Means For Maintaining Spacing In A Continuous Press

Abstract

An improved apparatus for maintaining constant spacing in a continuous press of the type which has two rotatively driven endless conveyor belts forming opposed, substantially linear spans defining a press zone with press platens applying pressure through the travelling spans to work carried therebetween in which a plurality of hydraulic cylinders or spindles are inserted between the press platens and rigid supports, with pressure supplied to the cylinders through a pressure controlling valve or guiding valve which is sensitive to movement of the pressure platen to regulate the pressure in the cylinders thereby maintaining a constant platen spacing.

Description

BACKGROUND OF THE INVENTION

This invention relates to presses of the type wherein two pressure platens are each supported by a support construction so that the forces of each of the press platens are transmitted to their corresponding support construction and more particularly such a press in which the transmittal of force from the press platens to the corresponding support construction is by means of a pressure fluid contained in a pressure element positioned between the platen and its respective support construction.

A press of this nature is described in U.S. Application Ser. No. 308,556.The press disclosed therein is a continuous press for the manufacture of wood chip board and the like in which the material to be treated is moved continuously between two flexible endless conveyor belt spans. Between the belts spans forming the press zone and the press platens a plurality of rotatively unpowered endless loops of roller chain are used, these roller chains being packed transversely together to form a bed interposed between the platens and the seal strip conveyor belts. The press platens in turn are positioned between support constructions comprising beams each positioned transversely to the movement of the belts with portions of such beams extending longitudinally above and below the press platens for the length of a press.

In one illustrated embodiment of the above application, a hydraulic pressure cushion or a series of hydraulically connected pressure vessels are positioned between the beams and the pressure platens. Such an arrangement causes transverse pressure on the work between the belts to be transmitted from the belt through the chain and the press platen to the beam, making possible equal pressure over the width of the work even when the beams deflect under forces acting thereon. In the construction shown in U.S. application Ser. No. 308,556each pair of beams is connected at each end by an actuator which comprises either a motorized or mechanical spindle or a hydraulic cylinder which can be positioned so as to determine the distance of the upper and lower belt and thus the ultimate thickness of the work. Regulation of such a spindle or hydraulic cylinder must be made with respect to the total forces and thus is very expensive. If a change in the counter pressure exerted by the work occurs, a hydraulically sensitive adjustment is not possible in this arrangement and thus variations in the thickness of work may occur before any regulation is effected.

Thus, it can be seen that there is a need to connect the beams in a simpler manner and be able to maintain constant thickness of the work under conditions of varying counter pressure.

SUMMARY OF THE INVENTION

The present invention provides an arrangement which solves these problems and permits constructing a press in which the regulation of the distance between the press platens is obtained with more accuracy, increase sensitivity and at a lower cost.

In order to achieve these objects, a rigid support is provided between the support connections, i.e., between the beams. To maintain accurate spacing of the platens, a guiding valve is installed which is sensitive to platen motion and regulates the pressure in the pressure elements installed between the platens and the beams so as to maintain a predetermined distance between the press platens.

In contrast to the previously disclosed press, in which the support elements, i.e., the beams, were each adjustable with respect to one another by means of the hydraulic cylinder or spindles which because of the need to use the total forces involved, resulting in a correspondingly expensive system, the supports in the present invention are rigidly connected with one another resulting in a simplicity of design. The pressure elements between the platens and the supports work directly against the press platens and can follow changes in pressure much more rapidly than when a shift in the relative position of the entire support structure must be made. The guiding valve is arranged so that when the distance between the press platens is as predetermined, the valve is inactive. A pressure pump coupled through the valve then causes an increase in the pressure in the pressure elements until the press platens begin to move together changing their position. At that point the guide valve opens to allow a bleed off of hydraulic fluid relieving the pressure so that the press platen moves back in a direction to cause it to again be at the predetermined distance, whereupon reaching this predetermined distance, the valve becomes inactive. Through this arrangement a dynamic balance about the predetermined distance betwee the platens is achieved. The extremely small variations which occur during this dynamic operation are well within the tolerances required and overall spacing accuracy is maintained to a much higher degree than was heretofore possible.

