Stevco Victoria were recently called on to repair a leaking SEW gearbox at the Norske Skog paper mill in Albury. Such problems are relatively common and this was reminiscent of a similar issue that Inpro/Seal recently faced in the US.
When Bill Kuczynski from Casey Industrial noticed a large amount of oil leaking from a gearbox on a SAG mill at a client’s copper milling facility in Arizona, he knew it was time to recommend a permanent sealing solution.
Bill, an Outside Services Manager for Casey Industrial, regularly visits the mill to monitor equipment and advise the client when to perform maintenance. Bill recalled ongoing leaks and related maintenance issues with this gearbox throughout the 10 years he had been visiting the mill. The gearbox used contact lip seals, which tend to have a short and unreliable service life because they use contact with the shaft to retain lubrication. Lip seals wear at the point of contact or groove of the shaft. As they lose contact, lubricant leaks at the point where the shaft enters the gearbox.
At the mill, the rising long-term costs associated with using low cost lip seals were becoming apparent. The lip seals needed to be replaced every three to six weeks. This was an expensive and time consuming repair because it:
- could take place only during scheduled downtime
- required three personnel
- took three to four hours to complete
Furthermore, the gearbox was in a confined location that limited access to the shaft, which complicated the already expensive repair. Between scheduled maintenance, the leaking gearbox caused a costly, messy and hazardous problem that was also an environmental concern. Large amounts of oil were being wasted as it leaked directly to the deck below the gearbox, causing a slip hazard personnel had to navigate. In addition, during each shift workers had to add oil to replace what was being lost because of the leak.
George Gillespie, General Sales Manager for Inpro/Seal said that, for many years, a leaking gearbox was considered an accepted cost of doing business. “I once asked a customer if he had any gearboxes that didn’t leak. He replied,’ I have one; it’s on a pallet on a shelf in the warehouse, and it doesn’t have any oil in it.’” George explained that leaking gearboxes are so commonplace that his clients often do not recognize them as a problem that needs to be corrected. “The problem is often reclassified as a preventive maintenance task. However, it’s not preventive maintenance if you fix the same problem every two or three weeks.” Stricter environmental laws, an increased emphasis on safety and efforts to control costs are changing the way customers view a leaking gearbox. Permanent bearing protection products such as Inpro/Seal’s Bearing Isolator provide an opportunity for a permanent fix.
Bill was familiar with similar applications that used Inpro/Seal’s Bearing Isolator. He turned to George, who had designed seals for many gearboxes, including a similar application at another local mill, to investigate the leaking gearbox. Bill was confident an Inpro/Seal design would solve the problem. “Inpro/Seal provides full support during and after installation to help with any issues the installer or end customer might encounter. They backup the products with an unconditional warranty. If they design a seal for you, and it does not perform as intended, they will re-engineer it on their own dime.”
Engineering a solution
George explained that high oil levels and oil splash make gearboxes notoriously difficult to seal, especially in industrial rotating applications. Lip seals are common on gearboxes, but because of their high failure rate they are ill-suited for industrial rotating applications such as SAG mills.
The sealing solution for the gearbox was based on Inpro/Seal’s patented VBXX-D Bearing Isolator. This is a non-contacting, complex labyrinth seal that consists of a stationary component, the stator, and a rotating component, the rotor. The stator has a large D Groove that captures the oil attempting to flow down the shaft, and through a drain port, channels it back to the gearbox oil sump. The rotor prevents outside contaminates from entering the gearbox by collecting them in the labyrinth design. Centrifugal force then expels the captured contaminants to the outside environment. The result is a permanent, non-contact sealing device that efficiently keeps the lubricant in the gearbox, where it belongs, and also prevents outside contaminants, such as water or dirt, out of the gearbox bearing housing.
An operational flood in the bearing housing compounded the challenge to a permanent seal for the SAG mill gearbox. Unlike most gearboxes that splash oil into the bearings, the gearbox on the SAG mill pumped oil into the center of the double row spherical roller bearings. This ensured continuous lubrication to the bearings, but also tended to push the oil toward the lip seal. Oil that was attempting to flow back through the bearings to return to the sump was impeded, creating an operational flood. The operation flood placed additional pressure on the lip seal and increased the failure rate. A permanent solution needed to be able to perform in an operational flood and be installed onsite without decoupling equipment.
George and the Inpro/Seal team customised the VBXX-D bearing isolator to fit the gearbox application. Customisations included:
- A split design allowed the seal to be installed at the mill without decoupling equipment
- A larger D Groove sized to capture the volume of oil flowing through the system
- An external drain and revamped system to return oil to the sump
On many gearboxes, like the one at the mill, the drain back system to scavenge the oil from the area between the bearings and the seal is not very efficient. “Back in the day, many companies didn’t care so much if the gearbox leaked.” However, today the Environmental Protection Agency (EPA) and Mine Safety and Health Administration (MSHA) place strict limits on the acceptable levels of materials, such as leaked oil, which can create environmental and safety hazards.
George modified the seal to incorporate an external drain. The drain was plumbed back into the gearbox above sump’s static oil level but below the bearings. This isolated the returning oil so that on its return to the sump it was not impeded by the oil sitting between the bearings and the seal. The returning oil had free flow back to the sump, and more importantly, was no longer leaking out of the gearbox through the seal.
According to George, Inpro/Seal’s custom-engineering expertise was the key to designing the permanent sealing solution. The Inpro/Seal team had experience with all the factors, including size restrictions, lubrication type, bearing type, and flooded applications.
The time and costs associated with maintaining this gearbox were greatly reduced because the customised seal and drain back system provided a permanent sealing solution. Less scheduled maintenance results in more production time for the SAG mill. Personnel have a safer work environment because the environmental and safety hazards are eliminated. Also, while it was not the reason for the installation, the gearbox now includes permanent bearing protection.
The two Inrpo/Seal Bearing Isolators installed on this gearbox have now been in operation for two years. According to Bill, “Everything continues to perform as expected, without any signs of a leak.” He added that George continues to check-in to monitor the performance of the bearing isolator. “That’s the thing about Inpro/Seal – they don’t walk away after the install.”
The inventor of the original Bearing Isolator, Inpro/Seal, has been delivering innovative sealing solutions and outstanding customer service for more than 30 years. Their unique technologies increase the reliability of rotating equipment and provide real cost savings by improving the mean time between repairs (MTBR). Inpro/Seal’s superior customer service and streamlined production processes allow for same or next-day shipments on most products, even new designs. Headquartered in Rock Island, Ill., USA, Inpro/Seal maintains a global sales and distribution network to provide responsive, localized support to customers worldwide. Inpro/Seal manufactures in the North America, South America and Europe.