A debarker is a machine used to strip or remove bark from logs before processing. Debarking refers to the process of using machines to strip or remove bark. Debarking is considered a part of normal sawmill operations. A more recent trend however is the debarking of logs at an actual logging site before they even reach a saw or pulp mill. This has led to the development of portable debarking units such as flail ring debarkers. One of the primary reasons for debarking is to minimize the amount of fibre loss from logs.[1]
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[edit] History
The debarking of logs was never a regular part of sawmill operations when sawmills were first established decades ago. The bark of logs was sawn off manually.[2] Debarking spuds, a small type of hand tool like a small adze was then used to strip the bark off logs. This was just one of many slow and rather uneconomical methods used. Another more fastidious method was the use of square cants. This involved cutting full-chord slabs from raw logs and then burning them.[3]
[edit] Features/Types/How it Works
Drum debarkers are used by pulp mills and chip plants and are best suited for stripping pulpwood.[4] In fact, drum debarkers have been used in debarking pulpwood for centuries. Logs are loaded into a hopper where a conveyor belt moves the logs into a ribbed drum. The drum is rotated and produces a rolling action that tosses and throws the logs around inside it. The abrasion caused from the logs hitting each other and being hammered against the inside of the drum walls removes the bark from the log. The bark is then released through slots located in the drum shell. When first developed, logs were fed through the machine in batches. Now drum debarking operations are designed to accommodate the continuous flow of wood through the machine. Sometimes water is added to facilitate the debarking process. This is known as hydraulic debarking.[5]
Ring debarkers are widely used in paper mills, pulp mills, chip plants, log processing plants, and sawmills. They are quickly becoming the debarking method of choice for mills producing a high value of both hardwood and softwood lumber products. A ring debarker features a ring of cutting heads or knives mounted in a circular position. The log is fed into the machine in a continuous fashion and as it rotates, the bark of the log gets peeled down to the cambium layer. The first ring debarker ever configured was developed in Sweden and called the Cambio.[6] Today, ring debarkers come in various configurations. For example, the tool pressure can be adjusted to match the thickness and bark characteristics of different tree species. The machines also rely on a centering feed conveyor system monitored by a weight sensing mechanism that steers logs into the center of the ring.
The rosser head debarker is popular for debarking hardwood. It functions similarly to a lathe in the way it cuts bark from trees and is better adapted for handling crooked logs. Logs are placed into the debarker from an infeed conveyor and dispersed from the machine via an outfeed conveyor. Inside the debarker, the log rests upon a cradle driven by rollers that rotate the log while a rotating cutter head travels over the length of the log and removes the bark. A manual operator controls the movement of the cutterhead. This method of debarking is slow but the machines cost less and are easier to manage.[7]
Flail debarkers consist of chains or other flexible materials that are flung and whipped against the log. This hammering action loosens and ultimately removes the bark from the log.[8]
[edit] Common Manufacturers
- Nicholson
- Morbark
[edit] References
- ↑ Ring Debarkers Lift Fiber Recovery, Profits. Timberline Magazine. 2008-11-05.
- ↑ Ring Debarkers Lift Fiber Recovery, Profits. Timberline Magazine. 2008-11-05.
- ↑ Basic Debarking Concepts. Nicholson. 2008-11-05.
- ↑ Sawmill Process Begins with Bucking, Debarking. Pallet Enterprise. 2008-11-05.
- ↑ Log Debarking. T.Brown. 2008-11-05.
- ↑ Sawmill Process Begins with Bucking, Debarking. Pallet Enterprise. 2008-11-05.
- ↑ Sawmill Process Begins with Bucking, Debarking. Pallet Enterprise. 2008-11-05.
- ↑ Ring Debarkers Lift Fiber Recovery, Profits. Timberline Magazine. 2008-11-05.
