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The Impact of Wet Spray Machine Nozzle Wear on Rebound Rate
Release time:
2025-10-04
Source:
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Summary:
I. The Mechanism of How Nozzle Wear Affects Springback Rate
Wear on wet spray machine nozzles primarily occurs at the nozzle outlet, as the high-speed flow of concrete slurry—containing hard aggregates—causes erosion and abrasion on the inner walls of the nozzle, leading to changes in the shape and size of the nozzle opening. These alterations, in turn, affect the morphology and velocity distribution of the concrete jet, ultimately resulting in an increased rebound rate. The specific mechanisms behind this phenomenon are as follows:
1. Increased divergence angle of the jet stream: Nozzle wear causes the diameter at the outlet to expand and results in an irregular shape, which in turn increases the divergence angle of the concrete jet stream. This leads to a more dispersed jet, reducing its contact area with the sprayed surface. Consequently, some concrete particles fail to adhere effectively to the surface, thereby increasing the rebound rate.
2. Uneven jet velocity distribution: Nozzle wear can lead to an uneven flow velocity distribution at the outlet, with some areas experiencing excessively high velocities while others have velocities that are too low. In areas with excessively high velocities, concrete particles strike the surface with excessive impact force, making them more likely to bounce back. Conversely, in regions with velocities that are too low, concrete particles lack sufficient kinetic energy to adhere effectively to the sprayed surface, also increasing the rebound rate.
3. Concrete Slurry Segregation: Nozzle wear can cause the concrete slurry to segregate during spraying, resulting in the separation of cement paste from the aggregates. Segregated cement paste exhibits poor flowability, making it difficult to effectively coat the aggregates, which in turn reduces the bond strength between the aggregates and the sprayed surface, ultimately increasing the rebound rate.
II. Main Factors Affecting Nozzle Wear
The main factors affecting the wear of wet spray machine nozzles include:
1. Concrete Mix Proportions: The hardness, particle size, and content of aggregates in concrete directly affect the degree of wear on the nozzle. The higher the aggregate hardness, the larger the particle size, and the greater the content, the more severe the wear on the nozzle.
2. Jetting Pressure: The higher the jetting pressure, the faster the concrete slurry flows, resulting in stronger erosion of the nozzle and more severe wear.
3. Nozzle Material: The hardness, wear resistance, and toughness of the nozzle material directly affect its service life. Materials with high hardness, excellent wear resistance, and strong toughness can effectively withstand abrasion, thereby extending the nozzle's lifespan.
4. Construction Environment: Factors such as dust, humidity, and temperature in the construction environment can also affect the degree of nozzle wear. For instance, dust accelerates nozzle erosion, while fluctuations in humidity and temperature may cause the nozzle material to expand or contract, compromising its sealing performance.
III. Strategies to Mitigate the Impact of Nozzle Wear on Springback Rate
To reduce the impact of nozzle wear on the springback rate, the following countermeasures can be implemented:
1. Optimize the concrete mix design: On the premise of meeting construction requirements, prioritize selecting aggregates with lower hardness, smaller particle size, and reduced content, while carefully controlling the water-to-cement ratio to enhance the workability and bonding performance of the concrete.
2. Properly control the spraying pressure: Select an appropriate spraying pressure based on construction requirements and concrete properties, ensuring it doesn’t exceed a level that could cause excessive wear on the nozzle.
3. Select high-performance nozzle materials: Choose materials with high hardness, excellent wear resistance, and strong toughness for nozzle manufacturing, such as cemented carbides or ceramics. Additionally, regularly perform heat treatment on the nozzles to enhance their surface hardness and wear resistance.
4. Strengthen nozzle maintenance: Regularly inspect nozzles for wear, promptly replace those that are severely worn, and clean and lubricate the nozzles to ensure they remain in optimal working condition.
5. Improve nozzle structure design: Adopting a rational nozzle structure design—such as installing wear-resistant bushings at the nozzle outlet—can effectively reduce nozzle wear and extend its service life.
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