ZKL BEARINGS (INDIA) PVT. LTD.

Mounting of Spherical Roller Bearings

in Paper Making Machines

B-3/1A,Gillander House.8,Netaji Subhas Road Kolkata – 700001.Tel:033-22138591 - 95 | E-MAIL: marketing@zklindia.com

Corporate &Registered

458, Aggarwal Metro Heights, Netaji Subhas PlacePitampura - 110034, New Delhi.Tel: +91 011-2735-1075 | E-mail: delhi@zklindiz.com

North

C-402 “Mangalya”,Marol Maroshi Road, Opp. Marol Fire Bridge StationAndheri (East), Mumbai - 400 059, MaharastraTel: +91 22 29250412/40157976/77/78/79 | E-mail: mumbai@zklindiz.com

West

C44 Armenian Street, 2nd Floor, Chennai - 600 001, Tamilnadu.Tel: +91 44 25227053 / 03 / 32976965E-mail: chennai@zklindiz.com

South

ZKL BEARINGS (INDIA) PVT. LTD.www.zklindia.com

Introduction :

123

4

55

78

9

10 12

12

11

13

7

66

4

444

4

Breast Roll Forward Drive Roll Wire Rolls Felt Rolls Suction Rolls

A papermaking machine consists of the following sections :

A wire and press section (the wet section)A drier sectionA calender &4. A reeler

A basic layout diagram of a papermaking machine is shown below :

Calender RollsReel DrumReel SpoolsDoctors

Press RollsM.G. Press RollsDrying CylindersM.G. Cylinder

A papermaking machine consists of a number of rolls, and each of these rolls is fitted with two spherical roller bearings.

There may be up to 3000 bearings fitted in a very large papermaking machine.

Spherical roller bearings are preferred for use in a papermaking machine because of their ability to accommodate axial

loads along with considerable radial loads. Furthermore, spherical roller bearings are able to withstand misalignment

between the shaft and the housing which is unavoidable in a papermaking machine, where bearings are invariably

mounted in separate housings placed at a considerable distance from each other.

Besides spherical roller bearings, other types e.g., deep groove ball bearings, self aligning ball bearings, cylindrical

roller bearings, taper roller bearings and thrust bearings are also used in a papermaking machine. However, most of

the equipment, where these bearings are used, are of peripheral nature, and that is why details of such applications

are not discussed in this publication.

Mounting of bearingsFits and tolerances :

Trueness of a tapered shaft also must be checked carefully by using Ring Gauges and Taper Gauges. While mounting a

spherical roller bearing on a sleeve or a tapered shaft, it's radial internal clearance must be controlled as per

manufacturers' recommendation.

Correct mounting of a bearing goes a long way to ensure that the bearing is likely to function without any premature

failure, provided proper lubrication and protection against entry of water and abrasive particles into the bearing is

ensured.

Calender

Production down-time cost in a continuous process industry like Paper industry can be very high, and one of the main

reasons for unplanned shut down of a papermaking machine is bearing failure. More often than not, such bearing

failures may be attributed to wrong method adopted for mounting a bearing.

A bearing is made of hardened steel. Hardness renders the bearing components brittle i.e., liable to develop cracks

when subjected to direct hammer blows. Today, there are a number of mounting and dismounting techniques available

for avoiding such situations e.g., Oil injection method, Induction heaters, Hydraulic pullers, etc., and care must be

taken to avail of such scientific methods, instead of resorting to hammering a bearing up a sleeve or a tapered shaft

while mounting.

The first step for correct mounting is to maintain correct tolerances on the journal and bearing

housings. A table is given below showing the recommended tolerances in different sections of a

typical paper machine:

See Note on

Fits & Tolerance

below

Tapered journal < 200 200 -400

> 400

Housing Bore

dia (mm)

Journal dia (mm)

Up

to

200

100

to

140

< 100Sleeve

mtg

h 9

(IT5/2)

Breast / Forward drive

Wire / Felt

Press

Suction

Suction box Support

Drying Cylinder

M G Cylinder

M G Press

Calender

Reeler Drum

Reeler Spool

Wet

Dryer

Machine

Calender

Reeler

S.

NoSection Roll

1 m 6 n 6

n 6 p 6

h 6

n 6 p 6

H7

H7

G7

H7

N7

G7

G7

H7

G7

H7

H7

F7H7

Direct mounting

Tolerances on cylindrical forms :

According to ISO 1101 – 1983, the form tolerances ( cylindricity, run out, perpendicularity etc.) should generally be 1 to 2 IT grades better than the recommended dimensional tolerances. For example, if a bearing seating on a shaft has a tolerance of n6, then the form tolerance should be IT5 or IT4. The tolerance value for cylindricity is generally taken as half the permissible deviation under the IT grade. For example, if a shaft has a diameter of 150mm, then the permissible deviation should be IT5/2 =18/2 =9 or IT4/2 -=12/2=6 microns.

