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Perfect sawing of expensive round logs
It took only two months for Linck to update the saw line of Theurl Holz. The first log passed the line at the end of January. The owners of the East Tyrolean sawmill can now process logs value-optimised with the new chipper canter profiling line – also thanks to a new scanning technology.
In the last six years only little money was invested in Austrian saw lines. Since 2011 Theurl Holz in Assling has invested around 30 Million Euro – the most recent investment was the modernizstion of the saw line. The machine manufacturer Linck in Oberkirch/Germany was awarded the contract to supply the equipment (see Holz-Kurier issue 10, pages 8-9). "When designing the extension of the Theurl Holz saw line, we strongly emphasised the economical processing of round logs with the latest technical possibilities of mechanical and electronical engineering", explains Martin Huber from Linck who was in charge of the Theurl project. According to Linck, several factors play a decisive role to achieve maximum and efficient recovery. These are for example 3D-scanners for measuring round logs as well as two- and four-sided cants, a log optimisation program, an automatic log rotation, profilers for producing sideboards without tear-outs and an automatic feed speed control with automatic control of gaps.
Optimisation of centre products and sideboards. The log feeding station feeds the logs small end first to the Linck chipper canter profiling line. Setting of gaps makes sure that the logs are fed with an even distance which is essential for getting the highest possible piece count with a continuous line operation. The logs first pass the Microtec Dishape 3D-scanner which transfers a 3D-pattern of each log to the Linck optimising system. “These data as well as the predetermined dimensions for centre products and sideboards are used by the program for calculating a value-optimised processing of the raw material”. The program also calculates the best possible cutting pattern position in the log by considering parameters such as curve, ovality and other geometrical deviations.
Two pairs of rollers in the infeed system rotate the log exactly to the calculated position while centering rollers feed it in a centered way to the first chipper canter VM45 with two 160 kW motors. The chipper canter tools are already positioned according to the cutting pattern. The tool axes are equipped with hydraulic servo cylinders for fast setting. The servo hydraulic axes adjustment is valid for all tool and positioning axes in the saw line. The shape and size of the chips produced at the first chipper canter are most suitable for the pulp industry. The log has now been converted to a two-sided cant.
Repeated scanning. A 3D-scanner following the chipper canter VM45 is now measuring the cant surface for re-optimising the cutting pattern. The value-optimised sideboards are determined first before turning the cant by 90° degrees to its flat side. The infeed system of the second chipper canter aligns the cant either centred, out of centre or diagonally. The chipper canter then produces a four-sided cant.
Sideboards free of tear-outs. The feeding system at the chipper canter outfeed side then transports the four-sided cant to the following machine group consisting of two profiler units VPF340 and VPM450 as well as a double arbor circular saw CSMK 375-A2/B2. The profiler unit VPM450 convinces with tear-out free sideboards by treating the surface with two precutting sawblades mounted at right angles. The units profile the corners of the two-sided cants for producing a maximum number of three sideboards per side; the saw unit separates the sideboards from the cant which are then transported to the sideboards sorting plant via separating and cross conveyors. The four-sided cant is again 3D-measured and re-optimised. After a repeated 90° turning, it arrives at the next machine group consisting of two profiler units VPF340 and VPK340 as well as a double arbor circular saw CSMK 325-A1/B1. The profilers again produce up to two sideboards per side. The resaw CSMK 325-A1/B1 then splits the center products and separates the sideboards in one operation. The boards produced are again forwarded to the sideboard sorting plant whereas the center products arrive at a separate sorting plant.
The more than 150 tons heavy Linck line is designed for processing 350.000 m³ of round logs per year with small end diameters up to 55 cm. Larger diameter logs are processed on an existing bandsaw. “The whole plant is equipped with a complex safety technology to meet the requirements of the machine directives.” Essential components of the safety technology are the safety fences which protect the danger zones on a large scale.
Full optimisation. "The Theurl plant is based on a particular processing philosophy”. The 3D-log patterns are not only used for calculating the ideal dimension and position of the sideboards; even the allowed center product dimensions are stored in configurable tables and taken for generating the value-optimised cutting pattern. “This requires a high calculating effort which can only be implemented by the latest efficient hardware and optimized complex calculating algorithms”, finishes Martin Huber.