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Improved fastening system for mill linings
2004 (English)Independent thesis Basic level (professional degree), 10 credits / 15 HE creditsStudent thesis
Abstract [en]

Metso manufacture mill linings in rubber and metal/rubber combinations for grinding mills. The mill linings are attached with bolt attachments. Lately there have been some problems with bolt breakage. According to the theory, bolts are sensitive to dynamic load, especially when it comes to high amplitude loads. To get low amplitude load the clamped parts should have a high stiffness and the bolts must be elastic. In Metsos case, most of the clamped parts are made of rubber which means that the bolts are stiff in relation to the clamped parts. This is not an optimal joint. The theory also says that soft materials result in bigger embedment (loss of preload). To find out how different parameters affect the joints and be able to improve the function of the bolted joints, some tests have been performed in the test bench. These are the test result: • Generally speaking the amplitude increases in all bolts, if one/some of the bolts loose the clamp load. • Decreased tightening speed results in less loss of preload. • The torque order has great influence when it comes to 3-bolt lifter bars. If the torque order is (censored) the loss of preload is quite uniformed for all bolts, but if the torque order is (censored) the bolt in the middle (2) will loose considerably more of the preload than the other bolts. • Generally speaking the size of the hole doesn’t have much influence, but when the tightening speed is high and the torque order is (censored) the variance in loss of preload gets pretty great with different sizes of the hole. • The loss of preload became bigger with a non flexible outside, that means a flat washer only, instead of a cup washer with a sealer. This indicates that the sealer and the cup washer work as a spring and help the joint to maintain its clamp load. • Higher torque results in a significant higher clamp load in the bolts. The loss of preload in % of initial preload is also less at higher torque. • After the bolt, the clamp block is the weakest part in the joint. Prior to a decision to increase the torque it is important to verify if the individual attachment parts can handle a higher clamp load. To be able to load the clamp washers to failure and record the load in a good way, a test jigg has been designed. Our recommendations: • Further investigations of how much load the joint can handle, maybe by using our test jigg to be able to use the measure equipment from the test bench. • If the joint can handle a higher load: increase the torque from recommended (censored) Nm to (censored) or (censored) Nm. • Low tightening speed. • Torque order (censored) (3-bolt lifter bar). • Lubricate the threads.

Place, publisher, year, edition, pages
2004.
Keywords [en]
Technology, Skruvförband, attachments, bolted joints, preload
Keywords [sv]
Teknik
Identifiers
URN: urn:nbn:se:ltu:diva-51689ISRN: LTU-HIP-EX--04/023--SELocal ID: 8e37cc90-2e4d-42f1-bf81-ba7a56813a00OAI: oai:DiVA.org:ltu-51689DiVA, id: diva2:1025053
Subject / course
Student thesis, at least 15 credits
Educational program
Mechanical Engineering, bachelor's level
Examiners
Note
Validerat; 20101217 (root)Available from: 2016-10-04 Created: 2016-10-04Bibliographically approved

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