Timber Seasoning 6m3i4k

TIMBER SEASONING NATURAL SEASONING ARTIFICIAL SEASONING

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UNIT III TIMBER 8 Classification of trees, structure of trees, Defects in timber, Storage of timber, Uses of timber, characteristics, seasoning of timber, Defects and diseases, Decay of timber, Preservation, Fire resistance, Conservation of timber. UNIT IV TIMBER PRODUCTS 8 Market forms of timber, Industrial timber, - Veneers and Veneer Plywoods, Particle board, Hard board, Fibre board, Block board and Lamin boards, Laminates, advantages and Blockboard uses. UNIT V PAINTING AND VARNISHING IN TIMBER 7 Composition, characteristics, preparation, Primer, Painting different surfaces. Enamels, Paint, Varnishing – types of varnishing Miscellaneous paints, defects, uses and cost of materials. TOTAL: 45 PERIODS

SEASONING Newly felled tree contains – 50% of its weight in water. WATER – is I the form of 1. FREE MOISTURE 2. BOUND MOISTURE

The process of drying timber is known as seasoning of timber and that moisture should be removed under controlled conditions as nearly as uniformly as possible. Wood is a hygroscopic material. OBJECTIVE OF SEASONING  Allows timber to burn readily  Decreases weight of timber  Imparts hardness, stiffness and strength.  Increases resisting power of timber to decay.  Makes timber easily workable.  Makes it suitable for receiving paints, for ting and gluing.  Reduces the tendency of timber to crack, shrink and warp.

METHODS OF SEASONING NATURAL SEASONING  Carried out by natural air.  Also known as AIR SEASONING 

ARTIFICIAL SEASONING  Various methods of artificial seasoning are 

BOILING  CHEMICAL SEASONING  ELECTRICAL SEASONING  KILN SEASONING  WATER SEASONING 

NATURAL SEASONING Timber Planks

Spacers

Stacked timber during seasoning.

STEPS INVOLVED 1. Log forms are usually not suitable, hence they are cut into scantlings or planks.

2. Can be stacked either horizontally or vertically 3. The ground is cleared and leveled for good drainage. 4. Platform is made slightly higher, about 300 mm from the ground level. 5. Timber pieces are sorted out according to the length and thickness. They are arranged in layers.

6. Each layer is separated by spacers of dry wood. 7. The distance between the spacers depends upon the sizes of the timber to be seasoned.

8. The stacks need to be covered by a roof of suitable material so that it is protected from fast blowing winds rains etc.

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ADVANTAGES

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Moisture content can be brought down to 10 to 20 % It does not require skilled Supervision Uneconomical to provide artificial seasoning to planks with thickness of more than 100 mm Cheap and simple

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DISADVANTAGES  Becomes difficult to control it.  Drying may not be uniform and even.  Chances of the ends sections not being dried properly  If not attended properly, attack of fungi and insects may take place.  Moisture cannot be brought down to the necessary level.  Space required is more 

Artificial seasoning Defects such as shrinkage and warping can be reduced  Drying is controlled  No attack of fungi or insects  Reduces the period of seasoning  Better circulation of air, humidity 

BOILING Timber is immersed in water and then boiled  Very quick method  3- 4 hours  Then taken out and dried slowly in a shed  Proves costly 

Chemical seasoning Known as salt seasoning  Timber immesed in solution of salt  Taken out and seasoned in the ordinary method  interior dries faster than exterior.  External cracks are reduced. 

ELECTRICAL SEASONING Uses high frequency alternating current.  Increases resistance to  Rapid method of seasoning.  Initial maintenance costs are very high. 

KILN SEASONING 

The process of kiln drying consists basically of introducing heat. This may be directly, using natural gas and/or electricity or indirectly, through steam-heated heat exchangers, although solar energy is also possible.

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For this purpose, the timber is stacked in chambers, called wood drying kilns, which are fitted with equipment for manipulation and control of the temperature and the relative humidity of the drying air and its circulation rate through the timber stack

Kilns are usually divided into two classes: 1. Progressive 2. Ccompartment Both methods rely on the controlled environment to dry out the timber and require the following factors: • • •

Forced air circulation by using large fans, blowers, Heat of some form provided by piped steam. Humidity control provided by steam jets.

