Kiln Tyre Grinding - Ball Mill Grinding

Ball Mill Trunion Grinding

A. Break down observed:

• Trunion journal got worn-out due to damage of seal and ingress of raw material in the trunnion bearing, leads to damage of the trunnion journal surface.
• Thickness of trunnion reduced considerably beyond repairs at four positions along the circumference.

B. M/s ALLAN SMITH has studied the root cause and repaired as:

• Removal of worn-out surface, circumferentially at the damaged area using minimum heat input.
• Care taken to ensure minimum distortion of the journal during the repairs (cutting and welding).
• Preparation of “V” groove at the 4 positions.
• Fabrication of 60 mm thick ring of 500 mm width and diameter 1628 mm.
• Machining of ring on the outside to ensure the circularity and required surface finish.
• Window cut damaged portion of the ring and refurbish on the trunnion.
• During the patch, it is ensured to maintain the straightness throughout the length.
• Upon conforming straightness, suitably weld to avoid “out of roundness”.
• After completion of the weld, following parameter were checked:
• a) Total Indicated run-out at three positions found 2.5 mm radially.
• b) Surface straight ness 1.3 mm low at end portion and 1.2 mm high at the center.
• Above deviations occurs due to welding distortion.

C. Trunion Grinding:

• ASEPL had especially developed precision grinding machine for similar grinding assignments
• Grinding machine installed at appropriate positions, parallel to the rotating axes at an angle @ 40 ⁰.
• Mill rpm in inching drive is 0.3, increases to 1 and maintain @1 rpm for the grinding.
• Suitably select grinding stone specification and depth of the grinding executed at every phase.
• Material removal on the trunnion is 3.5 mm radially.
• Final reading as out of roundness +/-0.35
• a) Straightness throughout length +/-0.7 TO +/- 1.0
• b) Surface finish up to 25 micron I.e. 30 to 35 rms value.

D. Blue matching of bearing liner:

• After completion of the grinding:
• a) bearing liner scrapping carried out to blue match the trunnion surface.
• The blue match contact pattern taken as:
• a) 100% at center along the length and width 300mm Rest of the portion is non-contact.
• b) Bearing clearance, radial of 0.35 to 1.7mm, gradually increase as per the standard.

E. Result (During trial run, after the correction):

• Mill lift observed 0.3mm whereas earlier recorded was 0.1mm, under the similar conditions.
• Mill operates on auxiliary 0.3 rpm for 10 hrs, no temperature rise observed in journal bearings.
• Mill taken on full rpm for 4 hours, observed operates in normal (no abnormalities observed).
• Finally mill charged with 70% grinding media and started, runs smoothly with normal feed.
• Further grinding media charged gradually up to 100% and observed mill operates normal.

F. Conclusion

• a) Time required for the above assignment is 30 days and the time break up is as:
• 1. Forming, weld repairing: 15 days
• 2. Grinding and blue matching: 11 days
• 3. Mill alignment measurement and corrections: 02 days
• 4. Box up: 02 days
• b) Delivery period of new trunion assembly is approx. 6 month, and above activities result in saving of 5 months production loss of client

G. Machine and tools deployed:

• Specially designed grinding machine for the trunnion grinding.
• Bearing scrappers.
• Laser Alignment measurement instruments.
• shims for alignment of various thickness.
• Prussian blue.
• Hydra, sling, D-shackles, etc.