Manufacture of burnt clay Mangalore pattern roofing tiles- Code of practice

IS 3978 - Scope Summary

IS 3978 primarily covers specifications for Plaster Shears, including performance tests and dimensional requirements.

Scope Highlights:

• Applies to plaster shears used for cutting stone-plaster slabs.
• Defines performance tests to ensure durability and cutting efficiency.
• Requires shears to cut a 20 mm thick stone-plaster slab repeatedly (10 times) without damage.
• Specifies a radius of curvature of cutting jaws = 43 mm (important for design and testing).

Key Specification Points:

Testing Procedure (Clause 6.1):

• Prepare stone-plaster slab as per detailed method (6.1.1).
• Cut slab 10 times with the shears.
• Inspect shears for damage.

flowchart LR
    A[Prepare 20mm stone-plaster slab] --> B[Perform 10 cuts with plaster shears]
    B --> C{Any damage to shears?}
    C -- No --> D[Shears pass performance test]
    C -- Yes --> E[Shears fail test]

This ensures the shears meet durability and functionality standards under IS 3978.

IS 3978 - Definitions Overview

• Clause 2.0 refers to definitions as per IS 1498-1959, which covers standard terms related to soils.
• IS 3978 relies on IS 1498 for foundational terminology, especially for soil classification and properties.
• No direct formulas or tables are given in IS 3978 for definitions; instead, it cross-references IS 1498.

Key Reference: IS 1498-1959 (Soil Classification)

• Defines soil types (Gravel, Sand, Silt, Clay) based on particle size.
• Provides terms like Liquid Limit (LL), Plastic Limit (PL), Plasticity Index (PI).

Typical Soil Particle Size Ranges (from IS 1498):

Important Soil Indices:

• Liquid Limit (LL): Water content at which soil changes from plastic to liquid state.
• Plastic Limit (PL): Water content at which soil changes from semi-solid to plastic state.
• Plasticity Index (PI): PI = LL - PL

Summary:

• IS 3978 defers to IS 1498 for definitions.
• For soil classification and properties, refer to IS 1498 tables and terms.
• No standalone formulas in IS 3978 for definitions.

flowchart LR
    A[IS 3978 Definitions] --> B[Refer IS 1498-1959]
    B --> C[Soil Classification]
    B --> D[Soil Properties: LL, PL, PI]
    C --> E[Gravel, Sand, Silt, Clay]
    D --> F[Plasticity Index = LL - PL]

For detailed soil property definitions, consult IS 1498:1959 alongside IS 3978.

IS 3978: Selection of Site for Manufacture - Key Points

1. Soil Suitability & Water Table (Clause 3.1)

   • Select site with suitable soil for kiln foundation.
   • Water table should be at least 1 meter below kiln floor during burning season to avoid moisture issues.

2. Raw Material Availability (Clause 3.3)

   • Clay must conform to quality requirements.
   • Clay source should be within economical distance.
   • Prioritize proximity to distribution centers over raw material source to reduce finished product transport cost.

3. Climatic & Atmospheric Conditions (Clause 3.4)

   • Weather should be congenial for drying raw tiles.
   • Avoid sites with extreme or rapidly changing climatic conditions to prevent drying defects and economic loss.

Summary Table for Site Selection Criteria

Practical Tip:

Site Selection Priority:

1. Climatic conditions
2. Distribution proximity
3. Raw material availability
4. Soil & water table conditions

flowchart TD
    A[Select Site] --> B[Check Soil Suitability]
    B --> C[Water Table ≥ 1m below kiln floor]
    A --> D[Check Clay Availability & Quality]
    A --> E[Assess Climatic Conditions]
    A --> F[Proximity to Distribution Centers]
    F --> G[Transportation Cost Minimization]

This guidance ensures economic and quality efficiency in burnt clay roofing tile manufacturing.

IS 3978: Raw Material Requirements for Clay Bricks

Key Specifications (Clause 1.5 & 4.2)

• Lime (CaO) + Magnesia (MgO): ≤ 1.5% by weight

  • Lime must be finely divided.
  • Reference: IS 1727-1960.

• Water Soluble Material: ≤ 1% by weight

  • Reference: IS 2720 (Part XXI)-1965.

• Iron Content in Clay: ≤ 5% by weight

  • Reference: IS 2720 (Part XXV)-1966.

• Mechanical Composition (Clause 4.2):

  • Total fines (particles < 75 microns): ≥ 75%
  • Minimum clay content: ≥ 40%
  • Reference: IS 1498-1959, IS 2720 (Part IV)-1965.

