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Curious coating

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Rik Shaw22/02/2019 10:14:02
1313 forum posts
352 photos

Some time ago I bought at auction a large amount of machined and part machined components that had come from a manufacturer of conveyor lines. Much of the stuff was in the form of stainless and aluminium rollers. To date this lot has come in quite handy as a store of material.

Yesterday, I fished out a piece to turn into a stub mandrel for facing of a pair of steam cylinders. You can see from the pic what happened to the tool tip when I tried facing the grey coated shoulder at the now shiny end of this aluminium like material.

As I fed the tool in using a light cut the tip glowed orange /red. I should mention that the tool bit is not bogstandard HSS but something much tougher and harder – I forget the trade name for it. The coating is so incredibly hard that a file just slides over it without leaving a mark. My guess is that it might be ceramic anti-scuff. I finished machining by using a carbide insert without further problem.

Also, the aluminium like material was much tougher to machine than any “aly like” material I have machined in the past. I wondered if it was titanium but I did a google and read that titanium swarf will burn with a bright light similar to magnesium. It didn’t – it just glowed orange.

If anyone can shed light on coating and/or material I would be very interested to read your comments.




Edited By Rik Shaw on 22/02/2019 10:15:19

SillyOldDuffer22/02/2019 11:15:25
4723 forum posts
1010 photos

I like your guess it's Titanium with a coating. Titanium Nitride is the extra hard layer often added to HSS tools like milling cutters and twist drills - TiN. Only a few molecules thick, but the layer multiplies the tool's life.

Your sooper-dooper HSS might be the very best available, but even so it's not in the same league as TiN. Even worse, HSS loses hardness when overheated, which is easily done by rubbing the cutting edge on a surface harder than the tool. As titanium compunds the problems by hardening at red heat, I suspect you're right - you have a Hardened Titanium roller. The description fits this failure mode :

  1. HSS blunted after failing to penetrate a very hard surface.
  2. Blunt HSS rubs and overheats, thus losing its hardness.
  3. Temperature rises to red-heat due to friction, but not enough heat &/or surface exposed to ignite the swarf. Metal removed from work and cutter more by melting rather than cutting. Not good!

Even though it too has limitations, Carbide is much better than HSS against hard surfaces. Carbide has more chance of breaking through a TiN layer than HSS. Also carbide is much less likely to lose its edge when it gets hot than HSS - even at bright red heat. However, flood cooling is advised for a tough job like this. It would protect the tool and, assuming it is Titanium, stop the work hardening due to heat. I don't think machining small quantities of Titanium is a major fire hazard, but flood cooling would fix that risk too. (Titanium experts might know different!)

Often worth scarifying the hard skin found on cast-iron with a grinder. Once the surface is broken up, HSS works well. Might be worth trying the same on your roller - could be a lot softer inside.

Times change - I bet LBSC never had to machine Titanium!


Journeyman22/02/2019 11:40:54
611 forum posts
96 photos

Looks similar to Sherardized steel. The finish is hard but whether hard enough to damage the tool I don't know. I would have thought that the tool would have got below the surface and removed it in the first cut.

Can't imagine titanium being used in conveyor systems, a bit pricey, unless very specialized!

More on *** Sherardizing *** here


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