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Old 22-10-08, 12:51 PM   #1
Spokey
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Default Grease - all you could ever want to know ?

I wrote this article for a magazine a year or so ago - apologies for the length but may be useful ?

Got a brake fluid one somewhere as well ....

Grease – what’s that all about then?

Grease? Well, grease is grease isn’t it?

Not quite – There was a time when grease was just a thick animal fat, more than likely tallow or lard. This was used to lubricate primitive machinery, such as the wheels of horse drawn carts. Problem was, as well as being limited in their load carrying capability, they soon went rancid and smelt bad as well as allowing corrosion to develop – not really very good as a grease then?

Modern greases have developed somewhat since the days of animal fat -
Modern lubricating grease is commonly a mineral oil, to which a thickening or gelling agent has been added. Typically, this thickener is a “metallic” soap – a soap made from the hydroxide of an alkali metal (such as lithium) and a fatty acid. Greases of this kind are available in a wide variety, each possessing certain characteristics that determine it’s precise application – low or high temperature ability, resistance to water, extreme pressure and so on.

So what is grease then?

Grease is a mixture of 3 main components – Soap, Base oil and additives. Imagine if you will, a sponge filled with water – the principle of grease is very similar. The soap thickener has a fine fibrous structure, which holds the oil in the same manner as a sponge holds water. Different soaps have different fibrous structures, each of which has an influence on the characteristics and service behaviour of the grease. Interestingly, the soap makes up only a small percentage of the actual grease, typically 5 – 20%, whereas the lubricating oil will normally be between 75 – 95%. The amount, dimensions and distribution of the fibres influence the consistency and mechanical stability of the grease. High temperature behaviour is dependant on the type of soap and the characteristics of the base oil. Pumpability is controlled by the viscosity (thickness) of the base oil, and the amount and type of thickener (soap)
For a grease to perform satisfactorily it must possess a variety of chemical and physical properties, which need to be matched to the service requirement. It must be able to resist changes to structure, consistency and performance, likely to occur as the grease is churned in bearings and between gear teeth and from environmental effects such as high temperature. Grease should not become excessively stiff with age, must be compatible with seals and gaskets. It must also be able to tolerate a degree of contamination (such as moisture) without any significant loss of performance.

Grease is designed to perform better than oil where the lubricant is needed to remain in place, whatever the position of the part it’s lubricating, especially where an oil would drip off or be flung away by rotation. It acts as a seal to prevent entry of contaminants, and sometimes exit of the lubricant if you have a leaky gearbox seal! Useful where the lubricant doesn’t need frequent replenishment or is only possible at infrequent intervals, it can carry suspended solids (such as graphite or moly) to prevent seizure. But, because of their relatively solid nature, greases do not provide the cooling function of straight oil. The main advantage of grease over oil is its potentially longer life and convenience of use regarding application, simplified maintenance and design.

So what are the properties of grease?

We know basically what grease is and what it’s supposed to do, but what about all the different types?
With oil we measure it’s viscosity – this is normally stated as either an ISO grade
(15, 32, 46 and so on) for hydraulic oils etc, or an SAE grade (10W-40, 80W90 etc) for engine and gear oils. Greases are stated as an NLGI Grade number.
The grades range from 000 – this is almost fluid, through 00, 0, 1, 2, 3 up to 6, which is literally a solid block. Most general-purpose grease will be an NLGI 2 classification – medium soft. The semi fluid greases such as NLGI 00 being used in central lubrication systems, and filled for life gearboxes.

Bear in mind though, that two greases that have the same NLGI number may have totally different base oils – the NLGI number is only a measure of the stiffness of the grease. The base oil is very important because this is that does the lubricating. Normally a mineral oil, but synthetic oils are sometimes employed where extreme conditions, such as high temperatures, are encountered.
As a rule of thumb – high speed, light load applications would use light base oil, and low speed high load applications would require heavy base oil for better load carrying ability. As an example – multipurpose grease would be an NLGI 2, with base oil somewhere around ISO 150.

Soaps (thickeners) are numerous, the range includes
  • Metallic soaps – Calcium, Lithium, Aluminium and other metals.
  • Metallic soaps with a complexing agent – Calcium complex, Lithium complex, Aluminium complex
  • Non Soap greases – Organo-clay, polyurea, carbon black

Graphite and Moly are not soaps, but extreme pressure additives that can be added to almost any grease.

