Reliability never tasted so good - metal bellows couplings in the food industry

A metal bellows made of highly elastic stainless steel is the heart of every metal bellows coupling. Metal bellows couplings are torsionally rigid and transmit torques from 15 to 10,000 Nm.

Before a delicate piece of chocolate can melt in your mouth, many production steps have to be executed with absolute precision. The production process in chocolate manufacturing generally begins with roasted cocoa beans as a basic ingredient and takes them on a long journey all the way to fully packaged bars. Each step in the process, whether grinding, rolling, conching, tempering or moulding, requires exceptional precision and stability. If even a single ingredient is temporarily lacking, the product can no longer be manufactured to the desired quality. For, as elsewhere in the food processing industry, temperature-sensitive ingredients have to be processed quickly to create a consistent end product. If this is prevented by a malfunction in production, producers run the risk of complaints or even damage to their image in the eyes of consumers – a serious risk in the hotly contested segment of confectionery and luxury foods. Furthermore, the loss of an entire batch cuts into a company’s bottom line and endangers relationships with distributors in the event of delays or even failure to deliver.

Process reliability for stable quality

“Safety couplings at critical points in production facilities help prevent interruptions and machine-damaging incidents, while also reliably ensuring process continuity,” explains Jörg Stang, head of sales at R+W Antriebselemente. The staff at R+W knows of several points along the chocolate manufacturing process chain at which a breakdown could be critical for the final product. When grinding and pressing cocoa beans, it is essential to ensure constant movement, and hence, consistent transfer of torque from the drive to the grinder. If the drive breaks down, this affects the grinding result, which in turn reduces the quality of subsequent processing. At the same time, there is a risk of damaging the gears if their torque limits are exceeded. The consequence at very least is a brief production stoppage – right there a major problem for just-in-time production. Heavily damaged gears may require costly, time-consuming repairs and may even force production to grind to a halt.

A consistent, undisrupted manufacturing process is essential in subsequent steps as well, and is key to producing creamy chocolate that melts in your mouth. This is also true of the rolling and conching stage – a readily apparent driver of quality. Tempered chocolate in particular is highly sensitive to any changes in the process. The tempering of the chocolate mass can be easily affected by a breakdown, because it is partly performed in a cooling tunnel where the chocolate is transported on a conveyor belt. This drive must be highly consistent and reliable – free of backlash and misalignment stress, so that an optimal cooling curve and surface structure can be achieved. That’s how chocolatiers achieve an ideal texture. The examples from chocolate production provided above clearly demonstrate the importance of absolute process reliability in food manufacturing. The same level of precision that is applied when selecting the ingredients and the recipe must be also applied when configuring the plant – and that includes installing the right couplings at key positions.

Case study: the food industry

The couplings used in all of these production steps can represent decisive safety factors. The primary task of a precision coupling in mechanical and plant engineering is, as a rule, to ensure rigid and backlash free transmission while compensating for lateral, angular or axial shaft misalignment. At the same time, a very high level of operational reliability is an obvious requirement. In the food processing industry, it is also necessary to fulfil hygiene requirements. That’s why R+W uses only the highest quality stainless steel for couplings in this sector. Metal bellows couplings are especially effective when used to compensate for misalignment and protect from overload here, thanks to their high torsional rigidity and precise torque transmission with exact positioning accuracy. This makes them ideal for the sensitive machinery used in the processing of foods.

The central component and compensating element is the stainless steel bellows. The bellows is designed based on practical requirements, for example, the amount of torque to transfer or the level of misalignment to compensate for. On the one hand, maximum stiffness is required in the direction of rotation, and on the other, minimal stiffness in all other directions is desired in order to reduce misalignment loading and prevent damage to downstream components. This compensation for radial, axial and angular misalignment plays an important role in ensuring a high level of operational reliability for the drive train as a whole. “Parameters such as acceleration torque, resonance frequency and torsion angle also play a decisive role in the design of metal bellows couplings. R+W factors them into the dimensioning along with general and basic requirements for inertia, ease of assembly and price efficiency,” adds Jörg Stang. Finely balanced versions of the ultra-precise drive elements are also available for highly dynamic applications.

Torque ranges from 0.05 to 10,000 Nm.
 
The smallest miniature metal bellows couplings in the MK series offered by R+W support torques from 0.05 Nm to 10 Nm with bore diameters ranging from 1 mm to 28 mm. They can be used, for example, for precise rotational transmission in connection with potentiometers or measurement and control systems. Thanks to the torsionally stiff metal bellows, these couplings can help yield extremely accurate measurement results while simultaneously compensating for misalignment. “The MK series is suited for numerous applications thanks to the multitude of different connection options, ranging from clamping hubs with slotted, split or conical designs to models with conical expanding mandrels for hollow shaft connections. Pluggable designs are available for even easier installation. They, too, are free of play and feature a fast and easy connection design,” explains Jörg Stang. At the same time, a special tapered segment made of fibreglass-reinforced plastic ensures that the couplings are backlash-free and maintenance-free, while also providing electrical and thermal insulation. Galling is avoided thanks to the use of two different materials in the plugs. These pluggable couplings are available in single-position or multi-position engagement designs.
 
Minimize damage from overload

Bellows breakage protection, where interlocking jaw sets engage in the event of bellows failure, also helps increase the reliability of many coupling models. This is often required in the case of rotary encoder connections, for example. “At R+W the compact dimensions of the couplings can be preserved despite additional components. This significantly increases the functional reliability of torque transmission should a bellows break as a result of, for example, torque overload,” explains Jörg Stang. Precise installation of couplings is crucial in order to take full advantage of the technical properties of the coupling and to enable shaft misalignment to be compensated for without transmission failures. That’s why R+W manufactures not only miniature bellows couplings, but also metal bellows couplings of the BK series, which can transfer torques of up to 10,000 Nm. To guarantee concentricity, they are assembled on on a highly precise mandrel, which holds the bores in alignment during the joining process. Like the MK series, the BK precision series is available in various sizes and different hub designs. In developing these types of couplings, special attention was paid to easy installation and minimal inertial load. The couplings of the BK series are free of backlash and are used in the machine tool, packaging and printing industries, among others.

Reliability is pivotal 

R+W, the coupling specialist from Klingenberg, offers technicians in mechanical and plant engineering a broad spectrum of standard products. Our standard products can be used anywhere from transport and rotary encoder applications to main drive axes and tool change rollers for shaping machines. The couplings can also be designed individually to the customer’s specifications. They are available in various iterations: balanced, static or dynamic, with flange mounting, keyway mounting or clamping hub mounting, or with welded joints if they need to withstand significantly higher torques or temperatures. Over and above the standard range of metal bellows couplings, R+W Antriebselemente offers tailor-made, customer-specific solutions for even the most unique requirements.