Oil Mist Extraction on a Portal Milling Machine
A portal milling machine is a milling machine, whose milling head is guided on a cross beam between two supporting elements, whereby it forms the portal which gives the machine its name. Depending on the design, the workpiece is positioned on a fixed clamping table or span, if the portal is moveable, or on a clamping table which can be moved through the portal in the case of a fixed portal construction.
Portal milling machines in industrial machine sizes are suitable for the effective processing of large-scale surfaces and are preferably used for face milling. Further applications are surface processing, refinement and engraving for components made of metal or non-ferrous metals.
Operators of the machinery value the positioning accuracy which is made possible through the very rigid structural form of the milling tools used and which is very high at up to 5/1000mm despite the frequently extreme dimensions of the machinery. Accordingly, the structural form is also relatively insensitive to vibrations, which is a very important prerequisite when wanting high dimensional accuracy, surface quality or for a high cutting efficiency.
On the Majormill 240 portal milling machines by Forest Liné, cooling lubricant is used as a water-based emulsion with 7-8% by volume when milling, which form a spray during the processing procedure and thus a harmful substance which contaminates the air in the working area of the machine.
On all 5 machines, it is necessary to remove this harmful substance taking into account the client’s desire for an optional air circulation or exhaust duct with motor-driven control system. In addition, there was the guideline that the residual particle exposure on the filter outlet is smaller then 1.0mg/m³.
Solution of Problem
From the very beginning, it was basically certain that these tasks could only be solved with electrostatic filters. Mechanical filters, whose filter elements become saturated with cooling lubricant, continually decline in performance or continually demand more capacity from the ventilator, are not an economic solution to this issue. In addition, there is the issue that cooling lubricant cannot be reused in filter elements and this must be disposed off as a harmful substance at great expense.
Quite the opposite with electrostatic filters. The contaminated air is aspirated by a vibration-cushioned ventilator and passes at first through a pre-filter, which filters the larger harmful substance particles and ensures even distribution of the air flow.
The so-called ioniser is next. This is where the remaining fine harmful substance particles are continually charged electrostatically by ionised molecules in split seconds. The collector undertakes the actual cleaning of the air. It is made of a row of vertical plates, which are parallel to the flow of harmful substances. Within the collector, the electrostatically charged harmful substance particles are deflected into an induced electrical field in the direction of the earthed plate.
The vertical installation of the panels guarantees an outstanding flow, as the filtered harmful substances can simply be drained off through a siphon.
As well as considerably lower life cycle costs (see also “Life Cycle Costs of industrial Air Filter Systems to filter Cooling Lubricants”), the entire concept also has the advantage that filtered cooling lubricant is recovered as an expensive substance, cleaned and can be recycled into the production process.
After commissioning the system on the Forest Liné portal milling machine at the beginning of July 2008, particle concentration measurements were carried out by the (French) supervisory body. These provided the result that in normal operation the residual pollution in the filtered exhaust air was <0.1mg/m³; the guaranteed value was consequently fallen short of by 1 decimal power.
We thank Mr. Bender and Mr. Wolf of Trumpf for approving this article.