Operating Manual

Tiebar Set up and Monitoring using Ultrasonics

Injection molding presses rely on tiebars to apply clamping forces to molds during plastic injection and cooling cycles.

Balancing the loads applied to individual tiebars ensures uniform clamping pressure of the mold improving overall process

quality. Irrespective of process quality another very important reason to measure tiebar-clamping forces is to ensure that

individual tiebars are not overloaded leading to eventual failure of the Injection molding press itself.

While numerous methods have been employed in an attempt to address this issue, the Ultrasonic Extensometer provides a

simple, fast, and repeatable alternative.

ULTRASONIC BASICS

Ultrasonic Extensometers are designed to provide precise length measurement of acoustically conductive materials. The

instrument applies an electrical pulse to an ultrasonic transducer creating an acoustic wave. Piezo electric material within

the transducer converts the electrical pulse to mechanical energy and vise versa.

The mechanical energy produced by the transducer is that of a sound wave with a specic center frequency typically in the

range of 1.0 to 25.0 MHz. The sound wave generated by the transducer travels through the material being tested to the op-

posite surface or back wall of the tiebar. The sound wave is then reected off of the back wall and returns to the transducer

where it is again converted to electrical energy. The ultrasonic instrument measures the time it takes the sound energy to

travel from the transducer through the tiebar and return to the transducer – referred to as time of ight. The instrument then

calculates the length of the tiebar based on this time of ight and the velocity of sound for the tiebar material.

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Tiebar Set up and Monitoring using Ultrasonics Injection molding presses rely on tiebars to apply clamping forces to molds during plastic injection and cooling cycles. Balancing the loads applied to individual tiebars ensures uniform clamping pressure of the mold improving overall process quality.
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LENGTH, LOAD, AND STRESS The Ultrasonic Extensometer compares the time of flight measurement in a tiebar under load to that of the same tiebar in a relaxed condition. This difference in time of flight appropriately factored for temperature and stress effects determines the elongation of the tiebar under load and is the basis for all other data provided by the Ultrasonic Extensometer.