Crosshead Engine & Crosshead Slider Design 1

[anyoldname]

I've been handed a design job that involves designing the cranktrain for a crosshead engine (think large ship engine type arrangement).

The one area of this where I have no previous experience is designing the crosshead & slide mechanism so I'm hoping that someone might be able to point me in the direction of some references that google hasn't found for me.

I'm interested in all design aspects of the cross slide, including contact pressure, sliding velocity limits/issues, running clearance, clearance adjustment mechanisms and lubrication. I'm assuming that a well designed cross head will run on an oil film (while its moving, the oil film may well collapse when everything changes direction at TDC & BDC), does anybody have any idea whether its necessary to inject the oil into the middle of the bearing/contact area or can you just spray it onto the slide rails and let the cross slide run over it?

We're also designing the crank train, the stroke and engine speed are already defined so the mean piston speed is out of my hands but we can influence the cross slide motion and thrust loads via conrod length.

Any experienced comments or suggested references will be greatly appreciated.

Thanks.

 

[MikeHalloran]

Terrible news: My primary source of info about old stuff has shut down:

http://www.lindsaybks.com/

Mike Halloran
Pembroke Pines, FL, USA

 

[MikeHalloran]

Following a link from Lindsay's Goodbye page, I found this, which may be of interest:

http://www.youroldtimebookstore.com/product-p/4104.htm

Mike Halloran
Pembroke Pines, FL, USA

 

[GregLocock]

Great project. I'd be booking a visit to look at similar products. Splash lube seems a bit steam age, but siting a pressure feed in the high pressure area is also a bit risky.



Cheers

Greg Locock


New here? Try reading these, they might help FAQ731-376

http://eng-tips.com/market.cfm?

 

[berkshire]

This site will give you information on prior art. Be aware that this is a massive web site with links to other engine museums, and links to technical data on some but not all engines.
B.E.

You are judged not by what you know, but by what you can do.

 

[berkshire]

Slide 139 Portland 2008 may give you some ideas. From the link I posted earlier
B.E.

You are judged not by what you know, but by what you can do.

 

[bcs5274]

most compressor apps run oil from the connecting rod thru the crosshead pin then up/down to the shoe, each shoe has oiling grooves that disperse oil across it top and bottom.
the only splash lube engine i have experience with is ajax.

 

[berkshire]

Here is another shot of a cross head and slide from the museum notice that this one has oil cups built in.
B.E.

You are judged not by what you know, but by what you can do.

 

[anyoldname]

Thanks for all of the replies.

Mike, I've purchased a copy of the book you suggested and its fairly interesting but a little vague on design limits. The way the old timers laid out equations is very different to what is taught nowadays (well, relatively recently anyway).

Question for Greg Locock, why do you think it is risky to locate the oil supply in the high pressure area? Is this a concern that the hydrodynamic forces would stall the delivery flow or that you could get errosion opposite the feed point at TDC & BDC? I've recently seen some examples of bearings with shallow grooves around the oil supply point to help distribute the oil, I think these could help prevent both of these issues.

Thanks.

 

[GregLocock]

The instantaneous hydrodynamic pressure in the bearing can easily exceed the oil feed pressure, so your source acts as a drain just when you need it most!

That being said analysing bearing pressures is a known art, it just needs doing properly. Worst case scenario is you build a single cylinder engine and install pressure tappings at likely points around the circumference.



Cheers

Greg Locock


New here? Try reading these, they might help FAQ731-376

http://eng-tips.com/market.cfm?

 

[MikeHalloran]

I'll second Greg's suggestion, and additonally suggest some alternate oil feed taps at low pressure locations, where the pump can actually push some oil into the gap.



Mike Halloran
Pembroke Pines, FL, USA

 

[DuncanM]

Crosshead is normally below the piston rod stuffing box / sealing arrangement, so will not normally be subject to high pressure atmosphere.

Some engines I've worked on have used telescoping tubes to the crosshead which also supply oil to a cooling circuit within the piston rod and piston crown. I believe other manufacturers use a swinging pipe arrangement.

I don't recall whether oil was sprayed or applied directly, but being as the slides are within the sump enclosure it shouldn't matter, so long as spraying is with large enough droplet sizes to avoid oil mist generation.