Metal detectable plastics use in cleaning tools and utensils

14 October 2016  •  Author(s): Debra Smith, Global Hygiene Specialist, Vikan

Foreign body contamination of foods can be a safety or quality issue, or both. Regardless, if a food is contaminated by a foreign body the repercussions for the food business can be expensive and damaging.


Metal detection is a well established and effective method of reducing the risk of metal fragments in commercial food products. Control of plastic foreign bodies is more difficult. Metal detectable plastics have been developed with the intention that metal detectors can also be used for their detection but how detectable are these plastics? Many food manufacturers are unaware that the metal detectability of any metal containing foreign body will depend on a number of factors, including the following:

  • Metal content of the contaminant; both the quantity and type of metal
  • Size of the metal containing contaminant
  • Orientation of the metal containing contaminant
  • The food product – size, composition
  • Food packaging
  • Speed of the conveyor belt
  • Detector used
  • Detector calibration. 

Each of these interfering factors has an effect on the detectability of the metal containing contaminant and the interferences are often cumulative, as illustrated in Figure 1.


Figure 1: Factors affecting the metal detectable threshold

Consequently, metal detection systems do not give 100% security even with regard to the detection of totally ferrous metal objects. Additionally, metal detection systems cannot detect non-metallic items such as bone, glass, or stone.

The metal detectable plastics used in the construction of food industry standard utensils and cleaning equipment only contain a small percentage of metal detectable material. Consequently, metal detection systems only work if the fragments of this equipment are large enough to detect (given other detector limitations).

Most manufacturers of metal detection equipment will provide ‘calibration test pieces’, to check the function of the detector against ferrous and nonferrous metals. These are regularly used by the food manufacturer to verify the performance of their metal detection system. Some manufacturers of metal detectable plastic equipment will also provide a test kit that enables the food manufacturer to find out what size of metal detectable plastic can be detected by their detector/in their product.

However, very few do this. Research undertaken by Vikan, Denmark, to determine the metal detectability of a range of metal detectable plastics available to the food industry, show that not all are sufficiently detectable.

Detectability of metal detectable plastics used in the manufacture of cleaning tools and utensils

Initial investigations were conducted in collaboration with Detectronic, a Danish based metal detection system manufacturer.

An example of a metal detectable plastic test kit, as provided by some metal detectable plastic equipment manufacturers is shown in the header image. Figure 2 shows the results of the investigation.

Figure 2: Metal detectable plastics test kit results

Figure 2: Metal detectable plastics test kit results


The results demonstrate that, even without the additional interferences of product and packaging, the detectability of metal detectable plastics varies greatly. None of the samples from Supplier 2 were detectable and even the best detected metal detectable plastics (Vikan) needed to be over seven times the size of the iron sample to generate a similar reading, i.e. an 11mm round piece of metal detectable plastic was required to generate a similar detection signal to a 1.5mm round piece of iron.

Consequently, if the use of metal detectable plastic equipment is deemed necessary, the selection of appropriately metal detectable plastic equipment is essential to minimise the foreign body risk from this source.

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