Metal Detector

Pharmaceutical industries are involved in manufacturing a large number of oral solid dosage forms like tablets, capsules, granules and powders.The manufacturing of these products involves different equipment and steps and there may be chances of any metal piece entrapment in the products during its manufacturing and it may be harmful to the patient so it is required by different regulatory bodies to use a metal detection system during manufacturing of these products to remove any entrapped piece of metal in products.

Possible Harms Of Metal

If any metal piece along with drug is taken it may result in following main harms,

  • Tooth damage
  • Tongue injury
  • Cut to oral cavity
  • GIT injury
  • Many other harmful effects

Reasons For Metal Entrapment

Following May be the possible reasons for metal pieces entrapment in different oral solid dosage forms during its manufacturing process.

Powders & Granules

Different powders are mixed to get a uniform blend by using different types of sifters and blenders.

Granules are prepared either by using wet granulation or dry granulation process and also involve mixers, dryers and dry mill or oscillating granulators.

  • The metal particles may shred in the product if blades of the Rapid mixing granulator strike with the bottom surface of RMG.
  • If a wet mill strikes with an installed mesh or sieve of the wet mill.
  • One main possible reason is the breakage of mesh or sieve installed in an oscillating granulator, multi mill or dry mill.
  • Oscillating granulator,  multi mill or dry mill are used to screen the granules after drying and sieves may be broken due to hard granules and these broken pieces may contaminate our product with metal pieces.
  • Manual sieving is also used for screening different powders and granules and there are chances of sieve breakage and pieces of metal may contaminate our product.


Tablets are compressed using different types of compression machines and chances of metal entrapment may be as follows,

  • Improper adjustment of the feed frame may scratch the turret and pieces of metal may be trapped in tablets during compression operation.
  • Any accident during compression operation like punch damage or breakage of the feed frame may also result in product contamination with metal pieces.
  • Metal pieces may be present in powder or granules and are compressed inside the tablets and are not visible.


Hard gelatin capsules are filled in the pharmaceutical industry using different automatic and semi-automatic filling machines.

Hard gelatin capsules are filled with powders, granules or pellets and chances of metal entrapment may be as follows,

  • Alignment issues of pins and cavities may shred pieces.
  • Breakage of a part during filling operation.
  • Metal contamination is already present in the product to be filled.


One important point to be discussed is that metal contamination may also be present in excipients or active pharmaceutical ingredients during its manufacturing at supplier manufacturing sites if these materials are not scanned through a metal detector at the supplier site after its manufacturing and before packaging.

What Is Metal Detector

In the pharmaceutical industry, a metal detector is equipment designed to detect and remove the metal contaminated product.Various types and models are available which can be used depending upon the requirements.

Working Principle Of Metal Detector

The pharmaceutical metal detector works on the following principle,

  • When a metal detector is turned on it creates a magnetic field in the product passing chamber.
  • When a metal-contaminated product passes through the chamber it results in a change in the magnetic field in the detector coil.
  • These electronic changes send signals to the rejection gate and it is opened to discharge the rejected product in box installed below the rejection gate.

Types Of Metal

Following types of metal are detected and removed by the pharmaceutical metal detectors.

  • Stainless steel
  • Ferrous
  • Aluminium
  • Copper
  • Bras

How to Use A Metal Detector

Pharmaceutical Metal detectors are designed in such a way that these are easy to use and can easily be installed to the desired machine and product pass under the effect of gravity.

  • For detection of powders and granules,metal detectors are placed in an area and powders and granules are fed from one side and pass under the effect of gravity and are collected in the containers.
  • A rejection holder box is attached below the rejection gate to hold rejected material.
  • For high-speed compression machines,inline metal detectors are used which are attached to the de-duster to make the process fast and efficient.
  • No extra time is required for metal detection,  it is carried out online during compression operations.
  • When a tablet containing a metal piece passes through the metal detector the rejection gate is opened and rejection goes into the rejection holder box.
  • As we know that on high-speed compression machines the compression operation is very fast and tablets pass through the metal detector at high speed so when the rejection gate is opened to reject the contaminated tablet,good tablets may also go into the rejection box.
  • At the end of compression operation, the rejected tablets in the rejection box are removed and can again pass through  metal detector one by one to exactly find or separate the metal contaminated tablets.
  • We manually add tablets one by one to the metal detector. So if the gate opens, only one tablet goes in the rejection box and we add the next tablet when the rejection gate is closed. 
  • For encapsulation machines, a metal detector is attached to the machine and after  filling all capsules pass through the metal detector and the remaining procedure is the same as discussed for tablets.

Verification Of Metal Detector

To ensure that our metal detector is properly working to remove the metals and does not waste good tablets, we have different types of coloured test tablets having different metals and also tablets without metal.

We add different types of artificial tablets containing different metal pieces and mark the performance of the metal detector in a checklist.

If all the metal tablets are removed we claim that our metal detector is efficient and works accurately.

Also Read

  1. Quality Assurance
  2. Dust cups for compression machines.
  3. How to compress Bilayer tablets?
  4. Stages and Mechanism of Tablet Compression.
  5. Advancements in tablet compression machines.
  6. Calculation of compression machine capacity.
  7. How to reduce compression machine breakdown.