Here is the diagram of a chain
drive setup you are inspecting.
pg.4
the feature industry this month is....
Beer and Breweries
Yes, it's an industry that many people are fond of. But when you're a millwright, you might think of a conveyor system or some fancy machines, instead of a pool party! Breweries need our mechanical expertise just as much as some of us may need that industry's products. (And to be perfectly clear, when I've done work at breweries, they always enforce a strict no-drinking policy on their job sites. If you want to drink that badly, then you obviously don't want the job that much.) Nevertheless, it's still an interesting job assignment, adding to the variety which makes millwrighting so great.
Conveyor systems are a big part of any factory. And whatever the system, somewhere it is run by a motor; and the power that motor puts out must be transferred to the conveyor. One of the many ways to do this is by a chain connecting the motor's output shaft to a drive roller on the conveyor system, via sprockets. Chain drives are more efficient and hardier than belt drives, and are usually cheaper and simpler than gear drives. However, they require lubrication and are often noisier than belt drives, and do not have the load capacities of gear drives. In other words, there is no one perfect system! For this month, let's learn a bit more about chains.
There are actually many types of chain, but the type you normally think of is correctly called, "precision type roller drive chain". When it is put on sprockets, it produces "positive" drive--that is, as each link of the chain meshes with the teeth on the sprockets, the ratio between drive and driven is maintained without slipping or power loss. This chain is numbered according to its size: if its pitch is 3/4", for example, it will contain the number "6", for 6 eighths of an inch. This number will be followed by a number which represents the type of roller: "0" is standard roller, "2" is large roller, "5" is rollerless, etc. The only kind of chain we'll deal with in this quick lesson is standard, "0". Therefore, a standard chain of 3/4" pitch would be known as "60" chain.
An ideal amount of contact between chain and sprocket is 120 degrees of the circle; of course, this is affected by the size of the sprockets, the distance between them, and the tension of the chain. To achieve this ideal as closely as possible, the millwright has a few "rules of thumb" to help him:
Quiz Question:
Here is the diagram of a chain
drive setup you are inspecting.
It consists of "50" chain. You've just replaced a sprocket, and now you're putting it back together. You measure the pitch of this chain at 0.638". Do you put new chain on here, or use the old one? When you install the chain, how much slack should there be in it?
Many people now are making their own beer, so this little feature on brewing may be well-known to you already. However, these are the basics: the ingredients of beer are mainly water, barley, and hops. Other more minor ingredients make for different flavours, for as we all know there are hundreds of brews to choose from at the local beer store. The alcohol is created by the action of yeast during fermentation, with different yeasts used in different varieties (ie lager/ale/etc.).
First the grains are milled to the right texture, then cooked separately. The barley is roasted and malted. Then the ingredients are mixed, and allowed to settle and clarify. Next the mix is boiled in the "brew kettle" to concentrate and develop the flavours, then cooled and allowed to ferment. It is then aged, and finally filtered before being bottled or canned. Of course there are also many inspection steps throughout the process. When you also consider the lines for taking back the "empties" and preparing them for reuse, you can see that a brewery has quite a lot of mechanical equipment and operations which require the care of the millwright. See, it's not all just fun and games after all, is it?!
Here are a few links to sites related to beer and breweries:
Take a virtual brewery tour at either
The "Beermasters" site has
This site has a brewery list and its author's personal ratings of many beers; also a jokes page: http://beerismylife.com
This is the American Homebrewers Association home page: http://beertown.org
The BreWorld site has info on breweries, conferences, organizations, beer making, and even a bulletin board in there somewhere: http://www.breworld.com/
And here's a site that has links to nearly every brewery on the web: http://www.people.virginia.edu/~rmr3g/breweries.html
Well, "50" chain has a pitch of 5x 1/8 or 5/8". In decimals, that's 0.625". According to your measurements, therefore, the stretch is less than 3%: you've got about 2.1%, actually. So you could reuse this chain. However, since this is obviously a relatively small piece of chain, and therefore not excessively costly, it is most likely that in practice you would put new chain here anyway. Of course it depends on the policy of the factory that owns the system, their tolerance for wear vs purchase costs, their maintenance schedule, etc. It may not be up to you, but at least you can give them the facts!
Once you've got that out of the way, and you're putting the chain on, it will definitely be up to you to do it right, though. So what's your ideal slack? Remember the rule of thumb says 2% of the horizontal center distance. The reason for this is, of course, because the more vertical the chain, the more likely it is that excessive slack will cause it to jump teeth; therefore, more slack can be tolerated the more horizontal the chain is. In this example, the horizontal center measurement is 12". Two percent of that is 0.24 or approximately 1/4", and that's your answer. Finally, the slack should be on the unloaded span, ie the "back side" of the drive sprocket.
See you on the next monthly update of the Construction Millwright Feature Page!
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