How to Extend the Service Life of Chain Grate Bars?

Extending chain grate bar life centres on reducing three kinds of damage: thermal fatigue, sulphur and slag corrosion, and mechanical jamming and impact. It also means keeping grate engagement accurate, air distribution even and load steady.

Optimising operating conditions

1. Control furnace temperature: keep air distribution reasonable and even, and avoid local air shortage, clinker build-up and long direct flame on one area of the grate, which cause local overheating, creep, thermal fatigue cracking and burn-off. Reduce frequent starts and stops and sudden hot-cold changes, run steadily and continuously, and cut banked fires, sharp load swings and rapid heating and cooling, so that thermal fatigue cracks from repeated expansion and contraction are limited. Clear clinker promptly so molten slag does not cling to and attack the grate surface and cause sulphur and carbon penetration, and so clinker lumps do not jam and deform the grate. Also control furnace negative pressure to reduce air leakage, one-sided burning and flame passage that scorches side bars and edge bars.
2. Improve coal quality and feeding: reduce long-term use of high-sulphur coal, high-ash slag, hard shale, large hard lumps and sand and grit, so sulphur corrosion and wear impact are lighter. Screen, crush and blend the fuel when necessary, and control coal size so oversize lumps do not strike the grate directly. Keep the coal bed evenly thick so no area runs thin and exposes the grate to flame; too much fine coal dust causes secondary combustion under the grate, wind box burnout and high-temperature attack on the grate underside, so it needs control. Blend fuel sensibly to limit long-term attack by corrosive flue gas such as sulphides and alkali metal salts.
3. Adjust grate speed: set grate speed to load so burnout occurs at the right point, avoiding long residence of fuel on one section of the grate under continuous high temperature, and avoiding excessive speed that causes impact wear at the engagement. Also keep the grate running steadily, without drift and without scraping the side clinker boxes, furnace walls and supports. Check side clearances and wear protection regularly and remove rubbing wear promptly.

Maintenance of the grate body and drive system

1. Periodic inspection and preventive replacement: daily rounds check for cracks, deformation, wear, jamming, abnormal noise and coal leakage, with focus on the combustion zone, edge bars, driving engagement bars and pin positions. During scheduled shutdowns, measure thickness, check for hidden cracks, pitch deformation and wear of pins and pin holes, and replace bars that exceed limits or have degraded, so the grate is not run in a faulty state with repeated repair welding. Replace in matched batches of the same material and model where possible, so differences in thickness and pitch between old and new bars do not cause abnormal engagement and jamming wear. Also check and replace pins, bushes, chains and sprockets on schedule to keep one uniform pitch and smooth engagement and to cut repeated tensile fatigue on the driving bars; keep side seals and wear protection in good order as well, so side flame leakage, wear and corrosion are reduced.
2. Lubrication and drive adjustment: lubricate the grate main shaft, sprockets, bearings and drive parts correctly to reduce jamming resistance and alternating load and to cut repeated tensile damage on the driving bars. Correct grate tension and the alignment device to prevent long-term drift, arching, jamming and local extra load; correct sprocket engagement to reduce impact wear at the mesh. Check air box distribution so each box has even air volume and sensible pressure, and prevent local high air temperature from burning the grate underside.
3. Material and part quality: in the main combustion zone use qualified RQTSi5 medium-silicon heat-resistant nodular cast iron, in high-sulphur high-temperature duty use chromium-series heat-resistant cast iron, and for load-bearing driving bars use malleable cast iron, avoiding low-priced inferior ordinary grey cast iron. On acceptance, check the material certificate, ensure casting quality and reduce gas porosity, sand holes and internal defects, and run a small trial batch to verify life when necessary. Compliant surface-hardened or heat-resistant coated parts may also be used to improve oxidation and corrosion resistance.

Repair and patching practice

Slight surface cracks can be repaired with a compliant heat-resistant electrode, with preheating before welding and attention to holding, to reduce welding stress cracks; bars with through cracks, serious deformation or reduced wall thickness must not be repeatedly repair-welded and returned to service. Shutdown cooling should follow natural cooling; the grate must not be quenched with direct cold water spray, which causes brittle cracking. During long shutdowns for maintenance, clear slag and ash and keep the grate dry, so rust and corrosion from moisture and residual acidic flue gas are reduced.

Daily management and operation

Strengthen stoker training and strictly prohibit overload operation, long banked smouldering fires, local over-temperature and blind high-volume air disturbance. Keep records of bar replacement intervals, fault causes and operating parameters, and set a preventive maintenance plan to avoid sudden chain breakage. Monitor coal leakage rate, furnace temperature and grate motor current, and trace any abnormality promptly. Protect the driving load-bearing bars and the edge bars on both sides, select the correct material parts for the duty, and put preventive maintenance in place of run-to-failure replacement.