Summary Table

Notes:

• These limits ensure durability, strength, and resistance to weathering in bricks.
• Testing procedures for these parameters are detailed in the referenced IS codes.

flowchart LR
    A[Raw Clay Material] --> B{Check Chemical Limits}
    B -->|CaO + MgO ≤ 1.5%| C[Pass]
    B -->|Water Soluble ≤ 1%| C
    B -->|Iron ≤ 5%| C
    C --> D{Check Mechanical Composition}
    D -->|Fines ≥ 75%| E[Acceptable Clay]
    D -->|Clay ≥ 40%| E
   

Preparation of Clay as per IS 3978

Key Specifications & Processes:

• Tempering (Clause 5.2):

  • Add controlled water to clay for workability without excess moisture.
  • Store clay in layers ~20 cm thick for at least 36 hours to ensure homogeneity.
  • Avoid excess moisture to prevent drying defects and dimensional changes.

• Mixing (Clause 5.3):

  • Mix two or more soils to meet clay requirements (Clause 4).
  • Use vat or proportioning box with double shaft mixer for uniformity.

• Grinding (Clause 5.4):

  • Pass mixed clay through high-speed grinding rollers.
  • Extrude through a pugmill for plasticity.
  • Hard clays may require pre-grinding in pan roller mills.

Chemical & Physical Testing (Clause 4.2.1):

• Follow IS 1727-1960, IS 2720 (Part XXI & XXV) for chemical analysis.
• Fire shrinkage test on 20 x 10 cm clay slabs; average shrinkage ~9% (drying + firing).
• Shrinkage measured longitudinally and laterally for mold design.

Summary Table: Clay Preparation Steps

flowchart TD
    A[Raw Clay] --> B[Tempering: Add Water & Store 36 hrs]
    B --> C[Mixing: Proportion & Mix Soils]
    C --> D[Grinding: Rollers & Pugmill]
    D --> E[Testing: Chemical & Shrinkage]
    E --> F[Clay Ready for Tile Manufacture]

This ensures clay with proper plasticity, homogeneity, and dimensional stability for tile making.

IS 3978 Key Points on Molding of Tiles

1. Mould Material & Construction (Clause 6.2)

• Moulds must be cast iron with a well-polished smooth working surface.
• Size accounts for clay shrinkage factor (determined by drying & burning tests).
• When closed, the gap between top & bottom moulds produces a uniform tile section.
• Frequent checks ensure mould wear is within permissible limits to maintain tile size accuracy.

2. Clay Preparation & Soil Composition (Clause 2.1)

• Use locally available soil with mechanical grading within specified limits for strength & low water absorption.
• Soil composition is critical for quality burnt clay tiles.

3. Tile Pressing Procedure (Clause 6.3.1)

• Place a clay slab on the bottom mould.
• Smear mould face with smearing oil (kerosine + vegetable oil) for easy tile release.
• Adjust top mould carefully to avoid section variation affecting flexural strength.
• Pressed tiles are received on a wooden pallet without applying force to avoid damage.

Important Specification Summary

flowchart LR
    A[Clay Preparation] --> B[Clay Slab on Bottom Mould]
    B --> C[Smear Mould with Oil]
    C --> D[Top Mould Adjusted & Closed]
    D --> E[Pressing Operation]
    E --> F[Tile Released on Pallet]

This ensures uniform tile size, strength, and quality as per IS 3978.

Drying Process Key Points from IS 3978:

• Drying Rate: Tiles must dry slowly and steadily to avoid warping, checking, cracking, and crazing. Rapid drying is prohibited.
• Moisture Content: Tiles are sufficiently dry for kiln firing when residual moisture ≤ 4.0% by weight.
• Appearance: Properly dried tiles show a light grey color.
• Artificial Drying: Artificial heat may be used cautiously during monsoon; indiscriminate heat causes breakage.
• Humidity Dryers: Can be used for faster drying but drying schedules must match clay type.

Key Formula: Drying Shrinkage (Clause 2.1)

[ \text{Drying Shrinkage } (S_{ho}) = \frac{V - V_d}{V} \times 100 ]

• (V) = Plastic (wet) volume of tile
• (V_d) = Dry volume of tile

Drying Recommendations Summary:

Kiln Draft and Moisture Removal (Clauses 11.3.1 & 11.3.4)

• Use draft gauges to monitor kiln draft.
• Adjust dampers to control airflow and moisture removal.
• During pre-heating, moisture is driven out slowly via first damper.
• Multiple dampers with varying openings optimize drying and firing conditions.

flowchart LR
    A[Pressed & Trimmed Tiles] --> B[Drying Racks]
    B -->|Slow & Steady Drying| C[Light Grey Tiles]
    C --> D{Moisture ≤ 4%?}
    D -- Yes --> E[Feed into Kiln]
    D -- No --> B
    E --> F[Pre-heating & Smoking]
    F --> G[Moisture Driven Out via Dampers]
    G --> H[Firing]

Summary: Maintain slow drying to prevent defects, ensure moisture ≤4%, monitor kiln draft, and adjust dampers for controlled

Firing Process in Tile Kilns (IS 3978)

The firing cycle consists of five stages (Clause 11.3.2):

1. Smoking
2. Pre-heating
3. Firing
4. Soaking
5. Cooling

Key Specifications:

• Firing Temperature:

  • Range: 800°C to 900°C (Clause 11.2.1)
  • Depends on clay quality
  • Temperature must be monitored frequently using high-temperature devices.

