S-Flex (Sleeve) Couplings: Failure Analysis

S-Flex Sleeve couplings are subject to many failure modes similar to other coupling types. Starting with the metallic hubs, excessive peak torques can cause keyway bursts... which would be a weak point in the hub and, barring a material defect, the most likely place it would fail.

Moving to the elastomer, similar to jaw couplings, an S-Flex sleeve can be degraded if exposed to environmental conditions it was not designed for (i.e. - excessive heat, cold, or chemical exposure).

Standard S-Flex Sleeve

Where failures get particularly interesting/unique for S-Flex couplings is with sleeve failures themselves. The signature failure for an over-torqued S-Flex coupling will be a diagonal tear (clear evidence of excessive wind-up) across the width of the elastomer.  In such a circumstance, a user would likely be well served to upgrade to a stronger elastomer and/or upgrade to a more torque intensive coupling (either a larger size or different design). 

A second failure mode in an S-Flex elastomer is a straight tear that runs parallel to the coupling flanges. Such a tear demonstrates either elastomer fatigue that can be attributed to misalignment, the flanges being too close to the elastomer (with them pressing in on it).

The third and least understood of the elastomer failures are when the teeth of the elastomer wear away (often on one side). At the highest level, it must be understood that S-Flex couplings are designed to accommodate misalignment through the flexing of the elastomer itself and that the tooth profiles of the elastomer are to be snug and engaging with the coupling's metallic flanges (not chattering). 

If the coupling is oversized for the application (or if there is a poor fit between the elastomer and flanges), and there is not enough wind-up to have the elastomer's teeth fully engaged with the steel flange teeth, torque transmission will be localized to the tips of the elastomeric sleeve, leading to premature tooth wear, chatter, and ultimately sleeve failure. If not detected early enough sleeve teeth can wear away completely, often only on one side, with the sleeve spinning freely inside the given flange.

This last scenario (the coupling being oversized for the application) is particularly vexing to most end user and even power transmission veterans because, across many elastomeric coupling types, a common way to address an elastomer failure is to either upsize the coupling or go with a strong elastomer material. Given the wind-up chatter issue... going to a stiffer material or even more oversized coupling will only exacerbate the problem. 

Lovejoy's Jaw In-Shear Coupling

So... if you are having rapid tooth wear on a S-Flex sleeve, the  first option you might consider is making sure that you cannot either select a softer material or down size the coupling (while still meeting your system's requirements). An excellent second option, particularly if you can't go down a size or switch to a softer material is to switch over to a Jaw In-Shear coupling. Like an S-Flex the elastomer is in-shear, but because it is using a standard jaw coupling the wind-up and chatter issue is eliminated. Furthermore, the product leverages standard off the shelf Lovejoy jaw coupling hubs (making it an affordable solution) and the design has a radially removable elastomer for fast inspection and change outs if/when required. 

For more information on sleeve coupling failures, consider checking out the MPTA bulletin on it (Sleeved Element Failure Analysis - MPTA C8c-2011), which Lovejoy contributed significantly to... or reach out to a Lovejoy application specialist directly. 


To keep learning about S-Flex couplings on this blog, go to:

S-Flex (Sleeve) Couplings: Product Overview

S-Flex (Sleeve) Couplings: Flange Types

S-Flex (Sleeve) Couplings: Elastomer (Sleeve) Types

S-Flex (Sleeve) Couplings: How To Select a Coupling

Article Shout Out: I would like to specifically thank Michel "Mitch" Bouchard of General Bearing Services in Canada for requesting that we cover this question on the blog. If you would like to submit or request a question be addressed on this blog, please fire us off the question here.

S-Flex (Sleeve) Couplings: How To Select a Coupling

While the Lovejoy S-Flex PDF catalog provides the necessary information and data to properly size an S-Flex sleeve coupling, a few things to keep in mind that you will need to know are: 

• Horsepower (HP or KW) and speed (RPM) of the driver and/or torque
• Shaft and keyway sizes of driver and driven equipment
• Application description
• Environmental conditions (such as temperature, corrosive chemicals, space limitations) as well as misalignment expected

Lovejoy's published torque ratings are maximum nominal values, and care must be taken to insure that proper service factors are applied for the application to come up with a design torque. 

