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Minimum lubrication leads to maximum benefits

Minimum lubrication leads to maximum benefits
Phil Burge, Communications Manager at SKF, looks at the issue of machine tool lubrication and explores the benefits of implementing a Minimal Quantity Lubrication (MQL) system.

Reliability, precision and efficiency are all vital when it comes to machine tools across a diverse range of industries. Perhaps most critical to achieving these objectives is the effective lubrication of moving surfaces to ensure that machines in industrial applications, ranging from milling and rolling to cutting and boring, operate smoothly and reliably, over long service lives. Without correct lubrication, companies can face sizeable and unavoidable costs arising from the need for repair work and production downtime, which will inevitably have an adverse impact on performance, productivity and, ultimately, profitability. Indeed, over 36% of all bearing failures come as a result of lubrication problems. 

However, despite its importance, plant operators often carry out lubrication inefficiently. The process is typically performed manually, which leads to moving parts being over lubricated, wasting materials and polluting the surrounding environment, lubricated at irregular intervals or, worse still, not lubricated at all. On the other hand, automated lubrication systems have until recently been typically costly to install and maintain, representing an unfeasible solution for many companies.

In response to these problems, leading manufacturers have introduced a new generation of centralised lubrication systems to provide plant engineers with a more effective way to manage the procedure. In particular, the latest single duct Minimal Quantity Lubrication (MQL) systems enable existing, proven tool components to be retained, optimising performance and offer a highly cost effective solution.

As the name implies, MQL technology delivers the minimum quantity of lubricant required to carry out a specific task as efficiently as possible. In operation, the optimum level of lubrication is automatically dispensed for efficient tool operation and consistently high quality result. This method of lubrication has been developed to offer a number of significant benefits to manufacturers, such as reducing the volume and cost of materials required, something that is particularly important at a time of fluctuating lubricant prices and an ever pressing need to reduce budgets for consumables. Perhaps most critically, MQL technology can increase productivity by up to 40% due to higher machine speeds and extend component life by as much as 300%.

Smalll quantities of lubricant
The latest MQL systems, such as the LubriLean range from SKF, are typically modular in design and feature compact and lightweight volumetric micro-pumps, capable of delivering extremely small quantities of lubricant at high frequencies through bi-fluid projection nozzles. Other system components include automatic fluid metering units, centralised or devolved fluid reservoirs and coaxial connecting hoses.

These high performance systems work with each micro-pump being pneumatically powered to deliver up to three metered pulses per second, with each pulse containing as little as 3mm3 of lubricant. Low pressure air is used as a carrier for the lubricant through coaxial hoses, with air traveling through the outer bore and lubricant passing through the inner capillary, before exiting through the bi-fluid projection nozzles.

Each projection nozzle is designed so that a swirl effect is created in a small, confined zone at the nozzle outlet. The air effectively atomises each pulse of lubricant into fine micro-droplets, of between 200 and 600 microns in size, and which are projected onto the surface to be lubricated. By adjusting the configuration of the nozzle it is therefore possible to change the shape, size and intensity of the spray pattern. This approach also eliminates the problem of oil mist, as the accurate pulse and atomisation control makes sure that all lubricant is delivered to the machine surface. 

When compared with traditional water based wet lubrication practices in the machine tool environment, MQL delivers other significant advantages that, as well as the environmental benefits, eliminate the mess and expense typically associated with such tasks. For example, wet lubrication is often a costly procedure to set up and maintain, while also being a breeding ground for bacterial and microbial contamination, which can be hazardous to the user, the machine and the environment, so expensive additives are needed to curb the growth of algae.

By contrast, MQL forms a lubricating film of cutting fluid only at the tip of the cutting tool, leaving the rest of the machine relatively dry. The amount of oil required is calculated according to the speed of the rotating component or workpiece in terms of surface area and size of cut, as well as the cutting time. Technical support teams at the leading providers work with customers to determine exact flow rates and all other necessary information needed to calculate the lubrication requirements of different tool sets.

Additionally, in wet lubrication applications where multiple machining operations are supplied from a centralised reservoir it is necessary to control the distribution of lubricant via a fieldbus network, as each operation will have its own cutting speed and feed rate. In the case of SKF's MQL system, the company's intelligent Profibus device is used to change the flow rate of lubricant to the workpiece as each procedure takes place, offering an effective and easy to control method of optimising the use and application of lubricants.

The need for accurate and appropriate lubrication is perhaps now more important than ever as companies find themselves having to work harder and faster to remain competitive in today's marketplace. By adopting innovative MQL procedures, plant operators can enjoy a range of critical advantages that traditional lubrication technologies simply could not offer. As well as the long term smooth operation of equipment with minimum maintenance and downtime, companies can also benefit from increased machine performance, reduced costs and enhanced productivity, which all translate to a positive effect on the bottom line.
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