Bing
Ajax  Loading... Please wait...

Chipping Tungsten Carbide

Our Newsletter

Chipping Tungsten Carbide

 From the book Building Superior Brazed Tools    Buy the Book

 

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 saw 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.  See more articles on Tungsten carbide and Cermet Properties. 

Weight Drop Test - Pretin 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.

 chipping_carbide-1.jpg

                  Untinned - Impact at failure            Pretinned - Impact at failure

Average                       17.63                                        33.132

High                             22.11                                        34.17

Low                             11.78                                        32.44 

 chipping_carbide-2.gif

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. 

chipping_carbide-3.jpg 

chipping_carbide-4.png chipping_carbide-5.png

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. 

 chipping_carbide-6.jpg

 chipping_carbide-7.jpg

chipping_carbide-8.jpg 

It is very simple.  You braze a saw tip onto a narrow piece of plain, clean steel.  See our Cleaning Steel article to find out the importance of the Steel being clean.  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.

chipping_carbide-9.jpg 

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.

 chipping_carbide-10.jpg

Brazing 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.

 chipping_carbide-11.jpg

 chipping_carbide-12.jpg

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.  

 chipping_carbide-13.jpg

 chipping_carbide-14.jpg

Tip in vise    

 Hitting tip with chisel and hammer

 chipping_carbide-15.jpg

 chipping_carbide-16.jpg

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.   

 chipping_carbide-17.jpg

 chipping_carbide-18.jpg

 chipping_carbide-19.jpg

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”


b2b lead generation