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Vertical hollow-shaft motors present some unique reassembly challenges, one of which is setting end play. Here's a tip that applies to assembly of vertical hollow-shaft motors in the 320 to 440 frame drip-proof enclosures with grease lubricated lower guide bearings and oil-lubricated upper thrust bearings.
Vertical motors differ from horizontal motors in numerous ways, yet some view them as “just a horizontal motor turned on end.” The obvious differences are the (usually) thrust bearings, with arrangements varying from single- to three-thrust bearings with different orientations suited for specific load, rpm and applications. Less obvious differences are in the ventilation arrangements, shaft stiffness, degrees of protection and runout tolerances. This recording will cover those topics.
Bearing construction is a key difference between vertical motors and horizontal motors that are mounted vertically. Vertical motors typically drive pumps using thrust bearings. Horizontal motors rarely have those types of bearings. Understanding relevant construction and configuration factors is crucial when confronting lubrication-related issues that can be associated with vertical-motor bearings.
Vertical motors can be identified by their capacity for an external thrust load. One common application with this factor is vertical pumps. The thrust load applied is the sum of the weight of the pump line shaft, the column of water in the casing that is being lifted, the weight of the pump impeller and the thrust produced by the pump’s volutes which forces the water to move upward. The distance between the motor and the impeller can be very short such as pumping from a tank at or above ground level to lifting water from a subsurface aquifer several hundred feet deep. In the latter example, the combined weight of the thrust load can be thousands of pounds (kilograms). The motor must then have a bearing design capable of these loads utilizing thrust bearings.
Los motores verticales se pueden identificar por la capacidad de soportar cargas de empuje externas. Una aplicación común en la que encontramos este factor son las bombas verticales. La carga de empuje aplicada es la suma del peso del eje lineal intermedio de la bomba (line shaft), la columna de agua que se está levantando, el peso del impulsor de la bomba y el empuje producido por las volutas de la bomba que fuerzan el agua hacia arriba. La distancia entre el motor y el impulsor puede ser muy corta, tal como sucede al bombear agua desde un acuífero subterráneo que se encuentra a cientos de pies de profundidad, hasta un tanque situado por encima o por debajo del suelo. En este último ejemplo, el peso combinado de la carga de empuje puede ser de miles de libras (kilogramos). El motor deberá estar diseñado con un rodamiento capaz de soportar estas cargas, por lo que se utilizan rodamientos de empuje.
Vertical motors are unique in their ability to carry external thrust. The thrust bearings that make this possible require care in assembly and application for optimum service and performance. Oil bath lubrication in vertical motors is critical and must be understood and maintained correctly.
The bearing construction of a vertical motor determines the definite purpose application of the machine. The difference between a vertical motor and a horizontal motor mounted vertically is the bearing configuration. A vertical motor has thrust bearings, except in the case of some close-coupled pumps; a horizontal motor rarely does. Typically a vertical motor is used to drive a pump and will have a P-base mount without feet. A horizontal motor may have a footed or footless mount with a C or D flange, or no flange. The thrust bearing is usually at the top of the vertical motor and may consist of one or more angular contact bearings, a spherical roller bearing or a hydrodynamic, plate type bearing. The thrust applied by the external load will determine the type and number of bearings used. The thrust may be manifest in upward or downward axial loading or it may be balanced. It is important to correctly apply the thrust bearing configuration to achieve the best service life and performance.
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Most of us have had to battle with the occasional two-pole vertical motor and survived. The following case study is a story not only of survival, but of success. The background A few years ago, our service center had a customer with six, two-pole 4000 VAC 900 hp solid-shaft vertical mo-tors; there were four installed and two spares. They were direct on-line start atomizer motors driving gearboxes in a coalfied power plant and were installed in the bottom of inverted conical structures supported from the roof of the building. The installation suffered from high ambient temperatures and a very marginal support structure for a vertical machine. Before coming to us, the customer had battled with the motor installation problems for years. The original motors, plagued with high vibration and frequent bearing failures, were replaced with another manufacturer's design. Unfortunately, that was no help. Several service centers had rebuilt these motors, but none of them had complete information regarding the installation and the high failure rate. Even motors returned to the OEM repair centers were extremely unreliable. The shortest run time was twenty minutes for one motor repaired by the OEM. The longest run time was less than two months. Cost had become virtually a moot point for the customer. The customer correctly decided to send all motors to one service center and communicate everything that was known about the problems associated with these motors. We were selected, possibly because of our close proximity to the plant.
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This 40-page booklet provides great advice for obtaining the longest, most efficient and cost-effective operation from general and definite purpose electric motors.
This booklet covers topics such as:
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The Effect of Repair/Rewinding on Premium Efficiency/IE3 Motors
Tests prove Premium Efficiency/IE3 Motors can be rewound without degrading efficiency.
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Recommended Practice for the Repair of Rotating Electrical Apparatus
This is a must-have guide to the repair of rotating electrical machines. Its purpose is to establish recommended practices in each step of the rotating electrical apparatus rewinding and rebuilding processes.
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Revised May 2021
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