Posted tagged ‘key concepts’

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

September 8, 2011


 

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.