Shoulder Couplings Ideal For Abrasive Surfaces

Victaulic now offers a new line of products for joining standard shouldered steel pipe. The product line features the Style SC77, a flexible coupling featuring Victaulic patented installation-ready technology, and a variety of prefabricated shouldered fittings designed to make pipe joining even more efficient. The product line is ideal for abrasive services, particularly in the mining industry, where maintaining full pipe-wall thickness is important.

www.victaulic.com

Six factors to remember about couplings in a motion system

Physical values such as torque, torsional rigidity, spring stiffness, moment of inertia, imbalance, and zero-backlash play a major role in coupling design. Here are a few facts to keep in mind when you design your motion system.

Torque (Nm): is the product of an acting force and the effective length of the acting force’s lever arm.

T = Fxr

T = Torque (Nm)

F = Force (N)

r = Lever arm (m)

With a force of 100 N and a 1 m long lever arm, you can generate a torque of 100 Nm. Or, you can generate a torque of 100 Nm with a force of 1000 N and a 0.1 m long lever arm. For couplings, a specific amount of torque can be achieved with a large outer diameter of the coupling and a correspondingly low acting force or with a small outer diameter and a correspondingly high acting force.

Torsional rigidity (Nm/rad): refers to the rigidity of a coupling when it is subjected to a torsional load. If the torque exceeds the maximum torsional value of the coupling, the coupling will no longer be strong enough to transmit the acting rotational force. Ex: If a coupling with a torsional rigidity of 10 000 Nm/rad is subjected to 10 Nm, the connection element will twist by 1/1000 rad. That is equal to an angle of twist of about 0.057 degrees (1 rad = 57°17’44.8”). For a torsionally rigid or vibration damping coupling, this angle of twist may still be within the admissible range.  In practice, torsionally rigid couplings normally have a maximum angle of twist of less than 0.05 degrees and vibration damping couplings have a maximum angle of twist of less than 5 degrees.

Spring Stiffness (N/mm): is the counterforce exerted by the coupling in case of differentiated position of the axes in an axial, radial, and lateral direction. Ex: If the axial spring stiffness of a coupling is 30 N/mm, the coupling will exert a force of 30 N in the case of an axial displacement of 1 mm. These forces are important in a design with couplings, particularly when selecting bearings or other drive system components.

Moment of inertia: is the moment resistance when the rotational speed is changed. Normally, the lower the total weight and the smaller the outer diameter of the coupling body, the lower the moment of inertia. The reverse is also true, the higher the weight and larger the outer diameter, the higher the moment of inertia. This feature is important in highly dynamic applications because the drive has to generate sufficient torque to overcome a body’s moment of inertia to accelerate and decelerate.

Imbalance: in a drive system, imbalance should be as low as possible for smooth operation. Caused by asymmetries in the drive system where mass is distributed unevenly, it affects centrifugal forces on the entire drive system. It can be rectified by “balancing bores,” which are normally drilled directly into the location of the disproportionally high concentration of mass.

Zero backlash: is a lack of empty space or “play” when the rotational speed, direction of rotation, or torque changes. It does not mean that there is no angle of twist. Backlash is an important factor in predicting bearing life.

Information courtesy of R+W America

Rw-america.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

Rebar Coupling Saves Time & Money

The LENTON^® LOCK S-Series, part of the LENTON LOCK Mechanical Rebar Splicing System from ERICO^®, provides many of the same great benefits as the B-Series, except in a smaller package. This unique bolted splice is smaller than the competition and has fewer bolts, which helps reduce installation time and save money on the jobsite. All LENTON LOCK couplers feature patented gripping technology that provides overall structural integrity in tension, compression and stress-reversal applications.

With a performance that exceeds 125% of specified yield on ASTM^® A615 Grade 60 rebar, this innovative mechanical rebar splice is designed for use in column splicing, bridge applications, piling, splicing to protruding dowels cast in concrete, closure pours, beams, chimney construction and other demanding splicing applications.

The couplers allow for easy field installation since no bar-end preparation, sawing or swaging is necessary, and they can be installed with just a standard wrench or an impact wrench, depending on coupler size. The bolt heads will shear off when proper installation tightness has been reached, which allows for complete visual inspection.

