Metal Terms and Properties AG MECH II COMP 10, 11, and 12

Metal Terms Alloy - metallic substance made up of two or more elements. One is a metal. Critical Point - temperature at which the properties of a metal begin to change ( °F)

Metal Terms Melting Point - temperature at which a metal changes from a solid to a liquid. (2700° F) Hardening - heating the metal to the critical point and then cooling it fast, which makes the metal hard.

Metal Terms Anneal - heating the metal to the critical point and then cooling slowly. This makes the metal soft. Normalizing - Heating the metal to the critical point and then cooling it freely in the air.

Metal Terms Tensile strength - the resistance of a metal to a force trying to pull it apart.

Types of Metals Ferrous - Contains “iron” and other elements also. Nonferrous - contains “no iron.” –Examples: Tin, Brass, Bronze Cast Iron - Iron remelted and poured into a special casting. It is heavy, strong, and cheap.

Types of Metals Steel - Alloy containing carbon and iron and small amounts of other elements

Carbon Properties Carbon is the property that makes steel hard. As the carbon content increases the strength of the metal increases. The more carbon you have in metal the harder it is to weld, bend, and machine.

Carbon Levels Low Carbon % carbon –Examples: Nails, Bolts, Chains, Screws Medium Carbon % carbon –Examples: Axles, crankshafts High Carbon % carbon –Examples: Tool steel, files, chisels, saws

Types of Welders Direct Current (DC) – current flows in one direction Alternating Current welder (AC) – current flows back and forth at 60 cycles per second. ~$350

Types of Welders Alternating and Direct Current welder (AC/DC) – produces AC or DC current. ~$380 Polarity – the direction in which the current flows.

Straight Polarity or DCEN Straight Polarity – the current flows in one direction, or electrode (-) to base (+). The heat builds up in the direction it flows. Therefore, Straight Polarity Melts more of the base metal 70% electricity to base, 30% to electrode

Reverse Polarity or DCEP Reverse Polarity – current flows from base to electrode, or (- to +).Electrode is positive. Melts more of the electrode 30% electricity to base, 70% to electrode Overhead welding uses reverse polarity Why? –Less heat is generated at the base metal allowing the filler metal to freeze quicker.

TIG Welder TIG – Tungsten inert gas uses either helium or argon gas. Also referred to as gas tungsten arc welding. (GTAW) Used mainly to weld aluminum and stainless steel TIG has no slag

MIG Welder MIG – Metallic Inert Gas Similar to TIG except for a consumable electrode is used. Also referred to as Gas Metal Arc Welding (GMAW) Arc welders are rated according to their output current: 180, 225, 600 amps

Electrode Classification Example: E7014 E – identifies the electrode for arc welding First two digits, 70; represent the thousands of pounds of tensile strength per square inch

Electrode Digits Third digit indicates the possible welding positions –1 = any position –2 = flat and horizontal position only –4 = vertical down only Fourth Digit – special characteristics of the electrode

Types of Electrodes 1.Coated electrode – has a flux covering 2.Bare electrode – requires excessive amount of heat (10,000 degrees F) 3.Carbon Electrode – melts slowly while supplying a stable arc. For special purposes.

Guidelines for Selecting Electrodes 1.Match rods to base metal composition 2.Position – flat, overhead, horizontal vertical 3.Select the largest electrode possible – allows high current which penetrates deeper 4.Penetration 5.Spatter 6.Strength 7.Appearance

Types of Electrodes E6011 – Deep penetrating all purpose rod. –Works well on rusty metal.Hard to weld with E6013 – used for welding thinner metal. – Shallow penetration and minimum spatter E7014 – low penetration, high speed rod. –Works well in vertical welding. Easy to use E7018 – Used for welding high sulfur and high carbon steels Nickel rod –melts with less heat, used on cast iron

INFO Storage – always keep electrodes in a clean dry place. –If flux gets wet it is difficult to strike arc Slag – impurities in the metal that float to the top of the welding bead. Flux – the outside coating on the electrode

Purpose of the Flux 1.Makes it easier to strike arc 2.Increases penetration 3.Creates gaseous shield (shields out nitrogen and oxygen) 4.Reduces Spatter 5.Stablizes the arc

Metal Steel is bought by the pound. Sold in 20 ft. lengths –Keystock – measure the sides –Round Stock – measure the diameter Cold rolled – more exact in diameter –Formed when the metal was cold –More expensive

Metal Hot rolled – formed when the metal was hot Pipe – know inside diameter and wall thickness –Pipe comes in 21 ft lengths Sheet metal – bought by gauges. –Higher the gauge the thinner the metal –Ex: 16 gauge is thinner than 12 gauge.

Bead - deposit left after a weld Crater- depression left at the end of a weld where the rod contact ends. Weaving - movement of the welding rod. –Use zig-zag or circular motions

Puddle - pool of hot liquid metal at the point of contact between the base metal and the electrode. Flux - chemical compound on a welding electrode that cleans the metal and forms a gas cloud over the weld

Tack Weld - small weld designed to hold the metal in place until a stronger weld can be made. REDUCES warping. Arc - Light formed as the electricity jumps across the gap between the electrode and the base metal.

An Arc produces two things Extreme heat up to 9000 degrees Ultra-violet light which can burn the skin and eyes.

SAFETY INFO Lens should be #12 or #14 rather than #10 for TIG and MIG because the light is brighter than arc welding. A MIG welder concentrates the heat in a small area. If a person changes from welding aluminum to welding mild steel, the wire and the gas should be changed.

TIPS To determine MIG wire feed in inches per minute, the trigger should be squeezed for 15 seconds, the wire measured, and multiply the measurement by 4. To improve welding skills, remember to watch the molten puddle when welding.

TIPS To make a uniform weld on a tee joint, most of the heat should be directed toward the base plate. Welding pipe is difficult because the welding position keeps changing.

TIPS Welding too slowly will make a bead wider, and welding too fast will make it too narrow. Carbon Dioxide used in GMAW often causes excessive spattering.

TIG INFO The way to increase or decrease the size of the gas shield and the rate of gas flow for a TIG welder is to change the ceramic cup.