Archive for the ‘Testing and Specifications’ Category

Tolerance for Scrap in Load

March 13, 2018

Andrew asks,

I had a customer ask me how much scrap they should tolerate in their product (slots/cutouts/etc). We aim for 100% scrap removal, but this is not always possible. So my question to you is if there an industry standard for this?

The answer is it’s what the customer demands or will tolerate. There is really no industry standard that I’m aware of for the amount of scrap allowed in a load. In the past customers were much more tolerant of “some scrap” in the load. However, as packing lines have become highly automated the amount of scrap a customer will tolerate has continued to decrease. Today many customers and brand owners have zero tolerance for stray scrap. Even a single piece of slot or glue tab scrap can result in costly downtime on an automated packing line. The customers don’t want the downtime, nor do they want to pay their employees to remove the scrap. In some cases with “hands-off” lines there may not be anyone to monitor the incoming boxes and remove stray scrap before it stops the line.

So we have to do our best to eliminate the scrap before it gets to the strapper or unitizer. We need to make sure our tooling is properly designed and the equipment is setup to optimize cutting and scrap removal. On the folder-gluer we need to make sure the slot knives and heads are sharp, properly adjusted and not damaged. The same goes for the tab knives and hand-hole devices as well.

On the diecutter we need to make sure the cutting die is designed and rubbered properly to provide a clean cut and proper scrap ejection. Make sure all rubber is in good condition and that the cutting die rule is not broken or damaged. If there is any impacted scrap in the cutting die, remove it and investigate the rubbering in that area. Also make sure the anvil covers are in good condition and even across the cylinder.

There are rotary diecutter stackers on the market that are specifically engineered to provide superior scrap removal even when running behind the industries fastest diecutters. These stackers are designed to remove scrap before it makes it to the stacking hopper and eliminate the labor involved in manual stripping or scrap picking. The saving in labor and returned product can have a very positive impact on your bottom line.

You’re correct, even though our goal is 100% scrap removal it can be difficult to make sure that one tiny piece of slot doesn’t make its way into the finished product. Sometimes it can become a battle between the customer and the boxmaker as to how much is too much.

Let’s toss these two questions out to our readers. We would like to know your thoughts and experience.

  1. If the customer and boxmaker agree on an acceptable amount of scrap when the order or contract is signed, will/does it help elevate issue down the road?
  2. I know there is an ongoing battle to control costs and offer the customer the best possible competitive price, but can a premium be charged to guarantee zero scrap loads?

— Ralph

Assembled Corrugated Blank Tolerances

February 23, 2018

Kevin asks,

Is there an industry-standard tolerance that would be applied to the assembled dimensions (Length, Width, Depth) of a 2pc carton?  I would question whether multiple processes should lead to alternate tolerances when compared to a single process 1-piece carton.  I would also wonder how carton size would play into the tolerance and if there are any steadfast rules and/or guidelines throughout the industry.

The particular carton I am trying to apply tolerance to is a 2pc Partial Overlap Top, HSC bottom where the width panels are die cut and the other scoring off of a press and then offset stitched within the length panel for reference.  I am trying to hold +/- 1/8” on all dimensions now.  These tend to be around 76 x 32 x 50” with 2” POL.

According to the Joint PMMI/FBA publication PMMI B155-TR2.2-2011,  the tolerance of a RSC panels are +/- 1/16 inch per panel with an overall blank tolerance of +/- 1/8 inch for both length and width. Also, I believe there is a TAPPI publication of dimensional accuracy which may make reference to tolerance.

Slot depth should be within 1/8 inch from the center line of the corrugator score. Slots should also be centered within 1/16 inch of the aligning scores.

No allowance is given for carton size, caliper, substrate or complexity of design in this specification.

I haven’t found any reference to multiple piece cartons which would lead me to believe that there would be an additional allowance for a multi-piece carton.

So, based in this information, it would make sense that the overall assembled dimensions (interior and exterior) should be within, and controlled by, the +/- 1/8 inch overall tolerance of the RSC or die-cut blank.

One other note to toss in here. While the PMMI/FBA publication above may note that +/- 1/8 inch over all is acceptable, today’s customers are typically demanding something closer. With today’s drive and anvil technology +/- 1/16 inch (1/8 total) may generally be considered the norm, but more and more customers are demanding closer tolerances and expecting little to no variation.

— Ralph

Calculating ink coverage based on weight

January 31, 2018

Ed asks,

“We are creating a program to quote customer requirements as quickly and accurately as possible but we are stuck with ink / printing issues.

Is there a conversion that may help us translate grams of ink to square centimeters / inches of printing?”

Your ink supplier should be able to tell you how many sq. in. or sq. cm. a pound or gram of ink will cover. This will change depending on the viscosity, substrate, anilox roll volume, ink manufacturer and ink type. So in your calculator (estimator) you may want to provide the option to select from a pre-programmed list of inks, or allow the estimator to enter a pounds per inch or grams per centimeter variable.

Then of course you’ll need to know the sq inches of coverage for each color. You could simply calculate the area of the sheet and then assign a light, medium, or heavy coverage variable to simplify the calculation of inches of coverage.

UPDATE: Roger Poteet, Poteet Printing Systems, has reached out to share their experience and knowledge with us through the Poteet Ink Estimator complied and provided by Poteet Printing. I also want to thank Andrew at Compass Packaging for sharing his knowledge and experience with the Poteet Estimator in the comment below.

– 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