Wednesday, November 3, 2010

Welding Basics

Welding and Farming - The Two Go Hand-In-Hand

Welding and FarmingWelding and farming? They have more in common than you might think. In fact, one astute farmer recently noted, "you can't run a farm without welding." This farmer was absolutely correct -- to keep equipment in working order for the critical seasons of planting and harvesting, welding and hardfacing during the off-season are musts. A good working knowledge of these processes also comes in handy when your equipment breaks down during off-hours and you need to quickly fix so you can continue your work.

In this article, we will introduce you to some of the key concepts in welding and hardfacing. When we refer to welding, we are talking about joining metal pieces together to build something. The weld is primarily for strength purposes. Hardfacing, on the other hand, is depositing (by welding with special hardfacing electrodes) wear- resistant surfaces on existing metal components which are under stress to extend their service life. Hardfacing is very commonly done to metal edges that scrape or crush other tough materials -like the blade on a road grader.

Welding and FarmingWe will discuss different applications, ways to identify metallurgy, basic welding procedures and safety. So often, the beginning or novice welder will not get the desired results and assume his welding machine or electrodes are not working properly. In many of these instances, though, the farmer did not take the necessary preparations before welding or has chosen the wrong process, parameters or consumables. In this article, we hope to educate you so that you will know what to use in a few applications and can get the best results. Realize that although a little welding knowledge could help you a lot, there is a lot to becoming a true welding expert, which would cover many books!

Welding Applications

Welding and FarmingFarmers constantly need to repair and modify machinery and equipment to suit their specific needs. This instant ability to alter steel gates, chutes, animal pens, and machinery is such a tremendous benefit to the farmer. Repairing a broken plow or combine in the field by welding it where it broke in minutes can literally save an entire crop. The needs of beef cattle can usually be taken care of with mild steel. Dairy cattle, and virtually their entire milk-handling system require stainless steel. Two similar appearing animals with very different welding needs. But both needing welding to succeed.

Hardfacing Applications

There are many different items that could potentially benefit from hardfacing on the farm. They can basically be put into three "wear" categories - abrasion, impact, and metal-to-metal. Abrasion is one of the most common wears you will see on a farm, in this category falls all earth engaging implements such as tractor buckets, blades, teeth, grain handling products and feed mixers. Under the impact heading you will find equipment used to pound and smash such as crusher hammers. Metal-to-metal refers to wear from steel parts rolling or sliding against each other. Metal-to-metal wear occurs on such items as crane wheels, pulleys, idlers on track-drives, gear teeth and shafts.

Although farmers use welding and hardfacing techniques to rebuild old, worn-out components, Lincoln recommends hardfacing many new components as well. By hardfacing something that is new, it may increase the overall life expectancy of that product.

Basic Metallurgy

Before you can weld or hardface, you first need to identify the parent metal. A good rule of thumb on the farm is that nothing is mild steel. Almost all implements are high strength steels (either high or low alloy) and many are higher carbon steels. But how do you tell the difference? There are a couple of tests that can help.

Welding and FarmingThe first is a magnetic test. If a magnet will stick to the implement then it is likely iron-based. A magnet that will not stick indicates probably a manganese or stainless product. Secondly, try the spark test. If you take a grinder to the item, do you get 30" long, moderately large volume of yellow sparks with just a few sprigs and/or forks indicating mild steel, or do you achieve 25" long, slight to moderate volume of yellow orange sparks, a few forks with intermittent breaks but few if any sprigs to indicate alloy steels or do you get 15" long short, red sparks in large volume with numerous and repeating sprigs, which are telltale signs of a high carbon metal? Another test, the chisel test, will help indicate the type of metal as well. If the metal fractures in large chunks when you take a chisel to it, this means you have cast iron, which can be very difficult to weld unless using special high-nickel electrodes and heat-treating. On the other hand, if the chisel yields corkscrew-like shavings, you are looking at a weldable steel.

What Is the Goal?

Now that you have identified the base material, you need to assess your final goal. In a farm type setting, you need to ascertain whether you need to strengthen the item or prevent wear? If the item in question is a hitch bar on a tractor, the ultimate goal is strength and ductility so that it will not break. WELD IT! If you are talking about an earth-engaging tool, you don't want it to wear out. HARDFACE IT!

Identify What Method to Use

There are three types of welding methods to consider. They differ by speed and cost. The methods are all available to all welding and hardfacing products. However, specific products often have properties that are somewhat unique and not exactly duplicated when utilized by a different process.

Stick Welding

Manual or stick welding requires the least amount of equipment and provides maximum flexibility for welding in remote locations and in all positions. Typically, each rod permits welding for about one minute. In seconds, one can change from mild steel to stainless to hardfacing. In seconds, the electrode can change from small to large diameter for small or large welds. Although simplest, this type of welding takes the greatest operator skill.

Semiautomatic

This type of welding uses wire feeders and continuously fed electrodes. The welding gun is hand-held by the operator. The gun keeps feeding wire as long as the trigger is depressed. This is also much easier to learn than stick welding. This type of setup is becoming more popular on farms, which do more than minimal repair work. Semiautomatic welding increases deposition rates over manual welding because there is no need to stop after burning each rod.

Automatic

Requiring the greatest amount of initial setup, automatic welding has the highest deposition rates for maximum productivity. The welding gun is carried by a mechanized carriage and the welding operator just pushes a start button. This would rarely be found on a farm, but is common at repair centers for heavy equipment that would rebuild your parts for you if the schedule was mutually acceptable.

Welding Procedures

There are five basic steps when welding that must be followed.Welding and Farming

  • Proper Preparation - You first need to ensure that the metal you are welding is clean and dry. Remove rust, dirt, grease, oil and other contaminants by wire brushing. If not removed, these contaminants can cause porosity, cracking and poor weld deposit quality. You must also remove badly cracked, deformed or work-hardened surfaces by grinding, machining or carbon-arc gouging.

