Operation Specification for Determining the Softening Point of Resin Using the Ring-and-Ball Apparatus

The softening point of resin is a key parameter for evaluating its thermal properties, which is of great guiding significance for the determination of material processing and application conditions. The global method is a widely used standard test method that determines the temperature of the resin specimen at a specified heating rate when it is dragged to a certain distance by the gravity of the steel ball in the steel ring, which is defined as the softening point. This specification of practice aims to elaborate on the standardized steps, precautions, and interpretation of the results for determining resin softening points using the Global Method instrument to ensure the accuracy and repeatability of test results.

Instrument and material preparation

Before testing, ensure that the following instruments and materials meet the requirements of relevant standards. The instrument should be calibrated regularly and all parts that come into contact with the specimen should be clean and dry.

The main instruments include: global softening point tester (including heating bath, stirring device, thermometer holder), steel ring (standard inner diameter), steel ball (specified weight and diameter), steel ball positioning ring, beaker (for heating medium), thermometer (accuracy meets standards) or calibrated electronic temperature measurement system. The heating medium should be selected according to the expected softening point temperature range, such as using freshly boiled and cooled distilled water when the softening point is below 80°C, and glycerin or silicone oil when it is above 80°C. In addition, sample preparation tools such as scrapers, heating plates, etc. need to be prepared.

Sample preparation

Sample preparation is the basic link that affects the accuracy of test results. Representative resin samples are taken and pre-treated according to their condition. For solid resins, carefully heat until melted (to avoid local overheating) or shred according to standard methods. The prepared specimen is injected into a preheated steel ring so that it is slightly higher than the torus, then cooled to room temperature and scraped off the excess with a scraper so that the specimen is flush with the torus. Bubbles should be prevented during preparation.

Test steps

The testing steps need to be strictly followed to ensure that the process is under control. The specific process is as follows:

1. Place the prepared specimen ring horizontally on the ring frame plate and put on the steel ball positioning ring.
2. Place the steel ball in the center of the positioning ring to ensure it is in contact with the specimen.
3. Immerse the device in a heating bath that has been adjusted to the starting temperature (usually 5°C±1°C), and the liquid level should be higher than the height specified by the ring frame plate.
4. Start the stirring and heating program, and control the heating rate to 5°C/min.
5. Observe the deformation of the specimen, and record the temperature when the specimen touches the lower support plate, which is the softening point.
6. Each sample is tested in parallel at least twice.

The result is calculated

The result is calculated by taking the arithmetic average of the two valid parallel measurements and correcting it to the specified accuracy (usually 0.5°C) according to the relevant standard. If the difference between the two measurement results exceeds the standard allowable range, the test needs to be retested. The report should include the following information: sample identification, test standard basis, type of heating medium, temperature rise rate, individual measured values and averages, and any observed anomalies.

The softening point (T) can be regarded as the characteristic transition temperature of the specimen under specific conditions, and its testing process follows the principle of thermodynamic equilibrium, and the following conceptual expression can be used to express the relationship between test conditions:

T = f(P, v, t)

Among them, P is the constant load applied by the steel ball, v is the program heating rate, and t is the time point when the specimen is deformed to the specified displacement. Specific function relationships are defined by standard methods.

Notes:

In order to ensure the safety of the test and the reliable results, it is necessary to pay attention to the selection of heating medium to match the range of softening points to prevent boiling or flashing; The instrument assembly should be leveled to avoid gravity direction deviation. The heating rate needs to be strictly controlled, and too large deviation will lead to the result shift. The temperature measuring device needs to be calibrated regularly; The instrument should be cleaned promptly after the test to prevent residue from affecting subsequent tests.

FAQs

The following table lists the issues you may encounter during testing and what you can do about them: