Metal detectors for vertical packaging machine

Hello everybody
We are buying vertical packaging form fill seal machine for pillow pack of cereals to 1kg. Does anyone have any experience with type of metal detectors to be used?
To chose metal detector for with gravity feed (instaled directy above forming tube) or the ones where already formed bag passes through head of metal detector on the belt conveyor . From my experience gravity feed type has the problem that product passes fast. Other type where already formed bag passes through detector head problem could be metallised film since sensitivity decreases.
Thanks in advance

Typically, this type of metal detector is considered a “Throat” metal detector.

The system sensitivity capability will depend on the diameter of the detector and the type of product being inspected.

When metal is detected, the reject signal is sent to the VFFS machine to create a “double-pack” along with a horn alarm to indicate reject.

The speed limitation of the detector is related to the diameter of the system and the product fall height and with this type of application, speed is rarely an issue.

I saw the topic and thought "throat metal detector" but the PP got there first.


It's probably worth getting a few manufacturers in as you have the options of a throat detector but also there is the option of detecting the whole pack. The throat detector is likely to have a smaller aperture (so more sensitive) but the speed of flow through it would be very high (less sensitive) whereas an in line packed product detector would be the opposite.


Although as your product is dry, it should be easy to detect metal whichever way you do it. It will come down to a balance of application and cost which the contractor should be able to help with.

Thanks everybody for answers.
I would like to hear experiences from people from production. My experience is that sometimes part which removes bag from conveyor belt can miss bag and also sensitivity with metalised film is lower. So I trust more to "throat metal detector"

Now I saw that there is forum for metal detection. Can this topic be moved to it?

Also consider x-ray detection. Sensitivity is often higher and possible through metalised film.

With the right gravity head the speed of the product transiting the head wont be an issue. Take a look at the THS/MS21 or THS/21 units from CEIA - out of everything that I have seen they give the best performance.

If you have an intermittent motion bag maker you can create a double bag / chain bag to capture the contaminant before it goes any further than the bagger.


If you are running foil laminate film then you're going to be very limited with what inspection you will get post bagging - this is where the gravity / drop through units are better for you. Otherwise if you want to check it when its in the bag look at say an Ishida Xray as they give good results for detection on packaged goods like this.

Milos, There is only one question that you need to ask at your company: "Are we planning to run metalised (foil) film for the bags?"
If the answer is "No" then the best point of inspection is in the finished bag. Contaminants cannot enter a sealed bag without leaving a mark (hole). Inspection of the finished sealed product is ALWAYS the No. 1 desired place for inspection.
If the answer is "Yes" then you need to consider two options:
1. Use an X-ray on the finished bag. X-rays can easily detect metal contaminants inside a foil bag, but metal detectors can really struggle with this if the film is thick.
2. Use a drop through (throat) style metal detector to detect metal in the product before it enters the bag. This is not ideal (because a contaminant can still enter the bag after the MD but the chance of this is very small) but commonly done on a VFFS machine.

Other comments:
Don't be talked into buying a "Ferrous in foil" metal detector unit - they are a waste of money - they only detect ferrous metal and most food processing equipment is S/S, i.e. NON ferrous metal.
The speed of the product dropping is irrelevant - whomever supplies the equipment just needs to calibrate the unit correctly.
A metal detector can achieve as good a result on dry product like cereal as an X-ray (sometimes even better) so long as you stick with the smallest possible opening (regardless of whether it is a conveyor or a throat unit).
Rejecting the bag off the line should be 100% accurate - but again it needs to be set up correctly by whomever supplies the machine.
Both units should be roughly the same cost (the throat unit will seem cheaper at first glance, but if you use the VFFS take away conveyor to mount the MD on, then the conveyor system should actually be cheaper i.e. you were going to buy a conveyor anyway for this job, so use the same conveyor for the MD).
Make a list of reputable brands (quick internet search). Reputable brands will all cost about the same and deliver similar results. Then I'd look at ease of use and service back up; these are often overlooked but are very important.

if you ever need any Packaging Machines & Goods contact me.