FARMING AHEAD No. 112 - April 200120

Hardfacing metal surfaces

Different point types require varied hardfacingtreatments, as they are prone to wear on differentsurfaces. These sweep points are to be used onrelatively soft country and hardfacing is mostlyrequired on the leading edges.

Hardfacing patterns differ depending on the soiltype. A common method is to place a bead ofhardfacing material at the tip of the point as this isthe first point of contact with the soil and isusually the most prone to wear.

Abrasive soils could require a bead along bothwing edges but vary the position of hardfacingalong wing edges according to soil conditions.

If wing tips are prone to wear, it might beworthwhile placing beads of hardfacing at theextremity of each tip. Try to keep heat even acrossthe point when applying a hardfacing treatment.One suggestion is to start by hardfacing all the tips on a set of points. Then, starting from thewing tip and welding inward, hardface each side ofthe sweep.

Pictured are tubular and solid welding rods suitablefor hardfacing. These are more easily applied usinga DC or high frequency welder or by reversing thepolarity as per the instructions on the box. In somecases, it is necessary to pre-apply an intermediatemetal between the base and the hardfacingmaterial. This metal is often known as a buffer layerand is used in situations where a soft metal is to be hardfaced with a very hard metal. The bufferlayer is of intermediate hardness and helps prevent cracking.

When hardfacing points it is important not to usetoo much heat. The aim is to apply sufficient andeven heat to attach the hardfacing metal withoutexcessive infusion of the base metal. Excessivemixing of the base metal and the hardfacing metalalloy could result in less abrasive-resistant metal.

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Hardfacing can be used to protect shank boltsfrom excessive wear. Bands of hardfacing beads infront of bolts act as an abrasive-resistant bufferand allow soil to flow over the beads and the boltwith minimal abrasion. On sweeps, this can causeweakness and failure parallel to the bead.

Pictured is a point which has been hardfaced usingthe Pratco Tuff Tung process. This process uses theplasma of a TIG welder to melt the surface metal ofthe point into a molten pool. A controlled streamof tungsten carbide chips are then fed into thepool to create a hard thin edge. Bottom: A TuffTung treated point showing a pattern of wear afterconsiderable work.

Metal surfaces prone to abrasive wear such asplough sweeps, points, earthmoving

buckets, blades and rippers can be protectedfrom abrasion using several methods such asapplying abrasive-resistant metal alloys.

The application of abrasive-resistant metalalloys is called hardfacing. Applying hardfacingto points can void the warranty. Check with thepoint manufacturer for more details.

It should be remembered that just as a metal can be extremely hard, it is not alwaysabrasive resistant, especially in stony soils.Impact resistance is equally important asabrasive resistance, especially in stony soils.Impact resistance prevents hardfacing metalsfrom chipping when striking stones in the soil.

Hardfacing is applied through arc welding ormetal inert gas (MIG) welding. Hardfacing withan arc welder involves using tubular or solid alloy welding rods containing very hard metalalloys such as chromium and niobium carbides or tungsten carbide chips. Tubular rods aregenerally easier to use and last longer but theyare expensive.

Arc welders do a good job but can take a considerable amount of time if there are manysurfaces to treat. Rods suitable for hardfacingwith an arc welder cost $16–$40 per kilogram.

MIG welders can be used to apply hardfacingmetals and are more popular. MIG hardfacingwire applies hard metals such as chromium alloysto create wear resistance. If hardfacing a large

number of sweeps, MIG welders are the bestchoice as less time is taken to perform thetreatment. MIG welding wire costs about $300for a 15kg roll or $20/kg. Some welding shopsadvise that when using a MIG welder withhardfacing wire, some simple guidelines couldmake the process easier:

. Use an oversize tip if excessive graphitebuild-up is a problem, otherwise a regulartip will give better precision in hardfacingplacement.

. Use oversized liner to assist wire feed.

. Some MIG wires have a flux core. Thismeans gas is not required. These wires areusually difficult to use and require knurledrollers to assist wire feed. A reversal ofpolarity may not be required with this wire asis sometimes the case with gasless MIG wire.

A third method of hardfacing (only availablecommercially) is the Pratco Tuff Tung process,which uses tungsten carbide chips to create ahard surface.

While the hardened edge is successful in mostareas, soils containing stones can chip the hardmetal away, causing the point to wear at the samerate as an untreated point.

The cost of applying Tuff Tung depends on thearea of treatment but is about $4–$6 a point.

Acknowledgements: Stafford Welding Productsand Tools, Toowoomba; Washington Motors, Dalby;Bob Earle, Subway Engineering, Toowoomba;Gessner Industries, Toowoomba.

FARMING AHEAD No. 112 - April 2001 21

Hardfacing bead running along top of edge

Weld beads at wing tips and nose of point

Hardfacing bead running along face of edge

Weld beads at wing tips and nose of point

Nohardfacing

Hardfacing

Self-sharpening edge: By only hardfacing thetop side of some earth cutting teeth, a sharpedge can be maintained as the bottom wearswhile the top retains the cutting edge.

Traverse bead pattern: This pattern is used inhighly abrasive situations as it traps soilbetween the beads laid perpendicular to thedirection of travel. The pattern protects thebase metal by using the soil trapped betweenthe beads to protect the teeth.

Diamond and spot patterns: These patterns provide an element of self-cleaning. Because of theuneven surface of the tooth, soil does not stick between the beads as easily, making this a popularpattern for earthmoving buckets.

Earth cutting teeth

Abrasive soils will wear points more quickly thansofter soils. For sweep points used in abrasive soils,apply hardfacing to the top of the leading edge asshown. Although draft is increased due to additionalwing width, the underside of the wing is quicklyworn away, resulting in a sharp hardfaced edge.

For extremely abrasive soils, it may be necessary toplace additional beads of hardfacing perpendicularto the sweep edge. This reduces wear along thebody of the wing. Several parallel lines along thelength of the sweep trap soil and help to protectthe base metal.

In soft soils, the underside of the wing is not wornaway at the same rate, resulting in a blunt leadingedge at the top of the point. The blunt edge inhibits the cutting capacity of the point leading topoor performance. For this reason, in softer soils,hardfacing is commonly only applied to the edge ofthe sweep point as shown.

Parallel bead pattern: This pattern allows thepart to lift and strike rocks while still protectingthe base metal. Because the beads are formed inthe same direction of travel, there is norestriction to the tooth movement through orover rocks.

Earth or soil cutting teeth found onrippers, earthmoving buckets and grabs

are rarely completely covered in hardfacingmaterial.

Alternatively, they are partially coveredwith selective patterns according to the typeof material they are handling. If metalcompositions are quite different from thehardfacing material, pre-heating the basemetal could be necessary to prevent thehardfacing metal from peeling. This isparticularly relevant for large parts such asearth cutting teeth. Because of their largevolume, larger base metal objects can have a quenching effect on weld deposits,causing undesirable residue on the weldbead, which may eventually cause cracking.

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