Mechanical PT - Motion Control Tips

Zero backlash featured in Miki Pulley CSZ electromagnetic clutches

January 10, 2019 By Miles Budimir Leave a Comment

Miki Pulley’s CSZ electromagnetic clutches have a zero backlash design and provide an efficient connection between a motor and a load with low inertia, minimal drag and zero backlash.

CSZ clutches function using the magnetic force generated by the energized coil providing engagement of input and output members of the clutch. They feature an integrated bearing design making mounting fast and easy while ensuring application concentricity and excellent system runout. CSZ clutches operate well in temperatures from +14 to +104 °F (-10 to +40 °C).

Available in bores ranging from 10 to 15 mm, with brake torques ranging from 1.77 to 7.376 ft lb (2.4 to 10 Nm), the CSZ uses corrosion-resistant materials, and is RoHS compliant like all other Miki products.

“Miki Pulley’s CSZ clutches are a great choice for high performance printing, paper processing, packaging, food processing and textile manufacturing systems,” reports Jon Davidson, Miki Pulley sales specialist. “They are proven performers in system applications around the world.”

For more information about Miki Pulley CSZ clutches, visit www.mikipulley-us.com.

Why is viscosity important for bearing lubrication?

January 10, 2019 By Danielle Collins Leave a Comment

Lubrication — or, more correctly, improper or insufficient lubrication — is one of the leading causes of equipment failures in industrial applications. Without it, sliding, rolling, or meshing surfaces experience significant friction, heat, and wear, leading to increased noise, loss of accuracy, and reduced equipment life.

One of the most important characteristics of a lubricant is its viscosity (or, in the case of grease lubricant, the viscosity of the base oil). But viscosity is analogous to friction in fluids. So why do you need friction (in lubrication) in order to reduce friction (in bearings)?

Tribology is the study and application of the principles of friction, lubrication, and wear between two surfaces in relative motion.

Viscosity = friction in fluids

Viscosity is a property of fluids and is caused by their internal resistance to shear. When a fluid is moving under laminar flow conditions, with no turbulence — as is the case with most bearing lubrication scenarios — microscopic layers of the fluid flow over one another, much like a stack of paper, with each sheet moving slightly faster than the one below it. Cohesive forces between these microscopically thin fluid layers must be overcome as the layers move past one another. The resistance caused by these cohesive forces is the primary determinant of the fluid’s viscosity.

In laminar flow, microscopic layers of fluid flow over one another. The layers’ internal resistance to this shear force gives rise to viscosity.
Image credit: Michael Fowler, virginia.edu

The role of viscosity in reducing bearing friction

Bearing surfaces, no matter how well they’re machined, finished, and cleaned, will always have asperities (peaks) and valleys. When two bearing surfaces are in contact (for example, ball and raceway or roller and raceway), the asperities of the surfaces interfere with each other. One of the primary roles of lubrication is to separate the surfaces and reduce or eliminate the interference of their asperities, which significantly decreases friction and wear.

But when the surfaces are stationary (or moving at very low speeds), the pressure between them essentially “squeezes” the lubrication from between the surfaces. There is a very thin lubricating film, but it is not sufficient to separate the asperities of the two surfaces, and significant contact still exists. This is referred to as boundary lubrication.

In boundary lubrication, friction, heat, and wear depend primarily on the interactions between the surfaces, although chemical reactions between the lubricant and the surfaces can also contribute to wear. The time spent in boundary lubrication conditions significantly affects bearing performance and life.

As bearing speed increases, lubrication is “pulled into” the contact zone.
Image credit: Wessex Petroleum Limited

As velocity increases, more lubrication is “pulled” into the space between the bearing surfaces, allowing a thicker lubrication film to develop. This causes the pressure on the lubrication film to increase, which, in turn, increases the lubricant’s viscosity (according to the lubricant’s pressure-viscosity coefficient). But there is a transition period where, as velocity increases, the surfaces are separated in some places, but in other places, interference between asperities still occurs. This is referred to as mixed lubrication.

