1. PREPARATION OFTIMBER
CUTTING OF TIMBER
A few hints on the cutting and handling of timber might be useful. The old-fashioned pit-saw was commonly used in the past in South Africa. In parts of Africa it is still used for converting logs into boards. Good work can be done with this tool, but the work is very arduous, frequent sharpening being the rule. Considerable skill is required to produce boards which are even in thickness, flat and straight.
Figure 1: Cutting Trees with a Chainsaw
At one time, teams of 2 or 3 sawyers could be found complete with saws. These teams would usually work on a contract basis. Machine cutting is usually done with a circular saw. With African hardwood the only suitable type is the inserted tooth saw blade. This saw blade, which is initially expensive has special removable teeth which are fitted in sockets on the rim of the blade. The teeth can be sharpened with a carborundum grindstone, some even with afile.
Another popular type of saw blade, especially for re-cutting heavy sections of timber into smaller boards is the tungsten carbide-tipped blade. This is very expensive but gives a long service between sharpening. It requires expert service for reconditioning and sharpening. Saws can be kept sharp for longer periods by debarking the log immediately before conversion. The bark obviously has collected sand and dust over the years and this is very hard on tool edges.
One rule for all timbers is that conversion into boards should take place as soon as possible after felling the tree. The wet sap in the wood makes cutting easier and cracks and shakes have no time to develop in the log. Logs left lying on the ground are also prone to insect attack.
The time of year for felling timber is not really very important; cutting in the wet season means greater risk of insect attack and cutting in the dry season can mean too rapid drying resulting in the degrading of the timber.
SEASONING OF TIMBER
Timber which is susceptible to borer attack and this includes most sapwoods can be given a wash, or
dip, in insecticide. Proprietary compounds are available but the insecticide powders used on crops are perfectly satisfactory. Of course this is only surface treatment and effective usually for the seasoning period only. Msusu wood for instance is almost immune to insect attack when dry but marula is likely to suffer even when dry. The ends of the cut boards can be given a coat of bituminous paint as a sealer. This helps to prevent the rapid drying of the ends of timber which causes the familiar splits resulting in a waste ofwood.
Some form of stacking of the sawn wood in the shade is essential. The Figure below shows what is meant. This air seasoning takes a long time. With most hardwoods rapid drying out is disastrous, splits, shakes and distortion being the result. The stack of wood therefore should not be exposed to drying winds and the stickers should be fairly thin, about 12mm.
Figure 2: Stacking of Sawn Wood
For rough farm work timber can be used in a half-dry state. There are many suitable wood preservatives on the market for rendering the timber ant-and rot-proof. Some woods need no treatment at all and some of the indigenous hardwoods are impenetrable by preservative mixtures. For finer work and for furniture in particular the wood must be well seasoned and rendered as stable as possible. If possible, avoid sapwood unless you require the contrast of colour often found in these timbers.
The following method of finishing works well with our indigenous timber:
- Sand down the surface to a perfect finish using fine glass paper in the final stages. Every single blemish must be removed, a difficult process as indigenous hardwoods are difficult to machine finish without tearing the grain. Faults in the wood surface will be exaggerated not concealed by the polish. Remove all dust in preparation for applying thefinish.
- Mix 1 part turpentine to 1 part of clear polyurethane varnish and apply with a clean brush. Work indoors in a dust free atmosphere. Work with the grain and not acrossit.
- Work should be completed quickly, without going back over areas previously coveredand;
- When completely dry and hard rub down with a fine steel wool until all bright shine has disappeared. This rubbing down is one of the secrets of getting a good finish and this work must be done thoroughly. Work with thegrain and not against it. Then remove all dust. This
process must be repeated at least three times.
- A layer of fine smooth polish will gradually be built up if the work is doneproperly.
- Most people are not willing to rub down the last coat but if a superior natural polish is aimed at the final coat of turpentine and polyurethane should also be rubbed downcarefully.
- Finally, a coat of ordinary furniture cream or wax polish will complete the worksatisfactorily.
In simple terms, the papermaking process has changed very little during 2000 years. The source of material to be used is chosen by the paper-maker, depending on the type of paper he wishes to make and also the part of the world in which he lives. Paper can be made from many sources other than trees. Cellulose is the framework of all land plants and anything which grows from the soil can be used to make paper. In fact, the first known paper-making process took place in China in about 105 A.D., using a mixture of hemp, ropes, and rags and fishing net beaten into a pulp. Today, 90% of paper made comes from wood pulp, produced mainly in the USA, Canada and Scandinavia. As the worId’s population expands and increasing demands are made on natural resources such as trees, other sources of raw material have had to besought.
THE PAPER-MAKING PROCESS
To begin with, the raw material is chopped up into small pieces and ‘cooked’ with steam and chemicals in a digester. The chemicals serve to dissolve or loosen most of the impurities leaving the skeleton, which is cellulose. This cooked pulp is then broken up and washed in a refiner. If necessary, it is also bleached at this stage. The washing further removes impurities not driven out by the chemical action.
The pulp fibre is now fed into a de-fibering machine which separates and teases the bundles of fibre into an even layer of crumbs. This layer is then beaten in a hydrating refiner which softens and loosens the fibrile, thus making the cellulose fibres plastic. The longer the pulp is beaten the stronger and more translucent the paper becomes. Unbeaten pulp is soft and bulky; well-beaten pulp produces a stiff and very dense paper. Once the pulp has been beaten sufficiently it is mixed with 200 times its own weight of water and is then ready to be made intopaper.
The diluted pulp is pumped onto a fine wire gauze screen, leaving the water to filter through the mesh which retains the wet paper fibres. As much water as possible is removed through presses like a wringer on an old-fashioned washing machine and the fibres passed over drying cylinders which are filled with steam and are at a temperature of around120°C.
The final stage of the process is the pushing of the fibre through very large heavy steel rollers running one on top of the other. The weight and friction between the rollers serves to smooth the paper, ironing out any tiny lumps. The resultant paper is wound onto rolls to become the raw material for any number of converting processes, from the manufacture of paper cement bags, liquid and conical containers to corrugatedboxing.
From the above description it can be seen that waste paper can be fed into the paper-making process at the ‘pulper’ stage to make up a large part of the raw materialcontent.
USES OF WASTE PAPER
Recovered waste paper recycled into the paper-making process is used for a variety of reasons in growing quantities and larger amounts of this resource is being utilised in order to conserve the forests of the world.
Figure 3: Bulk waste paper