Interference fit bearing sleeve

Good evening all

I want to make a phosphor bronze sleeve shaped plain bearing to be a moderately heavy press fit on a 50 mm OD hardened steel shaft. The bronze sleeve will be nominally 58 mm OD so fairly thin wall, and 22 mm long. The outside surface (sliding bearing surface) is pressure lubricated with EP90 gear oil.

How much interference should I be shooting for? The degree of interference must be less than that which would stretch the OD such that it will not run in its (lubricated) bore, let alone rupture the sleeve (hoop stress).

Can anyone quantify the force needed to install said bush - my press will cope with about 8 - 10T. Is this adequate for a "moderately heavy" press fit? Is there an empirical force vs interference relationship?

If it helps it's an experimental modification to an obsolete Land Rover overdrive gearbox, to replace an existing needle roller bearing where the outer running surface is damaged such that re-use of the roller bearing (or a new replacement) isn't going to happen. The bearing mustn't revolve on its spigot - hence the press fit - but I don't know how to quantify the tangential friction forces on the bush. If I've understood the mechanics of the original design these forces are pretty small, but that's the experimental bit!

Looking forward to the knowledge as ever

Rgds Simon

Bearing (?) in mind the wall thinness, and the hoop stress resulting from a press fit, might a Loctite product be safer?

Shaft bushes that are supplied from suppliers like SKF etc specify the bore diameter in the housing so that when they are pressed in the the bush will be the correct fit with the shaft.

If you are making your own, ream the bore to the working size after it is pressed in or Loctite in a clearance hole as suggested.

Instead of press fit, could you use shrink or heat expanded fit ? Same limits and finished size, but less stress in fitting the bush (If you are quick enough).

Bob

A thin bronze bush stretched over a shaft is unlikely to stay in place for long - it will expand as it heats up and loosen.

- can't you either

- fit a thin steel sleeve and re-adjust the current bearing / /housing to accommodate it.

- reduce the shaft end and fit a sleeve to bring it back to std. dia.,

- or build it up and grind it back as a reconditioner would do..

I would use Locktite 620 retainer as that is designed to retain bearings etc with high strength and high temperature. You fit it with a slight clearance to allow the Locktite to work on a very clean surface so clean it very well with a solvent cleaner first. You don't have to allow for press fit just size on outside and slight clearance of a couple of thou but check the Locktite web site for details. I used it on parts in a plastic mould where it was heated by the plastic and loaded with a pin which had a rotary pull on the part in question.

David

As a practical engineer I immediately thought that a press fit will not work, others seem to be of the same opinion.Maybe Loctite a bush to the shaft and turn the O/D to size.

Tony

To digress slightly, the usual way to fix something like this would be to grind down the damaged shaft, hard chrome plate and grind back to finished size. This us not the same as the decorative finish (bling) applied to cars.

Not having a picture or a drawing to work from.

As I see it the worn section of the shaft is no good for a Needle roller to run on?

Is the worn section in the centre or on the end of the Shaft?

If this worn section is on the end of the shaft then it could be turned down and a Needle bearing Hardened Sleeve, (commercially available), be secured with Loctite. This will ensure this bearing is always repairable.

If it is in the centre of the shaft then this area can be repaired using a spray welding technique. This area will need to be ground back to size afterwards. Distortion can be a problem but usually if this is done correctly this is minimal.

Regards

Gray,

The idea of har chrome platingb the bearing area and grinding back to original size appeals. (Keeps everythinbg to standard dimensions, although Imperial needle roller bearings may be becoming reare )

Unlike London Transport who used to grind worn shackle pins to their various standard undersizes, Southdown Motor Services used to have the pins hard chromed and ground back to original size. In this way, any pin could be used, in any vehicle.

Howard

I've used Graham's spray welding technique, the advantage of hard chrome is that it is a cold process, so won't affect any heat treatment of the rest of the shaft

Have a look at Glacier/oilite bushings, they give you all the information you need. Soft material thin wall bushes need a sized mandrel to create the correct size during deformation.

Sorry, but I'm confused. Why is it necessary to do anything to the shaft? - I thought the requirement was to permanently fit a new phosphor bronze sleeve to it, so why are we talking about hardening it?

So that he can go back to a needle roller.

I for one do not think the phos bronze will hold up long when used with a needle roller bearing.

I did think from reading the original post that the phos bronze bearing was to run in the original needle roller race housing bore?

This is where a drawing or better still a photograph saves a lot of speculation.

Regards

Gray,

Dear Simon

With a four millimeter wall thickness on that diameter of bronze sleeve any push fit will damage the sleeve and distort it. I assume you want to take the needle roller outer shell out and the bushing to rotate within the outer shells housing.

