Coupling (mechanical) vs Coupling (the TV Show) - A New Year's Eve Match-up

When searching for "coupling" online users will often see search result for both the UK sitcom "Coupling", which aired during the early 2000s as well as flexible mechanical power transmission couplings. (Users may also see results for pluming pipe couplings, but since there can only be two entities in a 1-on-1 boxing match they have been sidelined for this article.)

The intent of this tongue-in-cheek New Year's Eve article is to simulate a boxing match between two very different products that compete for the same search engine result space (for "coupling").

Spoiler alert: This article has been written by an employee of a leading flexible mechanical coupling manufacturer and has never seen the Coupling sitcom. This article is about to get extremely biases, so, if you are a fan of the show which has apparently drawn comparisons to Friends and Seinfeld in the US market, now would be a good time to stop reading this article. For those looking for more information or trivia from the show, consider visit either the show's Wikipedia or IMDB write up and rehash old memories... but the rest of this article will bring you no pleasure.

Round 1: Relevancy

Coupling the TV show is unfortunately way past its prime and has been retired for a decade. While it may have been well received and popular in its heyday, the television series wrapped up in 2004. With each passing year, it becomes less and less relevant. 

Power transmissions couplings meanwhile are in the midst of their prime. Every day, there are millions of them around the world ensuring smooth operations of applications large and small in just about every industry imaginable. Do I hear Eye of a Tiger playing in the background? This boxer means business.

Round 2: Global Reach

Power transmission couplings can be found not only in nearly every industry imaginable, but also in nearly every corner of the world as well. 

The television show may have been popular for a few years in the United Kingdom, but has nowhere near the global reach of power transmission couplings. When the television show attempted to cross the Atlantic, it was cancelled after only 4 episodes airing. (You can find a bit more trivia on its brief US run here.)

Round 3: Staying Power

Power transmission couplings have generations of staying power. While Coupling the TV show ran from 2000-2004 in the UK (and under one season in the US), power transmission couplings have been around long before the actors in the show were even born.

Ding, ding, ding!!!

Unanimous Winner: Mechanical Power Transmission Couplings!!!! 

After three decisive (and admittedly biased) rounds, mechanical power transmission couplings emerged as the clear winner. While fans of the television show may keep it popping up on search engines for a few more years, we predict (with bias) that overtime the television show will fall well into the second or third page of search engine results, allowing power transmission couplings (preferably Lovejoy) to reign supreme.

On behalf of the entire Lovejoy organization, we hope you have a happy and safe New Year's Eve.

Lovejoy Update: Who knows what's up with British television, but it also appears that there was a now defunct British comedy that ran from 1986-1994 titled Lovejoy! Wikipedia and iMDB both have pages on the show, and apparently it does still pop up in search engines when you search for "Lovejoy". Using the same logic as above, and being 100% biased, we similarly declare Lovejoy (the coupling manufacturer) as the head to head winner over the Lovejoy (the defunct British TV show)... but for two British television comedies to be titled "Lovejoy" and "Coupling"... really?

Top 10 Flexible Coupling Blog Posts for 2014

With 2014 being the inaugural year for the CouplingAnswers.com blog, we have been able to cover a lot of ground... but there also remains a tremendous amount of ground yet to cover. Early on, we covered a broad overview of coupling basics and covered a handful of pressing customer questions. Later, we took a deep dive into jaw couplings, and most recently completed a deep dive into grid couplings... inclusive of failure modes. 

Looking ahead to 2015, we will certainly take a deep dive into gear and disc couplings, as well as into any particular questions or topics that website visitors request. This blog has been designed expressly to be a tool for the general flexible coupling user. If you have questions that we haven't answered, or haven't answered to your liking, please let us know. Not only do we want to help you, but we also want to help others who likely have questions similar to you. (Chances are very good that if you've got a question, several hundred others will have a very similar question and will be seeking it out online.)

While blog posts that were posted earlier in the year tend to have more views, and we expect some of our most recent posts to pop over time... for the sake of posterity, we wanted to record what were the Top 10 most viewed blog posts for this site's first year.

Without further ado... here they are (with #1 being the most viewed/most popular):

#10. Jaw In-Shear Couplings - A Straight Forward Value Add

This article takes a deep dive into the jaw in-shear coupling, which, leveraging two standard Lovejoy jaw coupling hubs and a radially removable elastomeric spider and retaining ring, turns a traditionally fail-safe design into a non-fail safe design. The design provides for rapid elastomeric spider inspection and replacement without moving the hubs or use of any external tools (only your hands).