This calculated design torque must still be less than the published nominal torque rating. Service factors allow for adequate coupling life given that different types of equipment, even if the torque requirements are the same, will put different stresses and wear on a coupling.

Other critical characteristics to be sure to check before making a final coupling selection include:

• Maximum bore capacity of the flanges (as well as minimum bore in some cases)
• Maximum speed capability of the coupling size
• Resistance of the sleeve to the environmental conditions expected
• Size of the coupling (O.D. and OAL) fits into the "envelope" available

Lovejoy's catalogs also give charts with the specific UPC # (Universal Product Code) for each component of a complete coupling. For help with quickly determining design torque and selecting the proper S-Flex coupling size, consider downloading the Lovejoy iPhone & Android selection app or use a similar tool on your desktop. 

To keep learning about S-Flex couplings on this blog, go to:

S-Flex (Sleeve) Couplings: Product Overview

S-Flex (Sleeve) Couplings: Flange Types

S-Flex (Sleeve) Couplings: Elastomer (Sleeve) Types

S-Flex (Sleeve) Couplings: Failure Analysis

S-Flex (Sleeve) Couplings: Elastomer (Sleeve) Types

S-Flex elastomeric sleeve type flexible couplings come in three different standard material types, as well as single piece, split single piece, and split two piece designs.

Materials

EPDM - This is the standard material, a rubber-like compound which has the highest temperature rating (275°F/135°C) of the sleeves available. It provides good resistance to most commonly found chemicals and is not affected by dirt or moisture. This sleeve is a dull black color, can handle 1° of angular misalignment, .010" (size 3) to .062" (size 16) parallel misalignment, up to .124 inches axial misalignment, and up to 15° torsional wind-up.

NEOPRENE - This material has better chemical resistance than EPDM, especially to oil, but is rated only for a max. temperature of 200°F (93°C). The color of the sleeve is black with a shiny finish and a green dot for easy identification. The Neoprene and EPDM sleeves have the same torque rating, misalignment ratings, and wind-up rating.

HYTREL - This is a polyester elastomer designed for high torque and excellent chemical resistance. It carries four times the torque of the EPDM/Neoprene materials but is limited to ¼ ° angular misalignment and parallel from .010" (size 6) up to .035" for size 14 couplings. The Hytrel material is orange in color, with torsional wind-up up to 7°. When using this coupling, care should be taken to ensure the coupling is not over-sized and some wind-up occurs (otherwise tooth chatter could lead to premature elastomer wear and failure).  

 

Sleeve Designs 

 
One-piece solid - The one piece solid sleeve design is noted as the JE (EPDM), JN (Neoprene), and H (Hytrel) types, and is generally the least expensive of the rubber sleeves. It is available in sizes 3-10 for JE, 3-8 for JN, and 6-12 for H.

One-piece w/split - The one-piece split design is noted as the JES (EPDM) and JNS (Neoprene) types. This design is used for applications where the shafts are positioned closely together and the sleeve must be "peeled away" for replacement. The design is stocked by Lovejoy in sizes 3-9 for JES, and 3-8 for JNS.

Two-piece split - The two-piece split style sleeve is made up of two completely separated halves. For the E (EPDM) and N (Neoprene) styles, a retaining ring is used to prevent the sleeve from extruding outward under speed. The H (Hytrel) is such a rigid material that the ring is not necessary. The E sleeve is available for size 5-16 couplings, the N sleeve for 5-14, HS for 6-14. This design is popular given its ease of installation and replacement.

 

 

Bulk Packs

For high usage customers, the JE, JES, and E sleeves are available in the most popular sizes in bulk packs of 5 or 10 pieces. 

To get technical information on S-Flex couplings, please visit Lovejoy's S-Flex product page, or download the PDF catalog. Additionally, installation instructions and installation videos can be accessed here. 

