Abstract:
A belt press use a combination of vacuum and atmospheric pressure to provide the majority of the compressive force between platens. A first platen has a substantially rigid proximal side and a plurality of vacuum ports communicating therewith. The compressive force is generated by pulling a vacuum at the vacuum ports associated with the first platen while allowing atmospheric pressure to act against its distal side. Heat may be applied via at least one of the platens while generating the compressive force. Evolved gases are vented via the vacuum ports while applying the heat by continuing to pull the vacuum during heating. When the now-joined belt ends have cooled after the application of heat, the compressive force is relieved by ceasing the pulling the vacuum at the vacuum ports associated with the first platen. The second platen of the belt press may be similar to the first platen.

Description:
BACKGROUND OF THE INVENTION 
     The present invention relates generally to presses for forming belt joints, and more particularly to a press typically used for joining belt ends to form a belt joint. 
     Belts, and more particularly conveyor belts, are typically manufactured in long strips which are spliced together in one or more locations to form a continuous loop. Due to the stresses imposed on the conveyor belts, it is important that the splice be as high a quality as possible so as to prevent, or at least delay, belt failure at the splice. Over time, a number of methods have been employed to splice belt ends together. The simplest method is the butt splice where the opposing ends of the belt are cut and then bonded together, such as by glue or stapling. Such butt splices are weak. Stronger splices are achieved when there is some sort of overlapping of the two belt ends, such as when the top half of one end and the bottom half of the other end are removed and the complementary portions of the ends are overlapped and bonded together by gluing, etc., and thereafter vulcanized with presses having heated platens. For some applications, it is desirable to form stepped splices having staggered overlapping levels, as disclosed in U.S. Pat. Nos. 5,974,935 and 6,228,200, incorporated herein by reference. In addition, the belt material of the complementary opposing ends may be formed into an interleaved finger arrangement. 
     A number of belt presses have been designed. Typically, such presses rely on either hydraulic pressure or inflatable bladders to supply the compression force between opposing platens. For instance, U.S. Pat. No. 4,946,541 to Thies et al. discloses a hydraulic press, while U.S. Pat. No. 5,562,796 to Ertel discloses a inflatable bladder press. Hydraulic presses suffer from the disadvantages of requiring extra equipment, such as hydraulic pressure sources, and being unduly complicated. Inflatable bladder presses likewise require additional equipment, such as high pressure air supplies, involve undue complexity, and suffer from the potential for bladder failure. In addition, both types of belt presses require strong, massive reinforcing structures to handle the forces within the presses. Such reinforcing structures are heavy, cumbersome to move, and typically requires extensive assembly on-site. 
     In light of the above, there remains a need for a simplified belt press which can provide reliable performance for forming belt joints. 
     SUMMARY OF THE INVENTION 
     The belt press of the present invention generates a compression force between press surfaces facing a belt material, for joining or repairing the belt material, by pulling a vacuum on one side of at least one substantially rigid platen. In this manner, the present invention utlizes a combination of vacuum and atmospheric pressure to provide the majority of the compressive force between platens of a belt press. 
     Two belt ends are disposed between first and second platens, the first and second platens having respective substantially rigid proximal sides. At least the first platen has a plurality of vacuum ports communicating with its proximal side. A compressive force is generated between the proximal sides of the first and second platens by pulling a vacuum at the vacuum ports associated with the first platen while allowing atmospheric pressure to act against a distal side of the first platen. The vacuum may be applied at both a first group of larger ports disposed generally proximate a perimeter of the proximal surface of the first platen and at a second group of ports, smaller in size, disposed inwardly from the first group. Heat may be applied to the two belt ends via at least one of the first and second platens while generating the compressive force. Evolved gases are vented via the vacuum ports while applying the heat by continuing to pull the vacuum during heating. When the now-joined belt ends have cooled after the application of heat, the compressive force is relieved by ceasing the pulling the vacuum at the vacuum ports associated with the first platen. 
     The second platen of the belt press may be similar to the first platen. Accordingly, the second platen may have a plurality of vacuum ports communicating with its proximal side and the compressive force may be generated between the proximal sides of the first and second platens by pulling a vacuum at the both the vacuum ports associated with the first platen and the vacuum ports associated with the second platen. 
    
    
     BRIEF DESCRIPTION OF THE DRAWINGS 
     FIG. 1 is a side view of one embodiment of the belt press of the present invention. 
     FIG. 2 is a lateral cross-section view of one embodiment of the belt press of the present invention with the release paper removed for clarity. 
     FIG. 3 is a view of the proximal surface of the plate of a platen assembly showing one possible hole location and size relationship. 