In simplest terms, the guide valve of the present invention may comprise two parts movable with respect to one another, one of which is connected to the press platen and the other with corresponding beam. The guide valve has an inlet which is connected to the pressure medium pump and a first outlet connected to the pressure element between the beam and the platen. A second outlet to a reservoir is constructed so as to normally be blocked off when the platen is properly positioned. Movement of the platen from the predetermined position will, however, open this second outlet permitting a reduction in pressure and causing the platen to return to its predetermined position. In the preferred embodiment of the invention the guide valve comprises a glide valve operating parallel to the direction of movement of the press platens having a sliding element which has a sealing surface at its leading frontal edge, which sealing surface operates in a sealing manner with a counter surface into which is formed a channel opening to the inlet. The second outlet is located in the housing of the longitudinal glide valve at a level corresponding the sealing surface and the counter surfaces.

In this preferred embodiment the sliding member is coupled to the press platen and the valve housing to the beam. Obviously, the connections can be reversed. As long as a leading frontal surface of the sliding member abuts a counter surface, no pressure medium can pass out of the channel opening in the counter surface. Under these conditions the connection between the inlet and the first outlet to the pressure element permits the full inlet pressure to be passed through. This creates forces which increase tending to displace the press platen away from the board as it is acted on by the counter pressure of the work. The slide element connected to the press platen moves therewith thus separating its sealing surface from the counter surface. This results in the connection between the channel in the counter surface and the second valve being opened permitting the pressure medium to be diverted into the reserve container thereby causing the pressure in the pressure element to drop and the pressure platen to move until the point in motion where the sealing surface of this sliding member again abuts the counter surface. Thus, the position of the counter surface determines the position to which the press platen will always return.

This, in turn, permits adjustment of the position of the press platen and thus distance between the upper and lower press platens thereby controlling the thickness of the work. To accomplish this, the counter surface is placed on a counter sliding element which may be positioned axially within the valve body. Preferably, such positioning can be done through the use of a threaded spindle protruding into the housing. In order to avoid skewing of the press platens, a plurality of pairs of guide valves on each side of the platen can be provided. In such a case, it is preferable to drive the threaded spindles used for positioning the counter slide element using a common drive means in order to obtain parallel positioning of the press platen.

BRIEF DESCRIPTION OF THE DRAWINGS

FIG. 1 is an end view of the pressure of the present invention.

FIG. 2 is a cross-sectional view of the guide valve of the present invention.

DESCRIPTION OF THE PREFERRED EMBODIMENT

As illustrated in FIG. 1, the work 1 such as wood chips or the like which are to be pressed together to form press board or the like is passed between two endless conveyor belt loops 2, 3 made of thin strip metal in the manner described in the above identified copending U.S. application. Typically the conveyor belt loops 2, 3 will have a thickness of about 1to 1.5mm. The work 1 and the belts 2, 3 as shown in FIG. 1 move perpendicular to the plane of the drawing. The belts 2 and 3 move endlessly and return above and below the construction of FIG. 1 to the beginning of the press zone. Each of the belts 2 and 3 is supported by a press platen designated respectively 5 and 6 through roller chains 4. The press platen 5 comprises a heatable platen 5' through which pressure and temperature is transmitted to the roller chains, a grooved return platen 5" and an insulating intermediate platen 5'". As described in the above referenced application, the roller chain loops move to the end of the press section and reverse their direction over the edge of the press platen 5 and 6 and return without any forces thereon through the channels 11 in the inner portions of the press platens 5 and 6 to return to the lower end of the press platen where they again reverse direction and pass between the press platen and the belts 2 and 3. The press platen 6 is made up of the same segments as were described above in connection with press platen 5. For purposes of simplification, the roller chains 4 are shown as small rectangles on the drawing. More detail as to the actual construction thereof may be had from the above referenced U.S. application.

