STH-3 Manual Heat Seal Tester: Reliable Entry-Level Packaging QC

The STH-3 operates from room temperature +10°C to 250°C with ±1°C temperature accuracy — covering the sealing range of PE, PP, EVOH, PET, and aluminum foil lidstock. Sealing pressure is adjustable from 0.1 to 0.7 MPa, and dwell time is set by the operator for each run. These three parameters — temperature, pressure, and dwell time (the '3T') — are precisely what ASTM F2029 requires you to record and control for reproducible inter-lab results. The STH-3 delivers this in the simplest possible interface: reliable, operator-independent, and calibratable.

ASTM F88 ('Standard Test Method for Seal Strength of Flexible Barrier Materials') requires that test specimens be prepared at a defined temperature, force, and dwell time, then cooled and peeled at a controlled angle using a tensile tester. The STH-3 handles the first step: making the reproducible laboratory seal. You set temperature with the dial, apply the jaw, and record your 3T parameters. The sealed specimen is then tested on a tensile/peel tester for F88 peel strength measurement (N/15mm). For standard single-point QC testing — for instance, verifying that a production batch of dairy lidstock exceeds 10N/15mm — the STH-3 delivers exactly what you need.

The STH-3 is the preferred choice for: small R&D startups beginning a heat seal testing program; contract packaging labs that run occasional spot-checks rather than daily seal development; pharmaceutical packaging lines verifying existing known parameters (temperature and dwell already optimized); food factories running ASTM F88 QC on a fixed production recipe. If your lab needs to map a full temperature-seal strength curve across five temperature points simultaneously, consider the STH-5 gradient model.

Choose the STH-3 when: (1) budget is the primary constraint; (2) your testing involves a single, known temperature rather than process optimization; (3) you do not need printed test records; (4) your volume is low (fewer than 10–20 test cycles per day). The STH-5 5-point gradient model is worth the upgrade if you're doing any R&D, film qualification, or SIT (Seal Initiation Temperature) mapping. The STH-3A touchscreen model adds automatic sealing pressure, a built-in printer for test records, and ±0.5°C temperature accuracy.