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.)

Popular Jaw Coupling Option - The Snap Wrap Spider Limits Downtime

Changing out an insert from a jaw coupling can be fairly easy or a time consuming process.  A lot depends on the area around the coupling and the ease of access.  Many customer applications have the coupling placed in a restrictive area, which requires a major effort to dissemble the coupling and change the wearable spider insert.  Sometimes the connecting equipment has to be physically moved so that enough clearance is available to move and flange/hub enough so that the spider/sleeve can be replaced.  This is where the Snap Wrap (SW Type) style spider offers a time saving solution!

The Lovejoy Snap Wrap insert has been part of the Lovejoy Jaw product line up for years, but is sometimes forgotten as a solution to easy element replacement.  The spiders are available in the standard Buna-N material, which gives customers the maximum dampening benefits of all of the spider/insert materials.  This design also provides a fail-safe coupling connection that allows torque to be transmitted a short time even after the spider has failed.  The main benefit of the Snap Wrap is that the collar or snap ring that holds the spider in place can be removed and the spider can be replaced without moving either hub.  This feature allows downtime to be kept at a minimum during spider replacement.

The Snap Wrap spider is available in several popular Lovejoy Jaw coupling sizes from L090/095 to L190.  The torque capacities for the Buna-N Snap Wrap range from 144 to 1,728 in-lbs.  The Snap Wrap design is another example of Lovejoy providing the best coupling fit for every application.  

Note: The Snap Wrap is limited to a max RPM of 1750. For increased speeds of up to 3600 RPM, a similar fail-safe jaw coupling design with a collar attachment is available. This coupling type is called an LC Type (pictured at left), and consists of one standard L Type hub, one LC Type hub (which provides collar attachment), one standard snap wrap center, and one collar with screws. And for a non-fail safe design, consider the Jaw In-Shear coupling, which also make use of two common L line hubs.

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.).

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.).