Screw It! Intro to Fasteners & Bolted Connections

Summary

This video delves into the crucial role of fasteners in mechanical systems, covering a wide variety of types, materials, coatings, and drive mechanisms. It explores the differences between screws and bolts, the importance of proper material selection for strength and corrosion resistance, and best practices for preventing fastener failure. The video also highlights the significance of thread types, preload, and special features like locknuts, washers, and thread lockers. With a focus on high-performance applications in industries like aerospace and construction, it provides valuable insights into ensuring mechanical integrity through proper fastener design.

Takeaways

• 🔩 Fasteners are crucial for the mechanical integrity of products, and proper selection and usage are essential to avoid failures.
• 🔧 There are many types of fasteners, such as hex head screws, socket head screws, and flat head screws, each suited for different applications.
• 📏 Hex head screws require adequate space for tools, while socket head screws can fit into tighter spaces, making them more versatile.
• ⚙️ The drive type matters: for smaller fasteners, a Torx drive is recommended due to its robustness compared to Phillips and slotted drives.
• 🧰 The difference between screws and bolts lies in their usage: bolts are used with nuts in thru-holes, while screws are used in tapped holes.
• 🛡️ Material selection is vital for strength and corrosion resistance; options include low carbon steel, stainless steel, and alloys.
• 🌧️ Coatings like zinc plating and galvanization enhance corrosion resistance, but stainless steel or super alloys are preferred for harsh environments.
• 🔍 Fastener specifications are defined by standards (e.g., ASTM, ISO) to ensure quality and compatibility with specific applications.
• ⚙️ Proper thread engagement is crucial; typically, a length of two times the nominal screw size is sufficient for most applications.
• 🔒 Various locking mechanisms (like lock nuts, Nord-Lock washers, and thread lockers) are essential to prevent loosening under vibration.

Q & A

What are fasteners, and why are they important?

Fasteners are crucial components in machines that hold parts together. Proper selection and usage are essential to maintain the mechanical integrity of a product, as incorrect usage can lead to serious consequences.

What factors should be considered when selecting fasteners?

Key factors include thread type, preload, material choice, coating specifications, and drive selection. Understanding these factors ensures that fasteners are applied correctly.

What are some common types of fasteners mentioned in the script?

Common types of fasteners include hex head screws, socket head screws, low-head screws, button head screws, flat head screws, and various drive types like Torx and Phillips.

How do coarse and fine thread fasteners differ?

Coarse thread fasteners have fewer threads per inch and are typically the first choice, while fine thread fasteners are stronger and more resistant to vibration, making them suitable for high-performance applications.

What is the significance of fastener materials and coatings?

Fastener materials impact strength and corrosion resistance. Coatings are applied to enhance corrosion resistance, with options like zinc plating, galvanization, and cadmium plating, each serving specific environments.

What is preload, and how is it controlled?

Preload is the initial tension applied to a fastener to enhance its resistance to vibration. It is usually controlled by the applied torque, but factors like friction can affect its accuracy.

What are some methods to prevent fasteners from loosening?

Methods include using lock nuts, applying liquid thread lockers like Loctite, and physically preventing movement with safety wire. Additionally, washers can help distribute loads to prevent loosening.

Why should screws not be subjected to significant shear loads?

Screw threads are the weak point of a fastener due to the decreased area at the root of the thread. Shear loads can lead to fretting and potential failure, so alternative methods like dowel pins are recommended.

What is hydrogen embrittlement, and why is it a concern?

Hydrogen embrittlement occurs when hydrogen produced during the plating process becomes trapped in the metal's structure, leading to brittleness and increased risk of failure, particularly in critical applications like aviation.

What are some best practices for fastener design and usage?

Best practices include ensuring proper thread engagement, selecting appropriate materials and coatings, applying the correct preload, using washers to distribute loads, and marking fasteners post-installation for inspection.