Classification, Performance and Applications of Mainstream Grate Plate Materials

Classification, Performance and Applications of Mainstream Grate Plate Materials

Core requirements for grate plates: high-temperature resistance, thermal shock resistance, wear resistance, oxidation resistance and resistance to ash and slag corrosion. Listed below in order of most common use in industrial boilers:

I. Standard cast iron types (the preferred choice for small-scale, low-temperature, atmospheric-pressure coal-fired boilers; offering the best value for money)

1. Grey cast iron (HT150/HT200)

Characteristics: Lowest cost, simple casting, good thermal conductivity, self-lubricating and wear-resistant; highly brittle, poor heat resistance

Long-term operating temperature: ≤650–700 °C

Disadvantages: Extremely prone to oxidation and flaking at temperatures exceeding 700 °C; prone to thermal shock cracking when exposed to cold water; short service life

Suitable for: Domestic heating stoves, small 1–4 t chain-grate boilers, low-temperature biomass boilers, passive grate bars (non-load-bearing areas)

2. Malleable cast iron (KTH350)

Characteristics: Significantly greater toughness than grey cast iron; less prone to brittle fracture; resistant to minor impacts

Applications: Drive grate bars for chain-fired boilers (areas subject to load transmission and reciprocating friction from pins); standard specification for older, small-capacity boilers

3. Ductile cast iron (QT450/QT500)

With spheroidal graphite, it offers superior strength, toughness and resistance to thermal fatigue compared to grey cast iron, whilst providing a slight improvement in heat resistance

Applications: Medium-load reciprocating grates, biomass combustion furnaces; positioned between ordinary cast iron and heat-resistant cast iron

II. Alloyed Heat-Resistant Cast Iron (The most widely used mainstream material for industrial coal-fired and biomass boilers)

1. High-silicon heat-resistant cast iron (RTSi5, commonly known as ‘Silicon 5’) [Most widely used on the market]

GB grade: RTSi5 (silicon content 4.5%–5.5%)

Advantages: Forms a dense protective layer of silicon dioxide on the surface at high temperatures, providing excellent resistance to oxidation; moderately priced

Long-term operating temperature: 750–850 °C

Applications: Chain grate boilers, reciprocating grate boilers, biomass boilers, and most industrial coal-fired boilers; Standard material for straight grates, four-claw grates and fish-scale grates

2. Chromium-based heat-resistant cast iron (RTCr1, RTCr2, RTCr16)

RTCr1/RTCr2: Low-chromium cast iron, with heat resistance slightly superior to Silicon 5 and better resistance to sulphur corrosion; suitable for burning high-sulphur coal

RTCr16 (high-chromium heat-resistant cast iron): 15%–18% chromium, withstands temperatures above 900°C, and offers outstanding resistance to oxidation and corrosion

Suitable for: high-temperature combustion zones, waste incinerators, secondary grates in circulating fluidised bed boilers, and applications involving the combustion of low-quality, high-sulphur fuels

3. Aluminium-based heat-resistant cast iron (RTAl)

Excellent high-temperature resistance, but highly brittle and difficult to cast; mainly used in small high-temperature furnaces, with limited widespread adoption

III. Cast Steel Grades (Heavy-duty, high-temperature, frequent reciprocating motion applications)

1. Ordinary carbon cast steel (ZG230–450)

Excellent toughness, impact resistance and fracture resistance; average wear resistance; prone to oxidation and deformation at high temperatures

Suitable for: moving bars in reciprocating grates, heavy-duty beam grates, and waste incineration agitating grates (requiring repeated pushing and pulling forces)

2. Heat-resistant alloy cast steel (high-chromium cast steel, 1Cr18Ni9 stainless steel cast steel)

Withstands high temperatures of 950–1100 °C; offers resistance to acids and alkalis, flue gas corrosion, and possesses the highest resistance to wear and slag pull-out

Disadvantages: Most expensive

Applications: Municipal solid waste incinerators, hazardous waste incinerators, and grate plates for large-scale high-temperature power station boilers

IV. Niche Specialised Materials

High-chromium white cast iron: Emphasises wear resistance; moderate high-temperature resistance; commonly used for wear-resistant protective plates on the sides of grates

Vermicular graphite cast iron: Balances thermal conductivity and strength; rarely used for the main body of grates