Abstract:
A conveyor belt for conveying product in a direction of travel having a plurality of pivotal transverse rods extending laterally across the belt, the transverse rods having inner and outer ends along inner and outer edges of the belt; a plurality of connecting links arranged in at least one longitudinal row along the inner and outer edges of the belt and pivotally interconnecting the inner and outer ends of the transverse rods, respectively, with each of the connecting links having a pair of openings extending laterally therethrough such that the transverse rods extend through the openings; and a weld connection between the rods and the connecting links, at least one weld connection including only a first weld point between a trailing side of the transverse rod and the connecting link. A method of manufacturing the conveyor belt includes providing a plurality of transverse rods, providing a plurality of connecting links having a first pair of openings extending laterally therethrough and a second pair of openings extending therethrough, arranging the transverse rods through the first and second pair of openings so as to pivotally interconnect the transverse rods in a longitudinally spaced arrangement, and welding the connecting links to the transverse rods at the first pair of openings on only a trailing side of the transverse rod.

Description:
CROSS-REFERENCE TO RELATED APPLICATIONS 
     This application is a continuation-in-part of U.S. patent application Ser. No. 09/335,687, filed Jun. 18, 1999, the entire contents of which are hereby incorporated by reference. 
    
    
     TECHNICAL FIELD 
     The present invention relates generally to a conveyor belt and a method of making the same and, more particularly, to a conveyor belt capable of withstanding increased belt tension and exhibiting an extended belt life. 
     BACKGROUND OF THE INVENTION 
     One of the most commonly used types of conveyor belts for carrying diverse products along both straight and horizontally curved paths is a grid conveyor belt. Examples of conventional grid conveyor belts are the Cam-Grid® and the heavy duty Cam-Grid® conveyor belts available from Cambridge, Inc., the assignee of the present invention. A grid conveyor belt is shown generally in FIGS. 1 and 2 by reference numeral  100 . Conveyor belt  100  includes a plurality of spaced transverse rods  110  slidably interconnected by at least two rows of U-shaped connecting links  120  disposed respectively along the inner and outer edges of the rods. The terminal ends of the transverse rods  110  are formed into enlarged heads or button heads  130  which retain the links on the rods and welds  140  are then provided to secure the link to the button head and to the rod, thereby preventing rotational movement of the links on the transverse rods. Alternatively, bar links may be provided between the button head and the U-shaped connecting link such that the weld therebetween is eliminated. The connecting links are disposed in a nested relationship relative to one another with slots being provided in the links in order to slidably receive the transverse rods. Although not illustrated, the transverse rods may also be provided with an overlay which can be used to support smaller products which may slip between the spacing of the rods or which must lay flat during the conveying operation. 
     Grid conveyor belts of this type have met with overwhelming market approval because of their ability to travel in straight line conveyor paths as well as in curved conveyor paths, thus making grid conveyor belts ideal for use on spiral cage conveyors. In a spiral cage conveyor, the belt travels in a helical or spiral direction and is driven by cage bars disposed within the center of the spiral which engage the inner edge of the conveyor belt. Despite their popularity and commercial success, however, grid conveyor belts are prone to a number of operational problems which result in undesirable performance characteristics and may ultimately lead to complete belt failure. Examples of such operational problems include weld fatigue, tenting, racking, buckling, and shug, each of which is further discussed below. 
     Referring to FIG. 2, the cage bars  150  of a spiral conveyor move slightly faster than the speed of the conveyor belt  100  in order to lower the tension in the belt. As a result, all of the belt and product weight is transmitted to the outer edge of the belt which is not collapsed. The outer edge links and the welds thereon are thereby placed under increased tension. Further, because the cage bars  150  are moving slightly faster than the conveyor belt  100 , the bars  150  tend to push the inner edge links and the welds thereon into slight compression. 
     The cyclic nature in which the tension is caused in the conveyor belt leads to a variety of possible causes for belt failure. More specifically, while the conveyor belt is running in a straight travel path, the tension in the conveyor belt is evenly distributed to both the inner and the outer edges. As the belt moves into a curved path, however, the outer edge of the conveyor belt receives a much greater portion of the belt tension while the inside edge is put under a slight compression or tension. Each time this situation arises, that is, each time the conveyor belt transitions between a straight path and a curved path, the welds between the transverse rods and the links pass through a “duty cycle.” Repeated duty cycles of this nature may eventually cause weld fatigue, which generally occurs first on the outer edge links where the higher magnitude of tension occurs and which is followed by weld fatigue of the inner edge links. 
