Lubricating machines
in extreme environments Cement manufacture, chalk washing, AS-Interface networking communications
Control Lubrication, a Yorkshire-based system integrator specialising in lubrication systems for machinery in heavy duty industries, is using AS-I (Actuator Sensor Interface) to network proximity switches, zone valves, pressure switches, flow monitors and mobile plug-in reset push buttons in some of the toughest environments you could imagine.
An impressive example of Control Lubrication’s use of AS-I in extreme environments can be found at Lafarge Cement, Northfleet, Kent. In this particular application three separate mills undergo the process of washing chalk for cement production creating working conditions that at best can be described as constantly damp.
A Progressive Open Gear Spray System was upgraded last year by Controlled Lubrication to spray a layer of graphite grease onto the working face of the girth gear of the rotating Chalk Wash Drums to provide resistance to the process water washing and reduce wear.
Because of the size of the drums (they can be up to 12m in diameter) the open gear sets don't have oil baths and because they rotate at 30rpm any oil applied would just fly off. The Progressive Open Gear Spray System is designed to spray a fixed amount of grease at regular intervals and evenly across the face of the pinion tooth, which drives the girth gear and this grease subsequently transfers onto the girth gear itself.
This is achieved by pumping grease through a progressive distributor, to a number of air atomising spray nozzles. Using this approach Lafarge improved productivity and quality of planned maintenance, and reduced unscheduled downtime and the amount of lubricants consumed annually.
In the past the spray system has been controlled using conventional hard wiring, with individual connections for each of the sensors and modules. Unfortunately the damp working conditions caused considerable erosion to this type of wiring. In addition the communications systems are located directly on the open gear grease sprays, so there is a lot of vibration which combined with the erosion made the existing hard wired networking unreliable.
It was decided to replace the hard wiring and AS-Interface was selected to network the devices. AS-Interface is the simplest of the industrial networking protocols used in PLC, DCS and PC- based automation systems. It is designed for connecting binary (ON/OFF) devices such as actuators and sensors in discrete manufacturing and process applications using a single cable. It is an 'open' technology supported by leading automation vendors. AS-Interface is a highly efficient networking alternative to the hard wiring of field devices and proven in hundreds of thousands of applications.
The spray system is controlled using an AS- Interface communication network, which not only controls the opening of the grease zone valve when required, but also meters and checks the flow of grease to the spray nozzles and activates and monitors the air supply to the nozzles. Should a fault occur an alarm is set and the fault is stated in written form on the Human Machine Interface (HMI). A general alarm is also available for remote use. The unique two-wire AS-Interface cabling system and AS-Interface devices used all have an IP65 rating. They are immune to the vibration and damp conditions.
In addition to improved reliability of the Spray System communications, Controlled Lubrication was also able to reduce the existing three control panels (previously one per mill) to just one. Because AS-Interface is a decentralised system using a single two-wire cable with intelligent devices attached where they are needed the amount of hardware in the panel is significantly reduced. The single panel controls all three spray systems using AS-Interface modules to receive the inputs from both the air flow switches and the grease flow switches.
“The grease system works without fail and has cut our downtime significantly. The AS-Interface equipment is proving much more durable than the hard wiring, so we are extremely happy”. Said Paul Heathcote, Chief Mechanical Engineer, Lafarge Cement.
“AS-Interface is proving to be an excellent communications technology for controlling our lubrication systems. We have found it to be very versatile and flexible and most importantly extremely reliable in the toughest of environments.”
Andrew Hoyle, Managing Director, Controlled Lubrication
Link
www.as-interface.com
16 LUBE MAGAZINE JUNE 2007
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