CARE and USE of ACCESSORY EQUIPMENT
CARE and USE of ACCESSORY EQUIPMENT |
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Before mounting in the sharpening lathe, the burr is mounted on the burr plug. The burr plug has a hardened steel body larger than the inside diameter of the burr. With the use of a hydraulic press the plug is pushed into the inside of the burr. This interference, or press fit, keeps the burr in place while the pulpstone is being sharpened.
Fig. 27 Burr Plug
The interference fit of the plug in the burr causes the inside of the burr to assume the perfectly round form of the plug. Any distortion that was produced in the burr during heat treat is eliminated when the plug is pressed into the burr. This precise concentricity is necessary to insure that the burr runs smoothly across the pulpstone without vibration.
Fig.28 Burr Plug (exploded view)
Inside the burr plug are two sets of tapered roller bearings separated by a spacer. the bore of the spacer is machined to fit the burr pins. This spacer is longer than the width of the plug body thus preventing the rotating plug body from touching the sides of the lathe fork. End plates and retaining rings hold the bearing / spacer assembly within the plug body.
Fig.29 Burr Plug Pins
These are specially designed to fit each lathe fork. There are many different pins because of the variety of lathe forks now in use. The pin is hardened and ground to a close tolerance fit with the plug spacer and the holes in the fork. All pins are designed to force the end of the spacer against one side of the fork or against a shoulder on the pin so that the spacer will not turn on the pin. The exceptions to this design are for Canadian high magazine grinders where a key in the bore of the spacer engages a keyway in the pin. Burr pins are inserted into the lathe fork and hold either the burr plug or the bevelling burr in position in the fork. Do not use a pin designed for the burr plug when mounting a bevelling burr. The pin should be securely fixed in the lathe so that it will not rotate in the fork holes. The plug spacer should not rotate on the pin. All rotation takes place within the bearings of the burr plug. There should be a close, accurate fit between pin and plug. The bevelling burr does rotate on the burr pin. This pin must NOT be the same one used for the burr plug. The O.D. of the bevelling burr pin should be 0.003" (0.08mm) smaller than the I.D. of the bevelling burr bronze bearing. Lubricate both bearing and pin liberally with heavy grease.
Fig. 30 Fork and Plug Assembly
Voith and Tampella PGW grinders with split forks use a burr plug with an integral shaft. This plug combines the spacer and pin in one piece. Lubrication of this plug is accomplished through a grease fitting located on the end of the integral shaft.
Fig. 31a Integral Shaft Burr Plug (assembled)
Fig. 31b Integral Shaft Burr Plug (exploded view)
Maintenance of the burr plug involves regular greasing and adjustment of the bearings when they become worn. There is a socket head pipe plug on the periphery of the plug body. Remove this plug to install an Alemite grease fitting. Pump #2 multipurpose grease through this fitting until it is purged through the rubber seals on the ends of the plug spacer. The bearings should be greased before every sharpening and trueing of the pulpstone. Use the expeller ring attached to the press to remove the burr in order to get at the grease hole. With integral shaft plugs it is not necessary to remove the burr. Use the grease fitting on the end of the shaft of the integral shaft plug to grease the bearings. Most North American mills return their burr plugs to the manufacturer for reconditionng when the bearings are worn. Others can purchase repair kits containing special end plates that compensate for wear on the bearings. When the O.D. of the burr plug body measures less than 3.878" (98.5mm) the body must be replaced.
A bench type air / hydraulic press is used to press the plug into the burr. Normally 10 tons of force is enough to press the plug into the burr. The press has a max. capacity of 25 tons.
Fig. 32 Burr Press
To remove a used burr from the plug and to mount a new burr, the new burr is placed on the press base. The used burr, on the plug, is placed on top of the new burr. The press anvil, mounted on the end of the press piston, will push the plug from the used burr directly into the new burr. Make certain no pressure is exerted on the burr plug spacer or on the end plates.
To remove the plug completely from the burr for inspection or greasing, an expeller ring is furnished with the press. The I.D. of the expeller ring is greater than the O.D. of the burr plug. The expeller ring is placed on the press base plate. The burr, with the plug inside, is placed on top of the expeller ring and the press anvil will push the plug out of the burr and into the expeller ring. The lowest compressed air pressure that will operate the press is 70psig (4.7 bar). At this pressure the speed of the piston will be very slow. For optimum performance, air pressure between 80 and 100 psig (5.3 to 7.0 bar) is required. Air should be free of scale but need not be of instrument quality. The press is equipped with a filter / regulator / lubricator. The lubricator should be kept full of very light hydraulic oil to prevent rust in the air / hydraulic pumping unit. Two or three drops of oil should enter the air stream in each complete cycle of the press. Complete operating and maintenance instructions are suplied with each press.
Fig. 33 Sharpening Lathe
Lathes, old or new, require continual maintenance to insure quality stone sharpening. High accuracy and no vibration are major criteria of good lathe maintenance. It is suggested that each mill have one or two extra lathes kept in good operating condition and imediately available to replace a defective unit. A regular schedule of lathe inspection and repair should provide for inspection every six months and rebuilding every two years.
Every six months the following parts should be inspected:
