Stick (smaw)Electrode Welding



Дата26.04.2016
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Stick (SMAW)Electrode Welding
Stick, the most basic of welding processes, offers the easiest option for joining steel and other metals. Stick welding power sources deliver inexpensive options for welding versatility, portability and reliability. Stick joins metals when an arc is struck between the electrode and the work piece, creating a weld pool and depositing a consumable metal electrode into the joint. The electrode's protective coating also acts as a shielding gas, protecting the weld and ensuring its purity and strength. Best for windy conditions and adverse environments.
What are AC and DC?

"DC" stands for direct current in which the current flows in the one direction constantly throughout the circuit. One side of the power source is nominated as the positive (+) pole and the other as the negative ( ) pole. An automotive battery or dry cell gives DC.

In "AC" or alternating current the current periodically reverses its direction along the conductor, i.e. one fraction of a second the right hand terminal is "negative", the next fraction of a second it is "positive". In 60 Hertz AC current, such as is commonly used in Australia, this change from + to   to + occurs as a cyclic variation 50 times a second, the current thus changing direction of flow 120 times a second. See Fig. 5.




Arc Welding Electrodes

The electrode is a current carrying conductor which progressively melts away due to the heat of an electric arc held between it and the work, the molten metal solidifying to form part of the weld with the base metal. The original electrodes were bare wire and the resultant weld metal was of poor quality with the arc difficult to maintain even on DC.





The modern welding electrode combines a central current carrying "core wire", which acts also as the filler rod, and a flux covering which carries out a number of important functions:

1.   It provides a gaseous shield usually of hydrogen and/or carbon dioxide to exclude the air from the arc areas and so reduce the tendency to oxidation etc., of the molten metal.

2.   It produces a slag, which assists in the protection of the molten metal and the dual function of scavenging the metal of unwanted impurities and mechanically moulding it to a suitable contour in the positions and applications for which the electrode was designed.

3.   It provides a vehicle for adding alloying elements into the weld metal, over and above those elements normally available within the core wire. Thus, quite complicated alloy weld metals can be reproduced from a simple mild steel core wire. It also adds deoxidants to the molten pool.

4.   It can include arc stabilizing elements which permit smooth stable arcing characteristics, even on low voltage AC welding power, or other ingredients to increase arc penetration characteristics etc.

Modern electrodes can be classified into distinct groups based on the major constituents of the flux coating

The first two digits after the E (for electrode) are figures indicating the minimum nominal tensile strength. The last two digits are also meaningful as a "group" and indicate the flux coating and other usability characteristics.

PRACTICE SAFE WORKING HABITS

The best methods are invariably the safest and in the long run the cheapest and easiest. Safety is usually a matter of applied common sense. Apply it. Arc welding uses electricity, produces molten metal, flying sparks and injurious rays and can, if not handled properly, give rise to electric shock, hot metal burns, ray burns, nausea and fire. Intelligently used, it is one of the safest of mechanical/electrical devices and certainly one of the most useful and widely used tools of trade.



Electric Shock

High voltage electricity is a dangerous killer and yet for most of us we have it at our finger tips many times a day in the switches at home and at work. It is safe because it is insulated by the switch, cable or the equipment.

The human body is a poor conductor and therefore will not readily pass current unless the voltage is high. From this point of view, 240 volts and over must be considered as highly dangerous, and all such equipment (power tools, welders, etc.) should be properly earthed. Long primary cables (from switch to machine) are undesirable where they can be cut or burnt, exposing high voltage wiring.

The arc welder is restricted in Australia to a maximum of 80 volts (open circuit) on the welding power side and at this voltage it may generally be considered as "safe". Dry gloves, dry Buckboards or heavy leather boots (not hobnailed) or preferably rubber shoes are effective additional barriers. Moist hands, wet floors and moist clothing all assist in breaking down body contact resistance and increasing the chance of shock. Remember, even a mild shock may cause a "start" which could precipitate an accident like falling twenty feet from a hay shed!

The voltages employed for arc welding currents are not dangerous under normal circumstances, but should be treated with care.

Heat

The arc is a source of intense heat, producing molten metal in the fraction of a second. It is therefore a likely source of burns to hands, legs, etc., both by contact with the parts being welded or by molten spatter, slag, etc., lodging on the skin. It can also cause damage by lodging in folds of clothing, the hair, cuffs, etc. From this point of view, the user is advised to wear solid leather gloves, boots (rubber boots are ideal) which come up under the pants, long cuffless pants, clothing of slow burning material (long sleeves) and a cap.



