Text version of the page

LUBRICATION

tions where only very small amounts of lubricant are required, possibly over large areas. By adjustment of the drip rate higher oil delivery can be achieved to match that of an Oil-Fog lubricator at normal usage rates.The Micro-Fog principle has madepossible the application of aerosol lubrica- tion to general machine lubrication such as bearings, gears, chains etc.Both Oil-Fog and Micro-Foglubricators include a non-return valve in the syphon tube to ensure immediate lubrication as soon as the air is turned on. However forsome rapidly cycling duties or systems with small stroke cylinders it is sometimes notpossible to lubricate correctly with conven- tional lubricators. For such applications system modifications such as quick exhaust valves must be employed or a bi-directional lubricator suitably located can overcome such problems.The second type of lubricator, theinjection oil-pump is a positive displacementdevice. Because of its nature it cannot continuously deliver lubricant but has particular applications in multi-spindle nut runners where conventional lubricators will split air flows according to passageway geometry. The injection pump will deliver the same amount of lubricant to the application point every time it is cycled. This type of lubricator is often used on conveyor chains where their application will overcomeproblems of incorrectly located or adjustedconventional lubricators.Several such injectors can bemanifolded together to lubricate at several different points, but at the same frequency.Whichever type of lubricator isemployed it is important to remember that all lubricators are total loss systems in that the dispensed lubricant will reach its ‘bearing’surface and be broken down into smallerparticles and ‘lost’ as the system is cycled.The amount of oil which should bedelivered to a pneumatic system to provide sufficient lubrication is difficult to determine as all systems will be different. Pneumatic devices in a system may require different amounts of lubricant and so equipment manufacturers recommendations should always be followed, where they exist.For a general guide for mostpneumatic systems an oil output density of
Figure 29.OIL-FOG LUBRICATOR The next important step in processingcompressed air is that of introducing into the air a suitable amount of lubricant, usually oil to enable the operating equipment to perform to its requirements efficiently without exces-sive resistance or wear. Excessive resistanceto motion will result in extra power consumption and excessive wear will result in shortened equipment life. Both result in extra cost.There are two basic type of lubri-cator in general use, aerosol and injection pump.The most widely used is the aerosol,which was the first type of dependable automatic air line lubrication device, invented by Norgren in 1927.Aerosol lubricators are available intwo main types, Oil-Fog and Micro-Fog. In an Oil-Fog lubricator the fog produced generally has relatively large oil particles and so will only remain airborne for relatively short distances. As a general rule of thumb the maximum distance an Oil-Fog lubricator should be placed from the pneumatic device which it is to service is 9 metres. Large particles are more strongly affected by gravity and so Oil-Fog lubricators should not be used in attempting to lubricate a device at a higher level than the lubricator.The Micro-Fog lubricator uses aspecial fog generator to atomise only a fraction of the oil.Because the airborne fog is nowmade up of only light particles, less thanabout 2 microns in size, gravity does not have the same effect upon it and so this fog can travel not only “up-hill” but also for long distances and through more complex feed lines without wetting out in the pipe. Micro- Fog can also ensure proportionate distribu- tion through multiple lubrication outlets, ideal for multiple valve control circuits.A comparison of these two types oflubricators can lead to a simple division of them as being high delivery (Oil-Fog) or low delivery types (Micro-Fog). All of the droplets of oil shown in the Oil-Fog sight dome will be delivered into the system and for the Micro-Fog only about 5 to 10% of the droplets witnessed will be delivered. The Micro-Fog can therefore be used in applica- 60mg/m
3 is a good basic starting point.From regular inspection and servicing the optimum setting may be found by increasing or decreasing the amount delivered.

FILLING LUBRICATOR BOWLS

With all lubricators eventually the bowl or reservoir will need filling. Most Oil-Fog lubricators have a check valve fitted to allow them to be refilled whilst in use. Most Micro- Fog lubricators can be fitted with a quick fill nipple and so be topped up with lubricant, supplied at a pressure of approximately 1 bar above that within the bowl.Remote fill devices also exist whichcan do this automatically. Such devices can be used to supply several bowls or reservoirs from one central position.Another way to reduce the scheduledtask of refilling lubricators or to ensure critical operations never ‘run dry’ is toemploy a liquid level switch. Such devicesare normally float operated switches which can give an electrical signal on low or high liquid level. Such signals can then be built into a control system to fill or stop filling or give warning alarms.
14