Coupling Q&A
I recently happened across Howard Schwerdlin's article, “Torque by Magnetic Pull,” on your web site. I am working on a vacuum pump project where we intend to use magnetic couplings to overcome a seal leakage problem. We would like to know the effect of speed on magnetic couplings. Say the speed is increased from 3,000 to 6,000 rpm and power is in the range of 1.5 to 55 kW for different models.
Kasinathan Raghunath
India
The synchronous magnetic coupling will transmit the same amount of torque regardless of operating speed. The eddy current effect that will occur in metallic barriers is proportional to speed squared (N2). That said, a speed increase from 3,000 to 6,000 rpm would increase the eddy current losses by four times. These losses show up as additional drag on the motor and heat generation in the barrier that must be removed. This effect is eliminated when a nonmetallic barrier is used.
— Howard Schwerdlin
Women making strides
I just received the Feb. issue of Motion System Design and enjoyed the article on women in engineering. It is good to see a woman as the chief editor of a technical magazine. Just last night I told my 11-year-old daughter Sonia how great it was to live in this time, so she could be anything she wanted to be. Like your article, I explained to her that just a few decades ago, she could have asked a guidance counselor about becoming a doctor and might have been told she should just aim to be a nurse. I'll bring your magazine home tonight to inspire Sonia and her younger sister Sarah.
J.C. Delgado
Waco, Tex.
Red flag for efficiency
I am a retired engineer and have a patent-pending invention for a more efficient way to illuminate flags on vertical flagpoles than existing methods. The National Museum of the United States Air Force in Dayton, Ohio, is interested in my approach, which I plan to test on their 80-ft flagpole. They now use three 1,000-watt bulbs, whereas I can get equivalent or better results with less than 100 watts. I have installed my invention at home and it works very well.
Karl Schroeder
Clayton, Ohio