Maintenance free couplings for heavy engineering

Extreme temperature ranges, high pollution levels, high vibration levels, and 24/7/365 operation call for engineered drive components which can take the abuse. Extending component maintenance intervals is a priority, since industrial gearboxes, electric motors, bearings, and drive shafts typically require at least partial disassembly and replacement of wear parts. A new solution involves zero maintenance, stainless steel bellows couplings for up to 100,000 Nm, engineered to run smoothly for decades.

One challenge in the development of the BX series was the design of the metal bellows itself. The bellows serves to alleviate misalignment loading between adjacent bearing sets while transmitting rotary power. Traditional sizing calculations were used at first, having proved successful for high speed servo drive systems, which tend to be some of the most demanding of the customary applications for bellows couplings. After a short time it became clear that a widely marketable high torque bellows coupling could not be designed without FEA, as the first installed models were two to three times larger than the final product design. As life testing later confirmed, the software revealed some errors in the initial interpretation of the sizing, demonstrating that the traditional methods did not scale properly. In collaboration with a major bellows hydroformer, R+W reviewed and updated these traditional bellows sizing methods to better reflect the realities of what the formed bellows can tolerate in this physical size range.

A special welded joint between the bellows, intermediate tubing, and mounting flanges was also selected, involving a combination of TIG (perfect root) and MAG (low heat generation). This welding method is a recent development of RWTH Aachen University IME, a world renowned leader in mechanical and electrical engineering research, and has demonstrated superior fatigue characteristics in vibration and life testing. With these two important features in place, hubs, flanges, and intermediate tubing, fabricated from high strength steel, were configured to round off the complete product line. R+W has been able to launch the all new “BX” series, with a variety of standard and custom mounting options available, and presently broken down into three specific series.

BX1 with Flange Mounting

The BX1 is the basic model from which the complete BX series is configured. Mounting flanges are welded directly to the bellows, which are then used for adaptation to shaft mounting systems in the cases of the BX4 and BX6. Power is therefore transmitted through the BX1 by means of a frictional flange connection. A common misconception is that the torque is transmitted through the bolts themselves. This can have two negative consequences in that the coupling would exhibit backlash, and that ultimately the bolts would fatigue and fracture. In case of reversing applications or those with frequent load variation this failure would occur within a very short amount of time. Basically torque ratings of flanges are calculated based on the pressure generated by the bolt circle arrangement, the diameter into which they have been arranged, and the coefficient of friction of the flange surfaces. A number of safety and application factors are normally added to ensure a pure high-pressure frictional connection results.

BX4 with Keyway Mounting

The BX4 is described as a low backlash coupling, which transmits torque purely though the form fit of a shaft key or spline. Some potential for backlash always exists due to the clearance required to fit the hub over the shaft. However reduced, this is even in the case of an interference fit, and especially in cases where only set screws are used for the axial retention of the hub. The main advantage of a keyway connection is the quick and easy installation and removal of the coupling hubs. In lieu of keyway connections, spline connections provide additional security and surface area contact with superior stress distribution characteristics. In consideration of some extra cost, this can be a good solution for a more compact design, as the necessary shaft engagement length can then be reduced. Generally speaking, the BX4 is well suited to unidirectional drive applications, which must accelerate, even to high speeds, and maintain those speeds for prolonged periods. Drive systems with shock loading, reversals, and high duty cycles are better served by the BX1 and BX6 designs.

BX6 with Conical Clamping Ring

The BX6 makes use of a high pressure, keyless, frictional clamping connection. The conical clamping ring system consists of two components: the clamping ring and the hub. The clamping ring is drawn over a slotted tapered section of the hub by means of a set of fastening bolts. Sliding the two tapered surfaces against one another creates a high level of surface pressure in the vertical direction, compressing onto the cylindrical shaft. The resulting contact force eliminates the need for keyways and is suitable for transmitting extremely high torque levels depending on the diameter of the shaft. Since the BX6 has many planes of symmetry across its length, it is also well suited to very high rotational speeds, as a result of the low residual imbalance.

Variable Length with Internal Support

The intermediate section of the BX series consists of high strength steel tubing with adapter flanges common to the full product line. The length of the intermediate tubing section can be specified according to customer requirements and interchanged for machinery modifications as needed. The adapter flanges are made with a gimbal system which extends through the inside of the bellows and engages a concave receptacle on the opposite side. This support system causes the entire mass of the intermediate section to be carried by the shafting rather than the flexible bellows. It also serves as a safety feature in the event of a machine crash. Should the bellows or its connection be caused to fail by extreme overload, the tubing would still not be allowed to escape from the hubs, eliminating the need for coupling guards in some cases. This safety feature does not exist in flex disc or universal drive shaft products.

Summary and Outlook

The all new “BX” series offers standard torque ratings of up to 100,000 Nm and bore diameters of up to 280 mm. This technology provides a viable alternative to steel disc couplings, with improved torsional stiffness, balance, and safety features. Flexible design configurations allow for the BX to be made to suit applications with specialized flanges, hubs, materials and surface treatments for even the harshest of environments. The internal support system provides for a high degree of security unavailable in other similar types of couplings. The symmetrical design of the series BX1 and BX6 allows for an optimal balance quality in highly dynamic drive systems and test stands, with ISO Grade 2.5 certification available upon request.

The principle of the formed metal bellows as an equalizing element offers many unique performance advantages for today’s advanced drive technology. Designs capable of transmitting up to 2,000,000 Nm are currently in development.

