A press machine for forming a peripheral surface of a blanket

BACKGROUND OF THE INVENTION AND PRIOR ART

The present invention relates to a press machine for forming a peripheral surface of a blanket, wherein the press machine comprises a stationary portion, an opening for receiving of the blanket, a plurality of pressing elements which each comprise a press surface adapted to form the peripheral surface of the blanket, a rotatable holding device, a driving member which is adapted to supply a force to rotate the holding device around an axis and guiding elements which comprise guiding surfaces adapted to transmit the rotary motion of the holding device to stroke motions of the pressing elements towards said blanket when the holding device is rotated in a first direction.

WO 81/03456 shows an example of a conventional press machine for forming a peripheral surface of a blanket. The press machine comprises axially arranged power cylinders adapted to press together two annular portions provided with conically shaped surfaces. A plurality of pressing elements, which have portions with correspondingly shaped conical surfaces, are arranged between the two annular portions. When the power members press together the annular portions in an axial direction, the pressing elements are displaced radially inwards in a direction towards said blanket wherein they form the peripheral surfaces of the blanket.

US 4,345,453 shows a hydraulic press for forming a peripheral surface of a blanket. The hydraulic press comprises a holding device which is rotatably arranged around an annular frame work. The frame work comprises a plurality of pressing elements which each are displaceably arranged in a radial direction by means of a hydraulic cylinder. The holding device comprises a plurality of guiding elements having a curved cam surface. The cam surfaces are adapted to be in contact with cam followers which are connected to valves controlling the supply of hydraulic oil to the hydraulic cylinders. A further hydraulic cylinder is adapted to perform a rotary motion of the holding device in relation to the frame work when a pressing operation is to be performed. During this rotary motion, the cam surfaces of the guiding elements displace the cam followers in a direction radially inwardly. Thus, the cam followers act on the valves which activate the cylinders such that they displace the pressing elements radially inwards toward the blanket. A disadvantage with this press is that it requires one hydraulic cylinder for each pressing element and a further hydraulic cylinder to rotate the holding device. With so many hydraulic cylinders, the press will be expensive to manufacture.

SUMMARY OF THE INVENTION

The object of the present invention is to provide a press machine which is able to form a peripheral surface of a blanket with a very good accuracy at the same time as the press machine is able to provide high pressing pressures of all pressing elements by means of only one power member.

This object is achieved by the tool of the initially mentioned kind, which is characterised in that each of said guiding surfaces are adapted to be in sliding contact with a contact surface of a respective pressing element and that said guiding surfaces and said contact surfaces have a corresponding curved shape in at least a contact area which shape constitutes a part of a circle

having an extension in a plane perpendicular to said axis. For transferring large pressing forces, via surfaces which are in sliding contact with each other, it is required that the sliding surfaces continuously are in contact with each other within a relatively large contact area. If not, high local stresses will arise in areas which are more or less point loaded resulting in a risk for deformation of the surfaces. Consequently, a condition for avoiding point loads is that the guiding surfaces of the guiding elements and the contact surfaces of the pressing elements have a corresponding shape within a relatively large contact area. However, the guiding surfaces of the guiding elements perform a rotary motion around an axis and the pressing elements perform a substantially linear stroke motion in direction towards the blanket. Consequently, the guiding surfaces of the guiding elements perform a rotary motion in relation to the contact surfaces of the pressing elements during a pressing operation. It is thus not possible to give the surfaces a plane shape. A problem is here to find out if it is possible to give the surfaces another kind of shape which fulfils the above- mentioned condition. It has been found that only one shape of the surfaces fulfils the above-mentioned condition, which is that the surfaces are given a shape which constitutes a part of a circle having an extension in a plane perpendicular to the axis. However, only one size of the circle is possible for a determined stroke length motion of the pressing elements. By means of such a circle shape of the surfaces, they are able to maintain a contact within a relatively large contact area even when they slide and rotate in relation to each other during a pressing operation. The guiding surfaces of the guiding elements and the contact surfaces of the pressing elements may with such a shape transmit large pressing forces without damaging of the surfaces. Thereby, the press machine may obtain a long working life. The rotary motion of the holding device may with a suitable numbers of guiding elements be transmitted to stroke motions by all pressing elements. Thus, only one power member needs to be used for supplying stroke motions of the pressing

elements. Due to the fact that only one power member is used, a simultaneous activation of all pressing elements is provided in a simple manner. The peripheral surface of a blanket may thus be pressed to a desired shape and dimension with a very high accuracy.

