When dealing with heavy loads on factory floors, overhead lifting machinery such as cranes and electric wire rope hoists are irreplaceable. They serve the purpose adequately and have become an inseparable part of the daily operation. But when it comes to maintaining hoists, there are a few challenges that prove to be a bit too much. One such challenge turns up in the form of wire ropes.
The phenomenon is similar to that of the tires on a car. With time and everyday use, the wire rope is prone to tear and wear. If you tend to use them more often or with heavier loads, they get damaged faster and easily. However, with proper maintenance, they can last for an entire expected life. The wire ropes are also susceptible to ruining if one installs them incorrectly. Also, if you operate it improperly, it can get destroyed easily.
If you tend to replace the worn or damaged rope with a generic string, it can be pretty dangerous. As the existing rope that you are using on the hoist needs to be original. Otherwise, it can lead to the wrong type or size. On the other hand, rope identification done based on style and size can be a tricky thing. Most of the time, one can go wrong with the length, type, or size of the purchased rope.
Wire rope has a much shorter lifespan than the hoist. If it undergoes improper installation, then it can cause catastrophic accidents. One needs the supervision of experienced and adequately trained personnel while inspecting the damaged wire rope. Following the guidelines and standards of OSHA and ANSI, one must go for the different tests. The operator stays responsible for the complete visual inspection before loading the lift on every shift.
The Essence of the Hoist Wire Ropes
Hoist Wire ropes are arguably the most vital component of an Electric Wire Rope Hoist and undeniably the most replaced one as well. They are more prone to general wear and tear over prolonged usage than the other components of the hoisting equipment. They are analogous to the tires on the wheels of a car. The heavier loads lifted using the hoists and the more time it is operated for, the more wear and tear they are subjected to. Hence, they require proper maintenance in order to ensure optimum performance and long-lasting life.
Let us discuss in brief the roles hoist wire ropes play and why replacing them timely is an integral part of their maintenance.
The functionality of Wire Ropes in Hoists
Wire ropes are mechanical parts that consist of moving parts working in sync to support a heavy load and move it to its desired direction. The rigging and lifting industry benefits largely from the utilities of the wire rope. Especially when they are used in overhead lifting equipment such as cranes and hoists. The wire rope is attached firmly to a hoist or crane, and the load is fitted using swivels, hooks, or shackles, facilitating controlled movement. It is used in many applications to support suspension towers or bridges and lower or lift elevators.
Wire ropes have become the preferred lifting device in many industrial applications. It has its fair share of reasons as well. Firstly, the unique design allows flexibility, strength, and the ability to handle bending stresses. Depending on the rope's material, wire, and strand structure, it will provide different sets of benefits for the specific application it is used in.
The common configurations that determine its proper usage are listed below.
- Flexibility
- Strength
- Abrasion resistance
- Fatigue resistance
- Crushing resistance
- Rotation resistance
- Corrosion resistance
Selecting the right wire rope for the right application is a process that involves careful thought. Thoughts involving proper analysis of the above aspects of the wire rope and the particular lifting application is required.
What breaks or damages a wire rope?
The following factors might prove to be impactful in damaging or breaking a wire rope.
- Wear and tear on areas that are directly in contact with drums and hoist sheaves.
- Fatigue from repeated bending under normal operations.
- Overloading the hoist beyond the safe working limit.
- Mechanically abusing the wire rope through cutting, crushing, or dragging of the rope.
- Lack of proper lubrication and heat exposure leading to corrosion. At temp beyond 120 degrees Celsius, a fibre core wire rope will give way and break.
- Working with wires that are frozen or below 15.5 deg Celsius can lead to breaking.
- Improper installations are also a common issue that can cause the wire rope to break. Improper installation kinks create a weak section in the rope, which is exploited with prolonged use.
How to determine the need of wire rope replacement?
The following scenarios would indicate that the wire rope in use needs an urgent replacement to ensure operational efficiency and workplace safety.
- If three or more broken wires are found in one lay length of the pendant standing rope.
- If six or more broken wires are found in one lay rope length of the running ropes.
- If any form of heat damage such as burn marks, discolouration of the metal is observed.
- If the individual wire on the outside is subjected to wear off more than 1/3rd of its initial diameter.
- Any unstranding, cutting, kinking, or crushing that is apparent after prolonged usage.
- If the sling identification, such as workload limit, manufacturer's identification is missing.
Replacing the Wire Rope
When the time comes to replacing the hoist wire rope, one must not go for a generic rope as it can lead to hazardous working conditions. The rope can be of the incorrect type or size and hence not be suitable for the lifting task. The identification of the wire rope on the basis of its type and size is a crucial task that needs to be accomplished while replacing a wire rope.
Recommendation of load test after Wire Rope Replacement
Any load test excludes the replacement of chain or wire ropes for the hoist. The wire rope needs to be tested by the manufacturer; one should do this during production. The technician needs to perform the test without the load to check the loading and lifting function. With that, the break operation also needs to be restricted to avoid any disaster. One should do it concerning ASME B30.16.
However, some of the manufacturers recommend load tests for the ropes. After installation, one needs to start the process with light loads that the manufacturer recommends. One should do it with 20 to 25 lowering and lifting cycles at a lower speed. Gradually one should increase the weight to the total capacity. It allows the rope to adjust and adequately fix itself. After this procedure, one needs to secure the hook block and finally disconnect the rope end. To avoid any problematic situation, you need to correct the twist and torque developed during installation.
Conclusion
Proper inspection of the hoist is mandatory and helps largely in identifying the need of wire rope replacement of the hoist. One must also ensure that the inspection is performed by an appropriate technician adept in handling hoist equipment.
