Working in conjunction with a tool manufacturer in Arkansas, Centerline helped solve several problematic issues for this manufacturer and ultimately created a friendlier environment in the process.
The OEM Sakazaki VNC 90 spindle equipped with BT-40 tooling has a capability of operating at 12,000 maximum RPM. This VNC 90 spindle is belt driven and incorporates oil mist lubricated bearings. The original bearing arrangement utilizes a quad set in the front and a single tapered bore cylindrical roller bearing for rear shaft support.
One of the machining systems that the customer employs has four Sakazaki VNC 90 spindles mounted on each of seven machines. The machining cell process for this customer has these machines almost exclusively operating in a separate closed-in area of the plant. The customer requires four backup spindles to support the 28 spindles in operation on its seven machines when in full production. The machine uses a synchronous belt system to drive all four spindles in unison.
The problems the customer experienced using the machines with the Sakazaki oil mist lubricated spindles on its machines were numerous.
The main areas of concern that the customer wanted to address were high spindle failure rate resulting in unacceptable downtime, poor air quality and contamination in the machining area and safety issues. The heavy oil emissions escaping into the atmosphere surrounding these spindles when operating, as is inherit with oil mist lubricating systems, created multiple unpleasant issues in the close proximity to these machines. Besides the air being heavy with oil and the employees having to breathe oil heavy air, this oil contamination settled everywhere, making the floors slick and hazardous. Janitorial and maintenance were scheduled to clean this area multiple times per their daily shift to prevent unwanted safety problems. This company also needed spare spindles to support its operation and reduce downtime. All of these problems subsequently caused the company higher than necessary operating costs.
Centerline Solutions
Centerline determined that the high failure rate this company experienced was primarily twofold:
- First, the rear support bearing of this spindle was operating at near maximum allowable speed, creating excessive heat in the spindle while operating, and was a common source for premature spindle failure.
- Secondly, the spindle bearing lubricating oil system in use was vulnerable to contamination that further limited spindle bearing life.
Centerline's approach toward offering a viable and successful solution became two-fold. The answer was retrofitting the existing spindles to accept the elimination of the oil lubricating system while also manufacturing a couple of new spindles to allow the company to keep a few spare spindles. As the spindles failed and needed repair, Centerline began the retrofit process from oil lubricated spindles until all spindles made the transformation to grease lubrication.
The first issue addressed in order to retrofit this spindle to grease lubricated bearings was the change of the rear tapered bore cylindrical bearing. This cylindrical roller bearing is not suitable for operating with grease at the required spindle speed. This problem was solved by utilizing a duplex pair of high precision angular contact ball bearings. A duplex ball bearing set was selected with a dynamic radial load rating at or above (depending on operating speed) to the original cylindrical roller bearing. The advantage being the angular contact set can operate well above the required operating speed of the spindle with grease lubrication. Machining and resizing of the original rear bearing housing and shaft journals were required to complete this modification, which required minor alterations that were well within the original spindle dimensional envelope. Once the modification to grease lubrication was completed, the spindles ran at lower operating temperatures than the original rear bearing set-up would allow, resulting in extended spindle life.
The success of this project has not only helped this tool manufacturer realize a tremendous cost savings associated with the repair of these spindles, but just as importantly the green environment this project created resulted in safer and better working conditions.
Authored by Larry Love, Centerline, Inc.
For more information contact:
Centerline, Inc.
2110 N Ash
Ponca City, OK 74601
800-696-2865
info@centerline-inc.com
www.centerline-inc.com