Continuous conductivity monitoring

April 19, 2017

An aluminum rolling mill switches to a measurement system with enhanced filter control, improving safety and efficiency.

Safety and explosion protection are always a top priority in kerosene handling and when using light mineral oils. These products include rolling oil with a conductivity that needs to be constantly monitored for safety reasons. This continuous monitoring is necessary because the electrical charge of the rolling oil can become dangerous if the charge cannot be adequately dissipated because of insufficient conductivity.

Rolling oil is used in many plants where aluminium and its alloys are processed in rolling mills. In the so-called cold rolling process, aluminium bars are rolled up to thin aluminium foils. Rolling oil is applied to the working rolls and the surface of the aluminium to dissipate the heat produced during the process and to simultaneously lubricate the metal surfaces. After its use, the evaporating rolling oil is collected by stationary extractors, recovered in a waste air treatment plant and then returned to the production process.

This moment is when extreme caution is required. As the light oil moves at high speed through the rolling oil filter system, an electrostatic charge can be generated.

Until recently, staff at an aluminium rolling plant in Northern Germany had to manually measure the conductivity several times each day. If the measured value were too low, an additive was dosed into the oil to increase the conductivity.

Exact conductivity setting

Rüdiger Gollnow, a chemical engineer in the quality department and the occupational and environmental protection department of metals manufacturer Mansfelder Aluminiumwerk, wanted to end this costly practice by introducing a continuous conductivity measuring system. He chose the MLA1000 from MBA Instruments GmbH. With this measuring system, the operation of the filter could be controlled to render the addition of additives to increase conductivity unnecessary or to set the conductivity exactly. Controlling the filters meant Gollnow’s team could forgo the additives.

For approximately two years, the system has operated at Mansfelder Aluminiumwerk providing a safe working environment. Since its introduction, the measured value has remained constantly at the required level. Thanks to the control software, the data are easy to read from a computer.

“The optimum conductivity for our plant is between 150 and 160 picosiemens per meter,” Gollnow said. “By using the MLA1000, we have been able to constantly maintain this level – a task that could hardly be achieved manually. The positive effects are considerable and greatly simplify the operating procedure: Staff [members] check the conductivity once per day at the start of their shift.” He said the system deals with the measurements in the background, allowing team members to focus on their tasks.

“Thanks to the exact conductivity setting, the principle of ‘as much as necessary, as little as possible’ normally applies to the introduction of additives,” Gollnow said. “For Mansfelder Aluminiumwerk, working without additives not only means that explosions in the tank are prevented, but [they] also [experience] environment benefits.”

Positive conclusion after the changeover

Gollnow said the changeover to the system was a smooth process.

“For us, the increased safety plays a significant role and meets all our expectations. The reduced time and personnel expenditure is also a contributing factor in our positive assessment.”

The device was originally designed for measuring conductivity in kerosene for safety reasons, and it was used mainly by refuelling companies at airports. The use of the system for rolling oil demonstrates the potential of this measuring method and its ability to ensure smooth functioning even under the most difficult conditions. Small changes can have a big effect.

Hans-Heinrich Westphal is managing director of MBA Instruments. He may be reached at 49-4106-123-88-80 or [email protected].

MBA Instruments, part of SMB Group

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