|Metal Detection / Testing Procedures
BALL-BEARING TESTING COMES UNDER SCRUTINY
Safeline is now using “real life” contaminants such as wires, pins and swarf, as well as ball-bearings, to monitor the effectiveness of its latest metal detectors because, the company says, this is the only true test of high performance detection.
Ball-bearings are currently used throughout industry as a standard method of testing metal detector performance and as a measurement of comparison between different equipment on the market.
A tiny ball with a set diameter of, say, 1.5mm is passed through the detector to check it is performing to the correct sensitivity level. The assumption is that the detector will find any similarly sized metal contamination.
In reality, however, long thin strips of wire and swarf may still pass through undetected if their diameter is less than that of the ball-bearing, a phenomenon known as orientation effect.
Says MPI Product Manager, Naresh Aggarwal: “It is pieces of wire and slivers of metal, not ball-bearings which pose the biggest threat to product security and people are often lulled into a false sense of security by the current test standards.
“It is our job as the ‘metal detection experts’ to inform customers of all the aspects of metal detection technology and that sometimes may come as a shock to the less experienced or less well informed user.”
He adds, many detectors on the market are judged in relation to their ability to detect non-ferrous and ferrous metals - brass, copper, aluminium and mild steel. This performance specification is a legacy of early metal detection manufacture when detection of stainless steel to any reasonable level was virtually impossible.
“People are fooling themselves and their customers if they think a detector sensitive to a 3.5mm - 4mm diameter stainless steel sphere will do the job demanded in the majority of today’s modern and hygienic factories,” adds Mike Bradley. “Large pieces of wire and swarf routinely show up in product and consumer complaints are still higher than the industry should tolerate.”
Safeline’s latest detector, the Signature 2F, is said to be twice as effective as other conveyorised detection systems on the market when it comes to picking up tiny slivers of metal and wire.
In “ball-bearing terms” this often represents a 1mm or 0.5mm improvement in sensitivity which sounds insignificant until wire lengths are compared (see illustration).
A number of unique features contribute to the effectiveness of the new Signature 2F and Profile 2F/3F, among them “Uni-Phase” technology which enables the detector to be operated on one setting while inspecting multiple products.
This form of single setting operation at high frequency levels is not possible with conventional technology because of product signal changes. Uni-Phase reduces the product effect signal at source avoiding the need for adjustment and, more importantly, maintaining the set performance standard across a wide range of products.
The new Safeline Signature 2F and Profile 2F/3F also allows operators to switch from one frequency to another to accommodate different products - a facility never available before.
Normally, the operating frequency, and therefore maximum sensitivity, of a detector is fixed at the level required for the largest or most difficult product it handles. A detector set to check multi-packs wrapped in metallised packaging is, therefore, forced to remain at that frequency even when monitoring smaller size or non-metallised packs.
The Safeline Signature 2F and Profile 2F/3F can switch to a higher frequency for packs with a lower product effect and therefore deliver a greatly improved detection sensitivity.
The Signature 2F and Profile 2F/3F also features a new electronics package with Super Drive which improves detection sensitivity for dry products such as biscuits and confectionery, whilst the company’s Performance Validation software can give a hard copy read-out for quality assurance testing.