Finally, when a sufficient velocity is reached, the lubricating layer becomes large enough to separate the asperities of the two surfaces, and the increased viscosity gives the lubricant sufficient film strength to support the load, by elastically deforming the bearing surface. This lubrication regime is referred to as elastohydrodynamic lubrication.

A Stribeck curve shows the development of the lubrication film and the resulting change in friction. As velocity increases, the bearing surfaces “pull in” more lubricant, creating a thicker lubricating layer under higher pressure, which results in higher viscosity. Finally, the layer is thick enough to separate the asperities of the surfaces, and the viscosity provides sufficient film strength for the lubricant to support the load.
Image credit: Anton Paar GmbH

Feature image credit: Exxon Mobil Corporation

New Spirawave nested wave spring series from Smalley

January 8, 2019 By Lisa Eitel Leave a Comment

Smalley now offers a new nested Spirawave wave spring series. Smalley has been producing nested wave springs as customs for over 30 years, but this will mark the first standard series on the market.

These multiple turn, flat wire wave springs are coiled in parallel to produce two to three times as much force as traditional single-turn wave springs. Nested Spirawave springs can be used to replace stacks of single-turn springs, eliminating misalignment and inconsistent loading.

The sturdy, tangle-resistant design allows for simple, time saving automated handling. Reduced costs can be realized from the use of a single spring and a simplified assembly process.

“Introducing a standard line of nested springs gives customers the ability to streamline production while meeting their high force requirements,” says Dan Frank, Research and Development Engineer.

Standard Nested Spirawave springs are available from 0.500 to 4 in. or 16 to 3,000 mm in carbon and stainless steel. Stock parts are available for overnight shipping.

Nested Spirawave springs are specified for many applications including heavy duty bearing preload, connectors, valves, and seals. The increased forces produced make them suitable for industries that need precision wave springs with high loads.

If a standard nested spring doesn’t meet the application requirements, Smalley has a team of experienced engineers capable of designing a custom nested spring. Custom or standard, Smalley will get the right part, in the right material, with No Tooling Charges.

Request a copy of the brochure or a free Nested Spirawave Wave Spring sample at nestedsprings.com.

For more than 50 years, Smalley has been the leading manufacturer of retaining rings and wave springs for OEM engineers worldwide. As an ISO 9001 and ISO 14001 company, we deliver quality products certified to: IATF 16949, AS9100 and ISO 13485. Custom or standard, we are dedicated to delivering the right part, in the right material for application. For manufacturing news and product updates, visit smalley.com/blog.

Laser marking now part of Gear Motions production

January 7, 2019 By Lisa Eitel Leave a Comment

Gear Motions now has a fiber laser marking machine which was recently installed at its Nixon Gear Division in Syracuse.

The Beamer Laser Systems Model FL53 uses a 50-watt high powered LED laser to mark products quickly and safely. The machine offers fast cycle times and a wide range of marking intensities. It has a 12.5 x 26-in. total marking field and can accommodate a part up to 3.5 ft long with the side panels attached, and even larger parts when the panels are removed.

An optional 5C collet indexer was also purchased for radial marking of shaft-type parts.

This is the first time that Gear Motions has been able to offer laser marking as a manufacturing service. Previously, operations such as dot peening and engraving were used as a method of marking parts for customers. Laser marking produces a higher quality mark with a better visual appearance, which is particularly desirable for customers that may resell their gears at retail. It can also provide a more data-dense marking solution, via 2D bar codes, QR codes , and so on. for those customers that need it.

Gear Motions is now able to meet the laser marking requirements of its existing customers without sending to an outside vendor. This will streamline the entire process and make complete gear manufacturing even quicker and more efficient. The company can now also offer this value-add service to attract new business from customers that need laser marking on their precision-made gears and may also consider laser mark only business in the future.

