Shielded Metal Arc Welding SMAW Sometimes called Stick

Shielded Metal Arc Welding (SMAW) Sometimes called "Stick Welding" most popular form of electric arc welding.

Electric arc between flux covered electrode and base metal 2/28/2021

§ relatively inexpensive - $1500 § mobile when used with a generator § used for maintenance, small production welding, heavy pipe welding § heat from arc melts both base metal and electrode 2/28/2021

Arc welding station includes: § 1. arc welding machine (power source) 2. electrode lead and work lead terminals 3. electrode holder 4. ventilation 5. safety equipment 2/28/2021

Electrodes § Electrode: solid metal wire core with a coating material § electrodes are specified by the wire diameter and by the type of flux covering. § common wire dia: § 1/16, 3/32, 1/8, 3/16, 7/32, 1/4, 5/16, 3/8" lengths of 9 to 18" with 14" most common. § usually come in 50 lb packages § electrodes must be kept very dry - some use ovens § used for welding many metals: § 2/28/2021 carbon and low alloy steels most common

Functions served by the electrode other than adding molten metal to the weld area; § 1. shielding gas - prevent air from contacting and oxidizing 2. fluxing agents, impurity scavengers and deoxidizer to clean the weld pool 3. produce (slag) to prevent oxidation - and cool slowly - prevent brittle 2/28/2021 weld

Functions (Cont. ) § 4. establish the polarity and electrical characteristics of the electrode 5. adds alloying ingredients to the weld metal area to change the physical properties. 2/28/2021

Selecting the proper electrode: 2/28/2021

Electrode type normally determined by the welding procedure specification and or code used. § 1. weld groove design 2. tensile strength of the required weld 3. the base metal composition 4. position of the weld joint 5. rate at which you want to deposit the weld metal 2/28/2021

Electrode Selection (Cont. ) § 6. type of arc welding current used 7. penetration required 8. metal thickness 9. experience of the welder 10. specifications for the weld to be made both AC and DC arc welding are done 2/28/2021

American Welding Society (AWS) electrode ID system § 4 or 5 digit numbers 2/28/2021

Letter E = welding electrode used for arc welding 2/28/2021

First two or three digits = tensile strength § 60 = 60, 000 psi § 70 = 70, 000 psi § 100 = 100, 000 psi 2/28/2021

Next digit (second from right) = recommended position § 1 = all positions § 2 = flat or horizontal 2/28/2021

Last two digits together are type of current (AC, DC+, DC -) and electrode covering 2/28/2021

Occasionally additional two digits (letter and number) indicates alloying elements 2/28/2021

Common Electrodes 2/28/2021

6011 § XX 11 l organic covering - paper ect. § unstable arc - bead looks poor § good penetration - good quality § good for out of position welds 2/28/2021

6013 and 7018 § XX 13 l Rutile covering - iron powders § stable arc - bead looks good § less penetration § not good for out of position l l 2/28/2021 deposits lot of metal cools slower

Electricity as it arcs across the gap - temperatures 6500 to 7000 deg F. Welders are AC and DC 2/28/2021

DC welding machines of the following types: § 1. motor driven generator 2. motor driven AC alternator with DC rectifier 3. AC transformer with DC rectifier 2/28/2021

DC electrode negative (DCEN) and electrode positive (DCEP) fundamentals: 2/28/2021

§ DCEN Electrons flow from neg terminal of machine to electrode. Electrons continue to flow across arc into the base metal and to positive terminal of the machine. § electrode (-) polarity § base metal (+) polarity 2/28/2021

2/28/2021

DCEN - direct current electrode negative (DCEN) § also known as “Direct Current Straight Polarity” (DCSP) § electrode melts faster § deposits filler metal at a faster rate § heats base metal more slowly § used for welding thin metals 2/28/2021

DCEP § By reversing the direction of the electron flow or polarity in the arc welding circuit. § This may be done by disconnecting the electrode and work leads and reversing their positions. § Also known as “Direct Current Reverse Polarity” (DCRP). 2/28/2021

Electrons flow from neg pole of the welding machine to the work. Electrons travel across arc to electrode and then return to positive terminal of machine from electrode side of arc. § electrode (+) polarity base metal (-) polarity 2/28/2021

Results in deeper penetration 2/28/2021

The decision to use DCEN or DCEP often depends on such variables as: § 1. depth of penetration 2. rate at which filler metal is deposited 3. position of the joint 4. thickness of the base metal 5. type of base metal § Normally use DC+ 2/28/2021

Alternating Current AC arc welding fundamentals: 2/28/2021

Two basic types of machines: § 1. motor driven alternator 2. transformer type 2/28/2021

