Part 3_Forest Engineering_Chapter 4_Timber Preparation

8/12/2019 Part 3_Forest Engineering_Chapter 4_Timber Preparation

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CONTENTS4.1 Felling4.2 Debarking4.3 Debranching4.4 Cross-cutting4.5 Infield stacking4.6 Mechanised timber preparation4.7 Mechanised felling4.8 Mechanical debarking

Timber preparation normally includes the activities of felling, debranching, topping, debarking, cross-cuttingand stacking. These activities can be done motor-manually or mechanically. A major portion of felling inSouth Africa is still done motor-manually.

4.1 Felling

As with all other forestry operations, fellers must be suitably trained for the job.

Further information regarding chainsaw operations can be found in the South African ChainsawSafety and Operating Handbook published by FESA.

4.1.1 Equipment for motor-manual felling: chainsaw;

felling lever.

4.1.2 Personal protective equipment:

approved hard hat with visor and earmuffs;

brightly coloured T-shirt and/or high visibility vest;

appropriate gloves if required;

approved cutter pants;

steel capped safety boots;

First Aid kit and pressure pad (bomb bandage),

rain suit when required.

4.1.3 Other:

tool pouch with required tools (round file, flat file, combination spanner, depth gauge tool);

fuel and oil container;

cloth or brush for cleaning purposes;

fire extinguisher;

first aid kit.

forest engineering

chapter 4

timber preparation
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4.1.4 Felling technique:

Ensure that no other person is within the felling danger zone of at least two tree lengthsradius from the tree to be felled. The danger zone is 360 around the tree to be felled.

Determine an appropriate escape route. Normally 45 away from the felling direction.

Ensure the escape route is open and clear of obstacles.

The following schematic drawing shows the danger zone and the escape route around the treeto be felled (see Figure 4.1).

Check the possible felling direction by taking into account t he following:

the angle at which the tree is leaning;

crown size and overhang;

neighbouring trees;

wind direction;

planned extraction direction;

slope on which the tree is growing;

environmental considerations;

silvicultural requirements.

Fell the tree using the following three cuts:

directional notch (top cut);

directional notch (undercut) - angle to be at least 45;

felling cut.

The tree is steered in the desired direction by creating a felling hinge. Figure 4.2below showsthe three felling cuts.

Felling directionEscape route

Two tree length radius

Figure 4.1: Schematic representation of felling danger zone and escape route.


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Hinge

Felling direction

Directional notch

Felling cut

4.1.5 Felling product ion

Felling operations are normally controlled by giving a pre-determined minimum production (task)level.

The following factors could influence felling productivity:

safety considerations;

tree size;

tree diameter;

espacement;

terrain;

tree species;

debarking percentage (where applicable);

stem form;

crown shape and size;

lean of the tree;

felling direction;

undergrowth;

serviceability and suitability of equipment;

operator skills;

cutter working alone or with an assistant;

subsequent operations to be completed by the operator and assistant (where applicable);

environmental considerations; and

Figure 4.2: Schematic representation of felling cuts.


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silvicultural considerations.

The production levels for Eucalyptus and Acacia felling, debarking and stacking, which aregiven inAnnexure B, are based on the following task descriptions:

The cutter and an assistant are responsible for felling, cross-cutting, debranching andstacking of brushwood.

The debarkers are responsible for debarking the logs.

The stackers are required to build stacks for further extraction or transport.

Guidelines for task determination for Eucalyptus grandis can be found in Annexure A, andtasking guidelines for pine species can be found inAnnexure C.

4.2 Debarking

Debarking is the process of removing the bark from EucalyptusandAcaciaspecies after felling. This

can be done manually or mechanically.

4.2.1 Manual debarking

Manual debarking is normally performed with a sharpened hatchet. The bark is detached eitheras long or short strips or small plates. As far as possible, effort should be made to ensure thatlogs are free of cambium.

Debarking spuds (hoe type piece of equipment) and shaped spades can also be used todebark. Either tree lengths or logs can be debarked.

4.2.2 The following is seen as the minimum protective clothing that must be worn by manualdebarkers:

overalls; hard hat;

safety boots;

leg protectors;

rubber gloves;

eye protection.

Manual debarking is a strenuous job with an awkward posture and debarkers must be trained inthe correct debarking techniques.

4.2.3 Debarkers must take note of the following :

Always debark on the far side of the log away from feet and legs.

Always use a properly maintained debarking tool.

Always chip away from yourself.

Do not walk or stand on wet logs.
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4.2.4 Debarking percentage

Debarking percentage is the term used to express the ease of removing the bark from freshlyfelled Eucalyptusand Acaciaspecies. It is the percentage of cleanly debarked logs in a totalnumber of debarked logs.

Debarking % = (number of cleanly debarked logs total number of logs sampled) x 100

Cleanly debarked logs are logs where no cambium or less than 30% cambium remains on thelog. Chiselled or shaved logs are where more than 30% cambium remains and the bark has tobe chiselled off in small pieces. See Photo 4.1and 4.2below:

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Debarking is expressed in classes as shown in the following table. Note that the table gives thedebarking class, the corresponding debarking percentage and the debarking percentage as youwill find it in the tasking sheets in the annexures.