Gear Motions, Inc. is an employee-owned company, with gear manufacturing facilities in Syracuse and Buffalo, NY. Specialists in precision ground gears, the company manufactures custom cut and ground gears for OEMs all around the world. Products include precision ground helical gears, spur gears, pump gears, bevel gears and worm gears, as well as multiple types of sprockets, timing pulleys, shafts and splines. For more information, visit gearmotions.com.

Why is static friction greater than kinetic friction?

January 4, 2019 By Danielle Collins Leave a Comment

Solid surfaces are subjected to two types of friction: static friction and kinetic friction. Static friction acts when the surfaces are stationary — think of a box on the floor. Static friction is what keeps the box from moving without being pushed, and it must be overcome with a sufficient opposing force before the box will move. Kinetic friction (also referred to as dynamic friction) is the force that resists the relative movement of the surfaces once they’re in motion.

The static friction between two surfaces is always higher than the kinetic friction (at least, in practical, real-world applications). But why is this? To find out, let’s look at the causes behind each type of friction.

Static friction

There are several theories regarding the causes of static friction, and like most friction-related concepts, each one proves valid under some conditions, but fails under other circumstances. For real-world applications (especially those related to industrial machinery and motion control) the two most widely-accepted theories behind static friction have to do with the microscopic roughness of surfaces.

Static friction keeps the box from moving until the applied force (F) exceeds the static friction force (f_s).

Regardless of how “perfectly” a surface is machined, finished, and cleaned, it will inevitably have asperities — essentially “roughness,” consisting of peaks and valleys, much like a mountain range. (Technically the “peaks” are the asperities.) When two surfaces are in contact, it may appear that they have a large, well-defined area of contact, but in reality, contact occurs only at certain places — that is, where the asperities of both surfaces interfere. The sum of these small areas of contact between the asperities is referred to as the “real” or “effective” area of contact.

Because these individual areas of contact are very small, the pressure (pressure = force/area) between the surfaces at these points is very high. This extreme pressure allows adhesion to occur between the surfaces, via a process known as cold welding, which occurs at the molecular level. Before the surfaces can move relative to each other, the bonds that cause this adhesion must be broken.

Because the surfaces are microscopically rough, with asperities and valleys, the real contact area between them is much smaller than the apparent contact area.

In addition, the roughness of the surfaces means that at some locations, the asperities of one surface will settle into the valleys of the other surface — in other words, the surfaces will interlock. These interlocked areas must be broken or plastically deformed before the surfaces can move. In other words, abrasion must occur.

So, in most applications, static friction is caused by both adhesion and abrasion of the contacting surfaces.

Kinetic friction

Overcoming the static friction between two surfaces essentially removes both the molecular obstacles (cold welding between asperities) and, to some degree, the mechanical obstacles (interference between the asperities and valleys of the surfaces) to movement. Once movement is initiated, some abrasion continues to occur, but at a much reduced level than during static friction. And the relative velocity between the surfaces provides insufficient time for additional cold welding to occur (except in the case of extremely low velocity).

Once the static friction is overcome, the box will move. Now, the friction opposing movement is much lower and is referred to as kinetic friction (F_k).

With most of the adhesion and abrasion being overcome to induce movement, the resistance to motion between the surfaces is reduced, and the surfaces are now moving under the influence of kinetic friction, which is much lower than static friction.

Assumptions regarding friction

Friction is an incredibly complex force that manifests differently under various conditions, making it difficult to express in terms of physical laws and mathematic equations. However, there are three assumptions regarding friction that apply in most real-world situations:

The frictional force is proportional to the normal force.
The frictional force is independent of the apparent area of contact.
The frictional force is independent of the relative velocity.

You might notice that assumption #2 (friction is independent of area of contact) seems to contradict the idea presented earlier that because the points of contact between the asperities are very small, pressure between the surfaces is high and adhesion (via cold welding) occurs, which increases friction. But notice that assumption #2 specifies the “apparent” area of contact.

