Hardening gauge plate

[David HaynesParticipant @davidhaynes53962]

Hi,

I want to harden some 1/8” gauge plate expansion links and die blocks and would like to confirm the process. The instructions stated ‘from 500 deg C preheat, raise to 790 deg C – 850 deg C, hold to become uniform and quench into oil’

Is this a heat colour of red heat, visible in the daylight preheat followed by dull cherry-red for the final stage?

Also, what sort of oil should be used? Would one of the Myford lathe oils oil be ok? Maybe a bit expensive and should some engine oil be used instead?

Thanks

Dave

[David HaynesParticipant @davidhaynes53962]

Hardening gauge plate expansion links and die blocks

[macmarchParticipant @macmarch]

It depends on whether its oil or water hardening gauge plate. When you have heated to cherry red and held it there for the heat to equalise through, and then quenched, it will be fragile. Don't drop it.

You don't mention what temper is needed. Which ever you want just clean the part to a bright surface and place in the oven. Most temper temperatures(!) are within range of the average cooker. You can then watch the colour change all over and let it soak. Remove and quench.

ray

[speelwerkParticipant @speelwerk]

1/8" (3mm) is thin and using water will probably distort your work, on the market is special hardening oil but probably difficult to get in small quantities.

Depending on the dimensions of your work you will need good size tank to hold it, dip it in quick, straigth and make sure to immerse it complete.

If you have delicate work you can coat it with a past (Condursal z 0095) too protect it against scaling.

[David HaynesParticipant @davidhaynes53962]

The link is about 1 3/4" long by ~1/2" wide

[David LittlewoodParticipant @davidlittlewood51847]

If you buy a copy of this book – it's only a fiver – it has some very good colour photgraphs of metal at the relevant temperatures, far more useful than any attempt I could make to describe them in words.

**LINK**

david

[MICHAEL WILLIAMSParticipant @michaelwilliams41215]

Hardening of gauge plate expansion links , though often advised , is not always the best thing to do . An unhardened gauge plate expansion link with a different metal , such as Al bronze , die block with polished rubbing surfaces can run for years before much wear sets in .

[Tony Pratt 1Participant @tonypratt1]

I stand to be corrected but I believe all gauge plate is the same ie O1 grade steel? if you quench in water versus oil you will get a more sever quench and a harder part but it is vital to temper afterwards to relieve the stressse in the part. I really don't think you will need special quenching oil for M E work even if you can get it in small amounts.

Tony

[Russell EberhardtParticipant @russelleberhardt48058]

Posted by MICHAEL WILLIAMS on 10/08/2012 22:52:52:

Hardening of gauge plate expansion links , though often advised , is not always the best thing to do . An unhardened gauge plate expansion link with a different metal , such as Al bronze , die block with polished rubbing surfaces can run for years before much wear sets in .

.. or make the die blocks from PTFE?

Russell.

[Roderick JenkinsParticipant @roderickjenkins93242]

Gauge plate is sold as "non-distorting", so it should not bend on heat treatment, provided it is quenched in oil. I've used new engine oil to good effect. 850 Celsius is hot, right at the top of the colour charts shown in Tubal Cain's book mentioned by David Littlewood. I think "cooked carrots" is a better description of the colour, as viewed in subdued light. The pre-heat is probably just to get it to temperature relatively slowly to avoid distortion. If you are heating with a propane torch then this will not be a problem. If you were to dump it straight into a furnace at 850C it might be.  There's a useful link here: http://www.threeplanes.net/toolsteel.htm

Cheers

Edited By Roderick Jenkins on 11/08/2012 15:51:18

[MICHAEL WILLIAMSParticipant @michaelwilliams41215]

Russell :

Yes PTFE might be worth try . Not as a simple solid block of PTFE though – one of the PTFE filled porous bronzes would be just about right .

General  :

Gauge plate is sold as low distortion – no guarantee is offered that it won't distort at all . Basically it is fully normalised as sold meaning there is a very low level of trapped stresses in it .

The most perfect bit of low distortion steel can however distort horribly if a correct procedure is not followed for heating and quenching .

Heating is relatively easy to get right with small components – just heat slowly to begin with and then rapidly to hardening temperature .

Quenching on the other hand has to be planned carefully to suit the components shape . Hard to explain it all here but to take the expansion link as an example – if you quench one of the curved edges while the other is still hot a sort of 'bimetal strip ' effect is created and the link will distort . When you now quench the othe side the distortion gets locked in . This situation will arise if you just drop the hot link in to quenching tank one edge before the other – even though the two quenching events are only milliseconds apart .

There is a 'geometric' factor and a 'sequence of cooling' factor to consider in every case .

You can never get it perfectly right but dropping the link into quench flat on is far better – there is less geometric tendency to distort and all of link gets quenched almost at the same time .

More :

Getting good wear characteristics for a metal on metal rubbing situation depends as much on the surface finishes of the components as it does on their hardness .

Regards ,

Michael Williams .

 

Edited By MICHAEL WILLIAMS on 11/08/2012 19:03:50

[mgjParticipant @mgj]

Agreed Graham.

 

But,- if you have to quench, one drops it in vertically to prevent bowing and keep it moving to prevent assymetric cooling..

Personally I'd use mild and case harden, for a couple of reasons.

1. Free cutting mild is a lot easier to cut than gauge plate

and while its not ideal for volume hardening,

2. The surface will still be much harder than tempered gauge plate and

3. Less prone to wearing the die by having a better surface finish

3. Stronger by being less prone to crack propagation

4. Its a lot easier to make a new die block after a few years, than a new expansion link.

For me I'm afraid its a bit like making driving pins out of silver steel. Sound like a good idea but metallurgically a little less than sound.

Edited By mgj on 11/08/2012 22:26:02

[David HaynesParticipant @davidhaynes53962]

Hi folks,

After a bit of thought, I have decided not to harden either the expansion link or the die block, but to re-make a die block from phosphor bronze, on the premise that this already has good bearing properties.

Just one question, does anyone know of suppliers of 1/8" sheets of PB? I don't want to have to cut down 1/2" sq bar.

Thanks

Dave

[Ian S CParticipant @iansc]

Here in NZ I think my supplier has it in 523 Phospher Bronze sheet, up to 3.0 mm, X 1800 mm x 250 mm, in what is listed as 'spring hard". Its such a little bit of metal, you could cut a slice off your 1/2" stuff, and you will find a use for whats left over, maybe just split it in half, there won't be too much waste. Ian S C

[David HaynesParticipant @davidhaynes53962]

Thanks Ian, that was the way I was thinking I would be going. I did think about using PTFE sheet, but when a piece 300mm x 300mm x 3mm (nearest I can get to 1/8&quot costs ~ £30, I don't think that is an option I will be using.

Dave.

[Sub MandrelParticipant @submandrel]

I quench in cooking oil. Interesting bit of bucket chemistry, as over time it becomes much thicker – presumably due to cross-linking of the carbon chains? Unless someone knows different.

Works well though.

Neil

[WindyParticipant @windy30762]

I have made a of couple of simple form tools to machine some curves on two inner UJ for the prop-shaft ends.

They are out of 0.5in X 0.375in gauge plate will quenching in water crack them?

I made an simple outer UJ from silver steel and quenched vertical but it distorted too much.

Other outer simple UJ have been made in the past out of case hardened steel and various other hardenable steels with hardly any distortion.

Is the silver steel more prone to distortion?

Paul

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