Cylindricity of the shaft seating is required to be IT5/2 for h9 or IT7/2 for h10, whenever the bearing having a tapered bore is required to be fitted on either an adapter sleeve or a withdrawal sleeve.

32

Tolerances for Perpendicularity

Mounting of Bearings :

Before mounting the bearing, the radial internal clearance must be measured with a feeler gauge, since the reduction of

internal clearance is used as a measure of interference.

Stand the bearing on a clean surface and rotate the inner ring a few times. Ensure that the faces of both the inner and

outer ring are in the same vertical plane by using a straight edge. Use a feeler gauge blade slightly thinner than the

minimum value of the clearance before mounting. Insert it over the roller next to the uppermost roller. In that position,

measure with an increasingly thicker blade until, when attempting to pull out the blade, there is a slight resistance.

Push the bearing up on to the shaft and check the reduction in internal clearance during drive-up under the lowest roller,

see table for guidelines. The minimum values for internal clearance given in the table apply mainly to bearings in which

clearance is close to the lower limit. This will give the minimum permissible clearance.

To ensure proper shaft fitting when driving up bearings with greater clearance than Normal for example, C3 or C4-it is

recommended to keep to the upper half of the clearance reduction range.

Small bearings can generally be driven up on a tapered seating by means of hammer blows applied to a sleeve abutting the inner ring. Smear the

seating with a thin oil, as there otherwise is a risk of damaging it. Use a mounting sleeve and an

dead blow hammer. With firm hammer blows, drive the bearing up the predetermined distance. This mounting method is not recommended for

larger than 50 mm bore bearing and precision applications, such as machine tool spindles, and similar applications.

Tolerances for Tapered Shafts

Straight Bore Bearings :

For larger bearings, bearings should be mounted by means of heating. Heating can be done by an induction heater, heating cabinet or oil bath. The

bearing should be heated to 80-90 °C above the shaft temperature, but never to more than 125°C, with an induction heater or oil bath. When the

bearing after mounting has cooled down to the shaft temperature, clearance should be checked to ensure proper mounting.

Tapered Bore Bearings :

Abutments for bearing rings should be perpendicular to the shaft, in order to provide all round support to the ring so as to ensure transmission of thrust loads from the shaft to the bearing. However, the extent of perpendicularity should be governed by the tolerance as per ISO 1101-1983, which makes it mandatory for the perpendicularity tolerance to be better than the diameter tolerance on the associated cylindrical bearing seating by at least one IT grade. For example, if a bearing seating on a shaft has a tolerance of n6, then the form tolerance should be at least IT5.

Tolerances for tapered shafts need to cover the following three aspects:

Permissible angle deviation Straightness tolerance Radial deviation from roundness

While there is a major difference between the European and American systems, one of the leading bearing manufacturer has formulated a standard as depicted in Figure 1.2

Permissible angle deviation : +/- IT7/2xB where B is the width of the bearing in mm

Straightness tolerance : IT5/2

Radial deviation from roundness : IT5/2

Fig : 1.2

Fig : 2.1

Fig : 2.2

Fig : 2.3

Fig : 2.4

For heating a bearing in an Oil Bath, the bath should be clean and deep enough so as to allow the bearing to be suspended

within the oil bath and completely immersed in oil without touching any side of the bath. The oil should be clean and

should have high flash point. While heating the bearing, the oil should be continuously stirred and the bearing

temperature should be constantly monitored so as to prevent it's getting overheated.

In a Paper Mill, tapered bore Spherical Roller Bearings are usually mounted, either directly on a tapered shaft, or on a

straight shaft by means of Withdrawal Sleeves.

54

Tolerances :

The shaft and the outer surface of the withdrawal sleeve should be smeared with a thin oil (Fig 3.4). The bearing is to be

loaded on the shaft. and the withdrawal sleeve inserted by hand between the bore of the bearing and the shaft. The sleeve

may sometimes move rather sluggishly when pushed along the shaft. Opening the slot slightly with a screwdriver

can ease sliding.

Small bearings can usually be mounted cold. When mounting a bearing on a withdrawal sleeve, use a shim or calibrated

spacer, the thickness of which should equal the drive-up distance, as stipulated in the bearing manufacturers' catalogue.

(Fig 3.7) To prevent the sleeve from being mounted in a skewed position, it is advisable to use a specially designed

mounting sleeve, which will locate either on the shaft or in the bore of the withdrawal sleeve (Fig 3.5). Then the sleeve is

to be driven under the bearing with hammer blows applied to the mounting sleeve.