The S-Series is ideal for use in repair, bent bar, retrofit, precast closure pour and new construction applications. The couplers meet or exceed major international building codes and Department of Transportation requirements, including ACI^® 318 Type 1, UBC^® Type 1 and IBC^® Type 1.

There is no need to stock multiple parts to accommodate one-step transitions. LENTON LOCK works as a one-step transition on ASTM (in-lb) rebar. For Canadian rebar sizes, contact ERICO for transition compatibility.

www.erico.com

Tips to simplify coupling selection

For a coupling in a servo application to work properly, you need to satisfy a number of application factors including: torque, shaft misalignment, stiffness, speed, and space requirements.

Here’s a look at the available types of servo couplings and what you need to consider for each of them during the selection process.

Beam couplings
Beam type couplings are manufactured from a single piece of material, usually aluminum, and use a system of spiral cuts to accommodate misalignment and transmit torque.  For many applications, beam couplings are a good economical and maintenance free choice.

The single piece design transmits torque with zero backlash. Two basic variations exist: a single beam style and a multiple beam style.

The single beam style has one long continuous cut that usually consists of multiple complete rotations. It is very flexible and accommodates light bearing loads.

For many applications, flexible beam couplings are a good economical and maintenance free choice.

It is able to manage all types of misalignment, but works best with angular misalignment or axial motion. It is not well suited to parallel misalignment because the single beam must bend in two different directions simultaneously, creating larger stresses in the coupling that could cause premature failure.

Under misalignment conditions, the long single beam allows the coupling to bend easily. But the relatively large amount of windup under torsional loads adversely affects the coupling’s accuracy.

Single beam couplings are an economical option best used in lower torque application and in connections to encoders and other light instruments.

Multiple beam couplings, which usually consist of two or three overlapping beams, attack the problem of low torsional rigidity. The use of multiple beams lets the beams be shorter without sacrificing much of the misalignment capabilities.

The shorter beams make the coupling torsionally stiff. Overlapping them so the beams work in parallel increases the allowable maximum torque making them suitable for use in light duty applications with connections, such as from a servo to a leadscrew. A drawback is that bearing loads are increased by a sizeable amount over the single beam variety but, in most cases, remain low enough to protect bearings effectively.

Some manufacturers take the multiple beam concept to another level. Instead of using a single set of multiple cuts, they use two sets. The use of multiple sets of cuts gives the coupling additional flexibility to accept more misalignment, including parallel misalignment. With parallel misalignment, one set of beams bends in one direction and the second set bends in the other direction.

Most commonly, these couplings are made of aluminum, but they also come in stainless steel. Stainless protects against corrosion, and increases coupling torque capacity and stiffness to sometimes double that of aluminum versions. The increase in torque and stiffness, though, is offset by a dramatic increase in mass and inertia. Keep in mind that in applications using smaller motors, a large percentage of the motor’s torque is used to overcome the inertia of the coupling.

Oldham couplings
The Oldham coupling is a three piece coupling comprised of two hubs and a center member. The center disk, which is usually made of a plastic or, less commonly, a metallic material, transmits the torque. On the center disk, mating slots are located on opposite sides and oriented 90 degrees apart. Drive tenons are located on the hubs. The slots of the disk fit on the hub tenons with a slight press fit that allows the coupling to operate with zero backlash. Over time, the sliding of the disk over the tenons will create wear to the point where the coupling will experience backlash. The disks are inexpensive items easilyreplaced, so a new insert will restore the coupling’s original capability.

The choice of materials for Oldham couplings depends on requirements for backlash, stiffness, vibration, and noise.

In operation, the center element slides on the hub tenon to accommodate misalignment.

The only resistance to misalignment is the frictional force between the hub and disk, Oldham couplings have bearing loads that do not increase as misalignment increases. Unlike other types of couplings, there are no bending members that cause bearing loads to increase as the shafts get out of alignment.

These couplings only allow a small amount of angular misalignment (less than one-half a degree) and axial motion (less than 0.005 in.), and are limited to speeds of 4000 rpm. Larger amounts of angular misalignment cause the coupling to lose its constant velocity characteristic, and axial motion is limited by the three-piece design of the coupling, which does not allow for use in push-pull types of applications. Because the center disk is a floating member, both shafts must be supported to keep the coupling from falling apart.

Bellows couplings easily bend under loads that result from angular, parallel, and axial motion.

