Gage Care #1: Torque Wrenches

In the Gage Care series of articles we will be covering some of the best practices in caring for different types of gaging and measurement tools.

Torque wrenches.  From assembling a roller coaster to working on a car in your garage, torque wrenches are a common staple in many toolboxes.  In fact, when people ask what calibration means, I use torque wrenches as an example.  When I first started at Micro Labs I was trained in the calibration of torque instruments and the repair of torque wrenches.  From years of experience and discussion with other people in the field, I have built up a list of tips and recommendations on how to best take care of your torque wrenches and extend their life.

  • First and foremost, torque wrenches are a mechanical gage and will wear out eventually.  No amount of preventative maintenance will change this.  However, proper care can extend the tool’s life considerably.
  • A nice, smooth pull – Sometimes using a torque wrench can be difficult, especially when it is a high torque load.  One method that is sometimes used is a jerking motion to try to achieve the higher torque.  When using a type 1 torque wrench (indicating torque wrench) this can cause some of the internal components to slip and the accuracy to be compromised.  Type 2 torque wrenches (click type) can be overloaded by jerking.  The click will happen, but since the wrench is moving so fast, the set point can be exceeded by continuing the motion.  The solution is a nice, smooth pull, which will result in the highest accuracy torque application.
  • Seasoning a torque wrench – before calibrating a torque wrench, we are required to season a torque wrench three times, which means taking the torque wrench to maximum value three times.  Seasoning is required because the mechanical components inside of the wrench will settle and give bad readings the first few times used after sitting for a while.  This could be seen as “warming up” the gage.  I have observed up to 15% in error during the seasoning of a torque wrench.  Whether or not it makes sense to include seasoning in your process is up to you.
  • Type 2 torque wrenches are the most commonly used torque wrenches today, and are also known as click type torque wrenches.  Per ANSI/ASME, they should have 4% accuracy clockwise, and 6% counter-clockwise.
    • Overuse in one location – One common issue that arises with type 2 torque wrenches is overuse in one location.  Due to their mechanical nature, repeated use at the same spot causes that particular setting to wear out and the actual torque applied to drift.  This is common because assembly typically uses one torque setting per wrench.  Often this is compensated for by adjusting it so that it torques correctly, and then taping it so it cannot be adjusted.   I tend to be against this because, as the tape loosens, the setting can change by accident.  The best solution is to get a preset torque wrench and set it before it goes to the shop floor.  These wrenches are harder to adjust, and as long they are periodically checked and adjusted back to the nominal required setting, the life of the wrench tends to be lengthened as well.
    • Rotating torque wrenches – A good solution that I have observed to avoid wearing torque wrenches out is to rotate the gage’s location to change the torque setting.  Moving a 100 ft lb torque wrench to three different positions that require three different torque settings can avoid premature wear.  The mechanical components inside of the wrench will share the wear across the range rather than in just one location.
    • Storage setting matters- When storing a type 2 torque wrench for any length of time, it is recommended to set the wrench to the lowest setting.  Click type torque wrenches are typically spring loaded, so leaving them under tension can weaken the spring over time and apply unnecessary force to the other mechanical components of the tool.
  • Selecting the appropriate head or adapter for the torque wrenches.  This one is near and dear to my heart.  I think you’ll understand why:  A 250 ft lb torque wrench comes into our lab with a custom head for a custom process.  I go to season the wrench at maximum capacity and the head fails.  Best case scenario, it twists, bends or shears off, but every now and then i have one that just explodes, sending little metal fragments around the lab.  I get terrified and maybe cry a little bit, and your custom head is broken.  This is a lose lose situation.  The moral of this story is, if you use a 250 ft lb torque wrench at 75ft lbs, and have an adapter/head that is not capable of handling maximum range, you should get a smaller torque wrench.  At Micro Labs we take precautions at higher torques to avoid losing an eye, but there is always a risk of bodily harm and damage to the equipment with an adapter/head that is ill suited to the capacity of the torque wrench, both at our facility and at yours.
  • It is NOT a hammer – By nature torque wrenches are hardy tools, many of them are capable of handling large amounts of torque force.  It may be due to this, or the nice hefty feel in the hand, that i find many torque wrenches show significant signs of abuse.  Occasionally I will find a wrench come in with what appear to be dents in the metal from a nice, solid wack.  While this may be OK (by some standards) with a ratchet, this could cause damage and drift to a torque wrench.  The type 1 torque wrenches (indicating torque wrenches) usually have a sensitive apparatus that can slip under duress.  Type 2 torque wrenches have carefully assembled handles that can loosen or break with enough force.
  • Breaker Bars – This is a common misconception that also stems from ratchet use.  A torque wrench has a specific length handle that needs to be used when applying torque.  However, 250 ft lbs can seem a bit high to torque by hand.  This is where people will use a breaker bar and change the point at which torque is applied.  Given that torque is easy to calculate, you can see why this is a problem: Torque=Force*Distance.  Changing the distance changes the torque.
  • Basic Cleaning – Sometimes what your tools need is just a little TLC.  Given the amount of moving components, grease and oils involved in the basic functioning of a torque wrench, soaking a torque wrench to clean it can actually result in damage.  At Micro Labs we clean the outside of the wrench with isopropanyl (if appropriate) and ensure to remove any dirt or debris from the joints where the tool moves.  If we open the wrench up, we reapply grease or oil, where appropriate, to try to lengthen the life of your equipment.
  • Calibration – This may seem like advertising coming from a calibration lab (naturally), but routine calibration really is important to the proper functioning and use of any gage.  At our lab your tool will be cleaned, evaluated for functionality, calibrated and, if necessary, repaired.

