".
Original length is represented as capital L, the coefficient of expansion
as alpha, " 
",
and the change in temperature as delta-t,
"
t". Therefore
the formula is presented as
pg.4
the feature industry this month is....
Steel Manufacturing
Steel, one of the most indispensable construction materials, also partly owes its existence to construction millwrights, who often work throughout the mills where it is made, keeping them running. A steel mill is heavy industry, and the production machines depend on the maintenance and repair that millwrights do.
Since we're on the subject of hot steel, something that we might not normally think of is the fact that even seemingly solid things, like a piece of steel, aren't really as unchanging as they look. Everything expands and contracts with changes in temperature, and if the change is great enough, the expansion will also be large enough that it must be accounted for. This must be kept in mind when millwrights are installing machinery for hot work. Thinking back to last month's lesson on coupling alignment, it would be no good to get the motor and pump aligned perfectly, if after the line starts up the pump has a final temperature much greater than ambient. The pump would "grow", rising higher from the base, and throwing the shaft alignment off. In such cases, it is actually necessary to intentionally "misalign" the machine when cold, so that at its final working temperature and size, the shafts become aligned.
The coefficient of thermal expansion for mild steel is 0.000006"/1 inch/°F rise in temperature. That is, one inch of steel will expand by 6 x 10-6 inches for each degree Fahrenheit rise in temperature. For each degree Celsius, the equivalent factor is 0.000011" or 1.1 x 10-5 inches.
That is to say, if you have a piece of steel 100 inches long, and you increase the temperature by one degree F, the steel expands 0.06" in all directions. That's sixty thou, which is a lot when you're talking coupling alignment.
The common way to express this formula is: change in length equals
original length times coefficient of expansion for the material, times the
change in temperature. Change in length is usually represented as small
delta, " ".
Original length is represented as capital L, the coefficient of expansion
as alpha, " ",
and the change in temperature as delta-t,
"t". Therefore
the formula is presented as
This general formula for change in length of materials is relevant to coupling alignment when we use the change in length to mean the change in center height (shaft height) of one of the machines. If the machine is expanding in heat, it normally expands in all directions. However, the vertical growth will not occur up and down of center because the machine is sitting on a base, preventing downward expansion. Thus vertical plane expansion is all "up". As to horizontal expansion, left and right growth is equal and thus has no effect on alignment: the shaft will remain in the center. Of course, your coupling will have to be of a type which allows for both initial misalignment and a gap between shaft ends: these conditions will be taken up when the machines reach their final operating temperature. An additional thing to keep in mind is the possibility that you might need this calculation in negative, if conditions will cause the final operation temperature to be lower than ambient. In that case, you'd be dealing with thermal contraction, which will still affect the alignment but in a downward direction!
Quiz Question:
You are doing a pump-motor alignment. The ambient temperature is
70°F. The shaft heights above the base are 16". You know
that the motor will increase in temperature by 50°C when running, and
you are told that the operating temperature of the pump will be 320°F.
Calculate how this will affect your alignment shimming as you set up
the machines.
Steel comes from iron. Iron itself, however, is not strong enough to be used in the many ways that we use steel. Therefore, carbon is added to iron in specific ways to produce steel. The amount of iron in steel varies from 90% up to around 98%, depending on the type of steel being made. In any case, steelmaking begins with the heating of iron in a blast furnace with coal (mostly in the form of coke, basically a purer form) which supplies the carbon. Limestone is also added, primarily as a purifier: impurities in the iron ore mixture separate off with the limestone as slag. When molten scrap steel is added to this purified iron in one of several possible methods (the "basic oxygen furnace", the "open hearth furnace", the "electric arc furnace"), the end result is molten steel. Of course, different alloying ingredients may be added, depending on the specific final product desired (eg: nickel for strength, tungsten for high melting-point tool steel, etc).
The molten steel must now be cooled. Traditionally, it was poured into an ingot mold, and the ingots were held until, as required, they were reheated and reduced into slabs, blooms, or billets--shapes which the mill can then roll into finished shapes. A more modern method, however, is "continuous casting", which skips the ingot stage and sends the molten steel directly from the furnace to the bloom, slab, or billet form which are cut to length and then run directly to the finishing mills. Various finishing stages include, for example for slabs, the "hot strip mill", which produces hot rolled sheets and coils, the "pickle lines" which treat and oil coils of steel, and the heat treating for coating and finishing. Blooms and billets may be sent to structural mills to produce I-beams, or rolling mills to produce bars and rods. There are as many possibilities as there are forms and uses for steel itself.
Here are a few links to steel manufacturing related sites:
The American Iron and Steel Institute (AISI) has an excellent article on continuous casting, including photos and diagrams: http://www.steel.org/learning/howmade/concast.htm. Their Steelmaking Flowline is also a terrific diagram.
The International Iron and Steel Institute has basic facts and figures about the steelmaking industry: http://www.worldsteel.org/steelmaking/intro/index.html
Here's a page with links to technology and research, steel industry member companies, trade associations, government and policy, consumer organizations, steel news and publications, and marketplace: http://www.steel.org/hotlinks/index.html
The site of steel maker Dofasco has a technology page which mentions some new lines they're putting in (millwright work!): http://www.dofasco.ca
The Ultralight Steel Auto Body Web Site describes an interesting project to reduce the weight of a car's body while maintaining strength and low cost: http://www.ulsab.org/
Expansion = center height x coefficient of expansion x temp change .
For the pump, that means delta = 16 x (6 x 10-6) x (320 - 70) [remember, you want temp change, not actual temperature]
= 0.024"
For the motor, delta = 16 x (1.1 x 10-5) x 50 [notice, this temperature change was given in Celsius].
= 0.009"
The final position of the pump will be higher than that of the motor. The difference in expansion between the motor and the pump is 0.024 - 0.009, or 0.015". Therefore, the motor must be set 0.015" high at ambient temperature. Fifteen thou more shims must be added to the motor in your Vertical Offset calculation when you do the alignment to account for this expansion.
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