Chipping Carbide
During the
production of Tungsten Carbide the material goes
through a "green state" where it has the strength of
sidewalk chalk. As the tips are handled they are
sometimes chipped. After this green state the tips
go through a final sintering and become hard.
Unfortunately It has been common for carbide
suppliers to blame chipping and cracking on the
customer. What follows are some simple
demonstrations of Carbide properties.
Weight
Drop Test -
Tinned tips versus untinned tips
Experiment and
Results:
We dropped a weight
from different heights and measured where the parts
break. This gives us
a figure in
foot-pounds. The weight is 20.665 pounds. We
multiply that by the distance dropped.
The saw tips were
set on their sides so that the braze alloy wasn't on
the top or bottom.
Untinned
Impact at failure Pretinned
Impact at failure
Average
17.63 33.132
High
22.11 34.17
Low
11.78 32.44
Hammer And Cloth
Test
Wrap the carbide in
a cloth so the pieces don’t fly. Put the cloth on a
concrete floor
and beat the tips
hard with a steel hammer.
Shotgun
test
We bought a used
.410 shotgun and fired carbide tips at a concrete
block wall from distance
of twenty feet. The
concrete blocks chipped but the carbide did not. Do
this behind cover
as the tips ricochet
unpredictably.
Speed
Force
Vise Test (Testing
Carbide Strength and Braze Joint Strength)
This is a simple test to determine how easily your
saw tips break and how good the braze joint is.
It is very simple. You braze a saw tip onto a
narrow piece of plain, clean steel. Then you clamp
the saw tip into a vise making sure that you just
clamp the tip and not the steel bar. Do not clamp
the tip too hard or you will break it before you
start testing.
You lean on the end of the bar until something
gives. In some cases the tip breaks, and in other
cases the tip comes off. (Safety notes: you might
want gloves or some sort of padding when you lean on
the bar. If you do it right you have to put a lot
of force to break the joint. Make sure that you are
ready when it gives so that you don’t fall.) You
can also hit the bar with a hammer but be careful.
It can really vibrate and it can really fly when it
comes loose.
Result class 1 - The
tip breaks.
A
good carbide braze joint is stronger than either the
carbide or the steel being joined. In this case
you will break
the carbide and will
leave jagged chunks on the steel. There will be
very little or any area of the carbide that does
not stick to the
steel. If you do this with different grades of
carbide you should be able to feel that some are
harder to
break than others.
Most people can tell a difference if it is big
enough.
Result class 2 - The tip comes off clean and there
is no braze
When this happens
look at the braze alloy left on the steel. If the
tip was badly plated you may be able to
see a gray layer on
the braze alloy. The braze alloy stuck to the
plating but the plating came off the tip.
Look for bubbles in
the braze alloy to see if it was overheated.
Alloy tips
When we tested
these tips came off clean and there was braze alloy
stuck to both the steel and the tip. The braze
alloy actually ripped in half. You can see a good
amount of the gold colored alloy on both the steel
and the tip. It was very hard to rip the alloy but
if you put enough force into a braze joint then
something will eventually give.
Hit
It with A Stick
Put the tips on the
saw then beat on them with a Stick. I like this
because it is a good test, it
worked very well and
the guy that came up with it made a lot of money
because his saws
worked better. He
was also criticized because he was having problems
and no one else was.
Note: Many years
ago this customer called me in because he was having
problems with tip loss.
On the way down I
stopped to see another customer and asked him if he
had a tip loss problem,
the first guy said
he didn’t have a problem. I talked to the second
guy and then stopped into see
the first customer
again. Again I asked him if he was having a problem
with tip loss. He said
that he wasn’t
having a problem. Sure the tips came off sometimes
but it wasn’t a problem.
The difference was
in whether you considered tip loss a problem.
Hit it with a stick
problem
Put the tips on the
saw then beat on them with a stick
Problems:
1. No way to
measure the force accurately
2. Everybody hits
differently
3. This isn't the
way impact is applied in actual use
4. Takes too long
5. Costs too much
Benefit: It works
Steel Impact Test
We took a tip,
clamped it in a vise, put a chisel on the cutting
edge and hit it with a steel hammer without chipping
the edge.
Tip in vise
Hitting
tip with chisel and hammer
Impacted
area at 10x and 60x. No chips even
after being hit with a chisel.
Chipping in
tumbler cleaning
Experiment:
Determine whether tumbling saw tips during cleaning
damages them.
We went to the local
craft store and bought some small, fragile items.
We took a batch of
2,000 CWG
7165 tips that needed tumbling.
We added:
2 cheap pottery
flowerpots
6 glass beads
6 seashells
We ran ordinary
craft store, glass beads in a tumbler with tungsten
carbide.
Left - Test parts,
Center - Untumbled bead at 50x - caliper jaws set at
0.001” Right - Tumbled bead at 50 x caliper jaws
set at 0.001”