To keep learning more about S-Flex couplings on this blog, please see:

S-Flex (Sleeve) Couplings: Product Overview

S-Flex (Sleeve) Couplings: Flange Types

S-Flex (Sleeve) Couplings: How To Select a Coupling

S-Flex (Sleeve) Couplings: Failure Analysis

S-Flex (Sleeve) Couplings: Flange Types

The S-Flex (sleeve) coupling has 5 primary flange types, each with their own benefits. 

J Type

J Type 

The first four sizes of flanges (size 3J to 6J) are available in this type which differs from the S Type in that the J Type does not have as great a length-thru-bore. This is due to the absence of a projection in the cast material on the J-type flange at the inner face. Thus, where both J and S flanges are available (sizes 5 and 6 couplings), the S flange has a greater maximum bore capacity than the J.  

This flange is very economical and provides a coupling which is only slightly more expensive than a comparable jaw coupling. Due to the high torque of the Hytrel sleeves, the J-type flanges can only be used with EPDM or Neoprene sleeves.

S Type (with E Sleeve)

S Type 

The S Type covers the 11 coupling sizes from 5S through 16S. These flanges all have the projection at the inner face of the casting which provides for greater shaft engagement. The S-type flanges can be used with any of the sleeve materials.
 

B Type 

The B Type flange is modified to accept the industry-standard QD bushing, and is offered in sizes 6B through 16B. The use of bushings limits the bore capacity of the coupling, but provides a very firm grip on the shaft and can simplify the stock room of many customers (if they use bushings on other power transmission components). Due to the torque limits of the QD bushing, B Type flanges cannot be used with Hytrel sleeves. 


T Type 

Similar to the B Type for QD bushings, the T Type is a standard flange modified to accept the style of bushing called Taper-Lock.  There are two ways to mount the bushing to the flange, from the serration side (Rear) or from the same side of the flange as the shaft is inserted initially (Front). We call these versions the TR for Taper-Lock/Rear and the TF for Taper-Lock/Front. Be sure to determine if the bushing being used has either UNC threads (which have a 60° thread angle) or B.S.W. (55° thread). As with the B Flanges, the T Type cannot be used with Hytrel sleeves due to the limits of the Taper-Lock bushing ratings.
 

SC Type Coupling

SC Type

These meet standard API (American Petroleum Institute) spacing requirements for pump disassembly. One of the other benefits to the S-Flex spacer couplings is that the various components can be mixed/matched in combinations to achieve dozens of other shaft separations beyond the API standards of 3 1/2", 5", and 7". 

SC Type Flange

The SC Type spacer coupling is achieved by using a Spacer Flange (with nomenclature such as 8SC35 or 8SC44) to which is bolted a Spacer Hub (8SCH for example). There are usually three lengths of Spacer Flanges available in each size coupling. The Spacer Hub has the finished bore and keyway for the driver/driven shaft. Each half of the full spacer coupling uses a Spacer Flange/Hub combination. Half-spacer couplings are possible, as well as combining different lengths of Spacer Flanges.

SC Type Hub

S-Flex spacer couplings are available from size 5 through size 14 couplings. Any of the sleeve materials can be used with the SC Type coupling. The Spacer Hub is bolted to the Spacer Flange with four hex head cap screws. By removing these screws, the center section of the coupling can be dropped out.

To get technical specifications fo S-Flex couplings, please visit Lovejoy's website product page or download the S-Flex pdf catalog. Detailed installation instructions and videos for these products can also be found here. 


To keep learning about S-Flex couplings on this blog, go to:

S-Flex (Sleeve) Couplings: Product Overview

S-Flex (Sleeve) Couplings: Elastomer (Sleeve) Types

S-Flex (Sleeve) Couplings: How To Select a Coupling

S-Flex (Sleeve) Couplings: Failure Analysis

S-Flex (Sleeve) Couplings: Product Overview

The S-Flex (Sleeve) coupling is a coupling type that Lovejoy has been selling since 1985, and one that has very strong acceptance in the US pump industry. While this coupling has gained acceptance in other applications and in other parts of the world, the US pump industry (and especially the ANSI chemical process pump segment) remain its strongest core market.

