Protect Your Product From Contaminants: Metal Detection and X-ray Inspection Cut Product Loss

Automatic balance control and quartz crystal control are some of the software features that contribute to unit stability. Automatic balance control continuously monitors the out-of-balance voltage and automatically corrects it to zero. This feature eliminates the need for periodic fine-tuning by an operator and ensures that the detector is permanently set to its optimum operating condition. Similarly, quartz control allows for control of the frequency of the oscillator with great accuracy, eliminating frequency drift.

Other factors that influence sensitivity include type and shape of metal, orientation, operating frequency, and throughput speed. A good indication of a detector’s all-around capability is the sensitivity ratio between ferrous and the most difficult-to-detect grade of stainless steel 304L (EN58E). This ratio, which can be as good as 1:1? and as poor as 1:2?, has a major affect on the detector’s ability to detect forms of contamination, like slivers and screen wire, that exhibit an “orientation effect.” Non-spherical metals such as wire are easier to detect when they pass in one orientation than they are in another.

The higher the detector’s sensitivity, the more capable it is of handling orientation effect. With software features that include automatic balance control and quartz crystal control, newer systems are extremely reliable.

Today’s systems are also quite user friendly, some with full color touch screen monitors that are very easy to operate. All systems also have security safeguards: Users have passwords for management that determine what settings each operator has permission to alter. A wide variety of metal detector styles are designed for specific products, including rectangular aperture for packaged and conveyed products, gravity flow detectors for powdered or bulk products, and pipeline detectors for pumped liquids, semi-solids, or slurries. All types of automatic reject systems for any type of detector can be used to fit any line configuration.

X-Ray Detection

Although metal detectors are extremely reliable, they can only detect metals and, as mentioned earlier, the size of metal contaminant detected varies with the type of metal. X-ray inspection detects all types of metal, as well as calcified bone fragments from chicken and other meats and glass particles from packaging. Also, with larger product sizes, an X-ray system will often outperform metal detection. The signal from a given piece of metal contaminant gets smaller when its distance from the coil of a metal detector increases. For the larger size coils needed for larger apertures, sensitivity at the center of the aperture degrades, lowering the overall metal detector performance. Because of these factors, most plants need to supplement their metal detection equipment.

A product’s thickness, homogeneity, density, and size determine the accuracy of detection of a contaminant; with most products, the accuracy rate of contaminant is +/- 1% at 2 Sigma. As with metal detectors, there are many types of X-ray systems available to suit any product, including designs for various sizes of packaged, bulk, and conveyorized products; pumped liquids and slurries; and systems for inspecting plastic composite containers, glass jars, and cans.

Today’s X-ray technology is not affected by vibration, wind, or electrical noise and can detect many contaminants other than metal, including glass, stone, bone, and dense plastics. Also, new modular designs enable easy, quick repair.

Because X-ray systems operate by measuring density, they treat all metallic contaminants in the same manner, whether they are ferrous, non-ferrous, or stainless steel. X-ray inspection can offer additional benefits over contaminant detection. It is a very useful tool for quality assurance, for example, because it can verify product count, dimension, malformed products, product voids, fill level, and package seal—even for a product packaged in metal foil. X-ray systems measure mass or density and can therefore determine if a package is under- or overfilled, errors that can result in loss of profits. In addition, an X-ray machine can determine if the seal of a package is damaged—even one in metal foil—and can also identify a missing component intended for a particular area of a package.