Welding Cast Iron

Welding is sometimes used to repair broken and defective castings [6]. This process is more difficult than welding steel because the high carbon content in cast iron may lead to brittle structures on cooling, thus 

Tabic 3.6. Maximum Working Stresses for Various Grades of Cast Iron up to 600 C 

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Table 3.7. Rods and Electrodes for Fusion-Welding Cast Iron...

Rods and electrodes for fusion-welding cast iron. 61... 

Two cast iron pipe sections (Schedule 40, carbon steel), 4.5 in. (11 cm) diameter and 7 in. (18 cm) long, were used. Both ends of the pipes were sealed by welding cast iron round plates on them. They were contaminated internally with one of the debris wastes described in Section 17.5.1. 

Ni-Rod. [Inco Alloys IntT.] Welding prods, for welding cast irons. 

TABLE 8.7 Typical Preheat Levels for Welding Cast Irons... 

Copper alloys and stainless steel difficult to weld. Cast iron, lead or zinc alloys are not weldable. 

Pig-iron or cast iron contains impurities, chiefly carbon (up to 5 ). free or combined as iron carbides. These impurities, some of which form interstitial compounds (p. I I3i with the iron, make it hard and brittle, and it melts fairly sharply at temperatures between 1400 and 1500 K pure iron becomes soft before it melts (at 1812 K). Hence cast iron cannot be forged or welded. 

Lead and its alloys are generally melted, handled, and refined in cast-iron, cast-steel, welded-steel, or spun-steel melting ketdes without fear of contamination by iron (qv). Normal melting procedures require no dux cover for lead. Special reactive metal alloys require special alloying elements, duxes, or covers to prevent dross formation and loss of the alloying elements. 

Ferrophosphoms is produced as a by-product in the electrothermal manufacture of elemental phosphoms, in which iron is present as an impurity in the phosphate rock raw material. The commercial product contains ca 23—29% P and is composed primarily of Fe2P [1310-43-6] and Fe P [12023-53-9] along with impurities such as Cr and V. Ferrophosphoms is used in metallurgical processes for the addition of phosphoms content. Low concentrations (up to - 0.1%) of phosphoms in wrought and cast iron and steel not only increases the strength, hardness, and wear resistance but also improves the flow properties. In large stmctural members and plates, it is desirable to use a type of steel that does not need to be quenched or tempered, and thus does not exhibit weld-hardening. This property is afforded by the incorporation of a small quantity of phosphoms in steel. Ferrophosphoms from western U.S. phosphoms production is used as a raw material for the recovery of vanadium (see Vanadiumand vanadiumalloys). 

The largest use for calcium carbide is in the production of acetylene for oxyacetylene welding and cutting. Companies producing compressed acetylene gas are located neat user plants to minimize freight costs on the gas cylinders. Some acetylene from carbide continues to compete with acetylene from petrochemical sources on a small scale. In Canada and other countries the production of calcium cyanamide from calcium carbide continues. More recentiy calcium carbide has found increased use as a desulfurizing reagent of blast-furnace metal for the production of steel and low sulfur nodular cast iron. 

A drag chaia coaveyor coasists of a single strand of endless cast or welded steel chain that pushes or drags material through a trough. It is a simple, low cost conveyor for handling ash, coal, hot clinkers, and scrap waste materials. A variety of cast iron, cast steel, and welded steel chains are used for these conveyors. 

Metal Preparation. Sheet-steel parts are formed by stamping, bending, and shearing. Many parts require welding (qv), which needs to be carried out in a uniform, smooth manner so that the welded joint can be enameled without defects. Cast-iron parts are formed by the usual cast-iron foundry methods however, additional care is given to prevent contamination of the surface. Surface contamination causes defects in the enamel, particularly bUsters and bubbles. Aluminum metal can be formed in sheets, extmsions, and as castings. 

Y = coefficient naving value in Table 10-50 for ductile ferrous materials, 0.4 for ductile nonferrous materials, and zero for brittle materials such as cast iron t,n = minimum required thickness, in, to which manufacturing tolerance must be added when specifying pipe thickness on purchase orders. [Most ASTM specifications to which mill pipe is normally obtained permit minimum wall to be 12V percent less than nominal. ASTM A155 for fusion-welded pipe permits minimum wall 0.25 mm (0.01 in) less than nominal plate thickness.] Pipe with t equal to or greater than D/6 or P/SE greater than 0.385 reqmres special consideration. 

Part UHT also contains more stringent details for nozzle welding that are required for some of these hi -strength materials. Part UCI has rules for cast-iron construction. Part UCL has rules for welded vessels of clad plate as lined vessels, and Part UCD has rules for ductile-iron pressure vessels. 

High-silicon cast irons have excellent corrosion resistance. Sih-con content is 13 to 16 percent. This material is known as Durion. Adding 4 percent Cr yields a product called Durichlor, which has improved resistance in the presence of oxidizing agents. These alloys are not readily machined or welded. 

Cast iron body, feet or ribs etc. found broken or cracked during transit or otherwise. Replacement of the motor in such cases may not be practical. However, using the motor may not be advisable in view of a weaker foundation and insufficient cooling. In such cases the broken parts can be welded using cast iron electrodes. Cracks, however, cannot be remedied. Unless the cracks are wide and may cause extensive damage during operation, the body may still not require replacement. Minor cracks, however, which do not impair the motor s perfor-mance or cause development of further cracks, may be compromised. 

Furnace-type air heaters are manufactured from cast iron or steel, and cased in brickwork or steel. The cast-iron heaters are sectional, cemented and bolted together. The steel type are welded or riveted. It is essential that the joints are airtight, so that the cold air can pass over the heated surfaces of the furnace and flues without contamination by the flue gases. 

Figure 2-4B. Forged steel socket weld fittings, WOG (water, oil or gas service). Note the working pressures are always well above actual plant operating levels and are heavy to allow for welding. Pressure classes 3000 psi and 6000 psi, sizes % in. through 4 in. nominal. Do not weld on malleable iron or cast Iron fittings. (By permission, Ladish Co., Inc.)...

Mild steel welded Mild steel sectional Cast iron sectional Reinforced concrete... 

For all materials other than basic constructional steels and cast irons, reputable suppliers have information bases and applications laboratories from which information can be obtained. Trade organizations representing categories of materials suppliers are excellent sources of information some are listed at the end of this chapter. The materials suppliers should be consulted in conjunction with equipment suppliers in order to ensure that the information generated is fully applicable to the end use to which the material is to be put. Fabrication techniques should be agreed between the two types of suppliers, since some materials cannot be cast or welded and forging cannot make some items. 

Bimetallic corrosion of nickel-iron alloys may be of significance in welding operations. Ni-45 Fe alloys are used as filler materials in the welding of cast irons but the favourable area relationship of weld metal to base plate... 

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