Proceedings in MANUFACTURING SYSTEMS Proceedings in Manufacturing Systems, Vol. 5 (2010), No.
DEVICE FOR MEASUREMENT OF CLAMPED JOINTS FRICTION TORQUE
Anton PANDA1, Eva BATEŠKOVÁ2, Jozef MAŠČENIK3
Abstract: This contribution deals with a proposal of device for measurement of clamped joints. In the second chapter, we propose a model of clamped joint. In the experimental part we measured values of the friction torque depending on twisting moment, and in the conclusion we measured shaft surface abrasivity.
Key words: Friction torque, dynamometer, 3D model.
1. INTRODUCTION 3, Ing. Jozef Maščenik,PhD., KNTZ FVT TU Košice, Prešov Tel. 051/7722603, [email protected] One of the basic construction elements for construction production either in engineering or building and construction industries are clamped joint claws. From the point of view of working life and criteria on the 3. PROPOSAL OF 3D DEVICE FOR FRICTION clamped joint jaws, the main importance belongs to JOINT MEASUREMENT stating the correct clamping power, as well as stating the Fig. 1 shows the proposed device solution. The correct friction torque in the joint. If there is a small device consists of frame 1, to which bearing shell sliding clamping power on this joint, it can cause an insufficient surface 14 is screwed. Holder 8 is welded to the frame friction torque and subsequently damage the clamped and there are pegs 11 screwed in it. Via screw 4, through joint and thus damage the whole mechanism. On the collar 13, dynamometer 5, peg holder and peg, the contrary, high clamping power can cause a big clamping power is transferred on claws 3. Weight 12 deformation either on the hub or clamped joint claws, slides axially along lever 6. Shaft 2 is from both sides which can lead to cracks in the claws or disabling the placed in bearings 9, which are in shell 10. Screw 7 mutual re-assembling and disassembling of the hub and serves to ensure the shaft position. claws [1]. Measuring procedure: 2. BASIC REQUIREMENTS ON JOINTS By the screw rotation, clamping of the shaft by means of In appliances, there are two types of binding claws is generated. From the dynamometer, the clamping between components and knots – movable and non- power is read. By means of the weight, it slides axially in movable. The type of movable binding results from the the direction from the shaft axis along the lever until the required function and kinematic scheme. The non- clamped joint is broken. From the weight mass and the movable bindings ensure a constant position of distance from the shaft, twisting moment of the clamped components and knots. The non-movable bindings are joint breach is calculated. The friction torque is obtained by linking the components and knots. determined from the condition for transfer of the twisting The binding elements and methods are to ensure moment. The disadvantage of this device is measurement sufficient resistance and required constant position of the scope restriction by the lever length and relatively components and knots. In precise mechanics, a higher complicated construction, which, however, eliminates the number of binding methods is used. shortcomings from the two previous proposals.
Reasons: Power and deformation ratios, Requirements on simple assembly and disassembly, High requirements on precision, Simultaneous use of heterogeneous materials in one knot, Requirements on outward form [2].
