Timber Technology Flashcards
What is the centre of the tree called?
The Pith. It is not very good wood
Dead Part of the three trunk?
Heartwood. Protects from fungal
What is Sap Wood?
Nutrient Part of the tree. Living
Two Main Classes of Wood Species?
Softwood and Hardwood
Soft Wood Characteristics?
- Softer
- Easier to Handle
- Does not split when nailed
- Popular as sawn Timber
Softwood Trees?
Evergreen Trees such as Pine and Fir
Hardwood Trees?
Deciduous trees such as:
- Mahogany
- Oak
- Maple
- Gum Trees
- Walnut used in high quality furniture
Which direction is shrinkage least likely to occur?
Longitudinal
Two types of shrinkage?
Tangential - Results in timber stressing
Radial -
How Does Cupping occur?
When grains of wood are at angles
What percent mark does shrinkage occur?
25%
How is wood dried/seasoned?
Kiln drying:
- Steam
- LPG Gas
- Solar
- Off cuts
Air drying
Other:
- Chemical
- Microwave
What is EMC?
Equilibrium Moisture Content
What is external/inland EMC?
15%
Describe EMC flows?
- Wet atm/Dry Wood = Moisture moves to wood
- Dry Atm/Wet Wood = Moisture moves from wood
- Wood at EMC = No moisture movement to/from wood
Benefits of Seasoning?
- Better Resistance to decay by fungi
- Improved resistance to weathering
- Stale in dimension; Creep Alleviated; Protective coating adheres better
- Strength Improves
What are the timber products?
- Sawn Timber
- Laminated Veneer Lumber (LVL)
- Plywood
- Hardboard
- Glulam
Sawn Timber Examples. (Probably won’t examine)
- Stump: Foundation of houses
- Bearer: Bears load of house
- Floor Joist: Prevent bearer from bending
- Stud: Wall Timber
How is LVL made?
Timber is sawn into thin piles (Laminates) along the direction of the fibre
What is Plywood?
Similar to LVC but the fibres in adjacent sheets are orthogonal directions (Criss cross)
Difference between plywood and LVL?
- Alternative directions in plywood
2. Plywood is a sheet product whereas LVL is a beam
What is hardboard?
Hardboard is a compressed composite board
What is Medium Density Fibreboard (MDF)?
MDF is a type of hardboard which is made from wood fibres glued under heat and pressure
What is Glulam (Glue Laminated Timber)?
Plain saw timber bits glues together, enabling curved and tapered features to be achieved
What is cross laminated timber?
Plain sawn timber put into a panel. They are in layers. Sticking together timber. Used for big buildings. Layered in different directions. Alternating pattern makes a plate. We want stiffness in multiple directions.
Sorting timber classifications?
Appearance grading and Structural Grading
Structural Gradings Methods?
Visual stress grading
Machine Stress Grading
Proof Grading
Quality Control
Most common timber grade?
F7
Visual Stress Grading Characteristics?
- Size of knots relative to specimen
- Borer Holes
- Termite Galleries
Why are knots problems?
They change grain direction. This can cause localised weak spots
Durability Issues?
- Weathering
- Decay with Fungi
- Termites and bores
- Countering Measures
Weathering issues?
- Bleaching and erosion of surface
- Loosening of timbers
- Opening of cracks
- End of lumbers most vulnerable
- Metal connectors are prone to corrosion
Fungi occurs at:
- M.C >20%
- Presence of oxygen
- Ideal at 25-40deg C
- Sapwood at periphery is more vulnerable
Termite and bores facts:
- Hazard level increases with latitude
- End of member is most vulnerable to attack
Countering Measures:
- Sheltering and protective
- Isolation from ground
- Moisture control
- Use durable timber specie
- Chemical treatment
Difference between glulam and LVL?
Glulam uses plain sawn timber stuck together with reasonable thickness whereas LVL uses thicker ones stuck together
