FORE327 2023 and 2024 exams

1. Advantages of debarking

• Prevents saw and planer damage from bark, grit and stones

• Reduces wear on machinery

• Improves surface quality; Minimises chip contamination.

2. Ring vs Rosserhead debarkers

Ring: rotating ring scrapes bark; continuous, good for straight logs, less effective on crooked ones.

Rosserhead: spinning cutter peels bark; handles irregular logs, slower batch process.

The majority of harvested hardwood logs in temperate zones are of low quality.

Outline a processing strategy to obtain a high-quality appearance-grade solid wood product from such low-quality logs.

Cut into small, clear pieces (edge glue, finger joint), or use veneer-based panels (plywood, LVL)

optimise sawing and drying to hide defects.

4. Kiln drying defects

• Warping

• Cracking/checks

• Discolouration.

• Case hardening

Give two reasons why some timbers are more difficult to dry than others.

1. Heartwood vs sapwood permeability (extractive presence)

2. Density differences.

By which 3 physical principles can energy be transferred into wood

• Conduction - heat transfer through contact

• Convection - heat moved from moving hot air or steam

• Radiation - heat from electromagnetic waves

7. Methods to increase the life of timber

• Constructive: keep wood dry

• Modification: change chemistry (acetylation, heat)

• Preservative: toxic chemicals deter decay.

8. Methods for the disposal of treated timber in NZ

Landfill, controlled incineration, hazardous waste treatment.

Recycling limited due to toxic metals/organics; cannot reuse as mulch or board.

9. Give three (3) reasons for the large number of existing grading rules.

• Different end uses

• Different regional standards

• Different species.

10. Machine vs visual grading features

Machine: stiffness (MOE), density

Visual: knot size, distortion.

What is the main visual grading assumption and its problem

• Assumes visible defects correlate with strength

• Problem—correlation is imperfect and variable.

12. Grade recovery for old growth vs new growth pine

Grade recovery: Increases with new growth pine - more boards meet higher grades (fewer defects in faster grown material

Grade quality: Decreases with new growth pine- although recovery is higher, strength within each grade is lower due to lower density, large MFA and more juvenile wood

 

Ways of increasing strength of re-engineered wood

• Defect removal - Defects like knots or cracks are cut out to improve strength and appearance.

• Layer orientation - Veneer or strand layers are oriented at right angles to give uniform strength and stability.

• Adhesive bonding - Layers are glued together under heat and pressure to form a solid, durable composite.

14. Name three of the most important characteristics of non-structural panels.

1. Smooth surface

2. Dimensional stability

3. Easy machining.

15. Density profile in particleboard

High at surfaces, low at core (“M-shaped”) due to surface compression during pressing.

16. Plywood vs OSB characteristics

Plywood: strong/stable, but expensive and veneer-limited.

OSB: cheap, uses small logs, but rough surface and lower stiffness.

Name two (2) markets of paper products that are currently experiencing decreasing demand (i) and two (2) which offer increasing commercial opportunities (ii).

Decline:

• Printing/writing,

• Newsprint.

Growth:

• packaging and container board

• Tissue.

18. Fast-growing eucalyptus plantations have a considerable price advantage over softwood fibre. Why is softwood pulp still produced?

1. Softwood fibres are longer, giving strength and tear resistance, making it higher quality

2. Can be used in hardwood pulp as a blend to increase mechanical properties

 

19. Define Dissolving pulp, which two aspects describe its quality

Highly purified cellulose pulp

• >95% cellulose, low lignin/hemicellulose

• uniform molecular weight.

20. Describe what three (3) cellulose products/forms are (i) and give an example of a

    product in which each is used (ii)?

• man-made cellulose fibrils; e.g. viscose, rayon - regenerated from dissolved cellulose - used in textiles

• Cellulose derivatives: e.g. cellulose acetate, nitrocellulose - plastics, films, coatings

• Microcrystalline cellulose (MCC): mechanically reduced purified cellulose - used in food, pharma fillers 

 

21. Lignin use and alternatives

Currently burned for energy

Alternatives: adhesives/resins, carbon fibre, aromatic chemicals.

Acoustic measurement types and their advantages/disadvantages

• Resonance: accurate but impractical as it can’t be used on standing logs

• Time-of-flight: fast and portable, but less precise, only measures outside of log and influenced by moisture content

For which resources (i) and products (ii) are the 2 main saw milling cutting methods best suited

Band saw:

Resources: Large, high-quality logs

Products: Structural or appearance grade

Why? Produces accurate, thin cuts = less waste and good surface finish

 

Chipper canters:

Resources: Small to medium logs

Products: Commodity framing timber and wood chips

Why? Fast throughput, integrates chipping + sawing for efficiency

 

What factors contribute to the difference between target size and nominal product size for a sawmill cutting standard framing?

