4/19/2018. The heat generated for welding comes from an arc

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1 Foundations of Agriculture The heat generated for welding comes from an arc Develops when electricity jumps across an air gap between the end of an electrode and the base metal. A. Alternating Current (AC)- An electrical current where the electrode and ground change between positive and negative charges. B. Direct Current (DC)- Electrical current which flows in only one direction C. Polarity- Indicates the directions of the current in the circuit. Straight Polarity- Workpiece is positive and the electrode is negative. Also known as DCEN (Direct Current, Electrode Negative) Reverse Polarity- Electrode is positive and the work piece is negative. Also known as DCEP (Direct Current, Electrode Positive) 1

2 When more heat is needed on the workpiece Used on heavier gauged metal Used when welding a large piece of metal Used to weld thinner metals Directs the heat towards the electrode and off the metal An electric arc not only produces a brilliant light but also gives off invisible ultraviolet and infrared rays Extremely dangerous to the eyes and skin. A. Helmets- protect the face and eyes from the harmful ultraviolent light produced from the welding arc. Welding helmet lens shades: #8- under 75 amps # amps # amps Safety glasses should ALWAYS be worn underneath the welding helmet B. Gloves- should be worn to prevent hands from being burned by hot metal, weld spatter, and arc radiation. BE CAREFUL!! HOT METAL CAN BURN YOU THROUGH WELDING GLOVES. FRESHLY WELDED METAL SHOULD BE ALLOWED TO COOL OR BE HANDLED WITH PLIERS. 2

3 C. Coveralls- needed to prevent infrared and ultraviolent rays from touching the skin. D. Coveralls need to be in good condition (no cuffs, tears, or frays) D. Footwear- Leather work boots with steel or composite safety toes are preferred to prevent sparks and hot weld spatter from burning your feet. Getting a hot spark in your shoe is extremely painful (trust me) A. Electrode Holder (Stinger)- is a handle that holds the electrode during welding B. Workpiece Connection (Ground Clamp)- is attached to the workpiece to complete the electrical circuit C. The wires that connect the electrode holder and the workpiece connection to the welding machine are called LEADS D. Welding Screen- used to protect other people that are working in the area from ultraviolet rays. E. Ventilation is needed to remove smoke from metal arc welding. Be sure the fan is on and that the flex arm is positioned close to the weld 3

4 A. Never look at a welding arc without a welding helmet B. Always wear gloves and coveralls when welding C. Use an electrode holder that is completely insulated D. Weld only in areas where there is adequate ventilation E. Prevent welding cables from coming in contact with hot metal, water, oil, or grease. Avoid dragging the cables over or around sharp corners F. Make sure you have good ground connections G. Do not weld near flammable materials H. Never stand in water or on a wet floor. The minerals in water are electrical conductors and any wet surface will carry current I. Keep cables in orderly manner and do not wrap them around your body J. Always turn off machine when leaving your booth. 1. Mild Steel 2. High Carbon Steel 3. Special Alloy Steel 4. Cast Iron 5. Non-ferrous Metal (Aluminum) B. A SMAW electrode is a coated metal wire having approximately the same composition as the metal to be welded. E

5 E-Electrode E-6013 E The first 2 digits indicate the minimum allowable tensile strength of the deposited weld metal. i.e. A 6013 as a minimum pull strength of 60,000 pounds per square inch. E The third number indicates welding position 1. All Positions 2. Flat or Horizontal only 3. Flat welding only E The fourth number indicates any special characteristics of the electrode such as type of coating, weld quality, and amount of penetration. D. Fast Freeze- Produce a snappy, deep penetrating weld and fast freezing deposits with little slag. Ideal for vertical and overhead welding. i.e and 6011 E. Fill Freeze- Moderate deposits with distinct, even ripples. Considered a general-purpose rod i.e

6 F. Fast Fill- Heavy coated iron powder electrodes with soft arc and fast deposit rate. They have a heavy slag and produce smooth beads and generally used for building-up and area. i.e and 7018 Fast freeze electrode that is used for both AC and DC welding. Works for welding in all positions A general purpose rod that is easy to maintain. Considered a fill freeze electrode Good rod to use for beginning welders Iron powder coated rod Classified as a fast fill rod. Low hydrogen rod Developed to prevent hydrogen from entering the weld and causing cracks. Used for structural welding Store electrodes in a dry place where the coating cannot be damaged For some critical welds, rods must be dried and pre-heated in an electrode oven 6

7 A. Correct Electrode 1. Position of weld 2. Type of metal 3. Diameter of electrode B. Correct Arc Length 1. Arc too long- the metal melts off in large globules which produces a wide spattered, irregular bead 2. Arc too short- fails to generate enough heat to melt the base metal properly which produce high, uneven beads. B. Correct Arc Length 3. Length of the arc depends on the size of the electrode used and the kind of welding being done. As a rule, the length of arc should be approximately equal to the diameter of the electrode 4. Proper length is important to prevent impurities from entering the weld. Long arcs allow the atmosphere to flow into the arc stream. C. Correct Amperage Setting 1. Rule of thumb in the lab- 110 amps 2. Amps too high- electrode melts too fast and molten puddle is large and irregular 3. Amps too low- not enough heat to melt the base metal and molten puddle will be too small D. Correct Travel Speed 1. As a rule, the bead needs to be as wide as 2 electrodes that you are using 2. Travel too fast- molten puddle does not last long enough and impurities are locked in the weld 3. Travel too slow- metal piles up excessively and the bead is high and wide with straight ripples 7

8 E. Correct Electrode/Travel Angle 1. The angle in the line of welding and may vary from 5-30 Crater- as an arc comes in contact with the base metal, a pool or pocket is formed. This pool is known as the crater The size and depth of a crater indicate weld penetration. In general, the depth of penetration would be from 1/3 to ½ the thickness of the bead. A technique used to increase the width and volume of the bead. Crescent (most common) Figure 8 Rotary Motion No Motion 8

9 Tack welds are short sections of bead placed to ensure the metal will mot move due to the heat of the weld. Butt Joint- Two pieces of metal are placed side-by-side with an opening 1/8 to 3/16. A common method to use is to separate the distance equal to the bare end of the electrode that you are using. Closed Butt Joint- The edges of the two plates are in direct contact with each other. This type of joint is for metal under 3/16 V Butt Weld- When the metal is thicker, the two edges are beveled with a grinder to achieve greater strength. T-Weld- This weld is used frequently in the fabrication of steel structures. One of the most common weld joints Lap Joint- The joint consists of lapping one edge over another and joining. Used widely as it greatly enhances the strength of the structure being built. 9

10 Corner Weld- often used in constructing rectangular shaped objects such as tanks and other machine sections where the outside corner must have a smooth surface. 10