Dynisco/Theller Machine: ± 2 milliseconds.
Delay Machines: ± 25 milliseconds.

Theller Engineering designed its own electronic circuitry and wrote the accompanying software, so as not to be limited by the precision and accuracy of programmable controllers. We have designed our system to have a timing resolution of one millisecond and a control band of ± 2 ms, because time is the most important variable in hot-tack measurement. Machines using standard purchased controllers have lower accuracy.

2. TEMPERATURE ACCURACY; CONTINUOUS AUTOMATIC CALIBRATION

Dynisco/Theller machine: ± 0.2° C.
Delay machines: ± 0.5°-1°C.

Dynisco/Theller uses platinum RTDs -- not thermocouples -- to sense and control die temperature. The RTD electronic circuit measures resistance change of the platinum sensor with temperature. Using resistance sensors instead of thermocouples makes possible automatic temperature calibration of the system by the computer every few minutes. This feature improves accuracy of measurement by eliminating most zero drift, and permits a very tight control band (± 0.2° C). Only the Dynisco/Theller machine has these capabilities.

3. PEEL RATE

Peel rate is the rate the failure line advances into the seal during the peeling process. Peel rate is ½ of the grip separation rate, which is the parameter set into the machine by the operator. Performance specifications for machines are in terms of grip separation rate, but are often incorrectly labeled as "peel rate". The figures below are grip separation rates. Divide these values by 2 to get peel rate.

Dynisco/Theller machine: Typical: 200 cm/min ( 33 mm/sec).
Delay machines: " 1200 cm/min (200 mm/sec).

Delay-time machines typically are set to pull the seal at about six times the rate of the Dynisco/Theller machine. For a discussion of this point, see Peel Rate.

4. EARLY MEASUREMENT of HOT TACK

The Dynisco/Theller machine employs a patented two-stage fast withdrawal system to enable measurement of strength of the hot seal to begin within 100 ms after jaw opening, and still permit relatively slow peeling of the seal during the ensuing period of strength measurement.

The delay-time machines have only one rate for both withdrawal and peeling, and typically do not reach the hot-tack measurement point until 250-400 ms after jaw opening.

5. GRAPHIC of HOT-TACK STRENGTH VS TIME

The Dynisco/Theller machine measures and displays the development of strength in the heatseal during the first few hundred milliseconds after the jaws open, from 100 to about 800 ms. This curve is generated during every test cycle. From the curve, the computer will print out the hot-tack strength at any cooling time in its range requested by the operator.

The delay-time machines report only one value of hot seal strength during each cycle. If hot tack at other cooling times are desired, the delay time must be changed and additional tests run.

6. SEALING DIES; SIMULATION

The Dynisco/Theller machine has quick-change commercial-size sealing dies that can be easily switched to serrated or other styles to study the effect of die type on hot-tack or ultimate strength, or to simulate conditions on specific field packaging machines. Dynisco/Theller Engineering carries many types of dies in stock. See Sealing Dies for a description.

The delay-time machines have very small dies that bear no resemblance to those on commercial packaging machines.