Debarking class Debarking % Task Table

1 0 -40 40%

2 41 55 50%

3 56 75 60% - 70%

4 76 85 80%

5 86 - 100 90%

Rip-stripping is a term used where the debarkers rip the bark off in long strips from standingtrees. This practice is only viable when trees are debarking well. Debarkers should be on thelookout for falling branches and premature breaking of the bark when rip-stripping.

Photo 4.1 (left): Cleanly stripped log.1

Photo 4.2 (right ): Chiselled log.1

Table 4.1: Debarking classes.


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The stripability percentage can be influenced by the following factors:

species;

growing site;

season of stripping;

time of day;

temperature;

time after felling; and

whether the trees are stressed (drought, disease) or not.

Debarking tasking tables are presented for Eucalypts grandis, Eucalyptus macarthurii,Eucalyptus smithii as well asAcaciamearnsii.

4.2.5 Preparing wattle bark

Wattle bark is normally stacked in bundles of approximately 40cm x 40cm x 231 or 240cm. Thinstrips of bark are used to tie the bundle.

Bundle size is determined by the specifications of the receiving bark mill. Bark bundles vary inmass from 25kg to 40kg per bundle. Photo 4.4below is an example of a bark bundle beingprepared.

Photo 4.3: Ripped stripped trees.1


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Bark thickness is an important factor as mills pay a premium for thicker bark.

The tables in Annexure E2 give an indication of bark mass and volume for different bark

thicknesses.

4.3 Debranching

Debranching is the process of removing the branches from felled trees.

4.3.1 When debranching by axe the following should be noted: Work from the butt-end of the tree towards the top.

Always debranch from the far side of the log.

Axe strokes should be with the angle of the branch and not against it.

Only debranch merchandisable timber. Do not waste effort to debranch above theminimum diameter mark.

Debranchers should be outside the danger zone of two tree lengths from fellingoperations.

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Debranching by chainsaw is the preferred method to remove branches. There are mainly twodifferentmethods to approach debranching, namely the six point lever method and the sweepmethod.

4 See Figure 4.3and 4.4.

4.3.2 Irrespective of whi ch method is used, the following basic rules should be observed:

Work at a comfortable height and try to avoid bending over. This can be achieved byplanning ahead and by correct felling. Use already felled trees, rocks or the terrain tocreate a comfortable working height.

Get a firm foothold and work with the chainsaw close to your body.

Flex your knees and not your back.

Do not move your feet when you are sawing on the same side of the tree as you arestanding.

Photo 4.4: Preparing a bark bundle.1
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The weight of the saw should be against the tree and not your leg.

Lead with your left leg when starting to debranch.

4.4 Cross-cutting

Cross-cutting is the process whereby felled trees are cut into marketable lengths infield or at landings.It is important to use the correct technique when cross-cutting. Using the wrong technique can causeaccidents, pinching of the saw or splitting of the log.

4.4.1 Observe the following when cross-cutti ng:

Determine the stresses the stem is under, example upward, downward or sideways.

Observe carefully how the timber reacts to being sawn.

Be aware of where you are standing when you cross-cut.

Stand off to one side instead of right in front of the cut.

When cross-cutting stems with sideways tension one must always stand on the inside ofthe curve when cutting.

Figure 4.5, 4.6and 4.7demonstrate the cutting technique for the most common tensions a stemcan be subjected to.

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Figure 4.3 (left): Six point lever method of debranching.Figure 4.4 (right): Sweep method of debranching.


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Method to use:1. Start by making a cut downwards until the cut begins to pinch the guidebar.

2. Continue the cut from the bottom upwards. Try to make the two cuts meet.

Method to use:

1. Start by making a cut upwards until the cut begins to pinch the guidebar.

2. Continue the cut from the top side downwards. Try to make the two cuts meet.

Figure 4.5: Stem with downward tension.

Figure 4.6: Stem with upward tension.


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Method to use:

1. Cut an open directional wedge on the inside or non-stressed side of the stem.

2. Start at the top and saw in stages until the stem breaks.

3. Remember to always stand on the inside or non-stressed side of the stem.

Guidelines for cross-cutting can be found inAnnexure F.

4.5 Infield stacking

Infield stacking is the process whereby logs are grouped infield for further loading. The size of thestack is determined by the available volume, the log size and the loading method that will be used.

Stacking can be done by hand or mechanically. As excessive infield disturbance of the soil is notgood practice, mechanical stacking by 3-wheeler should be minimised where possible.

Stackers should always ensure that the stacking area is free of bark, branches or other debris.Building the stack on bearers will ensure that minimum debris is picked up at loading.

4.5.1 Stacking productivity and quality may be influenced by the following factors:

safety considerations;

log length;

piece size and mass;

available volume per hectare; terrain conditions;

stacking area;

stacking method; and

machinery employed.

Positioning of the stack is an important element. If the stack is positioned in between stumpsor standing trees, it could negatively affect the loading of the timber. The stack must be

Figure 4.7: Stem under sideways tension.


