1. Introduction
Screws play a vital role in mechanical and industrial production. As a key element of connection and fixation, screws not only support the proper functioning of millions of pieces of mechanical equipment and industrial systems, but also play an integral role in overall productivity and equipment safety. Whether in the automotive, aerospace, or construction industries, screws are a fundamental and irreplaceable component.
However, the problem of broken screws often poses a serious challenge. Not only can broken screws cause production delays, they can even lead to equipment damage and jeopardize employee safety. For example, under high loads or extreme environments, screws can inadvertently break, which can lead to machine downtime, equipment damage, and even production accidents. Therefore, understanding the types of screws that break and their causes is critical for business owners, purchasing managers and manufacturing professionals.
This article will analyze in detail several common types of screw breakage and the reasons behind them, and provide practical measures to prevent these problems according to international standards, such as ISO, ANSI and DIN.
2. Common types of screw breakage
Screw fracture can be caused by a variety of reasons and usually manifests itself in different fracture types. Depending on the stresses acting and environmental conditions, screws may experience the following common types of fracture:
In this article, our analysis and discussion is based on a variety of authoritative resources, including the findings in the article Bolt Failures– Why Learn to Recognize Mechanical Failure Modes. The article details the common failure modes of screws in mechanical use, emphasizes the early signs of screw failure and prevention strategies, and provides an important reference point for the content of this chapter.
2.1 Tensile Fracture
Static load fracture occurs when a screw is subjected to static tension. When a screw is subjected to excessive tensile forces, plastic deformation occurs, eventually leading to fracture. Static load fracture is usually characterized by a uniform tensile fracture, with the ends of the screw often showing distinct areas of tension. According to ISO 898-1 and ANSI B18.2.1, the material strength of a screw is an important factor in preventing static load fracture. Therefore, when designing and using screws, it is important to ensure that high-strength materials that meet the standards are selected and that overloading is avoided.
2.2 Fatigue Fracture
Fatigue fracture occurs when a screw is subjected to long periods of alternating stress. When a screw undergoes frequent load changes, especially under high-frequency vibration or cyclic loading conditions, tiny cracks will gradually expand and eventually lead to fracture. Fatigue fracture usually starts at the surface of the screw, and as the load is repeated, the crack gradually deepens, eventually leading to fracture.
2.3 Brittle Fracture (Brittle Fracture)
Brittle fracture usually occurs when the material itself lacks toughness, or at low temperatures when the material becomes more brittle, resulting in sudden fracture. Unlike other fracture types, brittle fracture usually has no significant deformation and the fracture surface shows a smoother fracture surface. Commonly, brittle fracture occurs at low temperatures, in harder materials, or with substandard heat treatment processes.
2.4 Stress Corrosion Cracking
Stress corrosion fracture is a fracture phenomenon caused by a combination of environmental stresses and chemical media. In certain chemical environments (such as salt water, acidic or alkaline media), the screw material may crack due to stress corrosion, eventually leading to fracture. Stress corrosion fracture is not only related to the chemical composition of the material, but also closely related to the corrosive media in the environment of use. In order to prevent this, the ISO 9227 standard provides a common way of testing the corrosion resistance of fastener surface treatments and emphasizes the use of corrosion-resistant materials in specific corrosive environments to avoid fracture caused by environmental factors.
2.5 Hydrogen Embrittlement
Hydrogen embrittlement is a phenomenon in which hydrogen gas enters the metal material and causes embrittlement. It usually occurs in high-strength steel screws or screws with surface treatment, especially when the metal is exposed to hydrogen, the hydrogen molecules will penetrate into the lattice of the metal, resulting in a decrease in the toughness of the metal and the production of micro-cracks under stress, which ultimately leads to fracture.
Hydrogen embrittlement often occurs suddenly, with the screw fracturing without significant plastic deformation. Unlike other fracture types, cracks in hydrogen embrittlement usually start at the surface of the screw and extend along grain boundaries or defects in the metal. This fracture mode carries a very high risk of hydrogen embrittlement, especially under high stress conditions.
Common triggers of hydrogen embrittlement include processing and use environments in electroplating, galvanizing, and hydrogen atmospheres. Screws exposed to hydrogen for extended periods of time during these processes may absorb hydrogen and form hydrogen molecules within the material, resulting in material embrittlement. In addition, high-strength screws are more susceptible to hydrogen embrittlement due to their higher hardness and greater ability to absorb hydrogen.
By analyzing these screw fracture types, we can better understand the risks that screws may face under different stresses and environmental conditions, and provide a strong basis for preventing these problems.
3. Main causes of screw breakage
The causes of screw breakage are complex and varied, and are usually closely related to materials, manufacturing processes, installation and use, and environmental factors. Understanding these causes helps us to identify potential risks and take effective preventive measures.
