Hardfacing Electrodes. Special tubular construction requiring low operating currents. Hardness : 650/700 HB.

Transcription

1 Hardfacing Electrodes Special tubular construction requiring low operating currents. Hardness : 650/700 HB. These electrodes have been engineered to provide extended service life at ambiant and elevated temperatures involving abrasion, erosion, impact and cavitation. 1 / 8

2 The unique Low Less High burn operating heat deposit yield distorsion properties - input through rates currents of tubular electrodes MATALLOY's baking This ideal abrasion - No Easy 6, 8 special de-slagging wastage et to 11 use m storage Size Length tubular electrodes with construction one holder Approx. construction for Our mm use resistant Electrode mm no in difficult per has properties types many site conditions in practical to stock "conventional : advantages but also is solid ensures designed over rod 8457 solid deposits". that for the welding hardfacing alloy rods, deposited wear which resistant has not superior only alloys. 7 4 make it Deposit rate kg/hr Low Currents = Low Dilution The low operation currents used with MATALLOY electrodes ensure that less heat is generated and less penetration of the base metal experienced. This not only reduces distortion and the risk of burn-through but also avoids dilution of the hardfacing alloy, with base metal. The result is a purer hardfacing alloy with optimum mechanical properties. Low currents = No Burn Through Low current hardfacing drastically reduces the risk of distortion and burn - through even on thin sections. With a little practice, it is possible to hardface right up to (and around) the edge of thin sections - a major advantage on augers, screw flights, scraper blades and worn sections. 2 / 8

3 High Deposition Rates & High Yield MATALLOY tubular electrodes comprise densely compacted alloy powders within a thin, flux coated, steel sheath. This construction ensures that virtually all of the electrode is "available alloy". No heavy slag is produced, no wastage created and without the need to de-slag between runs, application is fast and efficient. TYPICAL WELDING CURRENTS Size mm Amperages = Mini/Maxi The standard stub end enables electrodes from 6 mm to 11 mm to be used in one holder allowing rapid deposition of narrow or wide bands of hardfacing using a standard portable welder. Matalloy range - Alloy selection MATALLOY CHROMIUM CARBIDE AUSTENITIC IRON Composition 3 / 8

4 C 5,5%, Cr 40,0%, Mn 1,5% This alloy is designed for direct application onto manganese steels to obtain a very high abrasion and impact resistant surface. Grade 33 can also be used on carbon and low alloy steels with similar results. Typical uses include : crusher hammers, mantles and liners, blow bars, quarry screen plates, bucket lips and teeth. Mechanical properties Hardness: Single layer: Rc. Multi-layer: Rc. Color code : Electrode tip colour: White Basic welding techniques Preparation of Workpiece Before commencing any welding operation ensure that the surface of the metal is clean by removing rust, dirt, grease and any paint. The low operating current of tubular electrodes enables you to select the largest possible diameter electrode for the current available and the size of the workpiece. Avoiding Dilution UOptimum wear resistance depends on achieving a sound deposit with the minimum of base metal dilution. Tubular electrodes are designed to operate at low current so do not use excessive amperage, weld briskly and do not dwell too long in one position. Always deposit at least 5 mm of hardfacing to minimise dilution effects. 4 / 8

5 Cooling after Welding In most applications, the workpiece should be cooled in calm air, however, austenitic manganese steels require abrupt cooling in water. Finishing Hardfacing deposits can be ground to produce a finished surface. Generally their hardness prohibits any conventional machining. Repair in Good Time To avoid excessive loss of base metal and the necessity for lengthy rebuilding procedures, always repair / renew a hardfacing deposit before it is worn away completely. Using tubular electrodes Recommended welding currents for different electrode diameters should be taken as a general guide. Higher currents can be used but will result in greater dilution between the deposit and the parent metal. The best results are achieved by holding the electrode perpendicular to the workpiece and employing an arc length of approximately 2/3 of the electrode diameter. As the thickness of the deposit increases, it may exhibit surface stress relief cracks which do not penetrate into the base metal and are in fact a desirable feature on this type of extremely hard wearing alloy. Maximum Deposit Thicknesses While the unique construction of tubular electrodes reduces the level of base metal dilution, optimum wear resistance is generally achieved when subsequent layers are applied. However, there is also a point at which too thick a deposit will not improve wear performance. The table below gives a general guide to optimum hardfacing thicknesses. 5 / 8

6 Grade Maximum thickness Layers MATALLOY mm 3-4 layers Hardfacing techniques Hardfacing may be applied as a continuous surface, as stringer beads or dot patterns. The type of deposit employed will depend on the nature of the environment and the area to be covered. Where a continuous surface is required, care should be taken to ensure that weld runs overlap and for fine abrasion or erosion the weld runs should be deposited at right angles to the direction of travel of the abrasive material. Stringer Beads Applications where large irregular pieces of abrasive material are present, for example in quarries, hardfacing of items such as bucket teeth requires continuous stringer beads which run parallel to the direction of the abrasive material. The "rock" etc, will then ride on top of the weld bead leaving the base material unaffected. IConversely, fine abrasive material like sand and glass requires a stringer pattern running across the direction of flow to produce pockets of captured material which form a "material on material" barrier to wear. Some environments like earthmoving will involve a combination of the two conditions and the best hardfacing pattern is therefore a criss cross or chequered pattern. Dot Patterns Secondary wear areas requiring less protection are quickly treated using a regular dot pattern which allows material capture between the dots while providing high spots during impact and sliding contact. Dual electrode Technique Where very high deposition rates are required, a second tubular electrode can be introduced into the weld pool in a similar way to a gas welding filler rod. Currents of up to 300 amps may be used with this technique and with a little practice the welder will be able to combine the right degree of arc movement between workpiece and filler rod to ensure thorough fusion to the 6 / 8

7 parent metal. Cast Welding The dual electrode technique may also be combined with a graphite or copper mould into which very thick deposits of hardfacing can be cast welded. This technique is particularly useful for rebuilding / protecting hammers, bolt heads, etc. Where severely worn components are being rebuilt alternate layers should be deposited to minimise stress. These should be applied after restoring the component to its approximate shape with a conventional electrode giving a deposit compatibility with the original base metal. Typically, a low grade 316 type stainless steel welding rod may be used. Yield & Recovery rates Practical trials have shown that tubular electrodes offer twice the value for money of conventional extruded rods. A direct comparison between yield rates as calculated using conventional extruded rods and tubular electrodes is not possible for the reason detailed below: Yield rate of extruded rods is calculated as: Weight of alloy deposited Weight of solid core As tubular electrodes do not have a solid core this formula cannot be applied. However, the following comparisons demonstrate why tubular electrodes are better value for money. Conventional extruded rods 8mm Tubular Electrodes Total weight of electrode inc. 160 stub g end 120 g 7 / 8

8 Weight of solid core 50 g - Weight of powder / filler 100 g 70 g Weight of tube - 40 g Weight of deposit after welding 75 g 100 g Recovery rate 75 = 150% 50 Not applicable Efficiency / Yield 75 = 46,8% = 80% 120 Efficiency / Yield = weight of hardfacing deposited expressed as % of the weight of electrodes used. = Weight of hardfacing deposited x 100 Weight of electrodes purchased As can be seen tubular electrodes are twice the value for money of conventional extruded rods. 8 / 8