I’ll go along with MikeHalloran on this. Has there been a change in the nylon or in the way the nylon is cleaned or prepped? Tungsten carbide is susceptible to mass loss in a basic environment if there is an electrical influence. It is susceptible to mass loss if there is exposure to acid.
A lot of problems, such as this, get solved about the fourteenth time you ask someone if something was changed. Quite often they don’t remember a change. Maybe purchasing made a change. Made the nylon is different. First time I ran across this was about 25 years ago. Brazing problem. Tips coming off the saw. Customer sais he hadn’t changed anything. After a couple weeks the customer finally said that all they had changed was the flux. Then he added that it couldn’t be the new flux because the salesman had said it was better than the old stuff.
If your dies are 10 years old then it is probably elemental Cobalt as a binder. Elemental Cobalt is more reactive than modern alloy binders.
Another thought is metal fatigue. Possibly the Cobalt has been through enough compression / tension (or compression / release) cycles that it has become brittle and you are getting loss from the rubbing. This is a real guess. The stuff I see in tools doesn’t go though that many cycles before other wear factors over shadow any possible metal fatigue considerations.
If your dies are 10 years old then there are much, much better grades of carbide available. Think about the transition from cathode ray tubes to flat screens in monitors and televisions for an idea.
When I do carbide wear analysis I use a list of 17 factors. See following (This is designed for analysis of cutting tools.)
Tungsten carbide is actually tungsten carbide grains cemented with a metal, usually cobalt. What follows are failure mechanisms we have seen in industry.
The following list is open for discussion but we have found it to be a useful tool for developing new grades.
1. Wear – the grains and the binder just plain wear down
2. Macrofracture – big chunks break off or the whole part breaks
3. Microfracture – edge chipping
4. Crack Initiation – How hard it is to start a crack
5. Crack propagation - how fast and how far the crack runs once started
6. Individual grains breaking
7. Individual grains pulling out
8. Chemical leaching that will dissolve the binder and let the grains fall out
9. Rubbing can also generate an electrical potential that will accelerate grain loss
10. Part deformation - If there is too much binder the part can deform
11. Friction Welding between the carbide and the material being cut
12. Physical Adhesion – the grains get physically pulled out. Think of sharp edges of the grains getting pulled by wood fibers.
13. Chemical adhesion – think of the grains as getting glued to the material being cut such as MDF, fibreboard, etc
14. Metal fatigue – The metal binder gets bent and fatigues like bending a piece of steel or other metal
15. Heat – adds to the whole thing especially as a saw goes in and out of a cut. The outside gets hotter faster than the inside. As the outside grows rapidly with the heat the inside doesn’t grow as fast and this creates stress that tends to cause flaking (spalling) on the outside.
16. Compression / Tension Cycling - in interrupted cuts the carbide rapidly goes though this cycle. There is good evidence that most damage is done as the carbide tip leaves the cut and pressure is released.
17. Tribology – as the tip moves though the material it is an acid environment and the heat and friction of the cutting create a combination of forces.
Notes:
As with any chemical reaction of this sort the acids create a salt that protects underlying binder until the salt is abraded away so grain size and binder chemistry are also important.
Electrochemical effect – erosion compounded by the differences in electrical resistivity between carbide and cobalt
Heat from rubbing can affect carbide so a slicker grade can increase life.
Thomas J. Walz
Carbide Processors, Inc.
Good engineering starts with a Grainger Catalog.