• Tile Setting:

  • Green tiles are loaded with their long axis parallel to the ground floor on the sole flue platform (Fig. 1).

• Control:

  • Fuel feed and draft are adjusted to maintain temperature.
  • Dampers regulate heat progression through chambers (Clause 10.4).
  • Paper bafflers are destroyed before introducing fresh chambers to the firing circuit.

Temperature Profile:

• The temperature vs. time graph approximates a parabolic curve, reflecting gradual heating and cooling.

graph LR
    A(Smoking) --> B(Pre-heating) --> C(Firing) --> D(Soaking) --> E(Cooling)
    style A fill:#f9f,stroke:#333,stroke-width:2px
    style E fill:#bbf,stroke:#333,stroke-width:2px

Summary Table of Firing Stages and Temperature:

Note: Proper firing control requires skilled burner operation to ensure tile quality and kiln efficiency.

IS 3978: Key Points on Kiln Design & Operation

1. Kiln Types (Clause 8.1)

• Commonly used: Transverse/Barrel arch or top-fixed straight Hoffman kiln.
• Features:
  • Connected to masonry chimney or induced draft fans.
  • Induced draft fans improve control, independent of atmospheric conditions.

2. Kiln Draft Control (Clause 11.3.1)

• Use draft gauges at multiple kiln points.
• Adjust draft by operating dampers as per kiln designer’s instructions.

3. Tile Setting (Clause 9.1)

• Kiln floor paved with burnt bricks.
• Sole flues must be maintained; 10-12 openings across chamber width.
• Tiles stacked over sole flue platform with long axis parallel to floor.
• Tile arrangement: face to back, face to face, or back to back.
• Hoffman kiln capacity: ~1500 tiles between fire lines.

4. Fuel for Firing (Clause 11.1.1)

• Fuel types: firewood, coal, furnace oil.
• Fuel must conform to kiln design specifications.

Typical Kiln Draft Adjustment Formula (General Engineering Knowledge):

[ Q = C \times A \times \sqrt{2gH \frac{T_i - T_o}{T_o}} ]

Where:

• (Q) = Draft flow rate
• (C) = Discharge coefficient
• (A) = Area of chimney cross-section
• (g) = Acceleration due to gravity
• (H) = Height of chimney
• (T_i, T_o) = Absolute temperatures inside and outside chimney

flowchart LR
    A[Fuel Feeding] --> B[Combustion Chamber]
    B --> C[Hot Gases Flow]
    C --> D[Sole Flue Openings (10-12)]
    D --> E[Tile Chamber]
    E --> F[Chimney / Induced Draft Fan]
    F --> G[Exhaust]

This summarizes IS 3978 kiln design and operation essentials for effective tile firing.

IS 3978: Control of Temperature and Rate of Fire Travel

Key Specifications from Clauses 10 & 11:

• Rate of Fire Travel (Clause 11.2.2):

  • Minimum rate: 40 cm/hour
  • Fire travel must be controlled by coordinated damper operation and tile setting/removal.

• Temperature Control (Clause 11.3.3):

  • Gas temperature in pre-heating zones must be regulated by dampers.
  • Prevent thermal shock to tiles to reduce breakage.

• Fire Travel Control (Clause 10.4):

  • As heat progresses, more chambers with tiles are brought into firing via dampers.
  • Ensure paper baffler is destroyed before activating a new chamber.
  • Firing process and fire travel must be carefully regulated for uniformity.

Practical Control Measures:

Summary Diagram of Fire Travel Control:

flowchart LR
    A[Start Firing] --> B[Control Dampers]
    B --> C[Regulate Gas Temperature]
    C --> D[Maintain Fire Travel ≥ 40 cm/h]
    D --> E[Set Tiles in New Chamber]
    E --> F[Destroy Paper Baffler]
    F --> G[Advance Fire Cycle]
    G --> B

Ensure: Continuous monitoring of damper positions and tile conditions to maintain steady temperature and fire travel rate, minimizing tile damage and optimizing kiln operation.

IS 3978: Fuel and Combustion Control – Key Points

1. Fuel Specifications (Clause 11.1.1)

• Fuel types: Firewood, Coal, Furnace Oil
• Fuel must conform to kiln design specifications.

