Specification for Snatch Block for Use with Fibre Rope for Fire Brigade Use

IS 939: Scope and Key Specifications

• Scope: Covers specifications for snatch blocks used in lifting and rigging, ensuring compliance with quality, inspection, and testing under ISI certification.

• Marking (Clause 7.1.1):
  Snatch blocks may bear the ISI Certification Mark, indicating conformity to IS standards and continuous quality assurance by ISI.

• Units (SI Units):
  The standard uses the International System of Units (SI) for all measurements, including:

  Quantity	Unit	Symbol
  Length	metre	m
  Mass	kilogram	kg
  Force	newton	N
  Pressure, Stress	pascal	Pa
  Energy	joule	J
  Power	watt	W

• Conversions:

  • 1 N = 0.101972 kgf
  • 1 Pa = 1 N/m²

• Rounding Off:
  Final test or calculation values shall be rounded as per IS: 2-1960, maintaining significant figures consistent with specified values.

Summary Diagram of Scope

flowchart TD
    A[IS 939 Standard] --> B[Snatch Blocks Specifications]
    B --> C[Marking with ISI Certification Mark]
    B --> D[Use of SI Units]
    B --> E[Testing & Quality Control]
    E --> F[Rounding as per IS:2-1960]

This ensures snatch blocks meet quality, safety, and measurement standards under IS 939.

IS 939: Terminology and Definitions - Key Points

1. Terminology (Clause 2.0)

• Defines terms specifically for the standard’s context.
• Ensures uniform understanding of technical terms related to snatch blocks.

2. Units and Symbols (SI Units)

3. Derived Units and Conversions

4. Marking (Clause 7.1.1)

• Snatch blocks may carry the ISI Certification Mark.
• ISI mark ensures compliance with quality and inspection systems.

5. Rounding Off (Clause 0.4)

• Results must be rounded as per **IS: 2-

IS 939: Components and Construction Key Points

Materials (Clause 4.1)

Units & Conversions (International System, Clause 7.1.1)

• Force: 1 N = 0.101972 kgf
• Energy: 1 J = 1 N·m
• Power: 1 W = 1 J/s
• Pressure/Stress: 1 Pa = 1 N/m²
• Frequency: 1 Hz = 1 cycle/s

Notes

• Components must comply with specified IS standards for material quality.
• ISI Certification Mark ensures compliance and quality inspection.

flowchart TD
  A[Snatch Block Components] --> B[Swivel Hook - Steel Forging (IS 4367)]
  A --> C[Cross-head - Wrought Steel (IS 1570)]
  A --> D[Side Plates - Steel Plate (IS 226)]
  A --> E[Sheave - Iron Casting Grade 25 (IS 210)]
  A --> F[Axle Pin - Wrought Steel Bar (IS 1570)]

This summary ensures component material conformity and standard units for design and quality control per IS 939.

IS 939: Key Materials Specifications for Snatch Blocks

Additional Notes:

• Materials conform to specific IS standards ensuring quality and mechanical properties.
• Rounding off of test results should follow IS: 2-1960 for consistency.
• Units used comply with the International System of Units (SI), e.g., force in Newton (N), pressure in Pascal (Pa).

Common Unit Conversions:

This ensures material compatibility and standardization for manufacturing and testing of snatch blocks as per IS 939.

IS 939: Design and Dimensions Key Points

1. Head Fitting (Clause 5.1)

• Shape: Trapezoidal hook, forged in one piece.
• Shank: Threaded, fitted with screw collar/nut; collar/nut depth ≥ full diameter of shank.
• Engagement Length: Nut/collar engaged length on load side ≥ 2/3 diameter of shank.
• Sheave: Integrally cast; central boss width = rim width + 2 to 3 mm.
• Rope Groove: Depth ≥ 1/3 rope diameter; profile = circular arc radius 15 mm; edges rounded.
• Axle Pin: Diameter ≥ bearing portion diameter + 3 mm; tail end projects for split cotter pin.

