MRO Today - Rolls Royce factory grinds out cost savings

Rolls Royce factory grinds out cost savings

Installation of first machine at aerospace plant creates yearly savings of $59,000

Exasperation and hope drove the telephone call from Pat Huser, Manufacturing Engineer at Rolls-Royce Indianapolis, to Midwest Engineered Products early last year.

With two re-manufactured grinders installed to machine the turbine blades used on the engines Rolls-Royce supplies for the C130, P3 Orion and other planes, Huser needed a way to keep the cutting oil clean.

“The machining is critical,” Huser said. “Blade parts are ground to a tolerance of .0006 and used in a section of the engine that reaches nearly 2,000 degrees; so the oil is used under high pressure and must be clean and cool to avoid any burning of the parts as they are machined.”

In the turbine blade manufacturing cell, to filter the high volume of metal fines created by the machines, Huser was using any combination of filter bags, paper filtration, gravity filtration and two small mechanical centrifuges. Once the centrifuges reached their one-cubic-foot capacity, they had to be shut off, and the swarf had to be scraped out by hand. The filter bags often clogged, he said, then broke, ruining the coolant, and requiring the drain tanks to be cleaned, new bags to be installed and new oil to be added to replace the old.

“These are liabilities,” said Huser. “Your processes stop, the increased volume of ruined filter bags and paper have to go to the landfill and, with the inability to remove particles no smaller than 40 microns, the count of deviated parts and resulting scrap go up, reducing the quality and number of finished parts that you produce.”

His search for a solution led to Jeffery Beattey, president of Midwest Engineered Products Corp., an original equipment manufacturer based in Indianapolis and inventor of a state-of-the-art centrifuge.

What Midwest showed Rolls-Royce was an all-new unit that combines a revolutionary bowl/blade clutch design with a single AC motor and AC motor drive; the centrifuge can remove sub-micron-to-one-half-inch particles and fines from virtually any coolant or lubricant at a processing rate ranging from 25 gallons per minute to 135 gallons per minute. Called CentraSep, the centrifuge design appears deceptively simple; but it is more effective than all previous designs. It is able to remove as much as four times the quantity of fines traditional centrifuges can filter out, and extend the fluid life for any given process by at least four times.

Traditional begs for reinvention
“Market necessity is the mother of this invention,” said Beattey, who founded Midwest in 1981.

Through years of calling on all kinds of processing operations and selling them the company’s filters, proprietary ScaleBuster de-scaler and Water Ringer evaporator for oily wastewater from compressor applications, “an opportunity became clear,” he said.

“We realized that most of the centrifuges sold to get metal fines out of grinding swarf, coolants, phosphate baths, wastewater and other process fluids, were broken down or abandoned in the corners and bone yards of plants,” he said.

Like at Rolls-Royce, centrifuges usually are installed on a side stream or kidney loop treating a specific manufacturing process. Traditional centrifuge designs, unchanged in 15 years, are notoriously unreliable, resulting in tremendous downtime and operator attention for maintenance, and bearing replacement.

Typical units are extremely complicated mechanically and include two motors, one to operate the bowl (rotor) and a second gear motor to perform the scraping for solids discharge, pneumatic clutches, one-inch chains and sprockets or pinion gears, connecting the motors and loads.

High-speed revolution of the centrifuge’s bowl, required to separate and pack solid particles against the bowl wall, is brutal on rotor bearings. When bearings fail, it typically takes four-to-six hours to pull the rotor, just so maintenance personnel can begin to access the bearings. “And that’s on automatic units,” said Jeff Beattey. Mechanical centrifuges require solids to be removed manually, before the next processing cycle can begin.

A quantum leap
The vision and technology combined in Midwest’s new centrifuge reverses and removes virtually all of this downside labor, material and production/performance costs.

The centrifuge is completely automatic and, once set up, can operate unwatched while providing fluid filtration-performance and product production benefits, in addition to saving huge operating costs, Beattey said. That payback lies in understanding the machine.

