Shield pump is composed of centrifugal pump and three-phase asynchronous shield motor coaxial. Without mechanical seal without leakage, suitable for conveying a variety of toxic, harmful and expensive liquid, widely used in chemical, pharmaceutical, nuclear industry, aerospace and other devices. Shield pump to regular maintenance, in order to ensure reliable operation. During my work in Shanghai Petrochemical (to participate in overhaul), many imported shielding pumps, there are general maintenance, but also recovery overhaul. With the increase of the service life, the increase in the number of use, the damage is also increasing, the number of recovery overhaul increased year by year. I have repaired a variety of foreign shield pumps of various sizes. Power from 0.55 kilowatts to 130 kilowatts. 1, the structural characteristics and damage Shield pump is a pump and motor products, the motor stator and rotor parts have a special metal material made of the sleeve, each of them sealed, not the liquid medium and the contact, So that the motor core and winding from corrosion, so that the stator windings to maintain good insulation properties. Shielded pump structure shown in Figure 1. Shielded pumps using graphite bearings, rely on the delivery of liquid to lubricate. Bearing wear and tear, for reliable operation is very important. In order to monitor the bearing wear, usually equipped with mechanical or electromagnetic bearing monitor. When the bearing wear exceeds the specified allowable value, the pointer of the monitor dial will point to the red zone, which means "alarm". At this point should immediately stop running for inspection. If the bearing wear has exceeded the limit value should be replaced with a new graphite bearing, otherwise it may cause stator and rotor shield sleeve rub, until the shield sleeve damage, resulting in liquid medium erosion to the stator windings, etc., resulting in motor damage. Chemical shield pumps are mostly used in explosion-proof places, so the junction box is made of explosion-proof structure. Shielding motor coil end buried temperature relay, when the motor windings overheating, overheating protection, according to the insulation of the motor used in different levels, the temperature of the relay action temperature will be different. Some shield pump motor shell part has a heat exchanger, a serpentine tube, high temperature medium through the serpentine cooling and then for the graphite motor bearings lubrication, while the jacket cooling water can also play a cooling effect on the motor. Shielding pump has the following major damage: (1) graphite bearings, bushings and thrust plate wear or shortage of lubricating dry wear and damage. (2) The cause of damage to the shielding sleeve caused by damage to the shielding sleeve of the rotor is that damage or wear of the bearing exceeds the limit value, which causes damage to the stator and rotor shielding sleeves; secondly, leakage occurs due to chemical corrosion. (3) Stator winding damage In addition to the ordinary motor is the same: overload, inter-turn short circuit, on the ground breakdown caused by the stator winding damage reasons, there are also damaged due to the stator shield damage caused by erosion of the motor winding dielectric winding insulation. 2, Regular Maintenance of Shield Pump In order to avoid and reduce the sudden damage of shield pump, shield pump needs regular maintenance. In case of bearing monitor "alarm", must be immediately overhaul. Chemical plant is generally continuous operation, shielding pump regular maintenance only when the device is scheduled to stop. Most shield pumps can be serviced once a year. Shielding pump repair method is: Disassemble the shield pump: first clean up the parts, and then make an apparent inspection of them, whether there is any exception. Then measure the size of the key parts, electrical inspection of the motor windings. (1) Mechanical inspection Measure the bore diameter of graphite bearings and the shaft diameter of bushings and check the finish of their mating surfaces. Such as graphite bearings and bushings with clearance over the provisions of maintenance standards (0.55-11kw with the gap, the diameter difference of 0.4 mm, 15-45kw with the gap, the diameter difference of 0.5 mm) or with poor surface finish, the need to be replaced according to circumstances Bearings, bushings or thrust plates. Measure the dimensions of the upper and lower outer stops of the impeller and their matching buckle and pump seat inner diameter, whether these two clearances are within the scope of the overhaul standard, replace parts or take other measures when out of tolerance Such as: surfacing, set) to meet the requirements of the gap. Otherwise it will affect the pump performance, flow, lift, axial balance and so on. Observe the inspection set, the apparent state of the rotor shield sleeve, with particular attention to whether there is any abnormal weld, if necessary, should be for testing, leak check. After long-term operation, the balance of rotating parts may change. Therefore, it is necessary to rotate the rotor together with the impeller and other rotating parts assembled to do dynamic balancing test. (2) Electrical Check DC Resistance Check: Three-phase resistance unbalance shall not exceed 2%. Insulation resistance check: shielding pump motor winding insulation resistance can generally reach more than 100MΩ. Such as less than 5MΩ need to analyze the reasons for insulation is damp, or shielding the leak if there is no problem, such as leakage through the stator shield no problem, then purely moisture insulation, the need for drying treatment, such as stator shield has a problem, You need to change the shielding sleeve. 