Much like Lovejoy's signature jaw coupling (Lovejoy was the patent holder for the straight jaw coupling), the S-Flex is simple three part design.  A standard coupling is comprised of 2 flanges and 1 sleeve.  Unlike a standard jaw coupling, the sleeve of an S-Flex coupling is in-shear between the two flanges, with teeth around its perimeter which mate to corresponding teeth in the flanges (much like a gear coupling). The torque is transmitted through the twisting of the elastomeric sleeve. There are several features to this coupling which translate into tangible benefits to the user:

• As with other elastomeric couplings, it is maintenance-free and non-lubricated.
• Since the design is double-engagement, it is very soft radially. It provides very low reactionary loads when misaligned which protects bearings/shafts.
• The torsionally soft design of an in-shear elastomer helps to damp out most peak overloads and prevent vibratory torque from going back to the driver. The EPDM and Neoprene sleeves will twist as much as 15° at full torque, Hytrel up to 7°.
• The sleeve has a large open center which allows close positioning of the shafts.
• The in-shear design allows the coupling to act as a "fuse" to protect the driver and driven from torque spikes or system overloads which might cause more expensive damage than just a replacement sleeve. The torque overload capacity of this coupling is only 3 or 4 times the rated torque (the point at which the sleeve will tear, round-off the teeth, or "pop out"), versus the 6 or 7 times for a jaw coupling.

The S-Flex style of coupling is best suited in the following applications:

• Where coupling alignment may be hard to maintain over a period of time. The S-Flex is a somewhat forgiving coupling and will not load the bearings due to misalignment. The sleeves won't last as long but the coupling doesn't harm the equipment.
• Non-piloted pump applications, where the motor and pump are on a base plate but there is no pump mounting bracket involved.
• Closely coupled shafts.
• For shafts that are relatively small for the torque loads or the bearings are light duty.

Care should be taken however, that S-Flex is not used under the following conditions:

• High-inertial loads, especially if they produce variable torque loads.
• Where overloads/spikes are expected to be greater than 2x nominal ratings.
• Any reciprocating engine driven equipment. S-Flex does not respond well to torsional vibrations. This applies to reciprocating pumps and compressors as well.
• Do not select this coupling if it is used at anything less than 25% of its rated torque. The sleeve teeth will wear prematurely due to the rubbing action against the flange if too lightly loaded. This can be a concern particularly with the Hytrel sleeves since they have such high ratings.

In general, the S-Flex coupling will work well on electric motor driven applications with uniform loads such as; centrifugal pumps, blowers and fans, screw compressors, some conveyors, line shafts, and vacuum pumps. It competes primarily with other elastomeric designs such as tire types, jaw couplings, as well as Grid spring couplings for some pump applications.

The major manufacturers of this design all produce their product to be broadly dimensionally interchangeable. However, since the design has quite a few "mating" points with the sleeve/flange teeth, the possibility of imperfect fits from one manufacturer to another is always possible. This is due to the tolerance that is built into each company's initial design criterion (i.e. how tight or loose they want the fit between components to be), and the state of wear of the tooling that produces the sleeves and flanges. Furthermore, rubber quality/performance does vary between manufacturers. As such, Lovejoy recommends that mixing of components from different manufacturers be avoided if at all possible. This also assures that the product warranty is not voided.

To keep learning on the blog, go to:

S-Flex (Sleeve) Couplings: Flange Types

S-Flex (Sleeve) Couplings: Elastomer (Sleeve) Types

S-Flex (Sleeve) Couplings: How To Select a Coupling

S-Flex (Sleeve) Couplings: Failure Analysis

To get Lovejoy S-Flex technical data, part numbers, or download a product catalog, please visit Lovejoy's product page, where you can download catalogs, search for part numbers, and click through to watch installation videos. 

The Many Benefits of Power Transmission Distributors

Lovejoy has long been an active member of the Power Transmission Distributors Association, and been a loyal supporter of the mechanical power transmission distribution channel going back to its earliest days (several generations ago). Since this time, Lovejoy has expanded its product line, and joined the Fluid Power Distributors Association and our German operation has joined the European Power Transmission Distributors Association.

Taking it one step further, Lovejoy had designed its website largely to be a funnel for its trusted distribution partners. While the website is rich with content data, and it is Lovejoy's hope that users find any and all content they need... Lovejoy also puts prominent "Find a Distributor" buttons on nearly every page of its website as well. The goal is for end users to find the information they seek, and then be immediately able to find a distributor in their area that can help them.