     Referring also to FIG. 3, the conventional weld  140  between the connecting link and the transverse rod is subjected to a variety of forces during conveyor belt travel. That is, the weld is subjected to tension forces denoted by arrows A which represent the tension transmitted through the connecting link to the welded joint, and by torque and shear forces denoted by arrows B which represents the torque force encountered from the drive sprockets. The resulting combination of these forces may result in weld fatigue such that eventually the welded attachment point cracks, i.e., there is a weld failure. 
     While weld fatigue in itself may not significantly impede the operation of the conveyor system, it may be a precipitating factor for other belt problems, such as belt tenting. Belt tenting can be described as the connecting links bending upwards out of the travel plane of the conveyor belt. When the conveyor belt collapses into a turn, compressive forces act to collapse the inner edge links and thereby allow the belt to traverse the curved path. However, without the presence of secure welds to restrict the rotational movement of the link relative to the rod, the links may raise out of the travel plane of the conveyor belt and form an upstanding tent. Tenting may cause undesirable movement and damage to the conveyed product, as well as a complete failure of the conveying system if machinery components should become jammed as a result of the raised or tented connecting links. 
     In addition to the welds creating a potential source for system failure, the structural limitations of the transverse rods may also lead to a variety of belt problems such as, for example, racking and buckling, which are a result of the rods flexing when they are driven. Racking occurs when the outside edge of the conveyor belt leads the inner edge of the conveyor belt, or vice versa, due to the increasing tension in the conveyor belt exceeding the bending strength of the transverse rod. Thus, as the conveyor belt traverses either a drive sprocket, idler roll, or the like, it may cause damage to the rods, overlays, and/or sprockets, in addition to causing damage to the conveyed product and misalignment of the conveying system. A further condition which may arise when the strength of the transverse rod is exceeded by the tension in the conveyor belt is buckling. Buckling generally involves a bending of the transverse rod in one or more places when the rods are pushed into the cage bars of a spiral conveyor or into dead curves because of the increased tension in the conveyor belt. Buckling may cause rod failure and product damage, and in the worse case, it can also lead to structural jamming and failure of the conveying system. 
     Finally, although not directly related to the failure of any particular conveyor belt component, grid conveyor belts may also suffer from the phenomenon of belt shug. Since the connecting links of a conveyor belt are disposed in a nested relationship relative to one another, an internal clearance is produced between the mating links when in the extended position. As shown in FIG. 4, the accumulated lateral clearance of the conveyor belt, commonly referred to as shug and shown by the reference “G”, can cause the belt to run in a crooked path rather than the desired straight path. This especially creates problems with edge drive units, such as spiral cage conveyors, and can also cause potential problems in product movement, vibration, and/or damage to the conveying system and product. 
     SUMMARY OF THE INVENTION 
     In order to overcome these disadvantages, the present invention provides a conveyor belt having a plurality of pivotal transverse rods extending laterally across the belt, with the transverse rods having inner and outer ends along inner and outer edges of the belt; a plurality of connecting links arranged in at least one longitudinal row along the inner and outer edges of the belt and pivotally interconnecting the inner and outer ends of the transverse rods, respectively, with each of the connecting links having a pair of openings extending laterally therethrough such that the transverse rods extend through the openings; and a weld connection between the rods and the connecting links, each of the weld connections including only a weld connection point between a trailing side of the transverse rod and the connecting link. 
     The present invention also provides a method of manufacturing a conveyor belt including the steps of providing a plurality of transverse rods, providing a plurality of connecting links having a first pair of openings extending laterally therethrough and a second pair of openings extending therethrough, arranging the transverse rods through the first and second pair of openings so as to pivotally interconnect the transverse rods in a longitudinally spaced arrangement, and welding the connecting links to the transverse rods at the first pair of openings on only a trailing side of the transverse rod. 
