what is grease they use in gears and stuff? Why does it need to be replaced occasionally?
In: Engineering
The grease/lubricant is applied to parts that will frequently be exposed to friction via contact with other parts. The grease reduces the friction, thus extending the life of the specific part. The grease has to be replaced because over time it breaks down and loses the qualities which make it good for reducing friction.
Take a simple example, a bicycle with a chain, sprocket, and derailleur set up. Basically the standard cog change shifter that we understand for most bicycles. The metal touchpoints is the chain and the sprocket. A standard maintenance is to scrub the sprockets and then clean each link on the chain. Then, you do a dab of grease/lubricant on each chain link to assist smooth transition from different sprockets and to keep it from squeaking and sounding cruddy.
In the case of the bike, you have to replace it because, being that it is exposed to the elements, dirt and grime build up and that reduces the effectiveness of the lubrication. In, say, a wet dual clutch transmission, like many transmissions in small VW/Audi/Skoda cars; the lubricant loses effectiveness due to heat. Same reason you change the oil in your car’s engine.
Whenever you have two pieces of metal that have to rub against each other you usually need lubricant and often lubricant plus a bearing. Without that the metal would become so hot and scrape together so hard that they can literally change shape. You don’t want that.
You could be quite a bit more specific if you are asking about some particular object or machine, but generally speaking grease is a petroleum product, like oil, oil is meant to flow and grease is meant to sit where it is applied.
Fat could also be considered grease, imagine butter, but it would break down very quickly if used as machine lubricant.
That brings us to heat, bearing grease will be stable at several hundred degrees, maintaining it’s greasiness so to speak. Imagine a skateboard wheel, there is a fixed axle, and the wheel has to spin around to roll right? The middle of the wheel has metal ball bearings to allow it to roll and those are in metal housing, the bearings spinning around in the housing produce friction and heat, which wears the metal, the grease sits in there to slow that process and let the bearing run smoothly for a long time
Eventually the grease gets old and environmental contaminants make it lose effectiveness so you go in and put fresh grease in if you’re servicing something that hasn’t had it in a while
When they take oil and make gasoline, many other substances come from the process as well. The lighter ones are gases and fine oils. The heavier ones are diesel, grease, bunker oil, and other things.
People have come up uses for virtually all of the fractions. Bunker oil is the sludge at the bottom, and the use they found is to burn it at sea for ship’s fuel.
You know how machines need oil to run smoothly without getting stuck?
Grease is just oil mixed with something to make it thicker. Usually some kind of soap.
Why do this? The main reason is that oil tends to drip downwards and get lost. With grease, it sticks to the place you need it. Then over time, the grease “bleeds” small amounts of oil and the machine stays lubricated longer.
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