The Gear Box :

To prevent PF laden PA coming to the Shaft–Seal, original CE Mills were equipped with Asbestos Dust Guard Seal and Dust Guard arrangement.

This arrangement had a Housing, in which SA was introduced. This SA created a Pressure Chamber which prevented PF Laden PA to enter the running gap between Dust Guard Seal and Dust Guard. The seal failed as the running gap increased with time.  Increase in the running gap led to decrease in pressure of Seal Air in the Housing/Pressure Chamber.  PA thus found its way to the Shaft- Seal taking PF with it.

Because the above sealing arrangement proved to be grossly inadequate, the OEM, i.e. CE, through BHEL, its then licensee, introduced Mechanical Face Seal Assly (MFS Assly).  MFS Assly seals Seal Air and not PF. The sealing components of this Mechanical Face Seal Assly are:

1. Rotating Hard Face part called the “Seal Runner” which is Hard Chrome Plated,

    AND

2. Stationary Soft Face part called the “Seal Assly” which has graphite sticks embedded in it.

These are placed in a Seal Air Housing which is supplied with SA to create a Pressure Chamber. However, the CE/BHEL MFS Assly, suffers from some gross design deficiencies.

MFS Assly as a rule is Spring Loaded.  Higher the pressure of fluid handled (Seal Air in this case) higher the Spring Loading. The Spring Loading ensures proper sealing contact between the Stationary & the Rotating parts of the MFS Assly. In this case the Rotating Part i.e. the Seal Runner is supposed to have a sealing contact with the Stationary part i.e. the Seal Assly under its own weight/ gravity.  But this does not happen because the Sealing components are not Spring Loaded against each other.

For MFS Assly to work, i.e. to have effective sealing,  the sealing faces of the rotating and stationary components must be smooth and flat for a good sealing contact. 

In the existing MFS Assly it is neither possible to achieve the flatness nor is it possible to ascertain, let alone make them so in-situ. As for the ‘smoothness’ the graphite sticks are supposed to be soft enough to offer Sealing & Lubrication, neither of which is offered in the existing MFS Assly. Copious amounts of Seal Air can be noticed in exhausts of any 623 or 763/783/803 mills (with BHEL’S MFS Assly) in the country.  Anything more than just ‘bleed’ leaking of seal Air is an indication that the MFS is NOT Sealing.

The original MFS Assly is, therefore, NOT a ‘TRUE’ MFS Assly.

Our MFS Assly is SPRING LOADED. Checking and correcting (with our Special Purpose Tool) the flatness of the sealing faces in-situ positively and effectively is a special design feature of our MFS Assly. The grade and placement of graphite sticks in Seal Assly of our MFS Assly offer a wide Sealant Lubricant band. Seal Air in Exhaust, if at all, is the ‘bleeding’ Seal Air.
The design is Patented.  PAT Nos. : 196557  and 219460

The contaminants do get across to Shaft-Seal and once through, enter the Gear Box.

The Rubber Seals do not fail on their own quickly.  They, however, cut grooves into the shaft.  PF and ash/dust assist this groove formation. The pinch and profile of the seal also contribute to groove formation.

To prevent or to delay this groove formation it is necessary to have the Seal contact area of the Vertical Shaft hard and smooth.

Repair to shafts with grooves is possible but not permitted on Vertical Shaft.  Using Single Piece Wear Sleeve on Vertical Shaft is impossible. 

Our Wear Resistant Split Sleeve is the only and the best option for use on Oil Seal Portion of Vertical Shaft.  These are hardened to around 55 HRC, smooth/ mirror finished and can be replaced in-situ.

The design is Patented.  PAT No. 190470.

(It will be appropriate to mention here that the Single Piece Wear Sleeve on ED  Vertical Shaft of 623 & on Vertical Shafts of larger mills e.g. 883 & 1003 provided by the OEM ought to have been Split as it is very difficult to replace this groove formed Single Piece Wear Sleeve).

Regardless, worrisome amounts of contaminants are perpetually found in the Gear Box.

The contaminants cross the Vertical Shaft and the Rubber Seal.  The Upper / Top Radial Bearing is the first casualty.  This Bearing being strong and robust gets damaged, slowly but surely.  It also pulverizes whatever contaminants get between the Rollers and the Races. The contaminants then fall into the lube oil below causing havoc to the Worm Wheel, Worm Gear, Thrust and Roller Bearings, Pump attached to the lower end of the Vertical Shaft etc.