2. Materials (Clause 4.1)

3. Units (SI Units)

• Length: metre (m)
• Force: newton (N), 1 N = 0.101972 kgf
• Pressure: pascal (Pa), 1 Pa = 1 N/m²

Summary Diagram: Snatch Block Components

graph LR
A[Swivel Hook] --> B[Cross-head]
B --> C[Pin for Hook]
C --> D[Side Straps/Plates]
D --> E[Sheave]
E --> F[Axle Pin]
F --> G[Hinge]
G -->

IS 939: Performance Requirements and Testing - Key Points

• Performance Requirements:
  The standard emphasizes compliance with specified test results, rounded per IS:2-1960 rules (Clause 0.4). This ensures consistent precision in test data reporting.

• Testing:
  While IS 939 does not explicitly list test methods in the provided context, it mandates quality control under ISI certification, assuring products meet the standard through continuous inspection and testing.

• Marking:
  Snatch blocks may bear the ISI Certification Mark (Clause 7.1.1), indicating conformity to IS 939 and associated quality controls.

• Units & Conversions:
  The standard uses SI units for all measurements, with key conversions such as:

  Quantity	Unit	Symbol	Conversion
  Force	newton	N	1 N = 0.101972 kgf
  Pressure/Stress	pascal	Pa	1 Pa = 1 N/m²

• Rounding Off:
  Final test values must be rounded to the same decimal places as specified values (IS:2-1960).

Summary Table: Key Specifications

flowchart LR
  A[Raw Material] --> B[Manufacturing]
  B --> C[Testing & Inspection]
  C --> D{Conforms to IS 939?}
  D -- Yes --> E[ISI Certification Mark]
  D -- No --> F[Rework/Reject]

This flow ensures performance compliance and quality control as per IS 939 requirements.

IS 939 - Marking of Snatch Blocks (Clause 7.1 & 7.1.1)

All snatch blocks must be clearly marked on the strap with:

• Proof load (in newtons, N)
• Nominal size / Safe working load (in newtons, N)
• Inspecting authority's seal including date of test
• Manufacturer's identification mark

Additionally:

• Snatch blocks may bear the ISI Certification Mark as per Clause 7.1.1, which guarantees compliance with ISI quality and testing standards.

Relevant Units & Conversions (SI Units)

Summary Table: Marking Requirements

flowchart LR
    A[Snatch Block Strap] --> B[Proof Load (N)]
    A --> C[Nominal Size (SWL in N)]
    A --> D[Inspecting Authority Seal + Test Date]
    A --> E[Manufacturer's ID Mark]
    A --> F[ISI Certification Mark (Optional)]

This ensures traceability, safety verification, and quality assurance per IS 939.

IS 939: Inspection and Quality Control - Key Points

• ISI Certification Mark (Clause 7.1.1):

  • Snatch blocks may bear the ISI mark, ensuring compliance with IS 939.
  • The mark guarantees production under a strict system of inspection, testing, and quality control supervised by ISI.
  • Continuous conformity checks by ISI safeguard quality.

• Inspection & Testing:

  • Products must be tested as per IS 939 specifications.
  • Final test results are rounded off according to IS:2-1960 (round to same significant figures as specified values).

• Units & Measurements:

  • SI units are mandatory for all measurements.
  • Key units include:
    • Force: Newton (N), 1 N = 0.101972 kgf
    • Pressure/Stress: Pascal (Pa), 1 Pa = 1 N/m²
    • Energy: Joule (J), 1 J = 1 N·m

Summary Table of SI Units (from IS 939):

Inspection Flow (Simplified):

flowchart TD
    A[Manufacturing] --> B[Inspection & Testing]
    B --> C{ISI Certification?}
    C -- Yes --> D[Marking with ISI]
    C -- No --> E[Rework/Reject]
    D --> F[Dispatch]

Note: For detailed inspection procedures and quality control, refer to the full IS 939 standard and related material standards.