Are You Aware of Common Pitfalls in Fastener Selection?

When selecting and using fasteners, it is imperative to strictly adhere to relevant standards and specifications, and avoid using them in incorrect ways. Various factors such as load type and material must be fully considered to ensure safety and the normal operation of equipment without any issues.

 

1.Using coarse bolts as substitutes for fine ones:

 

Misconception description: During maintenance or assembly, when fine-threaded bolts are unavailable, some personnel may choose to use coarse-threaded bolts as substitutes.

Potential problems: Fine-threaded bolts, due to their larger inner diameter, smaller pitch and external angle, have advantages such as high strength and good self-locking performance, and can withstand larger impact, vibration, and alternating loads. Substituting coarse-threaded bolts may lead to loosening, detachment, or fracture, thereby causing mechanical failures.

 

2.Mismatched porosity:

 

Misconception description: During assembly, personnel may not pay attention to checking the fit clearance between the bolt and the bolt hole, and continue installation even if there is a large clearance.

Potential problems: This can result in bolt loosening or shearing, especially for bolts that bear lateral loads and shear forces (such as transmission shaft bolts and flywheel bolts), where such incidents are more likely to occur.

 

3.Increasing nut thickness to enhance connection reliability:

 

Misconception description: Some believe that increasing nut thickness can increase the number of working threads, thereby improving the reliability of the connected parts.
Potential problems: In fact, the thicker the nut, the more uneven the load distribution among the threads, which can easily lead to connection loosening.

 

4.Using multiple washers on one bolt:

 

Misconception description: During installation, to balance excessively long bolts, some personnel may install multiple spring washers on one bolt.
Potential problems: This can cause uneven force distribution on the spring washers, potentially leading to fracture, thereby reducing the preload of the bolt or creating eccentric loads, and lowering the connection reliability of the bolt.

 

5.Using oversized washers:

 

Misconception description: In cases where suitable washers are unavailable, some personnel may choose to use washers with larger inner diameters as substitutes.
Potential problems: This can reduce the contact area between the bolt head and the washer, thereby decreasing the bearing pressure or locking force of the washer. Under vibration and impact loads, the bolt can easily loosen.

 

6.Incorrect torque application:

 

Misconception description: One viewpoint is that bolts should be "tighter rather than looser," leading to intentionally increasing the tightening torque of bolts. Another viewpoint is that for important bolts that require torque tightening, personnel may use an adjustable wrench for convenience.
Potential problems: The former may cause bolt stripping, while the latter may result in loosening due to insufficient torque, both of which can lead to mechanical failures.