HVOF Tungsten Carbide Coated Wear-resistant Centrifugal Fan

Overview

HVOF spraying accelerates tungsten carbide particles to high velocity so that they form a dense coating. Heat input is low and bond strength is high, which suits high velocity fine particle erosion and makes it the least distorting of the common wear processes.

Coated Areas and Typical Figures

Erosion rate rises roughly with the 2.5 to 3 power of velocity, so coating is concentrated where gas velocity is highest.

Location	Process	Typical figure
Blade leading edge	HVOF tungsten carbide coating	Typical coating hardness HV 1000-1400
Impeller front plate	Local or full coating	Bond strength not lower than 70 MPa
High velocity casing area	Coating with sealing treatment	Controls fine particle erosion
Inlet cone	Coating or ceramic composite	Selected by erosion severity
Shaft and fits	Not coated	Preserves dimensional accuracy

Coating Process Control

Location	Process	Typical figure
Surface preparation	Grit blasting to specified cleanliness and roughness	Determines bond strength
Spray parameters	Control of gas flow, spray distance and feed rate	Stabilises coating density
Thickness control	Thickness set by duty and applied by zone	Balances life and cost
Sealing treatment	Sealing of porosity	Limits penetration by corrosive media
Bond strength specimen	Pull-off test per GB/T 8642	Coating acceptance basis

Applications

Applications include dust laden flue gas, catalytic cracking flue gas, metallurgical waste heat and coal or biomass fired boilers.

Coating life depends strongly on particle hardness and impact angle, so the scheme should be set from measured medium data.

Local coating damage can be repaired by re-spraying during maintenance, and repairability should be written into the maintenance plan to avoid replacing the whole rotor.

Acceptance and Verification

Standard	Title	Purpose
GB/T 8642	Thermal spraying - Determination of tensile adhesive strength	Coating bond strength acceptance
ASTM G76	Standard test method for conducting erosion tests by solid particle impingement using gas jets	Erosion wear evaluation
GB/T 4340.1	Metallic materials - Vickers hardness test - Part 1	Coating and hardened layer hardness
GB/T 9239.1 / ISO 21940-11	Mechanical vibration - Balance quality requirements for rigid rotors	Impeller balancing grade
GB/T 1236	Industrial fans - Performance testing using standardized airways	Air flow, pressure and efficiency testing

Please provide particle size and hardness, inlet velocity, medium temperature and air flow. Size and motor power are calculated for the actual duty.

FAQ

How do I choose between spraying and hardfacing?

Where particles are coarse and abrasive wear dominates, hardfacing is more economical. Where particles are fine, velocity is high and erosion dominates, tungsten carbide spraying is the better fit. Spraying has low heat input, so it suits impellers with tight dimensional requirements.

Why does a coating detach?

Detachment usually follows inadequate surface preparation or excessive thickness creating stress concentration. Blast cleanliness, roughness and spray parameters all follow a written procedure and are verified by a bond strength specimen.

How thick should the coating be?

Thickness is set from wear rate and inspection interval. Too thin fails early and too thick increases stress and cost, so thickness is specified by zone in the process document and checked by sampling.

Related pages: Wear-resistant fan range  Wear-resistant centrifugal fan  Dust collection and wear protection