What Material Should Be Used for Coal-Fired Chain Grate Bars?
For grate bars of coal-fired chain grates, medium-silicon heat-resistant ductile iron RQTSi5 is the first choice under normal duty. For duty with high sulphur or a rather high furnace temperature, chromium-series heat-resistant cast iron is the next option.
1. Normal material selection
Grate bars work for long periods under high-temperature oxidation and alternating hot and cold conditions, so the choice of material depends mainly on oxidation resistance, thermal fatigue resistance and wear resistance. RQTSi5 (high-silicon ductile iron) is the commonly used main material and resists high temperature, oxidation, thermal fatigue and wear. It suits conventional coal-fired chain grates, can take a rather high furnace temperature over long periods, balances cost against life, and fits most small and medium coal-fired chain boilers. Chromium-series heat-resistant cast iron is also available (RTCr, RTCr2, RTCr16 and similar alloy heat-resistant cast irons), which resists high temperature and sulphur attack better and suits high-temperature, high-sulphur coal duty, but it costs more and its toughness needs attention.
2. Other materials
Ordinary grey cast iron (HT200, HT250) suits only low-temperature, light-load, low-parameter old boilers and has a short life. Such material does not suit long-term high-temperature main duty. Malleable cast iron (malleable iron, KTH series) is used for some driving grate bars, has good toughness and impact resistance and suits heavily loaded driving bar positions, but it is not suitable for areas directly burnt at high temperature over long periods.
High-end duty and selection
High-chromium cast steel, ZG40Cr9Si2 and similar heat-resistant cast steels or heat-resistant alloy steels can be used for high-temperature, high-calorific coal and heavy-duty large boilers. These materials resist high-temperature creep, wear and corrosion well, but they cost significantly more.
| Material | Applicable duty |
|---|---|
| RQTSi5 medium-silicon heat-resistant ductile iron | Conventional coal-fired chain grates, most small and medium coal-fired chain boilers |
| RTCr, RTCr2, RTCr16 chromium-series heat-resistant cast iron | High-temperature, high-sulphur coal duty |
| HT200, HT250 grey cast iron | Low-temperature, light-load, low-parameter old boilers |
| KTH series malleable cast iron | Heavily loaded driving grate bar positions |
| ZG40Cr9Si2 and similar heat-resistant cast steel | High-calorific coal, heavy-duty large boilers |
Selection advice: for conventional industrial coal-fired chain grates, RQTSi5 is preferred; where sulphur is high and the furnace temperature is rather high, chromium alloy heat-resistant cast iron such as the RTCr series is used. Driving bars under load can be paired with malleable cast iron or malleable iron to raise toughness; for light-load duty in old boilers HT250 and similar grey cast iron can be used for a short time, but life is short and it is not the first choice. When replacing grate bars, keep the pitch and clearance within the same row consistent, which helps reduce local overheating and abnormal wear.
