Archive for the ‘Corrugating’ Category

Pin Adhesion Test (PAT)

August 30, 2019

Sam asks,

Do you have any formal reference of what the ideal pin adhesion test result should be.   For agro boxes (vegetables) we currently use values of 55 to 60  (pound/inch) and in industrial 40 and higher.

We have a particular customer that has experienced some delamination failures. The PAT test value is 27 (pound/inch) which we believe to be too low. However, we are lacking established information to back up our opinion.

I could not agree with you more.  I prefer a minimum, not average, of 45 for industrial application.  My technical associates at TAPPI like this 45 value while I would rather have 55 on all corrugated bonds.  It is most important to know where the failure is occurring: linerboard, medium, or in the starch itself.  Under ideal conditions we want 100% liner failure. As you can see in these photos a very low PAT value can have disastrous results. There is very little liner pull and very little glue with a poor bond.

A good reference for the PAT is the most recent version of TAPPI document TM 821 (TM 821-0M 17 at this writing), Pin adhesion of corrugated board by selective separation.

— Ralph

Pin Adhesion Test sample Pin Adhesion Test sample Pin Adhesion Test sample

Tuck Top vs Tuck with Locking Tab, or Friction Tuck

March 1, 2019

Rich asks,

I have a customer who orders a lock bottom box with a tuck top from us. It ends up at distribution in Walmart and Walmart is having issues with the top flap coming open. It does not get taped closed. They are asking if we have packaging engineers that can provide documented test results or studies on performance changing it to a tuck top with a locking tab, or friction lock tuck top tab, or extending the tuck on the top tuck. Have you seen anything like that or are you aware of any hard documentation that says how much it changes the function of the top tuck? Thanks for your help with this.

I would start by checking with your sheet supplier and/or their containerboard provider to see if they have any information regarding the information you are looking for. Often integrated companies do these types of studies. Some will be willing to share and others are not as open to sharing their results. I have an associate in Canada that may want to weigh in on this issue. I’ll touch base with him and then update this post with any input he may have. I also searched through my George Maltenforts’ books, but found no discussions or reported research in this area.

However I do believe that a friction fit is the best way to go short of some type of press applied coating.

— Ralph

Could Starch Lines Be Culprit to Metal in Boxes?

May 29, 2018

Ray asks,

 Since April of this year we’ve been fighting with major metal detection rejections with one of our customer that has a stringent HACCP/SOP in place.

We feel we may have finally found the source of our metal contamination. We believe that it may be our metal starch lines and perhaps rust form the lines is mixing with the starch and being transferred to the products. We’re waiting for metal chemical analysis results to come back to confirm my suspicions.

While we are awaiting the results of the test we have come up with a few more questions and hope that you can help provide an answer.

Best Practices:

How often should starch lines be flushed?

Should straight bleach used?

What types of strainers are being used in the industry and what are considered the best systems?

Is anyone using inline magnets in their glue systems?

How often should the schedule 80 pipe lines be replaced, and is there anyone out in the industry using Predictive Maintenance to replace lines?

Is PVC piping a viable alternative for starch lines?

Thank you and your readers for any insight that can be provided.

Just a couple thoughts. Have you ruled out the chance of contamination from sources outside of the manufacturing process? Do the conveyors pass a maintenance shop grinders could be in use? Are there any RFID tags used in any of your processes?

For input on the starch lines I reached out to Wayne Porell at Harper Love Adhesives to see what experience he may have with such issues.­­­

First, I don’t have any plants having this issue. There may be more going on here than what we typically see.  Most well-run plants flush their starch lines at the end of every week by at least running water through the system after they shut down. Some plants also use Clean Tank HP™ from Walla Walla Chemical. Others just use bleach. However, bleach only disinfects the lines to help control bacteria. It doesn’t help remove any build up starch in the lines.

Some plants have strainers in place but remove the filter because they get clogged and cause the pan to over flow. These filters need to be cleaned, but can only be cleaned when there is no starch in the lines and the machine is down. You also want to make sure the filters are in place and are not damaged.

I don’t know of anyone using inline magnets to catch metal parts. If the plant is getting enough metal inside their boxes to set off alarms, then I would, as obviously they are, be looking where the metal is coming from. There shouldn’t be enough metal from mechanical pumps or bearings causing this issue. If there was, I would certainly think they would be seeing mechanical failures by now.

Over time schedule 80 iron pipes rust inside and create areas where starch can build up and harbor bacteria. This shouldn’t cause enough metal to come off to trigger an alarm. If anything, they rust through and cause leaks or the starch builds up inside the lines and creates flow issues at higher speeds.

The timeline for replacing these metal lines depends on the house keeping over the life of the lines. Like anything in the plant, the better that is taken, typically the longer it will last. The chemicals used to clean the lines can affect the longevity of the lines as well.

Schedule 80 PVC can be used and is used in some plants. The issue with these lines is you need to have hanger braces every four feet to keep them from sagging. If they sag, then you have areas where starch could build up in the lines. However, they are easier to clean if you keep them flushed on a weekly basis.

PVC lines also have to be braced well, especially if using pneumatic pumps for starch supply and return which tend to cause a pulsating action. PVC doesn’t allow bacteria to build up since it doesn’t have cavities like those caused by rust as in metal lines.

I have seen some plants switch to stainless steel lines. These are probably the best, but also cost the most.

 Again, if the plant is getting that many rejections due to metal they should review their whole process. Small specs of metal should set off alarms at their customers. Are they using any types of foil tape in their process?

— Ralph

Is There a Repository of Corrugator Defect Documentation?

April 24, 2018

Daniel asks,

Ralph, you once mentioned digging up a 20 year old article on corrugator defect. Is there a repository of technical articles around boxmaking you can direct me to?

The document I was referencing is actually a book published by TAPPI. It’s called Corrugated Defect/Remedy Manual, Sixth Edition. TAPPI also has a number of other publications on corrugator and corrugating that may be helpful.

The trade magazine are another good source of information and often have technical article specific to corrugators. AICC’s BoxScore, Corrugated Today and International Paperboard Industries are the once we are most familiar with here. Unfortunately, there is not central repository for the articles in competing publications, but you may locate a list of article on their website, or by contacting them directly.

—Ralph