engleski

Testing of rollers for belt conveyors

The first belt conveyor was mentioned around the year of 1750 (Hetzel, F.V., Albright, R.K., 1941). The belt was sliding along the oiled boards. Since the resistance was too high the belt first leaned on wooden rollers and later on rollers made from cast iron. The bearings were sliding bearings without special insert - bushing with a considerably high resistance. The rollers were horizontal only ; the belts were straight, not troughed. Due to the fact that it was observed that material fell down from the straight belt, in 1870 troughed belts started to be used, the width of which had a larger cross-section. A special roller was developed for them, the roller body of which was not an ordinary cylinder but had conal edges and a cylindric central part. Upon low belt speeds and a small angle of troughing it was not very much noticable that the perihperal speed was different from the speed in the central part of the roller and that the belt (with the permanent speed) on some parts was relatively sliding over the rollers. In 1928 a roller was patented with freely rotating conal parts on each edge. This roller remained in use for quite a long time, although the sliding was not removed. One of the sub-variants of the same, bad principle had conal parts on one edge only. The rollers were arranged in a support with conal parts one after another, in an angle, so that the cones made a central, straight part of the troughed belt. The real improvement of such constructions was the introduction of rolling bearings. In 1890 there were some efforts to make a roller support for troughed belt made from two, three or more cylindrical rollers. The reason why this correct solution had not been introduced before was poor lubrication of the inclined sliding bearing. Development of the quality rolling bearing smoothed the path to the new solution. The disadvantages of sliding bearing were to a certain extent decreased by application of a felt packing in order to prevent flowing away of lubricants, by oil lubrication in closed housings and alike. However, later a sliding bearing started to be used again but it was made of synthetized and synthetic materials and used for specific operations (production of food items and alike). In Europe the ready-made regular single-row ball bearing are in use, whereas the US uses the conical roller bearings. Housing for the bearing are made within or outside the roller. In the first case the axis is fixed, it goes through the entire roller with the edges in the supporting frame. In the second case the axis is not made in one part, but has two journals, which are fixed to the bottom of the roller and therefore it spins together with the roller. The journals enter in bearing in so-called « ; cap» ; (therefore it is called “ cap housing” ), which is placed within the supporting frame. This solution was not long in use in spite of some very good characteristics. Through gradual improvement of lubricants the consistent greases based on lithium soaps were used exclusively. At first the rollers were lubricated periodically in the course of exploitation (installed grease cup) and later a permanent lubrication was accepted, which was made upon roller production ("once forever"). The roller body has gone through substantial changes too – from wooden, through cast iron to steel made from solid drawn and precisely welded pipes. The last one mostly replaced the solid drawn pipe. Important changes and improvements of the belt conveyor were made until 1925. This year is therefore considered as the year when belt conveyors were generally and widely accepted as good and efficient means of transportation The main reason was the opening of large surface lignite pits with vast overlay masses and large coal quantities. Until then the main transportation means in non-horizontal areas (conditions) were transportation with endless chain, endless rope, rope railways (brake inclines) and aerial tramways, whereas in horizontal areas the dominant role had a locomotion towing. After the WW II the belt conveyors were improved and its use expanded. Large quantities of the material, for which this type of transportation is convenient, as well as technical and technological improvements in machinery and chemistry contributed to the extended use of these conveyors. The rising transportation costs also preferred such means of transportation. The belt conveyors were introduced under the conditions in which traditionally train transportation was used (mostly trains with a locomotion towing), including trucks too. In the first case this was due to large distances and in the second case difficult field conditions. The improved belt conveyors enabled successful and competitive mastering of relatively large distances and morphologically extremely unfavourable terrains with high or valuable vegetation, deserts, swamp areas and alike.

belt conveyor rollers; testing

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