  • Proper Preheat - The combination of alloy content, carbon content, massive size and part rigidity creates a necessity to preheat in many welding or hardfacing operations. Most applications require preheating, as a minimum to bring the part to a room temperature of 70ƒ-100ƒ F. Medium to high carbon and low alloy steels may require higher preheat to prevent underbead cracking, welding cracking or stress failure of the part. Preheating can be done with either a torch, oven or electrical heating device. Special temperature-melting crayons can help you verify proper preheat. Too much heat and you can often ruin alloy materials!

  • Adequate Penetration - Correct Welding Procedure - Identify the correct amperage, travel speed, size of weld, polarity, etc. Make sure the completed weld meets your expectations in regards to size and appearance. Welds should be smooth and uniform, free from undercut or porosity. If possible, watch a video showing the type of welding you will be doing so you know what things are suppose to look like.

  • Proper Cool Down - Preheating is the most effective way of slowing the cooling rate of massive or restrained parts, which are inherently crack sensitive. Insulating the part immediately after welding with dry sand, lime, or a glass fiber blanket also helps minimize residual cooling stresses, weld cracking and distortion. Never quench a weld with ice or water as this will lead to greater internal stresses and potentially weld cracking.

  • Post Weld Heat Treatment - Some items may require tempering or heat-treating. What this means is that you warm the item up with your torch after welding and allow it to slowly cool.

Safety

There are a few rules you should follow as you are welding/hardfacing:
Welding and Farming

  • Protect yourself from fumes and gases - Always weld in an open, well-ventilated room and keep your head out of the fumes - especially with hardfacing

  • Wear protective clothing - Protect your eyes and face with a welding helmet designed for arc welding, not just gas welding goggles. In the same manner, protect your body from weld spatter and arc flash with woolen or cotton clothing, a flameproof apron and gloves, and boots. Also make sure to protect others around you from the arc rays as well.

  • Beware of electric shock - Do not touch live electrical parts and make sure that your welding machine is properly grounded. Never weld if you are wet or if your gloves have holes in them.

  • Fire/explosion hazard - Never weld in an enclosed space or near hay, feed bags, gasoline, diesel, hydraulic fluids or anything else that can be within the reach of your welding sparks that would cause a fire or explosion. Never weld alone. Always have a buddy nearby in case of an emergency.

Conclusion

After reading this article, you should be able to reap the benefits of welding in much the same way as you already reap the benefits of the earth on your farm.



Selecting Your Welding Process

Sure, you know you have a weld to make. . .that's the easy part. . . but you need to start by examining your application.. Everybody's job is individual and has specific requirements. Therefore, if you're really confused the best idea is to consult a welding expert in person. If you still have questions after reading this article, just ask us online.

However, this article can help you with welding process selection in four easy steps:

1.) The joint to be welded is analyzed in terms of its requirements.

2.) The joint requirements are matched with the capabilities of available processes. One or more of the processes are selected for further examination.

3.) A checklist of variables is used to determine the ability of the selected processes(s) to meet the particular application.

4.) Finally, the proposed process or processes deemed most efficient are reviewed with an informed representative of the equipment manufacturer for verification of suitability and for more information

Step 1 - Analysis of Joint Requirements.

The first thing to look at is whether your weld joint is large or small, whether the joint is out-of-position or not, and whether the base metal is thick or thin.

In welding, the needs of any joint are expressed in four terms: Fast-Fill (high deposition rate), Fast-Freeze (the joint is out-of-position - overhead or vertical), Fast-Follow (high arc speed and very small welds), and Penetration (the depth the weld penetrates the base metal)

Fast-Fill is required when a large amount of weld metal is needed to fill the joint. A heavy weld bead can only be laid down in minimum arc time with a high deposition rate. However, Fast-Fill becomes a minor consideration when the weld is small.

Fast-Freeze implies that a joint is out-of-position, and therefore requires quick solidification of the molten crater. Not all semiautomatic processes can be used on fast-freeze joints.

Fast-Follow suggests that the molten metal follows the arc at rapid travel speed, giving continuous, well-shaped beads, without "skips" or islands. This trait is especially desirable on relatively small single-pass welds, such as those used in joining sheet metal.

Penetration varies with the joint. With some joints, penetration must be deep to provide adequate mixing of the weld and base metal and with others it must be limited to prevent burnthrough or cracking.

Any joint can be categorized in terms of the previously mentioned four factors. To determine the appropriate welding process, keep your efforts focused on the requirements of the weld joint. A joint that requires, or can be welded by, just one arc welding process is rare. In fact, the majority of joints usually are characterized
by a combination of these requirements to varying degrees. Once you've determined your appropriate joint requirements and ranked them, have your assessment reviewed by an experienced engineer or welder. With time and experience, you'll be able to make these assessments more accurately and with less difficulty.

Step 2 - Matching Joint Requirements With Processes

Your equipment manufacturers' literature usually will give information on the ability of various processes to fulfill the needs of the joint. (Or, a telephone call or email will bring the needed information.) A wrong answer is virtually impossible at this point, since the deposition rate and arc-speed characteristics of each process can be clearly defined. Since you have characterized your weld joint it is simply a matter of selecting the process that suits your characterization. To view some machines and consumables with various characteristics click here to view Lincoln Electric's product line.

So what do you do when you find that two or more processes are suitable, which is sometimes the case? You create a checklist!

Step 3 - The Checklist

Considerations other than the joint itself have a bearing on selection decisions. Many of these are specific to your job or welding shop. However, they can be of great importance - and a key factor in eliminating alternate processes. Organize these factors into a checklist and consider them one-by-one:

Volume of Production. You must justify the cost of welding equipment by the amount of work, or productivity, required. Or, if the work volume for one application is not great enough, another application may be found to help offset the costs.

Weld Specifications. Rule out a process if it does not provide the weld properties specified by the code governing the work.

Operator Skill. Operators may develop skill with one process more rapidly than another. Will you have to train your operators in a new process? That adds cost!

Auxiliary Equipment. Every process has a recommended power source and other items of auxiliary equipment. If a process makes use of existing auxiliary equipment, the initial cost in changing to that process can be substantially reduced.