That’s all well and good, but what do I need?

The most widely used grease for industrial and commercial applications is Lithium.
Lithium based grease accounts for around 75% of all grease used today.

Lithium greases function over a wide range of operating temperatures (-30º to +130º typically) They have good chemical stability with a long operating life, have good load carrying capabilities and stick well to working surfaces and have good dispensing properties. They combine the water resistant properties of the calcium grades, and the high temperature capabilities of the clay based grades – so really, they will do almost any job where grease is required.

Calcium greases are designed primarily for water resistance. They are very tacky but have a temperature limit of around 70º

Clay based greases are designed primarily for high temperatures as the soap does not melt – the limit of the temperature is dependent solely on the base oil used

Sodium greases have a fibrous structure as opposed to the “smooth buttery” structure of the other greases. Sodium grease is very sticky and particularly resistant to throw off and water wash off. Found as an NLGI 0 in power harrow gearboxes and the like.

Lithium complex, Calcium complex – these have the same properties as their non-complex brothers, but with the added properties of higher temperature range, greater mechanical stability and less oil separation

There are other greases but the greases above are the most common found in agriculture today, with lithium grades making up most of the greases available.

Where should I use certain greases?

Ball joints - Lithium grease will give good results, usually NLGI 1 or 2. Grades with the addition of Moly will give extended service intervals. Stopping any dirt or water getting in by using rubber and metal seals also helps in prolonging service life

Wheel bearings. - Possibly the most important application for grease. The introduction of disc brakes and the associated temperatures would require the high temperature properties of clay or lithium complex grease which can handle intermittent temperatures of around 200º.
Non disc brake applications, such as trailers can use lithium multipurpose, but will generally give a longer service life if lithium complex grease is used.

Universal joints – The design of these varies, as does the lubrication. Sodium based greases were used because of their tackiness, but it is now common to use the same grease as the wheel bearings, i.e. Lithium multi purpose

Shackles and pins – Lithium multi purpose is adequate with all types except those with rubber bushes, which shouldn’t be lubricated. Obviously, the main requirement is that it should be easily dispensed, not easily washed off and good at corrosion resistance.

Steering gear -Usually semi fluid grease – manufacturers recommendations should be followed as an EP grade is often specified

Gearboxes – Although normally oil lubricated, greases are employed where leakage is a problem, where the maintenance of a thick film is required to prevent corrosion and stop “dry” start-up, where a gearbox operates in unusual positions where oil would drain off, and where a gearbox is filled for life. Semi fluid (NLGI 000 or 00) greases are the norm and are different from conventional greases in that they resemble thick oil rather than grease. In modern gear greases the soap is sometimes a polymer, which has excellent mechanical stability and adhesiveness.

General greasing – As suggested, lithium grades cover virtually all applications so these are ideal for general-purpose use. If water resistance were required, a Lithium complex would be a better choice. Lithium grease with moly is better for sliding applications, high loads, open gears etc as the moly will impart some anti seize properties and leave a residual solid lubricant once the oil reserves in the grease are depleted.

So, how do I apply this grease?

The same general rules apply with grease as with oil. The main factor is that the grease should be free from contamination. Make sure that any application equipment is also kept clean, as any dirt introduced with the grease will affect the service life of the component being lubricated. Grease guns are the normal method of application – unlike a tub, or keg of grease, which once the lid is removed, the possibility of contamination is likely, a cartridge placed in a grease gun will ensure that the grease is clean when dispensed. Care should be taken to remove any dirt from the grease gun nozzle, and the grease nipple before use.
If using tubs, only remove the lid when removing grease, and replace as soon as possible – any airborne dust and dirt will make the grease an effective grinding paste! If possible, use a drum pump and lid. If you must use a paddle, screwdriver, chisel, fingers etc, make sure they are clean before you use them.

The amount of grease and the frequency of regreasing will depend on hours run, size of the bearing, working environment and type of seals employed.
“Little and often” is a good general rule of thumb for regular maintenance greasing.
One of the main factors in bearing failure is over greasing. This leads to excessive churning and overheating. It is good practice to fill a bearing housing approx 30 – 50% (and the free space in the bearing itself should be filled completely) when installing a new bearing, or cleaning and refilling an existing one

Bearing manufacturers state that, if the relubrication interval is less than six months, then the grease should be replaced after three replenishments.
If however, the replenishment intervals are longer than six months, it is recommended that all the grease be removed and replaced with fresh grease.
Obviously, factors such as working environment and the possibility of ingress of water or other contaminants into the grease / bearing. Will have an influence on regreasing.




