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Theller Engineering
707-762-3820
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SEAL WITHDRAWAL |
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The objective of the hot-tack test is to measure the development of strength of the hot seal during approximately the first second of its life. Obviously, the measurement of strength must start in only a fraction of that time if we are to achieve the test objective. But to start peeling the seal, it must be withdrawn laterally about 5 cm to the vertical line of pull of the grips before it can be stressed. Since we wish to start measuring seal strength about 100 ms after the jaws open, air cylinders operating at high speed are used in the Dynisco/Theller machine for the withdrawal, which is then accomplished in less than 80 ms. It requires about another 20 ms to dampen the impact associated with the process, to the point where the load-cell signal is stable enough to measure seal strength.
The seal is then peeled at the desired rate of 200 cm/min (see previous discussion of peel rate), employing a DC servo motor driving a lead screw.
Other hot-tack machines that cannot use Theller's patented two-stage withdrawal/peel system must withdraw and peel at the same rate, forcing the peel rate to be unrealistically high in order to be able to complete the withdrawal in 500 ms or less.
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