Special consideration should be given to large bearings when disassembling and reinstalling components in heavy machinery, especially in rolling mills and manufacturing plants. A single bearing may weigh thousands of kilograms, so it is crucial to follow industry standards for proper and safe lifting when installing bearings. important. Timken repairs thousands of bearings for customers around the world every year and often observes damage caused by avoidable lifting and handling errors.
The service life of a bearing depends largely on the care and maintenance it receives, especially in industrial applications where operating conditions are often harsh, loads are heavy, and contamination and water erosion are common. Following proper lifting is a critical step in ensuring long-term bearing operation, minimizing total cost of ownership.
There are many types of bearings, each with its own disassembly process. Smaller bearings can usually be disassembled manually or with the help of a mechanical pulling device obtained from the bearing manufacturer or an approved supplier. For bearings installed with a press fit or that cannot be removed using a puller for other reasons, it is usually possible to heat the inner ring of the bearing to facilitate removal, usually using a heat lamp or similar device (never use a welding gun to heat the inner ring, the welding gun temperature If it is too high, it will change the performance of the bearing steel).
Moving larger bearings requires a crane and some simple fixtures, usually a variety of slings, hooks, chains and mechanical equipment, to safely perform maintenance. Some large bearings are manufactured with threads on the inner or outer ring surface. holes for inserting eyebolts or lifting rings (Figure 1), and some bearings have threaded lifting holes in the cage ring that can be used to lift the inner race assembly.
There are two ASME standards (BTH-1-2017 and B30.20-2018) that apply to the lifting industry regarding underhook hoisting devices. The American Society of Mechanical Engineers states that underhook hoisting devices are "used for attaching loads to cranes." A device that may include components such as slings, hooks and rigging hardware..." Bearing lifts fall into this category.
When it comes to major bearing maintenance, specially manufactured lifting assemblies should be used, especially in plants that require bearing lifting several times a week. There are two common types of lifting equipment, three-leg fixtures and sliding-foot fixtures. These fixtures can be used to remove bearings from the housing and reinstall them after maintenance is completed.
Three-legged clamps are used to lift entire bearings or handle one subassembly at a time while maintaining bearing assembly concentricity. Certain fixtures may work with certain types of bearings but not others, for example in applications where the bearings are changing from an open to a sealed design, this may be caused by the length of the old clamp legs. Bearing seal damaged.
At the same time, sliding base fixtures engage the bottom row of the bearing assembly, allowing the entire assembly to be immediately removed and then stacked outside the housing, thereby reducing the risk of raceway damage. This method requires sufficient overhead crane capacity and the availability of machined pressure relief devices in the bearing housing to enable the feet of the lifting fixture to properly engage the bottom row of the bearing assembly and, therefore, in some cases, the sliding feet Use of fixtures may be restricted.
As mentioned above, bearing functionality can make lifting individual components easier and safer when disassembly of the entire assembly is not required. These features typically include threaded holes in the bearing race surface for eyebolts and chain lifts, and blind holes in the inner race holes to allow the use of turnbuckle-type lifting devices.
It is recommended to consult directly with the bearing manufacturer to learn about the features that provide the best lifting arrangement for a specific application. Depending on the design of the bearing, adding lifting features may actually compromise the integrity of the bearing. At the same time, correct lifting operation is critical to safe handling. .
If correct procedures are not followed, using only two eyebolts to lift a large four-row cylindrical roller bearing with eight threaded lifting holes in the cage (set up in four pairs to accommodate the crossbars via the eyebolts) will result in the A broken weld connecting the roller pin to the cage may require the assembly to be repaired before the bearing can be used again, or in severe cases, the assembly may even become damaged, causing the component to fall to the ground.
Also, be sure to only lift the bearing from a level, resting position to avoid potential problems. For example, during installation, large bearings are sometimes supported at an angle, or may be leaning against a table in preparation for handling, and therefore eyebolts. The load of the lifting chain may not be evenly supported, which may result in broken eyebolts and stripped lifting holes, creating a serious safety hazard.
2024-03-11