Repairing shafts scored by seals

The seal has failed! That's the first assumption many maintenance technicians make when they spot a telltale oil film, or worse, dripping oil around a shaft seal location. Frequently, that's not the case.

12/01/1999


The seal has failed! That's the first assumption many maintenance technicians make when they spot a telltale oil film, or worse, dripping oil around a shaft seal location. Frequently, that's not the case. The technician may have recently installed a fresh seal, and blames his installation work or the seal itself.

A little detective work is necessary before leaping to the wrong conclusion. There are a number of paths that lubricants may take around seals to create a leak. While a careless installation or seal misapplication can be the cause of a leak, in many cases the problem is caused by a shaft that is worn because the seal has become a "grinding wheel'' that cuts a groove in the shaft. Many industrial environments generate dirt and other abrasive particles that get trapped under the seal and become an abrasive compound that wears the shaft.

If the seal surface on the shaft becomes grooved, a radial lip seal cannot effectively keep lubricant in and contaminants out. The shaft must be replaced or repaired in order to create an effective sealing surface.

Shaft repair sleeve kits

What, exactly, is a repair sleeve? A standard repair sleeve is drawn from a specialized stainless steel alloy. The outer diameter of the sleeve is then finished to provide a high-quality sealing surface. The resulting sleeve finish, texture, and roughness are optimized for use with elastomeric radial lip shaft seals. In many cases, the repair sleeve actually creates a seal running surface that is often superior to that of the original shaft (Fig. 1). A typical thin-walled repair sleeve adds 0.022 in. to the nominal shaft diameter, which means the original shaft seal size can still be used. This sleeve eliminates the extra inventory and possible problems that could arise if a larger ID seal was required.

In applications subjected to large amounts of abrasive particles, a recently developed plated sleeve offers improved seal life and performance. A 0.00012-in. thick metallic layer is added over the base sleeve. This sleeve increases the surface hardness to approximately 80 HRc and resistance to abrasive grooving. Unlike hard chrome, the bonded coating does not fracture during installation, is thermally and chemically stable, and resists most acids and alkalis.

A typical shaft repair sleeve kit includes an installation tool, requires only a minimum of surface preparation, and is driven into position with common shop tools (Fig. 2). Specialized tools, heating, or other extraordinary procedures are not required for installation. Usually, a complete shaft repair can be accomplished in less than 5 min with no shaft removal. Equipment downtime is minimized. Savings from both repair cost reduction and increased equipment uptime, when compared to alternative repair options, are very attractive.

In certain applications, it may be necessary or desirable to install two closely spaced shaft seals. To accommodate this application, the outer repair sleeve's flange can be removed, permitting the inner seal to slide over the outer sleeve and into position on the inner sleeve. Check the outer sleeve, where the flange was removed, for burrs that could damage the inner seal. Shaft repair sleeve kits are available in sizes from 0.472-8-in. diameter, including many metric sizes.

A repair sleeve is not recommended for installations in which it will be passed over splines, keyways, or ports on the shaft. Any irregularities from the shaft surface create a complimentary pattern on the thin-walled sleeve, resulting in leakage.

Repair sleeve kit installation is very straightforward; however, it must be performed with care in order to ensure the desired results

.-- Edited by Joseph L. Foszcz, Senior Editor, 630-320-7135, jfoszcz@cahners.com

More info

The author is available to answer questions on sleeve shaft repair. He can be reached at 800-323-8024, ext. 4438.

For more information on this topic, see the "Fluid and mechanical power transmission" channel on www.plantengineering.com

Key concepts

Leaks at a seal location aren't necessarily caused by a faulty seal.

Repair sleeves effect a fast, effective solution for repairing a grooved shaft

.

Shaft repair solutions

Replace the shaft. This remedy is doubly expensive because it involves production downtime to disassemble the machine, remove the worn shaft, and install a new shaft, plus the maintenance technician's time for this work. On top of this time loss, add the sometimes prohibitive purchase cost for a new shaft.

Regrind or metalize the shaft. These methods are as time-consuming as shaft replacement. Again, there's machine downtime and labor time to perform the procedure. In addition, many popular regrinding or refinishing techniques leave a shaft surface finish that is difficult to seal.

Install a shaft repair kit. A shaft repair sleeve kit is a quick and effective method to refinish a seal-worn shaft. The repair is done in place, and no further disassembly is required to install the repair sleeve.

Steps to successful shaft repairs

- Thoroughly clean the shaft where the seal makes contact.

- Run a fingernail across the shaft to detect the wear groove and any other nicks or burrs. These locations should be dressed with an abrasive; otherwise, sleeve integrity is destroyed by the imperfection.

- Pick a spot where the shaft is not worn. Using calipers, measure the shaft diameter in three positions and average the readings. Check the average shaft diameter against the sleeve maker's catalog to determine if that diameter is within the manufacturer's recommended specifications for a given sleeve size.

- Determine how far back the sleeve must be placed on the shaft to cover the groove created by the original seal. Measure to that exact point, or mark the spot directly on the shaft. The sleeve must be positioned directly over the worn surface.

- It isn't necessary to fill shallow grooves. If desired, a light layer of nonhardening sealer can be applied to the sleeve's inner surface.

- If the shaft has deep scoring, fill the groove with a powdered metal epoxy filler.

- Use an installation tool to mount the shaft. The flanged end of the sleeve goes on the shaft first. In most installations the flange is removed after installation.

- Once the sleeve is installed, check one more time for any burrs that could damage the seal.

- The repair sleeve should be lubricated with system lubricant before installing the seal.





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