According to a preferred embodiment of the present invention, each of said guiding elements have a guiding surface with a first point which is in contact with a point of the contact surface of the pressing element in a non-activated state and a second point which is in contact with the same point of the contact surface of the pressing element in an ending pressing state, wherein the circle is adapted to extend through said points. Thus, a first criterion is obtained for determining said circle. A second criterion is that at least the second point of the guiding surface is adapted to be rotated with substantially the same angle around the axis as around a centre of the circle during the stroke motion of the pressing element. Thus, at least this point of the guiding surface will provide a self compensating angle adjustment during the stroke motion of the pressing element such that a good contact is continuously maintained between the guiding surface in connection to this point and the contact surface of the pressing element. By forming the guiding surface and the contact surface of the pressing elements after a circle which fulfils the above mentioned criteria, the fault between the contact surfaces is substantially completely eliminated during the stroke motion of the pressing element. The difference between the radial distances of the points to the axis defines the stroke motion length of the pressing element.

According to a preferred embodiment of the present invention, said guiding surfaces and said contact surfaces are in sliding contact with each other within a contact area which has a substantially constant size during the entire stroke motion of the pressing elements. At least during occasions when large pressing forces is transmitted, it is a clear advantage if the

contact area has a substantially constant size to avoid increased local stresses. However, it is possible to make the contact area less during the part of the stroke motion when the pressing elements are displaced from a retracted position to the peripheral surface of a blanket since this part of the stroke motion does not require transferring of any appreciable force.

According to another preferred embodiment of the present invention, it comprises guide means which allows only motions of the pressing elements in a radial direction in relation to said axis. Consequently, such guide means allows only reciprocating linear motions of the pressing elements during stroke motions and return stroke motions. Consequently, motions of the pressing elements in other directions are prevented. Said guide means may comprise elongated recesses in the stationary portion and that portions of the pressing elements are adapted to be displaceably arranged in the elongated recesses. Said portions may have a suitable shape such that they may be displaced in the recesses and make displacing motions of the pressing elements along the elongated recesses possible.

According to another embodiment of the present invention, the press machine comprises a lever by which said driving member is adapted to rotate the holding device. By means of a lever, a force increase may be obtained such that the pressing elements obtain a larger pressing force than supplied by the power member. The power member, which advantageously may be a hydraulic cylinder, thus has to be prolonged a longer distance than the stroke motion of the pressing element. Such a force increase is also in view of accuracy an advantage when a fault in stroke length of the cylinder results in a considerably less fault in stroke motion of the pressing elements. The shape of said sliding surfaces which transmit the pressing motion of the power member also results in a force increase which increases the force and increases the pressing accuracy.

According to another embodiment of the present invention, the press machine comprises power members which are adapted to supply forces which provide return stroke motions of the pressing elements when the holding device is rotated in a direction opposite to the first direction. When the power member rotates the holding device back after a pressing operation, the guiding elements are rotated such that the guiding surfaces located radially outwardly of the contact surfaces of the pressing elements obtain a successively increasing distance to the blanket which has been formed during a pressing operation. The task of the power members is to move the pressing elements radially outwardly after a pressing operation has been performed. Advantageously, said power members are adapted to supply forces acting on the pressing elements such that their contact surfaces are continuously kept in contact with the guiding surfaces of the guiding elements during return stroke motions. Such a power member may be attached between each of the pressing elements and a suitable part of the stationary portion. The power member may be a spring member, a pneumatic power member or a hydraulic power member.

According to another embodiment of the present invention, the press machine comprises bearing means which is adapted to make a rotary motion of the holding device possible in relation to the stationary portion. Thus, the holding device may be rotated with a relatively low friction in relation to the stationary portion. Advantageously, said bearing means comprises sliding bodies which are slidably arranged in at least one circular groove. The stationary portion may here comprise one circular groove while the holding member comprises sliding bodies which are fixedly arranged in the holding member and slidably arranged in said circular groove. Alternatively, the holding device may comprise the circular groove while the sliding bodies are fixedly arranged in the holding member and slidably arranged the circular groove. Advantageously, said pressing elements are arranged with regular intervals around the opening

for receiving of blankets. With such a uniform distribution of the pressing elements they may perform a substantially corresponding forming of the entire peripheral surface of the blankets. Eight pressing elements may, for example, perform stroke motions towards the peripheral surface of the blanket from eight different radial directions with an angle difference of 45°.