Using the box example from above: Assume you move the contents of the box to a different box with a larger footprint. The mass (and hence, the normal force) hasn’t changed, but the apparent area of contact is larger. Despite the larger apparent area of contact, the friction force remains the same, as predicted by assumption #2.

Why does rolling motion experience friction?

In theory, a ball makes point contact with the surface. But in reality, the ball (and/or the surface) deforms due to the load, and the contact area becomes elliptical.
Image credit: SKF

Note that the discussion above relates to non-lubricated, sliding surfaces. In theory, rolling surfaces, such as those found in most rotary and linear bearings (except plain bearings), should not encounter friction forces. But in real-world applications, three factors cause friction in rolling surfaces:

Micro-slip between the surfaces (the surfaces slide relative to one another)
Inelastic properties (i.e. deformation) of the materials
Roughness of the surfaces

Gearbox service factor and service class explained

December 14, 2018 By Danielle Collins Leave a Comment

Sizing a gearbox (or gearmotor) for an industrial application typically begins with determining the appropriate service factor. In simple terms, the service factor is the ratio of the gearbox rated horsepower (or torque) to the application’s required horsepower (or torque). Service factors are defined by the American Gear Manufacturers Association (AGMA), based on the type of gearbox, the expected service duty, and the type of application.

Image credit: Cone Drive

While service factors may seem to be very specific, with thousands of combinations of gearbox types and applications each assigned its own numerical value, the criteria used to determine these values are based not on testing and empirical data, but rather on extensive review and analysis of gearbox manufacturers’ experience.

In general, the horsepower (or torque) rating of a gear tooth is based on the durability of the gear surface — its resistance to pitting — or on its bending fatigue. As the service factor of a gearbox is increased, the relationship between the gear teeth life (based on durability of the gear surface) and load is proportional to the increase in service factor, raised to the 8.78 power. In other words, if the service factor is increased by 30 percent (from 1.0 to 1.30, for example), the gear tooth life will increase 10 times (1.30^8.78 = 10.01).

To determine the gearbox service factor, start by consulting a set of tables or charts provided by the manufacturer, based on the type of gearing (worm, spiral bevel, helical, etc.). These tables list a wide range of applications (conveyors, cranes, winders, saws, blowers, etc.), each with (typically) three levels of service duty the gearbox is expected to see: zero to 3 hours per day; 3 to 10 hours per day; or greater than 10 hours per day. Each of these application-service duty combinations is assigned a recommended service factor.

Service factors by application type and gearbox service duty, per AGMA guidelines.
Image credit: Regal Beloit Corporation

Remember, the gearbox service factor is much like a safety factor to ensure the gearbox meets the application requirements, taking into account typical operating conditions known to exist for various types of applications. Once the AGMA-recommended service factor is determined, consider other, non-typical, working conditions that can cause additional stress and wear on the gear teeth, bearings, or lubrication. If any of these conditions exist, increase the service factor accordingly to ensure a sufficient safety margin and life of the gearbox.

Some conditions that may require an increase in the service factor are:

Elevated temperatures
Extreme shock loads or vibrations
Non-uniform loads (cutting versus conveying, for example)
Cyclic loads (frequent starts and stops)
High peak versus continuous loads

Once the appropriate gearbox service factor is determined, multiply the service factor by the horsepower (or torque) required for the application, and the result is the output horsepower (or torque) required by the gearbox.

How does service class differ from service factor?

In some cases, manufacturers cite gearbox “service classes” rather than service factors. Service classes are designated as I, II, or III, and are generally translated to numerical service factors of 1.0, 1.4, and 2.0, respectively, to be used in gearbox sizing calculations. It’s common that even if a manufacturer publishes service classes for general application types, they also publish the more specific service factors for specific applications as well.

Suggested service factors based on service class.
Image credit: STOBER Drives Inc.

Why don’t some catalogs list gearbox service factors?

