Q: In the May 1990, issue of Concrete Construction (page 464) you showed magnets being used to anchor blockouts to metal forms. Is this a new idea? And where can people get the magnets?
A.: We first heard of this use of magnets while working on the article for our May issue, but it appears to be more common in Europe. C. J. Wilshire, writing about steel forms in the book Formwork, published in London, says "It is possible to get magnetic fixings--at a cost!" Howard Gueldner and Bruce Harris of Symons Corporation's Steel Form Division in New Braunfels, Texas, told us that the magnetic blocks in the picture have pull-off load rating of 450 pounds, but the lateral force required to slide them along the form face may be only 40% of that.
The blockout forms for that hotel job were custom-designed by Symons to accept several of the magnetic holding devices. Since each blockout form was used up to 80 times, the magnets saved a significant amount of cycle time. The manufacturer quotes a price of $51 for the B-450 magnet, which measures 1 3/4x2 7/8x4 1/4 inches. Gueldner pointed out that such magnets may lose up to 20% of their strength over time. One manufacturer reports that battery-powered electromagnets are available in sizes that would work with form panels. Manufacturers caution that holding power depends on steel thickness as well as on magnet strength. A few of the magnet manufacturers, who may be able to offer more information, are listed below:
- The Magnet Store: South Gilbert Castle Rock, Colorado 80104, 303-688-3966 (800-525-3536 outside Colorado)
- Magnet Sales & Manufacturing Company: 11248 Playa Court Culver City, California 90230, 213-391-7213 (800-421-6692 outside California)
- Magnetic Division, Magni-Power Company: P.O. Box 122 Wooster, Ohio 44691, 216-264-3637 (800-422-4624 outside Ohio)