Hazard Identification (HAZID) vs. Hazard and Operability (HAZOP): A Comparati...
Basic construction skills
1. Basic Construction Skills
Timber Vocation
Basic Material
Softwood
Hardwood
Sheet Material
Softwood
Wood from coniferous trees are terminated softwood. Conifers are evergreen trees such as
Spruce, Deodar and Walnut etc.
Softwood forms 80% of the world's timber production.
Softwoods are not necessarily softer than hardwoods. In both groups there is an enormous
variation in actual wood hardness.
Some hardwoods (e.g. balsa) are softer than most softwoods.
There are about a hundred times as many hardwoods as there are softwood. The woods
of longleaf pine, douglas fir, and yew are much harder in the mechanical sense than
several hardwoods.
Properties of Softwood
Softwood is light in weight and color
Annual rings are very distinct
Comparatively weaker and split easily
Has straight fiber
Is resinous, contains resins and turpentine with a peculiar fragrance
Very strong is resisting tensile forces
Weak in bearing loads across grain
Has soft and regular texture
Use of Softwood
Many American homes are built of Canadian softwood lumber
In general softwood is easy to work. It forms the bulk of wood use by humans
Extensively use as material for structural components
Used in the manufacture of furniture, decorative timber items, machined items
As raw material for pulp in the production of paper and paper board
2. Hardwood
Hardwood is wood from dicotyledonous trees
These are usually broad-leaved trees are mostly deciduous, but
in tropics and subtropics mostly evergreen.
Hardwood should not be confused with the term 'heartwood', which means mature wood in the heart of
exogenous tress.
Hardwoods are not necessarily harder than softwoods. There are many hardwoods which are softer
Structure of Hardwood
Hardwoods have a more complex structure than softwoods.
The dominant feature separating "hardwoods" from softwoods is the presence of pores, or vessels.
Annual rings are not distinct.
The wood is hard and difficult to work with.
Contain large percentage of acid.
Strong in resisting, shearing stress.
Close grained and strong
No resinous
Teak, Ork and Mahogany are some examples.
Applications
Hardwoods are employed in a large range of applications including:
Construction, furniture and flooring
Solid hardwood products are more expensive compared to softwood
Countries with cold climates used to import hardwood such as Burma Teak, and Mahogany
Therefore cheaper "hardwood" doors, for instance, now consist of a thin veneer bonded to a core
of softwood, plywood or medium-density fibreboard (MDF).
Hardwoods can also be used in a variety of objects but mainly for furniture or musical instruments because of
their density.
Sheet Timber
Also called manufactured timber
Sheet timber is used with the intention of reducing tree cutting by manufacturing wood material from waster or
cheap (inferior) timber
Veneers
Thin sheet of wood peeled off, sliced or swan from a log
Manufactured by rotary veneer cutters or slicing machines
Thicknesses of veneers are from 4mm to 6mm
Veneers of expensive timber are glued to inferior timber to improve appearance and from decorative designs
Veneers are used in the manufacture of Plywood, Lamin board and Batten board ect.
3. Plywood
Veneers used for making plywood are called piles
Plies are glued in odd numbers to form plywood. Gluing is done under pressure
Direction of grain of adjacent plies is crossed to give more strength and to prevent shrinkage and wrapping of
plywood
The two external plies are called face plies and can be of rich grained expensive timber
Standers size of the plywood board is 2.4m x 1.2m
Advantageof Plywood
Givesbetterappearance
Strongera three plywoodboardisthree timesstrongerthana solidboardof same thickness
Can be easilybent
Shrinkage andexpansionisnegligible due tocrossgrainedstructure
Givesuniformtensile strengthinall directions
Available inlarge sizesthatare not possible withsolidboard
Doesnot splitwhennailednearthe edge
Uses of Plywood
Plywoodisusedfor;
Wall paneling
Doors
Furniture
Form workinconcrete
Cheapervarietiesare usedinpackaging
Laminboard