Methods for sampling burnt clay tiles

IS 8920: Scope - Key Formulas, Tables & Specifications

1. Definition of Range (Clause 2.5)

• Range (R) = Maximum observation − Minimum observation

2. Sampling & Conformity Criteria for Visual & Dimensional Characteristics (Clause 3.2)

• Conformity: If defective tiles ≤ permissible number → Lot accepted; else rejected.

3. Physical Characteristics Conformity (Clauses 4.3.1 & 4.3.2)

• For minimum specification limit:

  [ (x - 0.4R) \geq \text{Minimum limit} ]

• For maximum specification limit:

  [ (x + 0.4R) \leq \text{Maximum limit} ]

Where:

• ( x ) = Mean of test results
• ( R ) = Range of test results

4. Summary Flowchart of Sampling & Conformity

flowchart TD
  A[Start: Lot of Tiles] --> B{Determine Lot Size}
  B -->|Up to 1,000| C[Sample 20 tiles]
  B -->|1,001 - 3,000| D[Sample 32 tiles]
  B -->|3,001 - 10,000| E[Sample 50 tiles]
  B -->|10,001 - 35,000| F[Sample 80 tiles]
  B -->|35,001 - 50,000| G[Sample 125 tiles

IS 8920: Key Definitions, Formulas & Tables

1. Definitions & Criteria for Conformity

• For minimum specification limit (Clause 4.3.1): [ (x - 0.4R) \geq \text{Minimum limit} ] where:

  • (x) = average of test results
  • (R) = range of test results (or average of ranges if ≥10 samples)

• For maximum specification limit (Clause 4.3.2): [ (x + 0.4R) \leq \text{Maximum limit} ]

2. Sampling & Defect Criteria (Clause 3.2)

• If defective tiles ≤ permissible number, lot conforms.
• Otherwise, lot does not conform.

3. Range Calculation Note

• For ≥10 tests, calculate average of sub-group ranges (5 samples each) for (R).

flowchart TD
    A[Collect Test Results] --> B[Calculate Average (x)]
    B --> C[Calculate Range (R)]
    C --> D{Limit Type?}
    D -->|Minimum| E[Check (x - 0.4R) ≥ Min Limit]
    D -->|Maximum| F[Check (x + 0.4R) ≤ Max Limit]
    E --> G{Conforms?}
    F --> G
    G -->|Yes| H[Accept Lot]
    G -->|No| I[Reject Lot]

This

IS 8920: Scale of Sampling & Criteria for Conformity (Visual & Dimensional)

1. Sampling Table (Clause 3.2)

2. Criteria for Conformity (Clause 3.2)

• Inspect all sampled tiles for visual, dimensional, weight, and warpage.
• If defective tiles ≤ permissible number → Lot accepted.
• If defective tiles > permissible number → Lot rejected.

3. Physical Characteristics Conformity (Clause 4.3.2)

For characteristics with a maximum limit:

[ x + 0.4R \leq \text{Max Limit} ]

Where:

• (x) = Mean of test results
• (R) = Range (max - min)

If condition holds, lot conforms.

4. Sampling Method (Clause 3.1.1)

• Sample size as per Table 1.
• Tiles selected according to Clause 5 sampling methods (random, representative).

flowchart TD
    A[Lot Size] --> B[Select Sample Size (Table 1)]
    B --> C[Inspect Visual & Dimensional Characteristics]
    C --> D{Defectives ≤ Permissible?}
    D -- Yes --> E[Lot Accepted]
    D -- No --> F[Lot Rejected]
    B --> G[Test Physical Characteristics]
    G --> H[Calculate x + 0.4R]
    H --> I{≤ Max Limit?}
    I -- Yes --> E
    I -- No --> F

Summary: Use Table 1

IS 8920: Criteria for Conformity for Other Physical Characteristics

Key Points (Clause 4.3)

• For compressive strength, transverse/flexural strength, breaking load, and water absorption:
  • Calculate the average (x̄) and range (R) from test results.
  • If number of tests ≥ 10, calculate R as the average of ranges from sub-groups of 5 tests.

Sampling & Testing (Clause 3.2 & Table 3)

• Lot passes if defective tiles ≤ permissible number.
• For impact test and permeability (Clause 4.2): all tested tiles must pass.

Definitions

• Range (R) = Maximum observation − Minimum observation
• Average (x̄) = Sum of test results / Number of tests

Summary Formula for Range Calculation

If tests < 10: [ R = \max(x_i) - \min(x_i) ]

If tests ≥ 10: [ R = \frac{1}{n} \sum_{k=1}^n (R_k) ] where (R_k) = range of each subgroup of 5 tests.

This ensures quality control by statistically verifying physical properties of tiles for conformity.

IS 8920: Methods of Sampling for Burnt Clay Tiles

Key Clauses & Methods

• Clause 5.1: Sampling can be done by:

  • (a) Simple Random Sampling
  • (b) Stratified Sampling
    (Refer IS:4905-1968 for detailed random number tables and procedures)

• Clause 5.2.1 Sampling in Motion:

  • Divide the lot into ≥10 portions.
  • Draw equal number of tiles from each portion.
  • Alternatively, pick tiles at regular intervals during movement.
  • Use a random start from IS:4905-1968 random number tables.

• Clause 5.2.3 Sampling from Wagons/Trucks/Shipholds:

  • Select samples randomly from multiple vehicles.
  • Equal number of tiles from each vehicle to meet sample size.

Acceptance Criterion (Clause 4.3.2)

[ x + 0.4R \leq \text{Maximum Specification Limit} ]

• (x) = Mean of sample test results
• (R) = Range of sample test results

If true, the lot conforms.

Summary Table for Sampling

flowchart TD
    A[Lot of Tiles] --> B{Sampling Method}
    B --> C[Simple Random]
    B --> D[Stratified]
    B --> E[Sampling in Motion]
    B --> F[Sampling from Vehicles]
    E --> G[Divide into ≥10 portions]
    E --> H[Pick equal tiles at intervals]
    F --> I[Random from multiple wagons/trucks]

Use IS:4905-1968 random tables for selecting random start points and intervals.