The following practices are recommended to those specifying inspection equipment:
1. Proper spacing is essential.
For any piece of inspection equipment, make sure …your ability to inspect them properly. Improper package spacing can lead to poor inspection as well as incorrect or false rejects. Conveyor speeds for inspection should be matched and rated to product flow to avoid a bottleneck. If you do not have good control of the package, select a machine that can create a pitch (i.e., the distance between packages) so only one items is on the Checkweigher’s Weigh Table or going thru the Metal Detector’s Aperture at a time. Since most reject devices are time based, pay special attention to how the line restarts. Design in features so defective items are not allowed downstream because they were not moving at the line speed and were missed by the reject device.
2. Size your apertures correctly.
In metal detection applications, make sure your aperture is the right size. Do your research, or it can impact the sensitivity or readings and create too many false rejections. With the wrong aperture size, you won’t get the inspection you expect from your equipment. Metal detectors are not one-size-fits-all.
3. Isolation and vibration control are additional keys to good metal detection.
The environment is key to metal detection. Recycled cases, cartons, and overwraps may have tramp metal in them, so the metal detector doesn’t know if it is reading the product or the package. What often happens is recalibration of detectors, resulting in tolerances larger than they should be and distorted pass readings just to get materials through. This doesn’t protect the consumer as it should, and places operations at risk for the sake of expediency.
4. If what you’re looking to see doesn’t float, X-ray may be your answer.
X-ray is very good at inspecting things that don’t float. There’s a misconception that X-rays see everything. X-ray inspection is not suited for seeing wire ties or plastic tubing. X-ray does well with glass; it can see stainless and all metals the same. The technology has come a long way; it is much more reliable and less sensitive to heat and dust than it used to be, as well as much cheaper. Today, X-ray inspection systems cost a third to a half of what they did 15 years ago.
5. Educate operators.
Companies must educate the operators about the amount of X-ray to use in inspection, as its effects compare to being in the sun. Make sure the unit is properly guarded so they cannot look into the X-ray area or even stick their arms inside the machine. It’s not inherently …proper levels. Consider purchasing a hand held meter to detect radiation levels outside the unit, so operators know it’s safe. The FDA limits the allowable radiation emitted from an X-ray cabinet cannot exceed 0.5 milliroentgens in one hour at any point five centimeters from the external surface. In comparison, the average person in the United States receives a dose of 200 milliroentgens of radiation per year.
6. Consider all scenarios.
How does your machine handle a stream of rejects (e.g., 15 in a row)? Does it cause a jam, or jam up downstream? Think about a scenario where you reject a significant amount of product; does your equipment have built-in sensors to let operators know there’s a stream of rejects? It should.