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Exact replacements may not meet current operating demands. It is often economical to rebuild expensive gearboxes. Gearbox rebuilders should have adequate test facilities.
Cost is only one of many factors that enter into the decision of what to do when a gear drive fails or shows signs of damage from premature wear. The wide range of choices available means that, for the most part, there are few obsolete gearboxes.
It is increasingly important to expand what was once an either/or decision to "rebuild it or replace it" by considering other options, including:
* Repairing the gear drive, which involves minor work such as replacement of bearings and seals
* Rebuilding or remanufacturing by inspecting and reworking or replacing gearing and other major components
* Upgrading, including improvements that increase performance to prevent premature failures or meet higher operating demands
* Scrap the old drive and order a replacement. This approach is often the least expensive and most expedient option if the damage is significant and a replacement gear drive is readily available.
On older equipment, available gear drives may no longer be exact replacements and changes in operating conditions may require a different approach.
Analyze the application A common rule of thumb, known as the 60% rule, is a starting point in deciding whether to repair or replace a gear reducer. The rule states that if a repair costs more than 60% of new unit price, the old unit should be scrapped and a new one purchased (Fig. 1). This consideration is only a starting point because there are many other factors to consider.
For example, the 60% rule does not consider the cause of the malfunction. If the damaged gear set was overloaded, an exact replacement does not permanently solve the problem. If a replacement is no longer available, the cost of re-engineering the equipment to accommodate a new gear drive may be more than that of a remanufactured or upgraded unit.
If the original gear set was improperly selected or applied, a simple replacement does not last long. Gear sets are often selected based on motor horsepower and speed, but there may be many other factors to consider.
In one case, the lubrication system on the gear drive of...