Since I have been selling and consulting with customers on overhead bridge cranes, I have received several quote request for hoist with load brakes. Mostly these are government or military specifications, but also a few private companies request the same. There are only three reasons why this would be listed in someone’s specifications today. One, it is the same spec they have used for decades so the easiest decision for those that know little about cranes to just continue with this decades old specification. Two, someone actually believes that is a requirement set by CMAA or other governing body. Or three, they honestly believe they are getting a safer more reliable crane with a load brake Well… all three are wrong and I will explain why.
Mechanical Load Brake Operation and Inspection. Here you will get a basic introduction to the load brake and learn about a few misconceptions about it.
Most hoist today do not have mechanical load braking technology in them. This is because it is outdated and does not fit the technology of our electric motors today. A load brake does not make your crane safer. Many manufacturers who used to have load brakes in their equipment stopped decades ago. Yet, here we are still with new specifications requesting load brakes. The load brake was designed to control the load in it’s decent. In an emergency it should hold the load as well. This form of technology worked great back when all the hoist motors were wound rotor. A wound rotor motor cannot stop acceleration of the load from gravity. Therefore, load brakes were required for hoist and you certainly wouldn’t want to use a hoist without it. Today’s technology uses Squirrel Cage Motors. See video below for a two minute introduction. Squirrel cage motors are fully capable of regenerative braking. This technology meets all CMAA Spec 70 requirements.
Let’s also not forget that when you have high capacity cranes, or in process cranes you do not want a load brake. They create a lot of heat when stopping a load so it is very impractical for a process crane. This would also apply to any crane that would require a permanent below the hook device. If a below the hook device is connected to the load block permanently, the load brake is going to seize up causing costly downtime and repairs.
Today’s motor themselves are the secondary control braking function that is required by OSHA. Because people don’t really understand this process they disregard it altogether. The squirrel-cage motor functions using regenerative braking if the load tries to pull faster than the motors rated speed. Regenerative braking does not generate a lot of heat so it is a safer application for large capacity cranes and process cranes.
Hopefully in the near future we will start to see the industry change to where there will be no more request for outdated technology. It all starts with the best overhead crane companies training their customer's about the latest safety features available for their crane. You will get the safest cranes on the market using today's technology.