches

  to control amplifiers of each of the servo

valves of the circuit.

  Roll compensation, in this particular case

  to bind, is ensured by dividing the signals of the transducers

  X1 and X2 displacement by two (these are the only trans-

  drivers that control the roll over the axis 156), and

  this signal transmitted by line 180 is a traffic signal

  average person reaching an additional function 181 in the-

  which is added to a signal from a line 182 and which allows the selection of a particular roll. When operating in parallel form, the signal of line 182 is zero. An amplifier 183 applies a weighting factor to it and it arrives via a line 184

at the controls of the servo-valves.

  In this particular example, each of the cylinders A1, A2 and A3 has a separate servovalve which controls it, and

  the signal from line 166 reaches an amplification

  Servo valve controller for each cylinder. Signals reaching the servo valve amplifiers are located

  A1, A2 and A3, to the outputs of the amplifiers

185, 186 and 187.

  The error signal transmitted by the line 166, during the command, reaches a positive input of the individual addition amplifier 185 corresponding to the cylinder A1, of the amplifier 186 corresponding to the jack

  A2 and the amplifier 187 corresponding to the cylinder A3.

  In addition, the summed signal indicating the pitch error is transmitted through line 175 to the positive inputs of the add-on amplifiers 185 and 186 and to an input

  negative of the amplifier 187 corresponding to the cylinder A3.

  Thus, with regard to the pitch, the correction can be achieved by using a lower elongation for the cylinder A3 than for the cylinders A1 and A2, or by lengthening the cylinder A3 without lengthening the cylinders.

  A1 and A2 in such an important way, at each cycle.

  The error signal used for the roll compensation is transmitted via the line 184 and reaches only the amplifiers 185 and 186 of the cylinders A1 and A2 because the cylinder A3 does not participate in the roll adjustment. Thus, the signal of line 184 arrives at a negative input

  amplifier 185 and a positive input of the amplifier

  186. This arrangement obviously indicates that the

  correction of any roll error may be

  by extending one of the cylinders Ai and A2 by

report to the other.

  The signal coming from the amplifier 187 is multiplied by two in an amplifier 190, because the cylinder A3 has the same volume as the two cylinders A1 and A2 together, in this case. These signals

  reach the servo valves in the normal way. In pre-

  more cylinders (four per

  example), roll adjustment is transmitted to amplifiers

  addition caterers corresponding to the cylinders placed on either side of the axis 156, at the end of the plate 72 to which the cylinder A3 is placed in the first example considered, and an additional additional amplifier

  must then be used to control a servo

additional valve.

  If the cylinders were placed at different distances from the respective axes from which they can be set, the signals should be weighted

  function of the distance to such an axis.

  Thus, the lower plate of the molding press is hydraulically controlled with three degrees of freedom, vertically (Z) in pitch and roll, and mechanically with the help of the stop blocks, with three different degrees of freedom (X, Y and lace). The tray is thus adjusted with

  precision so that the parallelism of the two halves

  molds, detected by displacement transducers, be preserved. FIG. 10 is a graph which represents the control functions during the main operations of the molding press according to the invention, under the orders of the programmed control member. Figure 10 shows a complete molding cycle, increasing time to the right. The beginning of the cycle corresponds to the vertical line placed on the left, and the first operation that takes place is

  represented by curve 141 which represents the posi-

  the upper rail as a function of time. The segment 141A represents the lowering of the cross member and the segment 141B corresponds to the cross member in the lower position, the upper half-mold being suitably arranged for the molding operation. The curve 142 represents the operation of the jack of the clamps, and it does not

  only two positions. The position segment

  lower 142A corresponds to the cross-piece clamped in position

  tion. The jacks of the clamps are then under pressure.

  The curved ends of the segments 141A and 141C are created electronically in the form of a signal

  programmed transmitted to the servo control unit 69

  Figure 2. The curved parts of the signal

  allow for a progressive acceleration and deceleration

  from the top rail which, in most

  case, is very massive. This gradual movement is important

  both for the reliable implementation of the press according to the invention. At the moment when the upper cross member reaches the molding position, the segment 141A joining the segment 141B, the clamps of the cross member are quickly controlled and lock in position. As soon as the crossmember is blocked, the jacks 75 begin to be controlled by the servo-valves 152. The upper part of the diagram

  times of Figure 10 represents the operation of

  and more precisely the displacement of the lower

  laughter 72 and half mold 31 it carries. Two curves represent the molding operation. The upper curve

  143 represents the displacement of the mold and the inferior curve

greater than 144 the molding force.

  As soon as the jacks 75 begin to move the mold towards its closed position, the movement of the jacks is controlled according to the displacements, as indicated by the curve 143A in solid lines. We can

  note that the mold has risen to a sensible position-

  contiguous to the upper mold, as indicated by

  horizontal line 145. The slight space shown cor-

  This is the compression of the material introduced into the mold, this material keeping the half-molds at a distance corresponding to the thickness of the molded sheet.

