Article 6
T
he following several case studies highlight improvements that can be obtained by paying attention to small details in parts fit, design, and operational improvements in chippers. Acrowood has been fortunate to have been involved in the redesign and upgrade of several chippers, both domestically and overseas. Some of these stories involve changes that have been relatively simple, and some have been fairly complex, involving the replacement and redesign of fundamental components of the chipper. All of these case studies involve the whole log chipping on a grand scale, sometimes chipping logs of a size that are rarely seen as pulpwood in the world today.
Ust Ilimsk hardware parts upgrade
During the Cold War era of the 1960s it was not possible for manufacturing companies in the United States to sell and ship equipment to the Soviet Union. The Black Clawson Company, the predecessor to Acrowood, had established an engineering and manufacturing office in Bordeaux, France, to handle inquiries and opportunities in Europe and around the world. This office manufactured woodyard components based on drawings supplied
by the engineering office in Everett, Washington. One of these deliveries included five 116-inch whole log chippers for the Ust Ilimsk wood processing facility in central Siberia. These chippers were installed in the late 1960s and have been processing Siberian softwood and hardwood in short wood form ever since.
In 2003 this mill contacted Acrowood about the possible replacement of the disc hardware for their chippers. They had been manufacturing parts locally based on the original parts supplied by the Black Clawson French division, but in time the original patterns had been lost and the rebuild quality had deteriorated to the point where their chip quality suffered badly.
Chip length varied from pocket to pocket and was not consistent from the inside to the outside of the knife; the exposed face of the knife carriers were badly worn, and the surfaces of the faceplates were pitted and worn. As succeeding generations of millwrights learn from their predecessors about the care and maintenance of chippers, it often seems that bad habits and shortcuts are perpetuated to the detriment of the process. So it was recognized by the current mill management that something needed to be done to correct the problems they were having. In all these years there had not been a visit by a serviceman representing the chippers, and it was time to do something.
Featured in above image: Acrowood Slant Disc Chipper
To confirm that the discs remained consistent with the original design, and that they matched the drawings that Acrowood had originally sent to France, an Acrowood engineer was dispatched to the mill in March 2003, armed with templates and diagrams. He had the opportunity of observing the chippers in operation, meeting the mill’s operators and management, and of enjoying the late portions of a Siberian winter. Fortunately, the base disc had not been altered and the dowels, bolt holes, spout, and other critical dimensions remained faithful to the original design.
When the new parts arrived from America, the mill monitored closely the chip quality produced. Not only did the fines, pins, and overs levels fall dramatically, but the homogeneity of the chips and their size distribution was improved as well. The new parts fit perfectly, and mated with the mill’s existing supplies of knives and counter knives. Special metric threads were used on the faceplate studs to match the Russian equivalent of our North American standard thread system so that the mill’s existing supplies of nuts could be used. In all it was a great success. Prior to this project, the mill had not conducted much in the way of chip quality evaluations.
They lacked a proper classifier, so Acrowood supplied a ChipClass as a part of this order. Now they are able to track the chip qualities from each of their five chippers, two of which have the new Acrowood parts, and three of which have the older Russian parts. Interestingly, the mill now gets by on two chippers. Can you guess which ones they use?
North Forest Products D&A Replacement
In 1967 the Tamar chipping plant and chip export facility was established on the island state of Tasmania, Australia. It was set up to produce chips from the badly formed, fire-scarred, and often hollow native Eucalyptus trees that were unsuitable for lumber production. The chips were of mixed Eucalyptus species, screened over a bank of rotary screens, stacked out on the ground, and reclaimed into ships that take them to pulp mills in Japan.
To produce the chips the mill installed two chippers: a 153-inch, 8 knife horizontal feed chipper, and a 96-inch, 10 knife horizontal feed chipper, both made in the Everett, Washington factory and supplied by Black Clawson Co. Logs up to 40-inch in diameter were passed to the big chipper, while the “little” logs up to 28-inch diameter were processed in the smaller 96-inch chipper.
In the original installation they used a Black Clawson-supplied hydraulic “Bellingham Barker” which used high-pressure water to blast off the bark and had the additional benefit of removing a good deal of rotted wood from cracked and hollow stems, which are very common in the trees of the area. The hydraulic debarker of that time used water drawn from the nearby estuary and discharged the partially cleaned water back into the same body of water. A settling pond collected the bark and woody residues from the debarking process. Issues surrounding the handling of water, the high cost of operating and maintaining the pumps and nozzles in this debarker, and the changing nature of the logs have made the use of the Bellingham Barker obsolete, but it represents an interesting footnote in the history of log handling.
Over the years they maintained their chippers with parts supplied from the USA, and from parts made locally. In the late ’90s, an arbor supplied by a company in Melbourne, Australia cracked in half (actually broke in half at a point where it was inside the disc) while the 153-inch chipper was running − a potential catastrophe.
