Easy Guide To Understand Hardfacing Welding
Easy Guide To Understand Hardfacing Welding
What is Hardfacing?
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Before we jump to the techniques and process of hardfacing welding, let us primarily understand what does hardfacing welding mean. Hardfacing welding technique is used to make equipment more efficient by minimizing oxidation and distortion, resistance from chipping and corrosion. This process is cost-efficient compared to buying completely new equipment to replace the worn-out one. How is that?
Hardfacing a machine involves putting a tougher, harder material onto the base metal to increase its lifespan. Generally, hardfacing takes the form of specialized hardfacing electrodes for MIG welding or arc welding. This is a fast and easy method that also helps reduce the number of spare parts kept in the inventory.
Significant reduction in production cost and lessened machine downtime is the key reason why the use of hardfacing machines has become popular in food, petrochemical, mining, power, cement, sugarcane and steel industries. Using the hardfacing technique can make new machines resistant and lengthen their life by up to 300%. When used on old equipment, hardfacing can return worn parts to nearly new condition at 25-75% less cost than that incurred on replacement of those parts.
What materials can be applied in the hardfacing process?
No matter the industry in which a machine is used, there is a specified hardfacing welding electrode that can be appropriately used to offer maximum resistance to wear and erosion. The common materials, however, used widely across all industries include NOREM, chromium carbide alloys, stellite or cobalt-based alloys and nickel-based alloys. Carbide or chromium carbide alloys are generally used in case of low-stress scratching on machines. Here the wear is very minimal and can be caused by scouring actions of materials around the equipment. In case if you wish to add your band name or additional information or need to add color to refine the work, hot stamping can be used post hardfacing. Most commercial industries make use of films or foils to add an additional layer of protection and/or to give the machine a metallic effect.
What steps one should follow before hardfacing a machine?
Yes, the problem at hand is a worn-out machine and the immediately required step is to get it hardfaced. But before you do that, make sure you follow these steps:
Clean the machine and especially the parts to be hardfaced very well
Wipe it free of all contaminants such as grease, dirt, oil, or rust.
If necessary, remove the old hardfacing layers and/or cracks by using the arc or plasma gouging technique.
The size, shape and location of the equipment or its parts will determine the welding technique to be used while hardfacing. So make sure you keep that in mind.
Hardfacing most commonly makes use of the stick welding (SMAW) process as it is highly portable or the flux-cored (FCAW) welding technique. For welding large and thicker parts on regular basis, companies also make use of the submerged arc welding (SAW) process.
With this, your machine is prepped to be hardfaced and become more efficient.
Conclusion:
Hardfacing is a valuable technique that can help save your expenditure and time too. If you wish to know more about welding and everything around it, we are here to help you. The world of welding can be a little complicated but taking your time to learn the processes goes a long way.
Ultimate guide to welders: inverters, TIG, MIG, gas and more
What welder should you buy? With so many different welders for sale, you should review your choices for which welder is most suited to you.
Welding is defined as a joint where pieces or parts have been fused together, usually by heat. Most commonly welded materials are metals, but the process can include many plastics too. The heat is generated by an electrical spark or a gaseous flame.
With minimal training, pretty much anyone can join bits of metal together, but really specialised skills are learned and practiced over years.
There are various ways of creating welded joints and when youre making metal hot enough to melt together, you need some specialist equipment. Yes, weve seen the bush-mechanics who can weld using a car battery and some fence-wire, but theyre seldom permanent repairs!
Inverter welder vs arc welder
Theres no single machine that can really do it all, but depending upon the materials being joined together, the most commonly used equipment will fall into three main types.
Arc welders
Arc welders join two metals by generating an electric arc (spark) between a covered sacrificial metal electrode and the metals to be joined, using high voltage. Think of it as hand-held lightning and youll have an idea of the process.
The heat produced by the arc between positive and negative electrical charge melts the parent metal which mixes with the molten deposits of the coated electrode, or the wire and gas shield.
The most common arc welder is the good old stick welder: the electrodes the sticks are about 250mm long and look like stout bits of wire that were dipped in cement.
More correctly called shielded metal arc welding, stick welding works better than most other methods on dirty or rusty materials and in less than perfect conditions.
Depending on the metals to be joined, there are many types and diameters of welding electrodes, but with age the flux (the cement) can absorb moisture or crumble off, making fresh rods desirable; on some big job-sites, welding rods are kept in hot-boxes to prevent moisture in the flux.
