Case Erector Issues, Finish and Metal

June 27, 2022

Hagan asks:

We recently had a customer contact us in reference to issues in their automatic food packing line which they think may be related to the boxes. They are concerned that the finished surface of some of the outer liners is too porous and causing the suction grippers to lose their grasp of the sheet. They also referred to the boxes causing jams as being “fuzzy”. Their second concern is that occasionally their inline metal detectors are rejecting boxes for metal shavings. This happens after the product has been loaded into the box. Therefore, the package and the contents are rejected and dumped.

We don’t test for smoothness in-house, but we have contacted our paper supplier and asked for them the to provide test results for the rolls in question. Below are the results they provided.


The porosity range between 12 and 28 seems to be quite a difference, but the supplier says that’s within TAPPI standards. We don’t have a good benchmark. With your vast background in the paper industry, do you believe the data provided above is in fact satisfactory results for both categories?

 As far as porosity goes that does seem to be a bit of a variance between Roll ‘J’ and Roll ‘E’. The porosity does, as we would expect, coincide with the smoothness. The smoother the paper the lower we expect to see the porosity. The plant I was responsible for typically ran an average of 350 smoothness and a minimum of 16 for porosity. Even with the range of your examples, they do seem to be in tolerance.

The smoother the liner the better the grasp the suction cups are going to have. I would think it would take a rather porous liner to allow enough vacuum loss to lose the grip. However, I don’t know what that number may be. As well, it would make sense that a surface which may be “fuzzy” could lead to vacuum loss and loss of grip before the box was completely open.

Occasionally we hear of a bit of metal finding its way into the paper. End users, especially food and pharmaceuticals, take this very seriously. I assume at the customer’s plant there are no metal detectors prior to final inspection. It’s unfortunate that it’s not being found until the product has already been packed. At that point the paper/box has been through so many operations that it is possible the metal could have been introduced to the paper nearly anywhere, the paper mill, shipping, converting, storage and even the packing process itself. You mentioned [in and off-line conversation] that your supplier, as well as your own operation, was looking into the metal issue, reviewing operational and maintenance logs, and samples would be sent out for analysis. That sounds like a very good action plan and hopefully it will result in identifying the source. Please follow up and let us know what results you receive.

This points out how important it is to maintain good operational, maintenance, and service records of our operations. Not only can it help us prevent or reduce unscheduled and/or unnecessary downtime, but it can also help diagnose quality issues and sometimes help us pinpoint the source of the issue. Ralph

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

Outside Air Temp effect on Green Bond

May 23, 2022

Ron asks:

We had an overhead garage door installed prior to our 2018 corrugator project – the OEM had us install it for ease of bringing new equipment into the building. Certain times of the year, say April to October, the corrugator crews have the overhead door open and just have the screen door down to allow fresh outside air in.  This door is maybe 18′ from the corrugator stacker. Should we have any concern about green bond shock on a cooler morning. The stock coming off the hot plate section is 275 degrees +/- and if the outside air temp was 50 would you be concerned about that?  I haven’t been able to find any studies related to this. Your opinion would be greatly appreciated.

I would focus more on the final pin adhesion strength.  You should target values above 45 and up to 60 pounds per foot.  If the pH, viscosity, and starch temperatures in the pan are within your process parameters, green bond should not be an issue.

Let’s toss it out to our readers. Have any of our other corrugator operations had any experience with this scenario?

— Ralph

Need Help Running Quality Board Consistently

May 17, 2022

Debbie asks:

We’re looking for some training help for the proper operation of small format corrugators. We are looking to improve the quality and consistency of board produced across our shifts. Especially our “off shifts”. We are looking to develop a set of specification sheets or SOPs that all shifts will follow. We believe the specifications should include,

  • Pre-heating roll temperatures
  • Amount of wrap on preheating rolls
  • Flow rate for our moisturizers
  • Proper glue application
  • And any other specifications that should be controlled/maintained for the production of quality paperboard.

We understand there are many factors that go into making quality paperboard, but we would like to develop a baseline that could be used by our operators as a starting point or troubleshooting as well as the SOPs mentioned above.

Can you suggest some resources?

A good place to start would be the search functions on and On under the Learn tab you will find the “Packaging School”, you’ll find many educational resources focusing on everything from machine training (including corrugators) to sales, safety, HR training, and more.

AICC’s “Corrugated Essentials” is an excellent program that may meet many of your needs. If it’s not already on the schedule, it should be coming up on the schedule later this year. There are also online courses that are free to all registered members, many of which focus on corrugators, corrugator operations and production.

You can also contact me directly to discuss further.

— Ralph