Properties of Timber

Question 1

How equilibrium moisture content works?

Answer 1

• evap/absorb until equilib with air

- function of temp and relative humidity

Question 2

What is fibre saturation point?

Answer 2

• water free in cavities of cell of held in cell walls by absorption forces

Question 3

How does moisture content change wood? In relation to fsp

Answer 3

• above fsp doesnt change dimensions

- below fsp water is lost from cell walls causing shrinkage

Question 4

What is free water?

Answer 4

liquid filling cell cavities

Question 5

What is bound water?

Answer 5

liquid or vapour chemically bounded by hydrogen to cellulose of wood

Question 6

What is shrinkage?

Answer 6

loss of water from cell walls = compaction of microfibrils (bunch together)

• shrink more in tangential direction
• tot shrinkage in tangential is 5 to 12%
• radial shrinkage = 2/3 of tan
• 0.5% in the longitudinal direction

Question 7

List the 4 lumber process steps in order.

Answer 7

1) Harvesting
2) Sawing
3) Seasoning (Drying)
4) Surfacing (Planing)

Question 8

What is Harvesting (From the lumber process)?

Answer 8

• done when trunk is 400-800mm diameter
• radiata at 25 to 35 years
• douglas fir at 35 to 50 years

Question 9

What is Sawing (From the lumber process)?

Answer 9

1) live (rapid and economical)
2) quatersaw (max amount of prime (vert) cuts)
3) combination (most typical)
- boards in notes

Question 10

What is Seasoning (From the lumber process)?

Answer 10

enter with MC of 30-200%
out with MC of 12-15%
done by oven drying (slow, cheap) or kiln drying (fast, expensive), usually a combo.

Question 11

How do you know if the wood is kiln drying too fast?

Answer 11

Checks

Question 12

How do you know there is over evaporation?

Answer 12

Spaces between layers

Question 13

What is Surfacing (From the lumber process)?

Answer 13

• taking 2-5mm from each side
• sizes represent unsurfaced lumber
  ie 50 x 100 is actually 45 x 90

Question 14

What are some visible feature of wood?

Answer 14

• natural growth, seasoning too fast, diseases, parasites, faulty processing

Question 15

What do knots do to wood?

Answer 15

• reduce strength
• reduce stiffness
• tensile impact
• checks and splits around it

Question 16

What does sloping grain do to wood?

Answer 16

• reduces strength
• reduces stiffness
• reduces tensile strength
• from locally distributed grain from branch
• from log having taper
• spiral fibres

Question 17

Corewood?

Answer 17

• 5 to 10 growth rings
• less dense, small knots
• not all species, in radiata