BRIEF DESCRIPTION OF THE DRAWINGS

In the following, a preferred embodiment of the invention is described, as an example, with reference to the attached drawings, on which:

FFiigg.. 11 shows a front view of a press machine according to the present invention,

Fig. 2 shows a cross section view of the press machine in

Fig. 1 along the plane A-A,

Fig. 3 shows the press machine in Fig. 1 in a pressing state, FFiigg.. 44 shows a cross section view of the press machine in

Fig. 2 in the plane B-B when it is in a non-activated state,

Fig. 5 shows a cross section view of the press machine in the plane B-B in an initial pressing state, FFiigg.. 66 shows a cross section view of the press machine in the plane B-B in a concluding pressing state,

Fig. 7 shows the press machine in a non-activated state and

Fig. 8 shows the press machine in a concluding pressing state.

DETAILED DESCRIPTION OF PREFERRED EMBODIMENTS OF THE INVENTION

Fig. 1 shows a front view and Fig. 2 a cross section view of a press machine for forming of a peripheral surface of a blanket 1.

The press machine comprises a stationary portion 2 which is

stationary attached in a suitable manner. The stationary portion 2 comprises a front sheet 2a defining a front surface of the press machine and a rear sheet 2b defining a rear surface of the press machine. A holding device 3 is arranged between the front sheet 2a and the rear sheet 2b. The holding device 3 is provided with a circular peripheral portion 3a. A plurality of guiding elements 3b are fixedly arranged on the inside of the peripheral portion 3a. The press machine comprises a plurality of bolts 4 holding together the front sheet 2b and the rear sheet 2c. The bolts 4 are arranged in en position peripherally outwardly of the holding device 3. The front sheet 2a comprises, on an inside, a circular groove 2c which is shown with dashed lines in Fig. 1. The rear sheet 2b comprises, on an inside, a corresponding circular groove 2d. The circular grooves 2c, 2d are symmetrically arranged around a centre axis 5. The holding device 3 is provided with a number of sliding blocks 3c on opposite sides which are adapted to be slidably arranged in the grooves 2c, 2d. Thus, the holding device 3 is rotatably journaled in relation to the stationary sheets 2a, 2b and around axis 5.

The stationary portion 2 comprises a centrally arranged opening 6 for receiving of blankets 1 to be pressed in the press machine. The axis 5 extends centrally through the opening 6. The press machine comprises a plurality of pressing elements 7. The stationary portion 2 comprises U-shaped elements 8 which define elongated recesses 9 in the front sheet 2a and in the rear sheet 2b. In this case, eight U-shaped elements 8 are arranged in the front sheet 2a and in the rear sheet 2b at uniform intervals around the opening 6. De U-shaped elements 8 are arranged such that each of the elongated recesses 9 extend in a radial direction in relation to said axis 5 and with an angle of 45° in relation to adjacent recesses 9.

Each of the pressing elements 7 comprise a front portion 7a protruding into a recess 9 in the front sheet 2a and a rear portion 7b protruding into a recess 9 in the rear sheet 2b. The

front 7a and rear 7b portions of the pressing elements have a corresponding shape as said recesses 9 such that the pressing elements 7 are displaceably arranged in the elongated recesses 9. Each of the pressing elements 7 are thus displaceable in a radial direction in relation to the axis 5 and to a blanket 1 applied in the opening 6 of the stationary portion 2. Each of the pressing elements 7 have a press surface 7c adapted to come in contact with and form the peripheral surface of a blanket 1 during a pressing operation. The pressing surfaces 7c are arranged substantially around the periphery of the opening 6.

Consequently, the holding device 3 comprises guiding elements 3b which are fixedly arranged on the inside of the peripheral portion 3a. The guiding elements 3b comprises guiding surfaces 3c adapted to be in engagement with contact surfaces 7d of the pressing elements 7. The press machine comprises power members 10 which are attached, in a suitable manner, between the stationary portion 2 and the respective pressing elements 7. The power members 10 are adapted to supply a force to the respective pressing elements 7 such that the contact surfaces 7d continuously are kept in contact with the guiding surfaces 3c of the guiding elements. A driving member, which here is a hydraulic cylinder 1 1 , is adapted to supply a force which rotates the holding device 3 in relation to the stationary portion 2. The hydraulic cylinder 1 1 has a first end 1 1 a pivotally attached in a stationary unit 12 and a second end 1 1 b pivotally attached to an end of a lever 13. The opposite end of the lever 13 is fixedly attached to the holding device 3 in a suitable manner.