Accessory Equipment. Availability and cost of necessary accessory equipment - chipping hammers, deslagging tools, flux lay-down and pickup equipment, exhaust systems, et cetera - should be taken into account.

Base-Metal Conditions. Rust, oil, fit-up of the joint, weldability of the steel, and other conditions must be considered. These factors could limit the usefulness of a particular process.

Arc Visibility. Is there a problem following irregular seams? Then open-arc processes are advantageous. On the other hand, if there's no difficulty in correct placement of the weld bead, there are "operator-comfort" benefits with the submerged-arc process; no head-shield required and heat from the arc is reduced.

Fixturing Requirements. A change to a semiautomatic process requires some fixturing if productivity is to be realized. Appraise the equipment to find out if it can adapt to processes.

Production Bottlenecks. If the process reduces unit fabrication cost, but creates a production bottleneck, its value is lost. Highly complicated equipment that requires frequent servicing by skilled technicians may slow up your actual production thereby diminishing its value.

The completed checklist should contain every factor known to affect the economics of the operation. Some may be specific to the weld job or weld shop. Other items might include:

  • Protection Requirements
  • Range of Weld Sizes
  • Application Flexibility
  • Seam Length
  • Setup Time Requirements
  • Initial Equipment Cost
  • Cleanliness Requirements

Evaluate these items realistically recognizing the peculiarities of the application as well as those of the process, and the equipment.

Human prejudice should not enter the selection process; otherwise objectivity is lost - when all other things are equal, the guiding criterion should be overall cost.

Step 4 - Review of the Application by Manufacturer's Representative.

This may seem redundant, but the talents of experts should be utilized. Thus, the checklist to be used is tailored by the user to his individual situation. You know your application best and your welding expert knows his equipment best. Together, you should be able to confirm or modify the checklist. To contact a Lincoln Electric welding Expert click here.

Systemizing the Systematic Approach.

A system is of no value unless it is used. Create a chart and follow the steps to determining process. By taking the time to analyze each new weld joint, your operation will become more productive and your welding experience will be more fulfilling.

Source: Adapted from The Procedure Handbook of Arc Welding. The Lincoln Electric Company, 1994.

To order a copy of Lincoln Electric's Procedure Handbook of Arc Welding or other welding textbooks and educational aids, click here to print out and fax an order form.



Arc-Welding Fundamentals
The Lincoln Electric Company, 1994.

Arc welding is one of several fusion processes for joining metals. By applying intense heat, metal at the joint between two parts is melted and caused to intermix - directly, or more commonly, with an intermediate molten filler metal. Upon cooling and solidification, a metallurgical bond is created. Since the joining is an intermixture of metals, the final weldment potentially has the same strength properties as the metal of the parts. This is in sharp contrast to non-fusion processes of joining (i.e. soldering, brazing etc.) in which the mechanical and physical properties of the base materials cannot be duplicated at the joint.

Fig. 1 The basic arc-welding circuit

In arc welding, the intense heat needed to melt metal is produced by an electric arc. The arc is formed between the actual work and an electrode (stick or wire) that is manually or mechanically guided along the joint. The electrode can either be a rod with the purpose of simply carrying the current between the tip and the work. Or, it may be a specially prepared rod or wire that not only conducts the current but also melts and supplies filler metal to the joint. Most welding in the manufacture of steel products uses the second type of electrode.

Basic Welding Circuit

The basic arc-welding circuit is illustrated in Fig. 1. An AC or DC power source, fitted with whatever controls may be needed, is connected by a work cable to the workpiece and by a "hot" cable to an electrode holder of some type, which makes an electrical contact with the welding electrode.

An arc is created across the gap when the energized circuit and the electrode tip touches the workpiece and is withdrawn, yet still with in close contact.

The arc produces a temperature of about 6500ºF at the tip. This heat melts both the base metal and the electrode, producing a pool of molten metal sometimes called a "crater." The crater solidifies behind the electrode as it is moved along the joint. The result is a fusion bond.

Arc Shielding

However, joining metals requires more than moving an electrode along a joint. Metals at high temperatures tend to react chemically with elements in the air - oxygen and nitrogen. When metal in the molten pool comes into contact with air, oxides and nitrides form which destroy the strength and toughness of the weld joint. Therefore, many arc-welding processes provide some means of covering the arc and the molten pool with a protective shield of gas, vapor, or slag. This is called arc shielding. This shielding prevents or minimizes contact of the molten metal with air. Shielding also may improve the weld. An example is a granular flux, which actually adds deoxidizers to the weld.

Fig. 2 This shows how the coating on a coated (stick) electrode provides a gaseous shield around the arc and a slag covering on the hot weld deposit.

Figure 2 illustrates the shielding of the welding arc and molten pool with a Stick electrode. The extruded covering on the filler metal rod, provides a shielding gas at the point of contact while the slag protects the fresh weld from the air.

The arc itself is a very complex phenomenon. In-depth understanding of the physics of the arc is of little value to the welder, but some knowledge of its general characteristics can be useful.

Nature of the Arc

An arc is an electric current flowing between two electrodes through an ionized column of gas. A negatively charged cathode and a positively charged anode create the intense heat of the welding arc. Negative and positive ions are bounced off of each other in the plasma column at an accelerated rate.

In welding, the arc not only provides the heat needed to melt the electrode and the base metal, but under certain conditions must also supply the means to transport the molten metal from the tip of the electrode to the work. Several mechanisms for metal transfer exist. Two (of many) examples include:

  1. Surface Tension Transfer - a drop of molten metal touches the molten metal pool and is drawn into it by surface tension.
  2. Spray Arc - the drop is ejected from the molten metal at the electrode tip by an electric pinch propelling it to the molten pool. (great for overhead welding!)

If an electrode is consumable, the tip melts under the heat of the arc and molten droplets are detached and transported to the work through the arc column. Any arc welding system in which the electrode is melted off to become part of the weld is described as metal-arc. In carbon or tungsten (TIG) welding there are no molten droplets to be forced across the gap and onto the work. Filler metal is melted into the joint from a separate rod or wire.