Series of firsts
Mechanically, Midwest’s centrifuge positively synchronizes, for the first time, the bowl and blade assembly (which consists of two scraper blades and two stilling vanes). A unique positive locking clutch (see diagram) couples the bowl’s main spindle and the blade together so that both rotate at precisely the same speed when processing fluids. The motor is linked to the main spindle via a single chevron-style “timing” belt and pulley design that prevents any slippage.

“The fluid is forced to move smoothly throughout the bowl as it strikes an accelerator on entry and descends,” notes Beattey. “Physically, that even ‘quiet’ flow maximizes the law of centrifugal force: any particles heavier than the liquid are thrown outward and packed against the bowl wall.”

Such synchronized rotation also prevents any oscillation of the blade, maximizing separation efficiency and minimizing bearing wear.

Oscillation, he said, “ is what you want to prevent, as it creates a washout of solids from the bowl, particularly super-fines.”

Because the bowl is a thick centrifugally cast stainless-steel precision-machined part, vibration is dampened further enhancing bearing life.

When the automatic process cycle is complete, the feed pump turns off, the locking clutch uncouples the blade assembly from the main rotor spindle and locks the blades into a fixed position. The bowl is then rotated and the dry, dense particulate that is scraped loose by the blades falls into a collection drum, ready for recycling.

Secret is the electrics
With patents pending on the unique clutch and scraper design, Midwest credits new electrical control “for making the CentraSep a reality,” said Jeff Beattey. “In this design, the electrical and mechanical components are fused and inseparable.”

Accelerating the bowl and blade very rapidly for the processing cycle, bringing the loaded bowl to a controlled stop, and turning the bowl against the scraper blades, require high, breakaway torque and extremely precise motor control.

After trying several different controls and motor drives in designing the electrical panel for the centrifuge, a local distributor of ABB drives, Scherer Industrial Group Inc., provided an ACS 600, 10 HP drive.

Built into the drive is ABB’s unique open-loop direct torque control feature, which enables ACS 600 drives to calculate the state (torque and flux) of a motor 40,000 times per second. According to ABB, this responsiveness to the motor load not only makes the drives virtually tripless – but the absence of any required encoder for feedback from motor to drive also reduces capital costs for the controller by up to 25 percent, when compared to like flux vector or PWM (pulse-width-modulated) drives.

"Without this brand new drive technology, a single-motor centrifuge would not be a reality," said Beattey.

“Because this open-loop control of torque is so precise, the drives can adapt to and handle changes in load, over-voltages and even short circuits, immediately,” said John Emmert, the electrical designer who helped Midwest with the panel, motor and drive design.

This ability to anticipate what the motor is capable of based on its load provides a significant benefit to centrifuge users, Emmert noted. If the load in the bowl is too heavy, the AC motor enters a stall mode, rather than turning the bowl and breaking the shaft or blade assembly. Unlike competitors’ products that use gear motors which often break shafts and scraper blade assemblies under those loads, the electrics anticipate and prevent such an occurrence, Emmert noted.

Both Emmert and Jeff Beattey worked with ABB engineers closely, to develop the proprietary software that Midwest needed to program and operate the drive at extended torque parameters.

“We’ve had no drive failures from a single production unit,” noted Beattey. “And with ABB’s mean time between failure on this drive at 150,000 hours and counting, we have a lot of confidence in these critical electrical controls.”

To ensure that the exact same start-up software is programmed into every drive on all production units, Midwest uses ABB’s DriveWindow tool. The Microsoft Windows-based tool allows the company to backup the programming and restore it on each subsequent drive.

This critical programming is not application specific. Instead, to adjust the speed – and centrifugal force – of the bowl for different types of process fluids, Midwest uses a call-out on a PLC built into the panel. The drive, in tandem with the PLC, gives Midwest the flexibility to customize the centrifuge for any kind of application.

