Archive for the ‘Corrugating’ Category

Cracking Litho-lam, Does ‘Sides’ Matter

May 8, 2017

Clint asks,

I have a question that I hope you can answer.  When using the same liner board on both the inside and outside of a singelwall sheet, why do you see more of the “flute lines” on one side versus the other?  What causes that and does it have more effect on fracturing the liners when you are creasing one side versus the other?

This came up when one of my customers was laminating a litho label on SInglewall.  They normally laminate it to the good side (less visible fluted lines).  Because some of the sheets were slightly warped, they laminated some on the bad side (more lines).  After converting there was some fracturing of the litho (not liners).   We saw less fracturing of the litho on the labels that were laminated to the bad side.  From a logical standpoint, if you put the label on the bad side and it is a weaker paper, I think the label may stretch easier versus being glued to a heavier liner.  Also, the inside of the box would look better (less visible flute lines) so I would assume this should be the norm unless you are just spot labeling something.  Keep in mind, the liners on the inner and outer were supposedly the same paper.

What are your thoughts on this?


Thank you for an excellent question. Yes, I can add some insight.

Tensile strength and stretch of the liners are impacted differently in the singleface and doubleback operations. Also temperatures and starch application are different in the two operations. Fracturing can occur in one liner and not the other. Learning flutes can have an impact. Microphotographs of the cross section of the combined sheet can begin to reveal some issues.

Of course starch application and amount can signal issues as you described. World class consumption would be about 1.4 # per msf.

– Ralph

Checking Starch Viscosity

May 4, 2017

Ralph asks,

Lately we have been having a debate about the perfect temperature for the starch viscosity testing. We use the stein-hall cup for our tests. Is there any specific temperature where it is best to test at?

Temperature certainly plays a major role in the viscosity of starch. Starch viscosity changes about 10% for every 2 degrees Fahrenheit. We discussed your question briefly with Herb Kohler of Kohler Coatings. Herb says that most corrugating plants that he is familiar with try to maintain temperature of starch in their storage tanks between 100 and 105°Fahrenheit (37.8-40.6°C). This helps maintain a steady viscosity and optimizes the running speed of the corrugator. Above 105°F (40.6°C) and you’ll start to experience viscosity growth. Maintaining a set point of 102°F (38.9°C) is commonly recommended by industry experts. His experience has been that is far better and more accurate to check the starch viscosity at approximately the same temperature each time than to rely on temperature/viscosity correction charts.

Additional information about regarding corrugator starch viscosity can be found in this Ask Ralph article from Roman Skuratowicz Ideal Starch Viscosity for Corrugated.

— Ralph

Does 200# board require Mullen instead of ECT?

November 7, 2016

John asks,

If I order 200# C flute board with a 40# medium can I properly perform an ECT test on the board or do I have to stick with the Mullen test? We are trying to achieve 44 ECT by ordering a 42 – 40 – 42 liner combination. It is my understanding that if you order 200 flute board with any kind of medium it still requires a Mullen Test. Is that correct? Do you have to order an ECT liner combination such as 57 – 26 – 57 to properly test for an ECT value? Sometimes we do get the 44# ECT value but not always. Any suggestions would be helpful.

If I am being too complicated here, let me know. When you are considering that Mullen combination your incoming ECT levels will range from 45 to 60. That assumes that the corrugator has perfectly combined the liners to the fluted medium. This is not the real world. A good sheet supplier will know the strength characteristics of their containerboards and know what ECT levels they can achieve.

Have you ever considered EB double wall with even lighter and less fibre expensive that can still meet your needs?


Warp standards for micro boards and S-warp

August 25, 2016

Rick asks,

I am seeking written accepted warp standards for corrugated. I’m looking primarily for standards on C, B and E flutes.

I seem to recall 1/4″ per running foot as acceptable for B and C.

1. Is the same true for E Flute and other “micro”
2. Is there anything for “S” warp, as that seems to be issue with lower profile flutes.

I have not been able to locate “written” warp standards for E flute and finer corrugated board. And S warp is just a matter of compound warp in both the MD and CD directions.

Yes, the Fibre Box Handbook recommends that warp of corrugated board should not exceed 1/4” (6mm) over 12 lineal inches (305mm) of the material’s surface. However, there does not seem to be anything specifically relating to micro or finer flute board. I would think due to the nature of material and its uses that the warp standards would be different than that of larger flute board.

One has to look to setting standards on paper moisture variations, glue application rates, and corrugator process controls. It’s these input variables that a paper buyer, corrugator supervisor, and control system need to establish. Without getting the front end communicated there is not much chance of flat board.

Hey followers… We’re always open to your input. Please share your knowledge and experience on this subject with us.

— Ralph