Lucian.Stanescu

calculation of fasteners

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Hello everyone.

Recently I was asked for help in solving the problem of choosing some fasteners for an electric motor. 

Previously, the fasteners used (M28 8.8 Carbon steel) were corroding andit needs to be replaced with stainless steel. From what i know the mechanical properties of stainless steel fasteners are not as good of Carbon steel. So how can I check if the stainless steel fasteners are capable enough to keep the motor on place and in handling the loads induced by the electric nominal motor moment of torque of 1640Nm and weight of 1701 kg?

Thank you.

03_M3KP355SMB4-12_IMB3_2 separte terminal box_open deck_3GZF500135-328.pdf

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Hi Lucian!

Metric thread M28 doesn1 exist.

DIN 931 - Hexagon Cap Screws Partially Threaded Specifications: http://www.deepri.com/din_specifications/DIN-931-Hexagon-Cap-Screws-Partially-Threaded.html

PROPERTIES OF GRADE 8.8 BOLT & NUT (ISO): http://rocksideltd.co.uk/PDFS/23-GRADE%208.8%20BOLT%20&%20NUT%20(ISO).pdf

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There is another way....

...if you calculate the friction between the motor and its mount and "preload" the bolts to a specific torque such that the realised friction exceeds any force the motor is likely to experience in use, the "strength" of the bolds becomes secondary to the effect they have on the preloaded surfaces.

If properly calculates and "balanced", the overall strength of the bolts often falls down the pecking order of failure modes. 

This is a very often misunderstood reason for appropriate torque settings on screws and bolts....if appropriate, the preload eliminates any movement or losening as a result of hte loading of the unit....if inappropriate, the surfaces can experience deformation or premature cracking...not to mention the risk of hte bolt shearing!

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