Rather than a push fit, try as suggested above a heat shrink fit.

Put the shaft in the freezer wrapped in cling film and the bushing in the oven as high as your over will go.

When ready put the shaft in your vice with copper jaws get the bushing ready and a bit of pipe just over the size of the shaft, take the cling film off and it will remove the condensation and ice with it and lower the bushing on the shaft, being bronze it will have expanded a fair bit and should just drop in place if not use the pipe section to gently help it in place and then let it all come to the same temperature.

In regards to clearance this will depend upon the heating and cooling range but as its a gearbox assume it will be less than one hundred degrees i would allow two to three thou as your interfearance fit.

For my tuppence worth i would suggest making the bronze bushing a shrink fit in the housing and then shrinking or locktighting a thin high strength steel tube over the shaft roller surface and allowing that to be the running surface within the static bushing. however that may interfear with other items going onto the shaft and thats why you have chosen your approach.

BR Rolster

Is this summary of the situation correct?

You want to make a thin walled sleeve, pressed on to an existing shaft so will revolve with the shaft and the sleeve outer surface will be running within the (worn/damaged?) bore that the needles ran on?

Ian P

If the load is in one direction you're a lot better off having the steel shaft rotating in the stationary bronze bush. This is because ad the bronze wears the contact twixt steel and bronze remains a half moon shape, good for hydrodynamic oil film generation. If the bronze rotates in a stationary steel housing, the bronze just gets bigger all round. This is one reason why old fashioned wheelbarrows had the axle rotating with the wheel in rough cast iron bearings. Modern cheap ones with plastic wheels rotating on stationary axles soon develop wobbly wheels.

Well chaps, firstly thanks to all of you who have given this brain space, and replied as above. I guess I need to provide some additional information to eleaborate on my initial intentionally succinct query.

The application is part of a Fairey Overdrive for a series 2a diesel Land Rover. I have several of these - the o'd that is - and I'm optimistic of making at least one complete one out of the box of bits.

I bought this one recently - it's a good place to start.

In explanation, this unit is a completely mechanical gearbox which bolts into the back of the main gearbox. The helical gear is the output shaft, the input is concentric and runs on a needle roller bearing inside that lumpy looking gear.

The input spline looks like this:

These are two identical input sleeves, the upper one has damaged splines and the external roller bearing is worn. The lower sleeve is new but does not have the roller bearing fitted yet. That roller bearing runs on the inner of the overdrive output gear - the big helical gear in the first picture.

Or it would if the inner surface didn't look like this:

I don't know if this is technically brinelling, those marks are indents in the hardened surface of the internal bore.

There are several ways of getting out of jail here. The shaft is not available as a new spare part, so one is going to choose between remedial work or finding a serviceable secondhand replacement. Suffice it to say I have two of these units with the same problem.

One way of tackling this is the "grind it bigger, chrome plate it and grind back to original spec" approach. I'm prepared to follow this if I can find someone who is prepared to take it on. It's outside my comfort zone by some way.

Given that the differential speed between the two shafts is either zero or a maximum of about 1300 rpm,, and the bearing bore is amply lubricated, I'm interested to make a bronze plain bearing and try it. It's a very quick cheap fix, and while I'm prepared to agree it isn't in the same class of exoticness as the original needle roller bearing I can accept that risk for the potential advantage of it being within my capabilities to make.

Enough for one post, I'll continue in a second shortly.

My bronze bearing sleeve will occupy the space where properly the rollers and cage on the sleeve would be. I want to make it fast on the inner sleeve, and slide on the (brinelled?) surface of the inside bore of the helical gear which is lubricated via holes in the base of the gear teeth such that gear oil is squeezed into the bearing space by the meshing action of the gears.

Yes, I agree that if Mr Fairey didn't need to go to the trouble and expense of providing a needle roller bearing running in close tolerance and hardened surfaces he'd have fitted a bronze bush and called it good, but these things are intended for long periods of heavy service in arduous conditions with poor maintenance. The poor maintenance might be a good fit, but my application is light duty by comparison.

I'm happy with the logic that has come forward to say "don't make it a press fit, the sleeve will stretch and burst" Fair point. I'm equally happy to accept that the whole idea is barmy and won't last five minutes/5 miles/next service interval. Such is experimentation.

I like the idea of freezing the splined sleeve and heating the bronze bush to assemble them together, except I don't see why the resulting hoop stress in the bronze is any different to that left by a press fit, So the gospel according to Loctite has it at the moment.

I'd be grateful for your thoughts.