    
    
     DETAILED DESCRIPTION 
     The present invention utilizes a combination of vacuum and atmospheric pressure to provide the majority of the compressive force between platens of a belt press  10 . The belt press  10  may be used for joining new, or repairing old, conveyor belts or power transmission belts, and the like, but the invention is not so limited. For instance, the belt press  10  may be used to add or repair molding on belts, or to emboss belts, both of which fall within the scope of the present invention. The belt press  10  is particularly adapted for rubber belts, but may be used on belts of various thermoplastic materials. 
     One embodiment of the belt press  10  of the present invention is shown in FIGS. 1-3. The belt press  10  includes two platen assemblies, which will be referred to as the upper platen assembly  20  and the lower platen assembly  70 , and a vacuum source. The upper platen assembly (or the upper platen)  20  is disposed generally parallel to the lower platen assembly (or lower platen)  70 , but spaced apart therefrom. The space between the platen assemblies  20 , 70  is for the belt material  14  to occupy. For ease of reference, the terms “proximal” and “distal,” as used herein, relate to distance from the space normally occupied by the belt material  14 . Therefore, the proximal side  22  of the upper platen assembly  20  is located proximate the belt material  14  and the distal side is spaced from the belt material  14 . Likewise, the proximal side  72  of the lower platen assembly  70  is located proximate the belt material  14  and the distal side is spaced from the belt material  14 . 
     The upper platen assembly  20  has a proximal surface  22  (sometimes referred to as a press surface) and a distal side  24 . The upper platen assembly  20  includes a main plate  30  with a mesh layer  38  abutting thereto on its proximal side and a channel frame  40  mated thereto on its distal side. The plate  30  is either substantially rigid by itself or is made substantially rigid through support of other portions of the upper platen assembly  20  (e.g., the channel frame  40  discussed below). The plate  30  may be made from any suitable material, such as aluminum or steel. The plate  30  includes a plurality of holes, which in preferred embodiments may be conceptually divided into perimeter holes  32  and interior holes  34 . The perimeter holes  32  are disposed towards the perimeter of the plate  30 , while the interior holes  34  are disposed inward of the perimeter holes  32 . Better press performance may be achieved when the perimeter holes  32  are larger in size than the interior holes  34 , such as an order of magnitude larger. These holes  32 , 34  may be sometimes referred to herein a “ports” or “vacuum ports” due to their function, as described further below. 
     The mesh layer  38  is intended to help distribute the contact pressure between the upper platen assembly  20  and the belt material  14  so as to help avoid local deformations of the belt material  14 . The mesh layer  38  may be a tightly woven fine mesh and may be permanently joined to the main plate  30 . However, the mesh  38  may alternatively be releasably mated to the main plate  30  so that the mesh  38  may be replaced if damaged; for instance, the mesh  38  may be joined to a perimeter frame that attaches to other portions of the upper platen assembly  20  so that the mesh is held against the proximal side of the main plate  30 . The perimeter edges of the mesh  38  should be crimped or otherwise sealed to help prevent the entry of air around the perimeter of the mesh  38 . Further, there may be a perimeter gasket (not shown) to aid in forming a better seal around the perimeter edges of the mesh  38  and/or upper platen assembly. 
     The channel frame  40  is a relatively rigid structure typically made from aluminum channels. The channel frame  40  includes a number of holes that connect with a series of internal ducts  44 . The internal ducts  44 , in turn, connect with one or more vacuum nozzles  26 . The internal ducts  44  may be formed, in whole or in part, by suitable reinforcing ribs  42  disposed within the channel frame  40 . In addition, the channel frame  40  may include a number of internal conduits  46 , with some of the conduits  46  adapted to hold resistance heating elements  48  and other of the conduits  46  adapted to form a cooling water circulation system for cooling the platen assembly  20 . In addition, the channel frame  40  may have handles (not shown) disposed at suitable locations on its perimeter to aid in handling the upper platen assembly  20 . 
     The plate  30  and the channel frame  40  are aligned such that the holes  32 , 34  on the distal side of the plate  30  are aligned with the holes on proximal side of the channel frame  30 . In this manner, a flow path is formed from the holes  32 , 34  on the proximal side of the plate  30  to the vacuum nozzle  26 , such that a vacuum pulled at the vacuum nozzle  26  creates a vacuum at the holes  32 , 34  on the proximal side of the plate  30 , via the ducts  44 . Further, due to the nature of the mesh layer  38 , this vacuum is transmitted to the proximal surface  22  of the upper platen assembly  20 . 
