The principle of the sand falling method
The sand falling method is a test method to evaluate the wear resistance of the coating surface by simulating the impact of sand particles. The basic principle is that the standard sand particles of the specified particle size fall freely through a conduit of a fixed height and impact the coating surface. The wear resistance of a coating is quantified by measuring the mass or volume of the grit needed to wear through a coating of a certain thickness. The larger the amount of sand required, the stronger the wear resistance of the coating. This method can better simulate the wear effect of sand, dust and other particles on the coating surface in actual use, and is especially suitable for evaluating coating systems that need to withstand mechanical friction such as thick slurry coatings.
The wear resistance requirements of thick paste coatings
Thick paste coatings usually refer to coatings that can form a thicker coating film in one application, and are widely used in steel structure protection, flooring, ships and industrial facilities. These application scenarios often face harsh conditions such as mechanical friction and particle impact. Therefore, wear resistance is one of the key technical indicators to evaluate its durability and protective function. The sand falling method has become one of the important means to evaluate the wear resistance of such coatings because of its intuitive test principle and strong correlation with many actual wear conditions. The quantitative data obtained through this method can provide a scientific basis for the R&D optimization of coating formulations, the determination of construction processes, and product quality control.
Test method
The sand drop method test is performed under standard conditions to ensure repeatability and comparability of results. The main steps include: preparing a flat test plate that meets the requirements of the standard and fully curing it; Fix the test plate on the sample table of the test instrument and place the sand flow point in a specific area of the coating surface; Load the standard grit into the funnel so that it falls freely and vertically to the coating surface through a conduit with a fixed inner diameter and length; Continuous testing until the substrate is ground out or a predetermined end point is reached. Record the amount of sand consumed by the wear-through coating. Usually, the same sample needs to be tested in parallel multiple times, and the average value is taken as the final result. Key operational points include controlling the constant flow rate of the sand particles, ensuring that the sand flow hits the test plate surface vertically, and controlling the temperature and humidity of the test environment.
Influencing factors
Test results are influenced by a variety of factors. The properties of the coating itself, such as the type of resin base, the type and content of the filler, the thickness of the coating and the degree of curing, are decisive factors. In addition, the material, particle size, shape and sharpness of the sand particles, the inner diameter and verticality of the conduit, the height of the sand falling and the sand flow rate and other test parameters must strictly follow the relevant standards. The result is usually expressed as "the amount of sand required to wear through the coating per unit thickness", with higher values indicating better wear resistance. When interpreting the results, it is necessary to combine the actual application scenarios of the coating. For example, for heavy-duty industrial floor coatings, high sand wear resistance values are usually required; For general protective coatings, relatively low values are acceptable. The test data should be mainly used for performance comparison between products of the same type or series.
Relevant standards
A number of standard systems at home and abroad have stipulated the wear resistance test of the sand falling method. These standards are similar in principle, but there may be differences in specific test parameters. Common standards include China's national standards, American ASTM standards, and ISO standards of the International Organization for Standardization. The test instrument is usually composed of a sand funnel, a deflector tube, a specimen fixture, a bracket and a collector. The core requirement of the instrument is to ensure that the sand flow is stable, vertical, and the key components are dimensionally accurate. The user should select the instrument that meets the requirements according to the standard on which it is based and calibrate it regularly.
Notes:
When applying the sand falling method to evaluate thick slurry coatings, the following points should be noted: First, the preparation and maintenance of the test plate must be standardized, and the coating thickness should be uniform and known. Secondly, the test environment should be stable to avoid violent fluctuations in temperature and humidity affecting the coating state or sand flow rate. Thirdly, standard sand grains are consumables, and their performance will change with the increase of use, so you should pay attention to replacing the new sand regularly. Finally, this method mainly evaluates the wear resistance of the coating, and other properties of the coating, such as adhesion and impact resistance, need to be comprehensively evaluated in combination with other test methods. Correlating laboratory test data with actual service performance is an important part of accurately evaluating the suitability of coatings.
Summary
As a classic method for evaluating the wear resistance of thick slurry coatings, the sand falling method has the characteristics of clear principle, relatively simple operation, and good correlation with a variety of wear conditions. Through standardized testing, quantitative wear resistance data can be obtained to support product development and quality control. Understanding the principles of testing, following standard steps, and controlling key influencing factors are fundamental to reliable, comparable test results. This method plays a continuous role in product performance evaluation in industrial protection, flooring and other fields.
References
ASTM D968, Standard Test Methods for Abrasion Resistance of Organic Coatings by Falling Abrasive.
ISO 7784-2, Paints and varnishes — Determination of resistance to abrasion — Part 2: Rotary abrasive rubber wheel method.
GB/T 23988, Determination of wear resistance of coatings - Sand falling method.
Coating Process Editorial Board. Coating process. Chemical Industry Press.