3, shield pump overhaul In case of shield or shield damaged shield pump, you need to carry out a recovery overhaul. Damage is generally divided into two types: one is the stator shield is good, and the stator winding occurs on the ground, phase breakdown, winding inter-turn short circuit, overload caused by the winding burn. The other is due to damage to the stator shield to make the medium invade the stator winding stator winding damage. In either case, replace the stator coil and shield sleeve. Due to the special structure of the shield pump, it is more complicated to replace the stator winding. The stator shield and the both end shields must be removed to remove the stator winding. After the winding is repaired, a new shielding sleeve and sealing plate must be reworked. The material requirements of special, and the production of precision also requires higher. (1) Stator winding replacement Stator winding replacement and ordinary motor is similar, but higher insulation level, mostly with H-class insulation. QY polyimide enameled wire, slot insulation, slot wedge, bushing, lead wire and impregnated paint, etc. are required to use H-class insulation materials. Replacing the winding principle is: as it is, especially the number of turns of the coil can not be arbitrarily changed, the number of turns will significantly affect the main performance of the motor, the wire diameter is as close as possible to the original total area, the winding form, the coil span do not change . (2) the replacement of the shielding sleeve Replacement shielding sleeve is to repair the shield pump difficult and special, is to ensure that the key to repair the quality of shielding pump. To reach the original level, we must pay attention to the following aspects. (A) Screening material selection In the shield pump motor loss, the stator shield loss, sometimes up to 2 to 3 times the loss of iron, repair shield loss should be maintained at the original level. Loss of stator shield PB is proportional to the shield thickness, inversely proportional to the resistivity of the shield material Ï. Shield material must have good mechanical properties and corrosion resistance of non-magnetic materials, in order to reduce the eddy current loss to use a large resistivity material. Thickness should not be too thin, to affect the mechanical strength, it should not be too thick, thick shield will increase the loss. Imported shielding pump shield sleeve mostly adopts a special stainless steel material called Hastelloy-c containing more than 50% nickel. The performance of this material can fully meet the above requirements. The resistance factor can be twice as large as normal stainless steel 1Cri8Nig9Ti, that is, the shielding sleeve loss is one-half of that of ordinary stainless steel. (B) Production of Shielding Shielding shields should be the most difficult and critical part of shielding pump recovery overhaul. Shielding sleeve dimensional accuracy and shape tolerance requirements are higher, welding quality requirements of the weld is also very strict. From the unwinding of the size of the calculation, cutting, straight seam welding, full circle, press fit, girth welding, leak detection and so have a certain degree of technical difficulty. Shielded motor stator and rotor between the effective clearance is generally only 0.5 ~ 1.0 mm, so the required shielding sleeve not only can be smoothly pressed into the stator core, but also to make the shield sleeve close to the core, the only way to ensure that there is enough between the rotor Effective clearance. (C) Overall stator leak detection After the completion of the stator seal and the case of the welding, press into the shielding sleeve and the shield sleeve to complete both ends of the girth welding, the stator should be the overall leak check. The method is: the cavity between the base and the stator shield is filled with 0.5㎠/ c ㎡ of pressure, and then the overall immersion in the water in the stator, if there is a leak, the water will bubble, which is a simple The effective leak detection method. (3) Final assembly and inspection test After finishing the stator and rotor repair, prepare qualified graphite bearings, bushings, thrust plates, seals, etc. to be assembled. After the assembly is completed, turn the rotor by hand, the rotation should be uniform and flexible. The rotor should have a certain amount of axial movement. The displacement of the rotor should be within the range specified in the inspection standard. Shielded Pump Power kw 0.55 ~ 3.7 5.5 ~ 11 15 ~ 45 To move around mm 0.9 ~ 1.5 1.4 ~ 2.0 1.8 ~ 2.5 After the completion of the assembly, check the DC resistance and insulation resistance, etc., that the normal electrical performance, the shield pump immersed in the water tank as a whole (junction box on the water, water can not enter Junction Box) to do electric test (at this time pump outlet can be covered) to observe the current, running sound, vibration and other anomalies. If the test conditions can do the pump performance test is better.