     The upper platen assembly  20  may also include an insulation layer  50 , if desired, inside or over the channel frame  40 , or at other appropriate locations that do not interfere with the application of vacuum pressure to the proximal surface  22  of the plate  30 . 
     For some embodiments, the lower platen assembly  70  may be simple plate. However, in preferred embodiments, the lower platen assembly  70  is identical to the upper platen assembly  20 , but inverted so that the respective proximal surfaces  72 , 22  face each other. In the preferred embodiments, the two platen assemblies  20 ,  70  cooperate to generate a compressive force between the proximal surfaces  22 , 72 , as discussed further below. As such, it is preferred that the two proximal surfaces  22 , 72  be disposed generally parallel on opposite side of the belt material  14  during the compression portion of the press operating cycle. 
     The vacuum source  80  connects to the vacuum nozzle(s)  26 , via one or more suitable hoses. The vacuum source  80  includes a reservoir  82 , a valve  84 , and a pump  86 . The reservoir  82  is designed to hold a “charge” of vacuum. The capacity of the vacuum reservoir  82  should be larger than the capacity of the corresponding vacuum flow path (e.g., ducts  44 , etc.), and preferably much larger than, such as an order of magnitude larger. The reservoir  82  may be intermittently or continuously charged using a suitable vacuum pump  86 , as is well known in the vacuum art. Valve  84  controls the supply of vacuum pressure to the vacuum nozzle(s)  26 . 
     To illustrate the operation of the belt press  10 , it will be assumed that the belt press  10  is being used to join two belt ends  14   a , 14   b  to form a belt joint for a continuous belt. However, it is be understood that the belt press  10  may be used in other situations such as for repairing worn spots on belts and the like. The two belt ends  14   a , 14   b  are prepared in a conventional fashion and placed near each other on the proximal side of the lower platen assembly  70  so that they overlap in the typical fashion. The belt ends  14   a , 14   b  may be placed directly on the lower platen assembly  70 , or an optional porous release paper  16 , such as silicone coated porous release paper, may be placed between the belt material  14  and the platen assembly  70 . The upper platen assembly  20  may then be placed over the lower platen assembly  70 , sandwiching the belt material  14  between the two platen assemblies  20 , 70 . Once again, while not required, the porous release paper  16  may be placed between the belt material  14  and the upper platen assembly  20 . The respective positions of the platen assemblies  20 , 70  may be secured prior to application of vacuum, if desired, by suitable light hand clamps or the like. The vacuum reservoir  82  is charged with the valve  84  closed. At this point, negligible force is acting on the belt material  14 , essentially only that generated by the weight of the upper platen assembly  20 . As the upper platen assembly  20  is preferably relatively light, this force is relatively small. In order to apply the much higher compressive forces desired to form good belt joints, the valve  84  of the vacuum supply  80  is opened (preferably very quickly), thereby supplying vacuum to the vacuum nozzles  26  from the vacuum source  80 . This vacuum is transmitted via the internal ducts  44 , holes in the channel frame  40 , holes  32 , 34 , the mesh  38 , and the optional porous release paper  16  (collectively the “vacuum path”) to the proximal surface  22  of the platen assembly  20 . Any air or other gases present are sucked through the vacuum path, creating a low pressure area under the upper platen assembly  20 . The action of atmospheric pressure acting on the distal side of the platen assembly  20  forces the platen assembly  20  downward, as there is little or no corresponding pressure from underneath the platen assembly  20 . Thus, the difference between atmospheric pressure and the vacuum pressure supplies the compressive force that pushes the proximal surface  22  of the upper platen assembly  20  against the belt material  14 , including the belt ends  14   a , 14   b . Assuming the lower platen assembly  70  is similar to the upper platen assembly  20 , the combination of vacuum/atmospheric pressure also supplies the compressive force that pushes the proximal surface  72  of the lower platen assembly  70  against the belt material  14 . Assuming that the vacuum pressure is very “low” as measured in psia, the forces on the platens  20 , 70  may be very large, as the pressure differential may approach 11-14.7 psia. Thus, modest size platens, of dimensions thirty inches by thirty inches, may generate over ten thousand pounds of compressive force. 
     The use of different size holes  32 , 34  in the plate  30 , with the perimeter holes  32  being larger than the interior holes  34 , allows for a grabbing action to occur upon initial vacuum application. However, even the larger perimeter holes  32  should not be so large as to allow “dimples” to form on the belt material  14  when the pressure is applied. The inclusion of the mesh  38  on the proximal side  22 , 72  of the platen assemblies  20 , 70  helps prevent the formation of such localized deformations by distributing the vacuum “pull.” Likewise, the presence of the channel frame  40  distal from the plate  30  helps more uniformly apply the force from atmospheric pressure against the plate  30 , leading to a more uniform application of force against the belt material  14 . Further, because the cross-sectional area of the ducts  44  is typically much larger than the cross-sectional area of the corresponding holes  32 , 34 , with each duct  44  preferably serving multiple holes  32 , 34 , good vacuum pull may be generated and/or maintained even when one or more holes  32 , 34  are experiencing partial actual air flow (ambient air leaking in and/or venting of evolved gases discussed below). 
