It’s easy to take wire rope drums for granted. Their job seems simple.
But they’re a critical player in the safety and reliability of your overhead hoisting equipment. They require careful examination in preventive maintenance inspections, but before the first load can be hoisted, their features should be well thought out. Common problems, like structural cracking, can be avoided through thoughtful design and manufacturing techniques.
Design and manufacturing quality pay off, reducing the risk of a failed rope drum and the costly downtime that can go with it. It can also pay off fiscally if the drum can be rebuilt in the future. Rebuilds are a fraction of the cost of buying new.
Rope Drum Design Practices and Features on Which to Focus
1. Material and Barrel Size. The drum barrel of low duty class drums (Classes A & B) can be made of medium carbon level steels, while medium and process duty class drums (Classes C-F cranes) may require drums that have been heat treated to minimize drum groove wear and increase the components’ life under higher cyclic loads.
Specifically, for large process duty cranes, the drum designer should factor in the potential need to rebuild the drum in the future. This entails designing the drum barrel to match the rebuild technique used by the OEM.
2. Internal Diaphragms. Inside a wire rope drum, diaphragms can help distribute the load on the shaft and stiffen the drum. The additional stiffness reduces bending stresses and lowers the amplitude of fatigue cycles, which can lead to cracking later in the drum’s life.
3. Weld Joint Geometry, Shape and Transitions. To withstand the critical stresses a wire rope drum will encounter, weld joints must be the right size and type. When several weld passes are required, the designer should limit the possibility of having all welds terminations in one location. This is especially important for barrels formed by welding rolled plate, where multiple weld joints may be meeting in one area.
Rope Drum Manufacturing Practices
1. Material Sourcing. Drum barrels can be made with rolled plate or by casting. In the case of rolled plate, a weld brings together the two ends of the plate to form the barrel. Casting creates one continuous piece of steel. Casting is preferred as it eliminates the welded seam and the stress concentrations that accompany this type of process. However, using a cast barrel is not always economical for larger barrels.
For the most critical applications, the manufacturer should, upon request, be able to provide material certifications for the material used to manufacture the drum, as well as be able to certify that the drum meets ASME specifications (or other applicable standards).
2. Welding. Proper preparation and technique make all the difference in strong, long lasting rope drum welds. The following help assure good welds:
• Following AWS and other applicable standards.
• Making sure metals are clean, free of inclusions or other imperfections before starting the welding process. This is critical, because these types of unwanted materials can case weld inclusions, porosity and a host of other weld defects that can lead to failures.
• Ensuring all weld procedure instructions are followed. Weld procedures are designed to ensure proven results and help tame common defects, such as cold cracking, and reduce the effects of the weld heat affected zone (HAZ). This ensures the integrity of the weld throughout the lifetime of the drum.
• Using the proper welding process that matches the requirements of the weld procedure. MIG welding is a typical choice for OEMs that manufacture a variety of drum sizes. While a process like submerged-arc welding may be used to manufacture the same drum many times over.
3. Machining. The machining technique and processes are critical for the longevity of the drum.
Manufactures must take great care to ensure the machining process used produces a balanced, concentric product. This limits unintended cyclic loading that can occur during the drum’s rotation, leading to premature drum failure.
4. Heat Treatment. Heat treatment can stiffen the drum and improve groove hardness to increase life. This process is a critical feature for large process duty cranes who operate in harsh conditions.
• Flame hardening is the preferred method for rope drum grooves as it increases the rope groove’s wear life and strength.
• Carburizing is another technique to hardened the rope grooves. This method is typically less cost effective and leaves only a thin layer of hardened material in the groove.
Wire rope drums are a critical part of the health and overall performance of your hoisting equipment. For more information please contact [email protected] or your local Konecranes service representative.