Jaw In-Shear Couplings - A Straight Forward Value Add

While Lovejoy's straight jaw coupling is robust, ubiquitous and economical... is is also fail safe & requires no grease/maintenance free. (Fail safe means that if and when the elastomeric spider fails, torque will continued to be transmitted as the jaws of the two hubs interlock directly. Requiring no grease means both greatly reduced environmental leakage risk, which may not be true for grid or gear couplings, and no periodic re-greasing required.)

While being fail safe is great in some applications, is not desirable or valuable for all applications. Additionally, the traditional jaw coupling requires that at least one of the two hubs to be pulled back to replace the elastomeric spider. (Note: There is a fail-safe Snap Wrap version that enables spiders to be radially replaced without moving the hub for lower speed applications.)

The Jaw In-Shear Coupling (pictured right) is a straight forward 4 piece non-fail safe design (meaning the coupling will no longer transmit torque if/after the elastomeric element fails) that is optimized for quick elastomeric element replacement (with neither jaw coupling hub being required to be moved). 

Because the coupling is non-fail safe, the coupling behaves similar to a non-calibrated fuse to prevent equipment damage in the event of torque overloads. (Note: Elastomers are not rated or designed to fail at a specific torque level, so other methods such as rated shear pins or torque limiters should be used if a true fuse is required.) Instead of the spider being compressed between interlocked jaws of each coupling hub (a traditional jaw coupling configuration), the Jaw In-Shear coupling has the hubs drawn apart with jaws aligned axially. The wide spider is thus in a shear-plane.
 
Jaw In-Shear elastomeric spiders, being radially removable, results in saved maintenance time and money. The coupling's retaining ring encloses and secures the In-Shear Spider, using an intuitive twist-lock design that will not work loose and requires no fasteners. Furthermore, the Jaw In-Shear uses Lovejoy's industry-standard L-Type and C-Type jaw coupling hubs which are both cost effective, and quite possibly already installed on the equipment (meaning a retrofit cost will be reduced to the Jaw In-Shear elastomeric spider and retaining ring. The Jaw In-Shear spider is made from a tough Urethane formula offering high durability, chemical resistance, temperature range, and torsional softness. Jaw In-Shear coupling designs are available for jaw coupling hubs with max bores up to 9.0 inches (229 mm) and 183,333 in-lbs (20,714 Nm). 

 

 

Common applications for Jaw In-Shear couplings include rolling mills (pictured at right), electric motors to centrifugal pumps, fans, blowers, gear boxes, and plastic extruding machinery. The Jaw In-Shear solves many maintenance problems and creates on-going savings & environmental risk reduction opportunities in industries like pulp & paper, petrochemical, mining and steel.

Recommended Follow-On Reading: For a full review of jaw couplings, and additional commentary on Jaw In-Shear couplings, please read: Jaw Coupling Overview - Features & Benefits, Design Basics, and Element Options

Jaw Coupling Question - "How Much Life Can I Expect Out of the Spider?"

 

A frequently asked question for jaw couplings is: “How much life can I expect out of the spider?”.  The answer to this question is, unfortunately, nearly impossible to determine.  

Spider life is affected by a variety of factors (i.e. high/low temperatures, chemical exposure, operation cycle of machinery, etc).  Lovejoy does provide advice on spider inspection and replacement.  When the spider’s leg volume or thickness is at 75% of the original volume or thickness the spider should be replaced.  Inspection of this can be done visually and will result in disassembly of the coupling only if the spider needs to be replaced. 

Correct installation of a jaw coupling can greatly increase the life and performance of the elastomeric spider.  The installation process starts with the correct coupling selection.  The selection process starts with collecting the proper information about the application.  These factors would include: horsepower, RPM, shaft sizes, the type of driver/driven equipment, type of chemical exposure (if any), and temperature exposure.  After selection, proper installation and alignment are also key factors.

• For installation and alignment instructions: please check out "How to Install a Coupling" or download installation instructions from your favorite coupling manufacturer's website. Instructions should be step-by-step straightforward and speak specifically to your jaw coupling type (straight jaw, curved jaw, spacer jaw styles, and jaw in-shear, etc.)
• To learn more about coupling selection criteria, please check out "Top Ten Factors for Selecting A Coupling".
• For help with calculating required system torque, check out "Coupling Sizing Torque - How to Quickly Calculate (inclusive of Service Factor)".

Jaw couplings are not only one of the most popular and economical flexible coupling solutions in the world, but they also offer a solution that does not need lubrication.  This can be a tremendous time saver, but low maintenance couplings does not mean no-maintenance!  By following the helpful tips above (and two robust articles recommended below), coupling users can ensure that their jaw couplings are in proper condition and avoid unexpected downtime.

Recommended Follow-On Reading: For a robust report on jaw coupling failure analysis, please read: Coupling Failure Analysis - Jaw Couplings (includes hub & spider photos). For a broad overview of jaw couplings in general, please read: Jaw Coupling Overview - Features & Benefits, Design Basics, and Element Options.

Author Credit: This article was written by Charlie Mudra (National Accounts Manager, Lovejoy, Inc.)

Jaw coupling spider materials hold the key to solving customer application challenges

Customers are confronted with a variety of different challenges regarding selecting jaw couplings inserts.  With four different insert materials to choose from, several details about the application should be supplied to offer the best coupling fit.  The amount of existing misalignment is a concern when selecting an insert.  Ambient temperature of the area where the coupling will operate is an important part of insert selection.  The amount of torque a particular spider can handle is also a very important factor in selecting the insert material.  By looking at the different inserts available, Lovejoy can evaluate the advantages and disadvantages of each material and select the best fit for the application.

The standard SOX spider or Buna-N material rubber offers the advantage of vibration damping.  The Buna-N also has good resistance to oil and greater misalignment capabilities than Hytrel and Bronze inserts.  Some of the draw backs to Buna-N are its lack of resistance to certain types of chemicals and having the lowest torque rating of all of the inserts.   

Urethane provides customers with better chemical resistance than the Buna-N material and 1.5 times the torque capacity of the Buna-N material.  However, the Urethane material does not dampen vibration as well as the rubber material.   

The Hytrel insert has the advantage of carrying the most torque of the elastomers.  Hytrel also has excellent resistance to many different chemicals and a temperature rating (250^o F) higher than the Buna-N and Urethane inserts.  However, due to the hardness of the material, Hytrel only offers about half the misalignment of the rubber insert and does dampen vibration.   

The Bronze material insert offers the highest temperature rating (450^o F) and has good chemical resistance characteristics.  Bronze also has a high torque rating similar to the Hytrel material.  The main disadvantage of a bronze insert is that it can only be used in applications running at 250 RPM or lower.   

With all of the these choices available, finding out application’s horsepower, speed, type of machinery to be connected, possible chemical exposure, and ambient temperature of coupling’s environment are critical.

By outlining the strengths and weaknesses of each type of spider material, it is clear that one spider does not fit all.  If this were true, there would be only one spider material.  By considering the application information, the best material choice can be made.  The result is the best fit for the application, which results in longer life for the insert. 

Recommended Follow-On Reading: For a more complete perspective on jaw couplings in general, inclusive of a second review of elastomeric spider options, please read: Jaw Coupling Overview - Features & Benefits, Design Basics, and Element Options

Author Credit: This article was written by Charlie Mudra (National Accounts Manager, Lovejoy, Inc.).