More of the heat developed by the arc is transferred to the weld pool with consumable electrodes. This produces higher thermal efficiencies and narrower heat-affected zones.

Since there must be an ionized path to conduct electricity across a gap, the mere switching on of the welding current with an electrically cold electrode posed over it will not start the arc. The arc must be ignited. This is caused by either supplying an initial voltage high enough to cause a discharge or by touching the electrode to the work and then withdrawing it as the contact area becomes heated.

Arc welding may be done with direct current (DC) with the electrode either positive or negative or alternating current (AC). The choice of current and polarity depends on the process, the type of electrode, the arc atmosphere, and the metal being welded.


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Underwater-welding for saving while rescuing

SOLUTIONS with Effective, Powerful Advice

Underwater-welding
Should I take the plunge?

Underwater-welding , enclosure welding, hyperbaric enclosure welding, wet Underwater-welding, high pressure water jet welding, other welding processes: friction welding,resistance welding, arc welding, tig welding, mig welding, oxyacetylene welding, electron beam welding, laser beam welding, welding techniques, welding information, welding links, welding tips, welding instructions, improving welding results, welding safety issues, joining questions needing answers: these are some of the items developed in this Site for the benefit of interested readers.

What is in here for me?

Underwater-welding, one of the best examples of adapting a well known process to the harsh and dangerous environment of the sea, demonstrates what necessity, ingenuity and continuing efforts could accomplish, mostly to save huge investments in offshore structures that were damaged and needed repair.

What is there, deep in the water? Does it pay?

The advantages are of economical nature, because Underwater-welding for marine maintenance and repair jobs bypasses the need to pull the structure out of the sea and saves much valuable time. If one thinks of Underwater-welding the hull of a ship or of a partially submerged oil drilling tower, one understands that the alternative may be extremely expensive, if at all possible.

The limitations of Underwater-welding concern the inevitable bulky and expensive setup to provide the welder with all the support needed, for respiration, for protection from cold, for special welding equipment, for remote surveillance camera, for special non destructive testing.

Is it risky?

The main risks for the welder performing Underwater-welding are the potential for electricshock, the possibility of producing in the arc mixtures of hydrogen and oxygen in pockets, which might set up an explosion, and the common danger sustained by divers, of having nitrogen diffuse in the blood in dangerous proportions. Curiously the risk of drowning is not listed with the hazards of Underwater-welding.

First there were no demands for quality. Underwater-welding was just applied to weld apatch until a more thorough repair could be performed. But as soon as more experience was gained, ambitious individuals and companies joined forces to improve results and to establish achievable specifications.

Let us continue...

... with some more details on Underwater-welding. There are three main ways to perform Underwater-welding. One is to build an enclosure, a pit, around the place of repair and to pump away all the water: that amounts to prepare the conditions for normal welding in air, although the place may be deep under sea level.

Another method of Underwater-welding consists in preparing an enclosure to be filled with gas (helium) under high pressure (hyperbaric) to push water back, and have the welder, fitted with breathing mask and other protective equipment, weld quite normally out of water but under pressure.

The third is the wet Underwater-welding method, where no attempts are made to dry up the location of welding. Instead the power of the arc generates a bubble of a mixture of gases which lets metal melting and joining occur more or less normally, using specially covered electrodes to avoid that too much hydrogen be absorbed in the weld. The skilled welder must also be a diver, equipped for Underwater-welding, with all the extra equipment and protection a welder must use.

There is also a less used method of Underwater-welding which features a special torch which sprays a cone of high pressure water, within which protective gas under pressure insulates the weld location from the water during welding.

Frequently Asked Information

Basic informations and suggestions on this subject can be found by clicking on Taking the Plunge.

A short list of educational facilities is available by clicking on
Underwater-welding.

An informative article describing developments and achievements of this demanding specialty can be read by clicking here.

Another recommended article explaining the essential subjects of such a schooling and training program can be seen here.

Note: Let us make it clear at once that Underwater-welding has nothing to do and should not be confused with Submerged Arc Welding wich is a specialized process described in a page on Arc Welding, and which is performed outside water.

Other Welding Processes.

Even if you are not familiar with Underwater-welding, you certainly know your processes. But how could a different one be selected?


By first knowing what other processes look like. One can certainly learn the most by enrolling in training courses, if it makes sense.

You know that there is no universal welding process perfectly adapted and convenient to whatever form and material joining. However in most cases one or more processes may be selected which permit acceptable welds to be performed.

How would you select your process? Is the process you use the best one? How would you improve on it? What is the best process?

Tip! : The "best" process is the the least expensive and available one that can be used to produce acceptable welds performing the functions of strength and stability required for the joint.

If you are looking...

... for information on other welding PROCESSES, chances are you will be able to find what interests you just by browsing here. However, if you do not find what you look for, write us by e-mail. Click here.

The following descriptive information of only the most important processes is provided for general orientation leaving more specific details to be found in the underlined referenced pages hereafter.

For practical purposes of designation, processes are usually divided between PRESSURE and FUSION WELDING. In the first type, pressure is always applied, with or without external means to provide heat, while melting temperature may or may not be reached. In the second type melting temperature is usually reached locally without the use of pressure.

Did you know that...

Welding history recognizes FORGE WELDING, which belongs to the pressure category, as one of the oldest processes performed in the blacksmith's shop well before the twentieth century. Do you agree that it could be a very interesting experience for school-children to watch, if somebody wanted to revive the practice for a show? Would you organize that for your community?

This joining is achieved when two elements, usually steel bar ends, heated to white temperature in a coal burning forced air furnace, are brought rapidly together andhammered thoroughly on the anvil to expel any oxide layer which might be present and to work them intimately to complete union.

Similar but different...

A modern sophisticated version, called FRICTION WELDING was developed, which has some important applications, especially for mass production or for specialized repairs. In general it is not for job-shops, but small shops dedicated only to this specialty may thrive, given the right conditions. A description of the process follows in the dedicated page: click on Friction Welding Process.

