Oil Seals

Oil Seal:  

As products, oil seals may be simply described as devices that close or seal the spaces between stationary and moving components in mechanical equipment...they prevent lubricant from escaping.  Oil seals, often called grease, fluid or dirt seals, are the vital components of practically every type of machine and vehicle in operation. These seals fulfill an exacting function: they protect all types of precision constructed, close fitting ball, sleeve and roller bearings.

Oil seals are used wherever shafts rotate and bearings require lubrication. In short, a seal is a barrier with three basic functions: 1) Retaining lubricants and liquids; 2) Excluding contaminants; 3) Seal or separate dissimilar fluids or gases.

•  Precision bearings rely on the oil seal to prevent lubricants from escaping the bearings or a specific area.
•  Components of machines rely on the oil seal to prevent abrasives, corrosive moisture and other harmful contaminants from entering the mechanics of the machine.
•  Separation of fluids and gases may completely rely on the seal to prevent inter mixture of two different mediums such as lubricating oil and water.

In a typical application, the oil seal is installed adjacent to a bearing, sealing in or sealing out, as necessary, the various liquids, gases or solids encountered by the particular mechanism.

 The Society of Automotive Engineers (SAE) and the American Society of Testing Materials (ASTM) have developed and adapted a standard to identify component parts that make up an oil seal, as well as terminology and basic lip seal designs.

 

Maintenance Planning in Industries

The maintenance plan is needed for maintenance of industrial unit by adoption of appropriate maintenance policies.

The maintenance plan should lay down a rational basis for formulating a program of preventive maintenance and should provide guide lines for corrective maintenance.

The maintenance organization needed to execute the maintenance work load is dependent upon the maintenance plan. Gives factors influencing the formulation of maintenance plan.

Under this task is to select the best policy or combination of maintenance policies and then coordinating these policies in order to make best use of resources and time.

SELECTION OF POLICY:

The “best” policy for each item can be determined by first identifying the policies which is the most desirable. The choice will depend on many factors and the decision criterion is normally one of minimum cost given that safety criteria, statutory and otherwise, can be met. It is advantageous to apply this selection process separately to the different categories of item.

1.Simple-replaceable: A detailed schedule of actions, periodicity and resources required recommended by the manufacturer. Most number of different action (for the whole plant) in order to coordinate resources and then match them to schedule downtime. 

2.  Complex replaceable: The principle equipment, safety and cost factors can be ranked in order of importance and usually this is all that is necessary for selecting the best maintenance policy Characteristics of the item’s failure behavior can be used to determine effective policies and that the safety and cost factors can then be used to determine approach as used by some airlines.  

In only a few situations is it necessary to construct sophisticated statistical, mathematical or cost models in order in deduce the best policy.

  

3. Non-replaceable: Since these are not expected to fail it must be assumed that nor predetermined action is required. However in the rate event of such failure it should be recorded analyzed and where necessary the appropriate maintenance policy or redesign identified (as shown in figure).

Suitability of various policies can be summarized as follows:

1.   A fixed-time replacement policy is usually most suitable for low-cost simple replacement items.

2.      A condition - based policy is usually most suitable for high-cost complex replaceable items.

3.  All high cost maintenance items, replaceable or non-replaceable, should be considered for designing out.

4.   Where no preventive maintenance/design-out action is effective, or desirable, the item is operated to failure.

PREVENTIVE MAINTENANCE PROGRAM:

When the individual analysis are complete the aggregation actions and periodicity must be examined for opportunities of coordination (by joint scheduling into set periods of all actions on a group of items, or on a unit). This will involve a compromise between then individual optimum schedules, the most economic use in labor and maximum plant availability. These contingencies such as uncertainty of production schedule. Inspection routines, lubrication routines, servicing schedules, overhaul schedules result from this analysis.

CORRECT MAINTENANCE GUIDELINES:

When the plant is new it is difficult, even after the above type of analysis, to forecast the level and nature of the corrective maintenance load. During the early life of the plant the forecast is uncertain and will relay heavily on manufacturer’s information and the plant engineer’s experiences. Obviously this forecast will improve during the life of the plant and corrective maintenance load can be planned for with more certainty. The critical decision in this respect is the level of spares that is to be carried the lower is the unavailability cost on failure, and the easier it is to schedule corrective maintenance; on the other hand the holding cost’s are higher. The maintenance manager has the problem of essential to identify then critical units/ items of equipment and to ensure that the best corrective maintenance plan is adopted.