Case Study

• Problem: high vibration on a critical induced-draft fan, raising the risk of an unplanned kiln stoppage.
• Root cause: confirmed by vibration measurement; the usual causes are imbalance from material build-up on the impeller, soft foot or bearing looseness.
• Solution: correction matched to the confirmed cause: impeller cleaning and field balancing, soft-foot correction or bearing replacement with correct fits.
• Result: vibration measured before and after the correction and compared with the plant’s vibration limits.

Lesson: measure before you replace. Vibration readings point to the cause.

• Problem: frequent pneumatic cylinder and valve failures causing repeated packing-line stoppages.
• Root cause: traced to compressed-air quality and component specification: wet, unfiltered air or a valve not matched to the duty.
• Solution: air treatment restored (drains, filters and dryer checked) and valves re-specified for the duty cycle.
• Result: failures per month tracked before and after the change.

Lesson: pneumatic component life depends on air quality as much as on the component.

• Problem: short mechanical seal life and leakage on a cooling-water pump.
• Root cause: investigated against the usual causes: dry running, shaft misalignment or a seal type not suited to the water quality.
• Solution: alignment corrected, operating conditions checked and the seal re-specified for the duty.
• Result: seal life recorded before and after the change.

Lesson: a mechanical seal usually fails because of how the pump runs, not because of the seal.

• Problem: the OEM horizontal articulated spindle for stand 350 cost TK 800,000 with a 12-month lead time.
• Root cause: single-source dependency on the OEM for a critical spare.
• Solution: matched the full specification and drawings and qualified an alternative supplier. The same approach was used for shear plain blades.
• Result: spindle at TK 201,020 with a 5-month lead time (about 75 % lower cost). Shear blade TK 19,442 instead of TK 32,650, with a 4-month instead of 6-month lead time.

Lesson: with complete drawings and specifications, a qualified alternative can match the OEM part at a fraction of the cost and lead time.

• Problem: a cantilever vertical looper working about 1,500 cycles a day had short bearing and roller life, broken roller mounting bolts and worn moving shafts and bushes.
• Root cause: the cantilever design concentrated the cyclic load on the roller bearings, mounting bolts and bushes. Better spare parts could not fix a design limitation.
• Solution: modified the looper design and fabricated eight loopers in-house instead of importing them.
• Result: MTBF increased from 4 months to 36 months, spare life increased and looper delay fell. In-house fabrication cost TK 3,256,000 against TK 15,800,000 for imported units, a saving of TK 12,544,000.

Lesson: when a part fails because of the design, a better part will not fix it. Modify the design.

• Problem: pneumatic cylinder up/down downtime above the plant standard.
• 5-Why: (1) Why is downtime high? Solenoid valve spools jam. (2) Why do they jam? Particles in the valve. (3) Why particles? Rust inside the carbon-steel air supply pipe. (4) Why rust? Water coming from the dryer. (5) Why water? Wrong dryer type and capacity.
• Root cause: valve malfunction caused by particles from a wet, rusting air supply, starting at an undersized dryer.
• Solution: corrective: replaced the jammed solenoid valves. Preventive: installed a new filtration system and increased the FRL check frequency in the preventive maintenance plan.
• Result: reduced delay time and spare valve consumption.

Lesson: replacing the valve treats the symptom. Fix the air quality at its source.

• Problem: gearbox bearings failing repeatedly, causing unplanned mill stoppage.
• Root cause: investigated across bearing clearance class, lubrication condition and shaft alignment.
• Solution: bearing specification, installation method and lubrication practice corrected to match the duty.
• Result: running hours and downtime compared before and after the correction.

Lesson: when the same bearing fails repeatedly, investigate the conditions around it before ordering the next one.

• Problem: the vertical stand slowly lowered from its set position during rolling, moving the stand off the pass line and stopping the mill.
• Root cause: internal leakage in the hydraulic counterbalance (load-holding) circuit. A worn counterbalance valve seat and seals let the cylinder creep down under load.
• Solution: isolated and pressure-hold tested the cylinder and the valve separately to find the leaking component; replaced the counterbalance valve cartridge and seals and set it to the manufacturer’s pressure; flushed and filtered the oil; added a monthly hold (drift) test to the preventive maintenance plan.
• Result: the stand holds its set position under rolling load; drift and stoppages are recorded before and after the repair.

Lesson: a load that creeps down is almost always internal leakage. Test the cylinder and the valve separately before replacing either.

• Problem: spindle holder bearings failing, causing unplanned mill stoppage.
• Root cause: fishbone analysis traced the failures to a blocked air-oil lubrication distributor block. Contamination in the distributor starved the bearings of oil.
• Solution: corrective: replaced the damaged roller and the distributor. Preventive: fitted a new filter to every air-oil distributor, updated the preventive maintenance plan for the air-oil system, moved stand 1 to 18 bearings from grease to air-oil lubrication and started condition-based monitoring.
• Result: lower overall mill delay and lower bearing and spare consumption, with bearing life tracked after the change.

Lesson: bearing life depends on lubricant actually reaching the bearing. Check the flow at each distributor, not only that the lubrication pump is running.

• Machine name, manufacturer and model.
• Symptoms or replacement need: what happens, how often and since when.
• Operating conditions: speed, load, temperature and environment.
• Photographs of the failed part, the nameplate and the installation, plus drawings if available.
• Measurements and maintenance records, such as running hours, vibration or temperature readings.

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