1, doc. Ing. Anton Panda,PhD., KVT FVT TU Košice, Prešov Tel. 051/7722603, [email protected] 2, Ing. Eva Batešková, PhD., KNTZ FVT TU Košice, Prešov Tel. 051/7722603, [email protected] For equal pressure distribution on the claw hub perimeter with external diametre of 90 mm
Measuring method : Every measurement began by clamping the clamped joint by power of 2 kN by a screw. On the lever, the weight was set on 33 divisions, whereas every division corresponds with a different twisting moment and afterwards the screw was slowly loosened until the clamped joint was broken. The breach occurs if the lever moves. When the lever moves, we read the number of divisions from the dynamometer. Gradually, the weight moves towards the rotation axis by two division up to 9 divisions. Fig. 1. 3D device model. Subsequently, the measurement was performed 3.1. Process of device set-up from 9 divisions to 33 divisions. After these measurements, we carried out measurement of the Firstly, 8 holes were drilled into the construction surface abrasiveness by device Mitutoyo SJ 301, and frame, into which coils M8 x 1,25 were cut. Into these consequently soft regrinding of claws by abrasive-coated holes, sliding surfaces of bearing shells were screwed by paper and re-measurement. means of screws with fixed head and internal hexagon. The bearings were inserted into shells and ensured by snap rings 68. The pegs were screwed into the peg holders either into the external holes for big claws or into the internal holes for small claws. The holder with the sliding surface and collar were inserted into the tubes with the internal diameter of 12mm on the construction frame. The claws were put on the pegs according to the peg distribution. The shaft was forced into the bearings Fig. 3. Device for measurement of surface abrasiveness and subsequently ensured against drop-out by snap rings Mitutoyo SJ 301. 40. The lever was screwed by a screw with a washer. Afterwards, a locking element against lever fall was Measurement of equal pressure distribution on screwed into the frame. The weight was put on the lever. hub perimeter : The dynamometer was screwed into the collar on the peg For this measurement, we used big claws of the holder and on the opposite side of the dynamometer the clamped joint, which were put on the pegs and collar with bearing were screwed. The frame was subsequently tightened by the screw to 2000 N. The supplemented by screw M24 x 2, which presses on the measured values of the clamped joint breach, as well as dynamometer collar and serves for educing the axial the calculated clamping power is in chart 1. Conversion power. Finally, the entire construction was fixed to the of the number of dynamometer divisions to power F was work table. done according to the equation (1)
F 2000 / 552,1.ndivisions (1)
Table 1 Measurement on claws with external diameter of Ø 90 mm Number of lever 33 31 29 27 divisions 25 Number of dynamometer 155 145 131 122 120 divisions F [N] 561,5 525,3 474,6 441,9 434,7 Number of lever 19 17 15 13 11 Fig. 2. Complete clamped joint device. divisions Number of dynamometer 71 56 43 40 32 4. EXPERIMENTAL MEASUREMENTS divisions F [N] The sample for this measurement is a shaft with the 257,2 202,9 155,8 144,9 115,9 Number of lever 13 15 17 19 diametre of 40mm and one type of claws : 21 F1. Surname1 et al. / Proceedings in Manufacturing Systems, Vol. 5 (2010), No. 1 / 110 (8 pt, Italic) 3
divisions Number of dynamometer 55 55 78 80 81 divisions F [N] 199,2 199,2 282,6 289,8 293,4 Number of lever 27 29 31 33 divisions Number of dynamometer 101 105 109 110 divisions F [N] 365,9 380,4 394,9 398,5
The calculation of the friction torque for equal pressure distribution was done according to equation (2)
M F . f ´.d F . . f .d (2) T N N 2 where f is chosen from 0,15 to 0,2 , for our measurement we used the value .
Table 2 Chart of calculated friction torques for claws of Ø 90 mm F [N] 561,5 525,3 474,6 441,9 434,7 M T 5,2920 4,9508 4,4730 4,1648 4,0970 [N.m] F [N] 257,2 202,9 155,8 144,9 115,9 M T 2,4241 1,9123 1,4684 1,3657 1,0923 [N.m] F [N] 199,2 199,2 282,6 289,8 293,4 M T 1,8774 1,8774 2,6634 2,7313 2,7652 Fig. 4. Measured surface abrasivity [N.m] F [N] 365,9 380,4 394,9 398,5 Fig. 5 shows the friction torque dependence on M T 3,4485 3,5852 3,7218 3,7558 twisting moment, which results in the fact that the [N.m] measurement on the device was with minor errors during the first measurement, when the weight was moved from Surface abrasivity measurement : the end of the lever towards the axis of rotation. During Fig. 4 shows the recording of measuring abrasivity of the the measurement from the axis, a bigger dispersion arose. surface of shaft with diameter of 50 mm.
Fig. 5. Friction torque dependence on twisting moment
5. CONCLUSIONS The calculated values of the friction torque are distorted. They depend on many factors, among which there are e.g.: precision of clamped joint make-out; surface abrasivity; clamping power; conditions of measurement; number of measurement etc. This causes the fact that when more measurements are carried out, the value of friction torque varies, which causes the dispersion in measurements. Finally, for demanding applications, it is suitable to recommend modern hydraulic tightening machines for their higher precision, and precise digital torque wrenches for clamped joint breach. This contribution forms a part of the solution of the grant task VEGA 1/0047/10.
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