Blake Parker
Technical Education Committee Member
Integrated Power Services
When handling motors, lifting devices are often needed, whether they be cranes, forklifts or otherwise. As a new technician, many times one of the first things taken for granted is a rigging device’s weight handling ability. Given the risks inherent to lifting, EASA members must exercise caution and ensure our teams are well versed in proper rigging techniques. This is accomplished through classroom and hands-on training.
Identification of lifting ratings and general inspection is one of the first things to teach your employees. At first glance, it may not be clear that different steels were used to make similar looking chains or rigging components. However, reviewing the lifting rating tag or markings that must be affixed to the chains or rigging components will make the lifting rating of each understandable. Similarly, it can be difficult to notice an additional layer or missing layer of nylon in a nylon sling. Thus, reviewing the rating tag is a necessity for every sling regardless of appearance.
Inspection of slings and rigging items should be taught by qualified individuals. Identification of damaged threads, chain wear or other defects can be easily overlooked by an untrained eye. Failed items should be rendered useless upon inspection to prevent accidental further use. Cutting slings, chains etc. is the only sure way to ensure they will not be used again.
A commonly misused rigging device is the eye bolt (Figure 1). Depending on the design, eyebolts can only handle limited side loading. Some cannot handle any at all. Also, some manufacturers use the same forgings for standard and metric eyebolts. In many cases, the metric designation is a simple stamp on the side without the removal of the standard thread marking. The metric stamp can be easily overlooked and lead to poor thread engagement with subsequent failure. Measure the threaded diameter and thread pitch to verify the correct eyebolt is selected.
Shouldered eyebolts feature a shoulder where the eye and the shank meet. This reduces the bending stress on the shank. Shouldered eyebolts can be used at a reduced rating for angular lifts when the shoulder properly contacts the load. Refer to the manufacturer to determine actual capacity. Non-shouldered eyebolts (Figure 2) are designed for vertical or in-line lifts only with no angle. As such, it is considered a best practice for most facilities to dispose of and ban non-shouldered eyebolts.
One of the most common uses of eyebolts is when they are utilized at the ends of the frame of the motor and lifted. The lift angle often meets or exceeds 90 degrees. Depending on the construction and design of the eyebolt, most are rated at 25% or less of full capacity at that angle.
When sideloading of threaded holes is required, it is best to use a swivel-eye (Figure 3) or side load hoist ring (Figure 4). As the name implies, swivel eyes allow the eye to swivel 360 degrees at almost any angle provided the load does not contact the eye or impede motions. Side load hoist rings are designed to have the load applied at 90 degrees to the load being lifted. When used per manufacturer specs, no reduction in weight capacity is experienced, unlike eyebolts. Important: Do not disassemble or alter the configuration of swivel eyes or any other lifting devices. Doing so is a design change and should not be done without proper engineering support from the manufacturer.
Rewinding stators often requires flipping or rotating stators. Swivel eyes work very well for this task. Determining the proper attachment point is key as illustrated in Figure 5. If the swivel eye is attached near the top of the load, the rotation will not be sufficient to allow turning the part as desired. If the attachment point is too low, the load will rotate violently, possibly out of control, leading to potential injury, equipment damage or overloading of the rigging/lifting equipment.
When determining the appropriate sling for lifting, several factors should be considered. Nylon slings are often preferred due to their strength vs. weight ratio. Properly used nylon slings are an excellent option for lifting. When using nylon slings, ensure a thorough inspection is performed prior to each lift, ensure temperatures the sling will be exposed to are in the acceptable range, and use softeners on sharp edges and connection points. Some slings have "tell tails" that indicate when the sling has been overloaded and thus should not be used. Prior to overloading the "tail" is visible, and after overloading the tail is not visible. Never tie a knot in a sling to reduce the length; the knot acts as a stress riser and can lead to premature failure and lower than rated loads.
Chains and wire ropes can appear as more desirable options as they appear more durable than a nylon sling. Many of the same concerns exist for chains and wire ropes (cables). It's best to never double a cable, and kinked cable should be discarded. Ensure a proper inspection is performed, check for damaged links or wires, always wear gloves, do not exceed safe bend radiuses, and keep chains/wire ropes clean and rust-free.
One of the more difficult concepts to teach is the reduction of capacity of a sling as the angles increase (Figure 6). A common reduction in sling capacity is 4% at 30 degrees but the reduction in capacity is 50% at 120 degrees. One of the best ways to demonstrate the weight change experienced by the sling is to connect a sling in a straight vertical pull with a scale in line to a long object. A shaft or pipe works well; it doesn't have to be something fancy. Then take the same object and connect slings at both ends and then place a scale in line with one of the slings to show the weight experienced by the sling. As Figure 6 illustrates, the force experienced by the sling increases as the angle increases. While it seems simple, many will be surprised at the weight variation seen and then understand the stress a sling undergoes at an angle.
Once technicians have been trained in the general requirements of rigging, all should be given a sling angle chart to keep for quick access. Quick reference charts are reminders for the effects of angles and different connections such as basket vs. single choker (Figure 7). These are available from your rigging supply company or online. Ensure you select the appropriate reference chart for your sling type.
The other part of rigging for safety includes preventing damage to the lifted component. Work with your technicians to identify the lift points only rated for a component of the motor such as the hood. Attempting to lift from these points will result in damaging the motor as well as potential personnel injury. Also, use every lifting point provided. If a motor has four lifting points, use all four whether assembled or disassembled. Failure to do so can result in distorting the frame. Discussing the appropriate points to attach to an endbell or other components is critical as well to prevent overloading or frame damage.
At times, overhead lifting devices are not readily available. Many times, a powered industrial truck is utilized for heavy lifting instead. Ensure the proper attachments are utilized when using a powered industrial truck. This is usually in the form of a jib boom attached to forks. Simply sliding a sling over the forks is not adequate as the sling can unexpectedly change position. It also applies to an uneven load to the forks. Powered industrial trucks can also roll while lifting; there is more to consider when it comes to utilizing a powered industrial truck safely. Ensure a thorough review is performed prior to the lift and that all contingencies have been covered.
Lastly, when it comes to electric motors, there are often components that do not feature easy/clear attachment points. In some cases, it may be tempting for customers to fabricate lifting devices in-house. This should only be done with the assistance of a qualified engineer. The device should be designed for the task with appropriate safety factors considered and followed by load testing. All of this should be documented and stamped by a professional engineer. The lifting device must be serialized and added to a regular inspection rotation as well.
Utilizing cranes and other overhead lifting equipment is a great way to reduce back strain, equipment damage and generally necessary due to the scale of equipment. Doing so safely begins with proper training, equipment, inspections and a program to manage them jointly. Every year, thousands of injuries occur because of dropped or swinging loads. If you do not have the appropriate professionals in-house for overhead lifting training, some consultants can help ensure your overhead lifting program meets industry standards. They can help your company develop a plan to close any gaps.
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