#9. Coupling Spacers - How Long Can or Should They Get? 

The purpose of a coupling spacer is not always well understood, nor are the trade-offs and drawbacks of having longer ones. This article dives into the pros (allowing equipment to be spaced far apart if required, greater misalignment handling...) and cons (cost, overhung load, weight....) of coupling spacers, and also talks about several technologies (inclusive of composite materials). This article is an ideal starting point for anyone considering the trade-offs of a spacer couplings.

#8. Flexible Coupling Basics - A Quick Primer

This article provides a broad overview of many different flexible coupling types, inclusive of elastomeric (with flexing rubber elements) and metallic (gear, grid, disc) types is an excellent starting point for someone new to the power transmission industry. The article is also ideal for those looking to better understand the flexible coupling market space from a high 30,000 foot level. 

#7. Coupling Sizing Torque - How to Quickly Calculate (inclusive of Service Factor)

This post provides tools (both online and for smart phones) that allow a user to quickly calculate the required torque of a coupling, and to then be able to quickly select a coupling based on that calculation. 

This post is an ideal read for anyone who needs to make coupling selections on a regular basis, and or anyone who needs to calculate required torque (based on horsepower, rpm, and service factor) regularly.

#6. Jaw Coupling Overview - Features & Benefits, Design Basics, and Element Options 

This article was written to provide an excellent overview on the industry leading multi-purpose flexible jaw coupling. Lovejoy first launched the jaw coupling in 1927, drove it to be a widely accepted industry standard based on its technical merits (robust, affordable, low maintenance, etc.), and continues to hold a market leading position in the product line. Given Lovejoy's authority position on the jaw coupling, this article is an excellent starting point for anyone interested in learning more about jaw couplings. 

#5. Coupler or coupling? Which one is correct? 

This article was driven by repeated conversations that are constantly occurring within the walls of Lovejoy. Some customers call our product "couplers" while the vast majority (inclusive of ourselves) call them "couplings". We wanted to dive into this issue a bit deeper, and provide our findings for all to enjoy. 

#4. Clearance vs Interference Fit Couplings - Which Hub Fit is Better?

This is a common question we get, and one we felt was ideally suited to be answered on the blog. 

There are benefits and drawbacks to each fit, and the better fit is certainly application specific. For further information on the trade-offs, please read the article!

#3. Active Coupling Bore and Keyway Standards - What Are They & Where Can I Find Them?

Now we are getting into the blockbuster articles of 2014... the top 3. Earning the year's bronze metal is a posting that cleanly lays out the most common coupling bore and keyway standards, as well as direct links to where those standards can be downloaded. (Sorry, we don't have the authority or authorization to provide those standards without cost ourselves.) 

If you are looking to better understand what the standards are, and where you can find them... this is a post for you! 

#2. Cutting Keyways - Broaching, Keyseating, Wire-Cut EDM, Shaping, & Milling

This post was commissioned after the Lovejoy team realized that they could not find a solid comprehensive resource that covered this topic very well online. While many Lovejoy customers trust and rely on Lovejoy to provide final bore and keyways, there are also a substantial subset that like to have unfinished (rough stock) bores available on their shelves locally to address emergency breakdown situations.  

This article was written to provide an overview of how any why keyways are cut to both to the end user who may require a keyway to be cut in the field, as well as to Lovejoy's many end users who may just want to better understand the technology Lovejoy is using to make their requested product. 

#1. Coupling Failure Analysis - Jaw Couplings (includes hub & spider photos) 

As discussed in a recap of #6 above, Lovejoy is the authority on jaw couplings. Given the sheer volume of the installed base, and the fact that manufacturers generally do not like to failures (even though most couplings have wearing components that are designed to be replaced over time), it's not surprising that the posting on jaw coupling failures was our number #1 most popular post for 2014. 

We have since rolled out a similar article for grid couplings (see Grid Coupling Failure Analysis), and have several others planned an in the pipeline.

Thank you to all who have contributed to the success of both Lovejoy and the CouplingAnswers.com blog this year. We wish you a very happy and safe New Years, and a terrific 2015!

Where are couplings used? Check out your backyard!