  As soon as the mold is closed, at the corresponding moment

  laying to the vertical line 146, the control of the cylinders 75 is electronically switched to the force control as indicated by the curve segment 144A in the solid line of the curve 144. The force is maintained as indicated by the segment 144B, during the time the hardening of the molded compound (heating is also

usually used).

  When the mold must be opened for injection

  For a coloring or other purpose coating, the displacement control is switched as indicated by the solid line segment 143B and the force indicated by the curve segment 144C decreases rapidly as the mold opens. Then, as soon as

  injection of the coating took place, the control of

  mold placement causes the mold to move to its closed position (upward portion of the segment 143B) and, as shown by the broken line 143C, is closed again while the molding force represented by the solid curve 144D is applied and regulate the pressure applied to the mold until the end of time

  hardening as indicated by the vertical line 147.

  Then, the displacement control is switched again, in the control member, during the implementation of the jacks 95 (the jacks 75 being released) so that

  that the mold opens, and this control curve of de-

  placement is represented by segment 143D which indicates that the mold opens, the force also decreasing as

  indicated by curve segment 144E.

  When the mold started to open and

  separated, it is noted that the clips of the cross-member are

  As shown by the curve segment 142C and the demolding cylinders 60 are then pressurized, the cross member being raised as indicated by the curve segment 141C towards its up position. When the cross is recessed, the time represented by the arrow 148 is used for the unloading of the part that has been molded and for the introduction of a new load in

  the mold, the cycle starting again then.

  Thus, the control member transmits the implementation signals of the cylinders of the cross member, the jacks of the clamps and the molding and demolding jacks. The jacks of the clamps are not controlled in a controlled manner and receive all the hydraulic pressure when the distributor 60A is controlled so that it ensures the implementation of these jacks (with release of the jacks) so that the cross is clamped in. position of a

positive way.

  In FIG. 10, the switching between the force and displacement control (curves 143 and 144) is ensured electronically in a known manner. The solid line portions of the curves 143 and 144 correspond to the activity portions of the corresponding control mode while the dashed portions indicate that this control mode is not implemented or is turned off. The program allowing the control can be developed according to the existing control organ

  which transmits electrical signals controlling the

  placements and forces applied as indicated on the

figure 10.

  It should also be noted that although the figures represent a vertical press, the columns may

  horizontally if necessary, and the cylinders 75 of

  lage can move relative to the movable crosshead.

  The hydraulic press shown can thus be used in injection molding machines, presses

forging and similar presses.

Claims (18)

