Clutches and brakes are at the heart of many packaging systems. They enable fine control of movements and exact positioning of products and materials. Their performance directly affects packaging line productivity, package quality and operating costs.
A careful evaluation before choosing an electric clutch and/or brake for your packaging system can ensure reliable, trouble-free production over a substantial working life. A hasty choice can result in poor performance that diminishes productivity and leads to costly maintenance downtime and even excessive product rejects.
Investing time and effort in evaluating what's available and what meets your needs will reward you for years to come.
A number of manufacturers make clutches and brakes for use in packaging machinery. While many products have similar operating characteristics, there are subtle differences among them that can provide a system designer with not just a good choice, but also a best choice. A good choice will meet the cycle rate and accuracy goals of the system designer in an economical and simple-to-install package. The best choice will not only meet those goals, but it will also deliver longer operating life, minimize maintenance downtime, facilitate quick and easy removal and replacement and be capable of a rebuild if the customer requires one.
A variety of factors needs to be considered to get the best performance out of a clutch/brake application—performance that will make the difference between adequate and superior productivity, which is important to the customer's bottom line.
Many customers get the technical issues correct. They know their torque and cycle rate information and they can select an adequate unit on the basis of catalog data. But other factors are often overlooked—factors that can make a clutch/brake a best choice rather than just a good one. You don't have to make these choices alone. Most manufacturers produce a dozen or more versions of their clutch/brake designs. It's a good idea for equipment users to consult directly with a supplier's engineering group before purchasing such components in order to gain access to experience that will help make the most practical choice.
The following are some of the most critical factors to consider when evaluating these choices:
Commonality—Choosing a unit that will interact with other drive-train components in your system will enhance the life and performance of the total system. If you operate multiple systems, choosing a unit that offers commonality across all systems will result in even greater benefits and can substantially reduce the number of spares that need to be kept on hand for critical applications. While a choice driven by commonality may not provide the unique performance for each specific application that customized choices would give, it does offer the system-wide benefits of simplicity, inventory reduction and familiarity for the maintenance staff.
Complexity—Given the increased complexity of today's packaging systems, providing the maintenance department with common clutches and/or brakes will help ensure that they install replacements properly. Having to learn a new unit for each machine can lead to installation errors that may not be immediately evident, but that can cause performance problems for hours or days.
For instance, until recently, the most common motor in North American packaging systems was the 56C frame, 1/2-hp DC motor; now it's probably the 56C frame AC motor. It should come as no surprise that the most common clutch/brake sold in North America is one designed to mount with a 56C frame, 1/2-hp motor. When a packager considers a new piece of equipment, the experienced system designer will consult with the customer's plant engineer or maintenance purchasing agent to determine what clutch and/or brake units the customer uses elsewhere in the facility. If the unit offering the greatest commonality is not the least expensive, the customer will have to weigh the higher capital cost against the benefits derived from reducing maintenance inventories.
Automatic air-gap adjustment—Many applications in packaging systems involve indexing or placement of a product. Accuracy can be a key factor in these applications. Typically, units will have an air gap between friction faces of 1/32 to 1/16 in. If the air gap is more than that, it's possible that the unit may not even magnetically engage. Once the air gap is properly set, the unit will operate as designed. Units that include an auto gap will adjust this air gap for wear throughout the life of the unit, meaning that once the proper air gap is set, it will need no further adjustment for the life of the unit. When accuracy is a primary goal, a wise choice will be a unit that includes an auto gap function.
Some manufacturers use designs that require manual air-gap adjustment as wear occurs. In these cases, engagement time increases with normal wear, and regular maintenance is needed to keep a workable gap, adding to both operator responsibility and unproductive maintenance downtime.
Burnishing—This is simply a wearing-in process. In a new clutch or brake, the two friction surfaces may be a few thousandths of an inch out of flatness. Cycling the unit will wear these high spots down and result in full torque. Until this process is done, a new set of friction faces may yield as little as 1/3 of rated torque, which can affect both productivity and performance accuracy. As cycling occurs, the torque will improve as an increasing amount of the friction surfaces come into contact.
Clutch/brake units can be shrouded to protect them from contamination, or to prevent them from contaminating the packaging environment. In facilities where foods, medical products or even electronics are processed and packaged, the dust generated from friction material in brakes and clutches creates a hazard. For these environments, choose units that are completely enclosed. Also, choose units designed to withstand the washdown process used in most food processing plants.
Conversely, a clutch/brake can be negatively impacted by external contamination from such sources as lubricated chains and sprockets, leaking gearboxes or exposure to seemingly benign products such as bagel dough, which has a high oil content. Allowing lubricant to reach the friction surfaces of a clutch/brake can only lead to poor performance. An enclosed unit is usually the only reasonable choice for such situations.
Maintenance and repair—These functions should be as easy as possible. All manufacturers of clutches and brakes would like to be able to say that their products last forever. We would also all like to be able to see the future and predict breakdowns. Neither is likely. Therefore, we have maintenance. One customer may prefer a unit that can be removed quickly and replaced easily, minimizing production-line downtime. Another may sacrifice some time, but save inventory by choosing a unit that is easily disassembled and rebuilt without special equipment or skills. Evaluate the units you choose with your preference in mind.
A unit can be designed so that both friction faces can be replaced without removing the unit from the machine. Many pneumatic designs share this feature. When a unit is mounted on a long, difficult-to-remove shaft, this can be a very positive feature since it will avoid bearing removal, the realignment of shafts or the time-consuming effort involved in removing it.
Troubleshooting help is appreciated—Even the best choice clutch and/or brake, after it has been installed, will need occasional troubleshooting, when it is not performing effectively. That can be a challenge. When it is, the ability to obtain helpful advice from the manufacturer will help minimize the time and cost and the frustration of not knowing the best place to begin.
Clutch/brakes are a symptom as often as they are a cause. If a fuse blows, the clutch won't work. If a wire goes open, the clutch won't work. If the photoelectric sensor fails to detect its target, the brake won't engage. There are many external events that will cause a clutch or brake to fail. Therefore, when approaching a unit that's not performing, you might want to start at one end of the installation, at the power source, and work inward toward the clutch/brake.
The bottom line? Often, it's defined as raw financial costs, but the phrase can also mean final value. The process of choosing the best clutch and/or brake for your packaging system makes the distinction very clear: cost is finite and specific; value is tied to how well a unit performs, how easy it is to maintain and how well it will support your goal of keeping your line operating as close as possible to 100-percent productivity. Evaluating your choice with this distinction in mind may cost you a few dollars, but can eliminate a lot of headaches.