v As metals are heated they expand and when cooled they contract. During welding, heating and cooling of metals occurs unevenly resulting in high stresses ...
DISTORTION, CAUSES & CONTROL Distortion: Distortion to some degree is present in all forms of welding. In many cases it is so small that it is barely noticeable, but in other cases allowance has to be made before welding commences for the distortion that will subsequently occur. The study of distortion is very complex and the following is a brief outline of the subject. A) The cause of distortion - when under load metals strain or move and change shape.
▲ Under light loading metals remain elastic (they return to their original shape or form after the load has been removed). This is known as the “elastic range”.
▲ Under very high load, metals may be stressed to the point
where they will not return to their original shape or form and this point is known as the “yield point”. (YIELD STRESS)
▲ As metals are heated they expand and when cooled they contract. During welding, heating and cooling of metals occurs unevenly resulting in high stresses and the metal distorts.
If these high stresses pass the elastic range and go over the yield point, some permanent distortion of the metals will occur. A metals yield stress is reduced at high temperatures. *Distortion is the result of uneven expansion and contraction of heated metals.
Distortion Types - the three main types of distortion are:-
(i) The control of distortion before welding can be facilitated by:
224
▲ ▲ ▲ ▲
Tack Welding Jigs, clamps and fixtures Uniform pre-heating Pre-setting
T E C H N I C A L A N D I N F O R M AT I O N
T R A D E
DISTORTION, CAUSES & CONTROL cont. Distortion cont.:
(ii) The Control of distortion during welding can be facilitated by: Backstep welding Intermittent “Chain” welding Intermittent “Staggered” welding Balanced sequence welding A correct welding procedure to reduce the size of the weld beads
DISTORTION, CAUSES & CONTROL cont. Distortion cont.: The correct welding procedure uses a greater number of weld runs positioned to refine the grain size of the weld metal in the previous layer.
A small number of heavy runs will cause more distortion due to the greater heat input, and the contraction stresses set up by the cooling of the larger deposit of weld metal.
226
(iii) The control of distortion after welding can be facilitated by:
▲ ▲ ▲ ▲ ▲ ▲
Slow Cooling Flame straightening (also known as contra-heating) Annealing Stress Relieving Normalising Mechanical straightening
T E C H N I C A L A N D I N F O R M AT I O N
T R A D E
DISTORTION, CAUSES & CONTROL cont. Distortion cont.: Annealing -
is a heat treatment process designed to soften metals for cold working or machining purposes. The job or finished work is normally heated in a furnace so as the metal reaches its critical range (for .025% carbon steel @ 723-820˚C) and then the work is very slowly cooled.
Stress Relieving - is the uniform heating of welded parts to a temperature below the critical range, followed by slow cooling. This process allows the yield point of the metal to be lowered allowing it to stretch or yield, so reducing the residual stresses in the work.
Normalising -
is a process used to refine the grain structure of the metal so it improves its resistance to shock and fatigue. In normalising the welded parts are heated just above the critical point (820˚C for .025% carbon steel) for approximately 1 hour per 25mm thickness and then allowed to cool in still air.
v Always wear protective full covering clothing to shield your body from potential burns eg. - Overalls/flame resistant wool or cotton. - Leather apron and jackets.
hardfacing applications carried out in industry;. 1. Build-up or .... Manual Metal Arc Welding. 2. Flux Cored Arc ... The most common types of manual electrodes are those designated as A4 and A1 types in ..... tractor track grousers, anvils, pneumati
Iridium. Ru. Ruthenium. Ba. Barium. K. Potassium. S. Sulphur. Be. Beryllium. Kr ..... extremely thin oxide films, and vary in colour with temperature. It should be ...
Shielding gas supplies are controlled to very low moisture ... The temperature of the welding wire or base metal at any given time. .... v Chemical Cleaning: ..... Match colour selection in âAluminium Alloy Selection Chartâ. ..... Cast aluminium
v Safety glasses which will help to refract (bend away) the. UV and IR rays away ... base metals and gases (where applicable) involved in the welding arc.
on the weld face or in previously deposited weld metal. Causes: ... weld caused by metal flowing onto the surface ... A lack of bonding between the weld metal.
Weld passes are made in the opposite direction. Sequence to the progress of welding. .... electrode is propelled across the arc in small droplets. v Stringer Bead.
all steel gas metal-arc welding wires to AS/NZS 2717.1 satisfy the hydrogen ...... AS 1450 AS 1548 AS 1594 AS 1595 AS 2074 AS 3678/ AS 3679.1 NZS 3415.
These 310 materials resist oxidation up to 1,200° C ... Autocraft Silicon Bronze gas metal arc welding wire is ... Autocraft Silicon Bronze to complete the joint.
mechanical properties or introducing weld defects. 1) Types of ... heat treatment to increase mechanical properties. Welding or ..... v Sand blasting v Dilute ...
In GMA welding (spray or pulse transfer mode), the main force in the arc is axial to the filler .... The molten weld pool has a lower surface tension than with argon ...
Cobalarc Mang Nickel-O wire which is ... and shape using suitable build-up or build-up and overlay alloys as described above. ... Manual Metal Arc Welding. 2.
TECHNICAL FEATURE. Welding. It's Not Black Magic. BY BUDD DAVISSON. 11 right, everyone out ... sive TIG units which can also do "stick" or arc welding. Most are also plumbed for ..... MIG (Machine Inert Gas). Currently MIG welding is a ...
Read Online la discotheque de reference en cd musique classique 1ere edition french for free at Online Ebook Library. Download Now la discotheque de ...
... gas shield. It offers the advantages of high welding speeds, smaller heat affected zones .... that the arc length varies and this in its turn causes variations in arc voltage. .... gramme the power source instantly when wire size, shield gas, fil
tricity and makes no arc, instead using the heat of ... Welding and cutting with oxygen/acetylene has been ... can't install the oxygen regulator on the acetylene ...
Mar 23, 2018 - Tungsten arc inert gas shielded welding, EN process number 144 abbrevi- ated to TIG, TAGS or GTAW (USA), is an arc welding process that ...
acetylene outfit in anticipation of completing a homebuilt airplane pro- ject he had acquired. He was not so naive as to start on the airframe itself but did burn up ...
When removing or replacing plates bonded by spot welding, drill through the spot ... Use a stainless steel wire brush to burnish the bare surface of the aluminum ...
Year Paper, Bulova Accutron Manual, Business Objects 41 Installation Guide, ... y-roger-miller-10th-edition.pdf, Canadian History For Dummies, Cartier Lalbum, ...