     With the pressure applied, via continued application of vacuum pressure at the appropriate vacuum nozzles  26 , the heating elements  48  of the channel frame  40  are energized to heat the belt ends  14   a , 14   b . As the belt ends  14   a , 14   b  heat up, it is common for the belt ends  14   a , 14   b  and/or any adhesive/joint compounds employed to generate evolved gases, sometimes referred to as outgases. These outgases cause significant problems in the prior art, such as by creating bubbles in the belt material  14 ; this is one reason high forces are required during belt joint formation. In contrast, the belt press  10  of the present invention helps prevent the harmful build up of these outgases by exhausting them through the vacuum path via the “pull” of the vacuum. Thus, the vacuum serves two functions—compressive force generation and outgas exhausting. In addition, the substantial rigidity of the platen assemblies  20 , 70 , particularly the respective plates  30 , helps prevent formation of undesirable deformations. 
     The belt press  10  is held at the desired temperature for a suitable time, such as ten minutes, and then the heating may be terminated so that the belt material  14  may cool. Cooling fluid may be pumped through the conduits  46  in the channel frame  40  to aid in cooling the now-joined belt material  14 . After suitable cooling, the compressive pressure may be removed. To release the compressive pressure, the vacuum nozzle(s)  26  are opened to atmospheric pressure, thereby eliminating the vacuum against the proximal sides  22 , 72  of the platen assemblies  20 , 70 . This “vacuum release” may, for instance, be accomplished by closing the valve  84  and opening an atmosphere inlet (not shown) in the hose leading to the vacuum nozzle(s)  26 . The belt material  14  may then be exposed by moving the upper platen assembly  20 , and the now-joined belt material  14  may then be removed from the belt press  10 . 
     In the description above, reference has been made to pulling or applying a “vacuum.” This term “vacuum” is not used herein in it strict scientific sense (i.e., complete or almost complete lack of pressure), but is instead used herein to indicate pressures significantly below ambient atmospheric pressures. Thus, assuming that ambient atmospheric pressure is 14.7 psia, a pressure of, for example, 8 psia, would be a “vacuum” as that term is used herein. 
     In one exemplary 30″×30″ platen embodiment, the plate  30  may be made from 10 gage or 16 gage aluminum, with the channel frame  40  made from a plurality of approximately one inch tall 16 gage aluminum ribs bent in a wave or z-shape (when viewed from above) disposed above (distally) from a series of ½×2 inch extruded aluminum channels with the conduits  46  formed during extrusion. The mesh  38  is made from approximately 0.020-0.025 inches thick stainless steel, with a mesh size of 100-200 mesh, and a 1½ inch perimeter gasket. The interior holes  34  may be {fraction (1/32)} inch diameter, with one interior hole  34  per square inch, and the perimeter holes  32  may be ¼ inch diameter, placed one inch apart, generally as shown in FIG.  3 . This exemplary 30″×30″ platen embodiment produced good results when used with the porous release paper  16 . 
     It should be noted that the use of the porous release paper  16  aids in transferring the vacuum pressure to the belt material  14 , and helps prevent the belt material from entering the fine mesh  38  on the proximal side of the platen assemblies  20 , 70 . However, acceptable results might be possible without the porous release paper  16  under some circumstances. 
     The discussion above has assumed that, when the lower platen  70  is operating similar to the upper platen  20 , the vacuum source  80  connects to the vacuum nozzles  26  on both the upper platen  20  and the lower platen  70  via valve  84 . However, in such circumstances, the lower platen  70  may alternatively have its own dedicated line to the vacuum source  80  with its own valve and/or the lower platen  70  may have a completely separate vacuum source. Indeed, it is not required that the lower platen  70  be “vacuum powered” like the upper platen  20  in all embodiments. As such, the lower platen  70  is shown connected to the vacuum source  80  via a dashed line in FIG.  1 . 
     The present invention may, of course, be carried out in other specific ways than those herein set forth without departing from the essential characteristics of the invention. The present embodiments are, therefore, to be considered in all respects as illustrative and not restrictive, and all changes coming within the meaning and equivalency range of the appended claims are intended to be embraced therein.