With modern machinery constantly evolving, in terms of both complexity and sensitivity, plant managers face the ever-present challenge of updating maintenance practices while keeping pace with production demands.
One of the most important aspects of any overall maintenance and reliability programme is the effective lubrication of rotating and moving parts whose efficiency is crucial to optimal uptime. ‘Fit and forget’ auto lubricators are often seen as a solution to this problem and, while they can free up lubrication engineers to deal with more complex tasks, truly ‘forgetting’ an autolube device can result in under- and over-greasing – a frequent cause of the downtime they are intended to prevent.
Drip-feed bottles – the simplest type of autolubes available – depend on gravity and can either provide a constant stream via a wick from the main reservoir, or a more closely controlled feed through a needle valve which is adjustable for different ambient temperatures and viscosities. Modern needle valve models can be fitted with a solenoid control valve or even a small pump unit for light oils, giving even greater control over the discharge rate of lubricants.
An obvious drawback of an auto lubricator reliant on gravity is that oil will be continually expelled even when the machinery falls idle. So, while ideal for machinery which is constantly kept running, production lines which shut down periodically would require a lubrication engineer to manually close and reopen each drip-feed bottle as required – instantly dispelling the ‘fit and forget’ myth.
Although drip-feed autolubes can be configured to suit different operating temperatures, they do not adjust automatically and, as a result, need to be altered manually. This is of particular importance in facilities manufacturing a variety of products where heating or cooking temperatures may fluctuate, or for outdoor machinery which is likely to be affected by external weather conditions. It may be deemed safe to relax monitoring of a drip-feed autolube device when ambient temperatures remain constant and cannot be affected by the external climate. However, individual pieces of machinery can experience increases in temperature due to malfunction, vibration or friction – problems which may be compounded if the autolube device overheats, adversely affecting the viscosity of the lubricant and, in turn, its effectiveness. Drip-feed autolubes should therefore be regularly inspected and maintained, even in facilities where the temperature is believed to be stable and not subject to change.
Gas-powered autolubes are operated by a controlled chemical reaction between two substances which takes place inside a hermetically-sealed chamber to prevent the escape of both the chemicals and the gas which the reaction creates. The gas fills a chamber which, as it expands, pushes against a diaphragm or piston, forcing out the lubricant at a pre-determined flow rate. As with drip-feed lubricators, temperature plays an important role in correct functioning as a rise in ambient temperature will speed up the reaction, while a decrease will slow it down. Any prolonged change will negatively affect the rate of reaction and therefore the discharge rate of lubricant. If temperatures regularly fluctuate, so too will the flow rate, meaning manual adjustments must be made as necessary (and if possible) rather than fitting and forgetting.
Most gas-powered auto lubricators feature a pressure relief valve to counteract blockages in the bearing or lube line which may be caused by resistance to lubricant flow or any deviations from the recommended PSI level. While this prevents over-pressurisation, it usually means lubricant is released from the autolube before it reaches the bearing or component – potentially damaging the equipment and resulting in contamination or replacement. Each device should therefore be inspected for changes in pressure and potential blockages before the pressure relief valve needs to open. Looking for potential autolube blockages before the valve releases lubricant helps to reduce the costly downtime associated with replacing bearings.
Additionally, to prevent recurrence, the cause of a change in pressure should be fully investigated. It is important not to move gas-powered lubricators until they need replacing, as any movement or loosening can result in a loss of internal pressure which would halt the flow of lubricant. Accidental movement through pipework vibration, slippage of supporting steel work or simply an incorrect installation can all cause unwanted movement, rendering the autolube inoperable and the component unlubricated.
For applications requiring a faster and controlled flow rate, battery-operated autolubes are a useful option. Here, a battery powers a motor or pump to expel the lubricant at high pressure. Unlike drip-feed or gas-powered autolubes, which cannot be halted, battery-operated autolubes can be switched off as required making them suitable for infrequently or intermittently used machinery. Additionally, the drive and lubricant units are separate and can be replaced individually if required, making a battery-operated device more cost-effective than gas-powered alternatives which are generally single-use.
Electronic autolubes allow more sophisticated control over the device, as lubrication rates can be set based on a number of factors including runtime hours or machine cycles. Battery-operated autolubes can also be offered as multi-point systems, where one device can supply multiple components with lubrication thanks to a series of internal pistons operating sequentially to provide progressive distribution. While this cuts down on the number of autolubes required, it does pose a risk to a greater number of bearings as, if there is a blockage at any point, the entire device will cease operation. Here again, regular visual inspection is essential to identify blockages, while periodic maintenance can help prevent them forming.
The majority of models of autolube, whether drip-feed, gas-powered or battery-operated, feature a clear chamber or at least a window by which the volume of lubricant inside can be checked. By cross-referencing the amount of lubricant remaining with the expected discharge rate, engineers should be able to tell if too little or too much lubricant is being delivered to the component and adjust accordingly. However, visual inspection is not always sufficient, especially if the autolube device is not kept clean or the window is small. An obscured view can hide bubbles, congealed contents or incorrect viscosity, as well as dirt particles. These can distort the reading as well as putting the machinery at risk of under- or over-lubrication, or damage due to contaminants suspended in the lubricant. Samples of the lubricant should therefore be taken to ensure cleanliness and correct viscosity as these cannot always be determined by sight alone.
Auto lubricating devices of all varieties are often essential for the efficient operation of a modern production facility. However, the assumption that they will take care of themselves could prove costly. Regular monitoring and maintenance of each device is the only way to ensure a continuous and correct flow of lubricant to each bearing or component, and should be undertaken as part of an overall conditional-based monitoring and maintenance programme to ensure the health of the facility.