2. Temperature & Fire Travel Control (Clause 11.2)

• Control temperature and rate of fire travel carefully.
• Fire progression must be regulated to ensure uniform tile firing.

3. Draft and Air Supply (Clause 10.3)

• Use dampers to regulate draft.
• Ensure sufficient air supply for complete combustion.
• Maintain hot gas flow through chambers before exit via chimney or fan.

4. Chamber Operation & Fire Travel (Clause 10.4)

• Gradually bring chambers into operation by adjusting dampers.
• Ensure paper baffler destruction before activating new chambers.
• Control fire travel rate to avoid uneven firing.

Typical Combustion Control Formulae

• Air Required for Combustion:

[ \text{Air required} = \text{Fuel quantity} \times \text{Stoichiometric air factor} ]

• Draft Pressure (Pa):

[ \Delta P = C \times H \times (\frac{1}{T_o} - \frac{1}{T_i}) ]

Where:

• (C) = constant,
• (H) = chimney height (m),
• (T_o), (T_i) = outside and inside temperatures (K).

Summary Diagram: Fire Travel Control via Dampers

flowchart LR
    A[Fuel Combustion Chamber] -->|Hot gases| B[Dampers]
    B --> C[Chamber 1]
    C --> D[Chamber 2]
    D --> E[Chimney/Fan]
    B -->|Adjust dampers| C
    B -->|Adjust dampers| D
    style B fill:#f9f,stroke:#333,stroke-width:2px

Ensure:

• Proper fuel quality
• Controlled air supply & draft
• Sequential chamber firing
• Monitoring fire travel rate for uniform tile quality.

IS 3978 Key Points on Cooling, Unloading, and Sorting of Clay Roofing Tiles

Cooling and Kiln Control (Clause 11.3.7)

• In absence of scientific instruments, kiln performance is controlled by:
  • Observing fire color and tile appearance inside the kiln.
  • Monitoring intensity of hot gases blowing through feed holes.
• Proper burning affects flexural strength and porosity of tiles.

Unloading (Clause 12.2)

• Tiles must be unloaded carefully to minimize breakage.
• Convey tiles promptly to sorting shed.

Sorting (Clause 12.3)

• Tiles are sorted into quality classes as per IS: 654-1962 (Specification for clay roofing tiles, Mangalore pattern).
• Sorting criteria include:
  • Visual defects
  • Dimensions
  • Strength and porosity (influenced by firing quality)

Summary Table: Unloading and Sorting

Notes:

• For exact quality classes and detailed sorting criteria, refer to IS: 654-1962.
• Kiln temperature control (Clause 11.2) is critical for tile quality but requires experience without instruments.

flowchart TD
    A[Kiln Firing] --> B[Observe Fire Color & Gas Intensity]
    B --> C[Assess Tile Quality (Strength & Porosity)]
    C --> D[Unload Tiles Carefully]
    D --> E[Convey to Sorting Shed]
    E --> F[Sort Tiles per IS:654-1962]

This approach ensures quality tiles with minimal breakage and proper classification.

IS 3978 - Quality Control and Classification of Clay Roofing Tiles

Key Points from Clause 12.3 (Sorting and Classification)

• Tiles must be sorted into different quality classes as per IS 654:1962 (Specification for clay roofing tiles, Mangalore pattern).
• Sorting is based on visual defects, dimensions, and physical properties.

Soil and Material Specifications (Preparation)

• Soil composition must meet mechanical grading limits to ensure:
  • Adequate strength
  • Low water absorption
  • Controlled shrinkage (~9% average drying and firing shrinkage)
• Chemical analysis of soil as per:
  • IS 1727-1960
  • IS 2720 (Part XXI)-1965 (Total soluble solids)
  • IS 2720 (Part XXV)-1966 (Silica sesquioxide ratio)

Quality Control Tests

• Shrinkage test on 20 x 10 cm clay slabs (thickness same as tile), measured longitudinally and laterally.
• Visual inspection for cracks, warping, and surface defects.
• Dimensional checks against mold specifications.

Summary Table: Key Specifications

flowchart TD
    A[Clay Soil Sampling] --> B[Chemical Analysis (IS 1727, IS 2720)]
    B --> C[Mechanical Grading & Composition Check]
    C --> D[Molding & Drying]
    D --> E[Firing]
    E --> F[Shrinkage Test (~9% avg)]
    F --> G[Sorting & Classification (IS 654:1962)]
    G --> H[Quality Classes: A, B, C...]

Note: For detailed classification tables and quality grades, refer directly to IS 654:1962. This standard governs the acceptance criteria for defects, dimensions, and physical properties for clay roofing tiles.