Figs. 1 and 2 show the press machine in a position when the pressing elements 7 are in a retracted position. In this position, a blanket 1 to be pressed may be applied in the opening 6. When the hydraulic cylinder is supplied with hydraulic oil and is prolonged, it rotates the holding device 3 in a counter-clockwise direction around the axis 5. Thereby, the pressing elements 7 provide stroke motions towards the blanket 1 . When the

hydraulic cylinder is contracted, it rotates he holding device 3 in a clockwise direction around the axis 5. Thereby, the pressing elements 7 provide return stroke motions such that a pressed blanket 1 is released. Fig. 3 shows the press machine when the hydraulic cylinder 1 1 has been activated and displaced the pressing elements 7 radially inwardly. The pressing surfaces 7c of the pressing elements have here pressed together and formed the peripheral surface of a blanket 1 . When a pressing operation has been finished, the holding device is rotated back to the position shown in Fig. 1 .

Figs. 4-6 show a cross section view through the plane B-B in Fig. 2 during different phases of a pressing operation in the press machine. The guiding elements 3b are fixedly arranged radially internally of the peripheral portion 3a at uniform intervals. Each of the guiding elements 3b are arranged in a position radially outwardly of a pressing elements 7. The guiding elements 3b are provided with a curved guiding surface 3c adapted to be in contact with a correspondingly curved contact surface 7d of a pressing element 7. The guiding surfaces have a curvature such that different areas of the guiding surfaces 3c are located at varying distances from the axis 5. The guiding surfaces 3c and the contact surfaces 7d have a curved shape which constitutes a part of a circle 14 in a perpendicular plane to the axis 5.

During operation of the press machine, a blanket 1 is applied in the opening 6 when the pressing elements 7 are in a retracted position. Thereafter, the hydraulic cylinder 1 1 is activated which is prolonged such that it rotates the holding device 3 in a counter-clockwise direction around the axis 5. Thereby, the guiding elements 3b are also rotated in relation to the pressing elements 7, which thus are displaceable only in a radial direction in relation to the axis 5. The contact surfaces 7d of the pressing elements thereby slide along the guiding surfaces 3c of the guiding elements. During this sliding motion, the contact

surfaces 7d of the pressing elements will successively come in contact with guiding surfaces 3c which are located at an ever decreasing radially distance from the axis 5. Due to this fact, the pressing elements 7 are displaced continuously radially inwardly by the guiding surfaces 3c. Fig. 5 shows the pressing elements 7 when they have been displaced to a position in which the pressing surfaces 7c have come in contact with the peripheral surface of the blanket 1 . This first part of the stroke motion of the pressing elements 7 towards the peripheral surface of the blanket 1 may be performed relatively quickly and without any appreciable force.

Thereafter, the hydraulic cylinder 1 1 must supply an essentially larger force to provide a continuous rotation of the holding device 3 in a counter-clockwise direction around the axis 5. The contact surfaces 7d of the pressing elements continue to slide along the guiding surfaces 3c of the guiding elements and thus come in contact with the guiding surfaces 3c which are located at an ever decreasing radially distance from the axis 5. The guiding surfaces 3c press the pressing elements 7 radially inwardly such that the pressing surfaces 7c press together and form the peripheral surface of the blanket 1. When the blanket 1 has obtained a desired shape and dimension, the extension of the hydraulic cylinder 1 1 ceases and the rotary motion of the holding device 3. Fig. 6 shows when the pressing elements 7 have been displaced to a position where the blanket 1 has obtained a pressing to a desired shape and dimension. This part of the stroke motion of the pressing elements 7, which comprises a plastic forming of the peripheral surface of the blanket, is performed more slowly and it requires a large force.

Thereafter, the hydraulic cylinder is activated such that it rotates the holding device 3 in en clockwise direction around the axis 5 back to the position shown in Fig. 1. The power members 10 supply here a force keeping the contact surfaces 7d of the pressing elements in continuous contact with the guiding

surfaces 3c of the guiding elements. Thus, the contact surfaces 7d of the pressing elements will be sliding along the guiding surfaces 3c of the guiding elements also during this rotary motion. When the holding device is rotated in this direction, the contact surfaces 7d come in contact with guiding surfaces 3c which are located at an ever increasing radially distance from the axis 5. The pressing elements 7 are thus displaced radially outwardly by the holding device 3 until they reach the completely retracted position. When the pressing elements 7 reach this position, the formed blanket may be picked out and be replaced by another blanket 1 to be formed.

