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DC/796 2018-01-19

The six-point drive healthcheck

Electrical and hydraulic systems need regular check-ups to maintain peak operational performance. Richard Chamberlain, Service Product Manager, an expert in drive technology at Bosch Rexroth, offers a simple six-point healthcheck.

Drives, motors, hydraulic power packs and actuators are too easily forgotten until something goes wrong. I would recommend an annual or at least bi-annual health check for a hydraulic or electrical system, ideally as part of a preventive maintenance programme. The reality is that, with a little more care and attention, uptime can be dramatically improved and catastrophic and costly downtime avoided.

Although hydraulic systems have their own unique health checks for fluid condition, cleanliness, fluid filters and so on, electrical systems, such as electric motors, cables, drive cabinets, relays and contactors, are often not included in the checks. However, it is equally important to undertake regular checks to minimise the risk of breakdowns.

Excessive heat and shorting of contacts are the two main causes of failure in electrical systems and can be avoided using the steps below.

1: Drive and control cabinets are a good indicator of panel health

The exterior of a drives cabinet will often offer vital clues to the overall health of a panel. In particular, the chilling unit can show evidence of where the build-up of heat is slowly damaging the drive technology. For example, plastic trunking distortion or a blocked air filter can potentially be an indication of panel overheating or that too many cables have been squeezed into a confined space. Always check the control cabinet too because motor connections need to be checked along with other equipment, such as the gearbox, which is often prone to leaking oil.

2: Check for fluid ingress

A common fault is fluid ingress. On a CNC machine tool, for example, it is not uncommon for coolant to leak onto connections which can vibrate loose over time, or for coolant to ingress into the motor. My own experience includes a user of a honing machine who used low viscosity oil that leaked to the point that the whole motor was filled, short-circuiting the connections.

I’ve also come across oil ingress in electrical filters which opened the possibility that oil could be entering cabinets through lift lug holes on the top of the cabinet. The solution was a simple one, namely cleaning the oil and fitting bolts into the holes to seal them.

3: Stay connected

It is also important to check the physical connections of all drives, motors and power supply units for adequate installation and condition. Typical problems include trapped encoder signal wires or cables with clamps or glands missing. It is not uncommon, for example, to find cabling routed through a door aperture which has become kinked. This may sound minor, but a trapped cable wears much quicker through the external insulation, allowing coolant or other media to ingress.

Fibre optic cables also need checking to ensure they are secure. However, secure does not mean over-tightened, which can lead to damage to the transmitter or receiver.

4: Check for dust

It may look innocuous but dust build-up is the enemy of temperature control and a small increase in temperature, which could be directly attributable to a blocked filter, will prematurely degrade electronic components. Blocked intake filters, for example, restrict air flow to the drive fan, making it work harder and increasing the possibility of the drive overheating.

Cabinets are another problem. Blocked door filters on drive cabinets can easily result in dust being drawn into the cabinet with the risk of contamination. Similarly, the mesh underneath drive panels can become blocked and restrict air intake. In short, filters and cooling devices need a strict preventive maintenance routine. Hydraulic systems have breather filters on the reservoir to compensate for changing fluid volumes. These are vital to keep airborne dust and moisture out of the fluid and should be cleaned or replaced regularly.

5: Know your temperatures

Once operational, temperatures within the panel should always be checked. This can be done in one of two ways, either with remote temperature monitoring via infra-red temperature guns or through the use of self-adhesive, maximum temperature storing thermometer strips. These strips can be used in different areas of the panel to gauge the air circulation levels or any condensation issues which can affect the electrics.

Similarly, it is important to check the temperatures within the main drives using thermal imaging photography of main drive enclosures. This can help identify further faults, such as loose connections or excessive heat within the drive which in the worst cases can result in a fire.

6: Back-up and set parameters

I would always recommend a parameter back-up service for all drive and control equipment. These should be stored safely on CDs to ensure the optimum performance parameters for each drive are noted and can be quickly and easily recalled. Firstly, oscilloscope traces should be taken of actual velocity against actual torque force values for all nominated drives, which can effectively become a footprint for each drive.

Last, but certainly not least, it is important to stay safe. Hydraulic systems operate under very high pressures so be sure to shut it down and relieve pressure before opening any part of the system. Please be cautious of contact between bare skin and hot surfaces as pumps, valves and motors can become incredibly hot. I would also advise keeping hands and clothing away from moving parts of the system.

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Contact

Lynsey Cutler
15 Cromwell Road, St Neots 
PE19 2ES Cambridge
Phone: 01480 223290
Lynsey.Cutler@boschrexroth.co.uk