October 9, 2013
The American Society of Mechanical Engineers has established compliance standards for the use of permanent and electric-rated lifting magnets and the operators of those magnets. Familiarizing shop floor personnel with these guidelines builds a solid foundation for keeping employees safe as they move sheet metal and plate.
While lifting magnets have been widely used in metalworking and fabricating plants for years, in the past 10 to 15 years they have become substantially stronger with the introduction of technology based on rare-earth materials and improvements in other areas. Consequently, workers need to be more aware of safety precautions to follow while operating these powerful magnetic devices. Even a minor lapse in operating procedure can cause serious injury.
To this end, the American Society of Mechanical Engineers (ASME) continues to set new guidelines and safety standards for the operation of lifting magnets, some of which are engineered to lift up to 10,000 lbs. without slings, hooks, or cables.
Both permanent and electric-rated lifting magnets fall under the compliance standards established by ASME B.30.20-3. The scope of this section of the ASME code applies to close-proximity lifting magnets and specifically the marking, construction, installation, inspection, testing, maintenance, and operation of these types of magnets when used for single or multiple steel piece handling operations.
In addition, ASME B.30.20-3 addresses compliance guidelines for when the operator of the lifting magnet is required to manually position the lifting magnet on the load and manually guide the load during its movement (see Figure 1). It also applies to the use of remotely operated lifting magnets when used in close proximity to people.
Lifting magnet injuries can range from pinched fingers to crushed hands to the loss of extremities. For these reasons, plant managers responsible for safety training for the protection of workers should strictly adhere to the ASME compliance guidelines.
Section 20-3.4 of the ASME code addresses several safety-related issues, including qualifications and training for operators, personnel conduct when using lifting magnets, and standard operations practices. Metal fabricators needing assistance can contact the manufacturers of their industrial lifting magnets, many of which have establish detailed training and safety steps for customers to help them comply with ASME B.30-20.
Some general safety guidelines that pertain to all lifting magnets and plant operators that follow ASME B.30.20 procedures include:
It is very important that “strong magnet” warning labels be placed on or next to the area where the lifting magnet is being used. This will warn anyone in the area that extreme caution should be used in proximity to the magnet. Lifting magnets should already have warning labels affixed to them when they arrive from the manufacturer (see Figure 2).
Operators need to be aware of items in the area where magnets are being used, as they may inadvertently attract to carbon steel chutes, carts, tables, pipes, I-beams, or other magnets in a split second. If a worker’s hands or fingers are caught between the magnet and carbon steel, his fingers can get pinched, trapped, or even crushed in extreme cases. Therefore, employee training is crucial.
Workers should never stand below a lifting magnet or any lifting device carrying a load because of the potential for a dropped load. The rule of thumb is to stay out of the path of the overhead magnet as it transports loads from one area to another.
In the case of electromagnets, dropped loads can happen even without a total power loss. A split-second power spike is enough to disable the magnet and cause serious injury when the load releases.
Another potential for a dropped load is an oily surface on the magnet, which may attract debris that interferes with surface contact between the magnet and the item being lifted. As the workpieces are lifted from the ground or conveyor belt, they may not be fully engaged with the overhead magnet. This is difficult to detect from a worker’s viewpoint, so it’s best to assume a safe distance.
ASME B.30.20-4 addresses compliance issues when operating a lifting magnet. These recommended guidelines about the materials being lifted assist in creating a safe operating environment around the lifting magnet.
Composition. Be sure the material being lifted is made of steel. Alloys may not be as magnetic as low-carbon steel.
Configuration. The material should be as flat as possible, without any waves or bows. Check for dunnage between pieces that could cause the material to sag at some points. Use a straight edge to check flatness. (The longer the straight edge, the better.)
Surface Condition. The material surface must be as clean as possible (see Figure 3). Elements of rust, dirt, ice, snow, oil, or paint are all considered to be an air gap that creates a weaker pulling force. Make sure the full surface of the magnet is in contact with the material. For example, a cutout in the piece being lifted affects the magnet’s lifting capacity if the cutout is directly under the face of the magnet.
Weight. Verify the weight of the part before using a lifting magnet. (Steel weighs 0.238 lbs. per cubic inch.) To determine the total weight of a steel part, use this formula: Length (in.) x Width (in.) x Thickness (in.) x 0.283 lb./in.3.
Thickness.Thinner materials are more challenging to lift than thicker materials because thinner materials can’t accept all the lines of force, resulting in reduced capacity. This is not a linear function. For example, if a magnet’s full capacity is needed to pick up 1-in.-thick material, that doesn’t mean that half the magnet’s capacity can pick up 0.5-in.-thick material.
Temperature. The maximum recommended material temperature for ceramic permanent lifting magnets is 200 degrees F. The maximum recommended material temperature for electromagnets is 600 degrees F. Modifications may be possible on some magnets to lift higher-temperature materials.
In some cases, lifting magnets can lose strength, depending on the magnet’s characteristics. Permanent magnets do not lose their strength unless they are physically damaged (dropped and broken), subjected to extreme heat (200 degrees F), or subjected to a high electric field, such as welding.
Electromagnets can lose strength if coils burn out from being left on too long (15 minutes maximum unless constructed for continuous duty cycle) or parts in rectifiers fail. If an electromagnet suddenly stops working, it is likely that an electrical change has occurred in the building. Plant operators should be sure to supply the correct AC voltage to the rectifier.
Placing an electronic device in fairly close proximity to a lifting magnet can cause a loss of data or some type of erasure. Generally speaking, magnets are harmful to the magnetic storage devices on a computer, such as hard drives, floppy drives, and flash drives.
Anything with magnetic storage—including a cell phone—should be kept as far away as possible from the lifting magnet to avoid critical data loss.
Some medical devices, such as pacemakers and surgically implanted intracranial aneurysm clips, can be adversely affected by strong magnetic fields. Workers who have these medical devices are encouraged to keep away from operating lifting magnets.
Metal fabricators are more concerned with making metal parts and meeting delivery dates than ensuring their lifting magnets stay in compliance with ASME B.30.20. Those interested in maintaining the performance of their lifting magnets should check with a magnet manufacturer, which can regularly inspect the lifting magnet surface for any deficiencies; check the condition of handles, safety latches, and lifting ball and eye hooks; and inspect for cracked housings, welds, loose bolts, and missing warning labels and capacity markings.
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