Many manufacturing industries include metal detectors in their inspection systems to detect and reject products containing metal contaminants. If you have a manufacturing facility with an inline metal detector to keep metal contaminants out of your products, you may wonder what these systems may be leaving behind. What metals can a metal detector fail to detect?
Keep reading to learn from our pros at TDI Packsys about how metal detectors work to detect metal objects, what types of things they can’t catch, and their use throughout manufacturing and production facilities.
What Industries Use Metal Detector Inspection?
In commercial applications, metal detectors help manufacturers keep metal contaminants out of their products. These include any products with non-metallic packaging. Foil-wrapped products, for example, will not allow inspection by a metal detector.
Many food producers utilize metal detector systems to detect metals in meat, spices, baked goods, and many other food types. Other industries also regularly use metal detector inspection to keep pharmaceuticals, cosmetics, and similar products free of metal contaminants.
Can Metal Detectors Detect All Metals?
If you’re looking for a quick answer to the question of what metals cannot be detected by a metal detector, here it is: None. A well-calibrated, high-quality metal detector can find all kinds of metals. However, certain factors, such as the metal’s magnetic properties, can impact a metal detector’s accuracy and ability to pick up on tiny particles.
Let’s discuss exactly how a metal detector works, and understand a few factors that impact its ability to detect unwanted items like bits of metal.
Metal Detector 101
Metal detectors use electromagnetic pulse induction (PI) to detect metal objects within a magnetic field.
Please note that while other types of metal detectors exist, the detectors used in commercial production facilities function via pulse induction. This article will focus exclusively on the pulse induction type and not on hobbyist “treasure-hunting” detectors that search for lost jewelry, precious metal scrap, or beer cans.
PI detectors include an inductor coil, also called a search coil, that uses a pulsing electric current to induce an electromagnetic field. When unwanted items like pieces of metal pass through this inspection zone, the magnetic field causes electric currents (eddy currents) in the metal object. These, in turn, generate an opposing field. A second receiving coil detects this phase shift and alerts the operator to metal contaminants within the product.
Poor Electrical Conductivity
The answer to the question “What metals cannot be detected by a metal detector?” depends upon the conductivity of the specific type of metal.
Because metal detectors use electric fields to detect metals, those with poor electrical conductivity prove more challenging to detect. Less conductive metals have low magnetic permeability, which means they don’t react as strongly with electromagnetic fields.
For example, metal detectors can easily pick up on copper contaminants because this metal boasts high electrical conductivity. Stainless steel, on the other hand, has very poor electrical conductivity and requires more sensitive settings for detection.
Ferrous and Non-Ferrous Metals
Metal detectors can detect both ferrous and non-ferrous metal types, although they detect ferrous metals more easily due to their magnetic properties.
Ferrous metal contains iron and is often magnetic, while non-ferrous metal consists of other elements like nickel, aluminum, and zinc. Due to the existing electromagnetic fields in many ferrous metals, the detector’s receiver coil can detect a signal from a much smaller ferrous metal sample compared to non-ferrous metals.
Metal Piece Size
The sample size necessary for metal detection depends on many factors, including:
- Type of metal – Detectors require larger pieces to detect metal with low magnetic permeability and low electrical conductivity, such as stainless steel. Modern industrial metal detectors solve this problem in part by using optimal sensitivity settings.
- Product effect – This term refers to how the product affects the function of the metal detector. For example, products that are conductive in their natural state, like red meat, may cause false alerts.
- Metal detector settings – Users can adjust sensitivity settings to weaken or strengthen the electromagnetic field.
Tiny metal particles may not produce enough current for detection, and therefore may require a different inspection system.
Can I Improve the Metal Detecting Power of My Detector?
If your metal detector lets metal objects slip through the cracks, you can adjust settings or calibrate the machine to pick up on certain kinds of metal.
A stronger magnetic field detects smaller, less conductive metal objects, such as minor amounts of stainless steel, so your detector may need higher sensitivity to find metals in your products.
That said, users must be careful with higher operating frequencies to avoid false indications. When sensitivity settings become too high, electronic devices around the detector may cause interference.
Sensitivity settings present challenges because you want to avoid operating at a very low frequency, but using a higher operating frequency may result in false alerts. If you need help refining the settings on your metal detector, consult with an expert who knows the ins and outs of your machine.
False signals may also result when the coil has too much current within the pulse circuit. Users adjust this through the discrimination setting. Using this setting, you can identify a specific type of metal based on the smaller or larger phase shift.
Discrimination proves less relevant in product inspection because we want to detect every metal containment. However, metal-detecting hobbyists use the discrimination feature often to find tricky materials like gold nuggets hidden among iron-rich ground minerals, or silver dimes buried in wet salt sand.
Routine calibration proves essential to keep metal detectors functioning correctly. Your industrial metal detector may feature auto-calibration, or you may need to call in a professional to do so manually.
Visit our blog to learn more about troubleshooting your food metal detector problems.
What Do Metal Detectors NOT Detect?
Because metal detectors use electromagnetic fields to find unwanted contaminants, they cannot detect non-conductive materials. Keeping contaminants like stone, plastic, ceramic, glass, rubber, and bone out of your products requires a different type of inspection method, such as an x-ray inspection system
Rather than relying on electromagnetic fields, x-ray systems use a product’s density to detect foreign materials, allowing for the detection of smaller contaminants than metal detectors.
Why Is Metal Detection Important in the Food Industry?
Manufacturing, production, and packaging facilities contain a lot of metal equipment. Over time, this equipment sheds metal pieces and particles into the product during manufacturing or packaging. Metal contaminants in food products result in lost profits, costly recalls, and safety concerns for consumers.
The food industry attempts to stop contaminated products from reaching consumers by integrating food metal detectors into their production lines. A high-quality detector can help any company improve its food product quality and reputation by keeping contaminated products off store shelves.
Many types of food metal detectors exist, including flow-through equipment for detecting metal contaminants in liquids. Other metal detectors include conveyorized metal detectors,gravity-fed detectors,drop-through detectors, and combination systems
The best metal detector for your facility will depend upon your product type and the current inspection systems you have in place. To determine which system is suitable for your facility, contact our experts at TDI Packsys. We can help you determine the ideal system for your facility.
Food Metal Detectors From TDI Packsys
Does your manufacturing facility need a reliable inspection system for metal contaminants? Let our inspection and packaging pros at TDI Packsys help you choose, install, and maintain your new metal detector system. We’ll provide the technology you need to keep your products from being recalled because of unwanted metal objects, including even difficult-to-detect metals.
When you trust TDI Packsys with your inspection system, we’ll provide all the help you need to get your system up and running and then offer unmatched after-sales support. We’ll train your staff on the new equipment, provide routine calibrations, and offer on-site support within one or two days of receiving your call.
Now that we’ve answered the question of what metals cannot be detected by a metal detector, please contact us with any other questions about our commercial metal detectors. You can reach us at 877-834-6750 or by contacting us online