Application Note

Gearbox reliability for extrusion machines

Oil debris sensors improve gearbox reliability for extrusion machines

Background

Not so many years ago, to keep manufacturing production lines running without interruption, large buffer stocks of raw materials and components were held. This ensured that if there were any hold-ups in deliveries from either suppliers or in-house facilities, enough stock was maintained to keep production lines operating.

In order to remain competitive today under relentless downward pressure on margins, committing large amounts of capital in buffer stock is no longer feasible. Nor is the cost of providing and servicing the storage space or the costs of handling the stock into and out of storage.

Combined with just-in-time supply and flexible manufacture on demand – a requirement being accelerated by Industry 4.0 – has all but eliminated the comfort of holding buffer stocks.

Now to keep production lines running without interruption – another key element in protecting margins and meeting customer expectations – requires dependability of supply. And this means maximum reliability of manufacturing plant without costly unplanned breakdowns or downtime.

To facilitate this objective , monitoring the health of machinery by the use of an array of sensors to cover the broad range of failure modes is becoming much more widespread. This also allows for further reductions in overheads, by necessitating maintenance only when required.

Challenge

A leading manufacturer of plastic extrusion equipment, Hans Weber Maschinenfabrik GmbH, wanted to enhance their reputation for reliability by offering their machines with condition monitoring sensors incorporated at build. This provides the operator with a clear picture of the health of the extruder before problems arise that can adversely affects production output.

The gearbox of a plastic extruder is a highly loaded part and obviously critical to the reliable operation of the equipment. To reflect this, Weber was fitting four vibration sensors to the gearbox assembly to alert to any emerging problems. What they were finding, however, was that the sensors were not picking up faults early enough to prevent damage occurring to the gearbox.

To help alleviate this they were recommending changing the lubricating oil after 500 hours – or every 6 weeks on a typical two-shift work pattern. This resulted in machinery unavailability during the maintenance intervention plus the financial and environmental cost of purchasing and disposing of the oil.

Solution

Recognising that they wanted to improve further the reliability and running costs of the extruder, they chose to fit WearDetect, Gill’s oil condition sensor. This has a probe that is inserted directly into the lubricating oil and contains a powerful magnet in its tip to attract and retain the ferrous debris that can arise from either wear or the start of a component failure – such as gear tooth spalling or bearing breakdown.

Because the sensor measures the oil directly, it provides an earlier indicator of failure than that available from a vibration sensor. A vibration sensor detects the results of material loss from a gear tooth for example, rather than the loss of the material in the first instance. Because the Gill condition sensor detects this debris, it allows remediation to take place earlier before greater damage and downtime occurs.

Apart from the earlier indication that the oil debris sensor provides, it also delivers additional benefits. The sensor can differentiate between fine and coarse particles, enabling analysis of the failure. Fine wear particles would be a trend measurement over time advising, if nothing else, when an oil change is required. If the trend increases suddenly, it is an early sign of abnormal wear which can be investigated sooner. Coarse particles would be an alarm condition, requiring more immediate attention, but reducing the extent and cost of any failure.

As the sensor is immersed in the oil, it can also measure the temperature of the oil. This provides valuable insight into the health of the gearbox, as can the detection of water in oil, another parameter the sensor can provide. Water in oil will affect its lubrication properties which can be the root cause of bearing or gear failure, contributing to an even earlier opportunity to address problems before they impact on productivity.

Finally, the sensor can be supplied with a simple, coloured lights indicator unit for easy to understand condition status. While it can also be connected into a screen based dashboard, the illuminated display removes the need for any specialist training in data analysis. Additionally, the Gill oil condition sensor does not require the detailed calibration that devices such as vibration sensors require on installation.