Consequently, the press machine, according to the invention, does only need to be provided with one hydraulic cylinder for performing the above described pressing operation. By means of the lever 13 and the sloping guiding surfaces 3c, a considerable force increase may be obtained. Thus, it is possible to provide a large pressing force on each individual pressing element 7 by only one hydraulic cylinder 1 1 . This force increase also results in the hydraulic cylinder 1 1 having to be prolonged a longer distance than the stroke motion of the pressing elements. Thus, an accurate control of the stroke length of the cylinder 1 1 may result in an even more accurate determination of the stroke motion of the pressing elements. The use of only one hydraulic cylinder 1 1 to activate all the pressing elements also guarantees a uniform activation of the pressing elements 7 which further increases the pressing accuracy.

In order to make it possible to transmit a large pressing force from the guiding surfaces 3c of the guiding elements to the contact surfaces 7d of the pressing elements during en pressing operation, it is required that the surfaces 3c, 7d are in continuous contact with each other in a relatively large contact area. Thus, point loads must be avoided since the surfaces in such cases would be deformed or worn down very quickly. The only possible shape which the surfaces 3c, 7d can have which

makes a continuous mutual contact possible within a relatively large contact area, is if the surfaces have a circular shape in a plane perpendicular to the axis 5. In the shown example, the guiding surfaces 3c and the contact surfaces 7d are in sliding contact with each other within a contact area which has a substantially constant size in said plane during the entire stroke motion of the pressing element 7. Alternatively, the contact area would be made smaller during the part of stroke motion when the pressing elements 7 are displaced to the peripheral surface of a blanket since this motion does not require any appreciable force.

Figs. 7 and 8 show a way to determine the size and the orientation of the circle 14 which defines the curved shape of the guiding surfaces 3c and the contact surfaces 7d. Fig. 7 shows the press machine in non-activated state. In this state, a first contact point pi of the guiding surface 3c of a guiding element 3b is in contact with a point p ₀ of the contact surface 7d of the pressing elements 7. Fig. 8 shows the press machine in a concluding pressing state. In this state, the peripheral portion 3a of the holding devices and thus the guiding element 3c have been rotated in a counter-clockwise direction around the axis 5 such that the guiding surface 3c of the guiding element 3b has performed a sliding motion in relation to the contact surface 7d of the pressing elements 7. En second contact point p ₂ of the guiding surface 3c has here been displaced to contact with the point po of the contact surface 7d of the pressing element 7. The pressing element 7 has during this motion been displaced radially inwardly towards the axis 5. By drawing two straight lines from point p ₂ to the axis 5 in the two states, an angle x is obtained, around which the point p ₂ is rotated around the axis 5 during the stroke motion of the pressing elements. Point P ₁ as well as the guiding surface 3c as a whole are rotated a corresponding angle x around the axis 5. The points P ₁ , p ₂ of the guiding surface 3c provide a rotary motion around the axis 5 along a curved sliding path which thus constitutes a part of a

circle 14. The radial distances of the points P ₁ and p ₂ to the axis 5 are selected such that the pressing elements 7 are displaced a desired distance in a radial direction towards the axis 5 during the rotary motion of the guiding elements 3b.

In order to have the points P ₁ , p ₂ of the guiding surface 3c to follow a curve, which self compensates for the angle adjustments arisen during the rotary motion of the guiding surface 3c around the axis 5, the following condition has to be fulfilled. The points P ₁ , p ₂ of the guiding surface 3c must, when they are rotated an angle x around the axis 5, at the same time be rotated a corresponding angle x around a centre 15 of the circle 14. The angle part of the sliding path of the circle 14 will thus be just as large as the angle part of the sliding path of a circle extending around the axis 5. Such a circle extending around the axis 5 may be defined by the peripheral portion 3a of the holding devices. Certainly, the positioning of the circle 14 must be such that it extends through the points P ₁ , p ₂ and touches the guiding surface 3c. By this procedure, the fault, which otherwise arises between the guiding surface 3c and the contact surface 7d of the pressing element during the pressing operation is minimised, even substantially eliminated.

The present invention in not in any way restricted to the above described embodiments but may be modified freely within the scope of the claims.