Featured in above image: Acrowood Whole Log Chipper
Luckily the disc was able to wind down to a stop without actually jumping out of the bearings and wrecking the foundation, but a great deal of damage was done and the disc and arbor were ruined. No one was injured.
The owners of the chipper decided to come back to the original designers of the chipper for the replacement disc and arbor, but they had a special plan in mind. For all these years this big chipper had been running with 8 knives. They reasoned that if 9 knives could be fit onto the disc and mated with the original spout, they should get 9/8 additional capacity, or about an 11 percent boost. And, if it were done in just the right way, it should be possible to re-use most of the parts they currently used on the 8 knife disc, although some parts may need to be “trimmed a bit” to fit in the smaller space available.
To do this it was necessary to change the positions of the knives on the new disc, an engineering feat that took considerable discussion and time to resolve. The sweep of the knives, or the knife line position on the disc relative to the geometric radii nearest the knives, had to be reduced so that the additional knife had room to fit. Then the knives had to interact with the side anvil in such a way that logs of any diameter would continue to chip stably and not lift or twist during processing. It was a formidable engineering
challenge mostly because chipper discs are made in such a way to fit up with the base and anvil configuration that produces the best chipping action. If you know any chipper engineers, you know they don’t like “meddling” with something that works. And the results exceeded not only our customer’s expectations but our own, as well.
As a part of this project, we also added all the newer “bells and whistles” to this new disc: stainless steel slot and end liners, tapered chip slots, wear coatings to the faceplates, and special wear washers for the knife carrier bolts that were press-fit into the disc to prevent spalling and wear when the nuts were tightened. This chipper was truly a work of art when we were through.
Because of the change in knife location on the disc there was some concern about the feed arrangement. We were confident that any change in feeding would be minimal, but we were all interested to see just exactly what would happen when the disc started operation. We had considered the effect on the motor and had predicted the same 9/8 increase in horsepower use to achieve the higher throughput, but the customer’s experience told him that the motor had ample excess capacity. When all was in place and the results were known, it was quite a shock! The chipper did indeed make fine chips,
without any issues in feeding or log stability. The change in knife position did not upset log feeding or chip production. It was possible to show that the chipper was taking the logs in at an 11 percent faster rate, but the actual horsepower used was lower than for the 8 knife disc! Somehow the new angles used allowed the knives to slice through the wood more efficiently and effectively, actually lowering the horsepower per ton of chips produced.
The mill recently reported that seven million tons of chips have been produced by this 9 knife chipper disc, and all continues to run smoothly.
Griffin Chipping Chipper replacement
Whole log chipping of hardwood logs can be tough duty for a chipper. When Griffin Chipping of Woodville, Texas experienced a cracked disc in a new chipper after only 18 months of operation and could get no satisfactory solution from the supplier, they turned to Acrowood for help. They needed a chipper that could stand up to the challenge posed by this difficult resource, and would not let them down.
They installed an Acrowood 116- inch, 12 knife, horizontal feed chipper after their debarking drum. They were able to use the existing drum outfeed conveyor and chipper infeed chuting making the conversion easy and inexpensive.
They have two clients for their chips, each with its own chip specification. To meet the different requirements involves changing chip lengths. They would run for several days to make chips for one customer and then switch to the second chip length for the other customer. This is an area where some chipper operators try to “fudge” their chippers by either extending or retracting the knife width slightly to affect the apparent chip length. In helical face chippers, this has only a limited effect, as the overhung knife tip projection and the contour of the chipper faceplates must be matched to the chip length in order for the logs to feed correctly. It is a risky business as too much extension or retraction can result in an insufficiently supported knife and knife breakages, or “burying the heel” of the knife below the leading edge of the faceplate resulting in wood packing into this space and damaging (or wrecking!) the chipper and parts.
Griffin meets this requirement by using two sets of faceplates, each for the correct chip length, and simply changing the parts as needed. The knives and knife carriers do not need to change, only the faceplates. As a result, they are ranked as the highest quality of chips that each of their customers receives from any source, thereby earning a bonus for chip quality that more than pays them back for the time and effort they make to stay on top of their chip quality.
Summary
As each of these case histories shows, it is possible to improve the operation and condition of even the oldest chipper through a process of
By using the correct parts to make the right chips they avoid the problem of logs pounding against the faceplate needlessly, reducing wear and extending the life of their parts.
attending to the details of chipping, keeping the parts in top-notch condition, and ensuring that the disc and base are in good condition. It can be possible to upgrade some of the “fundamentals” of the chipper without replacing it entirely, like changing the disc for one with more knives, but this is a little out of the ordinary. Designs being supplied today include spout angles and designs that are not like chippers built 20 years ago, and the changes produce longer, thinner chips and much-improved chip qualities preferred by chip buyers. In this era of penalties levied on the supplier of poor chips, and bonuses for good chips, it pays to be in the bonus end of the supply chain.
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