DEVICE FOR TESTING CLOSED LOOPS OF MATERIAL

Abstract: Method for testing closed loops of material, such as endless conveyor belts (4), wherein said loops are arranged with pretension around at least two rollers. After this simulation of a load on the endless loop is effected. The device for realizing this method comprises a driven roller (2) as well as a breaked roller (3) being also provided with a tension roller.

Description: The invention relates to a process for testing closed loops of material, such as endless conveyor belts, comprising pretension­ ed arrangement thereof around at least two rollers and the simu­ lation of a load on the endless loop. Such a process is known, in which use is made of a device where the distance between the two rollers is varied, so that the loop is placed under a varying load. This load must simulate the operation of the conveyor belt. This process has a number of dis­ advantages. In a normally loaded conveyor belt the tensile force in the belt initially increases slowly in the bottom part, and there­ after increases considerably faster in the top part, and it finally falls very rapidly while the belt is running over the driving rol­ ler. In the process followed the tensile force in the upgoing part is, however, equal to the pulling force in the downgoing part of the tensioning roller used. The resistances which have to be over­ come are the bearing resistances of the rollers and the bending resistance of the belt. However, these are so small that the dif­ ference in tensile force in the belt between the upgoing part and the tensile force of the belt in the downgoing part can be taken as equal. The device used for carrying out this process also has the disadvantage of being complex. Due to the fact that it must be pos­ sible to move at least one roller hydraulically, a complex hydrau­ lic control and regulation system requiring considerable mainte­ nance is needed. From DE-A-2516271 a method is known for testing of magnetic tapes for carrying data. In this case synchronisation of the tape is important for correct recording and playing of these data. Because of this a tape to be tested is tensioned between two rollers, wherein one of said rollers is a driven roller and the other of said rollers is a braked roller. The driven roller is rotated with a speed being very effectly constant and differences in the running speed at the other braked roller are measured. During testing of conveyor belts this is not of importance whilst the load as a total difference magnitude. The object of the invention is to produce a process in which the above disadvantages are eliminated, and with which a more realistic loading of endless closed loops can be carried out, and said process has to be achieved in a simple manner. This object is achieved with a process of the type des­ cribed above in that the simulation of a load on the closed loop comprises the driving of the one roller and the braking of the other roller. This gives a better approximation of the load prevailing in an endless loop, and the tension need not be constantly varied, as in the device described above, for the simulation of a load. According to an advantageous further embodiment of the process, at least one of the rollers is caused to slip relative to the loop, in order to determine the coefficient of friction between loop and roller. It is also possible to subject the endless loop to a two-­ sided bending load, in order thus to obtain a better stimulation of the load under operating conditions. It has been found that in par­ ticular the joint of an endless loop when subjected to a bending load in two directions has a much lower endurance strength than when subjected to a bending load on one side, so that the latter testing method can give misleading results. According to a further embodiment of the process, after simulation of a load on the closed loop in the above-described manner, the loop is then loaded to breaking point. This can be achieved by increasing the pretensioning force, in which case no difference in speed of rotation exists between the driving drum and the brake drum. The invention also relates to a device for the above-des­ cribed process. As stated, the device according to the state of the art makes heavy demands on the hydraulic system. A device which does not have these disadvantages is achiev­ ed according to the invention through the fact that it comprises a driven and a braked roller, in addition to a tensioning roller. This means that the complex (hydraulic) control and regulating system can be dispensed with, while at the same time a better simulation of the operating conditions of a conveyor belt is achieved. It is possible to drive the driven roller with an elec­ tric motor and to load the braked roller by means of a generator which can thereby return some of the generated power to the elec­ tric motor. The use of a hydraulic motor and hydraulic brake is also possible, the hydraulic brake then also partially driving the hydraulic motor. According to an anvantageous embodiment, the braked roller is, however, connected by means of a differential device, such as a planetary gear system, to the driven roller. In this way, the ener­ gy flow can be conveyed back from the braked roller to the driven roller, while a relatively compact device can also be used. This is particularly important if heavier conveyor belts in which high stresses occur have to be tested. Other devices would require a particularly complex construction. According to another adantageous embodiment, the central axes of the driven, braked and tensioning rollers are parallel, and the central axis of the tensioning roller lies in a different plane from the plane which passes through the central axes of the driven and braked roller. This provides for a particularly efficient construction, in which the simulation of practice can be even further improved if on each side of the tensioning roller there is a bypass roller which is fitted in such a way that the free-running parts of the closed loop extend essentially parallel to the plane through the central axes of the driven and braked rollers or perpendicular thereto. In this way, the closed loop is subjected to bending on two sides, so that the operating load is thereby better approximated. According to another advantageous embodiment, the plane in which the central axes of the braked and driven rollers are located is essentially horizontal, and the tensioning roller is above it. In conjunction with the above-described differential device, a particularly well-ordered unit is obtained, in which through providing the tensioning roller above the driven and braked rollers, these driven and braked rollers can be located close to the bottom of the space in which the device according to the inven­ tion is set up. The rollers are freely accessible to a closed loop, so that it can be fitted without problems. According to another advantageous embodiment of the device according to the invention, it comprises a further roller affecting the course of the loop. In this way, further operating loads can be simulated, where the loop is bent at a slight angle. The invention will now be explained with reference to an example of an embodiment shown in the drawings, in which: Fig. 1 shows a schematic front view of the device for testing closed loops of material; Fig. 2 is a schematic diagram of the energy flow in the connection between driven roller and braked roller via the planeta­ ry gear system; Fig. 3 shows a details of Fig. 2; Fig. 4a, 4b are diagrams in which the load on the belt is plotted against time for loads approaching the actual operating conditions, the testing according to the state of the art, and the testing according to the present invention respectively. In Fig. 1 the device for testing closed loops of material such as endless conveyor belts is generally indicated by 1. It com­ prises a driven roller 2 and a braked roller 3. In order to main­ tain the tension in the conveyor belt 4, a tensioning roller 5 is present, on either side of which there are bypass rollers 6 and 7. The tensioning roller 5 is connected to a piston rod 8 which fits into a cylinder 9 of a hydraulic piston-cylinder assembly which is connected to a source of hydraulic fluid (not shown) in order to keep the tension of the conveyor belt 4 constant. Through the pre­ sence of the bypass rollers 6 and 7, the conveyor belt undergoes bending to both sides. The direction of travel of the conveyor belt is indicated by arrow 10. In addition, between the driven roller 2 and the braked roller 3, there can be a further roller 11, with which the tensioning angle of the conveyor belt can be changed. Fig. 2 shows very schematically the differential device as a planetary system 16, which connects the driven roller 2 to the braked roller 3, in order to convey back the energy released at the braked roller and to restrict the size of the device to acceptable proportions. In this figure, arrows 12 indicate the direction of the energy flow. By means of a right-angle transmission 14, an electric motor 13 drives the driven roller 2, and the latter drives the conveyor belt 4 to be tested, which in turn drives the braked roller 3. This braked roller 3, by means of a right-angle trans­ mission 15, drives a planetary gear system 16, which with a varia­ tor 17 constitutes a differential system which is known per se. In this way the energy flow which is released at the braked roller is conveyed back to the driven drum 2 and through the control of the variator the braking action can be regulated. The planetary system is shown in greater detail in Fig. 3. The device described works as follows: A conveyor belt for testing is fitted round the various rollers and brought to a predetermined tension with the tensioning roller 5. Thereafter, the driven roller 2 is set in motion with electric motor 13. Depending on the testing, roller 3 is braked more or less: in the extreme case even to a maximum slippage of 2% for the purpose of measuring the coefficient of friction between braked roller 3 and the conveyor belt for testing. If the operation of the conveyor belt is simulated, there is only a slight creepage between this roller 3 and the conveyor belt 4. In Fig. 4a, b the force experienced by the conveyor belt is plotted against time. The dotted line in both figures the tension during an actual operating situation. Here, part 21 represents the lower part of the conveyor belt, and part 22 the driving drum. It appears that the tension from the driving drum increases gradually to a maximum up to the driving drum. Fig. 4a shows by solid lines the load in the device according to the state of the art, from which it can be seen that there is a particularly high peak 23, followed by a low load. This peak is caused by the cycle time when the two rollers move apart. Fig. 4b shows by a solid line the change of the forces according to the present invention, where part 25 indicates the part on the braked roller. In can be seen that the load according to the present invention is much closer to the actual load than the load placed according to the state of the art. It must be understood that the invention is described only with reference to preferred embodiments, and that various modifica­ tions can be made to it which are within the ability of anyone skilled in the state of the art.