• Shrinkage during drying

• Planing allowance

• Saw kerf/tolerance.

By which two (2) physical phenomena can water migrate through wood (i)? What is the driving gradient behind each (ii) and to which state of the water are they most relevant (iii)?

Phenomena

• Capillary flow (liquid flow)

• Diffusion (vapour flow)

 

Driving gradients 

• Capillary: pressure gradient (liquid suction in lumens)

• Diffusion: concentration/vapour pressure gradient

 

Water states:

• Capillary: free water in lumens (above fibre saturation)

• Diffusion: Bound water in cell walls (below fibre saturation)

 

8. What is the main positive effect of a higher temperature on timber drying?

• Increases diffusion rate and vapour pressure

• reduces water viscosity.

Wood is prone to biological decay. Which two (2) criteria are used to estimate the service life of timber according to building standards (i), and what do they represent (ii)?

1. Hazard class (exposure category): Indicates environmental severity (H1 - H6)

2. Natural durability or treatment level: Indicates wood’s inherent or enhanced resistance to decay

These represent the expected exposure conditions and resistance capacity of the timber to biological agents

10. Alternatives to preservatives for timber health

• Design (keep dry)

• modification (alter chemistry to resist decay, acetylation).

List four advantages of re-manufacturing solid wood into engineered wood products?

1. Stable dimensions

2. Efficient use of low-grade wood

3. Higher strength uniformity

4. Large/custom sizes.

13. Rank engineered wood by quality and name their characteristics

1. LVL/Plywood: Veneer-grade logs

2. OSB: Thin, oriented wood strands from small logs

3. MDF: Chips, sawdust, residual fibres, low-grade chips, shavings (usually made of shavings)

4. Particle board: Wood shavings, sawdust, small chips, and planer waste (usually made of particles)

What is the function of heat (i) and pressure (ii) in the production of engineered timber

Heat cures resin and removes water; pressure consolidates mat and ensures bonding.

Why do thicker panels need longer press times (i)?

Give two techniques which can be used to shorten press times (ii). (3 pts)

Heat must penetrate to the core for resin curing, thicker panels take longer for centre to reach target temperature

Techniques to shorten press time:

• Pre-heating the matt (steam, radio frequency, or Infrared)

• Higher platen temperatures or pressing under steam injection

What is the main bonding mechanism by which paper holds together?

Hydrogen bonding between cellulose fibres.(Cohesion)

Which pulps are best suited to achieve high brightness (i) and high opacity (ii), respectively

Brightness: bleached chemical pulp (low lignin, white fibres)

opacity: mechanical pulp (retains lignin, light scattering due to fibre fragments)

Refining technology is used for the production of fibrous material from wood for MDF and paper making. How do the 2 processes differ

MDF = chips defibrated in refiner, longer, coarser fibres

paper = pulp beaten to develop fibrillation on fibre surfaces

 

Why do chemical pulp manufacturers separate the removal of lignin from wood into a pulping and a bleaching step?

• pulping step: removes most lignin to free fibres (preserves carbohydrates)

• bleaching step: removes residual lignin for brightness

• separated to minimise fibre damage and maximise yield

Describe three cellulose products/forms (i) and give an example of a product in which each is used (ii)

• Man-made cellulose (textiles)

• cellulose derivatives (plastics/films)

• microcrystalline cellulose (MCC ) (food/pharma filler).

What is the main technical obstacle that has prevented pyrolysis from becoming a viable industrial scale process for the production of liquid biofuel?

Because it’s chemically unstable and highly acidic, causing storage, corrosion, and handling problems.

22. Biofuel types and yield difference

• Pyrolysis: converts full wood mass (including lignin) - liquid carbon compounds - higher potential yield

• Fermentation: only carbohydrates (cellulose + hemicellulose) converted - lower yield, lignin not fermentable

 

Give an example of the 3 physical principals that allow energy to be transferred into wood being used in timber drying

• Conduction - in conventional kilns, heat conducted from air to wood surface to interior

• Convection - primary heating method in forced air kilns

• Radiation - Used in microwave or infrared drying

give an advantage of each of the 3 physical principals that allow energy to be transferred into wood being used in timber drying

• Conduction - Uniform heat distribution within solid timber

• Convection - Efficient for bulk loads and moisture control 

• Radiation - rapid penetrative heating, interacts with wt timber first, ensuring homogeneous transfer of heat

What are typical conversion rates for structural softwood (i) and appearance grade hardwood (ii) sawmills? (2 pts)

~50% for structural (more tolerance)

~25% for appearance grade (harsher grading)

 

What are the the five stages of a kiln drying schedule

1. Warming Up

• Purpose: Thoroughly heat the wood at a low wet-bulb depression.

