The need for regular check-ups
Published: 09 July, 2014
Electrical and hydraulic systems need regular check-ups in order to maintain peak operational performance. Paul Hickman, an expert in drive technology at Bosch Rexroth, says that all-too-often end -users neglect to give these vital pieces of equipment the TLC they deserve.
Drives, motors, hydraulic power packs and actuators are too easily forgotten until something goes wrong. This reactive approach to maintenance and servicing fails to predict problems and leaves industry at the mercy of production downtime, much of which can be easily avoided.
To be fair, some industries are better than others. The print industry, for example, is usually a very close monitor of its drive and motor equipment because downtime is exceptionally costly. An hour’s lost production of a national newspaper will usually mean the printer picks up the entire cost of that nights print run.
This approach to Hydraulic System and Electrical drive maintenance and servicing needs to be embraced much wider. I would recommend an annual or at least bi-annual health check for a Hydraulic and Electrical System, ideally as part of a preventive maintenance programme. This regime of regular checking should include external sensors and couplings for damage and visual checking for signs of clogging and leakage with filters, valves, pipes and hoses, cylinders and heat exchangers.
The exterior of a drives cabinet will often offer the first clue 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.
The next stop is the control cabinet housing the external equipment. Motor connections need to be checked along with other equipment, such as the gearbox which is often prone to leaking oil.
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 which used low viscosity oil that leaked to the point that the whole motor was filled until it short-circuited 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 screwing bolts into the holes to seal them.
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.
One of the most obvious signs of neglect or irregular cleaning and maintenance can be a build of dust in the cabinet. Dust 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.
Once the drives and motors are powered up it is possible to make a number of further checks. 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. It is also worth checking the panel housings to ensure that the optimum ambient conditions for operation are in place.
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 drives enclosures. This can help identify further faults, such as loose connections or excessive heat within the drive which can cause fire.
Finally, I would also recommend a parameter back-up service for all drive and control equipment. These should be stored safely on CDs to ensure that the optimum performance parameters for each drive is noted and can be quickly and easily recalled.
Hydraulic and electrical systems and all the associated components are vital pieces of equipment, but all-too-often they are forgotten about and given little thought until something goes wrong. The reality is that, with a little more care and attention, uptime can be dramatically improved and catastrophic and costly downtime avoided.
For further information please visit: www.boschrexroth.com
