askralph

Vincent asks:

I was just part of the webinar on crush you hosted January 30th and our GM wants my division to focus on minimizing crush throughout our facility. He wants to do a problem solving analysis on the issue. Can you help point me in the right direction for tackling a big project like this?

Where will we be most likely to experience crush on the corrugator and what are the best places to measure or take readings? I have the same question for the converting side as well. I know some of the obvious places, but I wanted to draw on your experience to identify places I may not have considered and also what you consider to be the most likely cause and therefore the best place to start.

Also, do you know if TAPPI has an Industry Standard for Caliper? If so where can I find it?

Since it is difficult at best to measure crush at each of the points on the corrugator mentioned below, you may want to focus your research on the area just before the cut-off knife and at the bottom of the stacks at the exit gates.

If you are considering using the DST method to collect your data, then you’ll need to measure five points on the corrugator, across the corrugator roll width, at each of the places listed below. Try to be consistent with the position of the five points as well. Let’s just say you select to record caliper (from the edge of the sheet) at 5″, 24″, 48″, 72″ and 91″. Then maintain those distances throughout your data collection process. Just a word of warning to keep everybody safe and happy, these measurements should only be taken with the machine stopped and/or with product off line from the machine.

• the nip of the corrugator roll (not able to actually measure the compaction of the medium in the fluting operation)
• the exit of the glue machine (entire machine would have to be stopped)
• the entrance to the double backer (entire machine would have to be stopped)
• the exit of the hot plates
• at the slitters
• exiting the scorer
• after the rotary knife
• measure the finished sheets in the down-stacker. Again check at five positions across the corrugating roll width.

With the converting machines it is a little easier to pull samples from various stages of the process, perhaps even more so with fixed architecture (non-opening) machines.

First, make sure your sheets aren’t crushed before they go on to the feed table. Many things can happen to a sheet between the corrugator and the converting machine. Units that are stacked beyond proper height/weight specification, strappers and unitizers, fork truck operators doubling-up for fewer trips, or somebody deciding to sit down and take a break on a stack can all contribute to board crush.
On the converting side of the equation, again determine from where you are going to take your measurements, just like you did for the corrugator, and maintain those locations throughout your sampling process. Again we stress… For safety reasons do not attempt to take these readings while the machine is running. Collect your samples, from each of these areas if possible, and then take the readings off-line from the machine.

Take readings,

• Before the sheet enters the feed roll on the feed section
• After the feed roll
• After each print station
• After the creaser and slotter (if you have an FFG)
• After the diecutter
• After the beater section of the stacker
• After the counter-ejector (FFG, the pull rolls and compression sections can cause crush)
• Anywhere else you have rollers or nip points.

If your operation uses bundle breakers/separators take readings after the breaking process. Improper adjustments can result in excessive pressure on the blanks. Improperly nicked bundles can require additional pressure to break the bundles and result in crush as well.

Crush can be speed sensitive. So as you’re collecting your data, you’ll want to record machine speed for further evaluation.

There is a TAPPI Test Method for measuring caliper, but it only measures “springback” caliper and not the minimum point of caliper during the thickness reduction that occurs at the various nip points.

These measurements can only properly be performed with the super sensitive DST equipment. Conventional caliper tools will not measure the amount of degradation in the corrugated sheets.

— Ralph

This entry was posted on March 3, 2014 at 4:40 pm and is filed under Containerboard, Testing and Specifications. You can follow any responses to this entry through the RSS 2.0 feed. Both comments and pings are currently closed.