cast iron pulley cracks

Can Cracks In Cast Iron Pulleys Be Repaired By Welding?

Pulley is a common mechanical device in life, which is widely used in many fields. Pulley occupies a very important position in the market, the pulley on the market is also a variety of different materials, different sizes, different uses, cast iron pulley is one of them, mainly used in bridge cranes and other lifting machinery. The casting process of cast iron pulley is very complex and needs to go through many processes.

Cast iron pulley process performance is good, easy to cut processing, especially the wear of steel wire rope is small, but because of its low strength and brittleness, durability is poor, easy to cause the fracture and breakage of the rim when used, small tonnage or use infrequent equipment is more economic ideal. Cast iron pulley adopts sand cast iron casting process; Due to its good fluidity in casting and relatively few casting defects, cast iron is an ideal material for making pulleys.

Causes of cracks in cast iron pulley

Cast iron pulley is made of iron carbon alloy with carbon content greater than 2%. In the casting process of cast iron, there are often defects such as pores, slag holes, sand inclusion, shrinkage holes, cracks and insufficient pouring. In use, due to overload, mechanical accidents and natural damage, it will cause damage to cast iron pulley. In order to repair these damaged positions and defects, according to the characteristics of cast iron, the corresponding welding process should be adopted to repair the welding of cast iron pulley.

Cast iron pulley repair welding process

(1) Preparation before welding

① First check the location and length of the crack of the cast iron pulley, and use carbon tetrachloride to clean the oil and oxide and other debris at the crack site to avoid porosity and slag inclusion during repair welding.

② Drill holes at both ends of the crack with a drill bit with a diameter of Φ3~5mm. For cracks in thick wall parts, the drill diameter can be larger. At the same time, use a flat chisel to pick cracks in the 70°~110° slot.

(2) Gas welding process

① During gas welding repair, white tissue is prone to appear due to the burning of carbon, silicon and other elements. In order to compensate for the burning loss of the elements, promote the graphitization of the weld metal, and obtain the weld metal with the chemical composition and metal structure basically the same as the base metal, the high silicon cast iron gas welding electrode should be used. The diameter of the electrode is Φ3~4mm. The flux is CJ201 cast iron gas welding flux.

② The welding moment and the welding nozzle are generally selected as medium or small, and the aperture of the welding nozzle is between Φ1.5~2.2mm. The flame is a neutral flame or acetylene has a residual neutral flame to reduce the burning loss of carbon and silicon and ensure the chemical composition of the weld metal.

③ Before welding, put the cylinder cover in the charcoal stove and heat it evenly and slowly to about 500~600℃, and keep it warm for about 1h. When preheating before welding, the crack part to be repaired can be placed in the charcoal furnace to be fully preheated.

④ Horizontal position is used when welding to prevent metal loss.

⑤ At the beginning of welding, the flame is aligned with the bottom of the crack in the welding repair part, so that more than 2/3 of the thickness of the welding crack on both sides is melted, and the welding rod is dipped in the flux into the solution pool and stirred at any time, so that the bubble impurities can be completely surfaced. At the same time, the flame should move back and forth around the weld to ensure that the temperature near the weld metal is not too low. Each crack should be welded by a gas, and the welding operation should be rapid and reliable.

⑥ Repair the weld surface and root. The operation is to use a flame for point-like heating, so that it is partially melted, the left hand with the iron plate, the weld surface scraping, scraping, and flush with the base material surface.

(3) Post-welding treatment

After welding, it is placed in the charcoal furnace for heat preservation, to prevent the stress generated during cold shrinkage and to prevent the white hole, and the temperature is the same as the preheating temperature. When the temperature slowly and evenly rises to the specified temperature, the iron sheet is used to block the cast iron pulley around, so that the furnace temperature slowly decreases.

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