Steel Coil Scale Verification Resolution

We have a standard check of our scales performed daily. We are weighing coils of steel weighing up to 70,000 lbs. Current reaction parameters are +/- 100 lbs. We are tightening this up to +/- 60 lbs based on an internal finding and there is some resistance by the supervisors in these areas wanting to know why we are tightening so much and what the expected benefit will be. Is there a rationale or standard practice that is used for what a scale should be verified to and how to set the parameters? Thanks for your help.

Are you saying the tolerance for weight of the coils is ± 100 lbs. or the scale tolerance is ± 100 lbs.? What was the internal finding, and why isn't it sufficient reason for what you want to do?

The tolerance for the test coils that are used daily is +/- 100 lbs and they weight anywhere from 30,000 to 70,000. We have multiple scales throughout the plant that are checked with coils that we had verified by an outside certified source to determine the actual correct weight.

The finding was that we neglected doing these checks on a certain shift so it really is not a reason for tightening the tolerance however the management team believes we should tighten it up now that this issue arose.

We do not want to over or under ship coil weights to customers and there is a general consensus of +/- 1% in the steel industry. This means that for a 50,000 lbs coil they are guaranteed +/- 500 lbs. To me this seems excessive but it is a generally common industry standard or practice at most mills.

Sean Kelley said:

The tolerance for the test coils that are used daily is +/- 100 lbs and they weight anywhere from 30,000 to 70,000. We have multiple scales throughout the plant that are checked with coils that we had verified by an outside certified source to determine the actual correct weight.

The finding was that we neglected doing these checks on a certain shift so it really is not a reason for tightening the tolerance however the management team believes we should tighten it up now that this issue arose.

We do not want to over or under ship coil weights to customers and there is a general consensus of +/- 1% in the steel industry. This means that for a 50,000 lbs coil they are guaranteed +/- 500 lbs. To me this seems excessive but it is a generally common industry standard or practice at most mills.

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I don't understand why management would tighten a tolerance when the finding was that checks were not being done on certain shifts.

This really is between the supervisors and management. The supervisors are essentially asking "Why aren't you addressing the finding, instead of tightening a tolerance that will not add value or improve anything?"

Sean Kelley said:

The tolerance for the test coils that are used daily is +/- 100 lbs and they weight anywhere from 30,000 to 70,000. We have multiple scales throughout the plant that are checked with coils that we had verified by an outside certified source to determine the actual correct weight.

The finding was that we neglected doing these checks on a certain shift so it really is not a reason for tightening the tolerance however the management team believes we should tighten it up now that this issue arose.

We do not want to over or under ship coil weights to customers and there is a general consensus of +/- 1% in the steel industry. This means that for a 50,000 lbs coil they are guaranteed +/- 500 lbs. To me this seems excessive but it is a generally common industry standard or practice at most mills.

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I'm no expert in this general area, but I think I might agree with the people who want to hear the rationale. I have more questions: Have you had any issues with measurement error? Why do you do the checks every day? Are the scales calibrated periodically?

Scales are calibrated on a quartely basis. The reason for checking them daily is the potential for damaging the load cells with a large coil being accidentally dropped or placed too harshly onto the scales using cranes and done manually by a person is fairly common. There are many thousands of tons of steel going through everyday. To be off more than a day is just not worth the risk of the existing situation. This is a fairly standard practice among most steel mills so it is not that we are worse than others.

In our plant our steel coils are weighed on scales too. Our service company uses NIST Handbook 44 to determine the displayed resolution for the scales. Probably the calibration reqiorements too. It is available for download from NIST. I'm pretty sure the requirements are pretty well fixed if you are using the scales for trade

Sean Kelley said:

The tolerance for the test coils that are used daily is +/- 100 lbs and they weight anywhere from 30,000 to 70,000. We have multiple scales throughout the plant that are checked with coils that we had verified by an outside certified source to determine the actual correct weight.

The finding was that we neglected doing these checks on a certain shift so it really is not a reason for tightening the tolerance however the management team believes we should tighten it up now that this issue arose.

We do not want to over or under ship coil weights to customers and there is a general consensus of +/- 1% in the steel industry. This means that for a 50,000 lbs coil they are guaranteed +/- 500 lbs. To me this seems excessive but it is a generally common industry standard or practice at most mills.

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Sean,

Customers accepting plus or minus 500lb and you weighing to plus or minus 100lb is right for your industry.

Do your customers check weigh to a greater accuracy? Do your competitors offer greater accuracy? These are the only reasons for narrowing the range. But narrowing the range of mutually acceptable measurement would probably require a more capable weigh-scale.

Making up for a missed check with a tighter tolerance makes no sense from the information you have provided. Determining the economic frequency of calibration and those verifications makes more sense to me.

The shift that missed a verification may be trying to tell you something. They may know it is too frequent. Or they may ignore other requirements. This is the area to investigate further to see what is going on and determine a course of action.

It may however mean a manager would have to work the late shift!

John