Amount and Duration of Air, Heat and Humidity depends upon: 1. Species 2. Size 3. Quantity

Progressive Seasoning 

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In the progressive kiln, timber enters at one end and moves progressively through the kiln much as a car moves through a tunnel. Temperature and humidity differentials are maintained throughout the length of the kiln so that the lumber charge is progressively dried as it moves from one end to the other. Progressive kilns may be further subdivided into natural draft kilns in which heated air is allowed to rise through the material by natural convection, and forced draft kilns in which fans are employed to force the air through the wood. A progressive kiln has the stack on trolleys that ‘progressively’ travel through chambers that change the conditions as it travels through the varying atmospheres.

Progressive Kiln

The advantage of this system, although much larger, has a continuous flow of seasoned timber coming off line

Compartmental Seasoning: 

A compartment kiln is a single enclosed container or building, etc.

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The timber is stacked as described above and the whole stack is seasoned using a programme of settings until the whole stack is reduced as required.

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Compartment kilns differ from progressive kilns in that the timber is loaded into the kiln and remains in place throughout the drying process.

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Compartment kilns are usually smaller than progressive kilns, and because of their construction the temperature and humidity conditions within them can be closely controlled.

Compartmental Seasoning: 

Consequently, they are often used to dry expensive material or woods which are difficult to dry.

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Circulation may be either forced or natural just as with progressive kilns.

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Drying conditions cannot be controlled as closely in natural draft compartment kilns, however, as in forced draft kilns, and the rate of drying is also slower.

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For these reasons kilns built today are of the forced draft type and many of the old natural draft types have been converted

Compartmental Kiln

Compartmental Kiln

Water Seasoning One of the best of these is to immerse the timber in water as soon as it is cut down, and after it has remained about a fortnight in water, but not more, to take it out, and dry it in an airy situation.  When timber is put in water it must be sunk so as to be completely under water, as nothing is more destructive than partial immersion. Salt water is considered best for ship-timber, ‡ but for timber to be employed in the construction of dwelling-houses fresh water is better  Timber that has been cut when the tree was full of sap, and particularly when that sap is of a saccharine nature, must be materially benefited by steeping in water; because it will undoubtedly remove the greater part of the fermentable matter. 

Methods of sawing timber ORDINARY SAWN OR FLAT SAWN 1. Parallel cuts made throughout the length of the log 2. Cutting parallel slices of planks 3. Easiest and economical method 4. Shrinkage of sapwood more than the heartwood 5. Causing warp and twisting of planks QUARTER SAWING 1. Tendency to cup i.e. to curve in a transverse direction 2. When applied to wood, not having distinct medullar rays ►this method produces very fine wood RIFT OR RADIAL SAWING 1. Timber cut parallel to medullar rays and perpendicular to annual rings

TANGENTIAL SAWING 1. Boards or planks sawn tangentially to annual rings 2. Not suitable for flooring 3. Planks cut by this method warp too much

INDUSTRIAL TIMBER VENEERS  PLYWOODS  FIBREBOARDS  IMPREG TIMBER  COMPREG TIMBER 

VENEERS 

veneer refers to thin slices of wood, usually thinner than 3 mm (1/8 inch), that are typically glued onto core s (typically, wood, particle board or mediumdensity fiberboard) to produce flat s

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A rotary lathe in which the wood is turned against a very sharp blade and peeled off in one continuous or semi-continuous roll. Rotary-cut veneer is mainly used for plywood, as the appearance is not desirable because the veneer is cut concentric to the growth rings.

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A slicing machine in which the flitch or piece of log is raised and lowered against the blade and slices of the log are made. This yields veneer which looks like sawn pieces of wood, cut across the growth rings.

