In his latest contribution to the popular thought leadership column ‘The Insider’ published in Lift & Hoist International (LHI) magazine. Mike Sparks, regional sales manager at Pintsch Bubenzer USA LLC, guides purchasing decision makers on brake selection.
Not with commercial intent, but to authenticate this guidance, it’s important to state at the outset that my employer is a manufacturer of high performance disc and drum brakes for steel cranes and other severe duty applications. We understand therefore, first, the importance of the technology and, second, the necessity of selecting the right brake for the application in hand. This is not, as some people believe, a one-size-fits-all marketplace.
Think about the whole application. The entire system must be considered before deciding upon a brake. If oversized, a brake can potentially shock the gearbox or, if undersized, the system could simply drive through the brake.
Even in a “Brakes 101” guide, we need to know:
1. The intention of the brake: holding, dynamic, or a combination of the two;
2. The safety factor required for the brake per specifications;
3. The safety factor used for the other powertrain components (motor and gearbox);
4. The environment in which the brake will be installed.
The intention of the brake
For holding applications one must ensure that there are safety elements in place that will prevent a scenario where the brake will be applied too early or released too late. This is typically handled via an encoder and programmable logic controller (PLC) combination where the brake only operates in a zero revolution scenario. When utilizing a PLC one should consult the brake manufacturer to determine if it can be powered through the PLC or if it must have its own power supply.
In my personal experience it is always better to have an independent power supply for the brake, but again the best practice is to consult the manufacturer. The torque required for the brake in this case can simply be calculated using the incoming horsepower (HP) or kilowatts (kW), a safety factor, and the speed of the system (revolutions per minute [RPM]). Additional items that we need to know are the desired mounting dimensions as well as the voltage that will be supplied to the brake.
For dynamic applications one must understand the requirements of the system, such as: What is the needed stopping distance? What is the required reaction time? Is this a safety brake or simply an application that will coast to a stop? When calculating the necessary torque for these applications, many items need to be understood, including the total max load, the max speed potential, the stopping distance, etc. Essentially, in dynamic applications, the brake needs to be designed in from the onset and not added as an afterthought; the entire system will need to be able to handle the forces created by the brake.
The safety factor required
Brakes are utilized on a wide variety of applications and therefore each industry will have its own set of requirements or standards that need to be followed. My company is highly active in the port and container handling industry where the cranes are an integral component. Therefore, a safety factor of 4 tends to be the standard requested by the consulting and engineering firms. There are no written standards that dictate this but it has become the expectation for these cranes.
The overhead crane industry itself has multiple standards that are utilized as well as classifications that determine how the crane will be utilized. Specifications such as the Crane Manufacturers Association of America (CMAA) 70 and 74, the Association of Iron and Steel Engineers (AISE) TR-11, the Association of Mechanical Engineers (ASME) B30.2, OSHA, and the European Materials Handling Federation (FEM) call for differing safety factors based on the application (hoist, trolley, or bridge) as well as crane usage and operator location.
Always consult the above documentation to ensure that you properly understand the braking system requirements.
The safety factor of other powertrain components
Another item to consider when reviewing the safety factor is what has been used on other elements of the powertrain system. If the gearbox has a factor of 2, then it would be wise to follow this same factor for the brake. For example if a brake with a factor of 4 is installed onto this system then it will shock the gearbox as the brake torque will be double that of the gearbox. This can result in unnecessary maintenance, the potential for a catastrophic failure, or at the least a shorter life for the gearbox. Using this same example, if the brake only has a factor of 1.4, then the system could possibly back drive through the brake. This will result in premature brake failure and the potential for a dropped load.
The environment in which the brake is to be installed
Due to the fact that the brakes rely on friction to perform as expected, one must consider where the brakes will be installed. All braking material has a coefficient of friction that will be affected by extreme temperatures as well as dust / dirt in the air. One must also consider if this brake will be installed into a humid environment or one where condensation could be generated internally within the brake. These types of environments can cause deterioration to the internal components and thus negatively impact the performance.
Again, discuss these conditions or potential conditions with your brake manufacturer to ensure that the proper product is selected.
One of the major issues we see is that our potential customers do not understand the above impacts when selecting their brake. Many customers will simply provide a motor torque and request that we supply a brake to this specification. However upon installation they learn that the gearbox was rated at a higher safety factor and therefore experience a shorter than expected brake life. It is always recommended that the customer consult the brake provider to ensure that it is properly sized. If proper care is taken for the selection of a brake it will provide a safe and reliable solution for holding or stopping a load.
As we’ve explored, brakes are much more than simply a component to be added to the application; they are an item that should be designed in and considered in the initial stages. However, there is often a need to retrofit a brake, and it’s worth concluding on those scenarios.
One may know that a retrofit is needed if they start to see slippage of the load and know that the brake is within manufacturer tolerances. This slippage could be due to initial under-sizing of the brake or a change in the way that the equipment is being used. For example there are many operators that purchase a 10-ton capacity crane, but then due to increases in plant or product capacity will use this crane for 12-ton, or greater, lifts. If the rest of the system can handle the weight then an operator could chose to increase the torque of the brake. In other cases, a system may have been initially designed to use the gearbox to hold the load via a backstop, but it is later determined that a brake should be added to the system for increased safety.
When considering a retrofit of a brake one must ensure that the replacement brake or additional brake will physically fit within the available space. Some brake types have a foot mount and a centerline that must be considered. Others simply need to ensure that they will mount onto the provided bolt circle. It is imperative that all information be provided to the brake supplier so that a proper form, fit, and function can be supplied.
Of course all of the additional items mentioned above will need to be taken into consideration as well. Whenever in doubt, go to the manufacturer.