Code of practice for testing of timbers for plywood manufacture
1987 Edition

Scope Overview - IS 12077: Timber Testing for Plywood Manufacture

Scope (Clause 4.2.1.1 and related):
This standard sets forth the testing requirements for timber veneers used in plywood fabrication, encompassing veneer characteristics, lathe adjustments, shrinkage behavior, and adhesive bonding properties.

Essential Tables & Parameters

Critical Guidelines on Timber Suitability:

• Timber exhibiting internal stresses, cracks, silica deposits, or poor adhesive qualities should be avoided.
• Veneers must dry evenly without warping or distortion.
• Lathe settings should be optimized to minimize surface roughness and defects.

Veneer Shrinkage Percentage Calculation:

[ \text{Shrinkage %} = \frac{\text{Original Dimension} - \text{Final Dimension}}{\text{Original Dimension}} \times 100 ]

Measurement Units (SI Units):

flowchart LR
    A[TIMBER] --> B[VENEER PEELING]
    B --> C{QUALITY INSPECTION}
    C -->|Shrinkage| D[Dimensions Measurement]
    C -->|Adhesion| E[Bond Strength Testing]
    C -->|Surface Defects| F[Lathe Parameter Adjustments]
    D --> G[Approval or Rejection]
    E --> G
    F --> G

Summary: This standard defines the parameters for veneer quality, lathe configuration, shrinkage measurement, and adhesive bonding to ensure the reliability and durability of plywood.

Key References and Data from IS 12077

1. Veneer Lathe Parameter Specifications (Clause 4.2.1.1)

2. Veneer Shrinkage Calculations (Clause 4.2.2.2)

• Shrinkage percentage formula: (\frac{Initial - Final}{Initial} \times 100)
• Table 4 provides shrinkage percentages for width and thickness as moisture contents change.

3. Adhesive Bond Strength Testing (Clause 4.2.4)

4. Timber Unsuitability Factors

• Internal stresses leading to bolt fractures
• Narrow veneer widths due to growth irregularities
• Presence of silica deposits
• Inadequate lathe parameter settings
• Uneven drying, splitting, brittleness
• Poor adhesive bonding
• Failure in adhesive bonding tests
• Severe veneer distortion

5. Units and Symbols (SI Units)

Definitions and Reference Standards in IS 12077

1. Definitions Source:

• Clause 2.1 references definitions from:
  • IS 303:1975 (Rules for numerical rounding)
  • IS 707:1976 (General purpose plywood specifications)

2. Key Data Tables:

Timber Suitability Notes:

• Unsuitable timber exhibits internal stresses, shakes, silica deposits, poor adhesion, or veneer defects like splitting and brittleness.
• Shrinkage and adhesive tests are vital for quality assurance.

SI Units Employed:

Formula for Veneer Shrinkage:

[ \text{Shrinkage %} = \frac{\text{Initial Dimension} - \text{Final Dimension}}{\text{Initial Dimension}} \times 100 ]

flowchart LR
    A[Timber Log] --> B{Check Internal Stress}
    B -- Yes --> C[Reject Timber]
    B -- No --> D{Check for Mineral Deposits}
    D -- Yes --> C
    D -- No --> E{Drying Quality Assessment}
    E -- Poor --> C
    E -- Good --> F{Adhesive Bond Test}
    F -- Fail --> C
    F -- Pass --> G[Approve Timber]

Overview of Requirements and Testing Methods in IS 12077

1. Veneer Shrinkage Measurement (Clause 4.2.2.2)

• Determined by comparing initial and final width and thickness.
• Percentage shrinkage is calculated as:

[ \text{Shrinkage (%)} = \frac{\text{Initial} - \text{Final}}{\text{Initial}} \times 100 ]

• Data recorded in Table 4:

2. Lathe Parameter Settings (Clause 4.2.1.1)

• Critical for producing quality veneer.
• Table 1 provides:

3. Adhesive Bond Strength Testing (Clause 4.2.4)

• Tested under dry, wet, and fungal conditions.
• Format as per Table 5:

4. Timber Unsuitability Indicators

• Internal stresses, shakes, mineral deposits, poor adhesion, and veneer defects.

5. Units Used (SI Units)

• Length: m, Mass: kg, Force: N (1 N = 1 kg·m/s²), Stress: Pa (1 Pa = 1 N/m²)

Process Flow Diagram: Veneer Shrinkage Test

graph TD
    A[Veneer Sample] --> B[Measure Initial Dimensions]
    B --> C[Dry Veneer to Target Moisture]
    C --> D[Measure Final Dimensions]
    D --> E[Calculate Shrinkage %]
    E --> F[Document Results in Table 4]

Inspection Guidelines for Timber and Logs (IS 12077)

1. Sampling and Handling (Clause 3.2)

• Utilize freshly cut logs, preferably sourced individually.
• Preserve bark during transport.
• Immediately apply end-coating and spraying treatments post-felling to deter fungal and insect infestation.

