Monday, 8 February 2016

BEARING INSTALLATION PROCEDURE

BEARING INSTALLATION PROCEDURE

Earlier we were discussing the basics of roller bearing & its various types and also ball bearing and its types, we have also seen the bearing removal and cleaning procedure in our last post. Today we will see here the basic procedure of bearing installation.

We will discuss here each and every step that must be followed for securing the correct installation and better service life of bearing and simultaneously we will also look here the importance of tools, installation guidelines and other various factors such as cleanliness during bearing installation.

So let us first see, what we will have to inspect before going for bearing installation

Shaft and bearing housing condition

Before going for installation of bearing, we must have to check the condition of bearing seat on shaft and seat in housing bore. Shaft and bearing housing bore must be cleaned and there should not be any dust, metal burr or any dent.

We must have to check the dimensions of bearing seat in housing bore and diameter of bearing seat on shaft and these dimensions must be within preferred tolerances provided by the manufacturer.

Seal condition

Sometime, it is observed that maintenance crew team members replace bearings but they do not replace the seals. Seals are provided to avoid the entry of dust, foreign particles and moisture in to the bearings. In my point of view, whenever we go for replacement of bearings, we should also replace the seals with new one of similar specifications. 

Before replacement of seals, we must have to inspect the seat of seals and there should not be any sharp edges or metal burr as these sharp edges or metal burr will damage the seals and allow the entry of dust, foreign particles and moisture in to the bearings and finally we will not be able to secure the desired service life of bearings just because of damage seals.

Seals provided next to the bearings will also avoid the flow of lubricant out of the bearings.

Working area

Working area, surrounding area where bearing installation job is being carried out, must be clean so that bearing installation job could be carried out safely and successfully.

Tools and other resources must be clean before the installation of the bearings.

We should not remove the bearings from its box until we are ready for installation. After removing bearings from their box, we should not remove the protective lubricants provided by the manufacturer over the bearing surface as these lubricants are provided by the manufacturer to avoid the damaging of bearings from corrosion or dust.

Shaft and housing fits

Selection of optimum shaft and housing fit is very important factor for securing the long service life of a bearing. Type of fit for shaft and housing depends on various factors such as operating temperature, bearing type, load and material of shaft and housing. 

Fit which is explained as the amount of interference that should be available between mating parts e.g. shaft and bore of bearing or bearing outer diameter and bore of housing.

Shaft and housing fits are divided in three types as mentioned here

Loose fit

It will allow the easy installation of bearing but we must have to note here that too loose fit will permit the bearings to slip in the housing or on the shaft and may lead the vibration and noise during operation and further premature failure of bearings.

Press fit

Press fit installation of bearings are quite difficult but if followed the guidelines of manufacturer then it will surely provide the long service life of bearings. If inner ring is press fit with shaft then it will run with the shaft and if outer ring is press fit then outer ring will run with the housing.

If we have to press fit the inner ring with shaft, in this case shaft diameter will be slightly higher than the bore diameter of bearing. If press fit is beyond the specified tolerance then it will eliminate the internal clearance of bearing and hence rolling elements of bearing will not be able to rotate smoothly and will lead the rising in temperature and further premature failure of bearing will be there.

Transition fit

Transition fit means slight press fit i.e. the amount of interference that should be available between mating parts, in this case, will be between loose fit and press fit.

Mounting the bearing

Now we have idea about the various points that must be considered before installation of the bearings. Now we will see here how a bearing will be installed over the shaft with press fit. First of all we will lubricate slightly the bearing seat on shaft with recommended lubricant.

We will start the installation of bearing with rounded corner of bearing going first over the shaft and we will check here that bearing is square over the shaft and bearing centre matches with the shaft axis.
Now we will apply the pressure force to the ring of the bearing which is being press fit and we will force the press fit race of bearing against shaft shoulder.

For applying the pressure force over the press fit race of bearing, we may use equipment named as arbor press as shown in figure. 
We can exert the pressure force here continuously and bearing installation could be completed within short period of time. For inner press fit, we will have to support the inner ring of bearing with the help of two flat bar or attachment for supporting the inner ring of bearing.

Once the bearing inner race is properly supported, we will check that bearing is in center or square over shaft. Now we will exert the pressure force with the help of arbor press and we must have to take care here about the pressure applying by the press because excessive pressure applied by the press will surely damage the bearings or slightly bend the shaft.

Once bearing will be installed over the bearing seat provided on shaft, we will release the press and remove the shaft carefully.

Do you have suggestion? Please provide in comment box.

Reference: SKF bearing maintenance manual
Image Courtesy: Google

We will discuss the lubrication of bearing in our next post.

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