Controlled dismount: The right way to remove bearings and seals

Mark Townsend, mechanical services and service engineering manager at SKF, outlines how to avoid common mistakes when removing bearings and seals


hile the main focus for technicians will be on mounting bearings in a way that will

not compromise their performance in service, or installing seals correctly to avoid contamination or loss of lubricant, the reverse operation – dismounting and removing these components – is no less important. Poor practice when dismounting bearings, or replacing seals, can damage or destroy otherwise serviceable parts and compromise future machine performance. When dismounting, there are a few basic,

common sense rules to follow. For example, you should never hit the bearing rings directly, allow the bearing force to be transmitted through the rolling elements, or heat the bearing with an open flame. The typical tools used for dismounting are reviewed below.

PULLING TOGETHER For externally mounted bearings that have an interference fit with the shaft, a purpose designed mechanical jaw-type bearing puller can be used. This equalises the removal forces around the outer ring of the bearing, thus avoiding localised damage. With the jaws clamped to the outer ring and the threaded part of the puller abutting the shaft end, the bearing is slowly rotated until it is eased from the shaft. Where the bearing is internally mounted and it is not possible to get behind the bearing ring, a special puller kit, available from bearing manufacturers such as SKF, can be used. In this

case, the puller is assembled by installing specially designed tips between the inner and outer raceways, ensuring that the pulling forces are on the outer bearing track. Bearings removed in this way should never be reused, but the method ensures that no damage occurs to the shaft or surrounding components. In applications where the only access is

through the bore of the bearing, a split-collet impact puller will be required. SKF’s Combi Kit TMMK series, for example, offers a variety of expandable split-collet designs and configurations to suit a range of bore sizes. The collet is placed through the bore of the bearing and expanded by tightening the collet nut. The slide hammer is then screwed to the collet and the bearing dismounted by impacting the slide hammer against the handle of the puller. Hydraulic techniques are often the preferred

method for dismounting larger bearings, where the application of substantial forces may be needed to affect a safe and damage-free removal. SKF’s TMMA series hydraulically assisted puller, for example, has a maximum withdrawal force of 100kN, while the heavy- duty TMHP series can exert 500kN.

A SLICKER METHOD Oil injection can substantially reduce the required puller forces or, in some cases, dispense with a puller altogether. The method separates mating surfaces by injecting a thin


A major global confectionary manufacturer has called on specialist seal design and expertise from SKF to solve a sticky issue in its manufacturing operations. The company turned to SKF after facing repeated failures in the seals used on its chocolate depositing machinery. The valves control the flow of liquid chocolate heated to C and pressurised to 10 bar, ensuring that each product


on the manufacturing line receives precisely the correct amount of chocolate. Each depositing machine is equipped with 72 valves, but the company’s previous seal design was suffering intermittent failures in production. When the needle valve seals failed, excess chocolate would leak into the production environment, resulting in reject product and costly downtime. After investigating the issue, SKF engineers suggested a new seal design, based on the company’s S01-P profile. To produce a seal suitable for use in the food manufacturing environment, SKF used its

proprietary CNC manufacturing capabilities to create special seals using H-Ecopur-95A-Blue, a polyurethane seal material engineered specifically to meet the unique regulatory and operating requirements of food and beverage manufacturing. The food manufacturer tested the new seal design, and during twelve months of full production the company experienced no seal failures or leakages. It has now decided to install the new seals at all six of its production sites.

film of oil under high pressure, virtually eliminating the friction between them. The method can be used for dismounting bearings and other components mounted on either cylindrical or tapered shafts. When dismounting bearings mounted on cylindrical shafts, the injected oil can reduce the required pulling forces by up to 90 per cent. When using this method to dismount bearings

mounted on tapered shafts, the interference fit is completely overcome by the injected oil. The bearing is then ejected from the seating with great force, making the use of a puller unnecessary. However, a stop-nut must be used to control the ejection of the bearing and ensure the safety of the operation.

THE HEAT IS ON Aluminium heating rings (SKF’s TMBR series, for example), are designed for dismounting the inner rings of small and medium-sized cylindrical roller bearings without flanges, or with only one flange on the inner ring. For larger, heavy-duty bearings, that are frequently replaced, it may be more appropriate to use either fixed or adjustable induction heaters, such as SKF’s EAZ Series, particularly if the mounting is a very tight interference fit. Raising the temperature of the inner ring causes expansion, which rapidly loosens the fit while the shaft remains cool, enabling removal without damaging the shaft or inner ring. While bearing size, shaft configuration,

bearing mounting arrangement and frequency of bearing replacement will dictate the application of a particular method of dismounting, maintenance operatives can rest assured that there is always a better approach than engaging the hammer or blowtorch.

SKF  DESIGN SOLUTIONS | MAY 2017 27

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