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Toronto Power Company Generating Station | | | On the Side of Caution | ![]() |
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Toronto Power Company Generating Station | | | On the Side of Caution | ![]() |
The flat box wrenches laying on the plastic sheet are "slugging wrenches". they are the most basic powerplant wrench out there. Slugging wrenches are box wrenches specifically made to be struck with a sledge hammer (AKA "Beater"). Once a nut or bolt is run up tight using plain muscle power on the wrench, it often has to be "slugged up". This is where the slugging happens. The slug wrench has a softer portion of the body designed to take the blow of a steel sledge. At least a 16 lb sledge is used, sometimes a 25 lb.
Three people often are required to slug: one places the wrench on the nut or bolt head and may jam it there with the sole of their boot or with a hunk of wood. The next person has a rope tied thru a hole in the hammer handle, and pulls hard on the rope. These two people have to keep the wrench hard against the bolt or nut and "take the bounce out". When they have the wrench "solid", the third person wales it with the beater.
There are two criteria for how much slugging is needed. If it is possible, an engineer (such as myself), will calculate the "stretch" of the studbolt to produce a given clamping force. Measurements are taken with micrometers or dial indicators once the bolt is snugged. Then, it is slugged and measurements taken again until the required "stretch" is had. The other method is "ring of the wrench", how the wrench rings and how the hammer feels.
Nowadays, slugging and using heavy "cheaters" (pipe extensions) on wrench handles is vanishing. Hydraulic wrenching systems make "breaking" or "making up" big bolting an easy and consistent proposition. I've worked many tubine overhauls where we slugged, and it wore out even the strongest people. We used to rotate the three people, so each took a turn holding the rope while the next person took a turn swinging the sledge. I've seen mechanics and millwrights of all shapes and sizes take their turn slugging. On one turbine overhaul, we had millwrights whose average age was over 65. I was in my 40's at the time. As engineer running the job, I was not supposed to handle the tools. I saw the older men wearing themselves out, so I used to take a turn slugging to give them a rest.
Turbine work is special- the parts are huge, but the degree of accuracy is quite tight. Even those old units would be built to tolerances down in the thousandths of an inch. A human hair is about 0.0015", paper is about 0.,004", so big as those parts are, that is how accurate the work is. A misplace blow of the sledgte can do untold harm when you are working on the turbine or generator, massive as they may be.
You've seen some of the wrenches, but you've not seen the "rigging" to take a unit apart and put it together. The cable slings and shackles even for these smaller old units are bigger than what most people might be used to. Makes the wire rope and hook on a tow truck winch look like a light fishing line.