Hardening gauge plate

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

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.

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

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

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 .

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

.. or make the die blocks from PTFE?

Russell.

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

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

Hello All,

Ground Flat Stock (01) or Gauge Plate will distort in heat treatment, by how much depends on the section of the material and the way it was heated. To effectively heat treat in a hearth the material wants to be heated until the surface starts to blister, then quench in Oil, new engine oil is to be preferred for ME work, but not Old engine oil.

Be prepared for some surface pitting where the blisters form, it can be reduced by smearing the component in liquid soap, i.e. washing up liquid, prior to heating. It also makes getting the carbon deposit off from the oil quench easier, if done correctly the surface after quenching is usually a matt grey with no deposit.

My experience tells me that the slot will vary in size at the centre of the link after heat treatment due to differing grain growth in each arm of the link. Depending on the design of the link this size variation could be smaller or larger.

Gauge Plate left soft will under sliding conditons develope a tough skin and this skin can become quite hard. Low cost assembly tooling made in this way lasts for many years, most of the time without lubrication.

Given the delicate nature of the expansion links I personally would leave them soft, and run a mild steel die block, not knowing how big the parts are, a Bronze die block might be too soft in a small section.

Gray,

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

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

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

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" costs ~ £30, I don't think that is an option I will be using.

Dave.

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