Switching Gears Can Cut Your Energy Costs

"Switching Gears" Can Cut Your Energy Costs

by Brian Schmitz, Emerson Gearing, Division of Emerson Electric Company

When trying to improve overall system efficiency, most people initially look to the electric motor. And while it is true that switching to an energy efficient motor is a smart investment in most cases, this is only part of the overall efficiency equation.

Most conveyor OEM's have long standardized on worm gear reducers due to their low initial cost, long service life and ability to withstand high overloads. However, one of the drawbacks of worm gear reducers is their relatively low efficiency, especially at ratings below 20:1.

Take, for example, a constant speed belt conveyor system. The conveyor operates 4,000 hours per year and is driven by six, 2 HP, poly-phase induction motors mounted to worm gear reducers with 40:1 ratios. The efficiency of the worm reducers is 67%. Each motor is operating at full load and has a nominal efficiency of 82%.

In our example you can see that an obvious candidate for replacement with a more efficient product is the worm gear reducer (see Figure 1). While a few points of efficiency can be gained from using a more energy efficient motor, much more can be realized from using a more efficient reducer combined with the original motor.

Figure 1

Much has been written about replacing worm gear reducers with their much more efficient cousins, in-line helical reducers. Making this change would not only offer energy savings from higher reducer efficiency, but also the opportunity to reduce motor horsepower.

Clearly, by implementing this type of solution, significant savings will be obtained by reducing kilowatt consumption since the motors would be operating at less than 3/4 load. In fact, the efficiency of induction motors actually increases slightly when operating at 75 percent load!

However, it is the role of the PT/MC distributor to educate customers that spending numerous man-hours of labor changing from one product to another could quickly eat up any potential energy savings. Changing from a right angle worm gear to an in-line helical reducer in this instance might also be questionable in its true cost savings, since implementation of this product change would necessitate a fair bit of re-work to the existing conveyor system.

Other Options

Right angle worm and in-line helical are the two most common types of gearing today in the industrial marketplace. However, there are other types of gearing which should be considered and may provide a better overall solution. The PT/MC distributor recommending a change in the type of gearing on any piece of equipment must not only be concerned with efficiency, but other factors such as:

Initial cost
Repairability
Ease of installation
Availability
Ability to withstand overload conditions
Expected life

The chart in figure 2 shows that changing the type of reducer involves making a number of trade-offs between these attributes. The goal is to choose a reducer with the right performance characteristics while maximizing efficiency.

Figure 2

In the case of our conveyor example, the configuration and average overload capability of the in-line helical reducer may not make it the best choice, even though it offers the highest efficiency (see figure 1). A better choice may be a helical-worm reducer, which offers only slightly lower efficiency than the in-line helical while preserving the configuration and overload capability of the original worm reducer.

A comparison of total yearly energy costs reveals that only a small portion of the potential energy savings has been compromised (see figure 3). However, the energy savings compared to the original product are quite dramatic and will more than justify the increased cost of the helical-worm gear reducer.

Figure 3

The ability to make similar intelligent choices for users make PT/MC distributors an invaluable resource. These professionals can help determine the most cost efficient solution for any application. Utilizing their expertise will help to evaluate total energy consumption and the best options for your operation.

This article is provided courtesy of PTDA.

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