GB2035889A - Toggle action press - Google Patents

Abstract

Process and device used for adjusting the depth of penetration of a hydraulic folding press. They allow to adjust the depth stop (3) of the pressure bed (4), without being necessary to lift the pressure bed from the workpiece. The depth stops (3) are relieved temporarily by a pressure in the cylinders acting in the opposite direction of the pressure bed (4), for example in double-acting cylinders (2) without any pressure drop on the workpiece. It allows a precision adjustment of the penetration depth in one operation. The process can be applied to folding presses having a mechanical or hydraulic travel limiting device.

Description

SPECIFICATION A toggle action press The present invention relates to a toggle action press. The operation of such a press may be pneumatic, hydropneumatic, hydraulic or oleodynamic.

Presses provided with toggle action actuating systems generally have a fixed crosshead and a counterplaten connected by tie rods, and a movable crosshead which moves towards the counterplaten on an operating stroke. A toggle lever system between the fixed and movable crossheads ensures that at least in the final stages of the operating stroke, a great force is applied to the movable crosshead.

The toggle lever systems currently known are subject to disadvantages of kinematic, dimensional and functional kind which will be made more clear in the following.

It is obviously desirable to reduce the space occupied by a press, with the other particular features being equal (die opening stroke and maximum closing force), with horizontal, vertical or anyhow located machines. Since a substantial part of the overall dimensions of each press, is absorbed by the toggle lever system, consequently a reduction of the dimensions of said system, if obtained without any detriment to the performance, allows important economic advantages in the installation as well as a greater flexibility in the use of the press either alone, combined with other presses or automated.

According to the invention, there is provided a press having a fixed crosshead and a counterplaten connected together by tension elements, a movable crosshead arranged to move between the fixed crosshead and the counterplaten, a first double-acting piston/cylinder unit arranged between the movable crosshead and a fixed part of the press to move the movable crosshead, a toggle lever system connected between the fixed and movable crossheads, and a second double-acting piston/cylinder unit arranged between the movable crosshead and a cross member forming part of the toggle lever system, said second unit being adapted to move said cross member relative to the movable crosshead to actuate the toggle lever system and to complete the movement of the movable crosshead toward the counterplaten.

In such a press the die closing phase is effected through two sequential operational steps, in the first of which (approach of the movable crosshead) the toggle lever system is inactive and is dragged by the movable crosshead, while in the second step (locking) said lever system becomes active and causes the locking of the die at the maximum pressure.

The invention will now be further described, by way of example, with reference to the accompanying drawings, in which: Figure la shows schematically an example of a press provided with a prior art toggle lever system: Figure 1b shows schematically a press provided with a toggle lever system according to the invention; Figure 2 is a schematic view of the press of Fig. 1 b in the open die position, on a larger scale; Figure 3, illustrates the press of Fig. 2 in the closed die position before the intervention of the locking members; Figure 4 represents the press of Figs. 2 and 3 in the closed die position; and Figure 5 is a plan view of the press.

In said drawings only the members directly relevant to the present invention have been represented, while to make them more clear, all the other known devices, which are commonly part of a press (such as the injection system, the hydraulic switchboard and others) have been intentionally omitted.

In Fig. 1 a, numeral 10 indicates the fixed crosshead of the press, 11 is the counter platen carrying an integral part 9 of the die (commonly called the matrix); 13 indicates the movable crosshead carrying the other half 8 of the die and sliding on columns 12 rigidly connected to the fixed crosshead 10 and to the counterplaten 11.

The known toggle lever system which actuates the movable crosshead 13, generally comprises a double acting cylinder 14 rigidly connected to the fixed crosshead 10 of the press, by a piston 15 connected to a rod 16.

Said rod 16 is in turn connected to a cross member 17 which slides on a stationary guide 18. The cross member 17, through pin 19, is articulated on connecting rods 20. Said connecting rods 20 are articulated through pins 21 on levers 22 which can rotate about pins 23 connected to the fixed crosshead 10 of the press; the levers 22 are articulated to connecting rods 25 and said connecting rods 25 are pivoted in turn, at 26, to the movable crosshead 13.