Oldham couplings can handle relatively large amounts of parallel misalignment, from 0.025 in. to 0.100 in. or more depending on coupling size. Coupling manufacturers generally provide smaller misalignment ratings to obtain longer life ratings. These ratings can be surpassed at the expense of coupling life.

These couplings are available in a range of disk materials. The choice depends on requirements for zero backlash, high torsional stiffness and torque, or vibration absorption and low noise. Nonmetallic inserts are electrically isolating and can act as a mechanical fuse. When the plastic insert fails, it breaks cleanly and does not allow transmission of power, preventing other damage from occurring to machinery components.

Zero backlash jaw couplings
Jaw couplings are either conventional straight jaw or curved jaw zero backlash versions. Conventional straight jaw couplings are not typically well suited to servo applications that require the accurate transmission of torque. Zero backlash jaw couplings, on the other hand, are well suited to servo applications. The curved jaws help to reduce deformation of the spider and limit the effects of centrifugal forces during high-speed operation.

Jaw couplings handle high-speed applications well, but are less able to handle large amounts of misalignment.

Zero backlash jaw couplings consist of two metallic hubs and an elastomer insert commonly referred to as a “spider.” The spider is a multiple lobed insert that fits between the drive jaws on the coupling hubs with a jaw from each hub fitted alternately between the lobes of the spider. As in the oldham coupling, there is a press fit between the jaws and the spider for the coupling to deliver zero backlash.

In contrast to the oldham coupling, where the torque disk is in shear under torsional loads, the jaw coupling’s spider operates in compression. Be careful not to exceed the manufacturer’s rating for maximum torque, which can be significantly below the physical limitations of the spider. The spider can be compressed so that there is no longer a preload and backlash will occur.

Jaw couplings are well balanced and able to handle high-speed applications, 40,000 rpm or more. They do not handle very large amounts of misalignment, especially axial motion. Large amounts of parallel and angular misalignment cause loads on bearing to be higher than those of most other types of servo couplings.

If a spider fails, the coupling will not disengage. The jaws from the two hubs will mate similar to teeth on two gears and continue to transmit torque with metal-to-metal contact. Depending on the application, such action may be desirable or it could cause problems in the overall coupling system.

An advantage of the jaw coupling is the ability to mix and match spiders based on the application. Manufacturers of zero backlash jaw couplings offer multiple materials with different hardnesses and temperature capabilities that let you choose exactly the insert that meets the application’s performance criteria.

Disk couplings
At minimum, disk couplings have two hubs and a thin metallic or composite disk that transmits the torque. The disk is fastened to the hubs usually with a tight fitting pin that eliminates any play or backlash between the parts.

Torsionally stiff, disc couplings can accept up to 5 degrees of misalignment with some of the lowest bearing loads available.

Some manufacturers offer disk couplings with two disks separated by a rigid center member attached to a hub at each end. The rigid center member is usually metallic, but plastic versions are available and can be used to electrically isolate the coupling. This configuration will reduce torque capacity and torsional stiffness.

The difference between the two variations is similar to the difference between the single beam style coupling and the multiple beam coupling with two sets of cuts. The single disk coupling is not adept at accommodating parallel misalignment due to the complex bending of the disk. The two-disk style allows each disk to bend in opposite directions to harness the parallel offset. The properties of this type of coupling are similar to those of bellows couplings. They transmit torque in a similar manner. The disks are very thin, allowing them to bend easily under misalignment loading, which allows the coupling to accept misalignment up to 5 degrees with some of the lowest bearing loads available in a servo coupling.

Torsionally, the disks are very stiff. The disk coupling has stiffness ratings slightly lower than that of bellows couplings. A downside to these couplings is that they are delicate and prone to damage if misused or installed improperly. For proper operation, take care to insure that the misalignment is within the coupling ratings.

Bellows couplings
The Bellows coupling is an assembly of two hubs and a thin walled metallic bellows. In most cases, welding or an adhesive marry the hubs to the bellows.

Although other materials can be and are used, the two most common materials for the bellows are stainless steel and nickel. Nickel bellows are made using an electrodeposition method. It involves machining a solid mandrel in the shape of the finished bellows. The nickel is electrodeposited onto the mandrel, which is then chemically dissolved leaving behind the finished bellows. Manufacturers can precisely control the wall thickness of the bellows, creating thinner walls than is possible with other methods of bellows forming.