• Goal: Avoid initial drying stresses on the surface.

2. Drying Phase

• Purpose: Remove moisture using increasingly severe conditions (high temp and/or low)

• Limitation: Severity is restricted by the development of drying defects.

3. Equalising

• Purpose: Homogenise the Moisture Content across the charge.

• Method: Set the Equilibrium Moisture Content to the target 

4. Conditioning

• Purpose: Remove drying stresses (i.e., case hardening).

• Method: Swell the surface to induce plastic deformation using moist, hot conditions.

5. Cooling

• Purpose: Prevent further drying or surface checking in storage.

• Method: Use a small wet-bulb depression.

Why is Air-Drying used in sawmilling? (2 reasons)

1. Energy/Cost Savings (Pre-Drying): To reduce green timber to the Fibre Saturation Point before high-cost kiln drying.

2. Drying of Speciality/Thick Timber: To achieve a very slow, gentle drying rate necessary for thick hardwoods (e.g., large oak beams) to prevent severe checking and collapse.

What is the primary functional difference between adhesion and cohesion in a wood glue joint?

• Adhesion is the bonding to the wood surface (achieved by Mechanical Interlocking in pores and Chemical Bonds).

• Cohesion is the bonding within the adhesive layer itself (achieved by entanglement of linear polymers).

What phenomenon is critical for a strong glue joint, and how is it measured?

Wettability is critical. It's measured by the contact angle (best is less than 30 degrees). Poor wettability often occurs if the wood surface is exposed to the atmosphere for too long or if pores closed by planing / sanding

What are the two main commercial technologies for virgin pulp production? (2 pts)

1. Chemical Pulping (Kraft Process): Uses chemicals (e.g., sodium sulfide) to dissolve lignin, producing strong fibers for packaging/fine paper.

2. Mechanical Pulping (e.g., TMP): Uses mechanical energy (grinding) to separate fibers, producing high-yield but weaker pulp for newsprint.

Chipping of wood is necessary prior chemical pulping. How is fibre length (i) and penetration of pulping chemicals (ii) influenced by chip length? What is the consequence (iii)? (3 pts)

(i) Fibre length:
Chip length should be large enough to preserve whole fibres. If chips are too short, many fibres are cut—reducing average fibre length and weakening the final pulp strength.

(ii) Penetration of pulping chemicals:
If chips are too long or thick, pulping liquor cannot penetrate evenly to the centre of the chip. This leads to uneven cooking (under- and over-cooked zones).

(iii) Consequence:
Uneven or improper chipping results in non-uniform pulp quality — some fibres are over-degraded while others remain incompletely delignified. This lowers pulp yield and mechanical strength and complicates bleaching.

 

Which paper property is strongly influenced by fibre length (i)? State its relationship to fibre length.

(i) Paper property: Tensile strength (or paper strength).

Relationship:
Tensile strength increases with fibre length, because longer fibres create more fibre–fibre bonding and entanglement, forming a stronger fibre network.
Short fibres produce weaker, less tear-resistant paper.

What are the characteristics of stone ground wood (SGW) and refined mechanical (TMP) pulp (i) and how do they affect the optical properties of paper from these pulps (ii)? (4 pts)

(i) Stone ground wood pulp has short, damaged fibres and high lignin.
Refined mechanical pulp has longer, less damaged fibres but still high lignin.

(ii) High lignin gives high opacity and initial brightness, but the paper yellows over time.
Stone ground wood pulp → higher opacity, lower brightness.
Refined mechanical pulp → better brightness, slightly lower opacity.

Name three technical disadvantages of wood as a fuel? (3 pts)

• Low energy density – Wood contains less energy per unit volume compared to fossil fuels like coal or oil, so larger volumes are needed to produce the same amount of heat.

• High moisture content – Fresh or unseasoned wood has high water content, which reduces combustion efficiency and produces more smoke and pollutants.

• Inconsistent quality – Variations in species, age, and density cause uneven burning, unpredictable heat output, and difficulties in boiler or stove operation.

1. Fast pyrolysis – Heat wood without oxygen → bio‑oil.

2. Gasification + Fischer–Tropsch – Convert to syngas → liquid fuels.

3. Hydrothermal liquefaction – High pressure/temperature → biocrude.

Refining technology is used for the production of fibrous material from wood for MDF and paper, what differences do these processes have on the refining process

• MDF requires steam explosion and fibre separation

• paper making uses mechanical shear

how does the fibrous materials differ in paper and MDF

• MDF fibres are coarse and intact

• paper fibres are flexible and fibrillated for bonding