So... the question remains, why does Lovejoy value its partnerships with local distributors so much?

While I could go on for a while, the short/distilled answer is customer awareness and engagement. Distributors have a wide selection of products and solutions that far exceed Lovejoy's high quality of solutions, and they also have the opportunity to readily and completely go out and see/understand an end users complete application.

At the end of the day, Lovejoy understands that its end users really aren't buying simply a component... but rather system up-time and reliability. As such, having strong distribution partners in the field who can eat, breath, and literally live to serve a given end user... and who completely understand the challenges and history of a given end users applications... are invaluable to Lovejoy, and we are honored to be partnered with them. 

The internet may be making information gathering much more accessible to end users, which is great (and Lovejoy's website continues to see increased traffic)... but the internet cannot replace the value of a well-rounded and seasoned brick and mortar distributor who can go out and really become an integral part of an end user's team. 

To elaborate on this point, given the internet age and end users increasing ending up on manufacturer websites, I believe it is critical (for both distributors and their manufacturing partners) that value adding distributors ensure they are well represented on their trusted manufacturing partners' websites.

More than ever a manufacturer's website is becoming their brand, and, given how important distributors are for maximizing value to our end users, we believe it is critical that we highlight and go to great lengths to encouraging end users visiting our website to reach out to our highly valued and trusted distributor partners. (For more on the topic of manufacturer websites, I wrote an article that was recently published in Industrial Distribution magazine that may be of interest to you.)

Going back to the question, to end with an example, if you are a steel mill... Lovejoy certainly has plenty of experience selling a variety of couplings into your market... but we do not have experience selling bearings, chain, and many other products that a distributor partner will have. Similarly, we have not lived in your specific facility the way your one or two preferred distributor partners have. This same logic applied to almost any and every industry Lovejoy serves... be it paper mills, or power generation, or logging... 

To find a Lovejoy authorized distributor located just miles from you who is ready to become a lifelong partner to you and your organization, please check out the Lovejoy "Find a Distributor" tool.

PTDA Manufacturer Website Support Levels - By The Numbers

For at least as long as I have been a part of it, the Power Transmission Distributors Association has seen no shortage of manufacturers anxious and interested in joining. However, what has been missing, both in manufacturing applicants and a surprising number of current manufacturing members, is universal manufacturer excitement in recognizing their distribution partners online. 

It was this lack of enthusiasm, particularly among current PTDA member manufacturers, that inspired me to write an article titled "Partners, Opportunists, & Competitors: Why It's Time to Start Caring About Supplier Websites" in the January/February edition of Industrial Distribution magazine. 

Taking the article one step further, I wanted to quantify the issue/opportunity for the greater benefit of the members of PTDA, not to name and shame, but rather to foster awareness and hopefully jump-start conversations that will lead to renewed trust and stronger relationships. It is obvious to me that there exists a significant number of underlying trust issues, and addressing this opportunity falls not just on one company or one set of companies but the entire association working together. I see it as incumbent on each PTDA member to develop ideas and concepts that will preserve and enhance future trust between distributors and their suppliers in ways that will allow each to recognize and celebrate the other to product end users... be it online, over the phone, or in a print catalog.

How Did You Quantify the Issue? 

I manually visiting the webpage of every one of the 193 PTDA member manufacturers currently listed on the PTDA website (as of February 15, 2015), reviewed each site's content, and, based on what I found, placed each website into one of three broad buckets: "Partners", "Opportunists", or "Competitors".

PTDA Manufacturer Website Support Levels

Website Partners - If I could find a "Find a Distributor" tool or a list of distributors on a manufacturer's website AND I could not find evidence of open direct sales (a web store with pricing and a shopping cart that does not requiring a log-in to check out)... I recorded the company as a "Partner".

