This application is related to U.S. application Ser. No. 924,775 and 924,639.
The invention concerns belts or straps, more particularly elevator conveyor belts. It relates to a method and a device for splicing the ends of belts, either to increase their length, or to make them endless by joining the belt to itself in a manner which is reliable during operation. The fastening device as well as the process will be described below, as an example, for application to an elevator belt, with the understanding that they are not limited to this use.
One conventional method of splicing the ends of belts is hot splicing after the ends of the reinforcing material have been interlaced.
Various forms of these hot splicing techniques are described in a number of patents, such as DE No. 1,165,354 of Franz Clouth Rheinische Gummiwarenfabrik; FR No. 74.03141 and DE No. 907,996 of Continental Gummi-Werke; FR No. 1,395,634, FR No. 1,582,190 and FR No. 1,440,605 of Pneumatiques, Caoutchouc Manufacture et Plastiques Kleber Colombes; and U.S. Pat. No. 173,686 of Goodyear Tire and Rubber. One method is recommended in German standard DIN 22131. Another method is described by Mr. Gozdiff of Goodyear in a paper entitled "Factors relating to vulcanized splice reliability for steel cable reinforced conveyor belting", delivered to the 125th Meeting of the Rubber Division, American Chemical Society, in Indianapolis on May 8-11, 1984. Finally, an article by H. P. Lachmann entitled "A survey of present-day conveyor belt technology", published in Bulk Solids Handling volume 4, number 4, December 1984, reviews the different technologies that can be used. Other proposals have been described in, for example, U.S. Pat. Nos. 2,446,311 and 3,093,005.
Examples of the prior art in hot splicing are illustrated in FIG. 1. There are, however, conditions which make hot splicing techniques inapplicable: for example the length of such a splice may be incompatible with the space available in the sheath or alongside the elevator, or again the mechanical strength may become insufficient to guarantee trouble-free operation of the elevator if the temperature of the products transported or that of the gases circulating in the sheath is greater than 100.degree. C.
Specifically, in the case of interlacing of metal cords, the two ends of the belt(s) are bonded together by the rubber mixture separating the ends of the cable(s). It is known, however, that as the temperature increases, the mechanical properties of elastomer-based mixtures decrease; the same applies to the bonding forces between the rubber and the metal. As a consequence, the tensile strength of such a splice decreases as the temperature rises.
Taking into account the risks encountered with a splice using hot adhesion and interlacing of metal cords, handling engineers have suggested replacing the adhesive bond with a mechanical bond designed to clamp the two ends of the belts(s) against one another. These techniques are referred to as "fastening", and are described, for example, in French Pat. No. 1,320,222 of Pneumatiques, Caoutchouc Manufacture et Plastiques Kleber Colombes, or in advertising materials of specialized companies such as Goro or Flexco.
Other mechanical fasteners are described in, for example, U.S. Pat. Nos. 2,447,855 and 1,918,255.
The compression force is exerted by metal flanges which are passed through by clamping bolts. The principle applied in mechanically splicing the ends of a belt or belts is theoretically more satisfactory than the hot-adhesion process, but an analysis of phenomena associated with operation of this type of device shows that there is only a slight improvement in operating reliability. This is because the lateral plates have a tendency to move away from one another under the tensile force exerted on the two ends of the belt. To remedy this problem, two lines of bolts are generally used to clamp the plates, with the line of bolts placed closest to the tension zone being designed to limit movement of the plates.
FIG. 2 illustrates conventional fastening techniques such as described in U.S. Pat. Nos. 4,489,827, 1,803,354, 2,330,434, 2,330,435, 3,618,384, and 4,450,389 and provide an example of changes which occur during operation, in terms of distribution of pressure over the belt ends.
When the fastening device is initially clamped, pressure distributed uniformly over the entire extent of the two clamped ends. When operation begins, the lateral parts are displaced, which tends to decrease the pressure in zone X and increase that in zone Y. As a result of the increased pressure, the rubber mixture located in zone Y tends to be expelled and to creep, i.e. rubber is displaced from the most highly compressed zones towards those least compressed. The effect of this creep is to encourage the clamping plates to move closer together in zone Y, which accentuates the effect.
As confirmation of this analysis, it is commonly observed that the second line of bolts has completely loosened, which proves that the pressure effect exerted on the ends of the belt(s) is due not to the bolts but to a rotary movement of the clamping plates. Since the clamping force in zone X has decreased considerably, the strength of such a clip fastener consists only of the retention of the metal cords in zone Y and the frictional forces existing in zone X between the belt and each of the clamping plates. When zone Y is unclamped, an examination of the ends of the belt(s) in said zone shows that the tensile stress has been so high that there has been local destruction of the rubber mixture and of the bond between the rubber and the metal cords. This fact makes the strength of such a clip fastener very problematical, especially when this mechanical effect is combined with the effect of temperature, since it is well known that increased temperature accelerates and facilitates the creep of elastomer-based mixtures, and decreases the strength of the bond between said mixtures and steel cords.
To remedy this problem, it is possible to attempt to increase the pressure exerted by the lateral plates by locking the ends of the metal cords.
Patent DE No. 2,341,992 of Bernhard Beumer Maschinenfabrik describes such a solution, in which each metal cord is stripped at its end of its rubber covering, and said end is inserted into a clamping device using screws. Such a technique, time-consuming and difficult to implement, presents a further risk due to the design of the metal cord clamping zone: if the clamping pressure is not properly controlled, there is a definite risk of cutting the metal cord, which would nullify the anticipated effect. In addition, the screws have a tendency to loosen under the action of vibration and temperature, and therefore require constant monitoring.
A similar solution of the type described above using bores steel balls to lock the ends of metallic cables is also proposed in U.S. Pat. No. 3,105,390.
A different solution, used in particular to lock pretensioning cords in prestressed structures, involves stripping the ends of the metal cords, unstranding them, i.e. untwisting the constituent strands to spread out the end, and pouring around it a metal with a low melting point. This technique is highly reliable when it can be used, but pouring the molten metal requires that the clip fastener be placed in a vertical position, which implies either that one of the drums of the elevator can be moved - which is not always possible--or that the clip fastener can be placed at the top of the elevator, although pouring molten metal onto the ends of metal cords at a height of several dozen meters is tricky and even dangerous. In addition, such a device is practically non-removable, which does not facilitate maintenance of the elevator or replacement of the belt.
The object of the invention is therefore a fastening device for splicing belts, and more particularly belts for bucket elevators, which comprises a reinforcement made of manmade fabric or metal cords. Other objects of the invention are the process for creating splices using the device described, and application to an elevator conveyor belt.
The fastening device which is the object of the invention makes it possible to create, using a method that is as simple as conventional splices and is completely safe since there is no handling of hot products or adhesives or heating equipment, a splice between two adjacent ends of two belts to produce a longer belt, or between the two ends of a single belt to produce an "endless" item, ready for operation on a conveyor or elevator.
The device, which requires only simple preparation of the ends, acts on the one hand by locking by means of a loop created around a locking core, and on the other hand by means of mechanical clamping of said ends over the greatest possible length.
This fastening device comprises, on the one hand, two central plates, designed solely for installation and serving to support the ends of the belts(s), to which are attached, on the upper part, two installation wedges allowing the assembly to be aligned, and on the other hand, two locking cores making it possible to create loops in the ends of the belt(s) and, finally, two lateral clamping parts each fitted with a ball joint.
This device acts like a pivoting self-clamping clip by means of its various component parts, with the lateral clamping parts acting to clamp the belt by means of through bolts.
The characteristics and variants of the invention will be better understood by reading the description below taken in conjunction with the accompanying.