How to Choose Between the Ring and Ball Method and the Cup and Ball Method for Softening Point Testers? Read This and Stop Worrying

Methodology Overview

The softening point is a key index for evaluating the heat resistance of polymer materials such as asphalt, resin, and plastic. The principle of determination is based on the temperature of the material when it undergoes a specific deformation under escalating conditions. At present, the determination of softening points is mainly based on two classical methods: the global method and the cup ball method. The two methods correspond to different standard systems and application scenarios, and the core differences are the specimen support method, heating medium and endpoint judgment criteria.

Global Law

The global method, also known as the ring and ball method, is the most widely used method for determining softening points. The basic principle is to pour the specimen into a metal ring of a specific size, with a steel ball of specified quality placed in the center of the top. The assembled specimen is placed in a heating medium (usually water or glycerin) and heated at a constant rate. When the specimen is softened by heat and sinks to a specified distance under the action of steel balls, the temperature at this time is read as the softening point. The standard formula of this method can be expressed as the relationship between the softening point temperature T and the sinking distance H and the heating rate v, which is usually simplified as:

T = f(H) | v = constant

The sinking distance H is the standard value (e.g. 25.4 mm), and the heating rate v is usually 5°C/min. The global method mainly follows ASTM D36, ISO 4625, GB/T 4507 and other standards, and is suitable for the determination of asphalt and some thermoplastic resins.

Cup ball method

The cup method is also known as the cube method or the specific cup ball device method in some standards. The device features a specimen placed in a cup-shaped container with a standard pore size at the bottom, with a steel ball load also applied on top. During the heating process, the specimen is heated and softened and flows out of the small hole at the bottom of the cup or makes the steel ball penetrate the specimen and fall, and the temperature of the steel ball when it falls to the lower plate is used as the softening point. The deformation mode was different from that of the global method, and the endpoint was judged to correspond to the mutation of the sample fluidity. The cup ball method is commonly used in the testing of certain resins, wax products or asphalt derivatives, and the main reference standards include ASTM D6090, DIN 52011, etc.

Comparison of methods and selection basis

The choice between the global or cup method is not based on the merits of the method, but strictly on the type of material being measured, the use of the final data, and the technical specifications that must be followed. The following comparison table summarizes the core differences:

Select a suggestion

To avoid choice difficulties, it is recommended to follow the following decision-making process: First, consult the product specification or the test standards specified by the upstream customer, which is the primary and mandatory basis. If there is no explicit regulation, it is necessary to analyze the industry practices to which the material belongs, such as the general use of the global method in the field of road asphalt. Secondly, considering the need for data comparison, if it needs to be compared with previous historical data or industry general databases, the same method should be continued. Finally, for material properties, for samples with high temperature softening points (e.g., above 150°C) or large differences in flow, refer to the special instructions for heating media and methods in the corresponding standards.

Considerations for instrument purchase

After determining the measurement method, a number of technical parameters should be paid attention to when selecting the corresponding instrument. For global instruments, it is necessary to confirm the temperature range, heating rate accuracy, automatic detection method of sinking distance, and whether it has the function of simultaneous testing of two specimens. For cup ball instrument, attention should be paid to the accuracy of the pore diameter of the cup, the compatibility and uniformity of the heating medium, and the reliability of the endpoint detection mechanism. Regardless of the instrument method chosen, the calibration traceability of the temperature sensor, the data processing and compliance verification capabilities of the software are common points to consider.

Summary

The global method and the cup ball method are two effective means of determining the softening point, and their choice is fundamentally based on the requirements of material standards and industry specifications. Understanding the differences in principle and scope of application, combined with clear test standards and material types, is the prerequisite for obtaining valid and comparable data. In the laboratory capacity building, the instruments of the corresponding method should be configured according to the mainstream testing requirements, and perfect calibration and operating procedures should be established to ensure the accuracy and reliability of the softening point measurement results.

References

• ASTM D36 Standard Test Method for Softening Point of Bitumen (Ring-and-Ball Apparatus)

• ISO 4625 Paints and varnishes — Determination of softening point

• GB/T 4507 Determination of asphalt softening point (global method)

• ASTM D6090 Standard Test Method for Softening Point Resins (Cube-in-Air Method)

• DIN 52011 Testing of bituminous binders - Determination of softening point