Industrial Metal Detector
A model garment is doing all products to be checked 100% with a industrial metal detector prior to shipment after all manufacturing operations have been completed. This check is being carried out after the final examination and packaging of the garment (incl. attachment of swing tickets) but before packing/boxing the goods in the metal free zone and are being the part of the final quality control procedure. Industrial metal detectors are an aid to prevent metal contamination and are the best way to ensure that needle control procedures are effective, but are not to being used to replace an effective needle replacement policy. Metal detection are being implemented within the production process and used in conjunction with the broken needle procedure.
Metal Detector Calibration Procedure:
- Machines are being calibrated every working day with this test card, at the beginning and at thend of each inspection lot, as well as when the machine is started up, then every hour and at the end of a working day as well as after any electricity cuts.
- If an issue is found with the machine at the next calibration, the goods that were done since the last successful calibration need re-checking, so the smaller the gap between calibrations checks the smaller the quantity of goods that are being re-checked.
- If the machine is to be found out of order after a check, it is being arranged for urgent repair and a replacement to cover for the time the machine will be out of order. This is being done through a static metal detector. It is being ensured though, that no orders leave the factory, that is not been checked, especially in case of children swears.
- The following metal detector calibration procedure are being adhered to when checking the machine. Please see below diagram for the width across the belt of the metal detector and where the test card should sit when tested at the bottom, center and top position:
CROSS SECTION TUNNEL NEEDLE DETECTOR
|TOP A7 A8 A9|
|CENTRE A4 A5 A6|
|BOTTOM A1 A2 A3|
Metal Detector Calibration Checklist:
- Switch on the machine and set the sensitivity level to less than 1.2mm sphere.
- Position the test card directly onto the conveyor belt at position A1.
- Let the card pass through the search head.
- The metal detector is being activated and the alarm is sound.
- Repeat the above steps 1-3 with the test card in positions A2 and A3.
- Again the detector is being activated and the alarm is sound.
- The test card is putting through on its own, we are not put it on a paper or put it through with a garment.
- Repeat steps 1-3 with the test card positioned in the middle of a stand (7-8cm high) or on top of a stand that is around 3-4cm high (depending on the height of the gap between conveyor belt and top of machine) at positions A4, A5, A6.
- Again the metal detector is being activated and the alarm is in sound. The stand are being a non-detectable block made of plastic material.
- Repeat steps 1-3 with the test card on the top of a stand (7-8cm high or as high as the gap allows for) at positions A7, A8, A9 and again the metal detector calibration procedure are being activated and the alarm are in sound.
Records are being kept of all of these checks by using the prescribe form.
In case the machine fails to pass the calibration test, it is immediately being turned off and re-calibrated by an authorised technician. All goods checked after the last calibration is being re-checked once normal operations of the detector have been re-established.
- Machines are being calibrated at least every 6 months by the manufacturer.
- Calibration certificates are being obtained and being kept for auditing purposes.
- If for any reason the detector are being relocated, it is being re-calibrated by the supplier’s authorised technical service.
- Regular maintenance (at least annually) of the detector is being carried out by the supplier’s authorised technical service based on the periods set up by them. Records for maintenance and any re-calibration made by the supplier are being kept, in case these need to be provided during any audits.
- When performing the metal detection it is being ensured that products are placed on the moving conveyor belt one by one with sufficient space in between products, so that there is no overlap.
- If goods are being shipped e.g. on hangers that are ferrous and cannot be passed through the metal detector, the goods are being taken off the hanger, passed through the metal detector and then re-hung. It is permitted for the hangers to be moved through the metal via a door. This process are controlling by the authorised person and only the correct amount of hangers per order are to be held at any one time, no spare hangers to be stored.
- As a general guideline though garments be metal detected as last as possible in the production process and any ferrous metal items are being attached in the metal free zone, such as security tags, hangers etc.
- The metal free zone are not being used for general storage and are being tidy. Once product is boxed or hung is to be taken to dispatch.
- Handheld metal detector also used for this
- In case of stone washing the garments are being metal checked prior to washing as the pumice dust contains small metal particles that have an adverse effect to metal detection.
- Any garments or part of a garment that are being outsourced for the application of a print, embroidery or any other process are being metal detected upon receipt back into the factory, prior to continuing production. This is to ensure that no whole or broken needle pieces, staples, other stray metals or sharp objects are in the returned pieces.
