Hard Surfacing: Tips and Techniques
Hard surfacing involves the deposition of special alloys on a metallic part, using various welding processes, to obtain more durable wear properties. Hard surfacing can increase equipment’s resistance to abrasion and impact, and in some cases, specialized hard surfacing alloys provide even greater resistance than the original part. Hard surfacing protects equipment and its components against wear caused by impact and abrasion by using four weld bead patterns: waffle, herringbone, stringer and dot. To determine which pattern or combination of patterns best meet your needs, you must consider the location of the wear, the type of wear and the type of material that causes the wear.
What You Should Know About Your Base Metal
Carbon or low alloy steels and austenitic manganese steels are the major types of base materials you can hardsurface. Materials containing a high content of carbon and/or alloy content, such as buckets or bulldozer blades, have a tendency to be brittle and are susceptible to cracks. You may need to pre- or post-heat, slow cool or stress relieve the welds to ensure that you have solid, long lasting weld. Pre-heating especially helps reduce cracks, distortion, porosity and other weld discontinuities. Note: preheating temperatures are directly proportional to the carbon and alloy content of the base material - higher carbon content require higher pre-heating temperatures.
Because of its high strength properties, manganese steel is among the most common materials used for crusher roll shells, hammers, impactor bars and other equipment used in the mining and quarrying industries. There are, however, some important factors to consider before hard surfacing manganese. First, be careful not overheat the work piece, as it can become brittle. As a rule of thumb, the temperature of the base metal should be kept below 500-degrees Fahrenheit. Using Tempil heat indicator sticks is the safest and easiest method to determine a base metal’s temperature.
Finally, to prevent overheating specific areas when hard surfacing manganese, distribute the heat from the arc across a wider portion of the work area by alternating welding locations on the component. Using higher travel speeds can also help reduce the heat affected zone, which will minimize rapid cooling and prevent cracking.
Waffle and Herringbone Patterns
The waffle pattern [Figure 1] consists of a criss-cross bead pattern that forms squares, and you form the herringbone pattern [Figure 2] by laying weld beads at varying angles. The waffle and herringbone patterns protect against abrasive wear from smaller grained aggregates such as dirt, sand and gravel. By using the waffle and herringbone patterns, the aggregate packs between the hard surfacing weld beads for excellent base metal protection.
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| Figure 1: The waffle pattern consists of a criss-cross bead pattern and protects against abrasive wear from smaller grained aggregates. |
In quarry and mining applications, the waffle pattern works well to protect crushers and rollers that are used to produce various sizes of aggregates. For example, on equipment producing three-eighths inch rock, apply parallel weld beads (or ribs) on the driver roll, spaced one inch apart, using multiple passes. The profile of the parallel weld beads should resemble a pyramid shape; apply more ductile hard surfacing alloys to create the base of the pyramid and the hardest alloy for the peak of the pyramid. This parallel weld bead pattern provides a gripping action to force the rock into the crushing zone located between the idler and drive rollers. On the idler roll, deposit one weld bead that measures approximately one-inch high in the form of a waffle pattern.
When producing larger sized aggregates, lay weld bead patterns on the idler and driver rolls spaced further apart. For example, when producing three-quarter inch rock, the ribs on the driver roll should be approximately one and a half inches apart and should form the same pyramid shaped profile as described above. On the idler role, create squares in the waffle pattern measuring about one and a half inches across.
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| Figure 3: The herringbone pattern, shown on the side of this bucket, is formed by laying weld beads at varying angles. |
Dot Pattern
The dot pattern is the easiest hard surfacing pattern to apply and is suitable for base metals that are sensitive to overheating. The dot pattern provides an effective wear pattern against low impact, high abrasive wear. To produce the dot pattern, begin on the center of the work piece and gradually fill in the spaces with additional dots until the area to be hard surfaced is covered with closely spaced dots [Figure 3]. Evaluate the amount of wear and use trial and error to determine the optimum amount of spacing between the dots.
Excellent applications for dot patterns include heat sensitive applications such as manganese steel or thinner gauge metal where embrittlement is a major concern. The dot pattern also works well to protect parts against high abrasion commonly found on the scraper sides of earth-moving and heavy construction equipment.
Stringer Patterns
Stringer beads are weld beads that run parallel to one another and are suitable for certain buckets used on earth moving or heavy construction equipment [Figure 4]. Stringer patterns run either perpendicular or parallel to the flow of the material, depending on the type of aggregate. A stringer pattern provides protection against abrasion and requires fewer pounds of hard surfacing wire compared to the waffle pattern—a factor that can help lower costs.
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| Figure 3: To produce the dot pattern, begin on the center of the work piece and gradually fill in the spaces with additional dots until the area to be hard surfaced is covered with closely spaced dots. |
To prevent wear on buckets caused by dry, larger sized aggregates such as boulders, deposit stringer beads parallel to the flow of the material. This type of stringer pattern allows large aggregates to skim more easily across the hard surfacing welds and protects the base metal.
Conversely, when working with smaller grained material such as dirt, sand or pulverized coal, stringer beads should be placed one-fourth to one and a half inches apart, with the weld beads perpendicular to the flow of the material.
Stringer patterns [Fig. 4] can also protect shovel teeth from wear. On shovel teeth handling large aggregates, place stringer beads that run the length of the entire tooth, parallel to the flow of the material. When the tooth is used primarily for clay, dirt and sand, deposit the stringer beads perpendicular to the flow of the material.
Hardsurfacing Tips
Base Metal Preparation:
Whether you are hard surfacing on carbon or low alloy or austenitic manganese steels, you need to clean your base material properly, ensuring that it is free of all contaminants, including grease, dirt, rust and oil. Old hard surfacing layers, as well as cracks, can be removed through arc (or plasma) gouging or grinding prior to adding new layers.
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| Fig. 4 Stringer beads are weld beads that run parallel to one another. |
Control your arc length:
Possible causes of porosity when applying a hard surfacing pattern include an excessive arc length and/or electrode extension (when flux cored welding), excessively wide weld bead width and/or an overheated base metal. To prevent weld bead porosity, adjust the voltage or electrode extension and check to ensure that the work lead and ground clamp are securely attached.
Use the correct drive roll tension:
When using FCAW wire, ensure that the drive roll tension is at the correct setting. Excessive tension deforms the FCAW wire, which causes poor feeding. Conversely, inadequate drive roll tension causes the wire to “slip.”
Conclusion
Hard surfacing can save you time and money by increasing your equipment’s resistance to abrasion and impact. Repairing worn equipment and extending equipment life helps reduce the amount of downtime needed to replace broken or worn parts and eliminates the need to maintain a large inventory or spare parts. To ensure you are reaching the maximum wear resistance, evaluate the type and location of wear on your equipment and determine which pattern or combination of patterns works best to protect your equipment.