“This unique drive and motor control capability, which creates up to 2,012 gravitational forces inside the centrifuge and delivers the low-end torque to scrape, literally saved the need for incorporating a second motor into our design,” Beattey said.

Reducing waste; improving products; meeting ISO 14001
At Rolls-Royce, the installation of the first CentraSep last April immediately began to remove up to 99 percent of the sub-micron fines generated from the first machine the centrifuge was hooked to, according to Pat Huser.

“It’s run 24/7 ever since, requires zero maintenance – and the quality of the grinds have improved immensely, along with reducing as much as is possible what we send to the landfill," said Huser.

Both nickel and aluminum oxide particles are removed from the coolant and recycled.

This ability to create solid swarf and increase reclaim ability has helped Rolls-Royce meet its ISO 14001 goals for qualification and certification.

Such effective removal of particulate also extends fluid life dramatically. Rolls-Royce maintenance personnel were changing the 350 gallons of cutting oil every three months; however, 15 months since the centrifuge installation, the oil is still in use.

“In oil, alone, we are saving $3,600 a year on just one grinder,” said Huser. “Add in cost of the downtime and maintenance and paper filtration, and it was easy to project yearly savings of $59,000 through just the first centrifuge installation.”

As an additional point of illustrating costs, Huser noted that the CentraSep is attached to one of the CNC grinders, while a second grinder has remained attached to the older, existing mechanical centrifuge (with a one-cubic-foot capacity). In the last year, the low-capacity centrifuge has had replacements of six motors, eight belts, and numerous bearings, he said. And the grinder with the CentraSep stays clean, while the other grinder needs to be de-swarfed about every three months.

Most importantly, the ability to maintain virtual particulate-free process fluids year-in-year-out reduces friction between tools and work surfaces so that the quality of parts produced is higher.

“This centrifuge is at 8,000 hours and counting in a zinc-removal application, one of the toughest possible,” said Beattey. “And its removing aluminum fines in a wire-drawing application where the oil is as viscous as 4,000 SSU. The filtering prevents problems, such as die impaction or streaking on the wire.”

Midwest notes such filtration capabilities also will play a more critical role in helping processors meet their zero-discharge commitments.

“Strategically, you capture the maximum quantity of any contamination at the point of origin,” said Pat Skidmore, technical support manager for the company. “It’s smart business; you improve and extend the life of the process fluids; you pack the particulate as tightly as possible – and you minimize any discharge of this captured particulate into the waste treatment stream.”

Built for a lifetime
The in-line performance of the first CentraSep units in a host of very difficult applications have only reinforced Midwest’s decision to offer a lifetime guarantee with the centrifuge. Through the warranty, Midwest exchanges, on an annual basis, the entire rotor assembly – all mechanical parts except the motor.

“It’s a win-win,” according to Beattey. “Our commitment to customers is long term. We know they want clean fluids, and we know this product can provide that. It’s why we were so deliberate in choosing the word revolutionary to describe this original design.”

The ability to change-out the rotor assembly in record time also keeps filtration lines moving in customer’s plants without a hitch.

“It’s eight bolts, the timing belt and air-line quick connects; the rotor exchange has been done in as little as three minutes and six seconds,” said Skidmore.

Given the early receptivity to the OEM’s re-invention of this product, what’s next?

Success with the first unit at Rolls-Royce proved so dramatic that Pat Huser is expecting shipment of a second unit from Midwest soon. The second centrifuge will be dedicated to filtering fluid from a third grinding machine, he noted. Additionally, relocation of the cell is allowing Huser to consolidate a second grinder onto the original centrifuge. He said other Rolls-Royce plants are studying the way the Indianapolis facility has made these changes, reducing both the physical capacity the grinding cell requires, while simultaneously making it far more efficient and productive.

For more information at Rolls-Royce, contact John Brown at . For more information at Midwest Engineered Products, contact Jim Beattey at . For more information on ABB Drives & Power Electronics, contact Becky Nethery at .

To see a diagram of the centrifuge process, click here.