Uncle's Log Splitter - outside Pittsburgh, PA

To follow on the heels of Bob Buesing's wonderful article and tutorial on log splitter couplings, several weeks ago I was at my uncle's house near Pittsburgh for Thanksgiving. He knew I worked for Lovejoy, and knew that Lovejoy was a leader in industrial flexible couplings of all types and sizes, but he really didn't fully understand what a coupling was or where it was used. 

As luck would happen, my uncle lives on a farm. Given winter is approaching, he had a well-used hydraulic log splitter sitting in his backyard and he had been using it all morning. Well aware that hydraulic log splitters commonly use Lovejoy jaw couplings, I walked out to his log splitter to find a Lovejoy L075 jaw coupling that had been manufactured in Lovejoy's Downers Grove, Illinois facility (where I work!).

The Unsung Hero - Lovejoy's L075 Jaw Coupling

With a Lovejoy flexible coupling application standing in front of us, it was very easy for me to visually demonstrate the need and many benefits that high quality (Lovejoy brand) couplings provide (inclusive of basic concepts to include misalignment handling, vibration dampening, and torque transmission). Should you be looking for a similar primer on couplings, please read Flexible Coupling Basics - A Quick Primer. Should you be looking for a deeper dive into Lovejoy jaw couplings, please read Jaw Coupling Overview - Features & Benefits, Design Basics, and Element Options. 

Now knowing that a coupling from Lovejoy had been working hard for years to keep his family warm for the winter, my uncle left our conversation with a great and deep appreciation for the value high quality (and, in his case "maintenance-free") couplings provide in ensuring reliable and long lasting mechanical power transmission.

While I'm confident that my uncle's Lovejoy jaw coupling will continue to serve him well for years to come, when I left Thanksgiving at his house, I assured him that Lovejoy has hundreds of the coupling he is using in stock... and that it would be my honor to Quick Ship him a replacement should it ever be required! Should you need a coupling fast, please consider using Lovejoy's Quick Ship program through an authorized Lovejoy distributor.

If Ryan Seacrest Were A Flexible Coupling, What Type Would He Be?

Ryan Seacrest (Born Christmas Eve 1974)

Given its Christmas Eve and Ryan Seacrest's 40th birthday (congratulations on going over the hill), the team at Lovejoy thought it would be fun to sit down and rationalize what flexible coupling type most suited Ryan Seacrest.

We started by creating a list of what we knew about him (and what we could find out about him on Wikipedia).

1. To start, he is surprisingly short (approximately 5'8").

2. We also know he wears a lot of different hats in the entertainment world (from co-hosting American Idol, to hosting several radio shows including America's Top 40, to being a producer on several shows including Keeping Up with the Kardashians. 

3. We also know he is certainly wildly popular/influential. Forbes Magazine, also highlighting a clothing line he has with Macy's and an iPhone device he created, pegs him as the world's #31 most powerful celebrity. (We also tried to see his current "Star Rank" on IMDB, but they force you to subscribe to see it... so we passed.)

So how does a small, multi-functional, and powerful celebrity translate to couplings? 

If you thought Lovejoy would nominate its flagship jaw coupling, well, you'd be wrong for one primary reason: maintenance. Jaw couplings are low maintenance (given they are not a lubricated design that needs to be re-lubricated), and it is our humble opinion that there is nothing low maintenance about Ryan Seacrest. He is a high powered Hollywood type after all. Dealing with the paparazzi alone would drive him out of the low maintenance category. 

Given a 4th attribute of requiring "some regular maintenance required", jaw couplings are out.

So what does a "power dense, some regular maintenance required" coupling look like?

Well, we quickly narrowed our options to lubricated coupling (gear couplings and grid couplings), as they seemed best to fit the description. Both are very power dense. Both are lubricated metallic designs that require grease to be inspected and added occasionally. 

Where they differ is in applications. While grid couplings have a unique metallic coupling ability to absorb peak loads and absorb vibration, they are not designed to handle significant misalignment. 

HercuFlex Gear Coupling (Flange Sleeve Style)

Gear couplings, while not designed to absorb vibration, can handle more misalignment and are thus the workhorse of countless industries and applications. From overhead cranes to steel mills to underground mining, gear couplings are found near and wide.

Based on the ubiquitous force that is Ryan Seacrest, we thus feel and conclude that should Ryan Seacrest be a coupling... he would be a multi-functional "occasional maintenance" gear coupling... but not just any gear coupling. 

