July/August 1989
Last year, Rose Metal Recycling switched its shredder motor from diesel to DC. And what a difference it has made.
By Susan Crissinger
Susan Crissinger is associate editor of Scrap Processing and Recycling.
It's been cleaner, quieter, easier to control--and it has made Irving Rose very happy. It's the new specially designed DC motor and drive package he installed last year on his car shredder.
Rose, president of Rose Metal Recycling, Inc., Houston, has nothing but positive things to say about the 2,000-horsepower-capacity motor and drive package he bought from Gulf Electroquip, Ltd., in Houston. His shredder, installed in 1974, was running on a diesel motor.
Rose, who has an engineering background and holds several patents on equipment improvements at his plant, had been working on the diesel motor's problems long before the city filed an air pollution suit against the firm. Improvements were made to the motor, reducing the amount of smoke and satisfying the city, but Rose knew that, eventually, more changes would be needed.
Carl Durham, Rose Metal Recycling's operations manager, had previous favorable results with DC motors and had suggested to Rose that a DC motor might be a wise next choice. The time came for a major ($80,000) overhaul of the diesel motor. Rose took into consideration this cost, the fact that another expensive overhaul probably would be needed in two to three years, plus all the troubles he'd encountered, and decided to take Durham's suggestion.
Rose bought the DC motor at a cost he believed was "much more reasonable than the alternatives" because of the advantages a DC motor offers. Since a DC motor runs on electricity, not fuel, the potential problems of smoke and oil spillage are eliminated. The firm's electric bill--now around $4,000 to $5,000 per month--is about half of what Rose had anticipated. The diesel motor, on the other hand, used around $2,500 a month in fuel and $1,500 in electricity (to power auxiliary components), and had the additional hefty costs of oil and maintenance.
Part of the reason for the lower-than-anticipated power bill is another tremendous benefit of the new motor: control. The electric company bases its charges on demand--the amount of kilovolt amperes (kva) needed for a given operation. This factor is controllable on a DC motor; Rose can predict the maximum demand the motor will need and set it at that level.
Even though the motor is rated at 2,000 horsepower, Rose currently needs just over 1,000.
In addition, the shredding speed is variable, unlike other motor types. Rose says the operators begin by using the lower kva and when an acceptable amount of production is reached, that kva setting is maintained. (The old motor generated 1,200 tons a month at Rose's facility, while the DC motor is putting out 2,000 tons.) The adjustable speed not only provides control but saves on the power bill, as does the motor's ability to start up quickly without excessively burdening the power supply.
Rose wasn't the only one surprised at the reasonable electric bills. The doubting local electric company removed its meter at the facility and installed two new ones, to rule out the possibility of a faulty meter. And because the DC motor's demand was lower than originally thought, the electric company reevaluated Rose Metal Recycling's rate structure after the first year and rebated the company close to $28,000 in power savings.
Rose says the shredder operators love the new motor. It's more dependable, requires less maintenance, and is easier to control. Besides, they get bonuses based on production levels, and the DC motor's lack of downtime is helping to fatten their checks. Operations Manager Durham is glad to be supervising a clean, efficient machine. And Irving Rose? "I've never been more pleased with anything I've done in my 45 years in this business."
Last year, Rose Metal Recycling switched its shredder motor from diesel to DC. And what a difference it has made.