US 3555329 A
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United States Patent  GEARLESS DRIVE FOR CEMENT MILL 3 Claims, 3 Drawing Figs.
52 US. Cl 310/218,
I 310/267  Int. Cl t HOZk 1/28  Field ol'Search 310/261.
 References Cited FOREIGN PATENTS 1,078,680 3/1960 Germany 310/218 1,196,779 7/1965 Germany 310/218 Primary Examiner-Milton O. l-lirshfield Assistant Examiner-B. A. Reynolds Attorney-Pierce, Scheffler & Parker ABSTRACT: A gearless drive for the drum of a cement mill or the like wherein the pole wheel, i.e. the rotor of a low-speed electric motor surrounds the drum and is connected to it by a circumferential array of uniformly spaced studs which project radially from the drum and are received in a similar array of uniformly spaced recesses located in the pole wheel structure. Elastic members located between each side of each stud and the corresponding end of the recess provide a resilient drive for the drum by the pole wheel, and expansions and contractions of the drum due to changes in temperature are accommodated by sliding movement of the studs in their recesses thus preventing deformations of the drum caused by heat from exerting any forces upon the pole wheel.
PVATENTEU m 2mm SHEET 1 [IF 2 gen Meyer PM 4 x Pm GEARLESS DRIVE FOR CEMENT MILL This invention relates to an improved gearless drive for cement mills and the like, and more particularly to a gearless drive of the type wherein the pole wheel rotor of a low-speed electric motor surrounds and is: secured to the mill drum and is surrounded by the stator element of the motor.
In the past, it has been the practice to drive the drum of a cement mill over reduction gearing by relatively high-speed electric motors. For this purpose, a ring gear has been secured around the drum and the ring gear has been meshed with one or several drive pinions distributed circumferentially around the ring gear. This ensures a very slow speed of rotation for the drum, which is necessary for operation of a cement mill.
With increasing size of the mill drums, and correspondingly higher driving torques needed, it was found that a directly driven drum represents a much better solution, since the transmission gearing together with its lubrication plant requires considerable space and also results in an additional power input requirement, particularly during starts and acceleration of the drum with its contents. Moreover, the transmission gearing requires costly attendance and maintenance.
It has already been suggested to use the drum as a shaft for the pole wheel, that is the rotor element of themotor, and to locate the stator around the mill. However, during operations of the mill, the drum can increase to a temperature which is 100 C. hotter than the pole wheel. Moreover, after the mill has been shut down, temperature differences of about 50 C. may appear on the circumference of the drum. Consequently, deformations appear which are transmitted to the pole wheel and which would reach to a considerable overall strain in cases of drums which have a-diarneter of several meters.
In order to eliminate this disadvantage of the direct drive, it is known to secure the pole wheel of the motor not directly to the drum but rather to interconnect it with the drum by way of an elastic coupling in the form of a circular array of elastic, rod-shaped elements which are designed as a spring pack, the outer ends of the rod-shaped elements being secured to the pole wheel and the inner ends to the mill drum. In the spoked wheellike connection between polewheel and drum, which forms a statically undefined system, .the individual springs cannot adapt themselves, however, to thexirregular load caused by the above-mentioned temperature differences, and consequently the life of such an arrangement is very limited.
The object of the present invention is to provide an improved electric motor powered gearless drive for the drum of a cement mill, the motor being of the low-speed type and whose pole wheel i.e. rotor and stator elements surround the drum, and which includes an elastic connection between the pole wheel and drum which is very simple, rugged and reliable from a structural point of view, but which does not transmit to the pole wheel rim any deformations of the drum caused by thermal expansions and contractions in radial and tangential directions. This is attained, in accordance with the invention by designing the interconnections between the pole wheel and drum as a circumferentially extending array of studs which project radially'frorn the drum and engage in correspondingly located recesses in the rim of the pole wheel, thestuds being elastically supported in the recewes by means of elastic elements located between the opposite ends of the recesses, as measured in a circumferential direction, and the opposite sides of the studs.
