During my research into grease I was a little surprised to find the term tribology didn’t actually refer to grease, but to the action of two objects moving over each other.
Tribology is based on the Greek word ‘Tribos’ meaning rubbing.
When two surfaces rub together they create friction, tribology is the science of studying the friction created by the interface of two surfaces, it is commonly used with lubricants to make objects slide efficiently reducing the cause or friction or stickiness.
In 1966, British mechanical engineer Peter Jost CBE, first used the term Tribology to describe the science of friction, whilst working on the problems of lubrication & wear in industry.
But it was in 1493 Leonardo Da Vinci studied and wrote about the ‘Laws of Friction’
Obviously shaping tools & runners to reduce friction brought about huge advantages when cutting, hunting & building, especially when moving heavier objects around.
In it’s earliest form, rotating a stick in a wooden hole, will if turned quickly with a little downward pressure, create enough friction to cause heat & then fire.
This was the start of tribology and man’s journey, through to today’s world.
The Chinese were known to be using water as a lubricant as early as 3500BC & the Egyptians around 1400BC were using animal fats & Olive oil mixed with powders on their chariots.
This is the basis of grease as we know it today.
What is Grease?
Grease used for heavy machinery or underwater camera kit is incredibly different, but amazingly very similar in how it is made up, so that it work’s efficiently.
First you need an oil that will lubricate the surfaces of the parts that will rub together.
It’s very important that this oil must be compatible with the materials these parts are made from & also be able to withstand the temperatures that this assembly will be subjected to.
Next you need a thickener that will ‘hold’ the oil in the right place for as long as possible, while also complying with the oil requirements of suitability for materials & temperatures.
These two basic components are then mixed to the point they are blended as one, this is grease.
Obviously this is a simplistic view as many variations and combinations of oils & thickeners are used for a huge variety of situations, but this is sufficient for what we need to know on underwater camera kit.
So how exactly does grease work?.
When you slap some grease onto a surface it should just sit there and within it’s designed limitations, not react to temperature or the material it is sitting on.
When you place another piece of material on top, the grease will be slightly pressurised, this action will ‘shear’ the grease and allow a little oil to ‘ooze’ onto both surfaces where they contact with the grease, this oil will act as the lubrication to allow both pieces of material to slide over each other with the minimum of resistance.
Simple I hear you say!
The trick is to design the grease in such a way that it keeps enough oil to carry on working for a little longer than the equipments scheduled service time.
This is the time when the grease & seals are removed, the surfaces cleaned and checked and of course the seals & grease are replaced.
The trouble starts when….
- It does not get serviced in time
- The grease gets ‘flushed’ out
- It exceeds it’s temperature rating
- Or it gets scoured away……….
That’s when the damaging ‘Friction’ occurs, ‘O’-rings start to wear quickly, surfaces get damaged by wear or scratching and in the case of our precious U/W equipment, sooner or later it leaks!
So that’s why manufacturers always say get it serviced every 12months, they know it will last longer but…….
If any of the issues you have just read about occur, it may be only work for a very short time after.
If the ‘O’-rings get damaged it’s possible to replace these cost effectively, but if the surfaces where the ‘O’-ring sits get damaged, fixing these is a major undertaking if possible at all.
So why do manufacturers all use different greases?
Very simply the materials they use are different, most manufacturers use a local source of material to build their products.
The material they choose is best suited for the type of product they make.
Is it designed for a once only holiday use, hobby, professional or industrial purpose.
Each scenario poses questions about the different requirements and of course the solutions needed.
The most suitable rubber source covers a spectrum from natural, to totally synthetic.
And I’m sure you will agree when I say most of us couldn’t count, let alone name, the different types of rubber just used around the home.
Couple this with the materials used in a common underwater rig and you can see why the choice of grease is carefully chosen by each manufacture to match their particular equipment build.
Basic differences in grease are very hard to see, obviously some are much ‘thicker’ or stickier than others, they come in a range of colours & hues.
But it’s the chemical make up, that stops them being absorbed into the materials they are designed contact with, or from being flushed out of the system when immersed in the type of liquid they are designed to be used in.
For our purposes we can assume they are all used in fresh or salt water, but in industrial situations this may be different.
As a general rule of thumb any grease that has the same ‘base’ as the material it sits next to, will be absorbed into that material.
The most common for U/W photographers is silicone grease being used with silicone ‘O’-rings, this will cause the ‘O’-ring to swell as it absorbs the silicone oil & it will eventually go soft & saggy, I think most of us have seen this play out at some time.
The same happens with petroleum greases used on natural rubbers, it will degrade them rapidly.
But seals made from Nitrile or Chloroprene (Neoprene) will operate without problems in petroleums.
Knowing the base material of the grease is generally not information we as photographers are party to.
This can be a big problem, especially when washing kit down in say, hot soapy water.
As much of the soap we generally use will act as a ‘degreaser’ great for dishes, but not for greased ‘O’-rings.
This is fine if you have taken the ‘O’-ring out & you are cleaning it, but the ‘O’-rings in the control shafts should not be subjected to the same process, as it’s not an easy process to re-grease these seals efficiently.
So How should we clean our ‘O’-Rings?
If you can remove the ‘O’-ring you can actively clean it, degrease it and re-grease it, knowing what the seal material make up is, will help you avoid the chemicals that will destroy your ‘O’-ring.
In our underwater photography world we have only a few basic types of seal materials.
- Nitrile Butane rubber
We would recommend each time using warm water and a dry cloth, this is often all you need to remove any detritus stuck to your ‘O’-ring seal and the existing grease.
For heavily soiled seals, all of these materials will tolerate cleaning in mild warm soapy water using a ‘little’ general household washing up liquid.
It’s can also a good idea to clean your seals with the base oil used in the grease, this can sometimes be skimmed off the grease from the top of the tube.
If your seals are badly stained or have deposits that are hard to remove using the methods above, then using something more harsh as a cleaner has to be done with thought and quickly, any seal will suffer if exposed to harsh chemicals for an extended period.
Most seals used in underwater camera kit will tolerate cleaning with a refined fuel like lighter fluid, but we would recommend only applying via a cloth so any residue will evaporate rapidly.
Cleaning the seals you cannot remove is best done using mildly warm water only, any de-greasing will require the seal to be re-greased in situ.
This is only possible if by applying grease to the inner shaft, you can transfer it to the ‘dry side’ of the seal, so the shaft/control has to move in/out and rotate.
Applying grease to the outside of the seal, acts better as a detritus magnet rather than a seal lubricant.
Many divers use products like oil sprays to keep things moving in their U/W rig, metal to metal is generally OK.
But don’t deliberately put oil sprays onto any of your rubber components, or get it near the plastic windows, without knowing what chemicals are in the spray product and what the propellant that expels it are made from, these must be compatible with the ‘rubber/plastic’ you are applying it to.
Also bear in mind, that any light covering of oil will generally be removed rapidly with flushing water during your dive, so a suitable grease may be a better option as it will last a lot longer.
I hope this brief explanation has helped you understand a little more about grease, the relationship between the components that are used in manufacture and a glimpse into the world of Tribology.
A fascinating subject that supports almost every single thing that moves, that we use today.