- The factory are making sure that procedures are in place to ensure that all garments including repaired and re-inspected do not go to packing without being checked by the detector.
- Clear separation and identification of the garments that are waiting to be checked and that are being checked to be strictly made.
- Records are being kept for all garments that are passing through the metal detector and are being completed as product passes through the machine to verify compliance with this requirement.
- If the alarm sounds, all garments on the halted conveyor belt are being put into a sealed bag, segregated and locked in a secure rejection box, to be located near the metal detector.
- The rejection bin are being taken to a clearly marked area and thoroughly checked for contamination by the assigned person.
- If the metal parts are found and the garment passes through the conveyor industrial metal detectors successfully, the garment can be returned to the bulk.
- If the metal part cannot be found, the contaminated product are being put into a polybag with details clearly marked on it and then placed inside the rejection bin (s. photo) locked away from the factory floor and THE GARMENT ARE BEING DESTROYED after authorised sign off by the factory manager.
Under NO circumstances can it be returned to stock for shipment.
- If a product is metal detected in its packaging, remove the packaging and detect the product and packaging separately as some packaging can contain traces of metal, especially if recycled, e.g. card, therefore may prevent the product being rejected.
- The rejection bin are being locked with a designated person holding the key. The bin is having a slit at the top through which the garment can be passed through. The slit is being big enough to let the garment fit through, but small enough to avoid a hand fitting through it.
- Any action is being recorded accordingly and any found metal parts are being taped securely to the metal detection failure record by sticky tape confirming source of contaminant and action taken to prevent future contamination.
- Records of garment destruction are being kept for a minimum of 5 years for auditing purposes.
- After the tested products are packed in a carton, the carton are being marked with a stamp stating date and ‘tested’.
- Any products that are being returned from the storage area / warehouse to the sewing/finishing floor are being checked again with the industrial metal detector and the cartons must be re-stamped with date and ‘tested’.
Requirements on the metal detector machine and accessories:
There are 2 types of conveyor metal detectors:
General Purpose Metal Detectors, which detect all metals (use them for garments that do not have any metal components such as zippers, press studs, buckles etc.)
Ferrous Only Metal Detectors (use them to inspect garments that contain approved non-ferrous, non-magnetic components).
We recommend to use metal detectors that detect ferrous metals only, so that garments can be passed through the detector with metal components on such as zippers, press studs, buckles etc.
Please specify when ordering components that they need to be non-ferrous and non-magnetic.
- A complete metal detection system comprises of a digital metal detector, conveyor belt, alarm reject system and test warning signal.
- Any new metal detectors purchased must have a printer or production data recording facility to record calibration checks, the style numbers of product detected and contaminants detected.
- The metal detector should be able to detect a metal part which is equivalent to a diameter of 1.2mm ferrous sphere at any point of the metal detector aperture at the supplied belt speed.
- The sphere should be chrome steel of AISI 52100 grade with AFBMA GD 10 size tolerance mounted on a test card. Please only use approved test cards from nominated suppliers/manufacturers, do not make up your own! The test card must be available at all times with the metal detector it belongs to.
- In case of garments with accessories, the metal detector must be capable of ignoring a representative sample of non-ferrous accessories and allowing it to pass undetected. In case of garments without accessories, the needle detector must at least ignore a non-ferrous test coin.
- A sample to test your machine can be obtained from the machine manufacturer.
- When passing the 1.2mm test card with the accessories or the test coin, the needle detector must detect the 1.2mm ferrous test card.
- Machines must have an audible alarm with automatic belt stop in case any metal is detected. The conveyor belt must not be able to operate when the detector is faulty or switched off.
- The audible alarm and conveyor belt should only be capable of being re-set by a key switch.
- Metal detectors must be installed to the manufacturer’s guidelines and the manufacturer must approve the sitting of metal detectors.
- Power fluctuation causes false alarms. Therefore the installation of a regulator will minimise the problem.
- All metal components must be non-ferrous to pass through a ferrous metal detector.
- Non-ferrous (non-detectable) and nickel free metal components (such as snaps, rivets, zippers etc.) should be used at all times and are mandatory for childrenswear to avoid false alarm during the detection. A special coating is applied to these components making them non-ferrous. Therefore it must be ensured that the trim supplier is alerted to deliver non-ferrous components for such garments.
