Shielded Metal Arc Welding Plate
INTRODUCTION
Shielded metal arc welding (SMAW) or stick welding is the most commonly used welding process. Stick welding is popular for a number of reasons. It can be used to make strong durable welds in a wide range of metal thicknesses and types. Transformer-type welders can sit for years without being used and still work when needed, and the welding rods have an almost unlimited storage life, as long as they are kept dry. These factors mean that the equipment is there when you need it to make a repair or build a project.
In addition to the standard rods that can be used to make welds in steel 1/8 in. (3 mm) and thicker, there are a wide variety of specialty electrodes. These specialty rods allow you to use the same welding machine to weld on cast iron, stainless steel, and aluminum. There are rods for cutting that will cut cast iron and stainless steel; these are metals that cannot be cut with oxygen and acetylene. Wear-resistant and buildup rods can be used to repair scraper and front-end loader blades and buckets. The basic stick-welding skills you will learn in this chapter are used for almost every welding fabrication project. Welding is a skill that takes practice to perfect. The repetition in the chapter practices and projects is designed to give you the opportunity to develop your skills. The more time you spend welding, the better your welding skills will become.
ELECTRODES
Arc welding electrodes used for practice welds are grouped into three filler metal classes (F number) according to their major welding characteristics. The groups are E6010 and E6011, E6012 and E6013, and E7016 and E7018.
F3 E6010 and E6011 Electrodes
Both of these electrodes have cellulose-based fluxes. As a result, these electrodes have a forceful arc with little slag left on the weld bead. E6010 and E6011 are the most utilitarian welding electrodes for welding fabrication. They can be used on metal that has a little rust, oil, or dirt without seriously affecting the weld’s strength. The E6010 electrodes can weld only with direct current (DC) welding machines. Because E6011 electrodes can be used with alternating current (AC), smaller transformer-type welders that put out only AC welding current can be used.
F2 E6012 and E6013 Electrodes
These electrodes have rutile-based fluxes, giving a smooth, easy arc with a thick slag left on the weld bead. Both E6012 and E6013 are easy electrodes to use. They do not have forceful arcs, so they can be used on thinner metals such as some thicker sheet metal gauges that are used as guards on equipment.
F4 E7016 and E7018 Electrodes
Both of these electrodes have a mineral-based flux. The resulting arc is smooth and easy, with a very heavy slag left on the weld bead. Of these two electrodes, E7018 is the one used most often to make high-strength welds on equipment. Store these electrodes in a dry place. If they get wet, they will still weld, but the welds will not be as strong. The cellulose- and rutile-based groups F3 and F2 of electrodes have characteristics that make them the best electrodes for starting specific welds. The electrodes with the cellulose-based fluxes do not have heavy slags that may interfere with the welder’s view of the weld. This feature is an advantage for flat tee and lap joints. Electrodes with the rutile-based fluxes (giving an easy arc with low spatter) are easier to control and are used for fillet, stringer beads, and butt joints. Unless a specific electrode is required for a job, welders can select what they consider to be the best electrode for a specific weld. Welders often have favorite electrodes to use on specific jobs. Electrodes with mineral-based fluxes, group F4, should be the last choice. Welds with a good appearance are more easily made with these electrodes, but strong welds are hard to obtain. Without special care being taken during the start of the weld, porosity will be formed in the weld.
Effect of Too High or Too Low Current Settings
Each welding electrode must be operated in a particular current (amperage) range. Welding with the current set too low results in poor fusion and poor arc stability. The weld may have slag or gas inclusions because the molten weld pool was not fluid long enough for the flux to react. Little or no penetration of the weld into the baseplate may also be evident. With the current set too low, the arc length is very short. A very short arc length results in frequent shortening and sticking of the electrode. The core wire of the welding electrode is limited in the amount of current it can carry. As the current is increased, the wire heats up because of electrical resistance. This preheating of the wire causes some of the chemicals in the covering to be burned out too early. The loss of the proper balance of elements causes poor arc stability. This condition leads to spatter, porosity, and slag inclusions. An increase in the amount of spatter is also caused by a longer arc. The weld bead made at a high amperage setting is wide and flat with deep penetration. The spatter is excessive and is mostly hard. The spatter is called hard because it fuses to the baseplate and is difficult to remove. The electrode covering is discolored more than 1/8 in. (3 mm) to 1/4 in. (6 mm) from the end of the electrode. Extremely high settings may also cause the electrode to discolor, crack, glow red, or burn.
