High Temperature Induced Draft Fan for 300 C Service

Overview

300 C is the entry level of high temperature induced draft fans. The task here is not to change to a heat resistant steel but to keep heat away from the bearings: Q235B carbon steel with an inorganic heat resistant coating is sufficient, and the emphasis is on insulation and cooling design.

Material Selection at 300 C

Below 300 C carbon steel retains adequate strength, so selection focuses on surface protection and thermal separation rather than on alloy content.

Location	Material / process	Basis
Impeller and casing	Q235B carbon steel (GB/T 700)	Stable strength up to 300 C at moderate cost
Surface treatment	Inorganic heat resistant primer with silicone topcoat	Limits oxidation scaling at 300 C
Bearing assembly	Standard bearing housing with external cooling wheel	Prevents heat transfer through the shaft
Insulation	50 mm rock wool over the casing	Lowers casing skin temperature
Clearance	Radial clearance set for thermal growth	Avoids rubbing at operating temperature

Structural Measures at 300 C

Location	Material / process	Basis
Bearing housing outside the hot zone	Extended shaft moves the bearings away from the casing	Keeps bearing temperature in range
Cooling wheel on the shaft	Fins create an air film along the shaft	Reduces heat conduction to the bearings
Balancing to G6.3	Static and dynamic balancing per GB/T 9239.1	Covers slight distortion after heating
Sliding support	One fixed foot and one sliding foot	Releases axial thermal growth
Removable insulation	Insulation supplied in removable sections	Allows weld and impeller inspection

Applications

Applications include baking and drying ovens, paint curing lines, food and herbal drying and printing dryers in the 200 to 300 C range.

The medium is usually hot air or low dust flue gas, so insulation rather than exotic material gives the better return.

Casing insulation is best made removable so that welds and impeller wear can be inspected without stripping the whole casing.

Acceptance and Verification

Standard	Title	Purpose
GB/T 1236	Industrial fans - Performance testing using standardized airways	Air flow, pressure and efficiency testing
GB/T 9239.1 / ISO 21940-11	Mechanical vibration - Balance quality requirements for rigid rotors	Impeller balancing grade
JB/T 10563	General purpose centrifugal fans - Technical specifications	General technical conditions and works acceptance
GB/T 2888	Methods of noise measurement for fans and blowers	Noise measurement and acceptance
GB/T 3235	Fans - Basic types, dimensions, parameters and performance curves	Impeller type and performance curve

Impeller size, air flow, pressure and motor power are calculated for the actual duty. Please provide medium temperature, dust load and available space.

FAQ

Can carbon steel be used for a 300 C fan?

Yes. Q235B retains sufficient strength at 300 C when combined with an inorganic heat resistant coating and casing insulation. If the medium contains sulphur or moisture, a higher grade or a protective coating is recommended.

Why is dynamic balancing required at this level?

Blades distort when they reach 300 C, which changes the mass distribution. Balancing to G6.3 per GB/T 9239.1 keeps vibration from rising as the fan runs.

What should I check if the bearing temperature is too high?

Check whether the bearing housing is outside the hot zone, whether the cooling wheel is effective and whether the grease is rated for the temperature. A water jacket or oil circulation unit may be needed.

Related pages: