How to Choose the Right Grate Bar Material Based on Actual Needs?
Material choice for grate bars starts with furnace temperature, then covers coal quality, load pattern, structural position and budget, and finally checks dimensions and fit. A mismatch between material and duty usually shows up as cracking, deformation or corrosion loss within one or two maintenance cycles after start-up.
Furnace temperature and coal quality
- Furnace temperature: for medium and low temperature, ordinary coal, a stable furnace temperature and no long open-flame burning, choose RQTSi5 medium-silicon heat-resistant nodular iron, which balances heat resistance, thermal fatigue resistance, wear resistance and cost. For a high-temperature furnace, high calorific value coal, long open-flame baking, repeated hot and cold cycling and a tendency to crack and deform, choose chromium heat-resistant iron (RTCr, RTCr16) or high-chromium heat-resistant cast steel (ZG40Cr9Si2 and similar), whose oxidation, creep and high-temperature deformation resistance is stronger. For old small boilers, light load, intermittent operation and lower temperature, grey iron HT250 can be used for a short period, but it is not suitable for long-term full-load running and tends to burn away, deform and break.
- Coal quality: ordinary low-sulphur raw coal is served well by RQTSi5, which gives a better balance of cost and performance. For high-sulphur coal, corrosive flue gas, acid slagging and serious sulphate corrosion, choose chromium alloy heat-resistant iron or high-chromium alloy material to strengthen sulphur corrosion and slagging erosion resistance and keep plain grey iron and plain nodular iron from being attacked quickly. For heavy hard slag, large coal particles, much gangue, severe wear and frequent impact, the base material must also resist wear; driving grate bars, that is the drive engagement area, can use malleable iron (Magan, KTH series) separately to gain toughness, impact resistance and resistance to breakage, while static grate bars still use heat-resistant iron.
| Duty condition | Recommended material | Notes |
|---|---|---|
| Medium and low temperature, ordinary coal, stable furnace temperature | RQTSi5 medium-silicon heat-resistant nodular iron | Balanced heat resistance, thermal fatigue resistance, wear resistance and cost |
| High-temperature furnace, high calorific value coal, repeated hot and cold cycling | RTCr, RTCr16 chromium heat-resistant iron or ZG40Cr9Si2 high-chromium heat-resistant cast steel | Stronger oxidation, creep and high-temperature deformation resistance |
| Old small boilers on light load and intermittent operation | HT250 grey iron | Short-term use only, not for long-term full load |
| High-sulphur coal, acid slagging, sulphate corrosion | Chromium alloy heat-resistant iron, high-chromium alloy material | Sulphur corrosion and slagging erosion resistance |
| Drive engagement load-bearing positions | Malleable iron (Magan, KTH series) | High toughness, impact resistance, resistance to breakage |
Load pattern and position differences
- Load pattern: large industrial boilers running 24 hours at continuous full load should choose heat-resistant alloy iron or heat-resistant cast steel first, to reduce creep elongation, deformation jamming and bar loss. Intermittent heating boilers, frequent starts and stops and heavy hot and cold cycling should choose RQTSi5 medium-silicon nodular iron with good thermal fatigue resistance first, to reduce thermal fatigue cracks, and high-chromium material that is too brittle needs care. Small heating boilers on light load and seasonal operation put cost first, so a qualified medium-silicon nodular iron is enough.
- Grate structure position: driving grate bars engage under load and pull the whole grate, so the core needs are toughness, tensile resistance and impact resistance; choose malleable iron (Magan) or tough alloy iron, not a purely brittle high-temperature material. Driven bars and grate bars in the main combustion zone face the flame and stay hot for long periods, so the core needs are high-temperature resistance, oxidation resistance and corrosion resistance; choose RQTSi5 or chromium heat-resistant iron. Side seals and edge grate bars need both heat resistance and wear and scrape resistance, so a suitable alloy iron can be used.
Budget and specification matching
- Budget and maintenance cost: a boiler that runs long term should put more into heat-resistant alloy material up front, which reduces the downtime loss of frequent replacement and keeps total cost lower. Short-term or standby boilers use standard medium-silicon nodular iron to hold initial purchase cost down. Low-priced plain cast iron products need caution, because they save money in the short term but need frequent overhaul and affect boiler operating safety.
- Specification matching: first confirm that the material grade meets the industry standard for boiler fittings, then match the dimensions, thickness and structure of the original grate to ensure the parts fit and do not jam. When ordering to drawing or sample, confirm the mounting hole positions and expansion clearance at the same time.
