Fastening components coming loose is a mistake that should never be overlooked. The consequences of loose components could be catastrophic.
In heavy industries like aerospace, automotive, or construction, fastening failures result in equipment breakdowns or, even worse, life-threatening accidents.
There are many factors to consider when talking about fastening performance. However, one often overlooked factor is the thread surface finish. You may wonder, how exactly does the texture of a thread impact its ability to hold components together?
Let’s break it down.
What is thread surface finish?
The surface finish of a thread is the texture and smoothness of a fastener’s threads’ surface. For example, the thread surface of bolts and screws. This texture is created during the manufacturing process through machining, rolling, or coating techniques. It may seem like a small detail, but surface finish does matter in fastener performance.
Why does this matter? The interaction between the surface of the fastener and the material it engages with affects friction, engagement, and the amount of torque required to secure the fastener.
Depending on the surface finish, the fastener can either grip more tightly or get loose under load.
Types of thread surface finishes.
Different surface finishes are used for threads. It depends on the various applications and environments. Let’s understand them in detail:
Polished finish
Polished surfaces on the threads create a smoother surface, which reduces friction. This finish is often used in places that require a controlled and consistent torque, such as precision engineering. Downside — low friction provides low grip strength if not properly accounted for.
Coated finish
Coatings provide additional protection to fasteners against corrosion. The common coatings for fasteners are zinc, chrome, and nickel. A coated finish is more common in outdoor environments where exposure to moisture or chemicals is more common. Coatings also make fasteners look aesthetically pleasing.
Plated finish
Plating is similar to coating. The only difference is it involves applying a metallic layer such as cadmium or galvanization. This finish is used to increase corrosion resistance and fastener performance in high-stress environments.
Rough machined finish
A rough surface finish creates more friction between the fastener and the material. This increases grip strength; however, it requires higher torque for proper tightening. This type of finish is used in construction and heavy machinery settings where high torque is less of a concern.
How surface finish impacts fastening performance
The relationship between surface finish and fastener performance is linked with friction and engagement.
When you tighten a bolt or screw, the friction between the two provides the necessary grip to keep the component secure. A smooth surface will reduce friction. It makes it easier to achieve the desired torque. However, if the friction is too little, the fastener will come loose under load.
If the surface finish is rough, the friction will be higher. It increases the grip but also requires more torque to achieve the same clamping force. In some applications, this can cause issues like thread galling (where the threads lock together too tightly).
Surface finish and corrosion resistance
Corrosion resistance of the fastener’s surface may also impact its performance. Corrosion occurs when metal fasteners are exposed to moisture, chemicals, or extreme temperatures. Over time, corrosion weakens the fastener and reduces its strength.
Coating and plating methods are used to fight such a situation. A layer of zinc or the process of galvanization protects the underlying metal from rust or oxidation. Coating and plating of fasteners are necessary in environments like marine, outdoor, or chemical applications.
Which surface finish is best?
There’s no one best surface finish for fasteners. It all depends on many factors, such as:
Environment
If the fasteners are exposed to extreme environments like moisture, rain, etc., a resistant finish is the best choice.
Load and vibration
In a high-load and high-vibration environment. A rougher finish will provide a better grip.
Metal compatibility
Some finishes like cadmium or nickel plating may be better for certain materials to prevent thread galling or material degradation.
Torque control
When precise torque control is required, such as in aerospace or automotive applications, a smoother, polished finish provides consistent tightening without over-torquing.
Conclusion
The surface finish of a thread may seem like a minor detail. But it has a major impact on fastening performance.
Due to its impact, various surface finish types are available. According to the project (large or small), one should pay attention to the thread surface finish to make sure fasteners stay secure and perform as intended.
Check out Jarvis Cutting Tools, as they specialize in manufacturing fasteners for aerospace, agriculture, automotive, heavy equipment, and engines.
