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the feature industry this month is....
Food Packagers
A while back we looked at how construction millwrights may be found in places which make cans. Here's a bit more background about the companies that actually make things which go into those cans, specifically foods.
Welding is something that every millwright has to know how to do. It's extremely rare to have a job site where there is no welding needed. We learn the skill during our apprenticeship, and any millwright who can't weld will certainly be less employable than his brothers. Some guys specialize in welding, and may do almost no other type of millwright work on jobs requiring a lot of challenging, structural or otherwise important welds. However, even without as many special tickets, all millwrights should be able to do enough welding for things like sticking a jig to a workbench for a few items, etc.
There are a lot of different types of welding. Firstly, you can divide it into gas welding (using a torch), vs electric welding. We deal almost exclusively in electric welding. Of this type, we usually do Shielded Metal Arc welding, commonly just called arc or stick welding. It's easy to get the equipment needed for stick welding onto a construction project: all you need is a power source (electric transformers or generators), some electrodes ("rods"), electric cables, and the welder's personal protective equipment. With that, we can put down welds anywhere that we can get our hands into. You may also find MIG (magnesium-inert gas) and TIG (tungsten-inert gas) welding on some job sites, but since their setups require gas cylinders, more complex machines, and (in the case of MIG) coils of welding wire, they're just not as adaptible to the construction end of the trade.
In arc welding, heat is generated when an electric current arcs between the electrode in the welder's hand and the metal being worked on. This heat melts the metal of both the work and the rod, fusing them together in a weld. Rods are coated in various substances, and as the rod melts, the coating on it burns away creating a shield of elements to protect the weld from atmospheric contamination, and forming slag to allow slower cooling. Coatings may also be designed to stabilize the arc as well as giving desired properties to the weld metal.
Electrodes for arc welding are prefixed by "E". The 4 digit numbers which follow refer to:
For example, E-6010 would be rod with a tensile strength of 60,000 psi, all position application, cellulose coating; E-7022 would be 70,000psi strength, flat/horizontal positions, rutile coating. Stainless steel electrodes use a different numbering system indicating the type of stainless steel followed by a code for positions and coatings, eg: 309-15 is chromium/nickel steel, all-position, lime type coating.
Quiz Question:
What things must be considered about your desired weld when selecting an electrode type?
In a way, it's not much different from what the home gardener might do to preserve his crop when making preserves. Fresh food is shipped to the factory and prepared: washed, peeled, sliced, or whatever it needs. It is placed in the open cans, juice or syrup is added, and the lid is sealed on. That's when it's cooked and sterilized, not before. On the other hand, if the item being canned is not fresh fruit or vegetables, it may arrive frozen and require cooking before the cans are filled. And if the factory is actually making a recipe for canning, well then the product is made and cooked before filling into cans, too. The sealed cans still go through the sterilization step after sealing, regardless. This generally occurs under pressure and heat in a big steamer. After that, if the cans aren't pre-printed, they get labelled; then they're shipped out for sale.
Buying canned food is a lot easier than doing it yourself, but the difference from home canning may really lie in the fact that commercially preserved foods are safe and easy to store for perhaps 2 years. Can you be sure that your efforts are air-tight?
Here are a few links to sites related to food packagers:
The Australian Canned Food Information Service site has great pages on history of canning, how different foods are canned, quality assurance, and commercial cookery: http://www.cannedfood.org/
Perhaps the most well-known food canner is the Campbell's Soup Company. Their site has history of their canned product, recipes of the day, and an online shop: http://www.campbellsoups.com/
Speaking of commercial tomato products, Heinz is the only ketchup available on my grocery shelves which has the "union made" label. Their site is at: http://www.heinz.com/
Another fairly well-known canned product is juice. Here's the Welchs grape juice site: http://www.welchs.com/
And for a millwright angle, check out the site of the North American Association of Food Equipment Manufacturers, to see some of the machines used: http://www.nafem.org/index.cfm
Although some electrodes are in more common use than others due to their ability to produce good results under a wide range of conditions, these are some things which may be considered in making a selection:
desired strength of the finished product
type of steel being welded
position of the weld
thickness of the metal being welded
required ductility of finished product
weld quality (can be improved by certain coating types)
rate of cooling (with some coatings, cooling is faster allowing more rapid welding)
ease of slag removal
polarity used in the welding machine
That ought to help narrow it down--now there's no excuse for a bad weld!
See you on the next monthly update of the Construction Millwright Feature Page!
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