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Recovery optimising processing
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Recovery optimising processing
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Introduction
Each company is interested in increasing its lumber recovery and so its benefits. LINCK offers several concepts for sideboard- and centre product optimisation depending on envisaged production process and capacity.
The most important advantages of these concepts are: |
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Recovery increase |
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Processing of round wood with bigger curve |
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Smaller round wood diameters |
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Less waney centre products and sideboards |
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Higher lumber strength and advantages in quality during drying by the fibre-parallel processing |
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Lower production costs |
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Curve sawing is well-known and has already been applied in sawmills using gangsaws by shifting of the infeed carriage.
The first profiling line with sideboard optimisation has already been supplied to Austria in 1983.
The first LINCK profiling line designed for curve sawing started its operation in Sweden in 1989.
Since then, the number of sawlines with optimised production has continuously increased.
The developments achieved in the scanning-, control- and servo technology in the past years result in better optimising results and increasingly arouses user interest.
Ill. 1: Linck profiling lines with curve sawing |
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Sideboard optimisation
As the real log shape is different in curve and ovality from its ideal shape, the symmetrically and parallel to the log centre produced sideboards normally present a smaller volume than possible. |
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A 3D-scanner at the outfeed side of the second chipper canter allows to calculate the optimimum sideboard position and width. It is possible to produce sideboards which are different in size and position on both sides, independently from each other. An additional 3D-scanner for round logs in front of the first chipper canter even allows to vary the board thickness.
However, decisive for a maximum recovery is, that optimisation can be carried out according to maximum volume recovery and maximum quality rating. The LINCK concept allows the users at any time to modify the optimising specifications depending on the achievable proceeds.
Ill. 2: Sideboards asymmetrically placed in the round log |
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Ill. 3: Sawline with asymmetrically profiled four-sided cant |
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| Modern and fast servo settings guarantee today shortest machine adjustments. The following components are particularly important for sideboard optimising: |
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Processor with high computing capacity |
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3D-log scanner at the infeed side of the first chipper canter |
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3D-cant scanner at the outfeed side of the second chipper canter |
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Profiling units with independently positionable tools |
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Centre product optimisation
To increase the centre product recovery, straight, split-taper processing is no longer applicable. Completely new concepts are required whereas different specifications have to be considered for pre-and recutting.
Precut. As the logs normally are bent in one direction only, logs are oriented in front of the first chipper canter according to their curve. This allows a straight processing of the logs. Log turning is carried out automatically during transport and according to the values of the round log scanner. A considerable advantage for further optimisation is the face cut by the first chipper canter. This face provides the reference level for the following processing.
Recut. Prior to profiling, specially developed infeed systems guarantee the precise centering “top end ahead” of the two-sided cant and its alignment in front of the chipper canter according to shape.
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Fast and accurate tool positioning |
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Little mechanical load by little masses |
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Continuous feeding of chipper canter with same log gap, both with straight and curve sawing |
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Feed speeds up to 170 m/min. |
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| For pre- and recut, the optimising result depends essentially on the log orientation-, centering- and aligning accuracy in front of the chipper canters. |
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Straight sawing with diagonal alignment |
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Increase in recovery already depends on how the cant is fed into the second chipper canter. Yet, a diagonal alignment or the parallel shifting with regards to the centre line increases recovery with straight sawing. This procedure results in an important additional recovery particularly withg short logs and heavier curve.
A new canter infeed, an adapted control and, if necessary, an appropriate scanning sytem are required for this purpose. This equipment requires small modifications in sawlines only and is therefore even interesting for the adaptation to existing profiling lines.
Besides the most accurate top end centering, it can be varied from log to log and without capacity loss whether to align diagonally or to shift parallel with regards to the centre line.
Ill. 4: Chipper canter infeed with diagonally aligned two-sided cant |
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Curve sawing
To achieve optimum results with curve sawing, it is required to also consider the cutting pattern and the machine arrangement resp. the machine design. These parameters allow to chose the optimum processing technology. The LINCK concept admits to decide from log to log whether to shift parallel to the centre, whether to align diagonally or whether straight- or curve sawing shall be applied. This flexibility is of utmost importance as it is possible to apply the best processing method for each log.
A difference is made between the operating modes "passive curve sawing" and "active curve sawing".
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Ill. 5: Passive curve sawn and profiled four-sided cants |
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With passive curve sawing, the two-sided cant is centred with top end ahead. Additional guiding elements in the area of the infeed- and outfeed systems copy the log shape. Curves up to a settable maximum value can be considered only, so that the following profiling- and saw units can handle these curved cants.
In addition to the recovery increase, sawing along the fibre results in a higher strength of the sawn goods.
Ill. 6: Four-sided cant with limited minimum radius |
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Active curve sawing does not copy the log shape, but calculates the optimum course by considering the following parameters:
• Log shape
• Cut surface
• Cutting pattern
• Machine arrangement
Consequently, irregular shape, knots, root flair and similar do not interfere the calculation of the curve, whereas the diameter increase towards the butt end is considered for a bigger radius.
An increased side lumber recovery can be expected as well.
Ill. 7: Achievable result with active curve sawing |
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Comparison of the various optimisation methods |
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Comparison based on the following data:
Log length 4,0 m
Top end diameter 20 cm
Taper 1 cm/m
Cant height 14 cm
Continuous curve over the total log length |
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For the analysis, the maximum cant width with set cant height was determined for each processing method.
Conclusion: Even with little curve, a noticeable recovery increase is expected by the optimising methods. A diagonal cant alignment with straight sawing already achieve very good results up to a bow height of about 25 mm. With increasing bow height, recovery increase even rises above average with curve sawing. |
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Linck has gained a longtime experience with regards to recovery optimised processing by having installed numerous sawlines. |
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From a large number of solutions, it is possible to offer a body-tailored concept. |
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