Screws
Screws are mechanical fasteners used to join two or more components together. They have a threaded shaft and a head that allows them to be tightened or loosened using suitable tools. Screws are widely used in mechanical assemblies because they provide strong and detachable joints.
Material of Screws
Screws are manufactured from different materials depending on their application and strength requirements.
- Carbon steel
- Alloy steel
- Stainless steel
- Brass
- Aluminium
Designation of Screws
Screws are designated according to standard systems such as metric or British standards. A typical screw designation includes the thread diameter, pitch, and length.
Example: M10 × 1.5 × 40
- M – Metric thread
- 10 – Nominal diameter in millimeters
- 1.5 – Thread pitch
- 40 – Length of the screw
Specifications
Screw specifications include:
- Thread size
- Thread pitch
- Length
- Head type
- Material
- Strength grade
Property Classes
Property classes indicate the strength of screws or bolts. These classes are usually marked on the screw head.
Example: 9.8
- First number (9) indicates tensile strength.
- Second number (8) indicates yield strength as a percentage of tensile strength.
Common property classes include 4.6, 5.8, 8.8, 10.9, and 12.9.
Tools for Tightening and Loosening Screws or Bolts
Various hand tools are used for tightening and loosening screws and bolts.
- Spanner
- Wrench
- Screwdriver
- Allen key (hex key)
- Socket wrench
Torque Wrench
A torque wrench is a special tool used to apply a specific torque to a bolt or nut. It ensures that the fastener is tightened with the correct force.
Advantages
- Prevents over-tightening.
- Ensures correct clamping force.
- Improves reliability of joints.
Applications
- Automobile assembly.
- Machine maintenance.
- Precision mechanical assemblies.
Screw Joint Calculation
Screw joint calculations are used to determine the required tightening force and strength of the screw joint.
Important factors include:
- Load on the joint
- Strength of screw material
- Thread diameter
- Torque applied
Proper calculation ensures safe and reliable fastening.
Power Tools
Power tools are tools operated by an external power source such as electricity, compressed air, or batteries. These tools increase efficiency and reduce manual effort in engineering work.
Constructional Features
- Electric motor or pneumatic drive
- Housing or casing
- Switch or control mechanism
- Power supply cord or battery
- Tool attachment or working end
Common Power Tools
- Electric drill
- Angle grinder
- Impact wrench
- Power screwdriver
- Electric saw
Uses
- Drilling holes
- Cutting materials
- Tightening bolts and screws
- Grinding and polishing surfaces
Maintenance of Power Tools
- Keep tools clean and dry.
- Inspect power cables regularly.
- Lubricate moving parts when required.
- Store tools in a safe place.
- Follow manufacturer maintenance instructions.
Conclusion
Screws and bolts are essential mechanical fasteners used in engineering assemblies. Understanding screw materials, designations, property classes, and correct tightening methods ensures reliable joints. Power tools further enhance productivity and efficiency in mechanical workshops.