Most important in the pressure category are RESISTANCE WELDING processes, further divided into spot, seam and projection welding, frequently highly automated. Many of our everyday household items and car bodies are held together by resistance welds. How would you decide if it is the right solution for your welding problems and how could you improve on it?

These processes share the fact that heating is produced by the resistance to the flow of a concentrated high electric current which is made to pass locally between special copper electrodes holding the elements to be welded together under applied pressure. For more details click on Resistance Welding.

On the other hand...

Of the fusion welding processes developed in the twentieth century, and acclaimed as a real and important breakthrough, GAS WELDING, using an open FLAME, is probably one of the earliest of modern welding history. In this manual process the heat required for local progressive melting is provided by the flame of combustion of acetylene gas (other gases were tried and abandoned) with oxygen. A filler metal rod of appropriate composition may or may not be used as required.

In preparation for Underwater-welding there may be a need to perform flame cutting using hydrogen gas. (Flame welding is not used). See details in Cutting.

ARC WELDING represents a family of quite different processes, each one best adapted to its particular application niche. In these processes the energy required for melting the metals is provided by an electric arc, struck between the electrode, held by the torch, and the workpiece, usually clamped on a welding table.

Underwater-welding is mostly performed by variations on this process, taking into account the particular environmental and operator's requirements.

In the general case, the electrode is either consumable, melting to provide filler material, or non consumable, being made from a refractory tungsten alloy. In this case, when needed, filler metal is provided separately either from a manually held filler rod or from a reel fed continuously in automatic or semi-automatic equipment.

The needed protective atmosphere is provided by gases from decomposition processes of suitable materials, enrobing the electrodes (sticks) or included in the core of specially prepared (flux cored) filler wires. Otherwise a stream of inert gas like Argon or carbon dioxide (CO 2) or mixtures thereof is continuously supplied to the molten pool through the torch.

Last but most important...

High Energy Welding processes are more specialized, in that they require sophisticated equipment, mostly precisely computer controlled, and are used for specific and important applications like aerospace, submarine (but not Underwater-welding!) and nuclear, or for mass production of delicate small implements.



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Aluminum: Experience in Application

What you should know about welding aluminum.

In recent years, the use of aluminum in manufacturing has become more prevalent because of its light weight and other attributes that make it an attractive alternative to steel. In fact, the aluminum welding market is expected to grow at a rate of 5.5 percent annually based primarily on the assumption that the automotive industry will continue to increase its use of aluminum.

But, those experienced in the welding of steel will find aluminum to be a different breed – the normal welding characteristics of steel don’t always apply to aluminum. For example, aluminum’s high thermal conductivity and low melting point can easily lead to burnthrough and warpage problems if proper procedures are not followed.

In this article, we will first take a look at various alloying elements and how they affect aluminum; then we will turn our attention to welding procedures and the parameters that will create the best quality weld. Lastly, we will examine some new technology breakthroughs that make welding aluminum a little easier.

Alloying Elements
To understand aluminum, you must first understand some basics about aluminum metallurgy. Aluminum can be alloyed with a number of different elements, both primary and secondary, to provide improved strength, corrosion resistance and/or general weldability.

The primary elements that alloy with aluminum are copper, silicon, manganese, magnesium and zinc. But, before we examine them in detail and what they bring to aluminum, it is important to note that these alloys fall into two classes: heat-treatable or nonheat-treatable.

Heat-Treatable vs. Nonheat-Treatable Alloys
Heat-treatable alloys are those that can be heated after welding to regain strength lost during the welding process. To heat-treat an alloy means heating it at a high temperature, putting the alloying elements into solid solution and then cooling it at a rate which will produce a supersaturated solution. The next step in the process is to maintain it at a lower temperature long enough to allow a controlled amount of precipitation of the alloying elements.

With the nonheat-treatable alloys it is possible to increase strength through cold working or strain hardening. To do this, a mechanical deformation must occur in the metal structure, resulting in increased resistance to strain, producing higher strength and lower ductility.


Further Distinctions
To further designate aluminum alloys, they can also be classified by a temper designation which are as follows: F = As fabricated, O = Annealed, H = Strain hardened; W = Solution heat-treated and T = Thermally treated, which can designated heat treatment, or cold working aging. For example an alloy may carry the designation of 2014 T6. This means that it is alloyed with copper (2XXX series) and the T6 refers to the fact that it is solution heat-treated and artificially aged.

For purposes of this article, we will discuss wrought alloys, which are those aluminum alloys that are rolled from ingot or extruded with customer specified shapes. But please note that alloys can also be divided into cast alloys. Cast alloys are those used to manufacture parts from molten alloys of aluminum poured into molds. Cast alloys are precipitation hardenable but never strain hardenable. The weldability of these alloys is affected by casting type – permanent mold, die cast, and sand – since the casting surface is critical to welding success. A three-digit number, plus one decimal i.e. 2xx.x designates the cast alloys. Weldable grades of aluminum castings are 319.0, 355.0, 356.0, 443.0, 444.0, 520.0, 535.0, 710.0 and 712.0.

Alloying Elements
Now, that you understand some of the terminology, let’s take a look at the different alloying elements:

Copper (which carries a wrought alloy designation of 2XXX series) provides high strength to aluminum. This series is heat-treatable and mainly used in aircraft engine parts, rivets and screw products. Most 2XXX series alloys are considered poor for arc welding because of their sensitivity to hot cracking. These alloys are generally welded with 4043 or 4145 series filler electrodes, which have low melting points to reduce the probability of hot cracking. Exceptions to this are alloys 2014, 2219 and 2519, which are easily welded with a 2319 filler wire.

Manganese (3XXX series) added to aluminum yields a nonheat-treatable series used for general-purpose fabrication and build-up. Moderate in strength, the 3XXX series is used for forming applications including utility and van trailer sheet. It is improved through strain hardening to provide good ductility and improved corrosion properties. Typically welded with 4043 or 5356 electrode, the 3XXX series is excellent for welding and not prone to hot cracking. Its moderate strengths do prevent this series from being used in structural applications.

