Lifting magnets can be one of the more durable pieces of equipment used by scrap metal recyclers, but these ferrous scrap yard workhorses do not last forever.
Among the many operations aspects yard managers and material handler equipment operators must monitor is how well their lifting magnets continue to lift.
In the following interview, Brian Taylor of Recycling Today asks Mark Volansky, the director of sales of Alliance, Ohio-based Winkle Industries, what operations personnel should keep in mind as they assess the performance of their lifting magnets and determine a path forward when it’s time to rebuild or replace them.
Recycling Today (RT): What is Duty cycle and how does it affect performance?
Mark Volansky (MV): Duty cycle is simply time on versus time off. Duty cycle is generally measured in 10-minute intervals, so for a 50 percent duty cycle magnet, every five minutes the magnet is operating, it should be off for five minutes. For a 75 percent duty cycle magnet, the magnet can be operated approximately seven minutes out of every 10.
Exceeding the duty cycle will have a negative impact on the productivity and life of the magnet.
RT: How do operating hours or number of duty cycles tie into when a lifting magnet will need an overhaul or rebuild?
MV: The time frame for remanufacturing a lifting magnet is dependent more on duty cycle rather than number of operating hours. If a magnet is operated according to its rated duty cycle and is not abused or damaged mechanically, it may go several years before requiring an overhaul or rebuild.
However, when a magnet exceeds its duty cycle, the integrity of the insulation is compromised. And if the duty cycle is exceeded frequently (as is often the case), the magnet life cycle can be decreased significantly and fail prematurely.
RT: What are some operations-related signs that a lifting magnet may be ready for its turn in the remanufacturer’s shop?
MV: Here are some key things to look for:
- The magnet loses lift rapidly after running for a relatively short period of time and the amperage drops quickly.
- There is a rapid decrease in current.
- The magnet pulls a percentage more current than the data tag located on the magnet at its designed voltage. (The magnet will not drop cleanly, and scrap wants to hang onto the magnet after the drop function has been activated. Sometimes this a true indicator, but I would first look at the controller and make sure the DSM [dual switch mixer] and drop circuit are set up correctly.)
- Excessive or premature wear or damage is visible on the pole shoes or the bottom plate of the magnet and could lead to an electrical failure.
- Electrical lead boxes are excessively damaged.
- Welds are cracked.
- Chains and pins are worn.
- Lifting lug bores are worn.
RT: What are the main causes of magnet failures? are there tests to help determine a magnet’s electrical condition?
MV: The main causes of magnet failures are heat and abuse. These two items can have a domino effect and cause a magnet to fail prematurely.
Any time a magnet is not allowed to cool and dissipate the heat generated by the coil, it can cause premature magnet failure. Any mechanical abuse may also contribute.
You can test the resistance with an ohmmeter and compare [it] with the nameplate data to determine the integrity and condition of the conductor. Also, take a Megger (insulation resistance) reading to test for grounding between the coil and case.
These two field tests will give you a pretty good indication of what is happening inside the magnet.
RT: What are some tips for extending a lifting magnet’s life?
MV: There are things that can be done to help extend magnet life. Two key components are operator training programs to help crane operators understand the consequences of mishandling or abusing a magnet, as well as developing and maintaining a consistent magnet inspection program.
Operators are the front line defense in preventing premature magnet failures, and if they truly understand the potential consequences of mishandling a magnet, as a scrap processor, they can be your best asset in extending service life. Consistent and systematic inspection programs for magnets are keys in identifying a magnet that is in the early stages of failure.
RT: When shopping for a lifting magnet remanufacturer, what are critical questions to ask of a potential repair provider?
MV: First of all, make sure the repair shop is fully qualified specifically to repair magnets, having the personnel, equipment as well as engineering support to properly diagnose and repair all types of magnets. Do they have OEM (original equipment manufacturer) specifications for different makes and models of lifting magnets?
Does the supplier have the proper equipment to salvage conductor material (copper or aluminum), which will certainly affect repair costs?
Does the supplier have the expertise to recognize when mechanical damage must be addressed so the magnet will withstand the tough environment in which it is placed?
Also, does the supplier have all the proper testing equipment that is calibrated on a consistent basis, and do they have the capability to measure lift capacity?
A rewind is not always necessary. A magnet that appears to have failed may be a candidate for a bake out to remove moisture from the magnet cavity or possibly damaged external and internal magnet leads. In these cases, a complete rewind may not be necessary.
RT: What costs go into remanufacturing a lifting magnet (materials and labor), and how can shoppers determine they are likely getting a fair deal?
MV: The majority of the cost of any magnet repair is materials. This could include copper or aluminum conductor, various types of insulation, etc.
Although “fair deal” is pretty subjective, always make sure you are dealing with a magnet repair supplier that has experience, has been in business a long time and has a good reputation in the industry.
As far as total repair cost, a typical rule of thumb has historically been that a repair should not be more than 75 percent the cost of new.
However, this is relative to the delivery time for the repair versus new, and if a magnet requires significant repair, it may be in the best interest of the customer to repair the magnet. If a major repair is done, and [a] conductor replaced, the customer is basically getting a “new” magnet back, with all the warranty coverage of a new magnet.