FOR WELDING ALL TYPES OF CAST IRON
What Are Cast Irons?
Generally speaking, cast iron is a brittle, porous, iron/carbon alloy containing from 2.5% to 4.5% carbon, 0.5% to 3.0% silicon and lesser amounts of manganese, phosphorous and sulphur with sulphur being an especially undesirable impurity. However it is the unusual amount or carbon in cast iron that gives it its chief characteristics and can make it so difficult to weld.
These may be conveniently divided into the following groups:
|PRODUCT NAME & SUGGESTED APPLICATIONS
|STRATA 845 - Furnace Grates, Dirty Casings etc....
|STRATA 880 - Ductile Irons, Malleable and Gray Irons
|STRATA 885 - Ductile Irons, Malleable and Gray Irons etc.....
|STRATA 899 - Arc Welding of Engine Blocks, Castings, Pump Housings, Gray Irons etc....
|STRATA 82F - Gas/Tig welding of broken parts, gear teeth, bearing seats, shafts and overlays. A tough and wear resistant alloy perfect for frictional wear applications..
|STRATA 89 - Gas Welding of Manifolds, Motor Blocks, Pump Housings etc...
- Grey iron which contains between 2.5% and 4.5% carbon mainly in the form of flake graphite and high silicon. This iron is relatively soft, made by the slow cooling of the casting.
- White iron is of similar composition to grey iron but having most of the carbon present in the form of intensely hard and brittle cementite or iron carbide. The silicon content is made lower by rapidly cooling the casting with 'chills'.
- Malleable irons-white heart and black heart. These are white cast irons which have been heat treated to render them more ductile than normal cast iron.
- Alloy cast irons. These are made for wear, corrosion and heat resistance and for extra strength. Examples are: 'Ni-resist' (corrosion resistance). 'Nicrosilal' (heat resistance) and 'Meehanite' (high tensile). Some of these cast irons contain sufficient alloys to make them austenitic.
- Spheriodal graphite cast iron (S.G. iron, ductile cast iron, nodular cast iron). This is a recent development in the search for strength in cast iron by the addition of a small amount of magnesium gene rally as nickel magnesium alloy. During tapping into the moulding, the graphite is made to form in minute spheres instead of the usual flake forms.
Some basic rules and hints to be observed when welding cast irons:
- Clean and remove all grease, oil and other foreign bodies
- Select and prepare joint design best suited for type of crack and thickness of part.
- Parts over 12mm (1//') in thickness may require pre-heating when maximum machineability is required.
- Hold electrode approximately 15 ° off vertical tilted towards the direction of travel using stringer beads or a very slight weave.
- Maintain an arc distance of three to five millimetres (3-5mm) from work piece.
- Hold arc over molten, deposited metal and follow the molten pool of weld metal. (Caution: Do not permit the arc to lead or get ahead of the molten pool.)
- Always extinguish arc by whipping the arc back over the deposited metal.
- Immediately after breaking the arc, peen weld deposit lightly with ball-peen hammer, etc.
- Always re-strike arc on previously deposited weld metal.
- Use strip weld technique on thin or complex shaped parts.
- Use an electrode of a diameter small enough to permit at least two passes to be applied.
- On thin- and middle-wall components, when gouging may not be desirable, prepare the crack by chiselling in tulip form as wide as possible; i.e.remove all sharp edges. The depth should not be greater than 50% of the wall thickness.
- Locate the ends of the crack and block them by drilling or by bridging runs as previously mentioned. Should the run break, this indicates a high stress area and the end of the new crack should be located and a further bridging run applied.
- On thick -wall castings and components requiring high strength, join with Strata 880 after buttering the bevelled sides with Strata 899. The purpose of the combined welding system is to achieve the best possible bond on all kinds of cast irons so that the deposit does not pull away under stress and to retain high tensile values, maximum elongation and a well-orientated structure. Multi-layer welding of heavy sections is achieved by inter-laying Strata 899 and Strata 880.