What is hardfacing?
Hardfacing is a technique used to make metal surfaces stronger and more resistant to wear and tear.
It involves applying a layer of a harder, more durable material on top of a softer metal. This is done by welding the hard material onto the surface, creating a protective layer that can handle more abrasion, impact, or heat than the original metal.
It’s commonly used on parts that experience a lot of friction, like tools, machinery parts, or equipment in mining and agriculture, to help them last longer and perform better.
There are several welding methods for hardfacing, including stick welding, submerged arc welding (SAW), laser welding, and TIG welding. However, MIG/GMAW (Metal Inert Gas / Gas Metal Arc Welding) is often the preferred choice for on-site hardfacing of large objects. MIG/GMAW stands out in these situations because it is fast, flexible, and produces a smooth, consistent layer. Additionally, it is easier to control, especially on larger surfaces, and allows for continuous welding with minimal stops, making it efficient for high-wear applications.
Examples of use
Hardfacing is a versatile technique used across various industries to enhance the durability and lifespan of metal components by applying a wear-resistant layer. Here are some tangible real-life use cases for hardfacing:
Agriculture
Plowshares and Tillage Tools: In remote locations where replacement parts are hard to get, hardfacing is applied to plowshares and tillage tools to resist abrasion from soil and rocks, extending their service life significantly.
Harvesting Equipment: Components such as cutter bars and threshing drums benefit from hardfacing to withstand the abrasive nature of crops and soil.
Mining
Crusher Jaws: Hardfacing is used on crusher jaws to enhance resistance against the impact and abrasion from crushing rocks and ores, thereby reducing downtime and maintenance costs.
Earthmoving Equipment: Buckets, blades, and other parts of excavators and loaders are hardfaced to endure the harsh conditions of mining operations.
Construction
Excavator Buckets: Hardfacing strengthens excavator buckets against wear from digging and moving materials like gravel, sand, and rocks.
Asphalt Paving Equipment: Augers and hoppers in asphalt paving machines are hardfaced to resist wear from hot, abrasive materials.
Forestry
Debarking Equipment: Hardfacing is applied to debarking equipment to combat the abrasive action of bark mixed with sand and other materials.
Saw Blades: Hardfacing extends the life of saw blades used in cutting timber by providing a hard, wear-resistant edge.
Manufacturing
Brick Manufacturing Equipment: Machines involved in brick production are hardfaced to handle the abrasive nature of clay and other raw materials.
Pulp and Paper Industry: Equipment like chippers and grinders are hardfaced to resist wear from processing wood chips into pulp.
Energy Sector
Coal Crushing Equipment: Hardfacing is used on coal crushers to withstand the abrasive nature of coal mixed with silica or sand.
Hydroelectric Turbines: Turbine blades are clad with hardfacing materials to resist erosion from water flow.
These examples illustrate how hardfacing enhances the performance and longevity of equipment across various sectors by providing a durable, wear-resistant surface that minimizes maintenance costs and downtime.
Hardfacing with GMAW welding
Hardfacing using Gas Metal Arc Welding (GMAW), or MIG welding, involves several key steps to ensure a successful application. Below is a detailed explanation of the process:
1. Preparation
- Surface Cleaning: The surface of the workpiece must be thoroughly cleaned to remove any dirt, grease, rust, or other contaminants. This is crucial to prevent weld defects and ensure a strong bond between the base metal and the hardfacing material.
- Preheating: Depending on the base material, preheating may be necessary to reduce thermal shock and prevent cracking during welding.
2. Selection of Materials
- Hardfacing Wire: Choose a suitable hardfacing wire based on the desired properties such as wear resistance, hardness, and impact resistance. Common materials include iron-based, nickel-based, and cobalt-based alloys.
- Shielding Gas: Use an appropriate shielding gas to protect the weld pool from atmospheric contamination. Pure argon or argon mixtures with oxygen or carbon dioxide are commonly used to achieve low penetration and dilution.
3. Welding Process
- Machine Setup: Set up a MIG welding machine. Adjust parameters such as voltage, amperage, and wire feed speed according to the manufacturer’s recommendations for the specific hardfacing wire.
- Welding Technique: Employ a consistent welding technique to ensure even deposition of the hardfacing material. The process involves creating an electric arc between the consumable wire electrode and the workpiece, which melts both materials and allows them to fuse together.
4. Application
- Layer Deposition: Apply one or more layers of hardfacing material to achieve the desired thickness and properties. The thickness can range from 1 to 10 mm depending on the application requirements.
Hardfacing Wire Types
Specialized hardfacing wires are typically used for applications requiring high wear resistance. These wires are designed to deposit a hard, abrasion-resistant layer on the surface of a workpiece.
Iron-based Alloys
Iron-based hardfacing wires are commonly used due to their versatility and cost-effectiveness. These wires often contain:
- High chromium content (typically 20-30%)
- High carbon content (3-5%)
- Other alloying elements like manganese, silicon, and sometimes molybdenum
The high chromium and carbon content form hard chromium carbides, which provide excellent abrasion resistance.
Cobalt-based Alloys
Cobalt-based hardfacing wires are used for extreme wear resistance, especially at high temperatures. These alloys typically contain:
- Chromium
- Tungsten
- Carbon
The cobalt matrix provides excellent hot hardness, while the chromium and tungsten form hard carbides for wear resistance.
Reasons for Material Selection
- Chromium: Forms hard carbides, enhancing abrasion resistance
- Carbon: Combines with chromium to form carbides, increasing hardness
- Manganese: Improves toughness and work-hardening properties
- Silicon: Acts as a deoxidizer and improves fluidity of the weld pool
- Molybdenum: Enhances high-temperature strength and wear resistance
The specific composition of hardfacing wires is tailored to the intended application, balancing factors such as abrasion resistance, impact resistance, and operating temperature.
Hardfacing and Robotic Welding
Hardfacing is an excellent fit for robotic welding because it is a tough job to do manually.
Hardfacing is a time-intensive and monotonous process that is physically demanding and requires significant focus. The extreme heat, fumes, and repetitive nature of the work take a heavy toll on welders, both mentally and physically.
Robots eliminate these challenges by doing the work without breaks, maintaining precision, and ensuring consistent quality. They can handle high heat and repetitive tasks without fatigue, making the process more efficient and safer while delivering better results.
Using robots for hardfacing improves productivity, reduces errors, and protects human workers from a demanding and exhausting job.