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created in such a position that the section of the stack at the point where the grab of theloading machine secures the logs is free of all obstacles.

All stackers should be issued with logging tongs and should be trained in the proper use of

them.

4.5.2 Stack types

Depending on the terrain, stacking method, piece size and loading method, there are differenttypes of stacks that can be constructed.

4.5.3 Rough-lining of timber

In this method the timber is just turned so that it all faces the same direction. The timber isnormally not stacked but lies on long roughly aligned rows. See Photo 4.6.

Photo 4.5: Logging tongs.

Photo 4.6: Roughlined timber.


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4.5.4 Classic stack

This type of stack is constructed by laying down two bearer logs approximately 2m apart.Uprights are hit into the ground to support the stacked timber. Depending on the loadingand/or extraction method, stack size may vary anything from 2 to 5 tons per stack. See

Photo 4.7.

4.5.5 Diamond stack

This type of stack does not require any uprights to be driven into the ground for support. Thestack is built to supply its own support. This type of stack works well in flat areas. See

Photo 4.8.

Photo 4.7: Classic stack.

Photo 4.8: Diamond stack.


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4.5.6 Stacking product ion

Stacking production is a function of the log size (length and volume), available volume, terrainand the type of stack to be built. Task tables for stacking of Eucalyptus are given inAnnexure D. These tasks are based on building a classic stack.

4.6. Mechanised timber preparation

Mechanised timber preparation is gaining acceptance throughout our industry. Various equipmentmanufacturers are actively importing harvesting machines and related equipment.

The mechanised timber preparation system can be classified into semi-mechanised and fully-mechanised systems. See flowchart below.

Semi mechanised systems are defined as a combination of motor-manual felling and mechanicaldebarking or further processing. The debarking, for example, can be done by a debarking head orother mechanical means like flail debarkers. Photo 4.9shows a locally developed debarking headand Photo 4.10a small flail debarker.

Mechanisedharvesting

Semi-mechanised

Fullymechanised

Wheeled based Tracked base Cut to length Multi stem

Purpose built Hybrid Wheeled

Wheeledleveling / non-

leveling

Trackedleveling / non-

leveling

Wheeledleveling / non-

leveling

Trackedleveling / non-

leveling

Figure 4.8: Classification of mechanized harvesting systems.


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Fully mechanised systems are systems where the felling and further conversion of the tree is done byfully mechanical means. The full mechanical system can further be categorised as Cut to Length (CTL)or multi stem systems.

Photo 4.9: Locally designed debarking head.

Photo 4.10: Locally manufactured flail debarker.


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CTL systems normally use equipment that can process one tree at a time. The tree is felled,debranched, debarked (where applicable) and cross-cut into lengths and deposited ready for loading byone machine. See Photo 4.11.

CTL systems can furthermore be classified into so-called hybrid systems or purpose built systems. Thehybrid systems are set up utilising an excavator or other suitable carrier together with a harvestinghead.

Purpose built systems are specifically designed to perform a harvesting function.

Multi stem systems can process more than one stem at a time. See Photo 4.12. The multi stem system

normally uses a felling and bunching piece of equipment, an extraction piece of equipment, a cross-cutor debarking system or even a chipping system.

4.7 Mechanised felling

Mechanised felling has the following advantages over motor manual felling:

Increased safety of the felling operation.

Increased felling production and productivity.

Improved downstream extraction activities due to improved directional felling andbunching.

Photo 4.11: Tracked single stem harvester (CTL system).

Photo 4.12: Equipment used in a multi stem harvesting system (feller buncher, grapple skidder,

slasher deck).


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Multi shift felling allows for better equipment utilization.

The following factors could inf luence mechanised felling productivity:

safety considerations; tree species;

tree size;

tree diameter;

espacement;

terrain;

underfoot conditions;

debarking percentage (where applicable);

stem form;

crown shape and size;

number and size of branches;

equipment type; and operator competence.

Mechanical felling heads use either a shear or a non-shear function to cut through a tree.

Shears cut through a tree like scissors. See Photo 4.13. Non-shear disks cut through the tree usingeither a rotating disk or a bar and chain. See Photo 4.14.

4.8 Mechanical debarking

There are various types of mechanical debarking heads on the market. They all work on the principleof grooved rollers rotating the stem under pressure, which causes the bark to be stripped off as thestem passes through the rollers. Cutting knives shear off the branches in front of the rollers (seePhoto 4.15).

Photo 4.13 (left): Shear type felling head.Photo 4.14 (right): Felling head utilizing bar and chain.

1


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As with manual debarking there are various factors that could influence the debarking production andquality. Such factors include:

species;

roller feed speed;

roller pressure;

tree form;

number and size of branches;

operator competence; and terrain.

1Photos by A. Immelman.

Photo 4.15: Felling/debarking head.

Photo 4.16 (left): Mechanically debarked timber.1

Photo 4.17 (right): Timber presentation from mechanical felling, debarking and cross-cutting.1


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2Tables taken from De La Bordes Timber Harvesting Manual 1992.

3Zaremba - 1976.

4Husqvarna undated.

5Photo by G. van Huysteen.

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