Stitching Tolerance

December 30, 2020

Dave asks,

 We have an old foot pedal stitcher we manually stitch boxes with. Is there a standard spacing between staples that we must maintain?

Dave, this was a new one for me.  Took a bit of research using a number of resources, but this should address your question.

Singlewall: Starting and ending staples shall be 1 to 1½ inches from the flap score lines.  Intermediate staples shall be spaced no more than 2½ inches apart.

Doublewall: Starting and ending staples shall be double stitched no more than 1 to 1½ inches from the flap score lines.  Intermediate staples shall be spaced no more than 2½ inches apart.  For products weighting 100 lbs. or more spacing of intermediate staples shall be reduced to 1 to 1½ inches apart.

Triplewall: Starting and ending staples shall be double stitched no more than 1 to 1½ inches from the flap score lines.  Intermediate staples shall be double stitched and spaced no more than 1 to 1½ inches apart.

— Ralph

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

Glue vs Staples

September 9, 2020

Andrew asks,

Glue joints vs. stitch joints. What are the benefits of each type of manufacturing joint and which is stronger? Often I am told glue joints are stronger because glue penetrates and bonds the liners. Are there any test results that support this?

The intended use and environment that the container is going to be used in are key factors in selecting glue or staples for your manufacturer’s joint. For the majority of uses, glue is the preferred method because it provides a higher strength in most cases. Glues also enhances productivity because, in the case of a flexo folder-gluer, you can print, fold, glue and stack or bundle in a single operation while stapling would require a second operation. In applications where gluing is a second operation, it can typically be accomplished at production speeds far greater than stapling.

So why use staples? Well, they still have their purpose. Staples are often preferable for containers that are subject to high levels of moisture or exposure to outdoor elements and temperature change. These types of containers are typically coated with materials that repel water such as wax and other weather resistant coatings. Glue usually does a poor job of bonding these types of materials.

Both methods have their disadvantages too. As mentioned above, glued joints can be more susceptible temperature and moisture changes and may not adhere well to some printed or coated surfaces. Glued joints take a little longer to set, but since they are going through a stacking to compression device that’s usually a non-issue.

Staples may have a few more disadvantages. They are typically not desirable for use with food products and can complicate the recycling process. Staples can also scratch or damage products inside of the container, though this is more likely in manual than automatic operations. They can also create a bit more of a safety risk especially if they are not properly installed.

Here are some documents that provide additional information.

— 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