FARMING AHEAD No. 112 - April 2001 20 Hardfacing metal surfaces Different point types require varied hardfacing treatments, as they are prone to wear on different surfaces. These sweep points are to be used on relatively soft country and hardfacing is mostly required on the leading edges. Hardfacing patterns differ depending on the soil type. A common method is to place a bead of hardfacing material at the tip of the point as this is the first point of contact with the soil and is usually the most prone to wear. Abrasive soils could require a bead along both wing edges but vary the position of hardfacing along wing edges according to soil conditions. If wing tips are prone to wear, it might be worthwhile placing beads of hardfacing at the extremity of each tip. Try to keep heat even across the point when applying a hardfacing treatment. One suggestion is to start by hardfacing all the tips on a set of points. Then, starting from the wing tip and welding inward, hardface each side of the sweep. Pictured are tubular and solid welding rods suitable for hardfacing. These are more easily applied using a DC or high frequency welder or by reversing the polarity as per the instructions on the box. In some cases, it is necessary to pre-apply an intermediate metal between the base and the hardfacing material. This metal is often known as a buffer layer and is used in situations where a soft metal is to be hardfaced with a very hard metal. The buffer layer is of intermediate hardness and helps prevent cracking. When hardfacing points it is important not to use too much heat. The aim is to apply sufficient and even heat to attach the hardfacing metal without excessive infusion of the base metal. Excessive mixing of the base metal and the hardfacing metal alloy could result in less abrasive-resistant metal. Compiled by Ben White, Richard Sulman and Andrew Green. Hardfacing can be used to protect shank bolts from excessive wear. Bands of hardfacing beads in front of bolts act as an abrasive-resistant buffer and allow soil to flow over the beads and the bolt with minimal abrasion. On sweeps, this can cause weakness and failure parallel to the bead. Pictured is a point which has been hardfaced using the Pratco Tuff Tung process. This process uses the plasma of a TIG welder to melt the surface metal of the point into a molten pool. A controlled stream of tungsten carbide chips are then fed into the pool to create a hard thin edge. Bottom: A Tuff Tung treated point showing a pattern of wear after considerable work. M etal surfaces prone to abrasive wear such as plough sweeps, points, earthmoving buckets, blades and rippers can be protected from abrasion using several methods such as applying abrasive-resistant metal alloys. The application of abrasive-resistant metal alloys is called hardfacing. Applying hardfacing to points can void the warranty. Check with the point manufacturer for more details. It should be remembered that just as a metal can be extremely hard, it is not always abrasive resistant, especially in stony soils. Impact resistance is equally important as abrasive resistance, especially in stony soils. Impact resistance prevents hardfacing metals from chipping when striking stones in the soil. Hardfacing is applied through arc welding or metal inert gas (MIG) welding. Hardfacing with an arc welder involves using tubular or solid alloy welding rods containing very hard metal alloys such as chromium and niobium carbides or tungsten carbide chips. Tubular rods are generally easier to use and last longer but they are expensive. Arc welders do a good job but can take a considerable amount of time if there are many surfaces to treat. Rods suitable for hardfacing with an arc welder cost $16–$40 per kilogram. MIG welders can be used to apply hardfacing metals and are more popular. MIG hardfacing wire applies hard metals such as chromium alloys to create wear resistance. If hardfacing a large number of sweeps, MIG welders are the best choice as less time is taken to perform the treatment. MIG welding wire costs about $300 for a 15kg roll or $20/kg. Some welding shops advise that when using a MIG welder with hardfacing wire, some simple guidelines could make the process easier: . Use an oversize tip if excessive graphite build-up is a problem, otherwise a regular tip will give better precision in hardfacing placement. . Use oversized liner to assist wire feed. . Some MIG wires have a flux core. This means gas is not required. These wires are usually difficult to use and require knurled rollers to assist wire feed. A reversal of polarity may not be required with this wire as is sometimes the case with gasless MIG wire. A third method of hardfacing (only available commercially) is the Pratco Tuff Tung process, which uses tungsten carbide chips to create a hard surface. While the hardened edge is successful in most areas, soils containing stones can chip the hard metal away, causing the point to wear at the same rate as an untreated point. The cost of applying Tuff Tung depends on the area of treatment but is about $4–$6 a point. Acknowledgements: Stafford Welding Products and Tools, Toowoomba; Washington Motors, Dalby; Bob Earle, Subway Engineering, Toowoomba; Gessner Industries, Toowoomba.