    
    
     BRIEF DESCRIPTION OF THE FIGURES 
     These, and other objects, features, and advantages of the present invention will become more readily apparent to those skilled in the art upon reading the following detailed description, in conjunction with the appended drawings in which: 
     FIG. 1 is a plan view of a conventional connecting link for a conveyor belt; 
     FIG. 2 is a plan view of a conventional spiral cage conveyor system; 
     FIG. 3 is a schematic illustration of the forces acting on a welded connection of the conveyor belt; 
     FIG. 4 is a plan view of a conventional conveyor belt; 
     FIG. 5 is a plan view of a conveyor belt according to the present invention; 
     FIG. 6 is a partial enlarged view of the conveyor belt shown in FIG.  5  and FIG. 6A is an enlarged view of the double compression weld according to the present invention; 
     FIGS. 7A and 7B illustrate a step in the welding methodology of the conveyor belt of FIG. 5; 
     FIGS. 8A and 8B illustrate a further step in the welding methodology of the conveyor belt of FIG. 5; 
     FIGS. 9A and 9B illustrate a still further step in the welding methodology of the conveyor belt of FIG. 5; 
     FIG. 10 is a cross-sectional view of a transverse rod according to a further embodiment of the present invention; 
     FIG. 11 is a side elevational view of a connecting link according to a further embodiment of the present invention; 
     FIG. 12 is a plan view of a conveyor belt according to a still further embodiment of the present invention and FIG. 12A is an enlarged view of a transverse rod thereof; 
     FIG. 13 is a plan view of a conveyor belt according to a further embodiment of the present invention; 
     FIGS. 14A and 14B illustrate a step in the welding methodology for the conveyor belt of FIG. 13; and 
     FIGS. 15A and 15B illustrate a further step in the welding methodology for the conveyor belt of FIG.  13 . 
    
    
     DESCRIPTION OF PREFERRED EMBODIMENTS 
     Referring to FIG. 5, a conveyor belt in accordance with the present invention is shown generally by reference numeral  10 . Conveyor belt  10  is a grid type belt comprising a plurality of longitudinally spaced, transversely extending rods  12 . Rods  12  have inner and outer ends  14  and  16 , respectively, located along the inner and outer edges  18  and  20  of belt  10 , with central portions  22  extending between the inner and outer ends  14  and  16 . Each of the rod ends  14  and  16  is provided with an integral, enlarged head or button head  24 . 
     A row of inner links  26  pivotally interconnect the rods  12  at the inner edge  18  of the conveyor belt and a row of outer links  28  pivotally interconnect the rods  12  at the outer edge  20  of the conveyor belt. As discussed further below, the inner links  26  and the outer links  28  are rigidly fixed to the enlarged button heads  24  by a welded connection point  38  disposed on each side of the link. Although not illustrated, reinforcing bar links may also be provided between the button head and the link. Still further, alternative end link terminations may be used, such as that disclosed in U.S. Pat. No. 5,954,187 issued to Cambridge, Inc. 
     Each of the connecting links  26  and  28  includes two transversely spaced, longitudinally extending legs  30  which are connected together at one end thereof by a base portion  32 . In a preferred embodiment of the invention, the legs  30  have at least one stepped portion which thereby results in base portion  32  being narrower than a distance between the free ends of the legs  30 . Thus, the links are allowed to be suitably nested together with the narrow base portion  32  being received between the free ends of the legs  30  when the conveyor belt traverses a curved path. The legs  30  of each of the links  26  and  28  are provided with longitudinally extending slots  34  for slidably receiving an adjacent transverse rod  12  and each of the legs  30  further include a generally circular opening  36  for receiving a transverse rod  12  to which the link is secured. 
     In a conventional conveyor belt, two weld connection points are used between each link and the leading edge of the respective transverse rod. The openings  36  in the links are generally slightly larger than the transverse rod passing therethrough. Thus, as the weld cools it contracts and draws the transverse rod toward the leading edge of the opening  36 . As a result, this causes the weld to absorb the full tension between the link and the weld without having the benefit of the cross-sectional area of the link which could assist in carrying the distributed load. However, even if the opening  36  was an interference fit with no clearance, as the opening elongated due to yielding and wear, the weld would still eventually come under full tension and result in weld fatigue. 
     In order to prevent the fatigue of weld connection points  38 , the present invention further provides a trailing weld connection point  40  between the trailing side of the transverse rod and the respective edge of the connecting link, as best shown in FIGS. 6 and 6A. The presence of the trailing weld connection point  40  in combination with the weld connection point  38  creates a state of residual tension in the cooperating welded arrangement. Thus, no matter which direction the rod is driven in the plane of the conveyor belt, at least one of the weld connection points  38  or  40  will come under compression and thereby reduce the overall tension within the welded arrangement. 
