Processing apparatus of wood to be chipped

The background of the present invention is to achieve with one processing line a very high uniform feeding capacity of long wood to a chipper. The wood processing apparatus according to the invention is especially meant for feeding debarked wood to a chipper, delivered as transportation bundles for chipping. Especially considered is the handling of transportation bundles of wood debarked in the forest, to be chipped for the pulp production, so that the wood can be transported to the chipper as an even flow. The wood to be processed has typically a length from 4 to 8 meters.

The traditional technique comprises a receiving table of log bundles and a proportioning hoisting device, i.e. a log elevator by means of which the log bundle placed on the receiving table is broken to smaller lots. These smaller lots are fed one after another forward, substantially as a uniform log flow. The logs to be processed have been debarked in advance, especially in connection with the felling, as so called forest debarking. Some loose bark is, however, unavoidably carried with the logs, the amount thereof being for example 3 % of the wood quantity. This loose bark should be removed from the log bundles prior to feeding them to the chipper by forwarding the log flow, portioned by a log elevator, along a roller conveyor. The separation of the bark, however, has proven to be problematic, and harmful quantities of bark are drifted into the chipper. Another problem with the apparatus is in reaching an adequate capacity with short or twisted logs or with logs having a small diameter.

In prior art, long logs having a length of a whole trunk are transported from the forest unbarked, as truckload bundles, to a debarking drum. Thereby a common problem is that the log bundles are not totally broken in the drum, and an even feed to the chipper is arranged by adjusting the log flow coming from the drum by means of a grab bucket crane moving the logs as smaller batches.

Also logs to be chipped, debarked in the forest, are transported as truckload bundles to chipping, whereby a so called tumbling drum can be used for breaking of the bundles into an even log flow. The tumbling drum in question has a basic implementation corresponding to a debarking drum, in other words, it is substantially a horizontal

cylinder, open at its both ends, rotatable about its longitudinal axis, but there are, however, certain differences with respect to the debarking drum.

The tumbling drum must be relatively short, because it is not meant for debarking of the logs and a long tumbling length would increase breaking of the logs and wood losses. A typical design is about 1,5 to 3 times the average length of the logs to be processed, preferably about twice the average length of the logs. The diameter of the drum is chosen according to the required capacity, usually ranging from 3 to 6 m. The shell of the drum is usually solid. If necessary, there can be also openings in the shell for discharging eventual rock material and/or loose bark. The drum is arranged inclining in the flow direction, having an angle of inclination in the direction of propagation about 1:30 to 1:100. A suitable receiving and feeding apparatus precedes the drum. A suitable conveyor apparatus is arranged after the drum for feeding the log flow discharged from the transport bundle to be chipped. The conveyor apparatus can be for example a roller conveyor, whereby there is arranged the possibility for the loose bark and the other loose material to drop off from the wood flow.

One problem discovered in the devices comprising a tumbling drum is the incomplete breaking of the log bundles. Increasing of the length of the drum is not a recommendable solution to the discovered problem, due to the increasing wood damages mentioned above.

An essential improvement to the problem has been provided by means of an apparatus according to the present invention, comprising a feed conveyor receiving the log bundles, a tumbling drum of the bundles and a receiving conveyor, said apparatus providing implementations characteristic of the invention, as stated in the enclosed Claim 1.

By means of the controlling system of the apparatus according to the invention, an even feed of the logs can be achieved, comparable with the receiving system implemented with the receiving table-grab bucket crane technique with respect to the evenness, but superior with respect to the capacity. In addition, the bark does not cause problems, because the eventually incomplete barking in the forest can be completed in the

tumbling drum and the discharge of the bark is performed in the point chosen for this purpose in the assembly.

It has been discovered that a prominent breaking of the bundles happens in the transition point between the feed conveyor and the drum. This stage has proven to be very important, and by increasing its duration, the breaking of the bundles becomes more effective. On the other hand, a new bundle must be received quickly to the drum mouth. For this reason it has been discovered to be an advantage that the speed of the feed conveyor can be adjusted: An adequate transportation speed for achieving the required capacity, and a slow speed when the log bundle is at the mouth of the drum. The control data of the speeds is gained based on the positioning information of the log bundle, for example based on the input power of the drum or the torque of the drives. Also optical systems transmitting the position information are useiul.

By means of the described method, a relatively effective breaking of the bundles can be achieved in the drum having a length of about twice the length of the log. The amount of wood discharged from the drum, however, varies a lot, and big capacities require still another equalization process. A prominent equalization of the wood amount discharged from the drum is achieved when using a lower number of revolutions when the amount of wood coming out of the drum is high, and when the amount of wood is decreasing, the number of revolutions is increased steplessly or stepwise. The control of this operation is preferably implemented by means of the torque moment of the drives of the drum, the required information being available for example from the frequency converter required by the speed regulation of the drum. Also equipment based on optical monitoring of the discharged amount of wood is applicable for this purpose.