Rather, Ryan would be the latest and greatest Hercuflex gear coupling. When Ryan took over Dick Clark's New Year's Rockin' Eve as Executive Producer, he didn't rest on the laurels of history. Rather he updated and continued to reinvent the show. 

The Hercuflex is a the optimized gear coupling that modern technology has enabled, and we see no more fitting a coupling association for Ryan. 

Do you see any other coupling types matching up well with other celebrities? Please share your thoughts and comments below. If you really wow us, it may even inspire another post (where we will naturally cite your contribution)! 

Happy 40th Ryan, and Happy Christmas Eve to all! 

Log Splitter Couplings (Lovejoy Jaw Couplings)

Guest Post: Bob Buesing, Lovejoy Application Engineer

 Lovejoy’s Applications Engineering team receives quite a few inquiries each year that are related to log splitters.  Log splitter equipment typically consists of a small gasoline engine driving a hydraulic pump, often coupled together using a standard Lovejoy elastomeric jaw style coupling.  

The questions received by the applications engineers most often deal with replacing worn or damaged spiders, or possibly complete couplings.  Spiders can display wear due to misalignment, a torque overload, possible exposure to harsh environmental conditions, or something as simple as wear due to normal use. (A comprehensive article on jaw coupling failure analysis can be found by clicking here.)  

Inquiries received by Lovejoy’s Applications Engineering team also are typically confirming the proper size spider replacement has been selected, and/or requesting help to select the ideal coupling size to use when replacing one of the log splitter components such as the hydraulic pump or engine.  When replacing an engine or pump, changes in shaft size or engine horsepower are common and the coupling size may change.

It is common knowledge that gasoline engines, regardless of size, can be very tough on couplings.  The pulsing from the compressing and burning of the fuel sets up a vibration in the engine called torsional vibration.  The coupling needs to dampen some of this vibration while transferring torque from the engine shaft to the pump shaft.  For this reason, both the coupling size and the type of spider, or insert material is critical to the successful performance of the coupling and the operation of the log splitter.  If the coupling is not sized correctly, or the incorrect elastomeric material is selected, the coupling could fail prematurely, possibly as soon as the engine starts.  To avoid this frustration, some common steps, or “rules of thumb” for selecting a jaw coupling for a log splitter have been included in this article.
 

1.  To size a jaw coupling for a log splitter, it is necessary to identify the peak torque output from the engine being placed in service.  This peak torque can usually be found in the engine documentation that is supplied with the engine.  This torque may appear in the form of a power speed curve chart as shown here, or could be provided by the small engine manufacturer as the “rated” speed at which the engine achieves the published horsepower.  If a rated speed and horsepower is supplied, the following formula can be used to calculate the torque.
  

Torque (in-lbs) =     Horsepower  x  63,025 (constant)

                                RPM (rated speed)

2.  Multiply this published or calculated torque times a combustion engine service factor of 2.0 or greater to get what is called the selection torque.  If the engine power speed curve as shown above shows a peak torque of 40.5 ft-lbs, or 480 in-lbs, the coupling selection torque would be 480 in-lbs x 2.0 =  960 in-lbs.  If the engine manufacturer prefers to define the engine by horsepower at a rated speed, their data might define (example only) an engine capable of 23 horsepower at a “Rated” speed of 3,000 RPM, the torque would be 483 in-lbs.  Selection torque would be 483 in-lbs x 2.0 = 966 in-lbs.  Again, the rated speed and horsepower must come from the engine manufacturer or their published specifications.

3.  The spider, or insert material for this application should be as torsionally “soft” as is available to dampen vibration and dissipate heat associated with dampening the vibration.  The most torsionally “soft” spider material offered from Lovejoy would be the Nitrile Buna-N, or NBR (sometimes referred to as SOX) rubber.  In addition, since log splitters typically run well in excess of 1,800 RPM, the spider would have to be a solid center spider.  An open center spider will not hold together at the typical log splitter running speed.  The maximum speed for each size jaw coupling is shown in Lovejoy’s on-line catalog.

4.  In the Lovejoy jaw coupling catalog, find the coupling size and part numbers that match the shaft size for the engine AND the pump.  Both of the hubs and the spider must be the same coupling size.  If one hub is an L100 (example: L100 HUB 1” 1/4x1/8KW), the second hub must also be an L100.  Likewise, the spider must be an L100 spider.  For a log splitter application, the spider must also be a solid, or closed center type of spider.

