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Cutting of Cast Iron - It is difficult to cut cast iron as compared to carbon steel, because iron oxides of cast iron melt at a higher temperature than the cast iron itself.
When cast iron melts, the oxides and impurities mix together and make it difficult to cut.
Various techniques to cut cast-iron are
(i) Oxy-acetylene cutting using torch oscillation.
(ii) Waster plate method.
(iii) Powder cutting method.
(iv)Chemical flux cutting method
Oxy-acetylene cutting using torch oscillation
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The following points are taken into consideration while cutting cast iron:
(i) The preheating flames are adjusted to have an excess of acetylene in order to prevent oxides from forming on the surface before the cutting starts. The excess acetylene also helps to maintain preheat in the kerf as it burns.
(ii) Longer preheating is necessary. Cast iron must be almost molten before the cut will start.
(iii) The nozzle must be held farther away from the metal and it must be oscillated continually across the line of cut. The torch oscillation helps the oxygen jet to blowout the slag and molten metal in the kerf. The kerf is normally rough and wide. The width of kerf depends upon the diameter of the arc or semicircle described by the torch (nozzle) during cutting.
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Steps involved in Cutting Cast Iron
(i) Preheat the plate along the edge to be cut from top to bottom. The warmer the whole mass of cast iron, the easier it will be to cut.
(ii) Hold the torch so that the tip points backward at an angle of75°.
The inner cones of the flames should be 3 to 6 mm above the surface of the plate.
(iii) The cut is started by giving the torch tip a swinging motion describing semi-circles across the line of cut.
(iv)A semi-circular area about 12 to 18 mm in diameter is heated to molten state. As the metal begins to boil, cutting oxygen is supplied to blow off the slag, etc.
Gradually the torch is straightened up at an angle of about 900 as the cut progresses.
Cutting of cast iron as compared to cutting of carbon steel of the same thickness requires
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(i) A larger cutting tip
(ii) Higher preheat temperature
(iii) Higher oxygen flow
(iv)Higher oxygen pressure (25 to 100% greater).
Cost cast iron cutting is done to
(i) Remove gates, risers or defects from castings
(ii) Repair castings
(iii) Cut scrap.
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