Fire

The same problem of flying sparks and hot metal makes it mandatory to clear the area of sawdust, wood shavings, straw, lacquer thinners, petrol, paints, etc., and choose a sealed concrete floor rather than a gapped wooden floor as the regular welding bay.



Rays

The arc gives off both ultra violet and infra red rays. The former can be particularly injurious, giving rise to an effect similar to severe sunburn. Never work in shorts or bare to the waist   ordinary clothing is adequate protection. Gloves protect the hands. Do not watch the arc with the naked eye. As far as the face and eyes are concerned, a proper hand screen or helmet with protective filter is essential. Use the correct shade filter lens for the current you are using (No. 10 or 11 is a good average). Keep these aspects in mind, particularly with regard to the interested bystander or children, dogs etc.



Fumes

Most electrodes give rise to a degree of fume and smoke, which in general reaches a point of annoyance or murkiness in confined spaces before it becomes a health hazard. Welding, however, should always be conducted in well ventilated conditions. Welding on galvanized iron can give rise to copious fumes, which cause temporary nausea if ventilation is inadequate and similar precautions should be taken with painted and other coated surfaces.

Finally, remember the people around and give warning (“eyes”) before striking the arc, chipping slag, etc. The welder is recommended to always use safety glasses when chipping, grinding or in other ways preparing or finishing a welded joint. Your eyesight is precious, and hot flying slag or a spark stream from a grinding wheel can be dangerous

LET'S START WELDING

While the preceding information is important to your intelligent progress in welding   we suggest you re read at the start of each practice session in the early stages   the actual skills of laying down a weld can only be achieved by practical application. "Practice makes perfect" must also be interpreted as "Practice makes imperfect" if you are not using the correct techniques. In manual welding a number of actions must take place simultaneously, such as maintaining a correct electrode feed in, correct arc length, correct placement of metal, etc.   certainly too many for continuous conscious effort by the welder over a long period. Many of these aspects will soon become a natural reflex action or habit with practice. So learn good habits, not bad habits.



Striking the Arc

(Are you wearing suitable clothing, gloves, etc., and have you checked the area for fire hazards?)

Select a piece of clean steel (say 250 x 75 x 6mm)   heavy rust is a poor conductor and makes bad electrical contact   and attach your work clamp to it or seat it in good contact on your welding bench. Set your machine at 120 amps and place the bared end of a 3.2mm o electrode (Austarc 12P is fine) in the holder. Turn on the welder.

If you lightly touched the end of the electrode on to work, you would complete the circuit and current would flow, the electrode end rapidly getting hot and possibly melting sufficient to momentarily weld the electrode on to the work. (No doubt you'll see what we mean before this session is finished!) On the other hand, the low voltage current we are using won't jump an air amp (as in a spark plug). We must therefore establish an arc by first touching the electrode to the work and then immediately lengthening the distance between electrode and work until the droplets of metal and slag melting from the end of the electrode can cross to the molten pool below without bridging the gap and causing a short circuit with the electrode freezing onto the work.

A simple action of striking an arc (Fig. 7) in much of the same manner as striking a match achieves this effect.




The electrode tip moves down and across, touches (a flash) and up, the arc still going until it becomes too long and extinguishes. Now, restrict your raising of the electrode tip to a maximum of 6 mm after striking the arc and endeavor to hold it steady at that point for about 10 seconds. This will necessitate feeding the electrode into the arc as the end burns off. Practice striking and holding an arc until it becomes child's play. This arc length is, of course, too long for useful welding, but will give you the feel of maintaining a length without fear of shorting. Any longer becomes unmanageable or may extinguish it, the resistance to current flow across the arc becoming too great.

If for one reason or another your action is incorrect and the electrode freezes on to the work, i.e. becomes welded to it, a sharp backward angling of the electrode should break the weld. Maintain your shield over the face until freed as it releases from the plate or the electrode, will be accompanied by an arc flash.



Laying Down a Weld Bead

Once the arc has been established, reduce the arc length to about 3 mm and note that metal is beginning to mount up under the tip. Start moving the tip of the rod slowly away to the right (to the left if you are left handed) attempting to maintain a pool behind the arc approximately 6 8mm wide. You will have to feed in the electrode at a steady rate, progress at a steady rate across the plate, maintain a steady arc length etc. Don't lose heart   a little more practice and some of these actions will begin to happen automatically!



If you’re not familiar with Stick (SMAW) welding basics, the following information can make choosing an electrode easier.