Claims: 1. Method for testing of closed loops of material, comprising tensioned arrangement thereof around at least two rollers, driving of said one roller and braking of said other roller, characterized in that, the belt is loaded with constant forces. 2. Method according to claim 1, characterized in that, at least one of the rollers is just slipped relative to the loop, in order to dertermine the coefficient of friction between loop and roller. 3. Process according to claim 1 or 2, characterized in that the endless loop is subjected to a bending load on two sides. 4. Device for carrying out the process according to one of the preceding claims, comprising a driven and braked roller, characterized in that, this device also comprises a tension roller. 5. Device according to claim 4, characterized in that, the driven roller and the braked roller are connected to each other by means of a differential device. 6. Device according to claim 5, characterized in that a variator is added to the differential device. 7. Device according to claim 5 or 6, characterized in that the central axis of the driven, braked and tensioning rollers are parallel, and the central axis of the tensioning roller lies in a different plane from the plane which passes through the central axis of the driven and braked roller. 8. Device according to claim 7, characterized in that, on both sides of the tensioning roller there is a bypass roller, which is fitted in such a way that the free-running parts of the closed loop extends essentially parallel to the plane passing through the central axis of the driven and braked rollers and are perpendicular thereto. 9. Device according to claims 6, 7 or 8, characterized in that the plane in which the driven and braked rollers are located is essentially horizontal, and the tensioning roller is above it. 10. Device according to any of the claims 5-9, characterized in that, it comprises a roller affecting the further running of the closed loop.

Inventors: SPAANS, CORNELIS
Applicants: DUNLOP-ENERKA B.V.
Application year: 1986
Main classification: G01N3
IPC codes: G01N3, G01M13, G01N19