Rigid couplings can suit servo applications, especially if misalignment is tightly controlled.

The thinner walls give the coupling greater sensitively and responsiveness, which makes them suitable for precise small instrumentation applications. However, thinner walls also reduce the torque capacity of the bellows putting a limit on useful applications.

Stainless steel bellows are stronger than nickel versions and usually manufactured through hydroforming. A thin walled tube is placed into a machine and hydraulic pressure is used to form the convolutions of the bellows around specialized tooling.

The uniform thin walls of bellows allow it to bend easily under loads caused by the three basic types of misalignment between shafts: angular, parallel, and axial motion. Generally, bellows allow for up to 1 to 2 degrees of angular misalignment and 0.010 in. to 0.020 in. of parallel misalignment and axial motion.

The thin, uniform walls result in low bearing loads that remain constant at all points of rotation, without the damaging cyclical high and low loading points found in some other types of couplings. All of this is accomplished while remaining rigid under torsional loads.

Torsional rigidity is a key factor in the accuracy of the coupling. The stiffer the coupling, the more accurately it translates motion from the motor to the driven component. In the area of servo couplings, bellows type couplings are some of the stiffest available, making them ideal in applications that require a high degree of accuracy and repeatability. Some manufacturers offer bellows couplings with stainless steel hubs, which can be useful in applications requiring corrosion resistance, but their mass can be a factor in their operation. A coupling with aluminum hubs has very low inertia, a feature important for highly responsive systems. Some manufacturers balance their couplings to suit high-speed applications of more than 10,000 rpm.

Rigid couplings
These couplings were not often considered for servo application. Recently, however, smaller sized rigid couplings, especially in aluminum, operate in motion control applications because they offer high torque capacity, stiffness, and zero backlash. Torsionally rigid with virtually zero windup under torque loads, they are also rigid under loads caused by misalignment.

If misalignment is present in the system, however, the shafts, bearings or coupling will fail prematurely. Thus, the couplings cannot be run at extremely high speeds because they cannot compensate for thermal changes in the shafts from heat buildup in high-speed use.  However, in servo applications where misalignment can be tightly controlled rigid couplings perform admirably.

Ruland Manufacturing Company, Inc.
www.ruland.com

Miniature Beam Couplings for Micro Component Applications

Marlborough, MA – For micro component applications, Ruland now offers miniature beam couplings. Available with outer diameters of 9.5 and 12.7 mm and bore diameters of 3 mm, the couplings are made from a single piece of aluminum or stainless steel with overlapping spiral cuts.

Ruland’s P-series beam couplings are made from aluminum and cover a peak torque range of 0.62 to 0.9 Nm. Available in set screw style or clamp-style versions, these couplings have zero-backlash and can accomodate angular misalignment of up to 3° and radial misalignment of up to 0.2 mm. For increased torque capacity and corrosion resistance, the beam couplings are also available in stainless steel.

Beam couplings are part of Ruland’s complete product line which also includes shaft collars and rigid couplings with precision honed bores, and five types of zero-backlash motion control couplings including bellows couplings, oldham couplings, jaw couplings and miniature disc couplings.

Ruland Manufacturing Company
www.ruland.com

Improved Clamp Design for Flexible Beam Couplings

Marlborough, MA - Ruland Manufacturing Company has introduced a new clamp design for its zero-backlash flexible beam couplings. The couplings now clamp with a single screw on each end, which eases installation, and are balanced for increased rpm capability.

The beam couplings now feature both a radial and cross-cut to enhance surface contact with the shaft. This increases holding power and while eliminating the need for the additional screw used in the original design. Balancing is achieved by the removal of material opposite the screw. Better balancing allows for increased speed with less vibration. This can both extend the life of the coupling and decrease settling time in stop and start applications such as machine vision systems.

Ruland offers two series of zero backlash flexible beam couplings with distinct performance features suitable for different types of applications. The couplings are machined from a single piece of aluminum and feature multiple spiral cuts. The multiple cut design provides higher torsional stiffness and torque capabilities, and greatly reduced wind-up when compared to a commodity type single beam coupling. The multiple spiral cuts also allow the couplings to accommodate angular misalignment, parallel misalignment, and axial motion.

