STH-3 Manual Heat Seal Tester: Reliable Entry-Level Packaging QC
The STH-3 is KHT Instrument's entry-level manual heat seal tester — a straightforward, reliable instrument for labs that need ASTM F88/F2029-compliant seal strength data without the complexity or cost of gradient testing.
STH-3 Key Specifications: Temperature, Force, and Dwell Time Ranges
The STH-3 operates across 0–300°C with ±0.5°C temperature accuracy — covering the full range required for PE, PP, EVOH, PET, and aluminum foil lidstock sealing. Jaw closing force is adjustable from 0 to 600N with a manual control, and dwell time can be set from fractions of a second to 60 seconds. These three parameters — temperature, force, 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.
How the STH-3 Performs ASTM F88 Heat Seal Strength Tests
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.
Ideal Applications: Food Packaging, Pharma Lidstock, Flexible Films
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-3A gradient model.
STH-3 vs STH-3A vs STH-5: When to Choose the Manual 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 automated data logging; (4) your volume is low (fewer than 10–20 test cycles per day). The STH-3A 5-position gradient model is worth the upgrade if you're doing any R&D, film qualification, or SIT (Seal Initiation Temperature) mapping. The STH-5 touchscreen model adds IoT data export — critical for 21 CFR Part 11 pharmaceutical environments.
STH-3 Specifications
Temperature Range
0–300°C
Full range for flexible films, pharma, food
Temperature Accuracy
±0.5°C
Consistent repeatability
Sealing Force
0–600N
Adjustable jaw pressure
Dwell Time
0–60 seconds
Programmable
Seal Width
10mm (standard)
Other widths available
Test Positions
1 (single-point)
One temperature at a time
Control Type
Manual dial + LED
Simple, robust interface
Standards
ASTM F88 / F2029
Full compliance
Power
220V / 110V
Dual voltage
Dimensions
~320 × 200 × 280mm
Benchtop
Frequently Asked Questions
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