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the feature industry this month is....
Paper Manufacturing
An industry which plays a big part in employing construction millwrights is paper manufacturers. Whether they make writing paper, cardboard, or toilet paper; whether they use pure virgin wood chips or 100% recycled materials; paper mills have a lot of machinery. And machinery needs maintenance, care, and sometimes repairs or replacement; it goes out of date and gets upgraded; or a mill might simply change its product line; any of these conditions is a job for a millwright. Sometimes they can be messy jobs, since this industry needs to use a LOT of water in its processes, but any job is a good job when you're doing millwright work!
Now, before we get to the actual story on the feature industry, it's time to do your homework. Whenever you have machinery, you have to have a source of power to drive them. At home, you just plug in the cord and your drill works. At a plant, with huge rollers to turn or enormous pumps to drive, you probably first start out with an electric motor but then you transmit its power through various gears, belts, or chains in the proper ratio to control your final working machine. The motor might be connected to the pump by a line shaft, or directly through one of many kinds of couplings. This transmission of power can be tricky, though: you have to do it efficiently so that you aren't, among other things, overworking the initial motor or creating imbalances with damaging vibrations. Perhaps the most important thing to get right in this kind of system is the coupling alignment. Depending on the machines, tolerances for both angular and offset alignment can be less than a thousandth of an inch.
Angular misalignment
Offset misalignment:
Coupling alignment is most often measured with dial indicators. As you turn the shafts of the motor and driven machine (let's say a pump), any misalignment will show up as non-parallel movements which the dial indicates. Misalignment can also be measured with lasers connected to computers, which can not only sense and measure the degree of misalignment, but also calculate how to go about correcting it. However, these are expensive and sometimes it's just not possible to set them up in some awkward location where the coupling needs to be made. One of a millwright's skills still remains the reading and interpretation of dial indicator readings.
To simplify a difficult subject for the purposes of this page, I will just quote a common "rule of thumb" used to calculate alignment problems. This rule says that the shims to use to correct vertical angular misalignment equals the total indicator reading multiplied by the distance between the feet of the moveable machine, divided by the "wipe diameter" at which you set your indicator. A companion rule of thumb regarding vertical offset alignment goes that the shims required is equal to the total indicator reading divided by 2. That is to say:
V.A. shims required = T.I.R. x bolt center
wipe diameter
V.O. shims required = T.I.R. / 2
Horizontal misalignment, which is just as important as vertical, can be corrected by jacking or otherwise moving the machine side to side, so does not require a shim calculation.
Quiz Question:
You set up your dial indicator on the pump and motor to be coupled, in the manner pictured. In this case, for argument's sake, let's say it is the pump which is the moveable unit. The front and back foot pads on the pump are 12 inches apart. The diameter on the face of the coupling where the dial indicator is resting is six inches. You zero the indicator in the 12 o'clock position, and then rotate the two shafts together until the indicator is in the 6 o'clock position. By that point, you have watched the indicator move until it is now reading +10. Calculate the shims you want to put under the pump feet to correct angular misalignment.
Part 2.
Having done that, you now set up your indicator on the coupling rim to measure
offset misalignment. You zero the indicator at 12 o'clock, and rotate
the shafts to the 6 o'clock position.. There, the reading is +20.
What does this mean you should now do about corrective shimming?
Paper manufacturing is important to our society, and probably getting more important with the increased use of computers in business and at home. (Anyone remember the idealism when computers were young, specifically the hyperbole about them making paperwork obsolete?)
Basically, paper is made from pulp which can come from wood or recycled paper. In the case of wood, the pulpwood logs must be debarked (by abrasion), chipped up, and then cooked to dissolve the lignin which binds the fibers. This cooking process is actually called a "digester". It involves heat, pressure, and chemicals. After the digester process is complete, the fibers are free and in the "blow pit" they can be suspended in water and separated. By this point it is called pulp.The pulp will then be washed of the cooking chemicals, bleached, and "refined". Refining means roughening the surface of the pulp fibers so that they will stick together as paper during the forming process.
In the case of recycled paper, these processes have already been done, so it just needs to be broken down into its component fibers again. Things like staples and plastic strips have to be removed. This pulp has to be processed with ink-removing chemicals, and then these chemicals must be themselves removed. One interesting method is "flotation", in which the dissolved ink particles are removed from the mix by attaching them to air bubbles!
In both cases, the pulp at this point is ready to become paper although other chemicals may still be added to affect the paper's end properties--such as dyes, for example. Water is now added to the pulp and then this liquid concoction is converted into mats of paper by pouring it over fabric in thin layers. The mats are then dried by pressing the water out and then winding it through hot dryer rolls. From that point, the paper's treatment depends on its final purpose: it can be treated with sizing to allow it to accept printer's ink; it can be pressed smooth by polished rollers; it can be cut and rolled into packaging materials; and so on.
Here are some links to paper manufacturing related sites:
The University of Minnesota's Forest Products Management Development Institute has a great site on pulp & fiber products, which includes an illustrated step-by-step explanation of the stages in papermaking: http://www.forestprod.org/cdromdemo/pf/pf8.html
The Union Camp company's site also has a nice clear summary of how paper is made, including diagram: http://www.unioncamp.com/paper/technology/how.html
Here's a listing of paper mills with sites on the web: http://www.onlinevalvemagazine.com/pulp.htm
This is a link to the Canadian union which represents the most workers in paper mills: the Communications, Energy, and Paperworkers: http://www.cep.ca/en/
Here's a site called "Recycler's World", which lists sources and buyers for recycled materials of all kinds. For example, a paper mill looking for raw materials to make recycled paper would shop here; but I thought it was interesting too. I've linked you right into the paper section: http://www.recycle.net/recycle/Paper/index.html
This is an article in the Environmental Science & Engineering magazine about a millwright job that a paper recycling mill ordered to improve its filtering ability, in terms of removal of debris from the process water. The article also gives you a bit of a sense of what's going on, machinery-wise, in a recycling plant: http://www.esemag.com/0798/screen.html
1. For angular misalignment, use the formula: Shims = (T.I.R. x bolt center)/wipe diameter
Therefore, shims required = (0.010 x 12) / 6; which works out to 0.020".
By looking at the numbers you can tell that these 20 thou shims are needed under the rear feet of the pump (the feet furthest away from the coupling).
2. For offset misalignment, use the formula: Shims = T.I.R. / 2
Therefore, shims required = 0.020 / 2; which works out to 0.010"
Since the angular correction is not involved in the offset calculation, you need to add 10 thou shims to ALL feet.
Thus according to your calculations, you will now place 10 thou shims under the front feet, and 30 thou shims under the rear feet.
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