D3470-97 – Standard Test Method Technical Guide

🔬 Test Method Scope and Significance

ASTM D3470-97 (Reapproved 2007) establishes a standardized procedure for determining the removal lug strippage force of Type IIA child-resistant closures. As defined in the standard (Section 3.1.1), a Type IIA closure is a lug finish closure requiring a random push down while turning, aligning with Classification D3475.

The significance of this test method is twofold. First, it serves as a manufacturing quality control tool for comparing closures against manufacturer specifications and contrasting similar closures made from different materials (Section 5.1). Second, it provides a critical metric for evaluating the continued effectiveness of the package for child resistance and adult opening and reclosing during its entire expected use and shelf life (Section 5.2).

🛠️ Apparatus Requirements and Specimen Preparation

Apparatus: The primary instrument is a torque-measuring device (Section 6.1) with a measurement range suitable for the container/closure system to be evaluated. The standard explicitly permits the use of digital or automated torque instruments, which must have an appropriate design and scale capacity. Results are accepted in electronic display or printout formats (Note 1).

An optional gripping device (Section 6.2) is specified to standardize the test setup. This grip must secure the closure perpendicular to the vertical axis of the container without applying any vertical or radial forces that could interfere with the pure strippage measurement. The device must not contact any portion of the container body.

Specimen Preparation: Test specimens must be prepared by assembling the closure to the appropriate container. The standard mandates pressing downward and turning the closure to reduce or eliminate initial closure lug wear, ensuring the test reflects the inherent strippage resistance of the design rather than pre-existing damage (Section 8.2). Prior to assembly, all samples and containers must be examined for compliance with manufacturer dimensional and material specifications (Section 8.1).

⚙️ Test Procedure and Measured Properties

The core procedure (Section 4) involves securing a preconditioned, capped container in the torque-measuring device. The closure is then rotated using mechanical or non-mechanical aid to determine the torque needed to force the closure across the container lugs. A critical requirement, which distinguishes this test from standard removal torque tests, is that no downward force is applied during the rotation.

The reported property is the Strippage Torque (Section 3.2.1), defined specifically as the moment of force required to produce rotation over the container lugs while exerting no downward force. Data analysis requires sufficient random sampling from the lot (Section 7.1) to ensure reproducibility. The average strippage force and the range are calculated for the test lot. Results are recorded in units of pound-force-inch (lbf·in) or newton-metre (N·m).