With this known toggle lever system, the closing or downward movement of the movable crosshead occurs in the following way: The fluid pressure conveyed in the cylinder 14 causes the downward displacement of piston 15, rod 16 and cross member 17. In said conditions the cross member 17 acts on connecting rods 20 causing the rotation of levers 22 towards counterplaten 11. Consequently, the connecting rods 25 push the crosshead 13 towards the counterplaten 11.

The stroke of piston 15 continues until the toggle becomes completely extended, that is, until the pins 23, 24 and 26 lie in a straight line or very nearly so. In said position, the die is closed and the press exerts the maximum pressing effort.

The known type of toggle system which has been described will now be discussed.

Since the movement of movable crosshead 13 is generated by the piston 15 and the cross member 17 in both the approach phase and the phase for the locking of die parts 8, 9, the kinematic motion must be obtained in such a way that, in any point of its stroke, a thrust on the piston 15 transmits a suitable thrust to the movable crosshead 13. The same must occur in the return stroke of the crosshead 13. In order to have said condition at the beginning of the gripping movement it is necessary for the angle-a-between a straight line joining the pins 19 and 21 a straight line parallel to the direction of movement of the movable crosshead 13, to be smaller than the angle-ss-between a straight line joining the pins 19 and 23 and the line parallel to the movement of the crosshead 13.

In effect, since the connecting rod 20 trans mits the thrust of the cross member 17 along the direction given by the line passing through pins 19 and 21, the above stated condition is absolutely necessary to ensure that a thrust on the cross member 17 causes rotation of levers 22 around pins 23 towards counterplaten 11.

The angular difference ss-a may be called the thrust angle of the motion connecting rod 20. For the above stated reasons, when the thrust angle is positive, operation of the lever system is possible; if the thrust angle is negative, operation of the toggle lever system would not be possible.

The necessity to have, in the known toggles a positive thrust angle, restricts the opening stroke of the movable crosshead 13, which cannot open for the whole stroke which would be theoretically be possible in the kinematic motion, since that would imply the reaching of negative thrust angles which would prevent operation in the traditional manner. The opening movement of the movable crosshead 13 must therefore be limited to the position which implies a thrust angle which is positive and sufficiently wide as to assure the correct operation of the machine. This fact increases the space occupied by the kinematic group, because, as its stroke con not be utilized fully, it ends up being oversized since the lengths of lever 22 and of connecting rod 25 are not fully utilized.

It is furthermore clear that, in the known actuation device illustrated on Fig. 1 a, the length of the connecting rod 25 is conditioned by the length of the stationary guide 18 for the cross member. This constitutes a further limitation of the stroke of the movable crosshead 13.

Another drawback derives from the space taken up by the stationary cylinder 14 protruding longitudinally from the casing of the machine by a substantial length ("A" on Fig.

1 a) greater than the stroke of piston 15.

In many presses provided with a toggle lever system, it is advantageous if the die gripping terminal phase, immediately before closure, takes place for a very short while at a very reduced speed and applying the smallest effort possible, in order to allow the intervention of security devices in case the terminal gripping encounters any obstacle. The sensitivity of said security devices, which are often prescribed even by the accident prevention rules, is strictly connected, for obvious reasons, to the existence of the two above mentioned conditions.However, the known toggle system of Fig. 1 a, while capable of providing the first condition (low speed in the final phase of the gripping stroke) because the toggle is nearly in extension, is not capable, just for this reason, to provide the second (a limited final closing effort), except if the pressure acting on the cylinder 14 is reduced in a very valuable manner.

Fig. 2 represents schematically a press provided with an improved toggle system.

Numeral 29 indicates the fixed crosshead of the press, which is made in a known manner and has dimensions and shape adapted to the lever system, providing the most appropriate distribution of the efforts and the elastic deformations in the pressing operation. Numeral 11 indicates the counterplaten rigidly connected to the fixed crosshead by cloumns 12, on which the stationary part 9 of the die is appropriately mounted; 30 indicates the movable crosshead, carrying the also mobile part 8 of the die and sliding on the columns 12. In Fig. 2, the press is shown with the die open.