This Upper / Top Radial Bearing, therefore, needs constant flushing as much as it needs lubrication and the lube oil must be clean.

Other than 623 mill with ED Vertical Shaft the existing system of lubrication of Top Bearing is simple and the design is excellent.  A pump is attached to the lowest end of the Vertical Shaft. This pump pushes the Oil in the Gear Box below the Vertical Shaft.  There is a hole in the Vertical Shaft from the lower end till about half way where it meets an angular hole which in turn opens just above the Top/Upper Radial Bearing.  The Oil pushed by the pump below the Vertical Shaft travels through these holes and falls on the Top/Upper Radial Bearing.

This pumped lubrication of the Top/Upper Radial Bearing, however,  suffers from THREE  major shortcomings. 
FIRST     -  over time the pump looses its capacity.
 SECOND - the pump pushes up whatever muck (including metal particles) already there.  AND
THIRD    -   the lubrication starts after a while the mill starts.

(There are  instances of the inner race of Top Bearing rising (sliding) up, blocking the oil outlet hole in the Vertical Shaft starving the Top Bearing of lube oil (pumped through Vertical Shaft) thus causing the bearing to fail.  The inner race, aided by the intrinsic property of rotation tends to rise. It tends to rise when it becomes loose (on the shaft). It becomes loose when it becomes hot.  And it becomes hot when the lubrication is inadequate).

External filtration is one good thing happened to the life of the Gear Box internals.  We provide a Centrifuge Filter for this.  This filtration, however, solves only part of the problem.

To flush and to lubricate the Top Bearing we offer an External Lubrication System. Filtered oil from Gear Box is pumped directly on to the top of the Top Bearing. This system apart from offering positive continuous lubrication also keeps the bearing flushed at all times, even before the mill starts. We are working on external cooling of the filtered lube oil.

The design is Patented.  PAT No. 1881/MUM/2010.

The  Journal  Assembly :

As in the case of Vertical Shaft/ Gear box, the Journal Assly also faces the brunt of contamination.

The cause of groove formation is also the same. The effect of contamination is also the same but multiplied thrice over.

The normal procedure of repairs of such groove formed Journal Shaft is simply to undercut the shaft where grooves have formed, weld fill & machine to size.  However, weld deposit being softer than the parent material subsequent groove formation is quicker still.

MTBF thus remained notoriously short.

Continued/ repetitive repairs as above introduces run-outs in the shaft. Welding also introduces stresses in the shaft resulting in accelerated fatigue failure.

Several procedures were tried to achieve hard and smooth surface on the shaft where the Rubber Seal is in contact with the shaft. Providing a Single Piece Wear Sleeve was an option and tried at several plants.  But these Single Piece Sleeves have not proved to be satisfactory.

Single Piece Sleeve, necessarily Shrink Fitted, necessitates removal of bearings during first and subsequent replacement fitments, always resulting in damage to seating portion of the Sleeve and the bearings, and often to the bearings themselves. The Single Piece Sleeve has THREE other inherent draw backs. 
ONE    –  it tends to rotate around  the shaft,
TWO   –  it tends to slip from its position, AND
THREE –  it remains once use and throw type.

(The OEM, some time ago, obviously to overcome the second drawback as above, incorporated a Single Piece Wear Sleeve ON a modified Journal Shaft. The Sleeve is introduced from the top i.e. from taper (Journal Head) side of the shaft.  The sleeve is shrink fitted.  The first and the third drawback remain unaddressed and new problems are added.  Seal size has changed leading to keeping separate identified inventory plus the bother to log as to which (out of 3) Journal Assly has such modified Journal Shaft & Seal and in which of the mills).

Our Wear Resistant Split Sleeve came into being and has been very well received.  We make these in EN-31/ SAE 52100 material with surface and through Hardness of around 55 HRC. Surface is ground smooth with an option of mirror finished surface.

With chosen placement position and its width our Split Sleeve is Reversible for use twice over. First, reversed & replacement fitment is easy and quick.  MTTR is, therefore, very short and vastly extended MTBF is achieved.

The design is Patented.  PAT No. 190470.