  1. Press to mold the leaves, to order   fully hydraulic, characterized in that it   takes a base (16), several columns (17) which are elongated and protrude from the base, a crossbar (20) slidable along the columns, mounted clamps   on the cross-bar and cooperating with the columns, pre-   first hydraulic cylinders (54) for closing the clamps   and to tighten the crossbar on the columns, second   rins (22) mounted on the base and having a device   which can be lengthened and set back and which is connected   strung to the cross-member, a first mold part (30) mounted on the cross-member, a second mold part (31) mounted on the base, and third hydraulic cylinders   (75) placed between one of the mold parts and its   corresponding positive mounting so that a molding pressure is applied between the mold parts when   the crossbar was put in position and kept in   clamps close to the base, and a   control rod (67) for successively moving the cross member from a remote layout of the base   to a position adjacent to the base, to tighten the   pour and order the third jacks so that the   parts of the mold are close together and allow   a compound to mold the sheets together.   2. Press according to claim 1, characterized in that it comprises fourth cylinders (95) mounted between the mold part which moves under the control of the third cylinders (75) and the mounting device of this mold part so separating the mold parts (31) and compressing the third cylinders (75) under the control of a single servo valve which controls a third and fourth cylinders.   3. Press according to claim 2, characterized in that the mold part (31) which is displaced by the third jacks (75) is that which is supported on the base, and the fourth jacks (95) transmit a reaction charge from the base to the second part of mold so   that the two mold parts separate.   4. Press according to claim 1, characterized in that the first mold part is mounted on a rigid plate, the third cylinders (75) comprise at least three separate cylinders each controlled by a separate servo valve and set in position so that they adjust the displacement of the two mold parts (30, 31) relative to one another about two axes perpendicular to each other and forming a plane parallel to the plane of the mold parts and substantially transverse to the direction of movement when the mold closes, devices (140) for detecting the displacement of the mold parts at at least three locations, these devices being intended for   transmitting action signals representing the posi-   mold parts around its axes, and a   additional positive control commanded by the dis-   displacement detecting means (140) for transmitting a signal to each of the servo valves controlling the individual cylinders, which signal is a function of the signals   position of all movement detection devices   cement. 5. Press according to claim 1, characterized in that it comprises fifth cylinders (60) placed in each of the clamps and intended to cause the opening of the clamps when the fifth jacks receive the fluid under pressure.   6. Press according to claim 1, characterized in that it comprises guiding assemblies placed on the mold parts (30, 31) so that they are aligned when they come closer and they can not be move relative to each other parallel to the plane of separation of the two mold parts and that they can not rotate relative to each other about the axis of movement of the mold parts when these mold parts are moving, a device placed on the base and intended to support the second mold part and comprising a lower plate (72), hydrostatic bearings (80) for supporting the lower plate on the base and comprising at least a hydraulic cylinder (75) of plate mounted between the base and the lower plate, each of the plateau cylinders   having a cylinder surface facing the lower plate   seals (83) placed on each of the cylinder surfaces and delimiting a chamber of dimension slightly smaller than the diameter of the plateau cylinder, the seals bearing against the surface to be displaced on the hydrostatic bearings, and a passage (84). ) connecting   the inside of the platen cylinder and the corresponding chamber   so that pressurized fluid from inside the cylinder reaches the corresponding chamber   and tends to support the lower tray.   7. Press according to claim 6, characterized in that it comprises a plurality of movable platen cylinders (75) towards the first mold part, the platen cylinders being mounted so that the displacement around two perpendicular axes one to the other, parallel to the plane of separation of the mold parts, can be controlled by individual movements of the cylinders of   platform, the control device comprising servo   valves (152) allowing the individual control   each of the platen jacks, devices (140) for detecting the movement of the parts   mold relative to each other about axes   pendicular to each other and transmitting signals   reaction representing the position of each of the   Detection detectors individually and a device for combining the signals of the detection devices with a programmed control signal, this device forming a   separate signal for each of the individual servo valves   to regulate the position of the parties   mold around the axes perpendicular to each other.   8. Press according to claim 7, characterized in that it comprises separate demolding cylinders (95) applying reaction forces between the base (16) and   the lower plate (72) and ordered so that they   voce the setting back of the cylinders (75) of the plateau   lower, each of the demolding cylinders (95) being   associated with one of the platen cylinders, the servo-valves (152) of each of the platen cylinders being also connected so that they control the release cylinders associated with the corresponding plateau cylinders.   9. Press according to claim 8, characterized in that it comprises stop devices disposed   between the base and the lower plate and intended to   miter the displacement of the lower plate (72) towards the   base under the action of the demolding cylinders (95).   10. Press according to claim 9, characterized in that it comprises two rails (125) mounted on the base below the lower plate, and wheels (127) placed on the lower plate and aligned with the rails, the devices stopper can be selectively set back so that the lower platen (72) moves and places the wheels in contact with the rails so that the lower platen can move along the rails when   the stop devices have been indented.   11. Press according to claim 9, characterized in that the abutment devices comprise shafts (116) having tapered ends of the side of the plate (72), and guides (117) protruding under the plate and intended to house the axes. , the guides being mounted so that they protrude from the second plate, the axes having a surface portion which is housed tightly in the guides when the second plate is in the stopped position determined by the demolding jacks (95), the axes being sufficiently tapered so that the second tray can move relative to the tapered ends of the axes as the second tray is moved to the molding position.   12. Press according to claim 6, characterized in that the platen jacks (75) have pistons (77) having wall portions which allow pivoting of the tray surface in the corresponding chamber during use.   13. Press according to claim 10, characterized in that it comprises support blocks (108) which can slide along the sides of the lower plate (72) and allow sliding of the latter relative to the support blocks when the bottom plate moves along rails, release cylinders   (95) bearing against the lower plate through mediary support blocks.   Press according to Claim 13, characterized   in that it comprises sliding mounting devices   supporting blocks (108) on the lower platen, comprising an elongate groove (110) formed on each side of the lower platen (72) and a support block rail (108A) protruding laterally from the support block and sliding in the an elongate groove, support devices (135) being placed on the base so that they support the support blocks independently of the lower plate when the latter is supported by the rails, the support devices comprising a surface which causes a pivoting of the support blocks relative to the lower plate and thus causes the control of the rail surfaces of the support blocks and the elongate slots which normally cooperate with the demolding cylinders so that the rails and the slots are mutually separated. 15. Press according to claim 1, characterized in that the clamps for holding the crosspiece (20) relative to the columns (17) comprise a slotted clamp (46) mounted on the cross member around a column   corresponding, a clamp mounting device -   slotted on the cross-member, comprising two wings protruding from the central part of the cross-member so that the wings are arranged close to the column (17), the first jacks (54) being intended to close the slotted claws by   same time as the bent wings by allowing the setting of the split forceps.   16. Press according to claim 15, characterized in that the fifth hydraulic cylinders (60) when controlled by fluid under pressure, tend to spread the slot of the split clamp and release it when under pressure.   17. Press according to claim 15, characterized in that the wings form a space projecting laterally from the central portion of. the cross member and allowing the split tongs (46) to be withdrawn between the wings by   distance from the central parts of the cross.   18. Press according to Claim 1, characterized in that the crossmember (20) is arranged between the columns (17) and has several substantially parallel plates (37).   distant from each other and arranged between the   lons, the grippers (46) being controlled by the first jacks (54) to temporarily clamp the plates on the columns, devices (41) connecting the plates to each other near the central portions of the cross member between the columns, an upper plate (35) being connected to the plates and having edges protruding from the guides and supported by the plates only in the central portions of the beam, and reinforcement brackets (43, 44) protruding from the central portion of the the crossbar towards the edges of the upper plate so that they collect the charges transmitted by the edges of the plate   towards the central part of the crossing.