5.  Now if we do a sample selection, it would look like this:

Sample engine:    18HP gasoline engine, rated at 3,200 RPM, 1” shaft with a 1/4” x 1/8” keyway,  but will be running at 3,600 RPM.

The hydraulic pump has a 3/4” shaft with a 3/16” x 3/32” keyway.

Torque =    18 HP x  63,025 (constant) x 2.0 (service factor) = 709 in-lbs
3,200 RPM                                           

The first coupling size in the catalog where the NBR spider torque rating will accommodate 709 in-lbs is the L110 size jaw coupling.  The NBR rubber spider is rated for 792 in-lbs of torque which should be acceptable for this engine and pump combination.  The solid center spider is designed to operate at speeds up to 5,000 RPM which is more than enough for this log splitter application.

From the catalog, the spider part number would be 68514411724 (see page JW-10 in the catalog), the hub for the 1” engine shaft would be part number 68514411739 (see page JW-11), and the hub for the 3/4” hydraulic pump shaft would be part number 68514411735 (see page JW-11). 

Please note that Lovejoy also supports an assortment of splines.  If the motor or pump has a spline shaft, please feel free to contact Lovejoy Customer Service for details regarding which splines are supported.

Care should be taken to ensure the shaft separation matches the gap dimension for the spider selected.  The chart on page JW-24 in the Lovejoy catalog shows a ‘G’, or ‘Gap’ dimension for each size coupling.  Since the solid center spiders will not allow a shaft to extend inside the spider, the shaft separation must be equal to or greater than the gap value shown.  If the shaft separation is greater than the ‘G’ dimension, the hub(s) can hang off the shaft a small amount.  The ‘rule of thumb’ for hanging a hub off the shaft is the hub/shaft engagement should be as close as possible to, or more than the diameter of the shaft.  If this is not feasible with your equipment, the engine or pump may need to be moved to allow for proper spacing.

To summarize:
1.  The spider, or insert should be NBR (SOX) rubber spider with a solid center.
2.  Use the “Rated” torque for the engine as supplied by the manufacturer.
3.  If “Rated” torque is not available, use the engine manufacturer’s “Rated” horsepower with the “Rated” speed to calculate the engine’s peak torque.
4.  Calculate the selection torque by taking the engine’s peak output torque and multiply this torque times a service factor of 2.0 or greater.
5.  Contact Lovejoy Technical Support at 630-852-0500 with any additional questions or concerns.

Please note that recommended procedures and techniques for performing jaw coupling installations can be found in the installation guides and demonstration videos available at Lovejoy's website. To find a quality authorized Lovejoy distributor, please see Lovejoy's Find a Distributor tool.

About the Author: Bob Buesing has a rich legacy of serving Lovejoy and Lovejoy's clients as a coupling application engineer and product trainer. To tap into Bob and Lovejoy's rich industry knowledge and experience, please contact call (630-852-0500) or email Lovejoy and request to speak with an application engineer.   

Shaft Laser Alignment - 3 Benefits over Dial Indicators

Lovejoy Disc Coupling being Laser Shaft Aligned

As discussed in prior posts, shaft misalignment is one the major causes of premature coupling, bearing, and seal failures in a power transmission system. Even while staying within the misalignment limits of a flexible coupling, it is still advisable to keep misalignment to a minimum.

While dial indicators offer an excellent shaft alignment solution for many applications, for those looking for a best in class solution, laser shaft alignment tools are available. (Note: Lovejoy does not sell laser alignment tools, but we do sell a dial indicator kit.)

A major advantage of laser alignment tools is their accuracy. Unlike some dial indicators, there is no bar sag that needs to be measured and accounted for. Readings are also very precise.

A second major advantage of most laser shaft alignment tools is that they come with a computer system that automatically calculated what adjustments are needed and records measured values (which maintenance crews can use both to verify proper installation and watch for trends or changes in equipment movement). Dial indicators generally require hand calculations and adjustments (assuming you don't use the Lovejoy Dials free new smartphone app). 

A third major advantage of laser alignment tools is that they can be spread fairly far apart, which is very useful when working on two sides of a long spacer type coupling.