 

These articles are supported by the work that you send in.  If you feel that this information was valuable to you, consider choosing Micro Labs as your calibration provider, we’re happy to help!

Big News for the SI Units

On June 27th, 2017 NIST released an important article about the progress towards redefining the Kilogram with a fundamental constant of nature rather than a physical artifact.

The Kilogram is currently the only SI unit that is still traced back to a physical artifact.  The salt shaker sized hunk of iridium and platinum currently lives outside Paris in a secured vault, exactly where it has lived since 1889.  At the time of its creation, the standard had several copies of it made, which all weighed exactly the same.  Nested inside three bell jars, the kilogram standard has been pulled out only three times, all for comparison against its copies.  Over the course of 100 years, the kilogram standard appears to be losing weight.  Yes, this means 100 years ago if you bought a kilo of meat from the butcher, you got more than you would today.  However, along with most of the world, you would never know the difference because the loss is relatively small (about 0.000050 grams).  This is assuming that the standard lost mass and its copies didn’t (it could just as well be that the copies are gaining particulates).  We know that something has changed, the main issue is that we cannot precisely identify what it is.  This is a major issue in the scientific community; and this is where the Planck Constant and the Kibble balance come into play.

The scientific community has pushed forward in their efforts to standardize mass by using a Kibble balance to determine the Planck Constant.  This was done by measuring masses with nominal values from 500 grams to 2 kilograms on NIST’s Kibble balance, NIST-4.  The Kibble balance (formerly known as a watt balance) measures the mass of an object by utilizing coils of wire, rare earth magnets, and electromagnets to relate mass to amps, another SI unit.  This principle is demonstrated in this video by NIST:

Operating Principals of the NIST-4 Watt Balance

Through over 10,000 tests the Planck Constant was determined to be  6.62669934(89)x10-34  Joules.  The Planck Constant is an important constant when dealing with quantum physics, and a is probably best explained in another video from NIST:

Measuring Planck’s Constant

So what does this mean to you?  For most of the world this means nothing.  For most metrologists, quality personnel and technicians this is a forecast of changes in the industry and something to keep an eye on as the kilogram is due to be redefined in 2019.  But for the few metrologists that work in world class labs this will change the definition of mass and quantum physics! Not only is this big news for the SI Units, some might even say its massive!