Silicon (4XXX series) reduces the melting point of aluminum and improves fluidity. Its principle use is as filler metal. The 4XXX series has good weldability and is considered a nonheat-treatable alloy. Alloy 4047 is becoming the alloy of choice in the automotive industry, as it is very fluid and good for brazing and welding.

Magnesium (5XXX series), when added to aluminum, has excellent weldability with a minimal loss of strength and is basically not prone to hot cracking. In fact, the 5XXX series has the highest strength of the nonheat-treatable aluminum alloys. It is used for chemical storage tanks and pressure vessels at elevated temperatures as well as structural applications, railway cars, dump trucks and bridges because of its corrosion resistance. It looses ductility when welded with 4XXX series fillers due to formation of Mg2Si.

Silicon and Magnesium (6XXX series) combine to serve as alloying elements for this medium-strength, heat-treatable series. It is principally used in automotive, pipe, railings, structural and extruding applications. The 6XXX series is somewhat prone to hot cracking, but this problem can be overcome by the correct choice of joint and filler metal. This series can be welded with either 5XXX or 4XXX series without cracking – adequate dilution of the base alloys with selected filler alloy is essential. A 4043 electrode is the most common for use with this series.

Zinc (7XXX series) added to aluminum with magnesium and copper produces the highest strength heat-treatable aluminum alloy. It is primarily used in the aircraft industry. The weldability of the 7XXX series is compromised in higher copper grades, as many of these grades are crack sensitive (due to wide melting ranges and low solidus melting temperatures.) Grades 7005 and 7039 are weldable with 5XXX fillers.

Other elements (8XXX series) that are alloyed with aluminum (i.e. lithium) all fall under this series. Most of these alloys are not commonly welded, though they offer very good rigidity and are principally used in the aerospace industry. Filler metal selection for these heat-treatable alloys include the 4XXX series.

Pure Aluminum (1XXX series), though not an alloying element, is considered nonheat-treatable and is used primarily in chemical tanks and piping because of its superior corrosion resistance. This series is also used in electrical bus conductors because of its excellent electrical conductivity. 1XXX series are easily welded with 1100 and 4043 alloys.

In addition to the primary aluminum alloying elements, there is a number of secondary elements, which include chromium, iron, zirconium, vanadium, bismuth, nickel and titanium. These elements combine with aluminum to provide improved corrosion resistance, increased strength and better heat treatability.

Physical Properties
Now that you have a basic background on aluminum metallurgy, we will move into the physical properties of base metal aluminum and how it compares to other metals, primarily steel.

The reason why aluminum is becoming specified for so many jobs is its physical properties. For instance, aluminum is three times lighter than steel and yet offers higher strength when alloyed with the right elements. It can conduct electricity six times better than steel and nearly 30 times better than stainless steel. This high electrical conductivity makes the effect of electrical stick-out in GMAW (Gas Metal Arc Welding) less significant when compared to steel (we will cover this concept in more detail later in this article.)

In addition, aluminum provides excellent corrosion resistance, is easy to shape and join, and also is non-toxic for food applications. Since it is non-magnetic, arc blow is not a problem during welding. With a thermal conductivity rate that is five times higher than steel and being less viscous, aluminum can easily be welded out-of-position. Aluminum does have its drawbacks, though, since its high thermal conductivity tends to act as a heat sink making fusion and penetration more difficult.

Since aluminum has a low melting point 1,200 degrees F (half that of steel) for the same wire size, the transition current for aluminum is much lower than it is for steel. Also, for the same welding current, the burn-off rate is about twice that of steel.

Chemical Properties
In terms of chemical composition, aluminum has a high maximum solubility for hydrogen atoms in the liquid form and a low solubility at the solidification point. This means that even a small amount of hydrogen dissolved in the liquid weld metal will tend to escape as the aluminum solidifies and porosity is likely to occur – a great cause of concern during the welding process.

Also, aluminum combines with oxygen to form an aluminum oxide layer instantaneously as it is machined. This layer is very porous and can easily trap moisture, oil, grease and other materials. The oxide provides excellent corrosion resistance, but must be taken off before welding as it prevents fusion due to its high melting point (3700 degrees F). Mechanical cleaning, solvents, chemical etching and purging are used to take off the oxide layer.

Mechanical Properties
Mechanical properties such as tensile strength, yield and elongation are affected by the choice of aluminum base and filler alloys. For groove welds, the Heat Affected Zone (HAZ) dictates the strength of the joint. In nonheat-treatable aluminum alloys, the HAZ will be completely annealed and the HAZ will be the weakest point. Heat-treatable alloys require much longer periods at annealing temperatures combined with slow cooling to completely anneal them so that weld strength is less affected. Such items as preheating, lack of interpass cooling, and excessive heat input from slow, weaving weld passes all increase peak temperature and time at temperature, which means minimum strength levels might not be met.

For fillet welds, strength is dependent on the composition of the filler alloy used to weld the joint. In structural applications, the selection of 5XXX instead of 4XXX series filler can provide twice the strength

The nonheat-treatable alloys offer excellent ductility when using matching fillers, though lower ductility results from welds made with 4XXX series. Heat-treatable alloys do not exhibit high ductility, and post-weld heat treatments generally reduce ductility.



Taking Metallurgy to the Next Level
Now that we have some background on aluminum metallurgy, we now want to apply that knowledge to the actual welding of the alloy. To do this, we will first take a look at technology that produces outstanding welding characteristics on aluminum, combating common problems such as poor penetration, high spatter levels, burnthrough and porosity.

Today’s quick response inverters using Lincoln’s patented Waveform Control Technology™ precisely control welding waveforms for more efficient control of droplet transfer. This reduces the amount of spatter caused by the low density of aluminum while a high-energy pulse peak insures proper penetration.

In addition, since variations in chemistry dramatically change an alloy’s physical properties, these custom waveforms can be designed for specific alloys to best suit the physical properties of what is being welded.

Because aluminum has a high maximum solubility for hydrogen in its liquid state and a low solubility at its solidification point, pulsing output waveforms are further designed to minimize arc length by trimming the output as low as possible and reduce the likelihood of porosity.

