Refurbished Heat Transfer Rolls—Good as New

February 9, 2010

multipage

Either way, the roll manufacturer must have the capability of reverse engineering the worn roll during the disassembly process. To facilitate this process, the machinists will produce detailed drawings that can be used to accurately refurbish the existing roll or fabricate a replacement.

“As a major OEM supplier, we find it very beneficial, particularly with older roll designs, to have our engineers create computer-aided design (CAD) drawings to prove the design accuracy for repairing a roll,” Menges explains. “That also enables us to incorporate design improvements. The new drawings will expedite the fabrication of a replacement roll, if necessary, and provide the designs necessary for future reference.”

A case for refurbishing
In a recent case where refurbishing proved to be the best solution, Brian Varley, plant engineer at Sonoco Clear Pack, needed to repair or replace one of the large heat transfer rolls at the firm’s sheet extrusion operation. Clear Pack thermoforms plastic containers for several consumer product and food service companies, including packaging for single-serve condiments, fresh produce, and other food service needs.

“The shell surface on one of our tungsten carbide rolls was excessively porous,” Varley explains, “so it would not accept replacement tungsten carbide well enough, and would not polish properly.”

Varley had worked with Menges Roller for many years, so he consulted with them to analyze the problem and evaluate whether a new roll was needed or refurbishing the existing one was the best solution.

Even with laser welding, the supplier determined that the super-finish required for application could not be achieved. However, Menges recommended refurbishing the roll to save both production time and replacement costs.

“They removed the outer shell, installed a new one, and applied the tungsten carbide super finish to the roll,” Varley says. “However, once they removed the shell they found a number of other problems in the roll’s internals. There were some leaks that they were able to repair, and they also re-balanced the roll. After the refurbishing, which was done fairly quickly, we had a virtually brand-new roll for less than half the price of fabricating a complete replacement.”

Varley adds that he was confident about the refurbishing choice because he had experienced success with the process several times in the past.

“I’ve worked at large converter operations throughout my 25-year career,” Varley says, “and have experienced several situations where we had to make the choice of replacing or refurbishing large and complex process rollers.”

In an earlier instance at a cast film operation, there was a complete blockage of a heat transfer roll that ran in a line of 25 large, rubber-covered heat transfer rollers used in the production of cast film. Because the roll had been in service for over 20 years, Varley worked with Menges to determine if the roll should be repaired or replaced.

“A new roll core like this was in the $40,000 price range,” says Varley. “Plus, of course, there was the substantial added cost of downtime. Menges recommended repairing it, which was done for less than 40 percent of that cost. They replaced the outer shell, machined the internals to remove oxidation, and the internal shell was rewound to produce an even better cooling rate then when the roll was new.”

According to Matt Menges, most operations understand what they want heat transfer rollers to do to their webs, yet don’t realize the engineering expertise needed to achieve optimum performance, particularly when it comes to the choice of refurbishing or sourcing replacement rolls.

“Given the complexities, the customer relies on suppliers like us to handle all the complex calculations of flow rates, BTU output and input, deflection, pressure testing, and roll balance,” Menges explains. “And the roll finish is certainly a specialty, whether plasma, High Velocity Oxygen Fuel, chrome, rubber, or urethane.”

In the end, of course, the customer is mostly concerned about keeping production going, and that means getting fast service, whether replacing or refurbishing rollers.