Objective
This spindle which is running on HMC at leading diesel engine manufacturer. This spindle was having problem of early failure of bearing and hence was leading to heavy downtime of the machine. The task was given to rectify the problem and enhance the bearing life. Before repairs the spindle was failing in 3 months and the needs to prolong this life to minimum 1 year.
General observations before dismantling of spindle
• Bearings used : 7017 ACD HCP4ADBA SKF make: 01 pair NN 3012 KTN/SP W 33 SKF Make: 01 no
• Lubrication : 8000 rpm.
• Axial play : Grease packed.
• Radial Play : 0.2 mm
• Quill bore run out : 0.015 mm
After opening spindle heavy coolant and dust was found inside the spindle. O rings which are used to prevent coolant seepage in spindle, were found to be worn out.
Activities carried out to recondition the spindle
Spindle shaft bore, which is BT 40 in size, and having run out of 0.015 mm was first ground with respect to bearing diameters and 90% blue matching. A due care is taken to maintain gauge length of spindle, which is mandatory for proper fitment of tool shank.
Spindle shaft is dynamically balanced to the level of 0.2 gm cm per plane.
The first thing which was observed that bearing failure was caused because of fatigue failure. This led us to conclusion that using only pair in the front end may not be sufficient to take cutting forces which are generated while machining. Hence we have taken decision to use a set of three in front side, instead of a pair.
Necessary modifications carried out in the existing spindle itself to accommodate a set of three and bearing no for the same was 7017 ACD/HCP4 ATBTB: SKF make.
Rear side bearing which is NN 3012 KTN/SP W33 which is unchanged. This is double row cylindrical roller bearings with taper bore. This type of bearing needs special skill to gain zero clearance which can be achieved by proper sizing of spacer. Our technical personnel possess skill to maintain the zero clearance because of hands on experience. The same zero clearance is maintained in this spindle as well.
A careful assembly practice is maintained while carrying out the assembly of this spindle in our temperature controlled clean spindle room.
Results achieved after assembly of spindle
• Quill bore run out : 1 micron
• Radial play : Nil
• Axial play : Nil
• Run out on test mandrel of 200 mm in length : 5 micron