Lincoln has recently taken custom waveforms to the next level with Wave Designer Software®. The software allows welding engineers and operators to manipulate and modify welding waveforms on their PCs as communicated from welding equipment in real time. This creates high quality, tailored performance, when used in conjunction with inverters.

New Welding Methods
The use of Constant Current power sources for the gas metal arc welding of aluminum has a long and very successful history. The use of “drooper” output has assisted in the delivery of a high energy axial spray transfer mode for aluminum that responds evenly and consistently with the proper welding current despite changes in arc length. The result of constant current is consistent penetration throughout the length of a given weld.

The evolution of the control of the arc has lead recently to the development of software controlled inverter power sources. The use of software to “optimize” arc characteristics for aluminum GMAW has been taken to a new level at Lincoln Electric and it is known as Waveform Control Technology. A modified constant current output is employed in a very high speed synergic pulsed output that incorporates many of the benefits of Constant Current GMAW for Aluminum. These benefits include the high energy input that occurs during the pulse peak. The pulse peak helps to provide a consistent penetration profile throughout the length of a given weld and the advantages of pulsing also includes reduced spatter levels, improved puddle fluidity with an increase in effective travel speeds, and reduced heat input and lower distortion levels.

Lincoln Electric’s Waveform Control Technology™ takes pulsing to the next level. This technology allows welding waveforms to be manipulated to form the “perfect”, user defined, waveform for a particular application. This Waveform Control Technology and the tailoring it provides, can be found in highly developed software such as that found in Lincoln’s Power Wave inverter power sources. The Power Wave can be utilized in either one of two ways. Operators can select pre-programmed waveforms for welding aluminum or, engineers can create their own tailored, waveforms using Lincoln’s Wave Designer Software. These waveforms, which are created on a PC, can be programmed into the Power Wave.

Anatomy of a Waveform

But what exactly is the waveform control technology provided by Wave Designer Pro? With this technology, the power source responds to changes demanded by the software instantaneously. Keep in mind that the “waveform” is the means for determining the performance characteristics of a single molten droplet of electrode. The area under the waveform determines the amount of energy applied to that single droplet. Current is raised to a level higher than the transition current for spray transfer for a few milliseconds. During this time the molten droplet is formed, detached, and it begins its excursion across the arc. Additional energy can now be applied to the molten droplet during its descent that allows it to maintain its fluidity or increase its fluidity. The pulse is now moving to a low background current that sustains the arc which cools the cycle but prepares for the advancement to the next pulse peak.

Lets look at the waveform in detail. The front flank (A) is the rise to peak, measured in amps per millisecond, where the molten droplet is formed at the end of the electrode. As the molten droplet reaches peak it detaches. A percent of current “Overshoot”, (B), provides arc stiffness and it assists with the detachment of the molten droplet from the end of the electrode. The time spent at peak, (C) determines the droplet size; less time results in larger droplets and more time results in smaller droplets. From here the detached molten droplet is affected by energy supplied by the rear flank. The rear flank is comprised of tailout, (D), and stepoff, (E). Tailout can add energy to the molten droplet if it is increased. It can assist with puddle fluidity especially when the tailout speed is decreased. Stepoff is the place where tailout ends but it has impact on the stability of the anode and manipulation of stepoff can result in the elimination of fine droplet overspray. From this point the waveform moves to the background current, (F), where the arc is sustained. The time at the background current as it decreases has the effect of increasing the pulse frequency. The higher the pulse frequency, the higher the average current will become. Increasing frequency will result in a more focused arc.

Superimposed, in a selective fashion, over the waveform is the “Adaptive” characteristic of synergic pulsed GMAW. Adaptive, or, adaptivity refers to the ability of the arc to maintain a specific length despite changes in electrical stickout. This is an important enhancement for weld bead consistency and sound weld metal.

Process Optimization via Manipulating Waveforms
Manipulating the waveform can have a predictable effect on travel speeds, final weld bead appearance, post weld cleanup and welding fume levels. The real beauty in the manipulation of the waveform in Wave Designer Pro is how easy it is to create a visual appearance for the waveform. The user can then make real-time “drag and drop” changes in a PC Windows™ environment while the arc is running. Real time changes, or the arc can be viewed on a five channel ArcScope where Current peaks, Voltage Peaks, Power, and heat input calculations can be instantaneously viewed. The ArcScope samples data at a rate of 10KHz and is a valuable, optional-addition to the Wave Designer Software. The ArcScope gives the engineer a visual compilation of the created waveform. Critiques can be made and adjustments can then be made to further optimize the Waveform.

On thin, .035”, aluminum base materials, we can reduce heat input, reduce distortion, eliminate spatter, eliminate cold lap, and eliminate burn-throughs with the use of Waveform technology. This has been done repeatedly in applications that can benefit from pulsed GMAW. Welding programs can be created that will apply to a very specific range of wire feed speeds and/or currents or they can be created to follow a very wide range of material thicknesses with a broad range of wire feed speed.

Conclusion
Aluminum has many attractive attributes that make it the material of choice for a host of applications, although it can be different to weld. But, with a good understanding of metallurgy and the latest tools and technology on the market, aluminum can be dealt with successfully.



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Guidelines for Welding Cast Iron

Background

Cast iron is difficult, but not impossible, to weld. In most cases, welding on cast iron involves repairs to castings, not joining casting to other members. The repairs may be made in the foundry where the castings are produced, or may be made to repair casting defects that are discovered after the part is machined. Mis-machined cast iron parts may require repair welding, such as when holes are drilled in the wrong location. Frequently, broken cast iron parts are repaired by welding. Broken cast iron parts are not unusual, given the brittle nature of most cast iron.

While there are a variety of types of cast iron, the most common is gray cast iron, and these guidelines are directed toward this type of material.

A few facts about cast iron help in understanding the welding challenges. Cast iron typically has a carbon content of 2% - 4%, roughly 10 times as much as most steels. The high carbon content causes the carbon to form flakes of graphite. This graphite gives gray cast iron its characteristic appearance when fractured.