VENEERS crown cut is shown on the left)

quarter sawn

Advantages of using veneers In addition to the obvious savings of our natural resources, many projects built using wood veneer would not be possible to construct using solid lumber. Due to expansion and contraction common to all wood products and caused by changes in humidity, many of the patterns and designs possible with veneers would self destruct, if attempted with solid lumber. The limitless designs done with marquetry and parquetry would also be impossible

TIMBER SUITABLE FOR VENEER MAHOGANY  OAK  ROSEWOOD  SISOO  TEAK 

INTERIOR APPLICATIONS

PLYWOODS Plywood is a manufactured wood, made by gluing together a number of thin veneers or plies of softwood or hardwood.  A common reason for using plywood instead of plain wood is its resistance to cracking, shrinkage, twisting/warping, and its general high degree of strength.  Also, plywood can be manufactured in sheets far wider than the trees from which it was made. It has replaced many dimensional lumbers on construction applications for these reasons 

1. Plywood for indoor use generally uses the less expensive urea-formaldehyde glue which has limited water resistance, while outdoor and marine-grade plywood are designed to withstand rot, and use a water resistant phenol-formaldehyde glue to prevent delamination and to retain strength in high humidity 2.Marine plywood is specially treated to resist rotting in a high-moisture environment. Marine plywood is frequently used in the construction of docks and boats. It is much more expensive than standard plywood:

Applications Plywood is used in many applications that need high-quality, high-strength sheet material.  Quality in this context means resistance to cracking, breaking, shrinkage, twisting and warping 

Softwood plywood applications Typical end uses of spruce plywood are: 1. 2. 3. 4. 5. 6.

Floors, walls and roofs in house constructions Wind bracing s Vehicle internal body work Packages and boxes Hoarding Fencing

Fibreboard 

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Fiberboard is a type of engineered wood product that is made out of wood fibers. Types of fiberboard (in order of increasing density) include particle board, medium-density fiberboard, and hardboard. Fiberboard is sometimes used as a synonym for particle board, but particle board usually refers to low-density fiberboard Plywood is not a type of fiberboard, as it is made of thin sheets of wood, not wood fibers or particles. Fiberboard, particularly medium-density fiberboard (MDF), is heavily used in the furniture industry.

Benefits of MDF

Drawbacks of MDF

1. Is an excellent substrate for veneers. 2. Is becoming an environmentally friendly product. 3. Some varieties are less expensive than many natural woods 4. Isotropic (its properties are the same in all directions as a result of no grain), so no tendency to split 5. Consistent in strength and size 6. Flexible. 7. Can be used for curved walls or surfaces. 8. Shapes well.

1. More dense than plywood or chipboard (the resins are heavy) 2. Swells and breaks when saturated with water 3. May warp or expand if not sealed 4. Dulls blades more quickly than many woods 1. Subject to significant shrinkage in low humidity environments. 2. Trim (i.e. baseboards) comes preprimed but this is insufficient for fine finish painting. 3. Painting with latex paints is difficult due to rapid water absorption. Most finishes appear uneven and nail holes tend to pucker a bit. 4. low weight and easy moving.

Manufacture 1. The debarked logs are sent to the MDF plant where they go through the chipping process. A typical disk chipper contains 4-16 blades. Any resulting chips that are too large may be re-chipped; undersized chips may be used as fuel. The chips are then washed and checked for defects. 2. The chips are then compacted using a screw feeder, and will be heated for 30120 seconds to soften the wood; they are then fed into a defibrator which maintains high pressure and temperature. 3. The pulp that exits from the defibrator is fine, fluffy, and light in weight and in colour. 4. Then steam is itted into the vessel 5. The pressure of the steam is increased to 7 N/mm2 6. The sudden increase in pressure, makes the wood pieces to explode, so the natural adhesive in them is separated out.

7. The fibres are then allowed to flow out. 8. They are ten cleaned of all superfluous or extra gums 9. Then they are spread on wire sheets or blankets of the suitable thickness.

Particleboard Particle board is an engineered wood product manufactured from wood particles, such as wood chips, sawmill shavings, or even saw dust, and a synthetic resin or other suitable binder, which is pressed and extruded. Particleboard is a composite material.

Particleboard with veneer.

IMPREG TIMBER    

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Fully or partly covered with resin Resin employed- phenol formaldehyde Veneers or thin strips of wood are taken and then immersed in resin. The resin fills the space between the wood cells and by chemicl reaction a consolidated mass develops. It is then cured at a tempersture of 150-160 deg. C Available as FORMICA, SUNGLOSS, SUNMICS

1. Not affected by weather conditions 2. Strong and durable 3. Possess more electrical insulation

4. Presents a neat appearance.

COMPREG TIMBER Similar to impreg timber.  Except that curing is carried out under pressure. 