Product category:
Lubrication - lubricants and lubrication systems
News Release from: Kluber Lubrication GB | Subject: Dry lubrication
Edited by the Manufacturingtalk Editorial
Team on 22 August 2002
Dry lubrication creates new
perspectives!
What makes dry lubrication an efficient alternative to conventional lubricating oils is not only clean handling and precise metering, but also environmental compatibility.
When mechanics mess about with Mika Hakkinen's McLaren they are far from getting dirty That is because the oil system in formula-1 racing cars is based on a process which is becoming an issue for an increasing number of production companies - dry Lubrication
This article was originally published on Manufacturingtalk on 18 Nov 2003 at 8.00am (UK)
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What makes dry lubrication an efficient alternative to conventional lubricating oils is not only clean handling and precise metering, but also environmental compatibility.
Experts are certain that the manifold application possibilities of dry lubrication create new perspectives also in view of economic and ecological benefits.
Again and again, machine element leakage, such as that of gears or rolling bearings, the breakdown of lubrication installations or inadequate maintenance, cause environmental as well as economic problems: lubricant leakage does not only contaminate skin and clothes (the lesser evil), but it also prevents the lubricant from being properly fed to the lube point and, if the worst comes to the worst, causes complete system failure.
Further reading
Lubrication switch saves bearing breakdowns
A major user of polythene extruders had a major problem of repetitive large taper bearing lubrication break-down, which was solved by switching to a grease lubricant.
Lubrication change solves oven conveyor problems
Seven major bakeries had contacted a lubrication producer over major problems with oven conveyor chains.
The solution may also be of interest to other industrial oven operators too.
Lubricant standards change caused problems
Historically, a major UK mineral water processing company has used a mineral oil for lubrication of an air compressor, but a lubricants regulation change generated problems with new lubricants.
Users of dry lubrication will not encounter such risks.
Unlike fluid lubricants which are applied by a sprayer, drip-feeder or a brush, dry lubrication is used as follows: * coating (surface-separating effect by a layer adhering firmly to the component's surface).
* self-lubricating compounds or dry depots (dry lubricant contained in depots, which gets between the sliding surfaces by "chalking" and thus reduces wear).
* Incorporated lubrication (the lubricant is already incorporated in the material, which does not need any additional lubricant for low-wear operation).
Dry lubrication must prevent wear as efficiently as any other lubricant.
Dr Ing Rudolf Zechel, expert in dry lubrication at the special lubricant manufacturer Klueber Lubrication Muenchen KG, presents the three application methods and their advantages.
Coating: The "pencil" principle - bonded coatings are characterised by a thin layer adhering firmly to the component surface.
Wear protection is not the result of extreme hardness, as is the case for example with hard material coating, but by optimising friction coefficients and sliding properties.
Since the layers are very thin, the shear stress occurring within the layer is fairly low and can be transferred from the coating across the boundary to the base material without causing problems.
Bonded coatings are processed similarly to other industrial lacquers, but they have different components: solid lubricant (PTFE, MOS2, graphite or a combination of solid lubricants), binder (organic or inorganic resin of one or two components), organic solvent or water.
Further components may be fillers (e g colouring agents) or additives (e.g corrosion inhibitors).
To explain the effect of such a coating, Rudolf Zechel makes his case with a pencil: "When friction sets in, the bonded coating is gradually worn off', like with this pencil - it keeps on writing until the lead has been used up".
That is why we also speak of a transfer or abrasive lubrication which ensures that a film acts as a separating and lubricating layer reducing friction and wear between the friction bodies in contact.
The service life of a bonded coating is limited, depending on a large variety of product characteristics, especially the binder's resistance to wear and the coating's elasticity and adhesion to the component surface.
The advantages of dry lubrication by coating speak for themselves: * very wide service temperature range.
* efficient wear protection.
* lifetime lubrication.
* prevention of stick slip and fretting corrosion.
* vacuum and radiation resistance.
* very little risk of environmental pollution.
* high cost saving potential.
All these advantages were defined in extensive tests performed by Kluber Lubrication in Munich : "As is common in tribology and lubrication engineering, tests are required for bonded coatings to evaluate their characteristics", explains Rudolf Zechel.
Besides measurements performed on original components, there are also suitable lab test systems which are extremely thorough and in most cases standardised (DIN).
The use of bonded coatings is restricted to applications where sliding distances are not too long and the opposing bodies not too rough.
Provided their capacity limits are observed, bonded coatings offer excellent characteristics for multiple applications, particularly in bearing technology, engine and gear components, screw-type connections and elastomers.
Self-lubricating compounds (dry depots): always top of the class - for special applications involving high loads and low speeds, so called compounds have been developed.
Kluber expert Rudolf Zechel explains the function of such compounds by taking the example of a self-lubricating compound for rolling bearings: "Before the bearing is put into operation, it is immersed into a separating agent and filled with the compound.
After hardening and free rotation of the bearing, a very small quantity of the hardened compound chalks off when the bearing starts up.
This enables the compound to ensure continuous dry lubrication." The rolling movement provides a consistent transfer of dry lubricant to the friction surfaces of the bearing (chalking effect).
The properties of the compound ensure that the chalking quantity is constant within a certain area.
Excessive chalking would otherwise entail a risk of bearing jamming, while insufficient chalking would mean increased wear from lubricant starvation.
These bearing compounds offer many advantages: * "clean" lubrication without lubricant dripping.
* thermal stability up to 550 degC (no temperature-related change in consistency/viscosity.
* lifetime lubrication.
* excellent corrosion protection.
* resistance to water and oil.
* water as solvent.
Both filled deep-groove ball bearings and spherical roller bearings were subjected to running tests, which were based on the test methods laid down in the SKF ROF rolling bearing test and the FAG FE 8 rolling bearing test.
The results show that the bearing compound can be used for high loads.
All known applications lie within a speed range of up to 50,000 mm/min.
Predominant applications include drive, idler and guide rollers in conveyor systems, bakery machines, furnace trolleys, autoclaves and strand guide rollers in steel mills.
In this context, R.
Zechel refers to a similar compound developed for dry lubrication purposes: "We have tested this compound intensively on a sliding bearing test rig and the result is tremendous: very good friction coefficients are achieved with pure dry lubrication! Tribo-system materials: - lubricant and material all in one.
Probably the most convenient option for the user is to utilise dry components without having to think about the lubrication aspect.
This is possible by using tribo-system materials which already include the lubricant and hence ensure lifetime lubrication.
Basically, there are options for manufacturing components of this kind either by cutting operations or by injection-moulding.
Depending on the number of pieces and the economic efficiency aimed at, the materials will vary in their structure.
The lubricating effect of injection-mouldable tribo-system materials is rooted in the restricted miscibility of lubricant and plastic.
During the manufacture of tribo-system materials, the lubricating constituents diffuse to the surface, thus forming a plastic surface with lubricating properties.
For this reason, these components must not be subsequently machined, as this may remove all or part of the lubricationally effective area.
All in all, Kluber Lubrication considers dry lubrication a real alternative to lubrication by oil or grease.
Rudolf Zechel feels very positive: "because of today's requirements in terms of consistent performance, quality, convenience, cost reduction and environmental protection, the trend towards dry lubrication looks set to continue". Request a free brochure from Kluber Lubrication GB ...
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