Look at all the options and weigh-up the pros and cons before deciding on a brake, says Mike Sparks, regional sales manager at Pintsch Bubenzer USA LLC.
Based on recent conversations I’ve had in the marketplace it might serve as useful guidance to look at choosing the proper brake based on a particular application. As is so often the case in industry, a huge step towards safety is taken when the right tool or component is chosen for the job in hand. Of course, we move closer to danger when a compromise is made or we expect a product or technology to perform beyond its capability.
It is important that all components in a system have been sourced and installed with a clear understanding of the environments, operating conditions, user needs, and other variables. A couple of editions ago we addressed the aspect of taking the entire system under consideration when selecting components, so we will leave this sentence as the reminder to keep this top of mind.
There are many styles of brakes available to the marketplace and each of them present advantages and disadvantages. There is not a product that will 100% of the time hit all of the desired requirements and therefore one must weigh up the pros and cons with any product selection. I will focus on the top-level conversation of the braking types by application and not dive into the different methods of completing the braking process.
It’s important to understand at the outset that there are different types of brakes; drum brakes, disc brakes, and motor mounted brakes are the most commonly encountered. Each of them can be achieved by different means; for example a motor-mounted brake can be of a wet design or a dry design as well as it can be AC or DC supplied. All of these options have their own advantages and disadvantages, but that’s an article in itself for another day.
Of course there are applications where a drum brake will outperform a disc brake and vice versa. This may not be simply a matter of torque but instead a discussion surrounding the entire form, fit, and function of the system. If a customer simply informed Pintsch Bubenzer that they needed 50 foot pound-force of torque then we could supply them three different solutions to achieve this, but they will not all work for the application.
The first application that we will address is the need for a direct acting brake. My definition of this is a brake that directly acts on the critical rotating portion of the system. In this case, a motor-mounted brake may not be the best option as it must be mounted to the motor or to the gearbox and therefore is stopping those components, but it is not directly grabbing the rotational element of the hoist, conveyor, elevator, etc. For this application a better fit would be a disc brake or a drum brake as these items can act directly on the rotational element.
Many readers of this magazine will be familiar with a hoisting application on an overhead crane. The drum brake or disc brake can be installed after the gearbox in the drive train and directly act on the shaft of the hoisting drum. Additionally a disc brake can be installed to act directly on the flange of the hoisting drum. One of the first things to consider in this application is the required torque. As we are on the low speed side of the power train system, this will require a larger value than the motor torque. A disc brake can offer higher torque limits due to the design and ability to be installed with a large diameter brake disc. The drum brake will max out at 30 inches and therefore be limited in the top end torque.
The next parameter to consider is the space permitted for the braking system. The drum brake can be designed to fit within tight tolerances around the rotating shaft as the unit is centred on the shaft, whereas the disc brake solution is mounted with the braking disc on the shaft, but the brake itself perpendicular to the shaft. This can cause the disc brake solution to take up more space on the crane deck. There is also the consideration that sometimes the disc brake will require a larger diameter disc and one must consider if there is overhead and / or deck clearance for this disc.
Other considerations for the selection in this application can be what is the total weight of the braking system, what is the required space to properly and easily service each brake system, and what are the forces generated by the braking system on the entire power transmission system. It has been our experience when there is a required torque that falls within the torque parameters of both designs and there is space permitting both designs, that the disc brake solution will result in a lower total weight, require less labour and time to maintain, and generate less forces on the total power transmission system.
Another common application is mounting a brake on the high-speed side of a system. This can be accomplished with a motor-mounted brake (coupler or non-drive end design), a disc brake coupled between the motor and gearbox, or even a drum brake installed on the shaft between the motor and the gearbox. The motor-mounted brake will provide the most compact solution, as this will allow the user to directly mount the motor to the gearbox and then mount the brake on the non-drive end of the motor. This solution will also allow for easy maintenance, as the motor does not need to be pulled to access the brake.
There are instances however where a brake is desired after the motor has been supplied without a means to install a brake on the non-drive end. This can lead us to utilise a coupler-style brake, a disc brake, or a drum brake. A coupler-style brake will permit the user to simply pull the motor and install the brake between the gearbox and motor. The drum and disc brake designs will require a coupler to be installed between the motor and gearbox so that the braking disc or drum can be added to the system. The benefit over a coupler-style brake is that both the disc and drum solutions can be primarily serviced without having to pull the motor, but one must also take into account the added weight, the required space, and inertia that the drum or disc will add to the system.
From both of the examples above we can see that while a brake may provide the proper torque, have the proper voltage, and tick some of the other “boxes” for an application, we must always look at all of the advantages and disadvantages to properly select the brake. This can be true of other component items as well so it is important to understand the features of each product and the benefit or flaws that this feature creates.
One should always review current technology and not simply get stuck into the mindset of “this is the way that we have always done it”. Technology is always advancing and new innovations hit the marketplace each year. It is important to discuss what options are available with the component manufacturers. Referring to the example above about the overhead crane, the common thought for a hoisting application has always been to utilize a drum brake, but as we reviewed there are instances where a disc brake will better serve the crane and the end user of the product.
When selecting component solutions for your equipment please explore all options and remember how they will affect the entire system. This will result in the best and safest products making their way into the industry.