Laser Cladding for Materials Processing Hammers - Tungsten Carbide reinforced Nickel Chromium Silicon Boron
Materials processing hammers are used in industry to pulverise hard and abrasive materials into a fine powder. The hammers are made from manganese steel, which although hard wearing, is prone to impact wear and tear.
Laser cladding the impact areas of the hammers is a cost effective method of applying a nickel based material reinforced with a high volume fraction of tungsten carbide, which provides a wear and impact resistant coating.
Laser cladding is a process that falls into the range of hard-facing solutions, which can be used to increase corrosion resistance, wear resistance or impact performance of metallic components, using a method of applying a fully dense, metallurgically bonded and virtually pure coating.
One of the major benefits of laser cladding is the ability to finely control the heat input to the substrate and the coating material, which allows a deposit of a two phase Metal Matrix Composite Structure. This means the coating can have a softer, lower melting point material (the matrix) where a harder wearing, higher melting point material (the hard phase) is suspended. The matrix material is typically a nickel based alloy, which provides a tough, ductile and impact resistant surface, while being wear resistant at elevated temperatures.
Laser clad hammers have been proven to last over three times longer than standard hammers, which reduced downtime and improves productivity.
Materials - Main Deposit: Tungsten Carbide reinforced Nickel Chromium Silicon Boron
Method
Preparation: The surface of the hammer components need to be cast and shot blasted to remove any contamination prior to being laser clad.
Equipment: Metallisation MET-CLAD system
Application of Laser Cladding
The images below show cage crushing machine material processing hammers in a granulated coal injection (GCI) plant. In this instance, coal is pulverised down by the hammers to produce a very fine powder, which is then blown into the blast furnace as an alternative to more expensive coke.
Using the MET-CLAD system, Metallisation can develop coatings that are tailored to suit a range of specific crushing applications.
To create an extremely strong wear and impact resistant coating for the CGI plant, the components of the hammers are laser clad with Tungsten Carbide reinforced Nickel Chromium Silicon Boron using a fine, accurately controlled laser beam.
The laser cladding process utilises a precisely focused high power laser beam to create a tightly controlled weld pool into which a metallic powder is applied. The powder is carried by a stream of inert shielding gas, which is blown coaxially through the laser beam. The highly accurate nature of the laser beam allows fully dense cladding with minimal dilution and a perfect metallurgical bond.
The very low heat input, associated with a laser, means the tungsten carbide particles remain un-melted and so retain their harness, which adds to the wear resistance of the coating.
Due to the high level of accuracy and control, laser cladding enables the cost effective application of high performance alloys to tackle a wide range of engineering issues. Typical deposition rates are between 60 and 100 g/min around 3-6 kilograms per hour, depending on the material being deposited and the geometry of the work piece.
To apply a laser clad coating the cladding head has to be fed the appropriate with four key things; a laser beam, process gasses, powder and cooling water. The Metallisation MET-CLAD laser cladding control console provides integration and control of the complex component parts. The MET-CLAD system is a simple to use control system with touch screen HMI and is based on the Metallisation HVOF and Plasma control concept.
The control console offers mass-flow control of the laser shielding and powder feed gas for repeatable cladding. The laser can also be housed and controlled within the cladding console.
The control interface for production operations is simple, but it can be drilled down to a great level of complexity for coating development. Repeatable operations are easily programmed or they can be linked to a barcode system for even simpler programming. The process gases are mass flow controlled for repeatability of the coating process.
Comparison of Coatings
The image above shows a Laser Clad hammer on the left and a conventionally coated hammer on the right.
Comparison of Coating Processes
The following table gives a broad comparison of coating processes. The data shown is based on typical applications and parameters. There can be exceptions to this data, dependent on the specific applications and parameters, MSSA will be happy to offer advice for specific applications.
| HVOF Thermal Spray | PTA | Laser Cladding | |
| Heat Source | Flame (Liquid or Gas) | Electric Arc | Laser Beam |
| Coating Thickness (Typical) | 0.05 - 1mm | 0.5 - 5mm | 0.2 - 2mm |
| Typical Deposition Rates | ≤ 5 kg/hr | ≤ 10 kg/hr | ≤ 5 kg/hr |
| Dilution | 0 | 5-15% | ≤ 5% |
| Type of Bonding | Mechanical | Metallurgical | Metallurgical |
| Bond Strength | ≤ 80 MPa | ≤ 800 MPa | ≤ 800 MPa |
| Heat Input | Low - Medium | High | Low - Medium |
| Porosity | ≤ 1% | < 0.1% | < 0.1% |
| Comparative Capital Cost | Medium | Low | High |
| Comparative Running Cost | High | Medium - Low | Low |
Conclusion
Laser cladding is capable of producing coatings with a combination of excellent toughness and abrasive wear resistance. Due to the low heat input the tungsten carbide particles remain un-melted, which means they retain their hardness and wear resistance.
Laser clad hammers have been proven to last over three times longer than standard hammers, resulting in reduced downtime and increased productivity.