Countering these three strong advantages of laser alignment tools is primarily cost. Dial indicators are generally much less expensive upfront and they are arguably more robust. (Laser alignment tools are electronics, and they also generally call for periodic recalibration of the lasers.)

If you've got a large maintenance budget and reliability is absolutely king (any downtime means big bucks), a high quality laser alignment tool is a wonderful tool to have in the toolbox. For those currently using dial indicators without the budget to throw down on a laser alignment system, the free Lovejoy Dials app will help provide some of the automated calculation benefits of using laser tool. For those not doing shaft alignment at all, for the longevity and reliability of your equipment, we highly recommend that you start now.

Grid Coupling Failure Analysis (includes photos)

Like other coupling types, grid couplings often have "signature failures" modes that can help root cause a given coupling's failure. Some of the common causes of grid coupling failures are fatigue, torque overload, lack of lubrication, misalignment, and environmental conditions.

Fatigue Wear

Signature fatigue wear, which can generally be viewed as normal grid coupling wear, shows up as cracks in the grid spring element approximately in the center of the grid spring element legs (as pictured at right).

With a few grid spring element legs broken in the center, a grid coupling will likely still be operational and transmitting torque through the remaining unbroken legs. However, once such a condition occurs, the coupling is operating in compromised state and the grid spring element should be replaced as soon as possible. 

Torque Overload 

Torque overload failures appear similar to fatigue wear, but the cracked grid spring element legs are not centered but rather further up or down on the given grid spring element legs.

Lack of Lubrication

Failures due to a lack of lubrication are often localized to one side of a grid spring (where lubrication was lacking) and may resemble or look like a fatigue failure. The reason for this is a grid coupling is a metal-on-metal coupling, and a lack of lubrication will lead to premature wear (or fatigue) of the grid spring element wherever there is not adequate lubrication (see How should you pack the grease in a Grid Coupling?).

Misalignment

While grid couplings are a very good vibration dampening high power density coupling, they are unfortunately not very good at accommodating misalignment. They are not designed to handle any parallel shaft misalignment, and are only designed to handle about a quarter degree of angular misalignment (see How sensitive are Grid Couplings to misalignment?).

Pictured at right is an example of a grid coupling element misalignment failure.  In such a failure, the grid spring break on the outer bends of the grid spring legs. Similar to fatigue failures, a grid coupling may have broken legs due to misalignment and still transmitting torque through the unbroken legs. This is not a desirable long term state. The grid spring should be replaced as soon as possible, and to prevent such failures (or to correct from such a failure from re-occurring) it is critical that the coupling shafts be realigned and within the misalignment tolerance of the given grid coupling.

 

Environmental Conditions

Environmental conditions include excessive temperature and/or chemical exposure. Operational temperatures above or below the temperature range of the grid coupling seals will lead to seal damage or failure. Similarly, grease can also break down given extreme temperature exposure. Chemicals can also lead to seal damage and failure. In addition to visible damage to seals and lubrication breakdown, environmental failures may appear similar to an overload condition. 

To learn more about Grid Couplings, please read Why a Grid Coupling - Features & Benefits, Design Basics, and Element Options. 

To learn more about coupling failure analysis, visit:

Coupling Failure Analysis - Jaw Couplings (includes hub & spider photos)

Gear Coupling Tutorial - Part V: Failure Analysis (with photos)

Coupling Peak Torque Failure at Keyway

Top Reason for a Coupling Failure

Why a Grid Coupling - Features & Benefits, Design Basics, and Element Options

Why a Grid Coupling

Grid couplings are a popular coupling option where both high torque levels and dampening requirements exist. Unlike gear and disc couplings (alternative metallic coupling types capable of transmitting a significant amount of torque), grid couplings have a unique ability to reduces vibration by as much as 30%, and cushions shock loads to safeguard driving and driven power transmission equipment. 

The grid spring element absorbs impact energy by spreading it out over time, and thus reduces the magnitude of the peak loads. This is possible because of the progressive contact that occurs between the curved profile of the hub teeth and the flexible grid. As the load increases, more of the tooth comes into contact with the flexible grid spring element. 

 

Additional Benefits

Horizontal Split Cover

Grid couplings are a versatile, proven technology with interchangeable components readily available from several major coupling manufacturers (including Lovejoy). 

Grid couplings have a high power density (transmit a high amount of torque relative to their size), and are relatively straightforward and simple to install. They also have good resistance to environmental conditions, and available for both inch and metric bores.