2. Timber Identification (Clause 4.1.1)

• Document:
  • Botanical and trade names of timber species.
  • Density measurements in green state and at 12% moisture content.

3. Lathe Settings for Veneer Production (Clause 4.2.1.1, Table 1)

4. Green Veneer Yield (Clause 4.2.1.2, Table 2)

• Typical yield ranges from 40% to 60% of log volume.
• Losses include rounding, trimming, and clippings.

Process Flowchart: Timber Inspection

flowchart TD
    A[Fresh Log] --> B[Bark Retention]
    B --> C[Apply Protective Coating]
    C --> D[Record Species & Density]
    D --> E[Set Lathe Parameters]
    E --> F[Calculate Green Veneer Yield]
    F --> G[Assess Processing Losses]

Note: Consult IS 12077 Tables 1 and 2 for precise settings and yield calculations.

Processing Trial Highlights (IS 12077)

1. Objective (Clause 4.2)

• Determine optimal processing conditions for each plywood manufacturing stage.

2. Lathe Settings (Clause 4.2.1.1, Table 1)

3. Drying Times (Clause 4.2.2.1, Table 3)

4. Veneer Shrinkage (Clause 4.2.2.2, Table 4)

Formula:

• Shrinkage (%) = (\frac{Initial - Final}{Initial} \times 100)

flowchart LR
    A[Raw Timber] --> B[Lathe Parameter Setup]
    B --> C[Cut Veneer]
    C --> D[Dry Veneer]
    D --> E[Measure Moisture]
    E --> F[Calculate Shrinkage]
    F --> G[Refine Processing Settings]

Refer to IS 12077 for species-specific and thickness-dependent parameters.

Veneer Peeling Parameters and Effects (IS 12077)

1. Lathe Settings Influence (Clause 4.2.1)

• Key parameters include:

  • Horizontal and vertical lathe gaps (mm)
  • Knife angles (degrees) at maximum and minimum bolt diameters
  • Knife bevel and height relative to spindle center

• These influence veneer uniformity, surface smoothness, and defect minimization.

2. Lathe Parameter Table (Table 1, Clause 4.2.1.1)

3. Veneer Shrinkage (Clause 4.2.2.2, Table 4)

• Calculated as:

[ \text{Shrinkage (%)} = \frac{\text{Initial} - \text{Final}}{\text{Initial}} \times 100 ]

• Measured for width and thickness post drying.

4. Adhesive Bonding Tests (Clause 4.2.4)

• Conducted on 3-ply plywood made with 1.6 mm veneers per IS 303-1975.

flowchart LR
    A[Timber Bolt] --> B[Set Lathe Parameters]
    B --> C[Parameters]
    C --> D[Horizontal Gap]
    C --> E[Vertical Gap]
    C --> F[Knife Angle]
    C --> G[Knife Bevel]
    C --> H[Knife Height]
    B --> I[Resulting Veneer Quality]
    I --> J[Thickness Consistency]
    I --> K[Surface Smoothness]
    I --> L[Lathe Checks]

Summary: Proper lathe configuration is crucial for high-quality veneer production.

Veneer Drying Parameters and Quality Control (IS 12077)

Drying Conditions (Clause 4.2.2)

• Typical drying temperature: approximately 140°C.
• Target final moisture content:
  • 6-8% for phenol-formaldehyde bonded plywood.
  • Around 10% for urea-formaldehyde bonded plywood.
• Post-drying stacking for 8-10 days ensures even moisture distribution.

Drying Duration (Clause 2.4 & Table 3)

Veneer Shrinkage (Clause 4.2.2.2, Table 4)

Drying Defects to Observe

• Cracks
• Waviness
• Metal stains
• Gum exudation

flowchart TD
    A[Green Veneer] --> B[Set Dryer Temperature ~140°C]
    B --> C[Drying Time Based on Thickness]
    C --> D[Check Moisture Content (6-10%)]
    D --> E{Presence of Defects?}
    E -- Yes --> F[Log Defects]
    E -- No --> G[Stack for Moisture Equalization]
    G --> H[Ready for Plywood Production]

Summary: Adhering to drying times and temperatures minimizes defects and achieves appropriate moisture levels.

Key Points on Veneer Splicing (IS 12077)

1. Splicing Speeds (Clause 4.2.3)

• Veneers ranging from 1.0 to 2.4 mm thickness are spliced at speeds between 5 and 26 meters per minute.
• Testing performed at 175°C using urea-formaldehyde adhesives.
• Speed depends on timber species and adhesive type (UF, UM resins).

2. Lathe Settings (Clause 4.2.1.1, Table 1)

3. Veneer Shrinkage (Clause 4.2.2.2, Table 4)

• Shrinkage percentages in width and thickness are measured before and after drying.

4. Adhesive Bond Strength (Clause 4.2.4)

• Evaluated on 3-ply plywood with 1.6 mm veneers.
• Testing per IS 303-1975 ensures compliance.

Splicing Speed Formula (Approximate):

[ \text{Splicing Speed} = 5 \text{ to } 26 , \text{m/min} \quad \text{for veneer thickness 1.0-2.4 mm at 175°C using UF resin} ]

flowchart LR
    A[Veneer Thickness] --> B[Adhesive Type]
    B --> C[Splicing Speed (5-26 m/min)]
    C --> D[Spliced Veneer Quality]

Refer to IS 12077 for specific values based on timber and adhesive.

Testing Adhesive Properties of Veneers (IS 12077)

• Test panels consist of 3-ply plywood constructed from 1.6 mm veneers according to IS 303-1975.
• Splicing speeds range from 5 to 26 m/min at 175°C using UF and UM resin adhesives.
• Drying durations depend on veneer thickness, moisture content, and dryer temperature.

Splicing Speed Summary

Additional Notes:

• Adhesive tests conform to IS 303-1975.
• Veneer thickness and moisture impact drying and bonding outcomes.
• Lathe settings influence veneer quality and are specified in Table 1.

flowchart LR
    A[Veneer Preparation] --> B[Drying Parameters]
    B --> C[Adhesive Application (UF/UM)]
    C --> D[Splicing at 175°C]
    D --> E[Adhesive Testing per IS 303]

Consult IS 12077 for detailed drying and bonding protocols.

Evaluation and Reporting Requirements (IS 12077)

Highlights from Clause 4.3 and Related Sections:

• Comprehensive assessment reports must detail veneer characteristics to determine plywood suitability.

• Veneer Shrinkage (Clause 4.2.2.2 & Table 4): [ \text{Shrinkage %} = \frac{\text{Initial} - \text{Final}}{\text{Initial}} \times 100 ]

  • Measurements include width and thickness at specified moisture states.

• Lathe Settings (Clause 4.2.1.1 & Table 1):

  • Includes veneer thickness, lathe gaps, and knife angles.
  • Proper calibration affects quality and processing efficiency.

• Adhesive Bond Strength (Clause 4.2.4 & Table 5):

  • Assessed under dry, wet, and fungal conditions.
  • Reports include failing load and failure percentages.
  • Poor bonding indicates unsuitability.

Timber Unsuitability Summary:

• Internal stresses causing peeling issues
• Excessive core unsuitability
• Silica deposits dulling blades
• Persistent surface defects despite adjustments
• Drying problems such as brittleness
• Weak adhesive bonding
• Severe plywood distortion

Example Shrinkage Data

Reporting Checklist:

• Timber origin and species
• Lathe parameters used
• Shrinkage measurements
• Adhesive bonding results
• Observations on defects
• Final suitability conclusions with rationale

flowchart TD
    A[Timber Sample] --> B{Testing Performed}
    B --> C[Veneer Shrinkage]
    B --> D[Adhesive Strength]
    B --> E[Defect Analysis]
    C & D & E --> F[Final Assessment Report]

Labeling and Documentation Requirements (IS 12077)

1. Labeling Protocols

• Each timber sample or plywood batch must have clear labels indicating:
  • Timber source and species information (see Clause 4.2.1.1, Table 4.1)
  • Grade and type classification
  • Manufacturing date and batch number
• Labels assist in traceability and quality management.

2. Documentation Essentials

• Maintain detailed records of:
  • Timber origin and species
  • Lathe settings used (refer Table 1 for veneer thickness and parameters)
  • Adhesive bond test outcomes (see Table 5 for dry, wet, and fungal conditions)
  • Observations of timber suitability (internal stress, mineral deposits, defects, adhesion failures)

3. Reference Tables

4. Indicators of Unsuitable Timber

• Internal stresses causing bolt failure
• Large unusable core sections
• Silica deposits dulling blades
• Persistent surface defects despite lathe adjustments
• Uneven drying causing splitting or brittleness
• Adhesive bond strength below thresholds
• Pronounced plywood deformation

Process Flowchart: Labeling and Documentation

flowchart TD
    A[Timber Source Details] --> B[Label Applied to Timber]
    B --> C[Lathe Parameters Recorded]
    C --> D[Adhesive Test Results Logged]
    D --> E[Suitability Assessment Documentation]