Wednesday, 28 November 2012

Lubricant? What are they and why do certain machines needs it?


The main purpose of lubricants is to separate the sliding or rolling of 2 or more different surfaces so that it reduces friction, the lubricant works by forming a cushion of lubricant molecule between the different surfaces; if the right lubricant is used for the right machinery, the lubricant will keep the surface apart even when its squeezed by high contact pressure. As the lubricant moves on the surface of the material, the lubricant is subjected and offers some resistant on both of the surfaces; this is far less than 2 different surfaces in dry contact.

Further more, another advantage of lubricants is that a steady flow of lubricant cools down the machinery by carrying the heat generated away from the moving part, the surface which is covered in lubricant cleans the surface by carrying away the deposits with it and also it minimises oxidation; corrosion can lead to rust and weakening of the material. If the surface of the material is exposed to oxygen (O2) and moist (H2O) it can cause corrosion witch will eventually cause rust on the surface of the material. Rust will eventually weaken the material and will increase friction between the surfaces. 

There are 3 main types of lubricants, synthetic oil, grease and graphite. Synthetic oil is a lubricant with is engineered for the job of a conventional lubricant, but much better. As they can be specifically be designed to fulfil a particular need. However because of this synthetic oil is very costly to produce and there for more expensive to buy, it can offer significant performance as it remain stable in extreme temperature.
All lubricants fall into one of their three different lubricant categories; liquid (oil), semi-liquid (grease) and solid lubricant (graphite). The lubricant are made from vegetable oil, synthetic base stock and minerals witch are hydrocarbon, hydrocarbons is a compound witch only contains hydrogen and carbon, hence the name “hydrocarbon”, also graphite is only made from carbon (c). raw lubricants are not in used because if additives aren’t added the raw lubricant alone can over heat, catch fire or evaporate which can lead to both of the surfaces to touch whilst dry which can led to irreparable damages. To prevent this from happening, all lubricants are processed to remove impurities and chemical such as additives are added.
The first main lubricant that is mostly used in formula 1 engine are synthetic oil, synthetic oil is different from the other lubricants because synthetic oil had polymer added to mineral oils to enhance there properties, furthermore, various types of ester, silicone and other polymers are added mainly to increase the viscosity and the wear resistant of the lubricant.
The second main lubricant used is grease, grease is mainly used for wheel bearing because it can function for a long period of time with out needed attention. However, grease doesn’t dissipate heat generated as well as liquid oil because of its higher viscosity compared to liquid oil. Graphite is not used on its own as it will turn into fine particles which is useless for the machine however graphite is a very useful lubrication when mixed with grease making Graphite grease, graphite is entirely made of carbon atoms only. Carbon bonded to 3 other carbon molecules making a lot of hexagon together. Since carbon could make 4 bonds in total it loses an electron from its outer shell so as each carbon loses an electron, they form a “cloud” of electron between each layer of carbon hexagon allowing them to slide over each other witch makes it an effective lubricant.
The last main lubricant is cutting fluid, this fluid is mainly used whilst cutting, hence the name “Cutting Fluid” this is used to keep materials clean whilst being cut and cooled so that the cutting edge doesn’t “stick” to the material whilst being cut or doesn't wear off easily. Lastly, they use this so that it doesn’t oxidise and give the material a good finish.

There are 3 main oil lubrication system, total loss, self contained and re-circulation. Total loss lubrication is when the oil is applied to the moving pars by means of an oil can or an aerosol spray, hence the name “total loss” because it needs to be reapplied once the oil evaporated, drips, takes in dust or dirt and becomes a semi solidified lubricant an example of this is a chain bike, the bike chain is lubricated using this method and needs to be re-applied once the chain has been cleaned or the lubricant has solidify. Another method witch is used on large equipments is supplying lubrication oil or oil mist periodically for a central reservoir by means of having a manual control or a semi-automatic pump.
The second method is self-contained, self-contained lubrication self contains the lubricant in a reservoir. Hence the name “self-contained lubrication” for example, the gearbox of a car is generally lubricated this way.
As shown on the picture, the partly submerged arm in the lubricant, "splashes" the oil sump to lubricate all moving parts, this process is known as “splash lubrication” oil is carried up to the other parts of the gears that are not submerge or/and need lubricant, this also creates a mist inside which keeps the gears well lubricated.
The last lubrication process witch is used is “re-circulating lubrication”, the oil from the reserve is fed under pressure through a filter  directly to the moving part using the delivery pump, the lubricant continuous and after each passing over the contact surface the oil runs back into the reservoir under the effects of gravity.
In an engineering workshop lathes uses “splash lubrication” to lubricate the gearbox, splash lubricant works by having one gear or more which is partly submerged in oil (show in diagram before). Lathes have been designed this way because this process is much more efficient for this machine, the splash will create an oil mist and will keep the gears lubricated and helps the gears moving. The best lubricant to use for this job is synthetic oil because this lubricate would be able to handle the pressure of the lathe and also it is engineered for a curtain job, the synthetic oil has an excellent viscosity for this job. If I would design a lathe I would use this process because this process is cost effective and also it is much more effective.