Methods for sampling burnt clay tiles
1978 Edition

IS 8920: Scope - Important Formulas, Tables & Guidelines

1. Definition of Range (Clause 2.5)

• Range (R) = Highest value 12 Lowest value

2. Sampling and Acceptance Criteria for Visual & Dimensional Attributes (Clause 3.2)

• Acceptance: Lot is accepted if defective tiles 64 allowed defects; otherwise rejected.

3. Conformity for Physical Properties (Clauses 4.3.1 & 4.3.2)

• For minimum limits:

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

• For maximum limits:

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

Where:

• (x) = Mean test value
• (R) = Range of test values

4. Sampling & Acceptance Flowchart

flowchart TD
  A[Start: Tile Lot] --> B{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]
  C --> H[Inspect & Decide]
  D --> H
  E --> H
  F --> H
  G --> H
  H --> I{Defects 64 Allowed?}
  I -- Yes --> J[Accept Lot]
  I -- No --> K[Reject Lot]

IS 8920: Essential Definitions, Formulas & Tables

1. Definitions and Acceptance Conditions

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

  • (x) = average of test values
  • (R) = range or average of ranges (if tests 10 samples)

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

2. Sampling and Defective Limits (Clause 3.2)

• Lot complies if defective count 64 allowed defective number.
• Otherwise, lot fails conformity.

3. Range Calculation Note

• For 10 or more tests, calculate (R) as average of sub-group ranges (each sub-group contains 5 samples).

flowchart TD
  A[Collect Test Data] --> B[Compute Mean (x)]
  B --> C[Compute Range (R)]
  C --> D{Specification Limit?}
  D -->|Min| E[Verify (x - 0.4R) 64 Min Limit]
  D -->|Max| F[Verify (x + 0.4R) 5 Max Limit]
  E --> G{Pass?}
  F --> G
  G -->|Yes| H[Accept Lot]
  G -->|No| I[Reject Lot]

IS 8920: Sampling Size and Acceptance Thresholds (Visual & Dimensional Attributes)

1. Sampling Table (Clause 3.2)

2. Acceptance Criteria (Clause 3.2)

• Examine all sampled tiles for visual defects, dimensions, weight, and warpage.
• Lot accepted if defective tiles 64 allowed defects.
• Lot rejected if defective tiles exceed allowed number.

3. Physical Property Acceptance (Clause 4.3.2)

For properties with maximum limits:

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

Where:

• (x) = average test value
• (R) = range

If the above holds, the lot is accepted.

4. Sampling Procedure (Clause 3.1.1)

• Sample size per Table 1.
• Tiles picked following Clause 5 random or representative methods.

flowchart TD
  A[Lot Size] --> B[Determine Sample Size]
  B --> C[Check Visual & Dimensional Defects]
  C --> D{Defectives 64 Permissible?}
  D -- Yes --> E[Accept Lot]
  D -- No --> F[Reject Lot]
  B --> G[Conduct Physical Tests]
  G --> H[Calculate x + 0.4R]
  H --> I{5 Max Limit?}
  I -- Yes --> E
  I -- No --> F

Summary: Follow Table 1 for sampling and acceptance.

IS 8920: Acceptance Norms for Other Physical Parameters

Highlights (Clause 4.3)

• For compressive strength, flexural strength, breaking load, and water absorption:
  • Compute mean ((x)) and range ((R)) from test data.
  • For 10 or more tests, average ranges of subgroups of 5 are used for (R).

Sampling & Testing (Clause 3.2 & Table 3)

• Lot passes if defective count 64 allowed number.
• For impact and permeability tests (Clause 4.2), all tested tiles must be compliant.

Definitions

• Range ((R)) = Maximum - Minimum observation
• Mean ((x)) = Sum of values / Number of tests

Range Calculation Formula

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) is the range of each subgroup of 5 tests.

This methodology supports statistical quality control by validating physical characteristics.

IS 8920: Sampling Methods for Burnt Clay Tiles

Main Clauses & Techniques

• Clause 5.1: Sampling approaches include:

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

• Clause 5.2.1 Sampling During Movement:

  • Divide lot into at least 10 equal parts.
  • Take equal quantity of tiles from each section.
  • Alternatively, pick tiles at regular intervals with a random starting point from IS:4905-1968 tables.

• Clause 5.2.3 Sampling from Transport Vehicles:

  • Randomly select samples from multiple wagons, trucks, or shipholds.
  • Equal tiles drawn from each vehicle to fulfill sample size.

Acceptance Criterion (Clause 4.3.2)

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

Where:

• (x) = average of sample test results
• (R) = range in sample test results

If satisfied, the lot conforms.

Sampling Method Summary

flowchart TD
  A[Tile Lot] --> 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 parts]
  E --> H[Pick equal tiles at intervals]
  F --> I[Random picks from several vehicles]

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