Column #5 discussed the reasons that rolls need to be re-ground. This column will deal with the options, after the decision has been made that roll grinding is required. This subject will be divided into two parts, the first will consider only dealing with the roll set, while the second part will deal with the remanufacture of the entire three roll mill (TRM).

As in my previous columns, I would like to offer this invitation and this promise. If you have a question regarding TRMS, please email that question to me (jon.hatz@keithmachinery.com)and I promise to answer it. It is my intension to have your questions drive the content of these columns. And now, here I go with my sixth column.

When the rolls on a TRM need grinding, the owner of the TRM has some basic questions to ask, and choices to make. In this column, the owner has decided to just deal with the roll set. The next decision the owner must make is whether to Rebuild the roll set, or whether the roll set should be Remanufactured. (The photos that accompany this column show a roll set for a Day 14”x30” Mid Production TRM).
 
REBUILT VS. REMANUFACTURED
When the roll set is Rebuilt, all components are made to work correctly, but components will not necessarily be brought back to the original OEM dimension. An example would be how a worn roll journal is handled. In the Rebuild, the worn journal could be machined down to a smaller diameter, and then the gear that rides on that journal, would be bushed, so that it properly fits on that smaller journal. This is a perfectly acceptable mechanical solution. The problem with this solution, is what happens in the future if this gear fails, and it needs to be replaced. A standard replacement gear will not fit.

When the roll set is Remanufactured, all components are brought back to the original OEM dimensions. In the example of a worn roll journal, in a remanufacture the journal would first be machined down to a smaller diameter, and then an oversize sleeve would be fitted onto the journal, and then the journal sleeve would be machined back to the OEM dimension. If a gear fails in the future, the OEM gear will fit the remanufactured journal. (Note: KMC only remanufactures roll sets or TRMS.)
 
 

 
RSJ (ROLL SET JOB)
For this example, the owner decides to do an RSJ, and he also decides to be his own GC. In this case, his employees will partially disassemble the TRM, so that the roll set can be removed. The rolls will then be sent to a roll grinder. Once the final roll diameters are known, the gears will be sent to a shop that can top off and recut the existing gears, or manufacture new gears. The endplates also need to be sent to another shop, where new endplates will be manufactured, or where the existing endplates will be machined to the new diameters of the feed and center rolls. Once the various pieces are completed, the owner must then supervise the assembly of the roll set with new bearings, seals, etc., and then he will supervise the reassembly and testing of his TRM.

More typically, the owner will partially disassemble his TRM, the roll set will be sent out to a qualified shop for a RSJ.  After four to eight weeks at the qualified shop, the RSJ will be returned. The owner can then either reassemble, and then test the TRM with his own employees, or he can hire an outside vendor to do this work. The bottom line is that with a RSJ, the TRM will be down for between 6 and 12 weeks.




 
RSS (ROLL SET SWITCH)
With a RSS, a rebuilt or remanufactured roll set is sent to the site. The TRM is partially disassembled, the existing roll set is removed. The RSS is installed, and then the TRM is reassembled and tested. When a KMC service team does this work, the TRM is out of service for 5 days or less. It should be noted that with a RSS, when the existing roll set arrives back at the vendor, there may be charge-backs applied, depending on what the inspection of the returned roll set discovers.
 
 
 
 

STEP BY STEP PROCEDURES FOR A RSJ OR RSS
Although any qualified TRM shop will have its own step by step procedures for a RSJ, here are the procedures used at KMC. Please note that that for a RSS, when the existing roll set is returned to KMC, and inspected, the additional cost items mentioned below, become “charge backs.”

The roll set is brought into our shop and it is disassembled to parts. All parts are then inspected so that we can prepare a specific quotation.  This quotation will outline the work that we intend to do, the parts (if any) that are required, and our estimate as to the charges involved. This is part of our standard charge.

All castings go into our heated and agitated cleaning tank, and once these are down to bare metal, these are then primed and painted.  This is part of our standard charge.

The rolls also go into our heated and agitated cleaning tank, allowing for the roll interiors to be chemically cleaned. The roll interiors are then visually inspected to check for scaling, using a borescope. This is part of our standard charge. In some rare instances when chemical cleaning is not sufficient, the roll end will need to be removed to mechanically clean the roll interior, and this is at additional charge.

At this point, there is a pre-grinding machining step. This includes drilling out the interior water pipe indent at the end of the annular space inside the roll. It also includes boring out the water end to remove the inevitable rust buildup. This is part of our standard charge.

The pre-grinding machining step also includes a thorough inspection of each roll journal, measuring the diameters of the gear end, the bearing undercut, and the seal undercut. If any of these dimensions are undersize, that part of the journal is first machined to accept an oversize sleeve, and once that sleeve is installed, it is machined back to the correct OEM dimension. If a sleeve is required, this is at additional charge.       

The rolls are ground on our roll grinders. Our customers normally leave the crown specifications to our expertise. On the other hand, we can, of course, crown to customers specifications. This is part of our standard charge.
After grinding, the roll bevels/undercuts are machined to ensure that all rolls match, making them into a roll set. This is part of our standard charge.

The gears are topped off and recut as required to conform to the new roll centers. This is part of our standard charge. If new gears are required, these are manufactured to suit, and this is at additional charge. A new set of endplates is supplied. If the existing endplates that arrive with the roll set are too worn or too small for remanufacture, then the customer is charged for a new set of endplates. Otherwise, this is part of our standard charge:

• Six new bearings are supplied.
• For Day and Lehmann roll sets, 12 new bearing box seals are supplied. This is part of our standard charge. If the bearing box covers arrive with the old style felt seal rings, they are machined to accept the standard seals. This is at additional charge.
• A new set of water pipes is manufactured and supplied. This is part of our standard charge.
• The roll set is then assembled, and prepared for shipment.This is part of our standard charge.
• If the roll set arrived at KMC in customer owned roll boxes, the roll set will go back into the customer’s boxes. This is part of our standard charge. KMC can supply heavy duty roll shipment/storage boxes at additional charge.