Design for Maintainability: The Innovation Process in Long Term Engineering Projects

The secret to making and keeping reliable electrical connections is contained in two elements: start with clean contact surfaces, and apply high force. Clean contact surfaces are a function of cleaning procedures, including joint compounds, and will be covered in a future article. Application of high force is the subject here. The trouble comes about because the terms "torque" and "force" are incorrectly used interchangeably. Force is NOT torque. Force is a function of torque.

Machine conditions change from the time the machine is off line to when it is running under normal operating conditions. Some of these changes are due to process forces (e.g., fluid pressures, airflow, etc.). The most notable of these changes is the change in the temperature of the machine bearings and supports. This is called the machine's thermal growth.

On the design of a new machine which is to be run with a hydraulic motor, a determination of required speed and horsepower must be made so a model with suitable ratings can be selected. This article describes several methods of making such a determination. Designers who are experienced only in selecting electric motor drives need to be careful in designing hydraulic drives because of important differences between these two motors.

In 1997-98, the facility was considering replacing the aging (1972-73) high, medium, and low voltage equipment because of several operational and maintenance problems with the breakers. We also were concerned about the overall grounding scheme of the facility. To find out the existing status of the grounding system, we procured architect/engineer (A/E) services to check and confirm the overall validity of the facility-grounding scheme.

Part one of a four-part series that will cover alignment fundamentals and thermal growth, and highlight the importance of field measurements through two case studies. Despite the best efforts to precisely align rotating machinery shafts, dynamic movement (commonly believed to be due to the thermal growth of the machine casings) has resulted in machines operating at less than optimum alignment conditions. This vexing problem has plagued machine reliability professionals for decades.

Electrical systems are grounded to limit the voltage imposed by lightning, line surges, or unintentional contact with higher voltage lines and to stabilize the voltage to earth during normal operation. Electrical systems can be grounded in several ways. There are induction grounded systems, resistance grounded systems, and high impedance grounded systems among others. The most common grounded system is the solidly grounded system, where there is no intentional grounding impedance in the earthing or grounding circuit.

Want to expand coupling life? Who doesn’t? You may want to look into advanced-design disc couplings. These couplings feature discs with optimized profile and thickness to provide a higher torque-to-outside-diameter ratio, higher service factors and up to 50 percent greater misalignment capability. All this provides for smaller reactionary forces on bearings compared to conventional disc couplings, which helps achieve infinite coupling life in properly specified applications.