thermochromic pencils

[foy9999]

Hi guys.

Years and years ago I read in a (Haynes?) manual that you could get pencils/pens to mark alloy casings before putting in oven to heat (bearing removal etc) and you'd know when they'd reached a certain temperature as the marks would change colour.

When I first asked about them in an engineering shop in Glasgow they looked at me with sympathy.

I've never came across them and Google doesn't throw anything up.

Did I imagine it?

 

[Country Joe]

No, you're not going mad!
They're right here!

All the Best,
CJ

 

[Jim Davey]

Tempilsticks we call them. It's like a crayon you draw a mark on a metal part you want to preheat to a certain temperature (the sticks come in lots of different temperature ranges) and I believe the mark goes from white to black once the temperature is reached. Clever thing is you could draw the mark for the temp you wanted, but if you didn't want to overheat the part you could use another marker with say a 50 degree higher temp than the desired heat and just make sure you don't get the second mark to turn black too.
Markall is the firm that make ours I think, not looked for a while.

 

[Jim Davey]

I should've clicked CJs link, Markal for sure.

 

[gordon stephenson]

Tempilstik were always the most common

 

[Parm]

Widely used in critical welding application. Last saw then used on the SS casings for MRI magnets at a place just outside oxford

 

[anto44]

As everyone else said they're called tempilsticks. got given a few by a sales rep for a bearing company a few years ago for using when fitting bearings. I could be wrong on this but I think the ones he gave me were 180°c as the max temp for a standard bearing was 200°c but check the figures with the bearing manufacturer to be sure.

 

[foy9999]

Thanks for the replies guys.

Thought I'd hit a dead-end at first as the links from Google took me to a UK supplier with footnote saying don't sell to general public. Then Ebay search for Tempilstick only yielded 3 hits worldwide but if you shorten it to Tempil there are loads. That's cos it's Tempilstik .

I've heard between 250C + 300C is sufficient for heating aluminium engine casting to tap out bearings or valve-guides. Another thing I've never had any luck with is using Lumiweld to repair alloy castings. I read in Haynes manual (1454 Motorcycle Workshop Practise Manual) that you need to get the casing up to about 390C for the Lumiweld filler rod to melt.

There are also some under Thermomelt. That's the Markal ones.

I should've asked years ago

 

[gordon stephenson]

I have used Lumiweld quite a few time with really good success. Takes practice to get good results, but worth the effort.

 

[foy9999]

I had a go once with a butane blowlamp. Pointed it at the casing for hours and very little happened. I believe the secret is heating the whole casting and having it sitting on vermiculite so you don't lose the heat as fast as it's going in. MAPP Gas perhaps?

 

[foy9999]

In case anyone is interested I finally bought, an used, my a 'heat crayon'

This was to get some steel components out of an engine casing (Yamaha RD125)

The manual said something about taking them up to 120 degrees C and the crayon I got was for 150C which is close.

It was just under £10 (posted) from Ebay.

I found the crayon didn't show up very well on the ally so tried it in different place and got a better result on a smooth part of the casting.

After a while heating up the marks vanished. I assumed they would change colour.

The parts came out easily fwiw

heat crayon

component marked

crayon vanished after part heated

stuck stud came out easily

as did shaft that was in blind bore and tight dowels

 

[Brad93]

ThermoChrom is the original german manufacturer/inventer afaik