3.1 Material issues
The problem of screw fracture is often closely related to the quality of the material. Material defects, uneven composition, or improper heat treatment can cause screws to fracture. For example, small cracks, pores or other defects in the material may become stress concentrations during use, leading to fracture. In addition, if heat-treated improperly, the hardness and toughness of the material may be substandard, increasing the risk of fracture.
ISO 898-1 standard and ASTM A307, ASTM A325, ASTM A490 standards for screw material requirements have strict provisions, requiring the material to have sufficient strength and toughness to cope with the actual use of a variety of stress. Material testing and certification is also an important part of ensuring the quality of screws. Quality management systems such as ISO 9001 require strict material inspection procedures, including composition analysis and mechanical properties testing.
3.2 Manufacturing process defects
Any process defect in the manufacturing of screws can trigger fracture. For example, poor process control in cold forging, thread rolling and surface treatment may lead to micro-cracks on the surface of the screw or uneven internal stress distribution, thus increasing the risk of fracture. The quality of the screw’s thread processing is also very critical. Rough thread surfaces can easily lead to uneven torque, which in turn can cause fracture.
3.3 Improper installation and use
The environment in which a screw is used and the installation process have a direct impact on its life. If screws are installed without being tightened to the specified torque, or if they are used in an over-tightened condition, they may be subjected to excessive stress, which can lead to breakage. In addition, the risk of breakage can be exacerbated by a mismatch between the material of the screw and the object to which it is attached, or if it is used in unsuitable environments such as high temperatures or humidity.
According to the international standard ISO 16047, screws should be installed in accordance with specific torque values and operating practices. When purchasing and using screws, purchasing managers and manufacturing specialists should ensure that the installation process complies with the standard regulations in order to avoid breakage due to improper use.
3.4 Environmental and corrosion factors
Environmental factors, such as chemical corrosion, temperature changes and humidity changes, are often important triggers for screw fracture. Screws are susceptible to corrosion in harsh environments, especially when exposed to chemical media, and the corrosion process gradually weakens the screw, leading to fracture. Temperature changes may also lead to expansion or contraction of the material, which in turn places additional stress on the screw, leading to fracture.
Especially in highly corrosive environments, anti-corrosion measures and high temperature resistance must be fully considered. The use of corrosion-resistant materials and surface treatment technology, such as galvanization, passivation treatment, etc., can effectively slow down the process of corrosion and extend the service life of the screws.
4. Preventive measures and recommendations for improvement
To minimize the risk of screw breakage, companies can take a number of precautions to ensure the quality and safe use of screws.
4.1 Strict quality control
Strict quality control is carried out throughout the production process, from raw material procurement to finished product testing. Quality management systems, such as ISO 9001, require detailed records and supervision of each production process to ensure that each batch of screws meets the standard requirements. At the raw material procurement stage, companies should select high-quality materials that meet international standards such as ISO 898-1, and ensure that they have sufficient strength and toughness through material testing and mechanical property testing.
In addition, finished screws should also pass a series of testing procedures, such as tension test, fatigue test and corrosion test, to ensure that they are sufficiently reliable in practical applications. Enterprises should regularly maintain and calibrate their production equipment to ensure a stable process and avoid quality problems caused by equipment failure or process fluctuations.
4.2 Environmentally Adaptive Design
For special environmental conditions, enterprises should design and produce screws that meet the requirements. In highly corrosive environments, enterprises should provide corrosion-resistant screws, such as Dacromet screws in accordance with GB 5267.2 standards or ISO 3506 standards for corrosion-resistant stainless steel screws. These screws have excellent corrosion resistance, can effectively resist the erosion of chemical media to ensure long-term stability in harsh environments. In high temperature and high pressure environments, should be selected in accordance with ASTM A194/A194M standard screws, these screws are designed to withstand high temperature, high pressure conditions under the workload design, with excellent high temperature resistance and pressure resistance, to ensure the safe and stable operation of the equipment.
5. Concluding remarks
The analysis of the types and causes of screw breakage is of great practical importance for purchasing managers, manufacturing specialists and business owners. By understanding the different types of breakage and the reasons behind them, we are better able to identify risks and take appropriate preventive measures to ensure smooth production and safe operation of equipment. As a key component in mechanical and industrial production, the reliability and durability of screws have a direct impact on productivity and safety. Therefore, an in-depth understanding of the various factors that contribute to screw breakage is undoubtedly an essential skill for every industry professional in their daily work.
As a professional screw manufacturer and wholesaler, we are always committed to providing our customers with high quality fastener products that meet international standards. By following authoritative standards such as ISO, ANSI and DIN, and implementing strict quality control during the production process, we ensure that each screw can withstand harsh usage conditions and reduce the risk of breakage. At the same time, our expertise and experience enable us to provide our customers with scientific advice and customized solutions to help them better cope with their production challenges.