The invention will be described in more detail in the following with respect to the enclosed drawings, wherein

Figure 1 shows a traditional chipper feeding line for wood debarked in the forest,

Figure 2 shows one feeding line of a chipper in accordance with the present invention,

Figure 3 shows the use of torque data for controlling the breaking of the bundles.

The logs debarked in the forest are fed traditionally with a loader as bundles 1 onto the receiving table 2, Figure 1. The receiving table 2 is comprised of a drag-chain conveyor being wider than the length of the logs to be transported. The logs are loaded onto the table transversely with respect of the transport direction. The receiving table 2 moves the logs 1 to a load elevator 4 being also a drag chain conveyor. Due to the high angle of elevation of the log elevator 4, the drags (not shown) take from 1 to 4 logs 3 at a time. The log flow moving from the log elevator to the following conveyor 5 is almost even. The conveyor 5 is arranged at an angle of 90 degrees with respect to the transport direction of the log elevator 4, so that the logs 6 are set onto the conveyor 5 directed parallel with the transport direction thereof.

The logs are fed by means of a roller assembly 7 and the feed conveyor 16 of the chipper to the chipper 17. The roller assembly 7 separates the loose bark of the logs from the wood flow. The bark falls down onto the bark conveyor 11 under the roller assembly.

Depending on the effectiveness of the debarking performed in the forest, an amount of bark comes with the logs to the process. The bark is partly fixed to the logs and partly loosened. On the receiving table 2 and on the log elevator 4 and between the pocket 8 between them, as well as on the chute 9 following the log elevator, the loose barks cause jamming and other disturbances. A part of the bark drops under the conveyor, requiring a separate collecting system 10 of bark and waste.

When the diameter of the logs is less than 10 to 15 cm or the length of the logs less than 2 to 3 meters, the log bundles easily form at the log elevator 4 wood stacks in disorder. Corresponding problems occur also with twisted logs and when there are lots of long

bark stripes among the logs. For good operation of the log elevator, the logs must be located parallel in the conveyor pocket 8.

In Figure 2, the breaking of the log bundles 1 ' is implemented by means of a drum feeder conveyor 12 and a drum 13. The drum feeder conveyor can be a chain conveyor or a beam conveyor. After the drum, the logs move to the discharging conveyor of the drum, like onto the roller assembly 7'. The loose bark coming with the logs and the bark not having loosened from the logs until in the bundle tumbling drum 13 are separated on the roller assembly 7'.

When the drum is short, about twice the length of the log, the log bundle does not break enough in the drum. The most effective breaking of the bundle happens between the feeder conveyor and the drum 14. By decreasing the transport speed of the bundle, the breaking of the bundle at the transition point between the feeder conveyor and the drum can be made more effective.

In the apparatus according to the invention, the position information of the log bundle can be received for example from the moment information of the drives of the drum or from the operational effect, in other words the current information. Diagrams of the Figure 3 illustrate the moment M of the drum drives, the speed v of the feeder conveyor and the speed of rotation n as a function of time t. The diagrams also show the changes of the above mentioned values when the logs travel through the drum. The changes of the speeds are shown stepwise. They can also be stepless.

When the bundle proceeds caused by the motion of the feed conveyor 12 to the drum 13, in a certain stage T _sl the barking knives of the drum casing catch the logs. The torque M of the drives increases strongly, and the wood bundle tends to rotate together with the drum. When the torque reaches the value M ₁ , at the moment fϊ, the program tells the drum feeder conveyor to drop the speed to for example 30 per cent of the maximal speed (diagram v/t). The transferring of the bundle into the drum slows down, providing an adequate breaking of the bundle. When the logs start to loosen, the torque of the drum starts to fall. When the torque is decreased to value m _ls once more, at the moment U, the program tells the feeder conveyor to reverse to the full (100%). In that

way a new bundle is quickly received to the space 14 between the drum and the feed conveyor, in the diagram M/t at the moment t _s2 . Increasing and decreasing of the speed is not necessarily happening with the same value M of the torque but they can also be chosen case by case.

In order to maintain a capacity with an adequate evenness, also the speed of rotation n of the drum changes according to the torque information of the drum, as shown in the diagram n/t of Figure 3. At the moment t ₂ as the torque reaches the value M ₂ , the speed of rotation n of the drum is decreased for example to half (50 %) of the maximum speed (100 %). In that way the overcapacity in the feeding line 15 of the chipper, after the drum, is avoided.

When the amount of logs has decreased in the drum and the torque decreases back to the value M ₂ at the moment t ₃ , the speed of rotation of the drum is increased back to its maximum value (100 %). Also hereby the increasing and decreasing of the speed is preferably chosen case by case and they need not happen with the same torque value or alternatively the same current value of the drives.

The adjustment shown in Figure 3 happens stepwise. The adjustment is in that case simple and easily implemented. The operation according to the invention can also be implemented steplessly without predetermined limit values. The adjustment program is in that case much more demanding, but as an advantage, better operation and less mechanical stresses are achieved as an advantage due to the speed changes.

One possibility to have influence on the throughput capacity of the drum is the changing of the angle of inclination of the drum, for example by means of a lifting/lowering device having influence on the height position of the support rolls.