Electrode Size and Heat
The selection of the correct size of welding electrode for a weld is determined by the skill of the welder, the thickness of the metal to be welded, and the size of the metal. The 1/8-in. (3-mm) electrode is the most commonly used size for metal fabrication. It can be used to make welds on thin metal up to thick plates. Using small diameter electrodes requires less skill than using large diameter electrodes. The deposition rate, or the rate that weld metal is added to the weld, is slower when small diameter electrodes are used. Small diameter electrodes will make acceptable welds on a thick plate, but more time is required to make the weld. Large diameter electrodes may overheat the metal if they are used with thin or small pieces of metal. To determine if a weld is too hot, watch the shape of the trailing edge of the molten weld pool. Rounded ripples indicate that the weld is cooling uniformly and that the heat is not excessive. If the ripples are pointed, the weld is cooling too slowly because of excessive heat. Extreme overheating can cause a burn-through, which is hard to repair. To correct an overheating problem, a welder can turn down the amperage, use a shorter arc, travel at a faster rate, use a chill plate (a large piece of metal used to absorb excessive heat), or use a smaller electrode at a lower current setting.
Arc Length
The arc length is the distance that the arc must jump from the end of the electrode to the plate or weld pool surface. As the weld progresses, the electrode becomes shorter as it is consumed. To maintain a constant arc length, the electrode must be lowered continuously. Maintaining a constant arc length is important, as too great a change in the arc length will adversely affect the weld. As the arc length is shortened, metal transferring across the gap may short out the electrode, causing it to stick to the plate. The weld that results is narrow and has a high buildup. Long arc lengths produce more spatter because the metal being transferred may drop outside of the molten weld pool. The weld is wider and has little buildup. There is a narrow range for the arc length in which it is stable, metal transfer is smooth, and the bead shape is controlled. Factors affecting the length are the class of electrode, joint design, metal thickness, and current setting. Some welding electrodes, such as E7024, have a thick flux covering. The rate at which the covering melts is slow enough to permit the electrode coating to be rested against the plate. The arc burns back inside the covering as the electrode is dragged along, touching the joint. For this class of welding electrode, the arc length is maintained by the electrode covering. E7024 electrodes require very little welding skill to use. Because of the size of the molten weld pool, they are usually used only in the flat position on thick metal. An arc will jump to the closest metal conductor. On joints that are deep or narrow, the arc is pulled to one side and not to the root. As a result, the root fusion is reduced or maybe nonexistent, thin-to-thick metal joints. Using this technique, metal as thin as 16 gauge can be arc welded easily. Higher amperage settings are required to maintain a short arc that gives good fusion with a minimum of slag inclusions. The higher settings, however, must be within the amperage range for the specific electrode. Finding the correct arc length often requires some trial and adjustment. Most welding jobs require an arc length of 1/8 in. (3 mm) to 3/8 in. (10 mm), but this distance varies. It may be necessary to change the arc length when welding to adjust for varying welding conditions.
Electrode Angle
The electrode angle is measured from the electrode to the surface of the metal. The term used to identify the electrode angle is affected by the direction of travel, generally leading or trailing. The relative angle is important because there is a jetting force blowing the metal and flux from the end of the electrode to the plate.
