What is intrinsic safety, and what is the premise of intrinsic safety? Is the safety of special equipment in the electromechanical category more focused on design and manufacturing or maintenance and inspection? How are material parameters determined during the
design phase? This article discusses these questions.
1. What is Inherent Safety?
The concept of inherent safety was first introduced by Trevor Kletz in 1976. It refers to eliminating risks from the source rather than relying solely on control, warning, or interlocking systems to reduce the probability and severity of accidents. The goal is to remove risks at the core, creating a fundamentally safer system.
Inherent safety represents an ideal state of absolute safety. Although difficult to achieve in practice, it can be approached by implementing technical measures to minimize risks and make specialized equipment inherently safer.
2. What is Inherent Safety in Amusement Rides?
Throughout the lifecycle of amusement rides—from development, design, construction, and operation to modification and maintenance—strategies such as minimization, substitution, moderation, and simplification can effectively reduce and control safety risks. These strategies are most effective during the early design and development phases, where their impact on risk reduction is greatest. Design reliability is the foundation of inherent safety, and incorporating reasonable safety factors at the design stage can significantly enhance equipment safety and reliability.
The prerequisite for inherent safety is design reliability.
3. What is Material Tempering?
Tempering is a process of adjusting quality by regulating various parameters that influence performance. It doesn’t necessarily mean improving all parameters, but rather finding a balanced adjustment. Tempering is a heat treatment process used to improve the overall mechanical properties of steel materials. It consists of quenching and high-temperature tempering, aimed at achieving an optimal balance of strength and toughness in steel components.
Tempered materials are widely used in parts subjected to complex stresses, such as gears, shafts, and connecting rods.
4. Purpose of Tempering 40Cr Steel
40Cr steel requires quenching followed by high-temperature tempering. As the tempering temperature increases, strength and hardness decrease, while impact resistance and toughness improve. For critical shafts in amusement rides, the tensile strength of 40Cr is set at 750 MPa (according to mechanical design manuals and university textbooks).
5. Common Material Parameters in Amusement Rides
In the design of large amusement rides, the tensile strength of 40Cr must be set at 750 MPa. Higher values, such as 1200 MPa, are unreasonable. Similarly, Q235 should have a tensile strength of 375 MPa, not 440 MPa. Overstating material strength values can lead to mismatches between the material and the design, forcing the use of inaccurate material certificates to pass inspections.
For important shafts in large amusement rides, 40Cr is used with a tensile strength of 750 MPa and a hardness of 241–286 HB after quenching and high-temperature tempering. If the tensile strength exceeds 980 MPa, the shaft becomes too brittle and loses impact resistance, which is detrimental for such critical applications.
6. The Disadvantages of Arbitrarily Increasing Material Parameters
During the design process, arbitrarily increasing material parameters, such as setting Q235’s tensile strength to 420 MPa or 40Cr’s to 980 MPa, can lead to shafts that fail to meet the true safety margin. This might result in the shaft breaking before reaching the expected service life under impact loads, regardless of how carefully it is maintained or inspected.
Material tensile strength values are dictated by standards, such as those found in mechanical design manuals. Setting overly high values negates the entire design process, rendering subsequent work meaningless.
7. Conclusion
Using unreasonable tensile strength values undermines the reliability of type testing, supervision inspections, regular maintenance, quality improvements, emergency response, and risk assessments for amusement rides. Regardless of how diligent or advanced your maintenance and inspections are, adopting improper material parameters compromises the equipment’s design reliability and, ultimately, its inherent safety.
Source: https://mp.weixin.qq.com/s/MY5R2EAyP-4pRjT4Gxgg1A
original author: 九妹婆婆