A representative embodiment of the invention will now be described in detail and is illustrated in. the accompanying drawings wherein:
FIG. 1 shows a part of the drive in axial section;
FIG. 2 is a fragmentary view'showing a portion of the rim of the pole wheel as viewed in the axial direction of the drum; and
FIG. 3 is a view in perspective of one of the elastic elements interposed between the pole wheel and the mill drum.
With reference now to the drawings, a fragment of the drum of a cement mill is'indicated at 1, and'thisisdrivendirectly by means of a low-speed, alternating current electric motor, the stator of the motor being indicated at 2, and the rotor or pole wheel being indicated at 3. A ring 4 encircles the drum and is welded thereto, and to this ring is secured arim portion 5 by means of a plurality of circumferentially spaced bolts 4a. Projecting radially outward from rim 5 is a circumferential array of uniformly spaced studs or projections 6 which are received respectively in a corresponding circumferential array of uniformly spaced recesses 7 that open inwardly from the inner portion 8 of the pole wheel sn-ucture 3, As can be seen from FIG. 2, an elastic-type drive assembly is located between-each side of the projection 6 and the corresponding end of the recess 7. Each elastic drive assembly includes a pair of like, beam-type elastic members 9, shown in detail in FIG. 3, arranged front-to-front, with their outer end portions 9a in contact with each other and with their intermediate portions 9b spaced slightly apart to establish the desired elastic or spring action in a circumferential direction when the pole wheel drives the drum. Positive stop projections are located at the opposite ends of each recess 7 and these have a rounded end which engage with a flat middle portion of the adjacent elastic member 9. A plate 11 made of an abrasion-resistant material such as bronze secured to each side of the projection 6 has rounded end which engages a flat middle portion of the adjacent elastic member 9. Thus, the contact members 10 and 11 are located at about the same radial distance from the center of the drum and exert their forces against the middle portions 9b of the elastic members 9. The plates 11 enhance the ability of the studs to slide radially with respect to the elastic members 9, i.e. radially with respect to the pole wheel 3 as the mill drum expands or contracts. In order to exclude dust from reaching the interior of the recesses 7 and perhaps jamming the elastic members 9 to prevent them from functioning properly, each recess may be walled off by means of side plates 12 which are shown in FIG. 1.
The elastic members 9 of each pair are prestresscd by means of a suitable clamping arrangement in the direction towards one another, andthe dimensions of the members 9 between their center parts 9b are so chosen that in case of a short circuit of the machine, the center parts 9b actually touch each other and thus transmit the short circuit torque directly. Due to the special form, a unifonn distribution of the load is achieved at the same time.
The improved interconnection between the drum and pole wheel of the electric motor, in accordance with the invention is thus extremely simple, space saving and requires no attention. The individual elastic elements can adapt themselves readily to the unequal forces which are caused by temperature differences on the drum shell, and the thermal expansions in a radial direction are absorbed by the.sliding movement of the studs in the recesses, so that transmission of any deformation of the drum to the pole wheel of the motor is positively prevented.
1. A gearless drive for the drum of a cement mill or the like comprising a low-speedelectric motor surrounding said drum, said motor being constituted by an outer stationary stator and an inner rotor of the pole wheel type, and means interconnecting said drum and rotor which include a circumferential array of uniformly spaced studs structurally united with said drum and which project in a radially outward direction therefrom, a corresponding array of uniformly spaced recesses located on said rotor in which said-studs are received, and elastic means located between each side of each stud and the corresponding end of the recess for providing a driving connection between said rotor and drum, said elastic means at each side of each stud beingconstituted by a pair of like elastic members arranged in front-to-front relation, the outer end portions of said elastic members being in contact with each other and the intermediate portions thereof being spaced slightly from each other to establish a driving elasticity in the circumferential direction, and said studs being free to shift radially in said as defined in claim 1 and which further includes means providing a surface of abrasion-resistant material such as bronze between each side of each stud and the adjacent elastic member.