lifting force

When they talk aboutlift force, many immediately imagine a dry figure from the technical description of an electromagnet or grab. Like, 12 tons and that’s it. But in practice everything is different. This very power is a capricious thing, depending on a bunch of factors that catalogs are often silent about. The biggest myth is that it is permanent. In fact, if a magnet lifted a slab in a workshop during testing, this does not guarantee that it will just as confidently lift a rusty, uneven, scale-covered piece from the ground in an open dock in winter. It’s these nuances that define the line between work and downtime that I want to speculate about.

From theory to the workshop: where kilograms are lost

We once bought a magnet for cutting up scrap metal. According to the passport - 16 tons. Everything was calculated, it would seem, with a reserve. But problems began at the facility. We grab the massive beam and it holds it. We are trying to lift a package of sheets of different thicknesses, rusty, with gaps - we are no longer so confident, we can feel slipping. And it's not about the magnet, but about the contact.Lifting forceis realized only where the magnetic flux passes through a ferromagnetic material. Air gaps, scale, surface unevenness - all this “eats up” the effective force. It turns out that the actual load capacity strongly depends not on the device, but on the condition of the load.

There was an incident while unloading the rails. The magnet from the same manufacturer as in the first example - the LONJI corporation (their website, by the way, is https://www.ljmagnet.ru, it’s useful to look at the characteristics), showed its best side precisely because of the design of the poles. They have a special shape that promotes better flow around the load. But even this is not a panacea. If the rail is lying in mud and slush, first you need to at least “expose” it, pick it up with the edge, lift it, let the debris fall off, and only then take it for stacking. This is no longer a question of technology, but of working technology.

Hence the conclusion, which now seems obvious, but which was reached after a couple of unsuccessful attempts: when choosing equipment, you need to consider not the “passport” strength, but the “operational” one. The safety factor must be serious, especially for dissimilar scrap. And it is important to look not at one number, but at the curve of the dependence of force on the air gap, which conscientious manufacturers, like the mentioned LONJI (their enterprise, Shenyang Scientific Electromagnetic Company LONJI LLC, has been working in mining and reloading equipment since 1993), always provide in the documentation.

Temperature, nutrition and other 'invisible' enemies

Another point that is often overlooked is heating. A constantly working electromagnet gets hot, this is inevitable. And as the temperature risesliftfalls. In a workshop with ventilation this is not so critical, but in a closed vessel or under the summer sun it is a serious problem. I saw how the crew, trying to speed up the unloading, did not allow the magnet to 'rest', and by the end of the shift its efficiency dropped by a third. We had to introduce a regulation: 15 minutes of work, 5 minutes of pause to cool down. Productivity even increased as a result, because downtime due to cargo failures was reduced.

The quality of the power supply is a different matter. A 10% drop in network voltage is not a 10% loss of power, but much more. This is a common occurrence at remote sites with an old substation. Therefore, now we always require stabilizers or generators with a power reserve at the site. I remember how at one construction site a magnet from LONGI with a thermal compensation system and protection against voltage sags came to the rescue, while the neighboring 'branded' analogue constantly went into protection and dropped the load. It turned out that their circuit did not have such strict current control.

And, of course, wear and tear. Not mechanical, but 'magnetic'. Over time, from constant shock loads (and load throws are inevitable), the magnetic properties of the core may degrade slightly. Plus winding insulation. Therefore, routine diagnostics is not a whim, but a necessity. It is good practice to measure the actual tearing force of a reference slab every six months.

Special tasks: when standard solutions don't work

Sometimes the task is specific. For example, not just lifting, but holding and accurately positioning a large, but thin-walled structure. Here a standard powerful magnet can simply crush it. You have to resort to tricks: use not one magnet, but a system of several low-power ones, distributing the points of application of force. Or use electromagnets with adjustable clutch force. LONGI also has such solutions for precision industrial assembly in its assortment. This is no longer just a cargo trucklift, but a tool for installation.

Another story is working with small objects: shavings, metal chips. It would seem as simple as shelling pears. But the force of attraction there is needed not so much as a force “evenly distributed” over the area in order to capture the layer and not tear out a piece. Both the design of the pole pieces and the shape of the magnetic system decide everything here. Experience suggests that special chip collector magnets are better suited for such tasks, rather than those converted from truck ones.

We also had the unfortunate experience of trying to use a standard weight magnet to remove long pipes from a stack. The problem was a misalignment: the magnet caught one side, the pipe rotated and slipped. I had to design and order a traverse with two magnets spaced at a certain distance in order to create a stable torque. This is to the question that sometimes the key to success is not in increasing strength, but in its correct composition.

Manufacturer: why experience and range matter

When you work on a topic for a long time, you begin to appreciate not only the parameters, but also the “biography” of the manufacturer. A company that has been making mining and material handling equipment for 30 years like LONGI has probably encountered most of the problems described above. And its engineers have already incorporated solutions into, if not all, then many basic models. You can see it in the little things: reinforced shock-proof cases, waterproof connectors, and the presence in the line of not only standard magnets, but also grabs and separators.

Their production base in Fushun, with an area of ​​140 thousand square meters and a staff of engineers (and among 1,200 employees, more than 60% are educated professionals), allows not only replication, but also adaptation of equipment. This is important. Because buying a 'box' is half the battle. And getting advice, a quote for a specific task, and then service is what turns hardware into a working tool. The annual production of 4,000 units of equipment indicates a serious scale and, most likely, a well-functioning quality control system.

In the end, back to the beginning.Lifting forceis a complex concept. This includes the physical parameters of the device, its correct selection for the conditions, and proper operation. The number in the passport is only a starting point for calculations. The real work begins where temperature, cargo condition, nutrition and a hundred other little things are taken into account. And the experience, including that of others, accumulated by such manufacturers is the best assistant in this matter, so as not to step on the same rake.