Kop Flex Logo




Figure 1

Product Cross Reference


The traditional paper machine drive train for fixed rolls consists of a motor connected to a reducer with a close coupled gear type coupling. The reducer is then connected to the paper machine roll with a floating shaft gear coupling (sometimes referred to as a jack-shaft). These couplings transmit the motor torque to the roll while accommodating any shaft misalignment through sliding friction between the coupling teeth. The resultant sliding friction between the coupling gear teeth will require coupling lubrication and re-lubrication on an ongoing basis. In the increasingly competitive global paper market, there is a need to reduce maintenance cost and improve machine reliability. With that in mind, the elimination of lubricated couplings on the paper machine drives will definitely provide a maintenance cost reduction – not to mention reducing unscheduled machine downtime when lubricated couplings fail.


Gear Coupling Maintenance Challenges:

The traditional gear couplings are plagued with a number of maintenance issues:



Figure 3




Figure 2






Figure 4

A. Lubrication
The gear coupling accommodates shaft misalignment through the sliding of the hub teeth across the sleeve teeth as the coupling rotates. This tooth sliding occurs twice per revolution. Lubrication, generally in the form of grease, is required to reduce this sliding friction. In addition to the initial greasing, couplings have a tendency to lose lubrication so regular relubrication is required.


As the gear coupling rotates there is a centrifugal force created within the coupling. This centrifugal force forces the coupling grease past the “O” ring seal in the coupling sleeve. The expelled lubrication is thrown inside the coupling guard and onto the plant floor causing an environmental concern which must be cleaned up regularly (Figure 3).


Figure 4 is a gear coupling with a broken lubrication fitting. Here you can see the lubrication coming out of the broken lubrication fitting and being sprayed inside the coupling guard. At some point the coupling will run dry, gear teeth will fail, and unscheduled downtime will result.


As mentioned before, there is a centrifugal effect within the coupling caused by the rotation. (Figure 5) As the coupling teeth wear, very fine wear particles are in suspension within the lubrication. These particles have higher specific gravity than the lubrication and under centrifugal force are thrown to the outer diameter of the coupling lubrication cavity. Coincidentally, the coupling teeth are located in this same area. The wear particles are then lodged around the coupling teeth.


When lubrication is added, the new grease generally stays in the center of the coupling and the old grease with particles is not purged out. (Figure 6) Through time the wear continues; the wear rate begins to increase based on the increase of wear particles. The end result is premature coupling failure - even when new grease has been added on a regular basis.


To correct this situation, the couplings must be disassembled and the old grease washed out. In many cases, a very difficult task - the equipment shaft is not long enough to slide the outer coupling sleeve back and expose the working teeth for washing.


Figure 5



Figure 6


B. Backlash

There is a backlash between the hub tooth and the sleeve tooth. This backlash is designed to allow the hub teeth to bend between the sleeve teeth, to provide for angular misalignment between the connected shafts. It is interesting to note that when the alignment is good the amount of backlash is at its highest level. In most facilities, the operating speed of the paper machine has increased over time. Subsequently, older D.C. drives are being replaced with newer AC drives with digital controls. These new drives and controls sense roll speed change in milliseconds and adjust roll speed to maintain tension. The accuracy of these drives can sense the backlash in the gear couplings and try to correct for it. This is referred to as drive hunting and in many cases, the drive needs to be de-tuned to reduce the hunting.

C. Heat & Humidity

In the dryer section of the machine, one end of the floating shaft coupling is often located inside the dryer hood. Inside the dryer, the hood is additional environmental challenges, including high heat and humidity. The high heat coupled with high humidity has an adverse effect on the coupling seal and lubrication properties, resulting in coupling failure of the roll end coupling - while the reducer side coupling is still functioning.

D. Visibility

Perhaps the most significant challenge with gear couplings
is that the condition of the teeth cannot be determined without
shutting the machine down and disassembling the coupling.
In many cases, the short equipment shaft makes it impossible
to slide the sleeve back to expose the coupling teeth to check
for wear. Inspection of gear coupling is very labor intensive and
is not always carried out on routine bases. Subsequently, the
end result is coupling failure and unscheduled machine downtime.


The Solution: Kop-Flex® Disc Couplings

A Kop-Flex® disc coupling (close coupled on the motor or floating
shaft design to the roll) has several advantages over a gear
coupling in paper machine drives. These advantages include:


  • Lubrication is not required.
  • They are dynamically stable.
  • They have no backlash.
  • They are not adversely affected by heat and humidity.
  • Perhaps most importantly, the disc coupling’s condition
    can be inspected while the machine is running.

The Kop-Flex® disc coupling utilizes a unitized disc pack assembly. The disc pack consists of a number of thin stainless steel “scalloped” discs, the design of which
reduces the bending force on the connected shaft bearings when misalignment occurs. The discs are assembled on a bushing and held together on each end with
a beveled washer.

Unlike a gear coupling that accommodates misalignment through friction, the disc coupling accommodates misalignment through flexing. Therefore there is no
requirement for lubrication and the disc coupling is truly maintenance free.


The Kop-Flex® disc coupling components are manufactured on modern CNC equipment. The various bolt circles which connect to the disc packs are held
to a very tight concentricity tolerance to help ensure that when assembled all coupling components run concentrically to improve the coupling dynamic stability.
Kop-Flex® disc couplings are manufactured to meet or exceed AGMA Class 9 Balance Standard as manufactured.


During operation, the coupling disc pack can be inspected with the use of a strobe light or a digital camera without shutting down the equipment. This allows
maintenance staff to inspect couplings on production days, not just down days.