Design Basics

Vertical Split Cover

A grid coupling is comprised of two hubs, a grid spring element, and split cover kit (which includes two cover halves, gaskets, seals, and hardware).

Like gear couplings, grid couplings are a metal on metal flexing design, and it is critical that the coupling be packed properly with coupling grease (see How should you pack the grease in a Grid Coupling?) 

Grid couplings are available with either a horizontal or vertical split cover design. Horizontal covers are generally viewed as easier to install, while vertical covers enable a grid coupling to be run at a higher maximum speed (see What is the difference between Horizontal and Vertical Grid Couplings?).

Spacer Design 

Full Spacer Design

Grid couplings are also available in a spacer and half spacer designs, which are ideal for allowing equipment to be serviced. Such designs are particularly popular in pump applications, where a drop-out section (full spacer design) or quick disconnect (half spacer design) allows for equipment servicing without disrupting the greased grid coupling element.

 

Limitations

One of the biggest, if not the biggest, limitation of grid couplings is their limited ability to accommodate misalignment. While great at dampening vibration, they are not designed to handle parallel shaft misalignment and only designed to handle about a half a degree of angular misalignment (see How sensitive are Grid Couplings to misalignment?).

Half Spacer Design

Additionally, grid couplings are also not "maintenance-free" because they require lubrication (grease), which must be periodically checked and topped off if required. Care must also be taken to ensure that lubrication does not leak on to the ground and create an environmental concern. 

For further information on grid couplings, please see Lovejoy's grid coupling product page.

How should you pack the grease in a Grid Coupling?

As completely as possible! Grid couplings are a metal on metal design. Without good lubrication, metal on metal rubbing and flexing will quickly lead to premature coupling failure! (The photo at left shows insufficient lubrication because the grid springs at the bottom are not packed.)

It is also important to note that coupling grease is not bearing grease (see Coupling Grease - Four Things You Should Know). Coupling grease is much thicker, and you will run into problems if you are not using the right type of grease. 

Grid coupling installation videos, highlighting the packing of grease are readily available for  Horizontal Split Cover Grid Couplings, Vertical Split Cover Grid Couplings, Full Spacer Grid Couplings, and Half Spacer Grid Couplings. Formal installation instructions for specific grid coupling types can be downloaded on Lovejoy's Installation Instructions resources webpage. 

An excerpt from one of these instructions can be seen below, with the segments speaking to grease being underlined. For further questions or information regarding grid couplings, please see Lovejoy's grid coupling product page.

Excerpt from Lovejoy's Installation Instructions for Horizontal Split Cover Grid Coupling (Sizes 1020-1220):

6.10  Prior to inserting the grid spring or grid spring segments, thoroughly pack the grooves on each hub with a qualified coupling grease (see Table-2).  If the grid springs consist of two or more segments, assemble the grid springs so that the cut ends of one segment extend in the same direction as the cut ends of the next segment. Spread the grid slightly so that the edge of the spring passes over the grid teeth in the hub.  A flat blade screwdriver can be used to stretch the grid spring.  Insert the blade through the grid spring and into the grid teeth groove a couple loops beyond where the grid spring is to be inserted.  Tilt the screw driver to stretch the spring and the grid loops should drop into place.  Towards the end you may need to switch to a soft face mallet and tap the edges of the spring into the respective grooves.

6.11  Pack the spaces around the grid spring with qualified grease (see Table-2) and wipe off any excess grease flush with the top of the grid spring and grid teeth on the hub.

6.12.1  When using a vertical split grid cover assembly, slide the cover halves over the hubs lining up the bolt holes so that the grease plugs are 180° apart.  Insert the fasteners through the cover holes and tighten to the torque specified in Table-5 using a calibrated torque wrench.

6.12.2  When using a horizontal split grid cover assembly, position the seals on the hubs so they align with the grooves in the covers. Position one cover half under the seals and place the two gaskets in position. Align the second cover half over the seals so that the match marks line up on the same end of the covers.  This ensures the recesses in each of the cover halves that receive the fastener nuts are 180˚ apart.  Insert the fasteners with the nuts fitted in the recesses provided.  Tighten the fasteners to the torque specified in Table-5.

6.13  If additional grease is required, replace one grease plug with a grease fitting and remove the second plug.  With the plugs oriented 180˚ apart in a horizontal position, fill until grease comes out of the second opening.  Then replace the plugs.