The platens 5, 6 are arranged between a support construction which comprises heavy I beams 7 and 8 oriented transversely to the direction of the work. Individual pairs of upper and lower beams 7 and 8 are connected at a point beyond the edge of the work and the belts 2 and 3 to a yoke 9. Connection is made by means of welding or through the use of nuts and bolts. The sequence of pairs of beams joined by yokes at their edges are positioned along the path of the belts 2 and 3. Between each lower I beam 8 and lower press platen 6 there are provided pressure vessels 10 which transmit pressure to the work 1 by lifting the platen 6 in the direction of the platen 5. The pressure vessels 10 between the I beam 8 and the platen 6 are hydraulically coupled so that hydraulic pressure is uniform along the width of the work 1 irrespective of any deflection of the beams 7, 8. Alternatively, instead of using individual pressure vessels 10, which are constructed as cylindrical units, which construction has certain manufacturing advantages, a single hydraulic pressure cushion or pressure chamber may be positioned across the entire width of the work.

At each end of the beam 8 a guide valve 20 is provided [only half of the press apparatus is shown so that only one yoke 9 and guide valve 20 is illustrated. It will be recognized that the same construction is present on the other side of the press.] The housing of the valve 20 is connected to the I beam 8. It has a thrust transmitting member 21 which is coupled to an intermediate platen 12 which is installed between the press platen 6 and the pressure vessel 10 extending parallel to the work 1 over its entire width. Thus, the thrust transmitting members 21 are connected directly with the press platen 6 and transmit their motion directly to the guide valves 20, the axes of which guide valves are parallel to the direction of the action of the pressure vessels and to the direction of the motion of the pressure vessels and the press platen 6.

FIG. 2 illustrates the construction of the guide valve in detail. The guide valve 20 comprises a cylindrical housing 22 into which are inserted cylindrical gliding bushings 23 and 24. As illustrated, the gliding bushings 23, 24 are inserted from each end and bolted into place. Within the gliding bushing 23, mounted for sliding motion therein is a slide 25. In order to avoid lateral transmission of forces, the transmitting member 21 is coupled to the slide 25 through a spherical cap or ball joint 26. Within the gliding bushing 24 is positioned a counter slide 27 which is axially displaceable therein. The counter slide 27 contains on its end a threaded spindle 29 which is threaded into an element 30 inserted in the end of the gliding bushing 24 and bolted to the housing 22. The counter slide 27 is coupled to the threaded spindle 29 through an axial ball bearing 28. Turning of the spindle 29 will result in positioning of the counter slide 27 up and down along the axis of the guide valve. A coupling 31 is provided for imparting rotary motion to the spindle 29.

The slide 25 contains at its leading edge a sealing surface 40. This comprises a ring formed ridge in a plane perpendicular to the plane of motion of the slide. The sealing surface 40 acts against a counter surface 41 on the counter slide 27. When the counter slide 27 and the slide 25 are in contact an effective seal is maintained to prevent any hydraulic fluid escaping from inside the sealing surface 40 to the outside.

An axial channel is formed in the center of the counter slide 27 running to the counter surface 41. This channel is connected with a circumferential groove 43 which is formed in the counter slide 27. A first inlet opening 43 is formed in the housing 22 and through the gliding bushing 24 to communicate with the groove 43. A passage through the groove 43 permits communication with the channel 42. A first outlet opening is formed on the other side of the housing being formed through the housing and the gliding bushing 24. The groove 43 is made with an enlarged width so that it will remain in communication with the inlet 44 and outlet 43 even as the counter slide is axially displaced. The width of this groove should be sufficient to allow communication over the range of work thicknesses expected to be processed in the press.

A second outlet 47 is provided which communicates with a groove 46 which is formed in a space between the bushings 23 and 24. This groove is formed in the area of the sealing surface 40 and the counter surface 41 and permits communication between the channel 42 and the outlet 47 when the sealing surface 40 and counter surface 41 are separated. The outlet 47 is coupled to a fluid reservoir via conventional hydraulic piping (not shown). The inlet 44 is coupled to a hydraulic pump and the first outlet 45 to the pressure vessels 10.

As illustrated in FIG. 1, the coupling 31 which displaces the counter slide 27 to adjust its position and thereby adjust the work thickness, is driven by a gear 50 which itself is driven by a pilot motor 51. A similar gear 50 will be provided to drive the coupling 31 associated with the guide valve on the other side of the press. Thus, there is shown a shaft 52 which couples the two gears 50 to insure that both valves are adjusted together to maintain the press platen 6 parallel. Additional valves 20 may be installed along the length of the press and similarly mechanically coupled to the pilot motor 51 to assure equal pressure over the press plate platen 6.

