PET is very versatile material. It is flexible, food grade, waterproof, dust proof, non-reactive etc. all such properties are making it very popular among packagers for storing liquids, solids, powder and semi-solids. The most important factor is its cost-effectiveness. In comparison to glass, it reduces the overall cost of packing by many folds, and transportation will be much safer due to break resistance.
PET bottles are made by blow moulding of preforms. So, to begin with the quality testing, the first step is to assess the quality of preforms. Preforms are checked for their consistent thickness and internal strain defects. PET allows the light to pass completely. Light would get refract doubly. The Polaroid lenses have an electron aligned parallel to the axis. The lenses allow only parallel light to pass through, rest will be absorbed by electron and thus creating isoclinic fringe.
Testing of Bottles
A bottle is commonly tested for its even thickness, buckling load, balancing and equal weight distribution. These tests assess the quality of the bottle and its behaviour in real working conditions during transits, storage and packing.
Hot wire bottle cutter – This device performs a destructive test on the bottle. As the name shows, it cuts the bottle into 3 equal sections without any deformity. The assembly uses 2 hot wires to cut the bottle into 3 equal sections, neck, walls and base. Each section is weighed to match the predefined specifications. If there is uneven weight distribution, this would lead to stability issues in the bottle. Apart from weighing, the wall thickness gauge is used to measure the uniform thickness.
Base Clearance Tester – This test determines the balancing property of the bottle. It calculates the depth of the base with respect to the circumference. It is very important to have the base as per the specification of the engineered design. Otherwise, the bottle will topple when filled or empty.
Top load tester – This test is performed to test the stacking load bearing capacity of the bottle. When stored in a warehouse, bottles are stacked over each other. If bottles are not tested for top load, they might develop buckling or deformity due to overloading. If packager issues instructions for a warehouse manager to keep the maximum load beyond a certain limit, which is fetched after top load testing; such failures can be avoided. This test is equivalent to compressive testing. Knowing buckling load will help the packager to identify the defect in the manufacturing line. This helps in avoiding product failure during transit.
Wall Thickness gauge – This test determines the uneven wall thickness of the PET bottle. Due to improper thickness distribution, the deformity easily occurs in structure. To make it fit to use in the stressful environment, it is very important that bottle should have perfect structure.
Magna Mike 8600?
It is a smart device to measure the thickness of non-ferrous surfaces. It works on the hall effect principle. It has a magnetic probe and a target ball. The magnetic tip has a hall effect sensor to convert the electrical into human readable format. The probe creates a magnetic field around it, due to which the ball creates a synchronised movement with the probe while scanning the body of the sample. The distance between the ball and tip is the calculated and converted into the human readable format by the device. For precise readings, it comes with a foot switch for hands-free capturing of readings. It has IP 67 certification, which means it is water proof and dust proof.
It comes with a set of wearable tips, to avoid the complete replacement of the assembly in case of damaged tips. The tips come in 2 shapes, standard and chiselled tip. The standard kit comes with round tip. For complicated surfaces, the chiselled tip can be procured for accurate measurements.
The target can be chosen as ball, wire and disk. The ball comes in 3 sizes, 1/8 inch, 1/16 inch, 3/16 inch. The disk is also available in 2 shapes, standard cylindrical disk and tapered edges disk. For complex grooves where the ball is unable to make surface contact, other target materials can be chosen. Disk and wires are procured on special request. They are not part of the standard kit.
It has multiple output ports. Micro SD card slot, VGA slot, RS 232 slot and micro USB port. So, the operator can have computer connectivity for data logging and transfer. It can be connected to a projector to mirror the screen. Apart from inbuilt memory, it allows mounting external storage.
It comes with the self-calibration kit. Complete step by step instruction can be followed to calibrate the device.