Millions of rands are wasted every year through inaccurately set pneumatic systems. The Stora Enso Kopparfors sawmill in Norrsundet, Sweden, also experienced this problem. In cooperation with Rexroth the pneumatic system of a sorting plant has now been completely checked over and optimised. The result: drastically minimised waste, noticeably fewer interruptions in production and increased production speed – and all this without any major new investments.
In pneumatics applications even minor measures can achieve a major impact. Kenneth Johansson, Rexroth employee and pneumatics specialist based in Älvsjö, Sweden, passes his experience on to his customers. With the numerous cylinders installed, sawmills in particular can benefit from a constant system pressure and the correct setting for cyclinder end position cushioning. "Unfortunately some companies still have completely unrealistic concepts as to what they actually require to ensure a pneumatic cylinder functions perfectly," rues Johansson. "It is not uncommon for this to cause machine defects and thus a reduction in production capacity, making the systems uneconomical."
Stora Enso asked for help from Rexroth, renowned particularly in Sweden for its extensive know-how in the field of sawmill technology. Since then employees at the Norrsundet production site have also been attaching more importance to the adjustment of cylinders. "The measures undertaken by Stora Enso set an example with respect to better utilisation of a production capacity that has been available for a long time. All you require for optimisation of a system is the relevant knowledge, a measuring instrument and a screwdriver," emphasised Johansson.
With sawmills containing around a thousand cylinders, like the Stora Enso mill in the Swedish town of Norrsundet, the improvement potential is often very high. The most essential requirement is that all components function perfectly. Only then is it possible to keep up with the constantly increasing production rate, which has doubled in the past 20 years. This motivated Stora Enso to form an optimisation group made up of employees, who then checked over the complete production line. Mikael Svensson, leader of this group at the Kopparfors sawmill, says of its aims: "We concentrated first of all on the smaller process faults, which caused delays of up to 30 seconds. Although these do not bring the complete production line to a standstill, they do reduce the capacity."
Less maintenance
During the comprehensive inspection the technicians discovered a number of continual, minor faults, which were a result of an excessively high system pressure in the pneumatic system. The sorting for example: wooden boards are removed from the conveyor belt by means of a pneumatically operated metal hook and placed in approximately 31 different compartments. An excessive number of the planks landed in the waste compartment, because there was no way they could be sorted. "Due to our mass production we had absolutely no chance of sorting these boards manually and therefore had to offer them at greatly reduced prices. However, the waste amounted to several cubic metres per day. Since the pneumatic system has been optimised, with only a few valves being replaced to improve the flow rate, we now only have a few boards ending up in the waste compartment each day. And this, of course, increases our yield," comments Jens Björk, project manager at Stora Enso. At the same time the sorting time was considerably shortened and the maintenance costs drastically reduced.
High production speed
Svensson is pleased with the results: "Some of the cylinders we installed have now been operating for three years without problems and with absolutely no maintenance." First of all the end position cushioning of all cylinders was reset. The one set at 9 bar was reduced to 6 bar and the feed rate was adjusted. The optimisation group from Stora Enso carried out these measures independently but with the support of Rexroth employees. "For me it was a real eye-opener that a reduced system pressure could increase the production speed. Furthermore, by reducing the pressure it can be maintained at a constant level, which also contributes towards reliable operation," summarises Svensson. These measures undertaken at the Norrsundet sawmill were greatly appreciated within the whole Stora Enso Group.
"Thanks to these considerably improved results from our complete installation we are now planning similar checks of other mills. The major benefit here is that we have been able to increase the production capacity of our system without even having to replace a single cylinder," says Björk, summing up.
With 46 000 employees in more than 40 countries Stora Enso is one of the world's major manufacturers of paper for commercial and industrial use, flexible packaging boxes and wood products. The company has 11 factories in Sweden: six paper mills, three sawmills and two pulp mills. Today, Stora Enso employs around 140 in Norrsundet's saw mill. The mill has an annual capacity of 300 000 cubic metres, which makes it one of the biggest sawmills in Sweden.
For more information contact Emil Berning, Tectra Automation, +27 (0)11 971 9400, [email protected], www.tectra.co.za
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