Not Cutting It
There is a distinct difference between fixing something or repairing it. A “fix” is a temporary solution, while a ®repair® permanently restores the object to its original condition.
When tires go flat as the result of a puncture, there is only one acceptable method for returning them to service. Repair.
According to tire manufacturer recommendations and industry standards, tire repair must include a number of specific steps and the use of certain materials and techniques. No one endorses “fixing” a tire.
Of course, tire technicians need to remove the protruding object and determine the angle of the penetration. After eliminating any contaminants on the innerliner with the appropriate cleaner, the injury must be prepared and the damaged material removed. This is one of the most critical steps in tire repair.
A radial truck tire is an engineering masterpiece. Rubber and steel are combined to create a flexible air chamber that can absorb the impact of irregular road surfaces, carry irregular loads over thousands of miles, and withstand extreme temperature ranges.
Only the highest quality steel is used in belt packages and body plies, so strength is not really an issue. However, and exposed steel cable will develop corrosion and will eventually weaken.
I still remember the first time a truck driver watched me use a carbide cutter (it’s not a drill bit) to remove the damaged steel from a tire injury. He started yelling that I was making the hole bigger and demanded an immediate adjustment on the tire. I tried to explain to him that a frayed steel cable continues to unravel as the tire flexes, but that required an in-depth discussion about tire construction.
He understood the need to prevent moisture from entering the injury, but couldn’t grasp the actual drilling I was doing. All I wanted to do was properly repair the tire and get him out of my shop and back on the road, so I explained what the tire warranty required and continued the process.
Clean Tools, Clean Repair
To the outside observer, the process of “drilling and filling” appears to cause more damage than the initial protruding object. In reality, it cuts the frayed cable cleanly in the injury channel and leaves them encased in rubber.
Once the rubber stem (it’s not a plug) is installed, moisture cannot enter from outside. And the combination of vulcanization (heat of chemical) and compression helps maintain the integrity of the belt packages and body cords.
The cleaner the injury channel the better, so the condition of your carbide cutter is essential to proper tire repair.
It’s literally impossible to estimate the lifespan of this tool because there are so many variables. Carbide cutters should operate at speeds less than 1200 rpm. Exceeding that speed accelerates wear and can cause scorched rubber, which can lead to reduced adhesion between the repair stem and the tire.
Choosing the correct diameter also has an impact because a shop that drills every injury to 3/8-inch will replace that carbide cutter more often. Proper use of any tool has a direct impact on its effectiveness, and this one is no different.
When Tools Go Bad
But how do you know when a carbide cutter isn’t doing the job? A quick check of the sides on the remaining portion of the rubber repair stem will reveal the answer. Once you pull it through and snip off the remainder, look at the sides of the stem. If a number of snags are present, then the steel cords are not being cleanly cut. A nice smooth stem indicates the cutter is sharp and cutting properly.
If the stem showing snags, the tire technician should either make a few more passes with the carbide cutter, or change the cutter to one that is sharp. On visual inspection, if the teeth of the cutter don’t appear to be sharp, they probably aren’t. Basically, when the cutter stops cutting, it’s got to go.
Watch Stones, Too
Another repair tool that is subjected to a lot of wear and tear is the buffing wheel or stone. Once again, these tools are designed to operate at specific speeds generally less than 5000 rpm ®“ and exceeding that speed accelerates wear and can reduces adhesion between the repair stem and the tire.
Failing to properly clean the innerliner will also reduce the lifespan of a buffing wheel because any contaminants become embedded between the wheel teeth.
As a result, the buffing wheel develops a smooth, black appearance. If you see smoke while buffing an innerliner, check the rpm of the buffer and replace the wheel or stone if it appears worn. Remember that scorched rubber cannot vulcanize.
Follow Repair Process
The key elements of any tire repair revolve around removing any damage and sealing the injury. A stem without a repair unit what some would improperly call a patch ®“ will not stop the loss of air or prevent moisture from entering the injury.
And a repair unit without a stem or other rubber fill material, such as in a section repair ®“ is an open invitation to rust formation on the tire’s steel cable. The result of either is an eventual separation.
The damage to an injured tire is not effectively removed without using a sharp carbide cutter that is the appropriate size and used at the correct speed.
The innerliner cannot be prepared without a buffing wheel or stone that is in good condition and used at the proper speed.
In other words, you can’t have one without the other. So make sure you have both.
Kevin Rohlwing is director of training for the International Tire & Rubber Association (ITRA), and this article originally appeared in ITRA’s Commercial Tire Service publication.