Archive for the ‘Paper’ Category

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

Tests for Quality of Board

August 14, 2019

Harendra asks,

We are in the process of evaluating the quality of OCC grade 11 & 12. Can you suggest what specific test should be performed for quality evaluation of these two grades for production of container boardpaper?

I would suggest contacting Bill Moore at Moore Associates in Atlanta. He is an expert in this area.

Moore & Associates
Phone: (770) 518-1890
www.marecycle.com/

— Ralph

Corrugated Shelf Life, Storage and Usage Temps, Toxicity?

April 9, 2019

Chris asks:

Do you have any resources for the following information regarding corrugated containers?

As the answers would appear to be specific to the material composition, these would be for plain C-Flute kraft containers.

  • Shelf Life
  • Service Temp Range
  • Storage Temp
  • Toxicity

These questions are asked quite often on Ask-Ralph. This may not be a complete answer to your question, but it is a start to the dialogue.

Corrugated under compression (loaded and stacked) ages/deteriorates at a different rate than KD boxes on a pallet. Environment, fill load, stacked load, potential crush during converting all contribute to the deterioration rate of a loaded box.

Ideally, whether loaded or stored as knock downs, corrugated should be stored at 72 degrees and 50% RH.  That’s a perfect world and few of us live in a perfect world. Any fluctuations in these conditions can reduce the fibre to fibre bonding and strength of the adhesive bond. Temperature does effect stored corrugated, but it’s the combination of temperature and humidity that has the greatest effect. High temps (90 plus degrees F) and low humidity and you’re likely to start to see score cracking and brittle paper issues. High temps and high humidity and you’re likely to start seeing bond breakdown and an increase of the compressive creep rate leading to increased chances of failure under load.

At extreme low temps and you may start to experience recharacterizations of adhesive that can lead to failures at joints and even at the liner to medium bonds. Same holds true here with humidity though it may not be as severe as with high temps.

General rule of thumb, if it is comfortable to work in, it’s probably good for corrugated. We don’t like to be hot and sweaty or numb from cold… neither does corrugated.

As far as toxicity, corrugated is considered an indirect food additive by the FDA and is detailed in 49 CFR.  Therefore, no toxicity for plain kraft. If there are inks or coatings involved, then you have to look that them on an individual basis.

Now there’s a start to the discussion. What input do our readers have?

— Ralph

Checking Moisture of Corrugated Sheets

January 31, 2018

Tim asks,

Recently we encountered corrugated sheets with dry liners and medium that created problems converting. Is there a way for us to test sheets for moisture content at our facility? If so, is there a listing of the ranges?

Moisture meters, or moisture analyzers, can be used to test the moisture content of corrugate sheets. There are a number of portable, hand-held models available. (Most look surprisingly like a taser) They are rather inexpensive (ranging from $50 to $600) and a modest range of testers with varying capabilities and features are available in this range. These units provide instant readings of paper moisture content and should meet your needs. If you purchase a meter/analyzer make sure it is suitable for measuring paper. Some of the least expensive models are only for wood or hard materials. Also check the accuracy rating of the device. If it has a .01% or .02% for paper it should do fine. The same devices may have a 1% – 3% accuracy for wood, but that won’t affect testing paper.

6 to 8 percent moisture is the sweet spot for corrugated paperboard. Below 6% and the risk of cracking scores will increase, perhaps significantly depending on the paper. If the moisture content goes above 8% you will start to see a decrease in compression strength. Reports indicate compression strength can decrease as much as 6.5% per every 1% of moisture over 8%.

Now, in your case (simple checking for machineability) moisture meters/analyzers should work fine. However, they are not the most accurate method for checking paperboard moisture. Should you ever need to certify board for food or pharmaceuticals you may want to find a testing facility that can provide results via the oven method.

– Ralph