Ajax Equipment makes all classes of screw equipment but, as we are unlikely to be competitors in the Indian market stone crushing industry, we will try to help a fellow manufacturer. Submerged bearings in abrasive circumstances are always prone to seal problems because long screws are not precision shafts and generally suffer some deflection and minute rotational eccentricities. However, spherical roller bearings are precision devices for a duty that does not call for that degree of accurate alignment. Essentially, the function of a tail end bearing on a screw conveyor is to support the load and orient the screw axis. Judicious design of the screw, with a large centre tube fitted with ribbon flights, which are generally good for de-watering duties, can often be made virtually buoyant over the immersed section. (To this end it may be practical to incorporate a buoyancy cylinder on the end of the screw). Taking the dead weight off the end of the screw will reduce the bearing load, allow smaller bearings to be used and reduce wear problems.

The second stage is to consider whether a ceramic faced shaft and chilled cast iron bush will suffice for the application, as the bearing should not suffer high wear if it is only acting as a steady. It may be possible to feed in clean water through an injection point to the bush, to wash away contaminants, particularly is the bush is mounted on an end plate to the tank and has the water entered from the outside. This type of arrangement permits loose tolerances to be used for the bush clearance. Such a mounting will also allow the bearing to be easily replaced if and when necessary. If there is a danger of the shaft wearing it is good practice to facilitate easy replacement by means of fitting end shafts with bolted flanged spigots. Plain bearings are often a good solution for rough duty applications, particularly if water lubricated. If a seal is to be used it is essential that the bearing area on the shaft runs true. On a long screw shaft this means that the tube should be straightened well and the seal area machined with the screw running between centres. Ceramic facing or a hard weld deposit with a ground finish can then be employed to reduce seal wear. No seal will be effective if the tube is wobbling about between the bearings and it is not small task to eliminate this on a long screw. Oil seals are not generally appropriate for this type of duty. A gland packing with lantern rings that are fed with a fluid or air to purge contaminants is usually superior in performance.

Lyn Bates ■

Since you have the possibility of using water for purging the contaminants in the seal area, you can use double mechanical face seals. The outter seal half is designed in a way that can be replaced without removal of the shaft.

There are very efficient seal arrangements in vertical wet milling that I believe are relevant to your application.

Contact us if you need assistance.

Antonio Reis

reis@vitrom.com

www.vitrom.com

Vitrom Manufacturing Consultants. ■

I know this may be already way too late to answer, but could you not put something similar to a boat prop to help generate turbulence to remove material away from the bearing when the machine starts to operate and then apply a memolube (pressurised grease) to the bearing during oiperation.

Just a thought. ■

have you tried labyrinth sealing?

we manufacture gearboxes for screw conveyors

give us your application drawing maybe we can device some system

alok goyle

involute tooling ■