The press is opened and closed by the following parts: -a double acting approach piston, or pistons, with a piston rod 32 connected to the fixed crosshead 29 of the machine at the point 50; -an approach cylinder, or cylinders, 33 rigidly connected to the movable crosshead 30; -a locking double acting cylinder, or cylinders 36 for the pressing stroke rigidly connected to the cross member 38, which is in turn connected to a coupling 51 axially slidable on seats formed on the cylinders 33 or engaged to the movable crosshead 30; -a toggle lever system, formed by the connecting rods 39, levers 42 and connecting rods 45. The connecting rods 39 are articulated on pins 40 connected to the cross member 38 and to the pins 41 connected to levers 42; the levers 42 are connected to the fixed crosshead of the press by pins 43, and are connected to the connecting rods 45 by pins 44; and the connecting rods 45 are connected to the movable crosshead 30 by the pins 46; -a double acting locking piston, or pistons 35 for the pressing stroke, rigidly connected to the movable crosshead 30.

The illustrated system, as can be seen from Fig. 5, is symmetrical with respect to two orthogonal planes, extending longitudinally with respect to the press.

As shown in Fig. 5, there are two approach cylinders 33 symmetrically located with respect to a single locking cylinder 36.

In the embodiment, there are four connecting rods 39 and eight levers 43, all arranged symmetrically.

The toggle system is actuated by cylinders with two different functions which act sequentially: (a) inlet of pressure fluid into the mobile cylinders 33, below stationary pistons 31, causes the movable crosshead 30 to be driven, at an adjustable speed, towards the counterplaten 11 to close the die.

(b) When the position shown in Fig. 3 is reached, the cylinder 36 and the corresponding piston are actuated to obtain the locking of the closing die; in this phase, the press exerts the maximum effort and moves from the position shown in Fig. 3 to the position of Fig. 4, where the articulation axes 43, 44, 46 are perfectly aligned for each of the toggles.

The use of the above described double actuating system permits negative thrust angles to occur in the opening of the die, by exploiting in a more complete manner the particular features of the kinematic group formed by parts 38, 39, 42 and 45. A press incorporating the lever system shown, of the same size as a press with a prior art system can thus achieve a greater opening stroke.

Alternatively, for an equal length of opening stroke it is possible to obtain a reduction of the dimensions of the press.

Furthermore, by said system it is possible to improve the conditions for compression moulding of thermosetting and thermoplastic resins containing expanding agents, since the closing system described adds the advantages of the stiffness of the connecting rods to the particular features of the piston system which allows, if required, to effect the degassing for the type of plastic material worked.

Moreover, the mobile cylinders 33 are placed inside the press structure instead of protruding outside as in the case with the cylinder 14 of the prior art press.

Numerals 8 and 9 indicate two parts of a die suitable for producing a moulding G. The dimension "A" indicates the reduction of the height of the press of Fig. 1 b compared with that of Fig. 1 a, and the dimension "B" is the greater stroke obtainable, deriving from the fact that the actuating cylinder is advantageously located inside the structure and the kinematic group is exploited more rationally.

The press shown in Fig. 1 b has a smaller overall height (L), but can open to provide a larger gap between counterplaten 11 and movable crosshead 13 than the press of Fig.

1 a If the height of the largest moulding which can be produced is denoted by H, the following relationships can be established.

L = 11,2 H for a toggle press of the traditional type (Fig. 1 a); and L = 5,5 H for the press shown in Fig. 1 b.

In a press of the traditional toggle type, the length L1 (defined on Fig. 1 a) which refers to the height, excluding the actuating cylinder, is related to the dimension H as L1 = 7,65 H.

The reduction of the press height is obtained because the angle-a-formed by the straight line joining the articulation pins 40 and 41 of levers 39 and a straight line parallel to the translation direction of the movable crosshead 30 may be considerably larger than the angle-ss-formed by the straight line parallel to the translation direction and a straight line joining the articulation pins 40 and 43. The kinematic group stroke is therefore more fully exploited.

The operation of the toggle system will now be described. When the system is in the Fig.

2 position, a thrust acting downwardly on the cross member 38 would not result in downward movement of the movable crosshead 30, because it would tend to rotate the lever 42 upwardly instead of downwardly, viewed in the drawing. For this reason, the movable crosshead 30 is initially moved towards the counterplaten 11 by means of cylinders 33 and pistons 31 instead of by the toggle lever system.

The approach pistons 31 are connected through stems 32 to the head or reaction plate 29 of the press at points 50. When the actuating fluid of the press is admitted to the cylinder chamber 33 below piston 31 in zones 33a, the cylinders 33 move towards the counterplaten 11 causing an approach movement of the movable crosshead 30 to which they are rigidly connected. The approach of the movable crosshead 30 to the counter platen 11 continues therefore due to the thrust of the fluid in the cylinders 33, until the two parts of the die come in contact and then it stops because the pressure acting inside the cylinders 33 is insufficient to drive crosshead 30 any further.

With this type of construction, the approach stroke of the movable crosshead 30 may occur, by adjusting the delivery and the pressure of the actuating fluid, at the most suitable speed and pressure in any point.

Particularly in the final phase of the approaching stroke it is possible to control the approaching effort with a higher precision than that allowed by the known systems, so as to attain a greater sensitivity for the security devices which may be present in the press.

During the approach phase, the levers of the toggle have no active function, but they follow the motion of the movable crosshead 30. More precisely, in its forward movement, the crosshead 30 drags the connecting rods 45 towards the counterplaten 11. The rods 45 turn the levers 42 which act in turn through rods 39 on the cross member 38.

The locking cylinder 36, which is also inactive during the approach phase is rigidly connected to the cross member 38.

The piston 35 integral with stem 37 may slide within the locking cylinder 36. Said stem 37 is in turn integral with the crosshead 30.

During the approaching motion, the cross member 38 is dragged by the levers of the toggle.

The congruence of the motion is assured by the overstroke 36a of the cylinder 36.

Fig. 3 shows the position of the various parts at the end of the approach stroke but before locking has occurred with the extension of the toggle.

In Fig. 3, the piston 35 is still in its initial position towards the bottom part of the cylinder 36.

In this position, the actuation of the toggle may begin. Fluid pressure is admitted to the bottom part of the cylinder 36. The cylinder 36 thereby moves downwardly and acts in the same direction on the cross member 38.

The cross member 38 slides through suitable couplings 51 on the external surfaces of the cylinders 33 or on other surfaces integral with the movable crosshead 30. The cross member 38 is linked to the connecting rods 39, and thus to the levers 42 and the connecting rods 45.

The toggle system moves to the position shown in Fig. 4, to effect locking.

In that moment the degassing phase, which has been previously mentioned may take place. The device allowing the effectuation of said phase consists in a variant of the system for the anchoring of stems 32 to the head or reaction plate 29 at points 50, which is illustrated in the detail of Fig. 2. According to said variant, said stems 32, instead of being stiffly anchored to the reaction plate, are connected to said plate with the possibility of a small axial sliding at points 50. Said sliding is adjusted by means of caps 60 and springs 61 whose preloadihg is adjusted through nuts. 63 or other equivalent system. The movement of stems 32 and caps 60 is connected to a valve regulating the delivery of the actuating fluid (not represented on the figure) and calibrated so that the flow may be progressively reduced up to the total closing when the caps move towards the reaction plate 29.

The springs 61 are calibrated to a predetermined and adjustable value of the arrow and the preload.

The elastic system may be provided by a single action hydraulic piston 99, (Fig. 2) kept under pressure in the working direction by a hydro-pneumatic accumulator or even by the pump pressure, so that the preloading value is kept nearly constant.

