lifting

When they say 'lifting', many people immediately think of cranes, lifting capacity, tons... but in real work, especially with magnetic equipment, everything is more complicated. I often come across the fact that customers demand 'maximum lifting force' without taking into account how this force is distributed, how the magnet behaves dynamically, on an uneven surface, or with partial contact. The very term 'lifting' in our context is a whole system, and not just one number in a passport.

From a number in a catalog to a real workshop

Here, for example, is a classic story. Order a magnetic grip for steel plates. They look at the 'lifting force' parameter - 5 tons. Everything seems clear. But the slab is not ideal: there may be scale, rust, or slight sagging. And this nominalliftinga figure of 5 tons under ideal laboratory conditions turns into 3.5–4 in practice if the design of the poles and the depth of the magnetic field are not taken into account. In such cases, we always put in a reserve, but not all manufacturers do this.

At our facility we once used a serial magnet from one well-known brand - everything seemed to be according to the standard. And when working with hot-rolled sheets, “breakdowns” began. It turned out that at temperatures above 80°C the magnetic induction dropped more significantly than stated. I had to shield the heat and recalculate the entire circuit. That is, the “lifting capacity” turned out to depend not only on the mass, but also on the temperature regime, which was mentioned in fine print in the technical specifications.

That is why inLONGI CorporationWhen designing, we always proceed from the real scenario. Not just 'lift 10 tonnes', but 'lift 10 tonnes of corrugated sheet metal from an outdoor warehouse at -20°C, cycled 15 times per hour'. This changes everything: the choice of core material, the winding of the coil, and the control system. Their websitehttps://www.ljmagnet.ruis, in fact, a collection of such cases, albeit designed as a catalogue. It is clear that people are from the workshop, and not just from the design bureau.

Structural subtleties that you won’t see in advertising

Let's take, for example, a diagram of the arrangement of poles. It would seem that the more poles, the more uniform the adhesion force. But no - with frequent switching on/off in a multi-pole system, parasitic currents arise, heating, and over timeliftingcharacteristic 'floats'. We experimented with configurations for a long time until we came to a hybrid design with alternating zones of high and medium magnetic flux concentrations. This reduced the peak load on the power supply while maintaining clutch reliability.

Another point is the 'dead weight' of the grip itself. Often, in pursuit of power, copper is wound, steel is reinforced, and the apparatus becomes so heavy that the usefulliftingability (minus its own mass) drops by 15–20%. I saw this with some solutions for the mining industry, where the magnet weighed about 3 tons. BLONGI, judging by their equipment for the mining sector, this problem is solved through the use of special alloys for the yoke and optimization of the shape - not just a cube, but a ribbed structure that is rigid, but lighter.

And of course, management. A smooth rise is not only a matter of safety, but also of preserving the magnet. A sharp start with a large inertial mass creates a shock load on the fastenings and the core itself. In our settings, we always introduce a smooth acceleration and deceleration ramp, especially for electromagnetic crane grippers. Interestingly, their 140,000 m2 facility in Fushun is likely to be testing exactly these kinds of dynamic conditions - because the full-time 1,200 employees, of which more than 60% are engineers and technicians, clearly do more than just assembly.

When theory diverges from practice: several failures

We had a project to automatically sort steel scrap. We calculated everything using formulas and ordered a powerful electromagnetic separator. According to the passport, he must confidently hold pieces up to 200 kg. But in practice, small scrap with sharp edges did not “grab” well, some simply fell off in transport. It turned out that due to the small contact area and high residual magnetization of some steel grades, the adhesion force was uneven. We had to modify it - install an additional vibration 'additive' for a tight fit and change the switching algorithm. This is the case when the standardliftingthe calculation did not work because the material was heterogeneous.

Another example is an attempt to use a standard lifting magnet to remove thick-walled pipes. The diameter seemed to be correct and the weight was normal. But the pipe is not a solid cylinder, it is hollow, and the magnetic flux did not close optimally, creating 'dead zones' on the sides. The object was swinging and could fall off. The solution was found in the use of a specialized gripper with an adaptive shape of the pole pieces, which seemed to grasp the curvature. You usually learn such nuances only on the spot, and they rarely find their way into textbooks.

That is why the experience of such enterprises asShenyang Scientific Electromagnetic Company LONGJI, created back in 1993, is priceless. Their 4,000 units of equipment per year is not just a circulation, it is, roughly speaking, 4,000 potential bottlenecks that were worked out and taken into account in the following modifications. Their mining products have clearly gone through similar iterations.

Line integration: more than just lift and move

Modernliftinga complex is often a link in an automated line. And here it is not only power that is important, but also response speed, PLC compatibility, and energy efficiency in a continuous cycle. For example, when feeding blanks to the press shop, a delay in turning off the magnet of just 0.5 seconds leads to a failure of the entire cycle. We set up a system with position sensors and preliminary de-energization in the last phase of movement - so that the part would “fall” into place due to inertia, and not be held by a magnet.

Energy consumption is a separate headache. A constantly switched on magnet with a large lifting force heats up and consumes a lot of energy. In schemes fromLONGII often see the use of pulse modes and systems for storing residual magnetic energy for short-term 'support' - this is smart, especially for lines where the cycles are short. This reduces the load on the network and increases the life of the coil.

And of course, safety. Redundant retention systems in case of power failure, mechanical safety hooks, and overheat alarm are a must have. I once saw an accident when, due to a power surge, the magnet suddenly weakened and the plate moved out. Fortunately, there were no casualties, but since then I have always insisted on an independent emergency source for the electromagnets responsible forrisecritical cargo.

Bottom line: lifting is about the reliability of the system, and not about one characteristic

So, back to the beginning. The term 'lifting' in our business is more of a promise of reliable operation under specific conditions, rather than a magic number. This includes correct calculation, high-quality materials (like those used in production with an area of ​​140 thousand square meters), and taking into account dynamics, and even weather conditions. This is knowledge of what will happen to the equipment after 10 thousand cycles, and not just on the first day of launch.

Therefore, when I now look at a specification or discuss a project, I already automatically decompose this 'lifting force' into components: static, dynamic, with a reserve, taking into account wear, adjusted for the environment. And I advise you to do the same. It’s better to overpay a little for a correctly calculated and tested system, like those that have been doing this for years.LONGI Corporationthan to urgently modify it in the field, risking both money and safety.

After all, a real 'lifting' machine is one that you forget about while you're working, because it just gets the job done day after day. And this is achieved not in design software, but on test benches and in real workshops, like those in Fushun. An experience that you cannot write down in your passport, but which is felt in every detail.