Guide to the Spraying Application of Polyurethane Elastomers

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Application Guide – Wear Resistance: Each type of grinding has its own particular characteristics. Its unique properties determine the hardness and thickness of the coating required for it. In practical applications, please follow these rules: 1.0 If you are not sure or unable to conduct tests, remember that the thicker the coating, the better. 2.0 The wear of polyurethanes does not follow an exponential pattern. If the coating thickness is doubled, its service life may be 4 to 6 times that of the original coating. 3.0 The wear resistance of the polyester coating in a mud environment is better than that in a dry friction environment. This is mainly because the mud acts as cooling water for the polyurethane coating. As a natural insulator, polyurethane retains the heat generated under dry friction conditions without releasing it. 4.0 Polyurethane protective coatings have a long history of being used to treat and support smaller components, such as objects 6 mm or smaller. However, the polyurethane material recently developed by our company shows that its coating can also be used to handle silica with a diameter of up to 355 mm. 5.0 Polyurethanes have a flexural modulus of 20%, and this factor needs to be given special attention during design for applications that are subject to loads. 6.0 In terms of wear resistance, only rubber materials and polyurethanes are comparable. The wear resistance of other materials such as polyurea, epoxy resins, vinyl plastics, and other polymer coatings cannot compare to that of polyurethanes. Corrosion resistance: Polyurethanes exhibit good overall resistance to chemical corrosion, and this property is even more pronounced when submerged. In practical applications, please refer to the following rules: 1.0 The brittle fracture temperature of pure polyurethane products is -56°C. 2.0 The thermal insulation performance of polyurethane varies significantly depending on the type selected. Aliphatic series such as BR-3S, NR-5S, and NR-7S can withstand contact with objects at temperatures up to 100°C. Our company’s NR-95HT product can withstand temperatures of 173°C to 225°C when in contact with materials such as hot asphalt. 3.0 Unless otherwise specified, all data regarding chemical resistance are based on ambient temperature. The corrosivity of an acidic solution at 70°C is much greater than that at 21°C. In cases where polyurethane is immersed in acidic substances, the temperature should not exceed 60°C. For temperatures above the above value, please consult Normank Company. 4.0 The resistance of polyurethanes to chemical corrosion is expressed as a pH value ranging from 3 to 11. Testing is required when the pH value is on the boundary, such as between 2-3 or between 11-12. It is not recommended to use such products in environments where the pH level is below 2 or above 12. 5.0 The Normank polyurethane coating performs better in water, saline water, and desalinated water. 6.0 In most cases, the smoke emitted is more corrosive than the actual liquid, especially at the liquid-gas interface. 7.0 When polyurethane is in water, it will continue to cure even 18 hours after initial curing. 8.0 For applications in vacuum environments, allow 7 days for the polyurethane coating to cure. This will give sufficient time for the bond between the polyurethane and the matrix to form. 9.0 If there are doubts about the performance of polyurethane coatings in a certain chemical environment, test, test again, and test once more. Tests on polyurethanes can be conducted using a metal block that is completely enclosed by a polyurethane coating of a fixed thickness; one end of this metal block must have a hole with a width of at least 6 mm. After measuring the weight of the metal, insert the hole-free end of the metal block into a chemical solution and leave it there for 7 days. Then remove the metal block and weigh it again. If the weight variation of the metal block is below 5% (or equal to 5%), it can be assumed with 99% certainty that the performance of polyurethane in such a chemical environment is satisfactory. At the same time, visually inspect the coating surface for any irregularities. Noise resistance: As a natural insulator, polyurethane also has the potential to reduce noise levels. Generally, the noise-reducing effect of softer coatings is better than that of harder coatings. 2.0 For our company’s product BR-3S, a 0.5mm thick coating can reduce noise by 7 decibels, while a 1mm thick coating can reduce noise by 14 decibels. This effect has been demonstrated in vibrating feeders. Conductivity 1.0 Polyurethane is a natural insulator. The resistivity of cured polyurethane sheets, typically 25 μm thick, can be as high as 400 to 700 ohms. When the sub-thickness of the polyurethane coating after spraying is 25 μm, the resistivity is as high as 13,000 volts. 2.0 The resistance coefficient of polyurethane can be reduced by embedding antistatic materials. Bent (impact) polyurethane materials will deform but will not be compressed. Just like stepping into a puddle, the water moves to other places but its volume does not decrease. The maximum deflection that polyurethane materials can withstand is 20%. A deflection of more than 20% can lead to premature degradation of polyurethane materials. The higher the hardness of a polyurethane coating, the lower its maximum deflection; the lower the hardness, the greater the deflection it can withstand. For example, a coating 25 cm thick can achieve a maximum deformation of 5 cm, while a coating 250 μm thick can achieve a deformation of 50 μm. 1.0 The thickness of the polyurethane coating itself needs to be determined based on the actual loading conditions. Factors that affect the coating thickness include the size of the load material, the falling height, the material’s movement speed, the degree of wetness or dryness, and the impact angle. Our company can provide recommendations regarding coating thickness based on the specific circumstances; please contact us if you need such advice. Fire resistance: 1.0 According to the classification of flame spread and smoke production levels specified in ASTM E-84 (the American standard), the flame spread rating for polyurethanes is usually below 40, and the smoke production level is usually below 30.2.0. Flame retardants can be added to polyurethane coatings to improve their fire resistance. Both solvent-based and 100% solid polyurethane spray products can be incorporated with flame retardants and possess self-extinguishing properties in some cases.