Carbide Bit Wear in Underground Mining
By: Scott Bahr
Underground mining is a complex environment. One area which stands out as particularly complex is understanding carbide bit usage, wear life and replacement intervals. We would like to share with you the typical wear stages and the replacement time which the operators would look for when swapping out worn bits for new ones. With vastly varying environments, different materials, and differing bit life, understanding when it’s time to replace a bit is certainly not always easy to grasp.
Why you should pay attention to bit wear
The biggest concern when it comes to bit wear in underground mining is that worn bits will reduce cutting efficiency, increase power requirements, and impact the handling ability of the mining machine. Bits worn to a reduced gage length will reduce the cutting clearance of the cutting assembly, further impacting the ability to maneuver the machine. These become huge issues, especially when you want to ensure the budget of a project stays on target, and no machinery parts have to be replaced because of excessive bit wear.
Additionally, mining productivity and efficiency have a direct relationship to the condition of the cutting bits and their ability to perform. If you’re performing the job correctly, your bits should also be doing the job. If a bit is wearing too fast or too much, it could be a sign that you need to change up the way you are doing certain tasks.
The stages of bit wear
In general, you can track bit wear in three varying stages. The first, and worst, is what is called catastrophic wear, which means there is essentially no carbide left to work with. This is a stage that indicates the bit should have been changed long ago. This is the point where the wear can start affecting other parts of the machine and can get costly.
The second stage is the correct amount of wear. It’s not catastrophically worn yet, but it’s dull and not as sharp as it used to be. This is how a bit should look when you change it out.
The third stage is a different indicator. The steel body supporting the carbide in this stage has worn excessively, which will compromise the structural integrity of the carbide insert. Once too much of the steel has eroded the carbide can lose contact with the body.
Replacement times
Unfortunately, due to the challenges of each mining environment, there is no universal situation for bit requirements. Some bits might be working harder than others and need to be replaced sooner—that’s okay. It’s more about ensuring the bits are changed before they are excessively worn, so they don’t wear on other parts of the machine. After a certain point, the performance of a bit will start dropping exponentially, so you want to make sure to change it before this point.
What are the indicators?
Besides typical inspection of the bits to see if they’ve gone dull, there are a few other things that will indicate it’s time to change your bit. Worn bits will require increased forces to cut, transmitting these increased forces to the blocks and cutting assembly and reducing their life expectancy. On a larger mining machine, you might notice pushing a little harder, or that the machine is not moving up, down, or side to side as easily. On smaller jobs requiring a bit, a good rule of thumb is that you should make sure to inspect your bits after each task. The indicators aren’t as physically noticeable in these jobs. Each application with a given bit profile will have a typical and ideal wear progression to its service life. This is something we work with the customer on to ensure they have the capability to inspect their cutting assembly and assess the remaining wear life on the bits in service, in order to replace at the correct intervals and maximize their value.
If you want to learn more about what bits are best for your work, reach out to the team at Bit Service.