Dropping point and softening point apparatus working principle

What Is Dropping Point?
Synthetic and natural products can gradually soften its temperature rises and melt over a relatively large temperature interval. Generally, the dropping point test is one of the few easily achievable methods available to thermally characterize materials like fats, greases, waxes, and oils.
Dropping point definition: The dropping point (DP) is a characteristic property of a material. Samples are heated until they transform from a solid into a liquid state. The dropping point is the temperature at which the first drop of a molten substance precipitates from a standardized cup with a defined orifice under controlled testing conditions in a furnace.
The drop point is a suddenly occurring event, as the liquefied drop is accelerated by gravity as it escapes the cup.

Illustration: Dropping point cup with 2.8 mm orifice containing sample in the furnace

What Is Softening Point?
Synthetic and natural products can gradually soften its temperature rises and melt over a relatively large temperature interval. Generally, the softening point test is one of the few easily achievable methods available to thermally characterize substances such as resins, rosins, bitumen, asphalt, pitch and tars.
Softening point definition: The softening point (SP) is a characteristic property of a material. Samples are heated until they transform from a solid into a liquid state. The softening point is the temperature at which a substance has flowed a certain distance under defined test conditions. Softening point tests require a dedicated sample cup with a 6.35 mm orifice in the bottom, which is wider than that of a dropping point cup. In order to force the precipitation of the softened sample from the cup when heated, the sample can be weighted with a ball of standardized dimensions made of stainless steel. Once the sample softens and extends down far enough to reach a 19 mm distance from the cup orifice, the furnace temperature is recorded as the softening point temperature of the sample.
Illustration: Softening point cup with 6.35 mm orifice containing sample in the furnace. The sample is weighed with a standardized ball.

What is softening point
Why Measure Dropping and Softening Points?
Some synthetic and natural products that are important raw materials for various industry segments, do not show a defined melting point and thus must be measured using other methods. They include ointments, synthetic and natural resins, edible fats, greases, waxes, fatty acid esters, polymers, asphalt and tars. These materials gradually soften as the temperature rises and melt over a relatively large temperature interval. Generally, the dropping or softening point test is one of the few easily achievable methods available to thermally characterize such materials.

Dropping and softening points are mainly used in quality control, but can also be valuable in research and development for the determination of use temperatures and process parameters of many different materials.

Automated Dropping and Softening Point Determination Test Principle
Generally, a dropping point or softening point is determined by heating the sample. The furnace is used to control the temperature program during an analysis. Temperature control and temperature recording is guaranteed by a digital platinum temperature sensor. In the Dropping Point instruments from METTLER TOLEDO, a white balanced LED light shines on the test assembly, which consists of the cup and holder inside the furnace. The sample behavior is recorded by a video camera.
Length diagram of a duplicate determination of the softening point shown in the graphic on the right side. The steeper the slope (indication of the flow speed), the lower the viscosity.

Manual Methods vs. Digital Methods (Dropping Point)
Manual methods use a thermostatic liquid bath and mercury thermometer. Depending on the dropping temperature of the test substance, different liquids have to be used in the liquid bath.  Manual methods require visual inspection of the dropping point process, which is tedious as the attention of an operator is required for quite a long time to continuously monitor the test process. The drop point itself is a suddenly occurring event, as the liquefied drop is accelerated by gravity as it escapes the cup. Once this happens, the operator needs to quickly note the temperature. Furthermore, a mercury thermometer is used to monitor the temperature.
In summary, manual dropping point testing is a time-consuming, hazardous, error prone process that is strongly influenced by operator bias.
If human observation is replaced with a device that records and evaluates the dropping point event automatically, the quality of the result is generally significantly improved: this is because there is no operator bias during the evaluation.
Ubbelohde method
Ring-and-Ball vs. Cup-and-Ball (Softening Point)
The two standard analytical methods for softening point determination used across a range of samples from bitumen to greases, waxes and resins, are the ring-and-ball (ASTM D36) and Jiahang's cup-and-ball (ASTM D3461) method.
Historically, the ring-and-ball setup came first. It involves the use of a thermostatic liquid bath, a mercury thermometer and a gauge for the distance. The specified sample holder is in the form of a ring, giving this method its name.
Although the ring-and-ball method has a simple setup, it has several disadvantages. Depending on the softening temperature of the test substance, different liquids have to be used in the liquid bath. As the substance under investigation is in direct contact with the liquid, there must be no reactivity between the test specimen and the medium. It is also important that the liquid should display uniform viscosity throughout the experimental temperature window. Once the ball has flown through the ring, the setup must cool down and be cleaned thoroughly: this makes the ring-and-ball method time and solvent consuming. A large volume of liquid needs to be replaced with fresh liquid after a few experiments.
Softening Point Ring-and-Ball

Jiahang's Dropping Point systems for softening point determination operate according the cup-and-ball method. This setup differs in various respects. The temperature control is ensured by a metal block heating principle and the cup-and-ball temperature is recorded by a digital thermometer. The sample is placed in a cup and can flow freely downwards through an aperture in the cup. As with the ring-and-ball setup, a ball also promotes the flow of the sample, however here it is blocked by the smaller diameter of the cup and does not flow through with the sample. The analysis takes place in a glass container that is disposed of after the experiment, thus avoiding furnace contamination.
The question that often arises is whether the two techniques deliver the same results. ASTM methods explicitly state that they have been designed to reproduce the results of the ring-and-ball methods. This is proven by ASTM Interlaboratory studies that were conducted.