Archive for the ‘Testing and Specifications’ Category

RSC Tolerances for Case Erectors and Packers

May 27, 2022

Brian asks:

Do you have any printed information, such as TAPPI, PMMI, FBA, regarding tolerances for RSC’s that you can share with me?  We have a customer that purchased a box erector/packer/taper that sometimes jams up and they would like to know what the tolerances are for the boxes that we manufacture for them. Any help would be appreciated.

There are industry guidelines, but they are just that…guidelines. Tolerances can be customer specific and should be considered when estimating a job. Then you consider your capabilities. What tolerances can your equipment hold from feeder through counter-ejector? Probably not your case, but if you’re diecutting RSCs, what tolerance does your diemaker guarantee?

The FBA Handbook discusses these tolerances and provides guidelines for carton tolerances and may be purchased at (Store Products – Fibre Box Association).

The PMMI/FBA publication PMMI B155-TR2.2-2011, recommends that any RSC panel, when measured from scoreline to scoreline should not exceed ± 1/16” (1.5mm). It also recommends that the overall length of the blank should not exceed ± 1/8” (3mm). From specified size of course.

The PMMI document also recommends that slot depth should vary no more than ±1/8 (3mm) from the centerline of the slot (corrugator) score to the tip of the slot. Slots should also be aligned within 1/16” (1.5mm) of the centerline of the aligning (relative) score.

The PMMI/FBA publication PMMI B155-TR2.1-2011 offers some tolerances for the manufacturers joint (MJ) which, as we know, is most important to creating a square box. Measured at the flap (corrugator) scorelines, the MJ should not be less than 1/8” (3mm) or larger than ½” (12.5mm). Skew or fishtail should not exceed 3/16” (4.5mm), again when measured at the flap scores. At no point along the MJ should the opening be less than 1/16” (1.5mm) and the alignment of the flap scores should not exceed 3/16” (4.5mm) at the MJ.

TAPPI has a very wide range of documents and specification available to TAPPI members, but in reviewing the lists we couldn’t identify any document specific to RSC tolerances. (If anyone know of such a document, please shar ethe name with us.)

Now of course, case erectors and case packers are going to want the box as square as absolutely possible. Perhaps equally as important is the consistency in size. We can often compensate if we are consistent. It’s when sizes or tolerances jump around that it becomes difficult to keep an automatic line running.

We also have to be cognizant of tolerance stackup. If we look at the tolerances above, the overall blank length can vary ±1/8”. So that’s a total of 1/4″. Now let’s add in the manufacturers joint. According to the specs we can be as small as 1/16” and as large as 1/2”. Now, we rarely see the MJ vary this much, but it can happen. Then, there is fishtail to consider. Remember that these tolerances tend to stackup, a combination of MJ width variation and fishtail can cause nightmares for case erectors and packers. This is especially true if the stackup causes the flaps to come into contact with each other.

We reached out to a few case erector/packer manufacturers, but it was hard to get a ballpark reference because of the number of possible variables from the squareness and size of the box to the forgiveness of the product being packed.

— Ralph

Linerboard Coefficient of Friction (COF) Target and Max

February 3, 2021

Cassie asks,

I’m doing some investigation to determine what is the minimum, target and maximum COF (coefficient of friction) for linerboard. Can you point me to any information on this?

Instead of answering your question directly from a mill process point of view, which we can do, here are a couple links to several specification sheets from domestic mills. (Domestic High Performance Linerboard, COF Spec Sheets or Slide Angle)

The Europeans do not seem to deliniate slide angle as a physical property characteristic.  Since they have been making linerboard from recovered fibre much longer than we have in the Americas, it may be just universally understood there.

Let me know more if you have more specific questions. I would also recommend membership in TAPPI’s Corrugated Board Technical Committee where you will have access to the best minds in this business.


Hazmat Linerboard Weight Tolerance

December 30, 2020

Dave asks,

What does the AICC hazmat guide say about tolerances on basis weight? Customer says they must run: “We must run the 31-31-35 hazmat board combo” but the corrugator no longer runs that combo.

The DOT has relaxed the “49 CFR 178.516 – Standards for fiberboard boxes” from +/- 5% to now allow +/- 10 percent basis weight tolerance in the linerboards.

Per the Legal Information Institute “UN4G combination packaging with outer fiberboard boxes and with inner fiberboard components that have individual containerboard or paper wall basis weights that vary by not more than plus or minus 10% from the nominal basis weight reported in the initial design qualification test report.” Click on this link to learn more at the Legal Information Institute.

How did your customer arrive at the 31-31-35 combination? Is it from a previous requirement? As long as they the meet the strength requirements for the content it should be acceptable to use another combination. The +/-10% relates to the base weight of the liner used and may not mean that you could directly substitute a 28lb for a 31lb. If a 28lb liner is used then the tolerance would be +/-10% of the 28.

So I think it would be important to first see if you can provide a combination that meets their strength requirements WHILE remaining while remaining within the +/-10% tolerance.

— Ralph

Roll Hardness Testing

June 12, 2020

Chris asks,

I was recently appointment QA manager at my company and have dove head first into the realm of Schmidt Hammer(roll hardness) testing.  A very significant issue we have is with warp.  I have noticed that most of the time when I see a difference of greater than 10 on the Schmidt Hammer test we suffer from unacceptable warp issues.   Since I’ve started hardness testing inbound rolls we have adopted a pass fail system where any roll that tests to greater than 10 is rejected.  To add to this problem our supplier has adhered to a system that says anything under 15 is acceptable by industry standards.

What is your take on this?  Do you feel that it is unreasonable to ask the mill to commit to less than a 10 difference?

Also, the mill is questioning my testing methods.  TAPPI T834 suggests to sample a roll every 6 inches across the roll (the mill uses this sample frequency).  I have always been taught that as for a scientific process that the larger sample size yields more accurate result.  With this being said, I chose to test my rolls at a frequency of every 3 inches which would increase my sample size.

Do you feel that my testing method is in some way negatively affecting the results?  As in, is my sample size causing the rolls to “fail” on a more frequent basis?


I love the three inch method. However, you would not be able to correlate to any of the 140 +\- containerboard machine out there. I would agree you are more likely to find a wet streak with your protocol, but mill specs usually call for moisture deviation to be six inches or less.

Do you have linerboard specification sheets from other companies?  You may want to investigate roll hardness from other manufactures. If your supplier is so entrenched in their thinking you might consider saving their rolls and having one of their Corrugator supervisors show you how to run the board without warp. It’s a bold move!


— Ralph