Shrink Fitting C/I Cylinder Liners

I would like to shrink fit a cast iron cylinder liner to a cast iron model steam locomotive cylinder block.

The finished bore of the cylinder is 50mm with an overall length of 90mm. I anticipate making the liner 2mm thick when fully machined. Reference to 'Model Engineer's Handbook' suggests that for shrink fitting the liner should be 0.07mm larger than the 'hole' into which it will be fitted - if I have understood correctly.

Has anyone any guidance that might assist me in this enterprise?

I have already 'had a go'.

I made the liner as a solid cylinder 150mm long.

I heated the cylinder in the oven to just over 200 degrees C, and cooled the liner in the freezer and gave it a good spray of 'pipe freezer'. It slid in easily.. until it stopped 30mm short of full depth of fit as surface heat transference meant that it fitted! And of course I could not shift it further... either way! So I have had to bore it out.

Obviously I will reduce the 'interference' this time - any suggestions or experience as to appropriate limits for my use and tooling? Would it make more sense to bore out a significant amount of the liner before shrink fitting? My thinking was that the large solid 'slug' would retain the cold better so giving me a little more time to work. Any views on whether this effect is significant?

I am a self-taught model engineer, and despite finding some very detailed charts of shrink-fitting data on-line am quite unable to make head or tail of them! Plus my equipment is basic, I do not have access to hydraulic press type tooling, etc.

Regards,

Phil

Edited By Weary on 30/09/2013 18:50:34

Phil,

Do you not think your "solid liner" might be cooling the main cylinder block too quickly, so that it shrunk onto the "liner" too soon ?

Richard.

Alternatively, just make the liner a press fit. The cylinder end caps will stop it going anywhere. Relieve the outside of the cylinder where a seal isn't important to ease fitting, and draw it in with a puller made of M12 studding.

Neil

Your liner will compress, so probably best to keep your planned interference, push it all in at once without stopping with eg an arbor press.

A well known local engineer who's own built Ford rally engine showed the works ones the way home many years ago told me he puts a smear of Rocal Molyslip Dry Paste on his liners to stop them picking up when pressed in.

Something I use on my cam and follower on the flash steamer as a dry lubricant also when pressing in my valve guide.

It is rather dear for a small tube but seems to work.

Paul

Thank you for your suggestions.

I have completed the shrink fit successfully!

I grouped all your wisdom and:

reduced the interference slightly to 0.06mm

drilled a 12mm hole through the 'solid' liner to allow pipe freeze to be introduced to the core of the liner 'slug' as well as exterior after a spell in the freezer; + if necessary the application of a 'puller'

Heated the cylinder to about 250 degrees centigrade.

And the core slid straight in to full depth and now that all temperatures have normalised is very firmly fitted!

I researched The Molyslip dry paste and didn't use it on this occasion, as it seemed to me that it left layers of slippery Molybdenum disulphide between the two surfaces, so reducing the final grip between the two. However I can forsee a number of potential other uses for this product so thanks for the tip!

Following my experience trying to remove the failed liner I would say that the shrink fit is far superior to other interference fits for this use as the liner seemed very firmly fitted and effectively an integral part of the cylinder down to 0.5mm wall thickness. Others might see this as 'over-engineering'!!

Speed and confidence are of the essence if anyone else 'has a go'.

Thanks again gentlemen,

Phil

Am I missing something, here? A cast iron liner in a cast iron cylinder block? Don't you just end up with a piece of cast iron with a slightly smaller hole in it? Why don't you just bore the cylinder block to size? I could understand it if the cylinder block was, say, aluminium, like a car engine. I'd be interested to hear the reasoning behind it. Maybe it's some spiffing wheeze known only to steam enthusiasts. I'll sit back and wait for the Flak to start bursting!

John

John,

Usually full size steam engines are fitted with a separate liner so the cylinder can be steam jacketed,

It makes the casting a lot simpler, also the liner can be replaced,

On my 6" Burrell the steam passages from the valve chest are partly machined into the outside of the liner which has a 3/8" wall thickness, also is steam jacketed.

Phil, well done! ...............Like you say , speed and confidence !

Richard.

Richard,

Thanks for the explanation. I just thought it was an awful lot of effort for a liner that was only 2mm thick. It makes sense when your cylinder is so much bigger - assuming the 6" to which you refer is the bore diameter. Looks like I'd better continue to stay away from anything with steam involved.

John

John,

The 6" I referred to is the scale of the traction engine, IE half size, the cylinder bore is 4 1/4" diameter, with the OD of the liner being 5"

Here are some pictures to show what I mean about the steam jacketing and the steam passages milled into the outside of the liner.

Richard.