6.14  Make sure grease plugs are in place.  Start the equipment and operate with the coupling in place for several minutes. Stop and recheck fastener torques and inspect the coupling for any grease leaks or other abnormalities.

What is the difference between Horizontal and Vertical Grid Couplings?

Horizontal Split Cover Grid Coupling

The difference between "horizontal" and "vertical" grid couplings lies simply in two types of split cover designs (and their corresponding cover kits). The grid spring elements and coupling hub technology are the same. 

Horizontal covers are designed for ease of assembly and removal, particularly in tight spaces, as they can be put on after the hubs and grid spring element have been already assembled.

Vertical split cover designs, require putting the split covers on the shaft prior to putting on the shaft hubs and grid spring element. Once the hubs and grid spring element have been attached, the vertical split covers can then slid over the hubs and grid spring element and fastened together. (This also means that to completely remove a vertical split cover off a shaft, the grid spring element and coupling hubs would have to first be removed.)

Vertical Split Cover Grid Coupling

The benefit of the vertical split cover design is that it can operate at a higher maximum speed (RPMs). The Grid Coupling Performance Data chart below (which was extracted from page GD-10 of Lovejoy's Grid Coupling Catalog) has the difference in maximum speed ranges between the horizontal and vertical split covers circled in red. Based on your application, it may be required to go to a vertical split cover design if the horizontal cover design maximum speed is too low. 

Installation videos of Horizontal Split Cover Grid Couplings, Vertical Split Cover Grid Couplings, Full Spacer Grid Couplings, and Half Spacer Grid Couplings are all readily available on Lovejoy's YouTube channel, and formal installation instructions can be downloaded on Lovejoy's Installation Instructions resources webpage.

For additional information on grid couplings, to include grid coupling interchanges, please see the grid coupling product page on Lovejoy's website.
 

How sensitive are Grid Couplings to misalignment?

Grid couplings are very sensitive to misalignment. They are designed to handle almost no parallel shaft misalignment, and only minimal angular misalignment (as called out in the Lovejoy grid coupling rating chart and the coupling pre-selection guide below).

While misalignment must be considered and proactively addresses when using a grid coupling (see Why Lovejoy Offers Shaft Alignment Dial Indicator Kits), there are several major benefits to using a grid coupling. The biggest is that it is an all metallic flexible coupling design that can transmit significant torque in a small footprint (high power density) while also (unlike metallic gear & disc couplings) providing system vibration dampening capability. Grid couplings are a well proven technology, and are readily available from stock from a few leading coupling brands (inclusive of Lovejoy). 

Lovejoy Grid Coupling Misalignment Capacity 

(Standard and Spacer)

	Max Installation		Max Operational		Nominal
	Misalignment (in)		Misalignment (in)		Gap (in)
Size	Parallel	Angular (X-Y)	Parallel	Angular (X-Y)	+/-10%
1020	0.006	0.002	0.012	0.010	0.118
1030	0.006	0.003	0.012	0.011	0.118
1040	0.006	0.003	0.012	0.013	0.118
1050	0.008	0.004	0.016	0.015	0.118
1060	0.008	0.004	0.016	0.018	0.118
1070	0.008	0.005	0.016	0.020	0.118
1080	0.008	0.006	0.016	0.024	0.118
1090	0.001	0.007	0.016	0.028	0.118
1100	0.010	0.008	0.020	0.032	0.177
1110	0.010	0.009	0.020	0.035	0.177
1120	0.011	0.010	0.022	0.040	0.236
1130	0.011	0.012	0.022	0.047	0.236
1140	0.011	0.013	0.022	0.053	0.236

While the power density of a grid coupling is enviable, one final drawback to consider when selecting a grid (or gear) coupling is the fact that it requires lubrication (grease). Unlike elastomeric flexible couplings (which generally also provide system vibration dampening capability at lower power density levels), this means your maintenance team will need to periodically re-grease the coupling through the lubrication ports on the coupling's cover and be careful to avoid and/or properly address any grease leakage environmental concerns.

Alternatives to grid couplings include disc couplings (see Why to Switch from Grid to Disc Couplings), which avoid lubrication concerns but do not offer the grid coupling's level of vibration dampening, and jaw in-shear couplings (see Jaw In-Shear Couplings - A Straight Forward Value Add) which avoids lubrication but has a lower power density.