Rich asks;
I have a food customer who must send product through a metal detector to ensure there is no metal in the food. Intermittently the detector has gone off and when they send my corrugated box through without product it still goes off leaving them to the conclusion that there is metal in the boxes. We are using recycled liners and the mill has essentially let us know that they cannot 100% guarantee that there will be no metal imbedded in the fibres of the box. The mill also provided me with a document from the FBA essentially saying that during the paper making process there is the slight possibility of small metal fibres getting into the paper. Is this consistent with how you understand it to be? Do we have any other options for guiding our customer and ensuring there will not be a chance of metal in the box? Is there a way to prescreen the boxes to determine which ones may have a trace of metal in them before I ship them? Is there a way to test the boxes to determine where the metal exactly is?
I must concur with the position of the FBA and the nature of the 140 domestic paper machines that manufacture containerboard. I have attended enough TAPPI CORBOTEC meetings over my 31 years to know that this concern comes up at every meeting three times a year. Even the sophistication levels at the different recycled mills vary in their ability to remove metals from the recovered fibre.
The sensitivity levels of different detectors vary as well and the food industry is going to be using a very sensitive detector. Remember, they are looking for the tiniest pieces of metal in food. So a piece of metal that is likely to trip the detector they are using may not trip a more standard detector. You might have passed another packer’s inspection process depending on their equipment and sensitivity settings. The only sure way to prescreen your boxes to your customers’ spec may be to have the same metal detection system and sensitivity settings as your customer is using.
As far as pinpointing the location of the metal in the box, I do not currently know of a way to determine the exact location of the metal IN the board. I would think that this would require some type of probe detector that would be extremely sensitive and have a very narrow scan range. I would also believe the process would probably be quite time consuming and costly.
I don’t know how sensitive the wand type scanners that security firms use are. If you’ve traveled through an airport you’ll know that these can detect something as small as a staple in a paper… when they want too. If you could locate one of those it might be worth trying to see if it would pinpoint the offending contaminant. I wouldn’t suggest asking the TSA though. They don’t tend to have a sense of humor.
Another possible means for pinpointing the metal in the box or sheet would be x-ray. This too will most likely be expensive and time consuming.
However, from past experience if there is metal in your box, it will most likely be found in the medium.
— Ralph
askralph 
October 30, 2014 at 9:03 am
Good morning, Ralph.
I have had this problem using recycled medium. It tends to not be mill specific. I agree with all your narrative as to possible suggestions, but the one that may be the ultimate solution for a very sensitive customer is the obvious one. You can’t take the chance on using recycled medium for very sensitive food customers.
Have a great day, Ralph.
Bill Heintz
October 30, 2014 at 6:38 pm
We are currently working through a similar issue centred around one particular customer who has a higher specification than typically seen in the market place. Their specification for metal detector test pieces is 1.0mm Ferrous, 1.0mm Non Ferrous and 1.5mm stainless steel. (Our market is typically 2.5mm ,2.5mm, 3.0mm)
At this detection sensitivity on a digital processor based metal detector we have found a couple of things from our investigations
– metal contamination is not always related to an individual fragment. It is more often an accumulation.
– where an individual fragment can be identified it was typically ~2x1x0.5mm in size. (eg aluminum can / foil or pipe scale) This would be dependent very much on the screens the paper supplier is using and the source of the commons.
To conduct our analysis we have used the customer equipment on shutdown and also hired the same equipment to run the isolated cartons back through the process. Gradually breaking the carton down until we have a metal fragment detected in a 30x30mm carton piece. Then separate the liners by wetting them and finding the metal fragment by analyzing under a microscope.
My investigations didn’t find a hand held detector sensitive enough to locate a 2x1mm fragment of aluminium.
Our decision analysis with the customer is focused on Virgin Fibre papers and replacing existing metal detection technology with X-ray. Both which come at a cost over and above the current position.
Best Regards
Clayton