In operation, a pressure pump which is not shown supplies hydraulic fluid at a constant pressure to the inlet 44 of the guide valves 20. From the inlet, the hydraulic fluid passes through the groove 43 into the outlet 45 and then to the pressure vessels 10. This results in an increase in pressure in the pressure vessels causing them to tend to raise up the platen plate 6 away from the beam 8. The slide 25 which is coupled to the platen plate 6 moves therewith because of the pressure acting on the end surface of the slide through the channel 42 which is in communication with the inlet 44. This tends to push the slide away from the end surface 41 of the counter slide. When the pressure platen 6 is raised, the slide 25 will tend to follow it. As the slide 25 moves up, communication between the channel 42 and the second outlet 46 will be established. This will result in a reduction of pressure in the pressure vessels 10 and a tendency of the pressure platen to return to the position where the sealing surface 40 and counter surface 41 will again be in contact closing off the path to the reservoir and again causing an increase in pressure tending to push the platen plate upward through the action of the pressure vessel 10. The result is the establishment of a dynamic equilibrium with a small amount of motion about the pre-established position. The resulting dynamic balance is maintained despite any changes in the counter pressure exerted by the work. Should the counter pressure increase because of uneven distribution of material, the pressure in the pressure vessels 10 will increase correspondingly until the pressure platens begin to move upwardly and the bypass of the surface 40 and 41 occurs. Thus, under all conditions of counter pressure, proper thickness is maintained.

The thickness of the work is regulated by the positioning of the counter slide 27 through the use of the pilot motor 51. For each position of the counter surface 41, a different equilibrium position is established for the press platen 6. Through the inter-connection of all the guide valves, this is accomplished simultaneously and results in a parallel displacement of the press platen.

Although the guide valve of the present invention has been described in connection with a continuous press with horizontally travelling flexible endless conveyor belts, it will be recognized that it can equally well be used in other apparatus. These and other modifications may be made without departing from the spirit of the invention which is intended to be limited solely by the appended claims.

Claims

What is claimed is:

1. In a press having two press platens, each of which is supported on an external support construction wherein the force from one press platen is transmitted to its corresponding support construction through a pressure fluid within a pressure element positioned between the platen and its corresponding support construction, apparatus for maintaining constant spacing between the two press platens comprising:

a. means rigidly coupling the support constructions associated with each of said two press platens;

b. means for sensing deviations of one press platen from a predetermined position and for regulating the pressure elements so as to maintain said one press platen at said predetermined position during a pressing operation so as to maintain said predetermined position throughout the pressing operation.

2. Apparatus according to claim 1 in which said means for sensing and maintaining comprises a guide valve comprising:

a. a first element coupled to said one press platen;

b. a second element movable with respect to said first element and coupled to the support construction associated with said one press platen;

c. an inlet port in said valve;

d. a first outlet port in said valve coupled to said pressure element and in communication with said inlet port;

e. a second outlet port in said valve coupled to a reservoir; and

f. means responsive to relative movement of said two elements corresponding to movement from said predetermined position to couple said inlet with said second outlet.

3. Apparatus according to claim 2 wherein said guide valve is a longitudinal sliding valve which operates parallel to the direction of motion of said one pressure platen, said valve comprising:

a a valve housing;

b a slide having a sealing surface on its leading edge slidably mounted within said valve housing;

c a counter surface within said valve housing which cooperates with said sealing surface to form a seal when said slide and said counter surface are abutting;

d an inlet formed in said valve housing;

e a first outlet formed in said valve housing in communication with said inlet;

f a second outlet in said valve housing;

g a channel formed in said valve housing, said channel being in communication with said inlet and said counter surface, whereby said inlet will be sealed from said second outlet as long as the seal between said sealing surface and said counter surface is maintained.

4. Apparatus according to claim 3 wherein said counter surface is contained on the end of a counter slide slidably mounted within said housing and further including a threaded spindle engaging threads in said housing and in contact with said counter slide whereby the axial position of said counter slide may be adjusted.

5. Apparatus according to claim 4 wherein a plurality of guide valves are provided and further including means to jointly drive the spindles of each of said plurality of guide valves.