Current reverses its direction of flow 120 times per second - (requires 1/60 th of a second to complete a cycle or hertz Hz) called 60 Hz (cycle) current 2/28/2021

Most AC welders have transformers which step down the voltage and increase the current (amperes) for welding purposes. 2/28/2021

Voltage and current are zero 120 times per second. Each time the current crosses the zero point, the welding arc stops. To reestablish the arc, the voltage must increase enough to enable the current to jump the arc gap and maintain the arc. 2/28/2021

It is important that the voltage lead the current as each passes through zero to help make the arc stable. 2/28/2021

Another method to stabilize arc is to increase ionization of the material in the arc. § IONIZATION is the phenomenon in which a particle obtains an electrical charge. These ionized or charged particles in the space between the electrode and the work make it easy for the arc to jump the gap. electrodes intended for AC welding have ionizing agents in the electrode 2/28/2021 covering.

Selection of either AC or DC arc welding machine 2/28/2021

ADV of DC § 1. the ability to choose DCEP or DCEN 2/28/2021

DISADV of DC § 1. the welder is generally more expensive than an AC machine of the same specs § DC arc blow: l 2/28/2021 AC arc is quite stable after starting: DC arc may wonder from the weld line. this wandering is caused by the forces of the magnetic field around the DC electrode called ARC BLOW the magnetic lines of flux ten to travel more easily in metal than air. concentration of the magnetic flux at the ends of the metal forces the arc toward the center of the base metal.

ADV of AC § 1. welds made with AC have moderate penetration 2. large dia electrodes can be used with high AC currents to obtain greater filler metal deposition rates and faster welding speeds 3. AC arc welding machines are generally less expensive 2/28/2021

DISADV of AC § 1. not all SMAW electrodes can be used with AC 2/28/2021

Choice on which to buy is made on basis of § 1. type of welds to be made 2. economics of the welding machine purchase 3. personal preferences 2/28/2021

Can buy combination AC and DC welders - more expensive. 2/28/2021

Starting / Stopping / adjusting the machine § never start or stop the machine under load usually a switch to turn off and on may need to start the engine of an engine driven machine 2/28/2021

SMAW utilizes a constant current welding machine 2/28/2021

On a constant current machine, current (amps) is set on the machine. voltage on the constant current machine is not set. It varies as the welding circuit resistance changes to maintain constant or relatively constant current. 2/28/2021

Amperage (current) controls vary in appearance, location, and operation on various machines - hand cranks tap type control with holes to plug into for course and fine adjustments handwheel for course and fine adjustments 2/28/2021

Striking an arc: 2/28/2021

Electrode must first touch the base metal then be withdrawn to the correct arc distance 2/28/2021

2 methods: § 1. glancing or scratching motion 2. straight down and up motion 2/28/2021

If the arc breaks continually, regardless of how careful the operator may be, it is probably due to too low a current adjustment on the machine. 2/28/2021

If the electrode spatters excessively, and if it becomes overheated while welding, the current setting is too high 2/28/2021

Running a bead: § once the arc is struck and the arc stabilizes, the ARC CRATER will begin to form. 2/28/2021

To run a good bead, the following must be controlled manually by the welder: 2/28/2021

1. arc gap distance - 3/16 to 1/4” § arc length too short, shorting out may occur arc length too long, spattering and metal drops seen on the base metal 2/28/2021

2. speed of forward motion § a. stringer bead - no motion is made except forward b. weaving bead - electrode is moved uniformly back and forth across weld line 2/28/2021

3. electrode angle or position § tipped forward 15 degrees in the direction of travel § it is kept in line with the weld line for a stringer bead § Slag = Drag 2/28/2021

4. bead width § a. stringer bead: 2 to 3 times dia of electrode b. weaving bead: weld bead no wider than six times the electrode diameter 2/28/2021

Weld height is normally about 1/4 of the bead width 2/28/2021

Restarting a weld bead: end of existing bead must be cleaned. Restart the arc about 3/8" ahead of the forward edge of the crater then move back rapidly until the new rater just touches the rear edge of the previous crater 2/28/2021

Finishing a bead without leaving a crater: § 1. Run-off tab: piece of metal tack welded tot the end of the base metal being welded. (also use for starting a weld) 2. reverse electrode motion by moving the electrode to the trailing edge of the crater. 2/28/2021

Cleaning the arc bead: must remove slag prior to restarting or welding over a bead or painting. slag inclusions are pieces of slag trapped or included in the weld: use chipping hammer and a wire brush (shot peening) 2/28/2021

To make a good weld must consider the following variables: § 1. current (amperage) 2. type and size of electrode 3. arc and it's manipulation 4. type of base metal 5. preparation of the base metal 2/28/2021