     Referring to FIGS. 7-9, the method of forming the double weld arrangement of the present invention is further explained. As shown in FIGS. 7A and 7B, the conveyor belt  10  is assembled as conventionally done by placing the transverse rods  12  through the slots  34  and openings  36  within the legs of the connecting links. As shown in FIGS. 8A and 8B, the trailing weld connection point  40  is preferably created by applying an undersized tack weld between the trailing side of the transverse rod and the respective link. Thereafter, the trailing weld connection point  40  is allowed sufficient time to cool and in so doing draws or pulls the transverse rod toward the trailing end of the generally oversized opening  36  and adds the cross-sectional area of the link to the compressive strength of the trailing weld connection point  40 . After the trailing weld connection point  40  has sufficiently cooled, the weld connection points  38  are formed by applying a standard sized weld to the leading side of the transverse rod between the rod and the connecting link. As the weld connection point  38  cools, it in turn attempts to draw or pull the transverse rod toward the leading end of the opening  36 , thus resulting in both weld connection points  38  and  40  being in residual tension. As a result, when the transverse rod is moved in either direction during operation of the conveyor, the welded joint is placed under compression rather than tension. Accordingly, through the formation of the trailing weld connection point  40  and thus a double compression weld in accordance with the present invention, weld fatigue is essentially eliminated as a source of belt failure. 
     In a preferred embodiment of the present invention, plasma welding is used to form the weld connection points  38  and  40 . As should be apparent to one skilled in the art, however, other welding techniques and various welding materials could of course also be used to form the double compression weld within the scope of the present invention. Still further, although in the above-described preferred embodiment of the present invention the trailing weld connection point  40  is formed first, it is within the scope of the present invention to form either the trailing weld connection point  40  or the weld connection point  38  first, and then perform the remaining welding operation to obtain the double compression weld of the present invention. 
     Still further, after much experimentation, it has been found that a conveyor belt  100  can be made nearly as strong as conveyor belt  10  described above by providing only a back weld or trailing weld  40 ″ between the transverse rod  12  and the link  26 ,  28 , as shown in FIG.  13 . 
     More specifically, referring to FIGS. 14A and 14B, the conveyor belt  100  is assembled as described above by placing the transverse rods  12  through the slots  34  and openings  36  within the legs of the connecting links. As shown in FIGS. 15A and 15B, the trailing weld connection  40 ″ is preferably created by applying an undersized tack weld between the trailing side of the transverse rod and the respective link, although the size of the weld could of course be varied as desired as would be apparent to one skilled in the art. Thereafter, the trailing weld connection point  40 ″ is allowed sufficient time to cool and in so doing draws or pulls the transverse rod toward the trailing end of the opening  36  and adds the cross-sectional area of the link to the compressive strength of the trailing weld connection point  40 ″. 
     As described above, trailing weld connection point  40 ″ may be formed by plasma welding or any other conventional welding techniques. Surprisingly, the use of only the trailing weld connection point  40 ″ for both links  26  and  28  has been found extremely successful in delaying weld fatigue as a source of belt fatigue. It is within the scope of the present invention however to provide only the trailing weld connection point  40 ″ on either the inner links  26  or the outer links  28 , and provide an alternate welding pattern on the other of said links, either a conventional leading weld or the double-compression weld of the present invention. Still further, although less preferred, it is possible to provide only the trailing weld connection point  40 ″ at one of the connection points between the transverse rod and the connecting link and provide an alternate welding pattern for the other connection point between the transverse rod and the connecting link. 
     While the double compression weld and the trailing weld methodology of the present invention are successful in overcoming the problems associated with weld fatigue and tenting which may be caused as a result thereof, these welding techniques do not compensate for the flexure strength of the transverse rods being exceeded by the tension in the conveyor belt, and thus leading to racking and buckling. In order to overcome these disadvantages, the present invention further provides a transverse rod  12 ′ which has been flattened, as shown in FIG. 10, so as to increase the strength of the transverse rod while minimizing the impact thereof on the overall belt weight. More particularly, the transverse rod is flattened by a rod forming apparatus or by a separate device so as to provide increased strength in the plane of belt travel, thereby preventing buckling and racking. In a preferred embodiment of the present invention, the transverse rod  12 ′ is provided with a height H of approximately 0.226 inches and a width W of approximately 0.192 inches, and it is formed by flattening a 0.216 inch diameter rod. By flattening the 0.216 inch diameter rod, the present invention achieves a strength in the plane of belt travel which is substantially the same as or greater than that achieved by a 0.225 inch diameter rod, but while still maintaining the weight of the 0.216 diameter rod. This ability to achieve increased strength without a corresponding increase in the weight can save as much as 0.65 pounds per lineal foot of belting. 
