D4640-86 – Standard Test Method Technical Guide

📖 Definition and Scope

This standard, designated D4640-86 (Reapproved 2022), establishes a test method for determining the stroke cure time of thermosetting phenol-formaldehyde resins. The test method covers the determination of the cure rate at any specified temperature.

The stroke cure time is defined in Section 2 of the standard as “the time required for a resin being held at a specified temperature on a hot plate and being stroked with a spatula, to adhere to the hot plate and not to the spatula.” This measurement indicates the speed of cure, marking the transition from a fluid mixture into a hard, immovable mass.

Per Section 4, this test is significant as a process control for polymerization time. When cure times are determined at several temperatures and plotted (e.g., time vs. temperature), different resins can be effectively compared for their curing characteristics. All values are stated in inch-pound units, which are regarded as standard.

⚙️ Test Apparatus and Procedure

The method relies on