The ammonia water circulation pump is mainly used to pump the ammonia water from the pool to the vertical carbonization furnace gas collecting pipe, and spray the gas from the furnace to achieve the purpose of cooling and oil and gas separation. The pump casing of the ammonia water circulation pump is generally cast with gray cast iron. Gray cast iron has good casting and cutting properties and is cheap, but it has high carbon content, brittle material, and many impurities, so it has low tensile strength and lacks plasticity and toughness. It may be produced during transportation and operation. Cracks or even partial damage.
1. How to repair the cracks in the shell of the ammonia circulation pump? The following methods are commonly used to repair the shell cracks of the ammonia circulation pump:
1) Hot repair welding method
The hot repair welding process is complicated, and it is suitable for parts with large forces or large changes in shape. Before welding, put the pump casing in a mold made of water-resistant bricks, covered with yellow sand, and put charcoal or coke around to preheat the pump casing for 2-5 hours. During preheating, the temperature should be gradually increased, gradually heating to 500. c, make the pump casing red through, then expose the parts to be welded on the pump casing, cover the remaining parts with asbestos plates, and then use cast iron electrodes or stainless steel electrodes for gas welding. After welding, the pump casing cools naturally in the furnace to relieve the internal stress.
2) Cold repair welding method
The cold repair welding process does not require special preheating before welding, and does not need to be heated during welding. It can be welded in all directions, which can simplify the process, save heating equipment, reduce costs, and improve welding conditions. The weldment is basically not deformed and the residual stress is small.
The cold repair welding repair process is introduced as follows:
(1) Weld the groove, and punch a 15-20mm deep crack stop hole at the front 5mm of the pump shell crack. Use an angular grinding wheel to dig out the cracks into a V-shaped or U-shaped groove with a depth of 10-20mm and a width of 15-20mm. The groove should be smooth and clean. Use an angular grinding wheel to grind the metallic luster surface with a width of more than 1OOmm around the repair welding area of the groove.
(2) Nickel-iron alloy electrode is used as welding material, and the electrode must be dried to remove moisture from the coating to prevent pores during welding.
(3) Before welding, use an oxygen-acetylene flame to heat the groove and 200mm around the groove to about 150°C to remove organic matter and moisture in the groove to prevent defects such as porosity and slag inclusion during repair welding, and at the same time repair the pump casing The zone temperature is balanced to prevent cracks due to temperature difference stress. Start welding when the workpiece is cooled to 40-60°C.
(4) When welding, use a small current and intermittent short arc to make the heat affected zone of the pump casing as small as possible to prevent shrinkage cracks.
(5) After each section of welding, when the arc is just extinguished and the weld bead is still in the red hot state, quickly hammer the weld bead with a pointed hand hammer, and use external force to help it extend plastically to reduce thermal stress and improve compactness. The residue is cleaned up.
(6) After the welding repair is completed, the pump casing should be kept warm with asbestos cloth immediately and allowed to slowly cool to room temperature.
3) Pasting method of epoxy glass cloth:
Epoxy resin has high bonding strength, strong toughness and good water resistance. The epoxy resin glass cloth paste method is used to repair the cracks or partial damages of the pump casing, which has the advantages of low cost, high efficiency, low labor intensity, and easy construction on site. The repair process is as follows.
(1) Surface treatment: First use fine cast iron welding rod to spot weld the surface of the pump shell, polish the surface of the pump shell with a polisher to remove the dirt and welding slag on the surface, and then clean the surface of the pump shell twice with dilute sulfuric acid and acetone. The rust, grease and grease on the surface should be clean, free of dust, oil, and dry.
(2) Production of lining board If the partial damage of the pump casing is to be repaired, a lining board shall be made on the inner wall of the pump casing and fixed with tools at the same time. The main function is to prevent the epoxy resin from flowing during the repair, and at the same time as the lining board for the epoxy resin to stick the glass cloth.
(3) Epoxy resin preparation The preparation method is the same as when repairing the impeller, the epoxy resin should not be too thin to prevent the epoxy resin from flowing during pasting.
(4) Paste First, use wool brush to dip epoxy resin to paint the surface of pump casing, then cut the first glass cloth, which is about 20-30cm wider than the crack or partial damage area of pump casing, and stick it on the pump casing. If the pump casing is damaged locally, a fine metal mesh can be pasted in the glass cloth to increase the strength. When pasting, gently push and pull with your hand or a sharp cone to squeeze out the bubbles in the middle, and at the same time use a scraper to gently scrape and compact, and then apply epoxy resin. After sticking the 3 layers of glass cloth, wait 3 to 5 hours for the epoxy resin to cure before continuing. The thickness of the adhesive layer depends on the length of the crack or the degree of damage.
(5) Curing. After repairing, place the pump casing in an environment with a temperature of 20 to 30°C and a low relative humidity, and slowly cure for 48 hours.
(6) Quality inspection Carry out quality inspection on the repaired pump casing, focusing on checking whether there are cracks on the surface of the epoxy resin, whether there is a peeling edge at the joint, the strength of the epoxy glass cloth and the geometric shape of the bonding.
