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, structural characteristics and damage
Shielded pump is a pump and motor products, the motor stator and rotor parts each 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 is not 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., causing the 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 several major damage:
(1) graphite bearings, bushings and thrust plate wear or lack of lubrication dry wear and damage.
(2) set rotor shield damage
Shielding sleeve damage caused by the main reason is the bearing damage or wear over the limit caused by the stator and rotor shield sleeve wipe and damage; followed by chemical corrosion caused by leaks at the weld.
(3) Stator winding damaged
In addition to the same as the ordinary motor: 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 insulation winding insulation.
2, shielding pump regular maintenance
To avoid and reduce the risk of a sudden damage to the shield pump, the shield pump needs regular service. 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 various 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 the graphite bearing and the shaft diameter of the sleeve and look at 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 ?, 15-45kw with the gap, the diameter difference of 0.5?) 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 inspection
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 recovery overhaul
In case of damaged shielded pump windings or shield, 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 so that the media 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) Shield sleeve replacement
Replacing the shield is to repair the shield pump difficult and special, is to ensure the quality of the shield repair the key. To reach the original level, we must pay attention to the following aspects.
(A) Selection of shielding sleeve
In the shield pump motor losses, 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 sleeve
Shielding sleeve production process should be shielded pump recovery overhaul the crux of the difficult and the key. 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. The effective gap between the stator and stator of the shielded motor is generally only 0.5 ~ 1.0. Therefore, it is required that the shielding sleeve should not only be pressed into the stator core and the rotor core but also be close to the core. Only in this way can there be enough between the stator and the rotor Effective clearance.
(C) Overall stator leak detection
After completing the welding of the stator sealing plate and the shell, pressing the shielding shell and completing the girth welding at both ends of the shielding shell, the overall stator leakage inspection should be carried out. The method is: the cavity between the base and the stator shield is filled with a pressure of 0.5? / C ?, and then the overall immersion in the water stator, in the event of leaks, the bubbles in the water, which is a simple The effective leak detection method.
(3) assembly and inspection test
After finishing, rotor repair, ready qualified graphite bearings, bushings, thrust plates, seals, etc. can 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, and its movement should be within the scope of maintenance standards:
Shielded pump power kw 0.55 ~ 3.7 5.5 ~ 11 15 ~ 45
Axial movement? 0.9 ~ 1.5 1.4 ~ 2.0 1.8 ~ 2.5
Complete the assembly and then check the DC resistance and insulation resistance, etc., that the normal electrical performance, the overall shield pump immersed in the water tank (junction box to be on the water, water can not enter the junction box) to do power-driven test (at this time pump out 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.
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