Key Considerations and Common Reeving Methods for Crane Sheave Block Wire Rope
This post mainly list some reeving methods for crane sheave block wire rope. In lifting and loading and unloading of large equipment, crane sheave block of wire rope how to wear around is an important issue. If wear around the wrong way, easy to make the wire rope bending too much, accelerate the wear and tear; in the case of more pulley doors, due to wear around the wrong way, but also make the upper and lower pulleys between the skewed, increasing the pulley and pulley shaft stress. Sometimes due to the wire rope transmission is not smooth, sheave blocks of wire rope local slack, in lifting equipment is easy to cause sudden impact load, even caused by pulling off the wire rope accident.
Crane Sheave Block Wire Rope Winding Method
In practice, the crane sheave block wire rope wearing method is divided into two kinds of smooth wearing method and flower wearing method:
Straight-through method
It is a relatively simple threading method. Depending on the number of winches available at the installation site, either single or double running head threading can be used.
Single Lead Sequential Reeving Method
As shown in Figure 1, the end of the rope is threaded around the fixed and moving pulleys in sequence starting from the upper pulley on the side, while the dead end is secured to the fixed pulley shelf at the end. This method is commonly used in pulley blocks with a small number of doors, such as 5 doors or less. From the analysis of the tension of the wire rope can be seen, in lifting equipment, due to the tension of T, and the dead end of the tension is small, each rope branch of the force and are not the same, from left to right in decreasing order, so the pulley rack often appear skewed phenomenon, unbalanced at work, for the safety of the lifting equipment and positioning is very unfavorable, and therefore often used in practice dual-lead sequential reeving method.
Dual-Lead Sequential Reeving Method
When lifting heavy equipment, the dual-lead sequential reeving method is often used. It has the advantage of avoiding the skewing of the sheave block, but also can reduce the running resistance of the pulley block and speed up the lifting speed. Figure 2 is the double running head of the two sheave block. It is generally appropriate to use an odd number of fixed sheaves, and in the middle of the rotating wheel as a balance pulley. If the two winches have the same winding line speed, the force is balanced, and the balance pulley can not rotate. In the case of equal pulley efficiency, the corresponding rope branches should have equal tension, so the pulley rack will not produce a skewed phenomenon. The disadvantage of this threading method is to have two winches with equal linear speeds.
Cross Reeving Pattern
In the lifting of large equipment, the pulley door number is more, if only a winch traction equipment, can be used to improve the working conditions of the sheave block and reduce the tension of the running head, which can also ensure that the sheave block force is uniform and lifting smooth. Cross reeving pattern is divided into single-cross reeving pattern and multi-cross reeving pattern.
Single-Cross Reeving Pattern
In the Single-Cross Reeving method, the rope end starts from the center of the sheave block. As shown in Figure 3, the lead rope sequentially winds around the fixed pulley and movable pulley in one direction, then returns to the center of the pulley block and reverses direction to wind around the pulleys again. The dead end is secured to the fixed pulley frame. During reeving, the rope typically skips 1 to 5 sheaves between passes, with the total number of cross passes always below two. This configuration results in opposing rotation directions for the left and right pulleys.
As can be seen from the figure, the branch tension of the steel rope leading from the fifth door pulley is, and the tension of the four pulleys on the right are greater than the tension of the four pulleys on the left.
Critical Limitations:
Excessive Rope Misalignment: When the rope transitions from the movable pulley to the fixed pulley during cross reeving, the misalignment angle within the sheave groove becomes excessive.
Mechanical Failures: Historical cases using this method reported pulley frame deflection and bushing burnout due to uneven load distribution. These failures necessitated replacement with the Multi-Cross Reeving method described below.
Multi-Cross Reeving Method
In the multi-cross reeving method, the rope end can start from the center of the pulley block, as shown in Figure 4, or from the outermost sheave. The dead end is always secured to the fixed pulley frame. During reeving, the rope typically skips 1 to 5 sheaves between passes, with the total number of cross passes exceeding three.
This method is more complex in its execution. The rotation direction of adjacent sheaves can either be identical or consistently opposite. A key characteristic of this method is the uniform load distribution across the pulley block, resulting in smoother and more stable operation. As such, it is commonly used for handling large-scale equipment during loading and unloading operations.
Key Advantages:
Uniform Load Distribution: Ensures balanced tension across all sheaves, reducing localized wear.
Operational Stability: Minimizes dynamic load fluctuations, enhancing safety and efficiency.
Critical Limitations:
Complex Reeving Process: The increased number of cross passes makes the threading process more intricate.
Increased Spacing Requirement: To prevent rope-to-rope friction, the minimum distance between the movable and fixed pulleys must be greater than that required for the sequential reeving method.
Points and Precautions for Winding
1. To enhance the lifting capacity of the sheave block, reduce resistance, and ensure safe hoisting operations during the handling or installation of large-scale equipment, a dual-lead double pulley block should be employed.
2. If site constraints limit the use of dual-lead reeving, a single-lead reeving method must be adopted, utilizing the cross reeving pattern. For lifting large-scale equipment with multiple sheaves, the multi-cross reeving method is recommended. In such cases:
The lead rope tension must not exceed the safe towing capacity of the winch.
The safety factor of the wire rope must be no less than 5 (as per ISO 4309 and ASME B30.5 standards).
3. After the wire rope is worn in the pulley, the rope should be tightened gradually for test hoisting, check whether there is any card rope, grinding rope and wire rope friction with each other. If there is something wrong, should be adjusted immediately and then continue to work.
4. Dynamic pulley and fixed pulley should maintain a certain distance, so that the angle of the wire rope to keep within the allowable range. Using the hook or ring pulley set should make the hook and ring weight plus the weight of the movable pulley can ensure that they are unloaded when the smooth descent.
5. In loading and unloading of large equipment, for the pulley door number of pulley group should be disassembled beforehand to check, and then clean, add enough lubricating oil, to ensure that they are in a good state of use.
This article describes several crane pulley block wire rope threading method is currently used more than a few methods, can be very good to complete the task of lifting.When you choose, you should choose the appropriate method according to the actual lifting scene.
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