Offered in aluminum for low inertia or stainless steel for higher torque and added corrosion-resistance, beam couplings are available as standard parts in twenty different body sizes with outside diameters ranging from 3/8″ (10mm) to 1 1/2″ (38mm) and bores from 3/32” (2mm) to ¾ “ (19mm). Ruland beam couplings conform to industry standard lengths, fitting in confined spaces and allowing for easy retrofits in existing equipment. Special designs, cut patterns suitable for specific applications, keyways, and threaded bores are also offered.

Beam couplings are part of Ruland’s complete product line which also includes shaft collars and rigid couplings with precision honed bores, and five types of zero-backlash motion control couplings including bellows couplings, oldham couplings, jaw couplings and miniature disc couplings.

www.ruland.com

HELI-CAL® Flexure coupling

The demands put upon today’s design engineers seem to increase yearly. It is little wonder engineers are reaching for the Rolaids with one hand and the assistance of industry specialists with the other. Clearly the pressure is on engineers to produce designs that create competitive edge.

Designs that provide a competitive edge combine simplicity of manufacture and assembly with durability and quailty in a compact design at a reasonable cost. Every component in an assembly should be evaluated and reevalulated routinely to determine if it could do more and do it better. Another name for its process is “value engineering.”

Each of the integrated, multi-featured products that Helical makes is a story unto itself. The diversity of the features displayed in these parts offers a glimpse into the productivity potential that can be had by using multi featured parts. The integrated, multi-featured part saves assembly time, conserves system space, and by virtue of its single piece name, assures backlash free performance. In almost every case, this means extended life and sizable cost savings to the customer. The only characteristic these parts have in common is the HELI-CAL® Flexure (flexible beam). All other features incorporated in each part were created specifically to customer requirements.

Visit www.Heli-Cal.com

Special Couplings for High Voltage Application

To meet the specific motion control needs of high voltage systems Huco Dynatork is exporting its expertise to Japan.  Its customer specialises in the design and manufacture of high voltage capacitors, one application for which is in an electronic assembly for plasma screens.  A miniature misalignment coupling is also part of this assembly but because standard materials of manufacture are unsuitable for this high voltage application the capacitor manufacturer turned to Huco Dynatork in the UK for a solution.

As one of Europe’s largest specialists in motion control technology Huco Dynatork is often asked to provide solutions to specific problems.  The answer for this particular application was to machine the required couplings in a non-standard, high dielectric constant material to prevent voltage leakage across the drive.

Victrex PEEK™ proved ideal for the job. The polymer is characterised by excellent mechanical properties maintained to high temperatures. As well as excellent electrical, chemical and temperature resistance it is hard wearing and provides dimensional stability. Trials of the special couplings proved successful and resulted in a substantial ongoing order for a range of the Huco Dynatork MultiBeam couplings made from PEEK™.

The general-purpose Huco Dynatork MultiBeam couplings readily accommodate any combination of axial motion and angular/parallel misalignment and as standard are machined in aluminium or stainless steel … and other materials by special order.

Couplings deal effectively with hostile environments

The sorts of hostile environment faced routinely by the military present challenges for engineering as well as personnel. An army has to be totally effective whether operating in deserts, jungles, swamps, mountains or arctic conditions. Similarly, the HUCO Dynatork coupling selected for position sensing in a rocket launcher control system had to prove its reliable operation in extremely aggressive environments. 

The brand of coupling initially chosen for the job failed consistently. A cocktail of heat, dust, debris and combustion products resulting from a missile launch created a viscous mass that completely solidified the coupling rendering it rock-hard and useless. 

World leading precision coupling manufacturer HUCO Dynatork was able to engineer a simple but clever solution. The resultant coupling is based on its standard 19mm diameter, stainless steel, Multibeam, a design that is ideal for accommodating both angular and parallel misalignment. A stretched version of the original was made – nearly double the standard length – and modified to accept a specially moulded neoprene gaiter that effectively shields the beam mechanism from debris attack. 

Nearly a year of exhaustive trials proved this tailored product to be the ideal solution and a quantity has now been ordered for retrofitting onto armoured vehicles and for stockholding. 

This is just one example of HUCO Dynatork’s ability to provide products for operation in hostile environments. The company produces a wide range of standard stainless steel motion components that resist aggressive solvents and are therefore ideal for use in wash-down conditions. It also offers a range of composite plastic products for a variety of applications including isolating high voltage. Beyond the standard range HUCO Dynatork welcomes the challenge of unusual applications.