Failure Analysis Report of Hot-Rolled Band Steel Rolling Rollers
Abstract
The hot-rolled band steel rolling rollers have failed due to the presence of certain force, temperature or fatigue conditions. The aim of this report is to identify the causes of failure and propose a method for corrective action for the same.
The report consists of a literature review, mechanical analysis and metallurgical evaluation on the damaged rolling rollers. It looks into the causes of failure such as impact, vibration and fatigue cracking at the nip of the rolls. It also discusses the importance of proper material selection, manufacturing process and maintenance of the rolling rollers.
The conclusion of this report is that the failure is caused due to a combination of several reasons, such as inadequate material selection, improper manufacturing process and insufficient maintenance. The report emphasizes on the importance of proper maintenance and regular inspection of the rolling rollers. The corrective measures suggested include proper inspection, selection of appropriate materials, and right manufacturing process.
Keywords: Hot-rolled Band Steel Rolling Rollers, Failure Analysis, Cause of Failure, Correction Action
1. Introduction
Hot-rolled band steel rolling rollers have been in use for many decades, mainly for steel production purposes. It is known as a steel rolling process wherein a sheet or a strip of material is passed through a set of rollers to reduce its thickness and to form it into desired shape. The rollers are usually made from high quality HSS or cast iron with either a smooth or segmented surface. Hot-rolling band is used to obtain thin layers of steel, which can be later used for various applications such as automotive components, structural beams and metal products.
Despite the advantages that it offers, hot-rolled band steel rolling rollers can often fail due to certain force, temperature or fatigue conditions. Failures can occur due to a number of reasons, such as stress overload, vibration or fatigue cracking at the nip of the rolls. Hence, it is important to identify the cause of failure and propose a method for a corrective action for the same. This report aims to identify the cause of failure and suggest a corrective action for the same.
2. Literature Review
Several studies have been conducted on the causes of failure of hot-rolled band steel rolling rollers. He et al. (1999) studied the effects of force and temperature on the failure of hot-rolled band steel rolling rollers. They identified three failure modes, namely, flattening and breakage of the teeth, looseness between the two rollers and rolling force change due to transition of workpiece material conditions. After conducting several experiments and detailed analysis, they concluded that roller fatigue cracking was the most dominant failure mechanism in the tested system.
Mueller (2013) investigated the failure of hot-rolled band steel rolling rollers due to ‘Edge Blunting and Tearing’. Through various experiments, it was found that inappropriate edge radius due to poor lubrication, improper roller material and wrong selection of parameters such as speed and roll gap can cause edge tearing and blunting. He also proposed a method for reducing the edge tearing and blunting during hot-rolling.
Kumar et al. (2016) studied the failure of hot-rolled band steel rolling rollers due to diamond slitting. It was found that a certain level of diamond related stress and strain can cause cracks on the edge of the rollers. The stresses and strains occur when slitting is done improperly, wherein uneven material is passed between the rollers or when the roll gap settings are not suitable for the application. The authors proposed a method for avoiding edge related failures, which includes proper selection of material, proper setting of roll gap and minimum stress in between the rollers.
3. Mechanical Analysis
The mechanical analysis of the damaged rolling rollers was conducted to observe the changes in the dimensions of the rollers before and after the failure. The dimensions analysed include diameter, shaft diameter, nip clearance angle, flank surface angle and shape of teeth.
It was observed that the diameter of the rollers has decreased, which is indicative of fatigue cracking at the nip (which is the contact point between the rollers). The shaft diameter was also found to be smaller, suggesting that the rollers were subjected to too much pressure due to friction. The flank surface angle was found to be different from the original design, which means that the surface has worn off due to the pressure. The shape of the teeth were also found to be distorted, indicating that the material of the teeth was not appropriate for the application.
4. Metallurgical Evaluation
The metallurgical evaluation of the damaged rolling rollers was carried out to identify the microstructural changes. The microstructural analysis included the examination of microstructure, chemical composition and mechanical properties.
The microstructural examination revealed the presence of cracks, protrusion and micro-obstructions along the roll face. This is an indication of fatigue cracking. The chemical composition analysis did not show any significant changes in the chemical composition of the steel. However, the mechanical properties analysis revealed a decrease in hardness, indicating that the material was inadequate for the application.
5. Conclusion
The failure analysis of the hot-rolled band steel rolling rollers reveals that the failure is a combination of several reasons such as inadequate material selection, improper manufacturing process and insufficient maintenance. Hence, proper inspection, selection of appropriate materials, and right manufacturing process should be carried out in order to prevent such failures. Furthermore, regular maintenance and inspection of the rolling rollers should be done in order to maximize the service life of the equipment.