Servo-rated gearboxes require detailed sizing to choose inertia, output torque, and speed for proper servo system operation.
Image credit: Wittenstein

Using service factor to guide the selection of a gearbox is appropriate for applications driven by traditional AC induction motors. But because gearbox output torque, speed, and inertia are much more critical for the proper operation of a servo system, sizing a so-called “servo-rated” gearbox requires a more detailed and exact method. For gearboxes that are used in servo systems, the primary emphasis in the sizing process is on required torque and inertia match.

Video on torque limiters: Examples of how to customize for industrial applications

December 6, 2018 By Lisa Eitel Leave a Comment

In a recent video with Lee Teschler, we go over three torque limiters from Mach III — a Kentucky-based manufacturer of stock and custom brakes, clutches, and torque limiters. The manufacturer can usually deliver custom designs within two days of obtaining application requirements. Mach III also meets or beats purchase-order ship dates 98% of the time. Catalog products ship in 2 to 5 weeks and custom in 3 to 6.

Recall that friction torque limiters transmit a set torque from the motor end of an axis to the driven-load end — and protect both from overload. Should torque exceed a set value, the torque limiter slips.

So let’s check out our first sample — a T2A2R-STL mechanical torque limiter … on which a sprocket, pulley, or sheave can mount. This is a spring-engaged design having low-coefficient friction discs. Minimum torque is 20 lb-in. and maximum torque (with 27% spring compression) is 200 lb-in. This one-pound torque limiter works on axes with speeds to 1,750 rpm.

Of course, torque limiters can integrate into motion systems in a few ways. We just considered one that accepts input via a sprocket-and-chain or pulley-and-belt assembly. Now let’s consider one for shaft-to-shaft mounting.

The V2R2R-STL is a mechanical torque limiter with adapter sleeve. The latter necessitates simple but precision installation with a torque wrench and other tools … But these torque limiters usually ship with the specified torque value to within about 10%.

Our third and final sample here is a V2G2R-STL shaft-to-shaft mechanical torque limiter. It’s complete with rigid coupling. This is a spring-engaged unit capable of torque maximums of 20 to 200 lb-in. depending on the setting.

One caveat: All these torque limiters are for momentary events and will continue slipping until the jam or other overload source is cleared. That means designs employing these components must include some way to detect torque overloads.

For more information, visit machiii.com and motioncontroltips.com.

Video: Spring or air-engaged friction brakes from Mach III (a Design World overview)

December 5, 2018 By Lisa Eitel Leave a Comment

In a recent video with Lee Teschler, we got the chance to handle two brakes from Mach III. Watch the video:

Our first sample — a D2F3R-STH spring-engaged brake — is one of more than a dozen standard variations … with many more customizable options.

This modular brake design has subcomponents grouped into kits — for drive-hub elements, drive-disc elements, piston elements, cylinder elements, and a final kit that includes two O-rings, 24 coil springs, and three friction discs. It’s recommended that end users keep these common wear items on hand for very critical applications where downtime must be minimized.

Torque is to 91 lb-in. and maximum speed is to 1,750 rpm. As with most all brakes, the manufacturer recommends a service factor of 1.5 to 2 when calculating required torque. Brakes shouldn’t be used at maximum rated torque for continuous duty.

So that was a spring-engaged brake … the other sample we show in the video is an air-engaged brake — the Mach III B2F2R-STH. Dynamic torque for this flange-mounted brake at 80 psi input is 100 lb-in.

Of course, torque capacity is only one factor to consider when selecting a brake. Mach III recommends that design engineers contact the engineering department for application review and assistance.

The pneumatic supply must include a flexible airline and correct fitting for the brake inlet’s NPT size — and fixing with a thread-sealing compound. Air supply should be both filtered and regulated. For more information, visit machiii.com.

Click to enlarge.

Video: Five air-engaged clutches from Mach III (a Design World overview)

December 4, 2018 By Lisa Eitel Leave a Comment

In a recent video with Lee Teschler, we investigated five air-engaged clutches from Mach III. The company designs and manufactures an array of air and spring-applied friction brakes and clutches — as well as mechanical torque limiters and combination clutch-brakes for industrial applications to 5,000 ft-lb. Watch the video:

First we detail a C2H2R-STH air-engaged shaft-to-shaft flexible-coupling clutch. These friction clutches (as with all the other samples we detail in this video) engage with air pressure and then are spring released upon air exhaustion.

