Considerations When Purchasing Your Next Lifting Magnet
Updated: Feb 12
The recommended procedures set forth herein are not substitutes for the exercise of care and judgement in each particular case.
The purpose for these guidelines is to recommend operating and safety procedures of close proximity operated lifting magnets. These guidelines apply to all lifting magnets when used for single or multiple steel piece handling operations in which the operator of the magnet is required to manually position the magnet on the load and manually guide the load during its movement. For multi-magnet systems where individual lifting magnets are suspended from a spreader beam or its equivalent, these guidelines apply only to the individual lifting magnet excluding the spreader beam or its equivalent and the associated control equipment. These guidelines do not apply to remotely controlled electromagnets.
PROPER MARKING – Lifting magnets that are utilized as general-purpose lifting devices or where the application of the lifting magnets is uncontrolled are to include the Rated Lifting Capacity of the magnet marked on the lifting magnet or a tag permanently attached to it. Other pertinent information should be disclosed on the tag and in accordance with ASME B30.20 standards. It is imperative that the tag be permanently attached to the lifting magnet and should not be removed.
GENERAL CONSTRUCTION – Lifting magnets may be modified or re-rated provided such modifications and the supporting structure are analyzed thoroughly by a qualified person or manufacturer of lifting magnets.
MECHANCIAL CONSTRUCTION - Lifting magnet electrical components are to be guarded or located to minimize the possibility of operator injury or the entry of foreign objects during normal operating conditions.
Lifting magnet suspension slings are to meet the magnet manufacturer’s recommendations and comply with ASME B30 sling specifications.
ELECTRICAL EQUIPMENT –
Controllers – The control device for an electromagnet should contain provisions for guarding the control switch in the “Lift” position to protect it from being inadvertently turned off.
Battery – Battery-operated electromagnets should contain a current flow device indicating safe battery operating conditions. Housing for wet cell batteries should be vented during charging to prevent the accumulation of gases. Batteries should be charged in a well-ventilated area and never with the power pack lid down. Battery gases are explosive. Recharging the battery every night will increase battery life and magnet safety. Although there is an automatic cutoff in the charger to prevent over charging and boiling the batteries, it is NOT recommended to leave the charger on for periods exceeding 24 hours.
Battery Precautions - Rubber gloves, rubber apron, and goggles should be worn when handling acids. The red battery lead should be connected to the battery post marked + and the black battery lead should be connected to the other battery post. The power pack should not be tilted beyond 30˚ to avoid spilling acid on the power pack or magnet.
Battery Installation - If a dry-charged battery is used, the electrolyte should be added to the battery before it is installed in the power pack. Lifting magnet operator should follow battery manufacturer’s recommended procedures for adding electrolyte to the dry-charged battery. Do not install battery in the pack until after activation and a thorough washdown. The performance of dry-charged batteries after activation may be quite variable, depending upon the storage conditions. There is no degradation in battery quality associated with this. Complete capacity is recovered after from one to two discharge-charge cycles.
Battery Charging for MagnaLift and Power-Grip Lift Magnets - Always check the electrolyte level of all cells and add distilled water as needed. The built-in charger is turned on by connecting the Power Pack to the 115 VAC line using the line cord packed with the magnet. The control switch must be in the OFF position when the charger is connected to the AC line. Leaving the control switch in the ON position will greatly increase the time required to recharge the batteries and damage the charger. An accurate meter indication is only achieved in the “on” position when the charging cord has been disconnected. The charger is designed to charge at the maximum safe rate. It is electronically regulated to automatically turn off when the battery is recharged. The meter pointer will be in the charge region while the battery is being charged and will return to the “zero” center position when charging is completed. However, only a hydrometer will show the true state of charge.
RATING CAPACITY – Capacity ratings are established under laboratory conditions with proper test equipment. A steadily increasing force is applied vertically to the lift magnet to separate it from a machined, flat low carbon steel plate of sufficient thickness to prevent bending and obtain maximum magnetic tractive force. Due to the many variables, such as surface roughness, flatness, material density and analysis, bowing, warpage, etc., a safety factor of about 100% is used when establishing a capacity rating.
Please note that capacity ratings must be reduced when lifting thin material. The flexing, bending, and peeling action added to the fact that thin material does not respond to a magnetic field as readily as thicker material are reasons for decreased ratings for thin material. Rating capacity and lifting magnet use must also factor in the effect of air gap, piece thickness and piece length and width.
Other factors to consider when using lifting magnets in relationship to capacity ratings and size and weight of load are as follows:
· End or edge overhang that allows material to sag 4” or more creates a questionable lift because sag increases rapidly beyond this point.
· Plate thickness of ½” or more are likely to peel from any reasonable overhang (up to 72”) providing the load is balanced on the magnets.
· Surface condition of material
· Straightness and flatness of material
· Lift and traverse speed of crane, or inertia forces
· Likelihood of jarring load loose by collision with other objects.
· The amount of sag form various unsupported lengths is constant. Width of a sheet is not a factor. (example: A 12” wide sheet will sag as much as a 72” wide sheet of any given thickness over any unsupported length.)
IMPORTANT FACTS FOR THE SAFE OPERATION OF LIFT MAGNETS
Load characteristics other than just weight must be considered in order to determine the safe weight that any magnet can lift. This statement is true for any lifting magnet because they all operate using the same fundamental laws of physics. Magnetic power is often pictured as lines of magnetic force flowing from north pole to south pole. Anything that limits the flow of these magnetic lines of force obviously reduces the magnets lifting ability. There are four important factors which limit the flow of these lines of force.
1. LOAD SURFACE CONDITIONS - Magnetic lines of force do not flow easily through air; they need iron in order to flow freely. Therefore, anything that creates an air gap between a magnet and the load limits the flow of magnetic force and thus reduces the lifting capacity of a magnet.
Paper, dirt, rust, paint and scale act the same as air. Also, a rough surface finish is the same as dirt because it creates an air gap between the magnet and the load.
2. LOAD LENGTH OR WIDTH - When the length or width of a load increases it ceases to lie flat and the load begins to droop at the edges. This drooping or sagging of the load can create an air gap between the load and the magnet. If this occurs, then the lifting capacity of the magnet is reduced.
3. LOAD THICKNESS - Magnetic lines of force are more effective when they flow through iron instead of air. The thicker the load is the more lines of magnetic force are able to flow. After a certain thickness of load no more lines of force will flow because the magnet has reached its full capacity.
Thin material (load) means less iron available and thus fewer lines of magnetic force flow from the magnet into the load. Therefore, the lifting ability of the magnet is reduced.
Every magnet should be rated to tell the user what minimum thickness of load is required to reach full lifting capacity. Below such thickness of load the user knows he must de-rate the lifting capacity of the magnet.
4. LOAD ALLOY - Low carbon steels, such 1020 steel, are nearly as good conductors of magnetic lines of force as pure iron. However, many other alloys contain non-magnetic materials which reduce the ability of magnetic lines of force to flow into the load. An alloy such as 300 series of stainless steel is almost as poor a conductor of magnetic force as air.
Type 416 stainless steel is considered magnetic, but it contains enough chromium so that it can only conduct one half as much magnetic force as 1020 steel. The carbon content of cast iron reduces the flow to one half of the magnetic force of 1020 steel.
All information contained herein is offered in good faith, without guarantee or obligation for the accuracy of sufficiency thereof, or the results obtained, and are accepted at user's risk. We reserve the right to change specifications or design without notice and without incurring obligation.
MagnaLift and Power-Grip are brands owned by Obsidian Manufacturing Industries, Inc.