Whitening

Hi Folks, I am progressing well with my build of the Vega Twin. I am at the stage of making the piston rings. In David Parkers construction notes he states that the rings need to be "painted with a thin paste of whiting in methylated spirits". Could any one educated me on what this whitening is and the object of it.

Many thanks

Whiting is finely ground chalk that is used as a pigment in paints and in papermaking. It is practically pure calcium carbonate. It is a fine white powder.

For information chalk used on blackboards is not calcium carbonate but calcium sulphate so do norrt be tempted to grind up these.

Whitening was used extensively to paint ceilings when mixed with water, whats the purpose of painting the piston rings with whitening mixed with meths ? To de-grease maybe?

John

Whiting in methylated spirit is a mild abrasive that may be used to clean silver or to prepare glass for gilding. In this case however could the whiting be there simply to protect the piston rings from corrosion until the engine is completed?

Brian G

I imagine the whiting is applied to protect the rings from scaling during heat treatment to introduce a sprung gap. Tippex will probably work.

Rod

I never bother to coat my rings with anything but as Rod says Tippex would stop oxidation though you will then have to clean off the remains of it.

Thanks guys, According to Mr. Parker you clamp the rings in a stack, paint on the Whitening, Heat to cherry red allow to cool and remove whitening with a wire brush. This seems a straight forward process but I was just trying to find out why one would do this ? reading on I think Rod has hit the nail on the head. Again thank you all

Edited By Alan Gordon 4 on 07/10/2020 14:28:46

As a child I remember plimsolls (remember them?) being smartened up by whitening them.

Quote " According to Mr. Parker you clamp the rings in a stack, paint on the Whitening, Heat to cherry red allow to cool and remove whitening with a wire brush. "
Having just spent many hours making Meehanite rings for the loco and breaking 50% of them during fitting, may I offer a note of caution?
Clamp the rings but do not heat to cherry red; that's far too hot. It is above the critical temp and will cause metallurgical changes in the iron which are not wanted. After much online searching, I found an excellent article which reviewed (& criticised) some of the expert writings of Tubal Cain, Prof Chaddock etc. Therein it states the correct temp is "480 -520 degC " and not hotter.
I borrowed a pyrometer, followed the guidance and no more breakages fitting them over the piston.
Don't bother with whiting - at the correct temp there'll be little or no scaling.

Unfortunately, the url I have for the article seems to have expired
http://www.btinternet.com/~sylvestris/rings/rings.html
but if you PM me I'll gladly email you a copy - it's a wealth of information.

If the whitening is calcium carbonate and its heated to 'cherry red' it will turn into calcium oxide. Isn't this a bit caustic to touch ?

Putty for glazing is whitening + boiled linseed oil.

Edited By KWIL on 07/10/2020 16:28:46

Not at that temperature. Around 900 degrees Celsius is required to decompose Calcium carbonate. I believe the reaction proceeds quite quickly at 920-930 degrees (the temperature in a the last of a 4 stage preheater - in a dry process cement kiln).

Rings only need to be heated until they relax, then cooled. The new ‘set’ of the ring can be repeated to a larger ‘set’ if required. For rings I have ‘set’, the ring was expanded to the required size and then heated until it fell off the expander. They were rather larger rings than the average model steam engine, I expect.

I had no idea of the actual temperature but if it is around 500 Celsius, that would be classed as dull-red, I would think. Well, dull-red to most - I can’t easily see it glowing until it gets really hot - being red-green colourblind.🙂

Jerry Howell provides some details of various methods at this link:

**LINK**

From what I have seen over the years most use the Trimble method.

Emgee

As Fowlers Fury says cherry red is too hot for this sort of thing leading to unwanted metallurgical changes.

Especially as most folks idea of cherry red is more like the "fake" dyed, flavoured and candied glace cherries wot mum used to put in cakes or on top of the icing. Toned down a bit in recent years but back in the day these were just short of Dayglo!

By colour 480 - 520 °C is when the barest hint of red appears in a dark environment. Odds are you will be high when going by colour but, probably not too high.

Clive

Emgee ~ thanks for posting that link, it is to the article I referred to above - but couldn't now locate its source.

My latest rings were made for the HP valve chamber and thus smaller in size than those for the main (5" scale) cylinders. As, NDIY comments, the rings take a set at the "right" temp. I over-heated the first batch and half snapped as they were gently spread over the valve bobbin. With the pyrometer, the 2nd batch were gently raised to about 500C and allowed to cool amongst the fire bricks. The pre-cut gaps of 2 thou were held apart in the clamp - as below before being covered with the 'fire bricks'. The 4 rings were then sprung over the bobbin without a problem.

Emgee,

Thanks for posting that link, I had not seen it before and found it very informative about issues beyond piston rings.

Rod

Ah, ye olde receipts recommending hard to find stuff like wrought-iron, ivory, gunpowder and opium. Back when people rode trams to work whiting was common as muck. Not waterproof or sturdy, but wonderfully cheap! Whitewash a cellar by adding some water and boiled horse hooves to a bucketful of whiting powder, and have an urchin stir it. Most of us have moved on to real paint, but it's still used by artists to prepare canvases.

Typex gets my vote!

Dave

Another (prettier) version of Howell's article: **LINK**

'The Trimble method' gets bandied about quite a lot, particularly in the USA. Prof. Chaddock (Loughborough, England) described 'the method' in 1967, long before Trimble's article in Strictly IC - in the '80, IIRC. It's difficult to believe that Trimble was unaware of Chaddock's writings, but his article made no reference to what had gone before. Let's give credit where credit's due - it's 'the Chaddock method'. Of course, Trimble was an American...

Interesting use of whiting on the Repair Shop series 5 episode 38. Used to make a mould to bend some glass to repair an SECR railway lamp.

Rod

Hi Kiwi Bloke

I thought the Chaddock method called for the ring to be turned a few thou over bore size but the Trimble method calls for a ring turned to the bore diameter.

Clearly Prof Chaddock was the first to publish a method as far as I know without research, but if the pages of ME's are searched I believe there may be others detailing a method before either Trimble or Chaddock, 1 candidate would be a Mr B Stalham of Kings Lynn whose air cooled vee twin model hydroplane engine appeared on the cover of the ME from memory during the 1950's.

Like many parts there is always a different method of producing it, best to use what suits you.

Emgee

1954    111    2782    341    B.Stalham    A Supercharged Vee Twin. Details of an Experimental 15 cc Engine for a Racing Hydroplane

name changed

Edited By Emgee on 07/10/2020 22:55:49

Edited By Emgee on 07/10/2020 23:00:15