|
BJD
Mar 18, 2013 7:22:41 GMT -5
Post by John on Mar 18, 2013 7:22:41 GMT -5
There was a question posed months back on the Magnamatic shearer motor, I stated it was prone to shearing, although I'd seen a few with sheared shafts when I worked in the repair trade, I had no idea why they tended to shear more than other electric motors. I put the question to an old friend of mine who worked in the repair trade for around 40 years, seems the splines wore causing a "jolt"to the shaft when starting under load, the rest is metal fatigue.
|
|
|
BJD
Mar 18, 2013 15:59:13 GMT -5
Post by dazbt on Mar 18, 2013 15:59:13 GMT -5
There was a question posed months back on the Magnamatic shearer motor, I stated it was prone to shearing, although I'd seen a few with sheared shafts when I worked in the repair trade, I had no idea why they tended to shear more than other electric motors. I put the question to an old friend of mine who worked in the repair trade for around 40 years, seems the splines wore causing a "jolt"to the shaft when starting under load, the rest is metal fatigue. Do you really believe that was the cause of rotor shaft shear failure J? I'm no expert by any means but I can't get my head round that one.
|
|
|
BJD
Mar 18, 2013 16:08:54 GMT -5
Post by John on Mar 18, 2013 16:08:54 GMT -5
There was a question posed months back on the Magnamatic shearer motor, I stated it was prone to shearing, although I'd seen a few with sheared shafts when I worked in the repair trade, I had no idea why they tended to shear more than other electric motors. I put the question to an old friend of mine who worked in the repair trade for around 40 years, seems the splines wore causing a "jolt"to the shaft when starting under load, the rest is metal fatigue. Do you really believe that was the cause of rotor shaft shear failure J? I'm no expert by any means but I can't get my head round that one. No idea Daz, I did see a couple of Magnamatic motors with shafts sheared, but it's over 40 years ago now. Could have been poor machining, I would have thought the splines would have been machined to a tight tolerance, but to be honest, I never saw the sheared off section of shafts, the motors came into our workshop as was, so no chance to examine the splined sheared off section. You're more qualified to come up with a reason being a mechanic, than myself, although I did work as an electrical fitter for a few years, but beats me why one manufacturer had so many catastrophic motor shaft failures and the others didn't.
|
|
|
BJD
Apr 27, 2020 21:29:58 GMT -5
Post by maverick on Apr 27, 2020 21:29:58 GMT -5
No it wasn't as there were two problems and they were both design and manufacturing defects; originally they were solid shafts which were too soft and twisted too much with the original start up torque and they fractured from the centre of the shaft outwards.
They were then hardened to a higher hardness and in the hardening process they got surface micro fractures which, when coupled to the additional hardness made them open up the micro cracks to visible cracks and when they joined together they simply sheared.
They changed the design of the shafts and made them harder than the original shafts, but softer then the updated hardened shafts so they were inbetween, but the key difference was they made the shafts hollow by boring a 3/16th hole along them and this allowed the shafts to flex without shearing them during the start up phase.
|
|
|
BJD
Apr 28, 2020 1:45:09 GMT -5
Post by quimbyj1745 on Apr 28, 2020 1:45:09 GMT -5
back in the 60s I was on DPT FOR 1year and was sent to Birch Coppice to finish the installation of 72s seven ft the face machine was a BJD trepan shearer and new to the face teams, The face was a success and went onto 3 shift working, the men taking over at the face to give continuous production. A major problem arose with the machine, After 3 weeks and 4 days of production the shaft to the trepan cutting head sheared. this became a regular failing and the team became used to the breakdown to the extent that the replacement cutting head would be on the face at the main gate end for when the failure happened.
|
|