Electrode Manipulation
The movement or weaving of the welding electrode, called electrode manipulation, can control the following characteristics of the weld bead: penetration, buildup, width, porosity, undercut, overlap, and slag inclusions. The exact weave pattern for each weld is often the personal choice of the welder. However, some patterns are especially helpful for specific welding situations. The pattern selected for a flat (1G) butt joint is not as critical as is the pattern selection for other joints and other positions. Many weave patterns are available for the welder to use. The circular pattern is often used for flat position welds on butt, tee, and outside corner joints, and for buildup or surfacing applications. The circle can be made wider or longer to change the bead width or penetration. The “C” and square patterns are both good for most 1G (flat) welds but can also be used for vertical (3G) positions. These patterns can also be used if there is a large gap to be filled when both pieces of metal are nearly the same size and thickness. The “J” pattern works well on flat (1F) lap joints, all vertical (3G) joints, and horizontal (2G) butt and lap (2F) welds. This pattern allows the heat to be concentrated on the thicker plate. It also allows the reinforcement to be built up on the metal deposited during the first part of the pattern. As a result, a uniform bead contour is maintained during out-of-position welds. The “T” pattern works well with fillet welds in the vertical (3F) and overhead (4F) positions. It can also be used for deep groove welds for the hot pass. The top of the “T” can be used to fill in the toe of the weld to prevent undercutting. The straight step pattern can be used for stringer beads, root pass welds, and multiple pass welds in all positions. For this pattern, the smallest quantity of metal is molten at one time as compared to other patterns. Therefore, the weld is more easily controlled. At the same time that the electrode is stepped forward, the arc length is increased so that no metal is deposited ahead of the molten weld pool. This action allows the molten weld pool to cool to a controllable size. In addition, the arc burns off any paint, oil, or dirt from the metal before it can contaminate the weld. Do not weave more than two-and-a-half times the width of the electrode. These patterns deposit a large quantity of metal at one time. A shelf can be used to support the molten weld pool when making vertical welds using either of these patterns,
Practice Welds
Practice welds are grouped according to the type of joint and the class of welding electrode. The welder or instructor should select the order in which the welds are made. The stringer beads should be practiced first in each position before the welder tries the different joints in each position. Some time can be saved by starting with the stringer beads. If this is done, it is not necessary to cut or tack the plate together, and a number of beads can be made on the same plate. Students will find it easier to start with butt joints. The lap, tee, and outside corner joints are all about the same level of difficulty. Starting with the flat position allows the welder to build skills slowly so that out-of-position welds become easier to do. The horizontal tee and lap welds are almost as easy to make as the fillet welds. Overhead welds are as simple to make as vertical welds, but they are harder to position. Horizontal butt welds are more difficult to perform than most other welds.
Positioning of the Welder and the Weld Plate
The welder should be in a relaxed, comfortable position before starting to weld. A good position is important for both the comfort of the welder and the quality of the welds. Welding in an awkward position can cause welder fatigue, which leads to poor welder coordination and poor-quality welds. Welders must have enough freedom of movement so that they do not need to change position during a weld. Body position changes should be made only during electrode changes. When the welding helmet is down, the welder is blind to the surroundings. Due to the arc, the field of vision of the welder is also very limited. These factors often cause the welder to sway. To stop this swaying, the welder should lean against or hold onto a stable object. When welding, even if a welder is seated, touching a stable object will make the welder more stable and will make welding more relaxing. Welding is easier if the welder can find the most comfortable angle. The welder should be in either a seated or a standing position in front of the welding table. The welding machine should be turned off. With an electrode in place in the electrode holder, the welder can draw a straight line along the plate to be welded. By turning the plate to several different angles, the welder should be able to determine which angle is most comfortable for welding.
STRIKING AN ARC
All welds start with an arc strike. It is the process of establishing a stable arc between the end of the electrode and the work. At first, striking an arc can be difficult because it may seem that the end of the electrode wants to stick to the plate. With practice, you will be able to strike an arc and establish a weld bead without much thought. One important thing to remember is that on most code welding jobs, an arc strike outside of the weld zone may be considered a defect. Start now building a habit of always striking the arc in the weld joint just ahead of where you are going to be welding. That way the arc strike will become part of the finished weld.
TACK WELDS
Tack welds are a temporary method of holding parts in place until they can be completely welded. Usually, all of the parts of a weldment should be assembled before any finishing welding is started. This will help reduce distortion. Tack welds must be strong enough to withstand any forces applied during assembly and any force caused by weld distortion during final welding. They must also be small enough to be incorporated into the final weld without causing a discontinuity in its size or shape.
STRINGER BEADS
A straight weld bead on the surface of a plate with little or no side-to-side electrode movement is known as a stringer bead. Stringer beads are used by students to practice maintaining arc length, weave patterns, and electrode angle so that their welds will be straight, uniform, and free from defects. They are also used by experienced welders to set the welding machine amperage. An example of an application for stringer beads is using them to build up a worn surface or apply a chemical- or mechanical-resistant weld metal to the surface. They may also be used to add an effect to the surface of a piece of art. The stringer bead should be straight. A beginning welder needs time to develop the skill of viewing the entire welding area. At first, the welder sees only the arc. With practice, the welder begins to see parts of the molten weld pool. After much practice, the welder will see the molten weld pool (front, back, and both sides), slag, buildup, and the surrounding plate. Often at this skill level, the welder may not even notice the arc. A straight weld is easily made once the welder develops the ability to view the entire welding zone. The welder will occasionally glance around to ensure that the weld is straight. In addition, it can be noted if the weld is uniform and free from defects. The ability of the welder to view the entire weld area is demonstrated by making consistently straight and uniform stringer beads.