- The factory should check that this is the case by checking incoming items with a ferrous detector prior to attaching them in bulk.
Machine Location and Set-up:
- The metal detector should be placed at the end of production (after all sewing operations, attachment of swing tickets and packing) in a so called airport system.
- The detection machine should be positioned half into the packing area, then shielded and separated by a solid panel/wall (fence is not sufficient, as items can be passed through it), so the product ends on the other side through the machine in an isolated metal free zone/area. This is to eliminate any external interference and to avoid that goods can bypass the metal detection by mistake.
- Please see photo for airport system:
- The detector must be installed in a permanent location free of other metal objects like metal frames, doors, shelves etc. to avoid electrical interference.
- It is recommended that the factory has at least 2 conveyor metal detectors at all times, to be able to carry on checking in case the one of them breaks down. It needs to be ensured though that any spare detector is in good working order and able to detect a metal part of 1.2mm ferrous sphere.
- Best practice can be found in using 2 metal detectors placed at 90 degrees or even through a twin head metal detector. Position across the conveyor belt in a 9 point check.
- Only authorised personnel should have a key that controls set-up and calibration of the machine. The key must not be left in the machine.
- Only authorised and trained personnel should be operating and maintaining the metal detector. The training should be held by the manufacturer or an approved agent and trained staff should be able to make minor adjustments when needed. Records must be kept of all training, maintenance, servicing and repairs.
- The operating personnel should be professionalised as full time workers.
- An organisation chart with the names of people in charge and their photograph must be posted at this area (incl. the person in charge of the process as well as any other operators).
- The metal detection policy must be translated into the local language, displayed where applicable and the management must ensure that workers fully understand the policy.
- The policy should be part of your induction programme for new workers.
- Cellular phones and other electronic devices must be kept away from the detector during operation. The supervisor should ensure that the assigned personnel must not wear clothing with pockets and should not wear items of metallic origin (e.g. wrist watches, rings, mobile phones, belts etc.) or carry a cellular phone while operating the machine.
- Uniforms for the authorised workers working in the metal free zone should have a different colour to the rest of the factory.
- The area the metal checked goods are going into, has to be a secured ‘metal free zone’ (so e.g. no clippers or scissors for cutting gum tape allowed), that is not too open and segregated/separated/isolated to avoid any possible contamination with the ongoing production.
- The zone has to be declared and clearly marked as metal free and only authorised personnel should be allowed into the zone. This again should be clearly marked and communicated to everybody and personnel should be identified as authorised, e.g. through different coloured uniforms or ID cards.
- The fencing of this zone should be solid, so that it can be avoided that metal objects can be passed through the fence and cause contamination.
- Entry to this area must be restricted and monitored. No one should be allowed access carrying any metal tool, e.g. scissors, blades, clippers, needle, stapler and or spare metal components. Unauthorised personnel are prohibited from accessing the metal free area.
- Anybody entering the metal free zone should be recorded with name, signature, in-time, out-time, purpose and signatures by person in charge & manager and again when leaving the area.
- The entrance to the metal free zone should be locked during breaks and at the end of the day after ensuring that no one is left behind.
- All product must pass through the metal detector into the secured ‘metal free zone’.
- Once the product has passed through the metal detector, it must be placed in a designated quarantine area within the metal free zone until the following calibration check has been successfully completed, only then can the product be released from the quarantine area for further packing.
- Packing can take place in this metal free zone, but no kimbal/tag guns should be used. Hangers can be inserted into garments and or put into the cartons in this area.
- Tools which are used in the metal free zone should be numbered, recorded and kept at fixed places. The manager should check quantities of these tools before and after working.
- Goods should be stored and kept in a metal free environment after the check is done and cartons are sealed.
Metal detection machine suppliers:
All the below suppliers are recommended and offer full calibration and maintenance service:
In summary, records that are being kept to support the operation of the metal detector are: – Calibration checks of industrial metal detectors, – Style number, date and time of products metal detected – Contaminants detected and follow-up action taken. These records are being retained for 03 years after shipment in case of any legal claims. Furthermore Personnel Training Records are being kept, listing the responsible people who have received training in needle control and metal detector calibration procedure procedures. All records are fully completed at all times.
Engr. Kh. Mashiur Rahman, Garments Auto Machine Technologist, Web: www.autogarment.com, Email: [email protected], Cell: +88 017 92 52 53 54