Performance characteristics and construction techniques of wear-resistant polyurethane

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The wear and corrosion of mining engineering equipment have always been a problem that plagues mining engineers and managers, and they are also one of the key reasons for high production costs and low production efficiency. For many years, the research on non-metallic materials with high wear resistance, high elasticity, high strength, and high corrosion resistance that are suitable for use in mining applications has been a very important area of scientific research. The mining industry is eagerly awaiting a completely new material and process to address challenges such as wear resistance and corrosion prevention in production. As is well known, polyurethane elastomers are a type of wear-resistant material that utilizes flexibility to overcome hardness, and they have been developed on the basis of wear-resistant rubber. It has been widely applied in various mining operations. However, traditional polyurethane elastomers are usually molded using molds, which makes it difficult to produce complex-shaped or large-sized parts, and such processes require high investment. Against this backdrop, a wear-resistant polyurethane spraying technology was developed. The emergence of this technology provides the mining industry with a completely new option, demonstrating unparalleled advantages in practical applications. It breaks through the limitations of molds used for molding wear- and corrosion-resistant non-metallic materials. It is a novel process featuring on-site curing and rapid molding. This process extends the molding techniques for polymer materials to an entirely new field, thereby greatly expanding their range of applications. At the same time, due to its excellent wear resistance, outstanding corrosion resistance, aging resistance, ease of installation on site, and low cost, this new material has very broad application prospects. 1. Performance characteristics of polyurethane spray coatings: Polyurethane spray technology essentially involves applying a coating material; upon curing, it forms a material with various mechanical properties. It goes beyond the scope of conventional coatings and represents an organic integration of new materials, new equipment, and new processes. Compared with traditional wear-resistant and anti-corrosion materials (or coatings), its advantages are mainly reflected in the following aspects: (l) It has a fast curing speed; it can be sprayed on any curved, inclined, or vertical surface without sagging. The gelation time is around 10^5 seconds, and it achieves walkable strength after just 1 minute. (2) It is not sensitive to moisture or humidity, and is not affected by environmental temperature and humidity during installation. (3) 100% solid content, free of any volatile organic compounds, and environmentally friendly. (4) It can be sprayed or poured at a 1:1 volume ratio; the thickness achieved in a single application ranges from several hundred micrometers to several centimeters, thus overcoming the drawbacks of previous multiple-layer applications. (5) Excellent physical and chemical properties, such as tensile strength, elongation, flexibility, wear resistance, aging resistance, and corrosion resistance. (6) The formulation system can be adjusted arbitrarily, with a texture ranging from soft rubber Shore (A30) to hard elastomers (D65). (7) The coating is dense, seamless, and exhibits excellent resistance to various media; it can withstand long-term erosion by water, seawater, acids, alkalis, salts, oils, and other substances. (8) It has good adhesion; the adhesion to steel is greater than 10 MPa, and it does not come off over time. (9) Resistant to ultraviolet aging; it does not powder or crack when used outdoors for extended periods. The typical physical properties of polyurethane spray coatings are as follows: gel time of 10 to 120.5 seconds, tensile strength of 12 to 45 MPa, elongation at break of 150% to 80%, tear strength of 30 to 90 kN/m, Shore hardness of 30A to 65D, adhesion to steel of 6 to 12 MPa, and low-temperature flexibility such that no cracks occur upon bending at -30°C. Polyurethane spray coatings are known abroad as “two-component spray wear-resistant linings”. According to laboratory tests of their wear resistance, the wear resistance of polyurethane spray coatings is 5 to 7 times that of ordinary natural rubber, and more than 10 times that of carbon steel. This material not only has high strength, but also exhibits good cushioning and energy absorption properties. Table 1 shows a comparison of the wear resistance of polyurethane spray coatings and other materials in laboratory tests. Table 1 Comparison of Taber wear between polyurethane spray-coated surfaces and other materials. Material name, Wear amount/mg; Material name, Wear amount/mg: Polyurethane spray-coated surface, 1–10; Natural rubber, 146; Polyurethane elastomer, 10–50; Styrene-butadiene rubber, 177; High-density polyethylene, 29; Butyl rubber, 205; Polytetrafluoroethylene, 4–2; Neoprene, 280; Butyl rubber, 44; Polystyrene, 324; Low-density polyethylene, 7–0. ABS 275. Note: Wear testing conditions: CS17 wheel, 1000 cycles/wheel, 5000 revolutions/min, 23 °C. At the same time, polyurethane spray coatings also exhibit good resistance to hydrolysis, dilute acids and alkalis, oils, and salt spray, as shown in Table 2. Table 2: Resistance of polyurethane spray coatings to various media
Name of medium | Immersion result
Acetic acid (10%) | Good; slight discoloration
*ao acid an | Good
Hydrochloric acid (10%) | Good
Gasoline | Good
Sulfuric acid (20%) | Good
Diesel fuel | Good
Phosphoric acid (10%) | Good
Kerosene | Good
Citric acid | Good
Mineral oil | Good
Lactic acid | Good; slight discoloration
Hydraulic oil | Good
Sodium hydroxide (20%) | Good
Antifreeze (50% ethanol) | Good
Sodium hydroxide (50%) | Good; slight discoloration
Xylene | Poor
Potassium hydroxide (10%) | Good
n-Hexane | Good
Potassium hydroxide (20%) | Good; slight discoloration
Isopropanol | Good
Ammonium hydroxide (20%) | Good
Saturated saline solution | Good

2. Spray equipment and application procedures
Polyurethane spray coatings consist of two components with extremely high chemical reactivity. Upon mixing, these components undergo a rapid reaction that causes a sharp increase in viscosity. Without appropriate equipment for conveying, metering, mixing, atomizing, and cleaning, this reaction cannot be controlled. Therefore, specialized spray equipment is required. The equipment must have a stable material conveying system, an accurate material metering system, a uniform material mixing system, a good material atomization system, and a convenient material cleaning system. Due to the fast curing speed of polyurethane spray coatings and the short time required for them to penetrate the substrate, high requirements are placed on substrate preparation. The steel substrate is generally required to be sandblasted to Sa2.5 grade; areas where stress tends to concentrate, such as edges, corners, and welds, should be smoothed, and the appropriate primer should be applied. Before spraying, it is necessary to ensure that the substrate is dry and free of any substances such as dust, rust, and grease that could impair the adhesion of the coating. The surface treatment of substrates such as plastic, rubber, and concrete must be carried out strictly in accordance with the manufacturer’s construction procedures. The application interval for polyurethane spray coatings is generally kept within 12 hours; if this interval is too long, it may result in poor adhesion between the layers. If it exceeds 12 hours, it is recommended to use an adhesion promoter between construction layers to ensure project quality. During the spraying process, it is essential to strictly control the pressure difference between components A and B; this difference should generally be kept within 2 MPa. If the pressure difference is too large, it means that the two components cannot be mixed in the prescribed ratio; such an imbalance can lead to a range of problems such as bubbling, stickiness, and poor mechanical strength of the material.