If the shaft has a threaded section, a lock nut and an impact spanner and a hammer may be used to drive the sleeve

between the bearing and the shaft (Fig 3.6). and then fixing a nut on the sleeve thread and then screwing the nut until it

pinches the shims (Fig 3.7). Then the shims have to be removed and the nut to be secured. The thread and the side of the

nut facing the withdrawal sleeve may be coated with molybdenum disulphide grease prior to mounting. Then the nut

should be screwed into position and tightened with the impact spanner till the desired drive up / reduction in clearance

of the bearing is achieved.

The mounting of a lock nut to prevent the sleeve from expanding is also recommended. (Fig 3.8)

Wear clean protective gloves when handling the hot bearing. Appropriately designed and fabricated Lifting gear

can also be used. As soon as the bearing is heated to the mounting temperature, push the sleeve with the nut in

position (Fig 3.9) under the bearing until the nut and bearing are in contact. Hold the sleeve in position and allow it

to cool. Check the radial clearance. If the withdrawal sleeve has gone in too far under the bearing, i.e. the clearance

is too small, use the nut to draw out the sleeve and remove the bearing. Correct the drive-up distance, reheat the

bearing to the correct mounting temperature and repeat the mounting procedure.

The easiest way is to employ a Hydraulic Nut. Bearings with a bore diameter larger than 50 mm can be simply and

reliably mounted using a hydraulic nut ( Fig 3.1). A hydraulic nut can mount bearings with bore diameters up to 1000

mm. For mounting the bearing (Fig 3.3), it should be first placed on the tapered bore and pushed up with hand to the

maximum extent. Then the nut should be mounted on the threaded part of the shaft with the piston facing the bearing.

After the nut has been tightened by hand, oil should be pumped to the nut with the Oil Injection Pump ( Fig 3.3) until the

bearing is driven up the tapered shaft to the desired extent. Then the Hydraulic Nut should be replaced with a locking

nut. After the Lock Nut has been secured, the residual internal clearance should be checked. If necessary, fine

adjustment to the drive up is to be effected with the help of the oil-injection method quite easily.

Easy dismounting can be ensured with the oil-injection method. For this, the shaft must be equipped with grooves and a

duct for oil-injection dismounting.

Mounting on Withdrawal Sleeve : Cold mounting :

After mounting, check the residual internal clearance with feeler gauges and ensure that the reading conforms to the

bearing manufacturers' recommendation.

Mounting on Withdrawal Sleeve : Hot mounting :

In situations where cold-mounting methods cannot be used, heat the bearing before mounting. There are proper hot-

mounting devices such as an induction heater or oil bath that are available. When hot-mounting a bearing on a

withdrawal sleeve, use a shim or calibrated spacer, the thickness of which should equal the drive-up distance. Push the

sleeve in under the bearing until it makes firm contact. Screw a lock nut on to the withdrawal sleeve, but leave a gap

corresponding to the axial drive-up distance. Lock the nut or mark the position on the sleeve with a line extending over

the nut face and the end face of the sleeve. Heat the bearing to a temperature about 80-90 °C above that of the shaft.

Never heat the bearing higher than 125°C.

Mounting on Withdrawal Sleeve : Use of Hydraulic Nut :

Use of a hydraulic nut and the oil-injection method, either alone or in combination, greatly facilitate mounting. For

small and medium-size withdrawal sleeves, use of a hydraulic nut is the best method. Fig 3.10 shows mounting by

using a threaded portion of the shaft for mounting the Hydraulic Nut, with it's piston pushing the withdrawal sleeve

between the bearing and the shaft. The arrangement shown in Fig 3.11 shows mounting with the hydraulic Nut

fitted on the treaded part of the withdrawal sleeve in the reverse, using a check nut fitted on the threaded part of the

shaft as the abutment for the pushing the sleeve in. Where there is no treaded part on the shaft adjoining the bearing

seating, but an undercut is available, the arrangement as shown in Fig 3.12 may be used.

Fig : 3.1 Fig : 3.2 Fig : 3.3

Fig : 3.4 Fig : 3.5 Fig : 3.6 Fig : 3.7 Fig : 3.8

Fig : 3.9

76

Fig : 3.13

For large withdrawal sleeves, a combination of oil injection and a hydraulic nut should be used. ( Fig 3.14)

Fig : 3.14

The oil should have a viscosity of about 300 rnrn2/s (1 375 SUS) at the mounting temperature.

SupportSpecer

Conclusion :

Majority of bearings used in Paper Mills fail on account of wrong mounting, improper

lubrication and ingress of contamination due to lack of proper sealing arrangement

design and maintenance. These require careful elaboration and therefore, not included

in this literature.

For expert advice and guidance, you may contact ZKL Bearings (india) Pvt. Ltd.

Large sleeves require considerable force' and are usually provided with distribution grooves and two ducts for

pressurized oil. Oil is injected between the sleeve and shaft through one duct, and between the sleeve and bearing

through the other. (Fig 3.13)

Fig : 3.12Fig : 3.11Fig : 3.10

98