AWS Class

Position

Polarity

Usage

E6010

All

DCEP

A great choice for welding on dirty, rusty, greasy or painted steel - especially in vertical or overhead applications.

E6011

All

AC,DCEP

All-purpose stick electrode; used for carbon and galvanized steel; 60,000 PSI tensile strength; deep penetration and ideal for welding light to medium amounts of dirty, rusty or painted materials.

E6013

All

AC,DCEN,DCEP

Light to medium penetrating all-purpose stick electrode; for use on carbon steel; 60,000 PSI tensile strength; good for general all-purpose applications and joints with poor fit-up.

E7014

All

AC,DCEN,DCEP

For higher-deposition requirements; 70,000 PSI tensile strength; ideal for applications requiring light penetration and faster travel speeds.

E7018

All

DCEP

Low-hydrogen electrode; for low, medium and high-carbon steels; 70,000 PSI tensile strength; ideal for out-of-position welding and tacking; not recommended for low-voltage AC Welders.

E
7018AC

All

AC,DCEP

Low-hydrogen electrode; for low, medium and high-carbon steels; 70,000 PSI tensile strength; ideal for out-of-position welding and tacking.






Helpful Hints
Use a drag technique for most applications.
Take precautions with flying materials when chipping slag.
Keep electrodes clean and dry - follow manufacturers instructions.
Common steel electrodes (refer to chart above).
Penetration: DCEN- Less penetration; AC - Medium (can be more spatter also); DCEP - Most penetration







Equipment Basics

Stick Versus Wire-Feed Welders: For home-shop purposes, stick and wire-feed welders perform essentially the same functions. Wire-feed welders are four to five times more expensive than stick welders. However, wire-feed welders are easier to learn to weld with, and they can handle thin-gauge sheetmetal more easily than stick welders. Also, wire-feed welders can be converted (or may come from the factory already equipped) to operate with inert, noncombustible gas (known as shielding gas). This allows you to leave nice, clean welds on thin sheetmetal that are almost paint-ready as soon as the weld is cool.

On the other hand, stick welders (also called rod welders) are mechanically simpler. They don't have drivewheels, gun liners, guns and gun tips that may need repair or replacement. Also, a wide variety of electrodes are available for stick welders, and this can be a great help when you're making welds under less than ideal conditions. These include working with rusty, dirty or even painted metal, welding vertically or welding overhead.





CHIPPING HAMMER/WIRE BRUSH

Hand Tools: Welding requires few unique hand tools. About the only one is a chipping hammer/wire brush (Photo 3). This tool is used for removing slag and scrubbing off smoke dust. Most of the other hand tools necessary for welding are those that you probably own for other metalworking operations: ball-peen hammer, tap-and-die set, drills bits for metal, punches and cold chisels, hacksaw frame and a variety of blades, and metal-scribing and marking tools. Other hand tools and accessories to consider are C-clamps, specialized welding clamps and locking pliers.

Power Tools: You can get by with just a small right-angle grinder and a 3/8-in. drill for bolted assemblies. Icing-on-the-cake-tools might include a large disc sander and a metal cutoff saw, though they're not necessary.



AUTO-DARKENING WELDING HELMET

Safety Equipment: The most important piece of equipment is a welding mask to protect your eyes and face. The intense light given off from the welding arc can damage your vision, so it's particularly important to cover your eyes. Welding masks come in a variety of styles and prices ranging from $25 to about $250. We show an auto-darkening model (Photo 4). It uses a lens that switches from clear to shaded in milliseconds - as soon as it detects the flash from the welding arc. Called auto-darkening helmets, these typically cost $150 to $250. Helmets in which the lens is always dark cost about $25. You'll also need safety glasses for drilling, grinding, cutting and sanding metal.





HEAVY-DUTY WELDER’S GLOVES

For protection against the fumes and particles released when welding, you should also buy a welder's respirator. These are sold through industrial-supply catalogs and at welding supply houses. These respirators look like the masks that people wear when sanding wood but are specially designed to protect against welding smoke.



Although welding is reasonably quiet, many of the tools used to work metal are not. If you plan on using an air compressor to power air tools, or you're running your welder off a generator, first buy some earplugs or earmuff-style hearing protectors.

Hand protection is a must. You'll need a good pair of heavy-duty leather gloves (Photo 5). These protect your hands from flying sparks, molten slag, sharp burrs left along cut edges, and hot metal. Finally, have a fire extinguisher handy, whether you're welding indoors or out
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