Can we estimate the impact of various factors on the amount of foreign objects removed by the current processes in a moving stream of milk powder?

Milk Powder

Fonterra Co-operative Group is the world's larger exporter of dairy products, owned by around 10,500 New Zealand dairy farmers and a leading multinational dairy company. The Fonterra Group's global supply chain stretches from Fonterra’s shareholders' farms in New Zealand through to customers and consumers in more than 100 countries. Collecting around 15 billion litres of New Zealand milk each year along with around 6.5 billion litres sourced globally, Fonterra manufactures and markets over 2 million tonnes of product annually. This makes the Fonterra Group the world's leader in large scale milk procurement, processing and management, with some of the world's best known dairy brands.

Fonterra continue to focus on our quality and food safety infrastructure, ensuring that we identify and remain ahead of emerging food safety risks. One such risk is eliminating the presence of any metal fragments that may be produced during manufacturing in our final products. Many critical control points have already been implemented to do this, including passing product through sifters and passing all product past magnets.

Problem for MINZ: Can we estimate the impact of various factors on the amount of metal picked up by magnets in a moving stream of milk powder?
Factors that will influence the ability of the magnets to work include:

  • flow rates and profile of the powder;
  • pipeline orientation;
  • the magnet itself - strength, design (spherical or bar), distance from the powder, spatial magnetic field and permeability;
  • how magnetised the material is (most equipment used in processing is 304 or 316 Stainless Steel);
  • the distribution of the metal fragments within the powder flow (including their size and orientation); and
  • how often the magnets are inspected and cleaned.

From the workshop we would like a model to be produced, taking into account a number of the above factors, that will provide us with an estimate of the amount (or likelihood) of metal being detected by the magnets and the limitations of this detection method. Specific questions we would like to explore are:

  • How efficient are magnets for detecting metal? (e.g. 10% of all metal contamination in the size range 0.5-1mm is removed by the magnets, or is it 50%?)
  • What is the probability of detecting metal of different sizes?
  • How do we express the success of magnets at removing metal?
  • How often should the magnets be checked? If we have a piece of metal on the magnet, what is the likelihood that it will be "pushed-off" by another piece?
  • Are two magnets better than one?

We have some information available in regards to flow rates and volumes, current magnet strengths and placements and pipeline orientation. However, we are happy for the Study Group to address this problem from a "clean slate" prospective and provide recommendations.