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Impact Loads on Steel Wire Ropes
Impact loads are essential in determining the friction and wear characteristics of steel wire ropes, particularly in ultra-deep mining applications like deep shaft and subsea mining, which use multi-layer winding hoists. Engineers must understand these effects to design more durable and efficient hoisting systems. This article explores how impact loads influence the friction and wear of steel wire ropes as they slide against each other.
Table of Contents
Coefficient of Friction (COF) Under Impact Load
The Coefficient of Friction (COF) measures the resistance to sliding between two surfaces and is crucial in understanding the behavior of steel wire ropes under impact loads. Unlike stable contact conditions, the COF behaves differently under impact. Under stable conditions, the COF remains constant with increasing load, stabilizing around 0.73 for dry-friction and approximately 0.35 when lubrication is used. However, the COF significantly decreases under impact loads, with maximum values around 0.36. This reduction is mainly due to the dynamic nature of impact, which affects the contact mechanics between the wire ropes.
Impact Load and Velocity
- Stable COF Values: The COF remains stable with increasing impact load.
- Maximum COF Under Impact: The maximum COF under impact load is significantly lower than during stable contact, stabilizing around 0.36.
- Rebounding Effect: Higher impact loads cause the stationary load wheel to rebound, leading to multiple impact peaks in the COF. This rebounding effect can significantly influence the wear and friction characteristics of steel wire ropes, requiring careful consideration in hoisting system design.
Sliding Velocity Effects
- Decrease in COF: Under sliding conditions without impact, the COF decreases with increasing sliding velocity in dry conditions, reflecting reduced adhesion time between asperities on the wire surface.
- Lubrication Stability: Lubrication stabilizes the COF regardless of sliding velocity, showing its effectiveness in mitigating the impact of sliding speed on friction.
Temperature Rise During Friction
Temperature rise is a critical factor affecting the performance and lifespan of steel wire ropes. Under frictional contact, temperature increases rapidly at the onset of sliding, especially in dry conditions, potentially reaching up to 103 °C. This intense heat generation is due to friction. Lubrication significantly moderates this temperature increase, with maximum rises around 10 °C, as the lubricating medium dissipates heat and reduces frictional forces.
- Initial Temperature Behavior: Temperature rises rapidly during the initial friction stage, especially under dry-friction conditions.
- Long-term Temperature Behavior: As friction continues, the temperature stabilizes, though achieving this steady state is more challenging under dry conditions. Lubrication helps in quicker stabilization and maintains lower overall temperatures.
Conclusion
In conclusion, the dynamic interaction between impact loads, sliding velocity, and temperature rise underlines the importance of careful design and lubrication in enhancing the performance and longevity of steel wire ropes in ultra-deep mining applications. Engineers must consider these factors to develop hoisting systems that can withstand the harsh conditions of deep shaft and subsea mining.
