Archive for the ‘Corrugating’ Category

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.


How Much Washboarding is Acceptable

April 24, 2018

Paul asks,

I would like to know about washboarding in corrugated – how much variation in surface flatness (in microns) is typically seen for the types of corrugated board used in applications like shelf ready packaging?

I don’t know that there is a published standard on how smooth the surface of a corrugated sheet should be for the type of printing used for display or shelf ready packaging, but I think we are safe to say pretty darned smooth.

One of the key elements of printing the type of quality high-graphics usually found in display work and shelf ready packaging is minimizing the impression (pressure) between the plate and the substrate. The greater the impression pressure the more the printing plates distort and that distortion results in growth and distortion of the dots that create your image. Typically in high-graphics printing we are looking for a kiss impression, just enough that the printing plate just touches or “kisses” the surface of the board and transfers the ink. For the best print results we want .0015” to .003” (~38 to 76 microns) impression when printing. Oh course the lightest impression we can get away with.

Now, if the high and low points of the board surface exceed this kiss impression depth then additional pressure will be necessary in order to obtain coverage in the low points caused by fluting. Then, as stated above, as we add more impression our printing starts to suffer. With large block print you might think you can get away with over impression and perhaps you can a tad more than you can with process or fine lines and text, but excess impression on solid coverage will result in color variation through striping of the print.

We should also note that typically washboarding is less prevalent on small flute (such as a E, F or N) because there are more support points and they are closer together than a C or B flute.

Digital printing may be a little more forgiving than offset, but we still have to remember that the smoothness of the surface contributes to the overall aesthetics of the packaging and not just the print quality.


Global Percent of Medium

March 6, 2018

Mike asks,

I have a question on what the % medium should be globally. I’m trying to get a handle on it algebraically so to speak.

Classic corrugated sheet, in my mind, is one 26# medium sheet and two 42# liner sheets.  The medium has a wiggle factor of ~1.3 so,

Medium % = 26*1.3/(26*1.3+42*2) = ~ 29%.

Does this sound reasonable?  As BWs tend downward, my gut tells me there is more % medium overall but I am thinking still less than a third.

Twenty five years ago, here, it was indeed 42/26/42 with C flute having a take up factor of 1.43.  Then the sheet feeders began to request 23# medium and corrugating rolls started to have lower profiles which reduced the take-up factor.  Then we moved to 35# and today that probably is 33/23/33.  Globally the World Containerboard Organization tracks total containerboard production.  Additional information may be available through them.

— Ralph