Percy Spencer's Brother - also an inventor
I had written about the
father of the Microwave Oven earlier today. Turns out his brother invented something that is in most home appliances and on most motors.
Meet John Alby Spencer -- inventor of the
Spencer Disk:
The Spencer Disc is a unique thermal element.
It is different from all other thermal elements in that it is inherently snap-acting.
It has been used for over thirty years in KLIXON Thermostats, which are manufactured by Spencer Thermostat Division of Metals & Controls Corporation, located in Attleboro, Massachusetts.
To date millions of KLIXON Thermostats have been manufactured and successfully used in all manner of temperature control applications.
Inevitably, people everywhere ask, "What is the Spencer Disc? How was it invented? How is it used?"
It is the purpose of this booklet to provide the answers to these questions.
This is a typically American success story that begins with a door in a furnace and an alert boy.
The story opens many years ago in a clothespin mill in northern Maine. The boy was fifteen. His job was a tough one - fireman for a wood-burning steam boiler that powered the machinery.
Clothespin machinery requires a lot of steady power and because the boiler was fired with waste chips and wood shavings from the manufacturing operations, the young fellow had to move fast to maintain a sufficient head of steam pressure in the boiler.
One day he began to puzzle over something he had noticed. Why was it, he wondered, that when the fire was well up, the round clean-out door in the top of the boiler would belly out with a loud report?
Why was it when he added more fuel and the fire cooled down temporarily, the door would snap back into its original shape?
He got an idea. He realized that the boiler was practically telling him when it needed more fuel. When the door bulged out, it meant that the last charge of fuel was burning well and the fire was hot. That was when he could put on more shavings and chips without smothering the fire. After that, the boy didn't have to run back and forth looking into the fire box to see if more fuel was needed. Instead, he waited until the door signaled. When it popped out, he knew the furnace was ready for another charge.
And a bit more about the actual operation of the Spencer Disc:
Like the common bimetallic strip type of thermal element, the Spencer Disc is made of two different metals bonded together permanently. When such material is heated, the metal on one side expands more than the metal on the other, and this tends to bend the material. Unlike a thermal element made from strip, however, the Spencer Disc is round and is dished into a concave shape. It resists being bent into the opposite direction, just as the curved bottom of an oil can resists being pushed in. As the disc gets hotter, one side expands more than the other, but the disc cannot bend slowly like a strip because it is arched.
Suddenly, the forces which have built up in the high expansion side overpower the structural resistance of the arch, and the whole disc snaps. When it is allowed to cool, it snaps right back into its original position by the reverse process. These changes of shape take place in approximately 16/100,000 of a second, and both can be preset with lasting temperature calibrations.
Very cool - these are used on coffeemakers to control temperature, on most ovens of any kind to prevent overtemperature problems, on motors to cut them out if there is an overload. Simple, cheap and bombproof.
Posted by DaveH at June 19, 2007 7:32 PM