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the feature industry this month is....
Tin Can Making
Last month we talked about steel manufacturing. Well, here's one of the thousands of things that steel is used for, and another industry in which construction millwrights work. Cans are used for so many things: there are soda pop cans, food cans, spray cans for all kinds of products. Although I mention it now for the link to steel, of course cans are often made out of aluminum, too. The basic method is the same. Besides, ultimately, when a millwright works on a machine it doesn't really matter what, specifically, the machine produces: the millwright's job is to get the machine working right, whether that means making cans or cars. A gear is a gear; a hydraulic valve doesn't change; and so on. However, it's still always fascinating to learn about a new industry, and the opportunities to do so are just more of the great things about this trade.
We've been doing a lot of math questions lately in the quizzes, so let's take a break and learn about something more personal. In any kind of construction work there are many hazards, and workers must be vigilant to avoid becoming injured or ill. One thing you can't do is stop breathing, so this month let's focus on airborne hazards. Equipment, materials, and manufacturing methods all have the ability to create respiratory dangers. These may include gases, vapours (the gaseous form of a liquid), fumes (the gaseous form of a solid--most often encountered as welding fume), mists (small airborne droplets of liquid), or dusts.
Procedures and machinery can be changed to minimize the danger. The building or area can be ventilated, guarded, or enclosed, for example. But often the problem remains and people in the area are still exposed, leaving them with little alternative but masks or 'respirators'.
Respirators are divided into two types: "air purifying" and "supplied air". Air purifying use filters (either 'mechanical' for dusts or 'chemical' for hazardous gases and vapours) to reduce contaminants in the air before you breathe it. Supplied air allow you to avoid breathing the contaminated air altogether, since in that way you are hooked up to a separate air source (airline, air tank).
If the problem with the air you are working in happens to be that there isn't enough oxygen (eg in certain enclosed spaces), then you have no choice but to use the supplied air solution. Also, certain hazardous gases are so deadly even in the smallest amounts that you can only trust using supplied air. More often, however, the hazard is a gas or vapour for which the solution is to wear a properly fitting (that is, no leaks around your face which would allow the contaminated air to be breathed) chemical filter air-purifying respirator. The filters have a colour-coding system to help you identify which type to use.
| dusts, mists, fumes | grey |
| dusts, mists, fumes, and radionuclides | purple |
| organic vapours | black |
| acid gases | white |
| ammonia | green |
| acid gases and organic vapours | yellow |
Quiz Question:
You are working in a large shallow machinery-access pit. Assume you have
done your confined-space testing procedures and found the oxygen level to
be acceptable. You are welding stainless steel. There is another tradesman
working nearby who is applying a polyurethane coating to seal a section
of floor. Do you think either of you should be wearing respiratory
protection? If so, what should you use?
At a factory making cans, the metal (often steel with a thin coating of tin) arrives in the form of thin sheets rolled into coils. The coils may be unrolled and cut into rectangles, which then get welded into a can without top or bottom. Another method is to pass the metal through a punch-press to be formed into a shallow cup, which then gets rolled and stretched into a can with integral bottom (but still no top), or further punched until it reaches that final shape. The factory also makes the tops, and bottoms if required, by punching more flat metal sheets into the required size and shape. (A factory of this type is often also able to manufacture lids for glass jars in this same way.) Next, if the cans being made are of the first type, the bottoms get sealed to the open cylinders. Cans also go through a step called "necking-in", which alters the shape of the top ends to fit the soon-to-be-added tops.
Usually too, the finished cans are not just blank metal, but product-specific: think of any beverage can--they've got the colourful logo on them, right? Therefore, an additional feature which is often part of the can manufacturing line is to imprint the final product's design onto the steel. This may be done at the flat metal stage or at the formed open can stage, but basically involves sending the can through series of machines which bake the colours into the metal up to four at a time until the final design is complete. Also, protective coatings are applied to the interiors of the cans.
Finally, the open cans are shipped to the manufacturers of the product which is to be canned, and after filling, the lids are put on at that location.
Here are a few links to sites related to can manufacturing:
The Can Manufacturers Institute has a great site abut the industry. Check out their "How Cans are Made" page including diagrams: http://www.cancentral.com/howmade.htm
The site of the International Tin Research Institute explains clearly the principles behind food canning, can manufacturing, and even recycling of cans: http://www.itri.co.uk/process.htm
American Aluminum in New Jersey has a page which gives specifics on their aluminum cans, size tolerances and processes. http://www.americanaluminu.thomasregister.com/olc/americanaluminu/five.htm
Here's a page describing a project at the Coors Brewing Company to improve the external surface printing process on the cans they make: http://www.pprc.org/pprc/rpd/fedfund/doe/doe_oit/uvcuring.html
The Kobe Steel Ltd. company explains the pros of aluminum use in can making: http://www.kobelco.co.jp/column/column-e/messages/14.html
Reynolds Metals talks about the introduction of aluminum use: http://www.rmc.com/corp/history/redefine.html
Well, first of all we hope that one of you has made sure that there is no possibility of danger from welding sparks contacting the product that he is applying. If there is, one of you better do something else till the other guy is done! Making that assumption, though, the next question would be whether or not you need supplied air. Since you've got the results from the "sniffer" that the oxygen level is OK, it's likely not a necessity, but it never hurts to check with someone from the safety office on site, if there is one. Anyway, you really both should be wearing at least an air-purifying respirator. Welding of any kind gives off fumes, and the welding of stainless gives off some extra toxic substances. So you need a "grey" filter for your work. The other guy's hazard is the chemical he's working with. That isn't a dust or fume--it comes under the category of organic vapour. So he needs a "black" filter. Now, if you are so close that you can smell his sealant and he can smell your fume, that means you should each be protected against both hazards. Combination cartridges are available, so your best answer is: both of you want a grey/black combination cartridge for air-purifying respirators.
See you on the next monthly update of the Construction Millwright Feature Page!
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