Archive for the ‘Containerboard’ Category

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

Calculating Partition Strength

February 28, 2019

Rodrigo asks;

Calculating Partition StrengthI’m trying to figure out the stacking strength of the partitions shown in the picture (How much weight can be held on top). A corrugated board bed is set on top covering all of it. Products are located inside the 4 cells of the partition. I would like to know what is the process or logic of calculating the maximum weight it can hold before it collapses. Resistance used is 26 ECT.

If I see correctly the pieces are set at an angle so we cannot determine compression strength because the elements are not fully vertical. (left-most sections in the image)  What is more significant here is the torsion or flexing of the components. Because of the distance between connecting points, failure is more likely to come from the twisting action of the components than an edge-wise crush. It’s just like a vehicle traveling over a rough road and all four wheels and suspension act independently of each other.  If the pallet of the load is uneven or starts to shift, then angular forces can be applied potentially causing the long spans to flex and collapse.

We can’t tell exactly how large your partition assembly is, but do you have access to a compression tester with a footprint large enough to test at least one square?

— Ralph

UPDATE:

Tom adds,

Consider pointing Rodrigo to the book Corrugated Shipping Containers An Engineering Approach by George G. Maltenfort. Chapter 7 of the book discusses compression strength estimation for boxes with inserts and shows 25 different styles. These are not the partition shown in your question but MIGHT give him a place to start your predictive work or at least highlight attributes he needs to consider.

Thanks Tom!

Student Question about Corrugated Use in North America

November 15, 2018

Christoph asks,

Hi Ralph, I was wondering if you may help me with a few questions. I am a German Master Student studying Printing Technology at CalPoly State University. The topic is about the corrugated packaging market and the most common used papers and purpose of the boards.

Therefore, I would like to ask you if you can provide me with information for the following questions:

  1. Which are the three most produced board qualities (e.g. Brown Kraftliner 35# – recycled fluting 30# – Brown Kraftliner 35#: C-flute) in the Northern American market?
  2. What is the most common purposes for corrugated boxes? (shipping, shelf-ready packaging, …)
  3. On average how many colors are printed on the above requested corrugated board qualities?

I am very thankful for any information you can provide.

 

Hi Christoph, happy to share a little information with a student of the industry.

  1. The most common combined board grade is 33/35 test liner / 23# test medium / 33# test liner.  While virgin kraft linerboard is still present, the US is about 50/50 new verses used fibre.  In Europe this is very different.  Mills that use the newest papermaking technology can use 28/26/23 C flute constructions.  We make heavier boxes here than you do in Europe.
  2. We ship durable and nondurable goods in corrugated packaging.  If you want this broken down by manufacturing segment I can provide that.  The biggest market is food.  Yes there is shelf ready packaging and displays.
  3. On average we probably print three colors via flexo. There is a great deal of four-color work done, but there is still a significant amount of two-color and one-color work being done (think Amazon, Home Shopping Network, etc.). Digital is gaining ground quickly, but it is not the ideal process for most boxes. It has its niche and its popularity is growing especially in the graphic market. However, digital has yet to reach the speeds necessary to make it ideal for high throughput orders. You’ll want to keep your eye on it though as the technology is continually evolving.

— 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