When castings are made, molten iron is poured into a mold and allowed to slowly cool. When this high carbon material is allowed to cool slowly, crack free castings can be made.Remembering this is helpful when welding cast iron: during and after welding, the casting must either be allowed to cool slowly, or should be kept cool enough that the rate of cooling is not important.

A critical temperature in most cast iron is about 1450 degrees F. When at this temperature, conditions that can lead to cracking occur. While the arc will heat the casting to temperatures above this level, it is important that the casting not be held at this temperature for long periods of time.

Electrode selection

If the part is to be machined after welding, a nickel-type electrode will be required. Use Lincoln Softweld® 99Ni stick electrode for single pass, high dilution welds. Softweld 55 Ni is preferred for multiple pass welds. Sometimes, root passes are put in with Softweld 99 Ni, followed by fill passes with Softweld 55 Ni. For welds where machining is not required, and where the weld is expected to rust like the cast iron, Lincoln Ferroweld® stick electrode can be used.

To Heat, or not to Heat

In general, it is preferred to weld cast iron with preheat--and lots of it. But, another way to successfully weld cast iron is to keep it cool--not cold, but cool. Below, both methods will be described. However, once you select a method, stick with it. Keep it hot, or keep it cool, but don't change horses in the middle of the stream!

Welding Techniques with Preheat

Preheating the cast iron part before welding will slow the cooling rate of the weld, and the region surround the weld. It is always preferred to heat the entire casting, if possible. Typical preheat temperatures are 500-1200 degrees F. Don’t heat over 1400 degrees F since that will put the material into the critical temperature range. Preheat the part slowly and uniformly.

Weld using a low current, to minimize admixture, and residual stresses. In some cases, it may be necessary to restrict the welds to small, approximately 1-inch long segments to prevent the build up of residual stresses that can lead to cracking. Peening of weld beads can be helpful in this regard as well.

After welding, allow the part to slowly cool. Wrapping the casting in an insulating blanket, or burying it in dry sand, will help slow cooling rates, and reduce cracking tendencies.

Welding Techniques without Preheat

The size of the casting, or other circumstances, may require that the repair be made without preheat. When this is the case, the part needs to be kept cool, but not cold.

Raising the casting temperature to 100 degrees F is helpful. If the part is on an engine, it may be possible to run it for a few minutes to obtain this temperature. Never heat the casting so hot that you cannot place your bare hand on it.

Make short, approximately 1” long welds. Peening after welding is important with this technique. Allow the weld and the casting to cool. Do not accelerate the rate of cooling with water or compressed air. It may be possible to weld in another area of the casting while the previous weld cools. All craters should be filled. Whenever possible, the beads should be deposited in the same direction, and it is preferred that the ends of parallel beads not line up with each other.

Sealing Cracks

Because of the nature of cast iron, tiny cracks tend to appear next to the weld even when good procedures are followed. If the casting must be water tight, this can be a problem. However, leaking can usually be eliminated with some sort of sealing compound or they may rust shut very soon after being returned to service.

The Studding Method

One method used to repair major breaks in large castings is to drill and tap holes over the surfaces that have been beveled to receive the repair weld metal. Screw steel studs into the threaded holes, leaving 3/16” (5 mm) to ¼” (6 mm)of the stud above the surface. Using the methods discussed above, weld the studs in place and cover the entire surface of the break with weld deposit. Once a good weld deposit is made, the two sides of the crack can be welded together.


SOURCE: Lincoln Electric


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Electrical Submersible Pump



Electrical submersible pumps (ESPs), much like vertical turbine pumps in design, are typically used to pump liquid. Essentially, an electric motor drives the pump, and the fluid’s kinetic energy is increased. This energy is then partly converted into pressure, which lifts the fluid through the pump. ESPs are centrifugal pumps with vertical shafts, and as a result depend on basic rotating impellers to pressurize fluid.

Centrifugal Pump Basics
Centrifugal pumps feature rotating impellers, typically made from metal, which contain rotating vanes. These vanes transfer energy from the motor to the fluid they propel. As fluid enters the impeller, it accelerates as the impeller rotates. Eventually, the fluid exits the impeller’s vanes at an increased speed, and the kinetic energy is typically converted into pressure.
In an ESP, mechanical seals are used to prevent fluid from flowing into the motor—the motor is coupled to the pump itself, and the entire unit is submerged in the fluid it pumps. Without mechanical seals protecting the enclosed unit, the motor could short circuit and fail.
In cases where more than one impeller is used, the pump is said to be multistage. Multistage centrifugal pumps may feature multiple impellers located on one shaft, or impellers on separate shafts. The result of connecting impellers in a series is higher pressure; connecting impellers parallel to one another results in increased output. Regardless, the fluid will still garner itsenergy from the electric motor that drives the impellers.
ESP Applications
ESPs are used in many different applications. Single-stage pumps can be used for basic drainage and pumping, as in many industrial applications, and can also handle slurry pumping. Multistage pumps are more often found in water removal applications, and can be used in water and oil wells. Regardless of the application, double checking manufacturing specifications for a given ESP will help ensure its proper use.

ESPs and Oil Wells

Because ESPs can work with a variety of flow rates and depths, they are well-suited to work inside oil wells. When used accurately, an ESP pump can decrease well pressure at the bottom, enabling the withdrawal of a higher amount of oil than otherwise could be extracted under normal pressure conditions. Pump diameter size ranges from 90 millimeters (mm) to 254 mm, and pumps can be one to 8.7 meters long.

ESPs and Dewatering Gas Wells

Some gas reservoirs can produce a high amount of liquid, but because gas can damage ESPs, care must be taken when using an ESP to remove liquid from a gas well. However, ESP systems can be designed that enable the gas to flow freely up the pump’s casing, while the pump efficiently removes fluid. The gas flow depends largely on casing head pressure—there are typically four methods with which ESPs can be used to dewater gas wells, but depending on the exact well situation all ESP set-ups should be sufficiently researched before a method is employed.

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