This blog doesn’t set out to dumb down or simplify electric overhead traveling (EOT) crane brakes; there are inherent complexities to the subject matter.
However, we do suggest that it shouldn’t take a great deal of industrial intellect to accept, first, that more robust braking systems should be installed on a greater volume of EOT cranes; and, second, that there is scope for maintenance and other professionals to better understand braking technology.
Brakes are essentially a device used for stopping motion using friction or power. They are designed to hold a load when the hoist motor is off. Essentially, there are three types of brakes that relate to EOT cranes:
They are an important component but the industry widely neglects to pay sufficient attention to ensuring the right braking technology is installed on EOT cranes. Further, many stop short of implementing a proper education, maintenance, and upgrade plan.
OSHA, of course, covers brakes, which it defines as devices used for retarding or stopping motion by friction or power means. Standard 1910.179 also says a drag brake provides retarding force without external control and describes a holding brake as one that automatically prevents motion when power is off.
However, it is not alone in North America in that it doesn’t outline requirements for emergency brakes that some leading crane and brake manufacturers say should become standard on certain EOT cranes. Pressure is also being applied to the Crane Manufacturers Association of America (CMAA) and the Association for Iron & Steel Technology’s (AIST) Crane Symposium, for example, to address an issue that we fear might only come fully to light in the wake of a major crane accident.
If (we hope not when) that accident happens, it is likely to be down to a combination of improper brake torque and redundancy of braking on the gearbox or drum. In Europe, more stringent requirements are outlined by Deutsches Institut Fur Normung E.V. (DIN). There are North American companies that request this criterion is met, but many are ignorant of the potential dangers of disregarding it.
Emergency brakes should be specified or suggested by the OEMs, not just at the request of a select few further down the supply chain.
The most commonly overlooked concept is the difference between holding and controlled or dynamic braking. A holding brake is like the one on your car; if it is released and the vehicle is on a gradient, it will roll towards the way of the downward slope. If it is released on a crane, the load will drop. Many are mistaken that the brake kicks in when the operator lets off a push button, but most cranes have what we call dynamic brakes that don’t switch on until the inverter has slowed a motor to near a stop.
When a crane only has a standard, high-speed brake on the back end of the motor and there is a malfunction, say, in the gearbox, that isn’t going to be enough to stop the load from falling. An emergency brake would do so. It’s important to stress that controlled braking doesn’t in all cases hold the load when the holding brake is released.
Some industries understand brakes more than others. High ambient temperatures and dust-filled air are typical environmental conditions associated with the processing of steel. This environment places tough demands on the drive systems and brakes used in steel-making facilities. Hot metal, semi-automated rolling mills, and overhead loading cranes require the safest, most reliable, maintenance-friendly systems available. Most steel cranes are fitted with emergency drum brakes, accordingly.
However, it’s a good idea for CMAA Class E (severe duty) cranes to have the same emergency braking, but they don’t always. This type of service requires a crane capable of handling loads approaching the rated capacity throughout its life with more than half of the lifts per hour at or near the rated capacity. Scrap yards, cement mills, lumber mills, and fertilizer plants are just a few examples of industries that place a high demand on their cranes but don’t always consider the emergency stopping required.
It’s important to understand torque: the measure of how much force is required to cause something to rotate. As it pertains to cranes, torque is the force applied to the brake wheel to stop motion. Torque is measured in lb.-ft.; 1 lb.-ft. is approx. 1.35-newton meters (Nm). Few acknowledge that the age, thus, the torque validation doesn’t remain the same as when it was first installed.
Does a maintenance manager know that his or her brake is still performing to 200 lb.-ft? or that one that is 20-years-old is still clamping to 20 Nm? Chances are the spring will be experiencing wear and not providing the same level of force. Think of a paper clip or clothes hanger that is repeatedly twisted; it fatigues and eventually breaks.
This is nothing that can’t be prevented by an appropriate maintenance program. Brakes don’t fail; people fail to maintain them. Thus, it is crucial that those responsible for their lifting and other technologies understand their equipment. Put simply, they need to know what they’re looking for and how to react accordingly.
Brake pads—whether they have organic or sintered linings—have a minimum wear point. The operating thruster or magnets are other key components to monitor. The air gap, meanwhile, should be checked at the start of every shift; is it too big or is the brake dragging on the drum or disc?
If you work with a Class E crane and don’t know these basics, speak to your brake provider—today!
Thank you for reading.
Tad Dunville
Membership Committee Chairman and Board of Directors, Crane Certification Association of America
Joel Cox
President
Pintsch Bubenzer USA
j.cox@pintschbubenzerusa.com
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