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Unique spindle designs add value to grinder line. (Manufacturing Solutions).

When the management of Campbell Grinder Co. designed a new standard grinder line, they searched for a supplier that could provide a stiff, rigid spindle that would be able to handle the high loads and operating temperatures associated with heavy-duty grinding operations.

Located in Muskegon, MI, Campbell Grinder designs and builds custom, standard and turnkey grinding machines. The company is recognized as a leader in the design of heavy duty superabrasive flexible grinding machines, rotary table grinders, grinding centers and special purpose grinders. Some of the special applications that Campbell has designed rotary grinders for include Space Shuttle windshields, radomes for supersonic and subsonic aircraft, large diameter mirrors for the Hubble Space Telescope and computer tape reels.

Recently, company management introduced a standard grinder product line, the 930 and 950 Series Superabrasive grinding machines. Campbell superabrasive grinders are designed for use in flexible manufacturing cells. The modular construction of these machines allows customer design variations to suit specific applications. Models are available in 3-, 4- and 5-axis configurations with rotary and tilt table operations. The machines are designed to handle CBN grinding applications with either plated or VIT-CBN wheels.

"Stiffness, rigidity and dampening capability are the keys to grinding machine design," says Tim Meador, Campbell Grinder VP of Operations. "These new machines are built to be extremely rigid, with a granite epoxy-filed structure, direct drive AC servomotors and linear guideways. This type of rugged structure allows these machines to perform at stock removal rates comparable to those of a milling operation with high accuracy and repeatability."

Maximizing strengths

A major consideration in grinding machine design is the spindle. Grinding applications not only require optimum spindle stiffness; they also require a spindle that can resist the high temperatures that are created during stock removal.

"We worked with several suppliers to develop a spindle that provided adequate cooling and was stiff enough to handle the heavy cuts we do with these new machines," says Meador. Campbell chose a custom spindle design developed by SETCO, the Cincinnati, OH-based manufacturer of precision spindles and slides for machine tool applications.

SETCO engineers designed a liquid cooled motorized spindle capable of 3,600 to 7,200 rpm for the 930 series grinder that includes an automatic drawbar, an HSK 80A taper, and maintains 30 hp throughout that range. The spindle optimizes bearing spread for maximum stiffness, using a design technique called beam deflection analysis, and incorporates two cooling circuits. One cools the motor area, and the other is unique in that it directs coolant to the jacket around the front bearings to reduce the effects of thermal growth and expansion. Campbell and SETCO engineers have developed a 9,000 rpm version of this design and are working together to develop a 15,000 rpm version.

"We guarantee the accuracy of our machines to 0.0002" per foot and repeatability of 0.0001"," says Meador. "If you don't cool the spindle nose in these types of applications, the spindle grows, throwing off the accuracy and repeatability."

For Campbell's 950 series, SETCO developed a 30-hp motorized spindle with twin cooling circuits and a manual HSK 80 taper.

Extending bearing life

SETCO is also working with Campbell Grinder engineers to develop a spindle design that will be used on wheel dressers. "Stiffness is the design focus for wheel dressing spindles, just as it is for the primary grinding wheel spindle," says Meador, "but there are other considerations as well, such as protecting spindle bearings from the fine particulates generated during wheel dressing."

The SETCO spindles used in the wheel dressers incorporate a new patented air seal design that is resistant to the high coolant pressures and volume found in wheel dressing applications without reducing spindle speed.

The new SETCO Air Seal spindle bearings in the dynamic mode when the machine tool is running and coolant pressure and volume are at their greatest, and provides an effective contaminant barrier in the static mode when the machine tool is stopped.

Seals that work well in the static mode generally fit tightly around the spindle shaft, reducing spindle rpm in the dynamic mode. Seals designed to work in the dynamic mode--common air purge seals, for example--are generally overcome by coolant pressure in the static mode.

Made of corrosion-resistant Viton material, the SETCO Air Seal really combines two seals in one, incorporating a novel geometric design with positive air pressure to protect the spindle form contaminants. The positive air system requires air pressure of 10 to 15 psi.

During spindle operation, a uniform outward flow of clean, dry air through the seal prevents contaminants from entering the spindle and keeps humidity levels low. The primary difference in the SETCO Air Seal as compared with traditional air seals is in the method air is distributed around the seal labyrinth. Unlike other air purge seals, the SETCO design provides positive contact sealing against moderate contamination even if the air supply fails or is shut off during machine downtime.

"Spindle design is a critical aspect of machine tool design," Meador says. "Working with a company like SETCO that has had experience in solving practical design problems and in meeting specific customer performance requirements helps us build optimum performance into our machines."

Campbell Grinder Co., Muskegon, MI, or circle 372; The SETCO Group, Cincinnati, OH, http://www.OneRS.net105tp-370 or circle 370
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Publication:Tooling & Production
Date:May 1, 2001
Previous Article:A small milling tool creates big productivity. (Manufacturing Solutions).
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