Warning: Do not operate equipment without guards in place. Be sure to adhere to all applicable local safety requirements.


The disc pack can also provide an indication of load that the coupling is transmitting and the misalignment condition the coupling is working under.



Figure 7


Figure 8


Figure 7 is a disc coupling actually operating at 3,800 RPM
on a blower application. In this image the disc pack is
perfectly straight which suggest the alignment is very good.
In Figure 8 we can see that the disc pack is flexing which would
suggest there is misalignment present and it should be checked
at the first available opportunity

This name is used, please enter another
{0} was created successfully.
{0} was deleted successfully.
New password and confirm password do not match.
The password entered does not comply with our password policy. Please try again.
The password entered does not comply with our password policy. Please try again.
You have already access to entered account.
Account already added
Your selected account has been changed probably in different window. Please refresh page and select correct account.
Please select an account
The entered account number is not valid or the account is not yet transitioned for use at Regalrexnord.com.
You must provide a valid account number to be added. Please contact your Sales Representative or Account Administrator if you don’t know your Account Number.
Please select Additional Access checkbox.
Please enter your address.
Please enter your address cont.
Please check to agree with Terms of Use and Privacy Policy.
Please enter your city.
Please enter your company name.
Please enter confirm password.
Please select your country.
Please remove the discontinued item from cart to proceed to checkout.
Your order contains discontinued items. Please remove from cart and proceed with rest of the items.
Please enter a valid format for your email address.
Email address required
Please enter your email address.
Please enter your first name.
Please review and select a warehouse for Catalog/Part Numbers: {0}
Please enter your job title.
Please enter your last name.
Please note: Your order contains Made to Order (MTO) items. Return requests on MTO products are subject to review and not guaranteed.
The current password entered does not match your password or new password is the same like one of the previous or password changed last 30 days.
Profile updated successfully.
Error while request access.
Registration Information has been received.   Thank you for your interest in Regal Rexnord.
Please enter new password.
Please enter old password.
Please enter a valid format for your phone number.
Please enter your phone number.
Please enter a valid format for your extension.
Please select at least one product category.
Please verify you are not a robot.
Registration Information has been received.   Thank you for your interest in Regal Rexnord.
Internal users can not request access for customer accounts. If you need access, please route through the customer service representatives.
You must provide the name of a Regal Rexnord employee who can confirm your need for access to Genteq technical documents.
Please make sure you enter Sales Order, Quantity, Reason, Part number, Invoice and Line Number fields.
Error submitting request.
Your request has been submitted successfully.
Please select your state.
Please select the training portal role.
This email is already in use. Please log in.
You do not have permission to access this page.
Confirmation code has been sent successfully to your new email address. Please enter the Confirmation code and update the profile.
Email Address has been changed successfully. Please check your email for information to login again.
Verification code required
Please enter your zip code.
Your session has timed out. You must log in again to access secure content. Any work on the current page will be lost.
Your shopping cart qualifies for free shipping.
Minimum order quantity is {0} {1}. Please enter a valid quantity for item: {2} .
Item must be ordered in multiples of {0} {1}. Please enter a valid quantity for item: {2} .
Add {0} more to your cart to qualify for free shipping.
Selected shipping date is on holiday. Please select REQ Ship Date.
Item {1} has been removed from cart.
You cannot delete Mod Product- {0}.
Add {0} more to qualify for free shipping.
This item is discontinued, but you may order against the remaining inventory. You have requested {4} items of the total remaining quantity of {2}.
The following item(s) have been added to your cart: {0}
Request of quotes should allow items in same segment
Please enter Application.
Competitor Requied.
Please enter Country.
Please enter Email Id.
Please enter Quote Estimated Annual Quantity.
Uploaded file is not supported, File upload supports word, excel and pdf.
File too Big, please select a file less than 20mb
Please enter FrameSize Validation.
The item you have entered have no business segment.
The item {1} allow maximum {0} quantity.
The item {1} requires a minimum of {0} quantity.
Please enter Output HP.
Please enter Quote Quantity.
No facet available for this product line
Please enter Required Specifications.
Error submitting request.
Your request has been submitted successfully.
Please enter valid product.
The item {1} must be in multiples of {0} quantity.
The {0} you have entered was not found. Please revise.
Please enter Speed (RPM).
Please enter Voltage (V).
File size requires longer download time
File is not found. Please try again or contact customer service.
Check Inventory
Compare Product
Some of the documents are missing. Please review.
Sorry, at this time this product does not comply with the standards of the country you selected.
This product complies with the standards of the country you selected.
One or more items added to your cart are not eligible for return.
I agree to the Terms of Use and Privacy Policy * is required.
Email has been sent successfully
All estimated shipping dates have a local warehouse cutoff time for shipment date shown. This time is displayed to the right of the date.
The account you are currently on does not have access to purchase this product. Please change to your {0} account to purchase.
Key Features
The following item(s) have been moved to {0}: {1}
Quantities over {0} may require additional lead time. A Regal representative will contact you if this occurs.
You can only order in multiples of {0}. Please enter a valid quantity for this item.
You have no products selected for comparison. Please select at least two products to compare using the 'Add to Compare' checkbox found on product list pages or product detail pages.
Sorry, this item is no longer available.
Product Specs
Related Products
Resource Center
Out of stock. This product is discontinued and no longer available for sale.
The item requires a minimum order of {0} pieces.
The item requires a minimum order of {0} {1}.
The item must be ordered in multiplies of {0} pieces.
The item must be ordered in multiples of {0} {1}.
Commercial Systems|Industrial Systems