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the feature industry this month is....
Sugar Refineries
Yet another place where millwrights work is at sugar refineries. This industry too uses its own specialized machinery as well as the omnipresent conveyors and drives which in their many varied forms are the foundation of a millwright's career. A bonus feature is that the work environment at food companies is often cleaner and free of many of the dangerous chemicals found in other industries where we might work.
The subject of bearings is one which occupies a large chunk of the formal training which millwright apprentices go through. The average person may automatically think of roller bearings when you mention bearings, although journeymen know that there are many different kinds of bearings for many different uses in machinery, each with their own rules to be followed when working with them. We will use roller bearings, also known as "anti-friction bearings", for the topic of this quick lesson anyway.
These are the bearings that almost always have an inner and outer steel ring with balls (or other-shaped rollers, maybe looking like barrels or cylinders) in between. The balls or rolling elements may be "caged", ie held in equal spacing by a "separator", or they may be loaded more closely together without one (this would be called "full complement" style). In "full complement", the load exerted upon the bearing can be higher than what the caged style can take; but on the down side, they cannot be operated at the speeds of the caged type. Depending on the position of the rolling elements, an anti-friction bearing can handle loads directed either radially (if the rings are inner and outer, and the rollers are parallel to the shaft), or axially (picture the rings being top and bottom of rollers that are located perpendicular to the shaft--a "thrust" bearing). Some bearings can take combination, or angular, loads, with the rings and rollers shaped and located for such a design.
With all these bearings to choose from, you need to be really specific when making your selection. Therefore, there is a "code" used when referring to bearings. Generally, the code will tell you the type of rolling element, the service use of the bearing (heavy-duty, medium duty, etc), the bore diameter (always in metric), and any other specific features which that bearing might have, such as a tapered bore, split ring, seals, shields, etc. It's complex, and if you aren't merely reordering the same bearing as an old one in your hand, you pretty much need a catalog to interpret all the possible codes to get just what you're looking for. Still, let's learn a bit about it just for fun.
The code will usually be 4 or more digits long.
Quiz Question:
What would a bearing with the number 6208 be like? How would this be different from a 6308? How different from a 6209?
Sugar starts out in certain plants which make lots of it during photosynthesis, such as sugar beets or sugar cane. When the plant is harvested, it is then pressed to remove the juice. This juice is then boiled until the sugar in it begins to crystallize. Syrup is removed from the crystals, which makes it into raw sugar. This is what a sugar refinery, in a country where sugar cane isn't grown, will receive as its raw material. There it will be washed and filtered, dissolving and removing the coating of molasses which is raw syrup from the initial processing, as well as any remaining plant materials. The refinery then concentrates and crystallizes it, and finally, when it is dried and packed, there's the sugar you see at the grocery store.
Here are a few links to sites related to sugar refineries:
The American Sugar Alliance explains details of how sugar is made, and also has an interesting article on "corn as sweetener": http://www.sugaralliance.org/facts.htm
The Sugar Knowledge International site has pictures of sugar cane and sugar beets, and statistics on world production by country: http://www.sucrose.com/
This site has research on the health aspects of sugar, information on the sugar industry in the U.S., and descriptions of the different types of sugar: http://www.sugar.org/facts_frame.html
6208 would be: 6 for single row ball bearing, 2 for medium duty, 08 for 8x5, ie 40mm, bore. A 6308 bearing would still have the 40mm bore but since it has a heavier service weight, it is a bigger bearing, and will have a larger outside diameter. A 6209 bearing would be bigger than 6208 also, but in this case it would have a larger inside diameter: 09x5=45mm. Its service rating would still be 2, medium duty.
See you on the next monthly update of the Construction Millwright Feature Page!
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