Website Opportunists - If I could find no evidence of either a "Find a Distributor" tool or list AND no evidence of open selling on the site, I categorized the company under the broad "Opportunist" bucket. (Note: I recognize every for-profit business is technically an "opportunist", so perhaps I could have come up with a better name such as "non-collaborator"... but this was the original term I used in the article so I've stuck with it for consistency.) Bottom line, these are PTDA manufacturers that, for whatever reason, do not highlight individual distribution partners on their website.

Website Competitors - Lastly, if I found evidence that the manufacturer was openly selling direct (without requiring a log-in) on their website, I categorized the company as a "Competitor".

Website Partners (37.3%, 72 of 193)

Starting with the good, of the 193 listed manufacturer companies, 60 companies had a "Find a Distributor" tool, and a further 12 offered a list of distributors.

These companies tended to be the mid-sized to larger companies (though there certainly were plenty of exceptions). The number of PTDA "Partner" manufacturers is also slightly inflated, as some large manufacturers have several individual member subsidiaries included in the PTDA list of 193 manufacturers, and fell into this bucket several times.

Website Opportunists (56.5%, 109 of 193)

For more than half of all PTDA member manufacturers, I could not find any evidence (at least from their homepage) of any list or tool recognizing the distributors they work with or prefer.

Many of these manufacturers did have the PTDA badge on their website (some of which did have a live link back to the PTDA website)... but these sites appeared geared primarily to getting end users excited about their products and "Request a Quote Now" appeared to be the primary call to action on these sites.

Of the 109, they fell all over the spectrum... with some leaning both dangerously close to "Competitors" and others apparently fairly supportive of distribution (despite not listing any recommended distributors).

Within the 109 websites, it is certain that I missed seeing something... and that at least a few of these should have been categorizes as either a "Supporter" or "Competitor". However, even given these adjustments... I would expect the overall result/conclusion remains the same: More than half of all PTDA member manufacturer members are currently not recognizing any individual distributors on their website. 

(This is a widespread issue/opportunity.)

Website Competitors (6.2%, 12 of 193)

Given my limited search, I found that at least 12 PTDA member manufacturers were selling on their website direct... and I say "at least" because I often did not find out that the manufacturer was selling direct until I searched for and found a product several pages into their website (meaning it's entirely possible that I missed a few others who are also selling direct). 

Of the 12, 8 had no reference tool or list of distribution partners... but, surprisingly 4 did (giving "Competitors" about the same percentage of "Find a Distributor" participation as non-open selling manufacturers). Three of these direct sales manufacturers offered a "Find a Distributor" tool, while the fourth provided a list.

And Why Does All This Matter Again?

To summarize the article I published in just a single chart:

Sample PTDA Manufacturing Member Website Traffic Growth from Organic Search Engines

Lovejoy is like many other leading mechanical power transmission companies, a single digit growth company. However, as more and more end users turning to finding solutions online, Lovejoy's organic web-traffic has far exceeded sales... growing by over 250% in the last 5 years.

This is not only a Lovejoy trend, but a worldwide trend... and one that shows no sign of slowing. As such, it is more critical now than ever that those who support the distribution sales model clearly and consistently communicate this to our user base (who are increasingly engaging with us online).... but currently this isn't happening with more than half of PTDA's manufacturing members. Only about one-third of PTDA's manufacturing members are actively helping connect their website visitors to their preferred distribution partners.

What Next?

As an association, how does PTDA respond to this trend? What best practices and tools can PTDA member manufacturers (many who support distribution but may be scared of losing business by promoting distribution on their website) be equipped with that will both better show support to distribution and minimize risk that website visitors end up buying a competitor product?

Among the 72 current "Partner" manufacturers, I found several fantastic "Find a Distributor" tools. Some were quite innovative and may go some way towards encouraging additional manufacturers to add a tool... so I will look to add a few of those to this blog in the coming days... but this is certainly not an issue that just a few people can solve in isolation.

If you have any thoughts, ideas, or feedback on how PTDA as an organization can encourage and support manufacturers to recognize their distributor partners online (especially if you are one of the many manufacturers currently not doing so)... please share those either in the comments section on this blog post below (starting what will hopefully be a healthy public dialogue) and/or send me a private message on LinkedIn. My hope is that, given enough awareness and dialogue, answers will be found.... and distributors and their supplier partners will have stronger and richer relationships.