For big welding jobs, stick welding is comparatively slow, since the consumable electrodes must be replaced every couple of minutes and because slag (the residue from the flux) must be chipped away after the weld is complete.
As for technique, if youre learning to weld using the stick process, remembering these five points will improve your technique. Think CLAMS: Current, Length of arc, Angle, Manipulation and Speed.
Arc welding current
Stick welders can be of AC (alternating current) or DC (direct current) types.
Among DC welding advantages youll count easier starts, fewer arc outages, less sticking, less spatter, better-looking welds and easier vertical up and overhead welding. Plus, with DC its easier to learn how to weld and you get a smoother arc.
DC reverse polarity (electrode positive) provides about 10 per cent more penetration at any given amperage than AC, while DC straight polarity (electrode negative) welds thinner metals better.
AC has advantages if welding on material that has become magnetised from friction, such as when hay, feed, grain or water constantly rub against a steel part.
In that case, a DC output doesnt work well because of arc blow, where the magnetic field blows the molten filler metal out of the weld puddle. The AC succeeds because AC output alternates between polarities, thus enabling welding of magnetised parts.
A machine rated at between 225 to 300 amps will be capable of handling most jobs that a decent mechanic will need to weld: beyond that, you might be in for a trip to a specialist.
In fact, most stick welding procedures require less than 200 amps. To weld material thicker than about 10mm, simply make multiple passes this is what the pros do, even when welding on 1-inch (25mm) structural steel.
When buying a machine, the welders duty cycle is important. This refers to the number of minutes out of a 10-minute cycle a welder can operate.
For example, Millers Thunderbolt XL creates a 200 amp DC output at 20 per cent duty cycle. It can weld continuously at 200 amps for two minutes, and then must cool for eight minutes to avoid overheating.
Duty cycle and amperage are inversely proportional. Operating at only 90 amps, the Thunderbolt has a 100 per cent duty cycle, meaning you can weld without stopping. Exceeding the rated duty cycle can damage the machine or cause it to overload and trip out.
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Arc welding rods
The details for welding rods are printed on the end of the stick, if you no longer have the packet. These designations were standardised in the United States by ASTM and WIA, with the first two digits representing the metals tensile strength. For example, 60 series rods have a maximum tensile of 60,000psi (415MPa) and the 70 series 70,000psi (485MPa).
Common electrodes used for general work include , , , and , each of which has specific properties: electrodes penetrate deeply, while electrodes penetrate less.
For much better bead appearance and work on higher strength steels say for an implement hitch use a rod. For better penetration on thick material, grind open the joint to a 30-degree bevel (leave a 2mm width vertical land on the bottom of the groove) and make multiple passes.
Alternatively, make the first pass with a rod, then make a cap with a .
The rod is perhaps the easiest to use. This is also known as a drag rod, meaning the electrodes thick flux automatically maintains the correct arc length, which allows you to drag the rod directly along the work piece. Thats pretty handy for better-looking welds.
Hard-facing rods can provide impact resistant or abrasion resistant welds or both, depending on the application. Because the type of rod required depends on the type of environment the tool will exposed to, its probably better to ask the local welding supplier for advice.
Inverter welders
An inverter welder has advantages over traditional welders. Both require a transformer to convert incoming current to suitable welding current, but an inverter welder does it more efficiently and is much smaller and lighter, and uses less power too.
Because theyre more efficient, their duty cycle is also higher. Using modern solid-state electronics, Inverter welders lose very little heat in comparison to traditional machines, giving the smaller inverter machine the ability to use nearly all of its input current where an older-style transformer could lose up to 20 per cent efficiency to heat loss.
The electronics on inverter welders make it possible to maintain an arc where a conventional transformer welder would allow the electrode stick to the work: big 5mm diameter rods can be run on an inverter machine and its practically impossible to make them stick to the job.
The higher frequency of the output current and computer software to monitor and adjust current and voltage while welding, produces a consistent, smooth arc thats easier to strike and to maintain.
When running on domestic single-phase power most inverter welder machines do need a 15-amp power outlet.
Welding supplies such as electrodes, welding wire and shielding gas typically last longer than when using a traditional welding power supply.
Adjustments to current and voltage can be made for different materials and thicknesses, giving the operator tighter control over the welding process.
The small size and weight of inverter welders make them popular where a traditional transformer welder is too bulky or uses too much power, so they are popular in maintenance facilities, general fabrication shops, construction sites and farms as portable, light-weight units for on-site repairs.
