How to select the appropriate grate bar material based on actual requirements?

A comprehensive, practical approach to selecting grate bar materials

Core selection logic: combustion temperature > fuel type (sulphur, ash, corrosion) > stress conditions of the grate structure > budget; simply compare these factors step by step to make your selection.

I. Step 1: Determine the long-term operating temperature of the furnace chamber (the most critical indicator)

The primary cause of grate failure: high-temperature oxidation and burnout, and cracking due to thermal expansion and contraction. Selection criteria based on temperature:

Operating temperature < 700°C (low-temperature conditions)

Suitable for: small-scale heating boilers, atmospheric hot-water boilers, low-load intermittent coal-fired boilers

Available materials: HT200 grey cast iron, malleable cast iron

Advantages: lowest price;

Disadvantages: cannot withstand prolonged high temperatures; frequent start-stop cycles may cause cracking.

700–850°C (the mainstream range for the vast majority of industrial coal-fired and biomass boilers)

 

 

Suitable for: 4t, 6t and 10t chain-grate boilers, reciprocating boilers and biomass pellet boilers (90 per cent of standard boilers on the market)

Preferred choice: RTSi5 silicon 5 heat-resistant cast iron

Offers a comprehensive balance of oxidation resistance and thermal shock resistance, with the best cost-effectiveness and the widest versatility.

850–920 °C (high-temperature combustion conditions)

Suitable for: pulverised coal co-firing, high-load continuous-operation boilers, and hot-air furnaces

Selection: low-chromium heat-resistant cast iron RTCr1/RTCr2

Superior heat resistance and resistance to deformation compared to Silicon 5; suitable for continuous high-temperature operation without shutdown.

Above 900 °C (high-temperature combustion chambers in incineration applications)

Municipal solid waste incineration, large-scale straw incineration, hazardous waste incinerators

Preferred choice: RTCr16 high-chromium cast iron / heat-resistant stainless steel castings

Maximum resistance to oxidation and high-temperature creep, preventing collapse, flaking and spalling.

II. Step Two: Selecting materials based on the fuel type (flue gas corrosion determines the corrosion-resistant material)

The higher the fuel’s sulphur, alkali metal and corrosive impurity content, the less suitable ordinary cast iron becomes:

1. Burning ordinary raw coal (medium- to low-sulphur coal)

Clean operating conditions; flue gas corrosion is mild

Optimal: Silicon 5 (RTSi5), the top choice for value for money.

2. Burning high-sulphur coal, low-grade coal and coal gangue

Severe sulphur dioxide corrosion in flue gas; Silicon 5 offers only moderate sulphur resistance

Recommended: RTCr1, RTCr2 low-chromium cast iron

Chromium provides resistance to sulphide corrosion and prevents perforation by flue gas.

3. Combustion of biomass (wood chips, straw, rice husks)

Straw fuel is rich in potassium and sodium-based alkaline ash, which causes high-temperature coking and sticking to the grate

Characteristics: Highly corrosive ash; prone to slag build-up and wear

Recommended: Silicon 5 > low-chromium cast iron;

Ordinary grey cast iron is not recommended, as it is extremely susceptible to corrosion and spalling by alkaline slag.

4. Incineration of municipal solid waste, sludge and hazardous waste

Alternating acidic and alkaline flue gases; extremely corrosive; significant temperature fluctuations

Required: High-chromium cast iron RTCr16 or heat-resistant cast steel, stainless steel castings.

III. Step 3: Selection based on grate structure & load conditions (requirements for fracture resistance and impact resistance)

Different grate operating modes result in vastly different load conditions and varying toughness requirements:

1. Chain grates (light traction, gentle loading)

Divided into driving and driven bars:

Driven grate bars: Subject to virtually no tensile or compressive forces → Silicon 5 or grey cast iron are both suitable

Driving grate bars: Subject to forces on pins, repeated pulling and friction → Ductile iron or Silicon 5 are preferred; ordinary grey cast iron with high brittleness must be avoided

2. Reciprocating grate (forward and backward pushing and pulling motion, high impact forces)

Grate bars are subjected to constant compression, impact and warping, making them highly prone to fracture.

High toughness is required:

Recommended: carbon cast steel ZG230–450, ductile iron;

Not suitable for purely brittle heat-resistant cast iron (Silicon 5 is relatively brittle and prone to fracture due to frequent pushing and pulling).

3. Beam grates, heavy-duty high-capacity boiler grates

High load-bearing capacity, heavy loads, and minimal thermal deformation required

Recommended: low-chromium cast iron and cast steel, which offer higher strength and are less prone to bending or deformation.

4. Fixed static grates (stationary grates, used solely to support fuel for combustion)

No mechanical stress; only high-temperature resistance and oxidation resistance are required

Silicon 5 is sufficient, offering cost-effectiveness and durability.

IV. Step Four: Operating Conditions (Start-stop Frequency)

Continuous 24-hour operation (industrial production boilers)

Stable temperature, minimal thermal shock: Silicon 5 and chromium-based heat-resistant cast iron are most suitable.

Boilers with intermittent start-up and shutdown (heating boilers, operated during the day and shut down at night)

Frequent alternation between hot and cold conditions, significant thermal shock, prone to cracking:

Avoid ordinary grey cast iron; prioritise Silicon 5 and ductile cast iron, which offer better toughness and resistance to thermal shock.