R+W America
www.rw-america.com

 

Compact stainless steel bellows couplings

The BKS series of stainless steel, welded bellows couplings are up to 1/3 shorter in length, reducing moment of inertia and saving space. Manufactured in Germany, the BKS makes use of 1.4301 (304) stainless steel hubs, precision machined to a high level of concentricity. Laser welded while mounted onto a common shaft to guarantee straightness, the couplings compensate for shaft misalignment and precisely transmit motion with zero backlash. Allowable temperatures range from -40 to +300° C. The BKS coupling is available in 6  sizes, with torque ratings from 15 to 500 Nm and English or metric bores from 12 to 75 mm.

R+W America
www.rw-america.com/bellows_couplings/index.html

 

Compact safety coupling

Making use of the existing BKC line of compact bellows couplings, the SL2 safety coupling is a compact, flexible and torsionally rigid option with integral torque overload release.  Designed for aggressive servo driven applications, it  is completely backlash free, relying on preloads and frictional connections, along with a hydroformed stainless steel bellows to relieve bearing loads resulting from misalignment.

In the event of a machine crash, power surge, or any other cause of unanticipated overload, the SL2 will disengage the motor or gearbox shaft from the load in less than 3 milliseconds.  Re-engagement takes place automatically with slow speed rotation of the shaft subsequent to the overload occurrence.  Available in four sizes, it handles a range of disengagement torque values from 5 to 400 Nm, and English or metric shaft diameters from 12 to 60 mm.

R+W America L.P.
www.rw-america.com

Misumi Now Offers Comprehensive Line Of Couplings

MISUMI Coupling types include high precision Single Disc and Double Disc Clamping models, many of which may be used with servomotors.  Also offered are Oldham, Slit and N Couplings, as well as Jaw, Sleeved, Bellows, and Resin types, in a variety of sizes and configurations.

The SCXW is a Double Disc type precision disc clamping coupling with high torque but no backlash.  Its torsional rigidity is up to 26% higher than conventional (standard) disc clamping couplings. It suits applications requiring fast positioning precision.  All the bolts are trivalent chromate plated and suitable for use in clean environments.

The MFJGWK is available as a high rigid Oldham coupling, set screw type. The MFJCGWK is a high rigid Oldham coupling, clamping type.  Both products feature an aluminum bronze spacer and have a keyed bore.  These couplings have allowable torque 2X higher compared to resin spacers.

The SCOC is a short Oldham coupling, clamping/spacer type. This space-saving version works with miniature devices because it is 17% shorter than conventional types.

Most MISUMI Couplings ship in six days, with the exception of the new High Rigid Oldham Couplings, which ship in eight days.  Some couplings offer optional express shipping for faster delivery.

MISUMI USA, Inc.
Http://us.misumi-ec.com

Products by Servometer

Servometer® / PMG, LLC designs and manufactures  electrodeposited nickel bellows, bellows assemblies, flexible shaft couplings, electrical contacts and  electroforms.

The company offers miniature nickel alloy metal bellows as small as .020 in. (.5 mm) in diameter. They are seamless and non-porous, resisting dust, dirt and moisture that cause contamination in critical applications. Servometer bellows are leak tight to 1 x 10-9 std. cc/sec., and can be designed for “infinite” life expectancy (100 x 106 cycles).
Also, the company’s line of bellows-type flexible shaft couplings have a torque range from 1.4 Ncm to 198 Ncm. Outside diameters range from .252 in. (6.4 mm) to 2.40 in. (61 mm) and overall lengths from .5 in. (12.7 mm) to 2.44 in. (62 mm). Larger sizes and greater torque capabilities are available on a custom basis.

Servometer self-aligning spring contacts  feature negligible insertion and inductance loss. They are well-suited for repetitive connect and disconnect. Outside diameters in stock range from .037 in. (1 mm) to .245 in. (6.22 mm). Custom contacts are offered with bellows diameters as small as .020 in. (.5 mm).

The company’s electroforms are suitable for  unusual shapes, close tolerances, high strength and ultra-thin walls. It can also withstand temperatures as low as -423° F. Diameters range from .020 in. (.5 mm) to 9 in. (229 mm). Surface micro-finishes as fine as 4 R.M.S. are also available.

Servometer
www.servometer.com

EZV Series Adjustable Line Shafts from R+W America

A convenient location for manual phase adjustment along a mechanical drive system is now available in the EZV series adjustable line shafts. Making use of a high strength intermediate collar between two telescoping sections of precision tubing, the EZV naturally places the location for phase adjustment in an easily accessible, open space. Due to the relatively large outside diameter of the drive tubing, the EZV also provides for a more secure clamping connection than would exist when clamping over standard diameter motor and gearbox shafts.

Length adjustability also results from this design, making the EZV reusable in different machine layouts, and easier to install, especially with certain alternate hub designs, like EK7 expanding mandrels and EK6 high strength conical clamp ends. For any size the EZV can also be made with ZAE torsionally rigid bellows couplings, or with integral ES2 mechanical torque limiters.

R+W America
www.rw-america.com

For the Best Load Control Look to Bellows Couplings

Properly selected bellows couplings result in the best control over the load in any servo application. Here are tips to ensure you choose the right size for the application.

Bellows couplings help maintain tight controls over loads.

For years, bellows couplings have been a mainstay for efficient motion systems because they offer high torsional stiffness, low moment of inertia, and minimal restoring forces under misalignment. They may help maintain tight control over loads, which is especially critical when considering that the flexible coupling often represents the point of least stiffness in an electromechanical system. In this way, couplings have a significant effect on the stability of the entire system, as well as the postional accuracy of the load. Bellows couplings benefits include misalignment compensation paired with precise transmission of velocity, angular positioning, and torque.

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