Selection of coarse and fine thread bolts
Thread Content
This post was last edited by sdwfsgyykai on 2018-5-12 07:53. As the title suggests, the HG20613 bolts of European origin that are larger than M30 come in both coarse-threaded and fine-threaded versions. I encountered a problem during maintenance: all the bolts in question were M30 bolts used in steam pipes. Those with coarse threads were almost all removed and reused, so not many bolts had to be discarded. However, only 1/4 of the thin bolts could be removed; the rest couldn’t be taken off at all. Among those that were removed, some had completely damaged threads and were unusable, while others couldn’t even be screwed back on by hand. In short, the thin-threaded bolts are essentially ruined, probably due to certain characteristics of these bolts. For the above reasons, I am thinking of replacing the fine-threaded bolts with coarse-threaded bolts while maintaining the same grade of bolts. This way, bolt waste can be reduced during maintenance, and the difficulty of such maintenance can also be decreased. I wonder if my colleagues have encountered the same situation? I hope to discuss this with everyone!
Advantages, disadvantages, and application areas of fine-threaded screws: Fine-threaded screws were developed to meet special usage requirements that coarse-threaded screws cannot satisfy. They also come in various pitch series, and are primarily used in metric piping components for hydraulic systems, mechanical transmission parts, thin-walled components with insufficient strength, components inside machines where space is limited, as well as shafts that require high self-locking properties. Fine-threaded screws are generally not used for applications involving heavy loads; they are mainly used for positioning, adjustment, fixing, and similar purposes ； It is particularly suitable for thin-walled cylindrical parts; fine-thread threads are widely used in various optical instruments. Additionally, single-start fine-thread threads have excellent self-locking properties, allowing for precise adjustments with ease; they are widely used in measuring instruments such as micrometers. The disadvantage of fine-threaded threads is that they are prone to damage, which affects installation and removal; even slight dimensional errors can lead to improper fitting during installation, resulting in damage to both the screw and the nut. Principles for selecting coarse-threaded and fine-threaded screws: Both coarse-threaded and fine-threaded screws are used for fastening purposes. Fine-threaded screws are generally used to secure thin-walled parts as well as parts that require high vibration resistance. Fine-threaded threads have good self-locking properties, thus offering strong resistance to vibration-induced loosening; however, due to their shallower thread depth, they have a weaker capacity to withstand greater tensile forces compared to coarse-threaded threads. Without anti-loosening measures, fine-thread threads provide better anti-loosening performance than coarse-thread threads; they are generally used in thin-walled parts and those with high requirements for vibration resistance. For adjustment purposes, fine-threaded threads have advantages. Disadvantages of fine-threaded threads: They are not suitable for use in materials with overly coarse structure and poor strength; when a high tightening force is applied, the threads tend to slip.
Do the process conditions of the steam pipeline permit the use of bolts with coarse thread? For low-pressure steam pipes, it should work; for pressures above medium and high levels, it is recommended to use bolts with fine-threaded threads