Can I mix different greases?

As a general rule greases SHOULD NOT be mixed, the usual effect of mixing greases of various bases is for both mixed grease to soften. This will obviously affect the ability of the grease to perform properly and could result in total loss of grease
If at all possible, any old grease should be removed before a new grease is introduced, especially if its not known what the grease is that is in the bearing already.

What about storage and shelf life?

The shelf life of a grease is effected by type of grease, consistency, soap type, formulation etc. General lithium, lithium complex and calcium complex can remain stable for a considerable period of time if stored in the right conditions. As a guide, two years is a general shelf life recommendation for many types of grease.
Obviously, the most crucial thing is keeping the grease free from dirt and contaminants. Dispensing equipment should be kept clean, especially the nozzles of grease guns and such.
The surface of a pail or tin of grease should never be left with hollows or depressions after use, but should be smoothed over. Likewise pressure on grease guns and other dispensing equipment should be released immediately after use.
If possible, use grease cartridges, these are easier to prevent from becoming contaminated as they are sealed in the grease gun and if a cartridge was to become contaminated, you only scrap a small amount of grease rather than a whole barrel.

So, use good quality grease suitable for the job. Regrease little and often with clean equipment and don’t over grease.

Simple?


Cheers

Nana
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Old 22-10-08, 01:00 PM   #2
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Default Re: Grease - all you could ever want to know ?

you need to get out more

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Old 22-10-08, 01:06 PM   #3
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Default Re: Grease - all you could ever want to know ?

tell me about it - why do you think I keep buying these bikes to take to bits and polish ...
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Old 22-10-08, 02:17 PM   #4
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Default Re: Grease - all you could ever want to know ?

Ta, a good read that.
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Old 22-10-08, 02:38 PM   #5
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Default Re: Grease - all you could ever want to know ?

Cheers. Interesting read.
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Old 22-10-08, 04:32 PM   #6
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Default Re: Grease - all you could ever want to know ?

So can i take it that the short version of this is Lithium grease is good for everything and the tin of it on the shelf in the shed will last forever
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Old 22-10-08, 05:39 PM   #7
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Default Re: Grease - all you could ever want to know ?

It would appear that lithium based grease also contains less desirable qualities, in association with agriculture, whilst working on a farm a number of years ago, the farmer and myself completed a thorough greasing programme of the various plant, (tractors, dumpers, trailers, bailers, conveyors, etc), only to accidently leave the farmyard gate ajar, adjoining the next field of bovine occupants.

the following morning it was discovered the Cows had let themselves into the yard and had spent the whole night licking every conceiveable component with the faintest smear of grease on it, completely clean... It would have been impossible to remove any more grease from any component or assembly, with any greater efficiency than that achieved by the herd of milk cows.......everything shone as brightly as a new pin !!!!
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Old 22-10-08, 07:22 PM   #8
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Default Re: Grease - all you could ever want to know ?

Quote:
Originally Posted by Interceptor View Post
It would appear that lithium based grease also contains less desirable qualities, in association with agriculture, whilst working on a farm a number of years ago, the farmer and myself completed a thorough greasing programme of the various plant, (tractors, dumpers, trailers, bailers, conveyors, etc), only to accidently leave the farmyard gate ajar, adjoining the next field of bovine occupants.

the following morning it was discovered the Cows had let themselves into the yard and had spent the whole night licking every conceiveable component with the faintest smear of grease on it, completely clean... It would have been impossible to remove any more grease from any component or assembly, with any greater efficiency than that achieved by the herd of milk cows.......everything shone as brightly as a new pin !!!!
Did the milk have a brown layer floating on top the next day ...
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Old 22-10-08, 07:24 PM   #9
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Default Re: Grease - all you could ever want to know ?

Quote:
Originally Posted by en4rab View Post
So can i take it that the short version of this is Lithium grease is good for everything and the tin of it on the shelf in the shed will last forever
Yes, more or less - don't know about the last forever bit, but I have seen greases a few years old that are still fine to use.


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Old 22-10-08, 08:01 PM   #10
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Default Re: Grease - all you could ever want to know ?

Brilliant because I found some castrol bearing grease (same as what I've got now that you can get from halfrauds) in my neighbours garage tht must be about 10 years old.
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