After the first locking of the die and the subsequent injection of the thermosetting or thermoplastic resins containing expanding agents, the toggle is locked and the actuating fluid is admitted in the acting chamber, with reference to the drawing, of the approaching cylinders 33 and controlled by the above said valve, at a pressure of a predetermined and adjustable value, such as to compress the springs 61 without exceeding the value which brings them in pack. This causes a temporary and minimum opening of the movable crosshead 30 regulated by the system through the said valve, which allows the degassing of the die; subsequently, the toggle is again locked at closure for the termination of the pressing cycle.

The open the die, the movements occur obviously in inverse order. At the beginning, Fig. 4, fluid pressure will be admitted above the cylinder 36; the cross member 38 will therefore move upwardly (referring to the drawing) and unlock the toggle, Fig. 3. Subsequently, operating fluid will be admitted to the cylinders 33 above the pistons 31, and the cylinders will move upwards together with the movable crosshead 30, to the opening position indicated in Fig. 2. The press may be opened until substantial negative values of the thrust angle, as previously defined, are attained.

The operation of the press described is more regular and controlled than that of prior art presses, and also allows the degassing and decompression operations required for some articles manufactured with some thermosetting or thermoplastic resins. Additionally, the space occupied by the press is remarkably reduced when compared with known presses.

The device described may advantageously be utilized on presses whose actuation is pneumatic, hydropneumatic, hydraulic or oleodynamic; in presses of the horizontal, vertical or inclined type, and may be used singly or associated with other stationary or mobile operating units.

Claims (10)

1. A press having a fixed crosshead and a counterplaten connected together by tension elements, a movable crosshead arranged to move between the fixed crosshead and the counterplaten, a first double-acting piston/cylinder unit arranged between the movable crosshead and a fixed part of the press to move the movable crosshead, a toggle lever system connected between the fixed and movable crossheads, and a second double-acting piston/cylinder unit arranged between the movable crosshead and a cross member forming part of the toggle lever system, said second unit being adapted to move said cross member relative to the movable crosshead to actuate the toggle lever system and to complete the movement of the movable crosshead toward the counterplaten.

2. A press as claimed in claim 1, wherein both piston/cylinder units are accommodated between the fixed crosshead and the counterplaten.

3. A press as claimed in claim 1 or claim 2, wherein the toggle lever system comprises a plurality of toggle lever pairs, each pair including a bell-crank lever pivotd at one end to the fixed crosshead, and another lever pivoted to the movable crosshead and to the angle of the bell-crank lever, the other end of the bell-crank lever being connected to the cross member by a pivoted link.

4. A press as claimed in claim 3 wherein when the movable crosshead is in its fully open position, the angle formed between a first straight line, through the pivot points of the pivoted link and a second straight line, parallel to the direction of movement of the movable crosshead is greater than the angle formed between a third straight line, through said one end of the bell-crank lever and the pivot point where the pivoted link is connected to the cross member and said second straight line.

5. A press as claimed in any preceding claim, wherein the first piston/cylinder unit has a piston with a piston rod secured to the fixed crosshead, and a cylinder secured to the movable crosshead.

6. A press as claimed in any preceding claim, wherein the second piston/cylinder unit has a piston with a piston rod secured to the movable crosshead and a cylinder secured to the cross member, the cross member being slidable on the outside of the cylinder of the first piston/cylinder unit.

7. A press as claimed in claim 5, wherein the piston rod is secured to the fixed crosshead in such a way as to permit a limited relative movement between the rod and the crosshead.

8. A press as claimed in claim 7, wherein said relative movement is limited by abutments on the inside and the outside of the fixed crosshead, and a spring biasses the inside abutment against the crosshead.

9. A press as claimed in claim 7 or claim 8, wherein the supply of operating fluid to the first piston/cylinder unit is controlled by a valve which is itself controlled by the position of the piston rod relative to the fixed crosshead.

10. A press substantially as herein described with reference to any one embodiment shown in Figs. 1 b, 2, 3, 4 or 5 of the accompanying drawings.