Delrin and Journals

[Fred_V]

I did an overhaul on an engine that had run hard for 25 years with Delrin rod bearings. They were worn badly and the crank pins too but they held up for all that time.

The question is, was the material Delrin AF, or just plain old Delrin? There's a huge difference in how each would hold up in service.

If you don't know, AF is a light chocolate brown color, unlike other types of Delrin.

H

This stuff was black.

[Fred_V]

What? Delrin... Plastic?!! I thought we were building a steam engine here.......... Cast iron, bronze bearings, STEEL!!!

So, I suppose you're also opposed to 3D printing a boiler?

LOL, good one!!

[Bill Shields]

Nylatron works very well in non-rotating situations - like the crosshead bearing. In pure rotation, it can overheat and 'smear'..had a bad experience with that.

Sintered bronze (oillite) does not hold up well in applications where reciprocating motion is present - it tends to 'pound out and crack'.

Did you see the jet engine that the guys from GE 3D printed with a LASER?

Will be a while before a boiler is a practical print job...but then there was the fellow that wanted to put a boiler together with JB WELD...

[Atkinson_Railroad]

Is it possible to clarify how the term “journal” is being used in this discussion?

The original post by Dick_Morris alludes to making a journal portion of a shaft from delrin.
“…I can't remember seeing a discussion of using it for journals.”

I understand the [railroad speak] term of journal bearings, but what’s confusing in reading this thread is what portions of the assembly are being considered for using the delrin material.

As I’ve interpreted the meaning of “journal”, it refers to the rotating surface portion of a shaft intended to fit with a bearing.
The journal area of a shaft is usually made to a very specific dimension to mate with a fixed bearing element such as a ball bearing, a babbitt bearing, a sleeve bearing, a taper roller bearing, and so on.

The nomenclature of a shaft/bearing assembly in its most basic arrangement shown here for example:

https://en.wikipedia.org/wiki/Plain_bea ... _angle.svg

Is this a discussion on using delrin material to make the fixed portion of a bearing arrangement/assembly?

Thanks for any clarity on this.

John

[Bill Shields]

TYPICALLY, a JOURNAL is something that supports an axle (wheel).

Rod - on the end of a main or connecting rod that has a 360 degree rotating shaft in the center.

Crosshead - the end of the main rod that is on the crosshead where the 'pin' in the center does not rotate through a full 360 degrees.

[Atkinson_Railroad]

Thanks for your reply Bill.

A reminder that Google is a friend in all of this (as usual).

A quick search on the subject of Delrin used for bearings finds this statement directly from DuPont engineering literature:

"Soft steel or stainless steel, as well as all non-ferrous metals do not run well with plastic bearings, even those with a so called ‘‘self-lubricating’’ filler.

Here is the URL to the PDF:
http://www.dupont.com/content/dam/dupon ... arings.pdf

John

[Bill Shields]

it is generally true that stainless is a TERRIBLE bearing surface and should be avoided whenever possible.

soft steels...well that is rather obvious to many, but not so to others.

"self lubricating' does not mean 'friction free'.

[Dick_Morris]

The original post by Dick_Morris alludes to making a journal portion of a shaft from delrin.
“…I can't remember seeing a discussion of using it for journals.”

I was thinking about the whole assembly, but you're correct, the Delrin would be for the bearing portion.

It looks like I'll modify the design slightly to allow for a wider journal box that will fit a ball bearing. The axle scales to 3/4" so the bearing will have an OD of 1-5/8" where the prototype box would scale to 1-1/8" wide.

While needle bearings might work fine, I'm reluctant to use them where a replacement would require pressing off the wheel. I also feel better about using a sealed unit that doesn't require the axles to be hardened.

[Fender]

TYPICALLY, a JOURNAL is something that supports an axle (wheel).

Rod - on the end of a main or connecting rod that has a 360 degree rotating shaft in the center.

Crosshead - the end of the main rod that is on the crosshead where the 'pin' in the center does not rotate through a full 360 degrees.

I don't know whether "railroad" terminology is different from "general engineering" terminology, but here is how the 1908 Car Builder's Dictionary defines a journal: "The part of an axle or shaft on which the journal bearing rests.". Journal bearing definition: "A block of metal, usually some kind of Brass or Bronze, in contact with a journal, on which the load rests."

[Bill Shields]

RR is specific about journal for their limited range of application.

In general engineering, the same concept applies to a journal bearing -> from the French / Latin (as many of our tech words).

My wife considers a journal to be 'something where she should write notes to herself but never remembers..."