Sand Abrasion Tester for detecting the wear resistance of thermal spray coatings

Overview

Thermal spray coatings are widely used in machinery, aviation, energy and marine engineering, and their wear resistance is one of the key indicators for evaluating coating quality and service life. As a test method to simulate the erosion and wear of solid particles, the sand drop test can effectively evaluate the wear resistance of the coating through standardized sand flow impact on the coating surface. The method is easy to operate and has good repeatability, and its results have important guiding significance for coating material selection, process optimization and quality control.

Test principle

The basic principle of the sand falling tester is to allow abrasives of specific particle size and material to fall freely at a constant height and impact fixed on the surface of the specimen at a specified angle. The abrasion resistance of a coating is quantified by measuring the abrasive wear coating to the mass of the abrasive required to expose the substrate or reach a predetermined level of wear. Generally, the more abrasive mass consumed, the better the wear resistance of the coating. The equipment is mainly composed of sand storage funnel, deflector pipe, specimen fixture, sand collection device and support. The inner diameter of the deflector pipe, the height of the sand and the angle of impact must strictly comply with the standard to ensure the consistency of the test conditions.

Test parameters

The accuracy and comparability of test results are highly dependent on tight control of key parameters. The main parameters include the type, particle size, shape and hardness of the abrasive, the falling height and flow velocity of the sand stream, the impact angle of the sample relative to the sand flow, and the judgment criteria of the end point of the test. Relevant domestic and foreign standards, such as ASTM D968, GB/T 23988, etc., clearly stipulate these parameters. For example, polygonal silica sand is often used as an abrasive, with a particle size usually controlled between 0.5 and 0.85 mm, and a fixed drop height of 1000 mm. Specimens are typically held at a 45° angle to simulate common erosion wear conditions.

Trial steps

A standardized test process is the basis for obtaining reliable data. First, the coating specimen is pre-treated, the surface is cleaned, and the initial thickness is measured. The specimen is then securely mounted on the fixture and adjusted to the specified angle. Calibrate the sand drop device to ensure that the sand flow is vertical and continuous. After starting the test, allow the abrasive to continue impacting the designated area of the coating surface until the end of wear. The end point is usually defined as the first exposure of the matrix material at the bottom of the wear pit, or the diameter of the wear pit reaches a specified value. Finally, the total mass of abrasives consumed is weighed and recorded as a basis for evaluating wear resistance.

The result is calculated

The wear resistance of a coating is usually expressed in terms of the wear factor or the amount of wear. One common calculation method is the wear volume method, which is formulated as follows:

V = M / ρ

Where V represents the volume of the coating worn (cm³), M represents the total mass of abrasives consumed (g), and ρ represents the bulk density of the abrasive (g/cm³). In turn, the wear resistance index of the coating can be calculated or compared with the reference sample. To visually compare the performance of coatings from different processes or materials, the key data can be summarized in the following table:

Note: The "data to be tested" in the table needs to be obtained through actual experiments. The results should be comprehensively evaluated based on factors such as coating microstructure, hardness and bonding strength.

Influencing factors

During testing, several factors can affect the accuracy of the results. The uniformity and flow of the abrasive must remain stable to prevent clogging in the funnel or conduit. Alignment of the sand stream is critical and it is important to ensure that the impact is in the center area of the specimen. Environmental conditions, such as temperature and humidity, can affect the flow of abrasives and the physical condition of the coating, and it is recommended to operate in a standard laboratory environment. In addition, regular calibration of drop height and inspection of abrasive size distribution are necessary measures to maintain long-term stability of the test.

Scope of application:

The sand drop test method is mainly suitable for evaluating the wear resistance of coatings under erosion of solid particles at low angles, and is especially suitable for comparing the relative wear resistance of different coating materials or processes. This method has practical value for quality control, process screening, and material development. However, this method also has limitations, it mainly simulates a specific wear form, which may not fully reflect the wear behavior of the coating under actual complex operating conditions (such as high angular impact, high temperature, or corrosive media synergy). Therefore, the test results are usually analyzed in combination with the results of other wear tests (such as friction and wear tests, sandblasting tests).

Conclusion

The sand drop test is an effective and standardized method to evaluate the wear resistance of thermal spray coatings. By strictly controlling the abrasive properties, test geometric parameters and operation process, quantitative data with good repeatability can be obtained, which provides a scientific basis for the research and development, application and life prediction of coatings. In practical application, the scope of application of this method should be fully understood, and the comprehensive wear resistance of the coating should be comprehensively evaluated in combination with other analytical methods.

References

ASTM D968-17, Standard Test Methods for Abrasion Resistance of Organic Coatings by Falling Abrasive.

GB/T 23988-2009, Determination of abrasion resistance of coatings - Sand falling method.

Thermal spray coating performance detection and evaluation method.

A review of solid particle erosion and wear test technology.