     Although the 0.216 inch diameter rod is discussed above as a preferred embodiment of the present invention, rods having a diameter of approximately 0.216 inches to approximately 0.220 inches, or greater or lesser diameters depending upon the end application, may be used in the conveyor belt of the present invention. In addition to increasing the strength of the transverse rod, the flattening operation also serves to align all of the grains within the rod perpendicular to the plane of belt travel and thus greatly increases the bending strength of the rod due to work hardening and improves the wear resistance of the rod in extended life operations. 
     In order to better accommodate the flattened transverse rod  12 ′ with the link, the present invention further provides an opening  36 ′ in the legs  30  of the connecting links  26  and  28  which is appropriately dimensioned to correspond to the flattened rod. As shown in FIG. 11, opening  36 ′ is dimensioned for receiving rod  12 ′ as set forth above and has a preferred height H of approximately 0.263 inches and a width W of approximately 0.205 inches. The dimensions of opening  36 ′ will of course be varied depending upon the dimensions of the flattened transverse rod, which will of course vary depending on the circular diameter rod from which it is formed, with the goal to be having an opening  36 ′ which is slightly oversized relative to the desired rod dimensions. The use of the flattened transverse rod alone and/or in combination with the similarly dimensioned opening  36 ′ sufficiently strengthens the rods of the conveyor belt such that the tension in the belt will not significantly exceed the structural limitations of the transverse rods. As such, racking and buckling can be substantially prevented. 
     The remaining problem to which the present invention is directed concerns belt shug. It has been found in grid conveyor belts that the lateral shifting or shug commonly occurring when a belt is new is gradually reduced as the belt wears from ordinary usage. More specifically, it has been found that as the belt undergoes repeated duty cycles, the transverse rods will eventually form a groove in the underside contacting portion of the connecting link and the rods will develop a corresponding cupped surface. This groove thereby seats the connecting link relative to the transverse rod and inhibits further lateral shifting. In order to promote the formation of these wear grooves in a predetermined location, i.e., one that would promote straight belt travel, the present invention further provides a rod  12 ″ having at least one crimp or wear mark  42  initially formed in the rod, as shown in FIG.  12 . The rod  12 ″ may be formed from a conventional circular transverse rod  12  or the flattened rod  12 ′ discussed above. In use, the connecting links  26  and  28  are each preferably initially seated within a crimp  42  and, as long as at least one edge of the belt remains in tension, the conveyor belt is prevented from laterally shifting or shugging. The wear mark  42  also ensures a contact surface between the underside of the link and the rod such that the load may be distributed over the contact surface rather than merely a point contact. The wear mark  42  does not interfere however with the ability of the conveyor belt to turn in either a left curve or a right curve travel path. Thus, the conveyor belt having transverse rods  12 ″ may be flipped or turned over for use in a conveyor belt in either direction. 
     Although shown and discussed above as independent features, it is within the scope of the present invention and most preferred to provide conveyor belt  10 ,  100  with one or more of the various features disclosed herein, more specifically, double compression welds or trailing welds, non-circular transverse rods and corresponding link openings, and wear marks on the transverse rods. By combining these various features, the present invention provides a conveyor belt which successively overcomes problems associated with weld fatigue and, while carrying a fifty percent increased load, it still achieves an average belt life that is 2.5-3.5 times greater than a conventional belt of similar weight and size. Although belt failure may ultimately occur, such failures have been found to be due to rod wear rather than fatigue or other deteriorative conditions. Other combinations could, of course, also be utilized, such as only double compression welds and non-circular transverse rods and corresponding link openings, or only trailing welds, and all such combinations would be apparent to one skilled in the art. 
     While the present invention has been described with respect to the preferred embodiments, it is to be understood that variations and modifications may be resorted as will be apparent to those skilled in the art. Such variations and modifications are to be considered within the purview and the scope of the claims appended hereto.