In this way, they connect and disconnect fully supported shaft pairs. An elastomeric element compensates for up to 3° of angular misalignment and up to 0.040 in. of parallel offset between shafts.

In contrast, a sprocket or pulley mounts on the pilot of the C2A2R-STH air-engaged clutch. This is a through-shaft-bored variation in a miniature-clutch line for torque requirements of less than 200 lb-in.

The C2D2R-STH air-engaged clutch we examine in the video is designed for end-of-shaft mounting … and for cycling and connect-disconnect applications.

It fixes to the shaft with setscrews or a customer-supplied key and includes a rotary air seal. Unlike the other clutches we consider in this video, this one does not need an anti-rotation arm to prevent rotation of the air housing.

Next check out this M2G2R-STH air-engaged shaft-to-shaft rigid clutch coupling. It has a two-piece coupling body — with both the clutch mechanism and coupling half bored to accommodate differing shaft sizes.

Last but not least, we have an M2R2R-STH air-engaged clutch mechanism with adapter. Torque capacity is to 190 lb-in. As with the other clutches here, torque is linear in response to input air pressure. It’s also available with friction linings having a low or high coefficient for the same price. Linings with a low coefficient of friction are for designs needing a bit of slip or a narrow torque range.

These are just a tiny sample of what the manufacturer offers — in more than 2,000 standard models — though most of what Mach III supplies are slightly custom to very custom designs. In that regard, the manufacturer is somewhat ahead of a growing trend we see in industry. For more information, visit machiii.com.

Click to enlarge.

Klüber Lubrication now sells grease for small gears subject to high loads

December 1, 2018 By Lisa Eitel Leave a Comment

Klϋber Lubrication, a worldwide manufacturer of specialty lubricants, introduces Klübersynth GE 14-151, a special grease for highly loaded small gears like those found in power tools.

This product consists of a finely balanced combination of ester and synthetic hydrocarbon base oils with an aluminum complex soap thickener. Klübersynth GE 14-151 has a wide service temperature range, good wear protection properties and a high scuffing load capacity. It also offers high protection against tribocorrosion.

Klübersynth GE 14-151 can be used to lubricate toothed wheels, bearings, joints and slideways. The optimized oil release behavior enables use in applications that are not sealed oil tight. With a high scuffing load capacity and good backflow behavior, the grease allows lubrication of gears with a high sliding ratio.

Depending on temperature, load and sliding speed, Klübersynth GE 14-151 can even be used on steel-steel, steel-aluminum, and aluminum-aluminum components. When used for lubricating trapezoidal and ball-and-screw spindles, it offers excellent wear protection and smooth running.

Klübersynth GE 14-151 can be used in gears operating at peripheral speeds of approximately 10 m/sec with a quasi-complete fill of the gear housing. It can maintain speeds of 20 m/sec over short-term or intermittent operation. Tooth flank lubrication allows a speed of 3 m/sec.

Klüber Lubrication is a manufacturer of specialty lubricants and high-end tribological solutions. Most products are developed and made to specific customer requirements. During its more than 80 years of existence, Klüber Lubrication has provided high-quality lubricants, thorough consultation and extensive services, which has earned it an excellent reputation in the market. The company holds all common industrial certifications and operates a test bay hardly rivalled in the lubricants industry. For more information, visit klueber.com.

Freudenberg Chemical Specialities Munich, was founded in 2004 as a new Business Group within the Freudenberg Group. Its objective is to promote innovation potentials in its field of activities and to expand world-wide market leadership in special lubricants and release agents. The Business Group includes five largely independent divisions which are active in more than 50 countries: Klüber Lubrication, Chem-Trend, SurTec, Capol and OKS.