TIG welders
Tungsten inert gas (TIG) welding, sometimes known as gas tungsten arc welding (GTAW), requires more skill than most other welding methods but is extremely versatile, capable of joining a huge range of metals in varying thicknesses.
The result is neat and precise, giving a beautifully finished weld bead where appearance is important.
In the TIG inverter welder process, the arc jumps between a non-consumable tungsten electrode and the work piece, generating high temperature. The inert gas shield, usually including argon or another noble gas, prevents weld oxidation.
There is no spatter or slag and thin metals are readily welded, and with less distortion.
The most obvious difference between a TIG welder and an AC/DC stick welder is the non-consumable tungsten electrode, which is held in the handle. The shielding gas is directed around the weld by a ceramic nozzle or cup, designed to withstand the heat of welding.
Different-sized cups are used: smaller cups for smaller welds and reaching difficult areas; larger cups for improved gas flow and coverage for bigger weld beads.
While theres no slag to chip off and clean up, TIG requires a clean prepared surface for quality welds. Any type of foreign matter, including moisture or cleaning solvents, will contaminate the weld.
Apart from the higher skill required with TIG wleding, there are some other considerations, such as cost and speed.
Although there are cheaper units available, a good TIG welder can cost several thousand dollars; in contrast, an inverter TIG can be had for around $400.
Thats still twice more than a beginner needs to spend on a modest stick welder, but its compactness and the ease of striking and running a smooth bead are impressive, once youre used to having both hands engaged.
Finally, TIG welding is a bit slower than other arc welding methods, so the time spent TIG welding is relatively high. Where time equates money, another process might be more cost-effective.
MIG welders
MIG stands for metal inert gas, and this process is also known as gas (shielded) metal arc welding (GMAW).
The MIG arc welder process has a continuously-fed wire electrode that melts in the arc to form a weld bead. Like TIG, the weld is protected from surrounding air by a shielding mixture of gasses, usually including argon.
Alternatively, tubular flux-cored self-shielding wires are available, which need no external gas. Ventilation is needed because of fumes, and the slag formed on the weld has to be removed between passes or before painting.
MIG welders with solid wire are more commonly used with industrial robots and on heavy, thicker work because the continuously-fed electrode wire and arc length are automatically controlled.
MIG weld joints are stronger, more ductile and have less distortion than other welding processes and are ideal for thin metal work, alloys and aluminium.
However, welding wire isnt cheap and theres a bit more to consider with MIG, like welding meter amps and volts, wire speed and position.
Theres a gasless wire option with MIG welding thats a lot cheaper than bottle rental but it isnt as nice as running a MIG on gas, and the power supply must be considered ideally a consistent current with very little drop in voltage is needed.
Duty cycle is also a consideration: the machine will need to be watched to avoid overheating. For example, a 200-amp welder with 30 per cent duty cycle should be operated for no more than three minutes in 10, allowing seven minutes for cooling.
Gas welders
More often than not, a gas welder uses a combination of (usually) oxygen and acetylene as the heat source which is why the process is also called oxy welding or oxyacetylene welding.
No electricity is involved so, as a result, its the most versatile system because it doesnt require mains power. If youre likely to be welding out in the paddock or even on a site where power is yet to be connected, a pair of gas bottles, some appropriate hoses and a gas torch are in your future.
A neutral (one-to-one acetylene/oxygen) flame the inner cone reaches 3,172 degrees C. This primary flame creates a molten weld pool that is protected by the outer flame.
The pool is filled with a welding/filler rod, usually made of the same material as the component(s) being welded. Mild steel melts at 1,485 degrees C.
While its certainly versatile, a disadvantage of oxy welding compared with arc welding is that a large amount of heat is absorbed by the part being welded and that causes distortion. Excess heat may also weaken the area due to changes in the crystal structure of the base metal.
Usually known simply as the oxy set, it might also be called the gas axe because the same equipment can be used for many things, including demolition and preparing large metal items for recycling.
An oxy set lends itself to many applications, including brazing, hard surfacing, tempering, soldering, heating and bending jobs.
What welder should you buy?
What is the best welder for you? Regardless of whether you opt for arc welders, inverter welders, TIG welder, MIG welder or gas, one essential consideration in all cases is to ensure that you have clean, dry work pieces. These are essential for the best welds. So is wearing the correct safety gear and welding in an area that wont easily catch fire. Working in a place which is well-ventilated, but not in the wind, will also give better results.
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