Factors Affecting the Wear of Hydraulic Sandblasting Fracturing Nozzles

The wear of the nozzle by the hydraulic sandblasting jet is mainly the erosion wear of the sand particles on the inner wall of the nozzle. The wear of the nozzle is the result of the action of the sand jet on the inner wall of the nozzle. It is generally believed that the macroscopic volume loss of the inner surface of the nozzle due to wear is formed by the accumulation of the material microscopic volume loss caused by the impact of a single sand particle. The erosion wear of sand on the inner surface of nozzle mainly includes three forms: micro-cutting wear, fatigue wear and brittle fracture wear. Although the three wear forms occur at the same time, due to the different characteristics of the nozzle material and the characteristics of the sand particles, the stress state after the impact is different, and the proportion of the three wear forms is different.

1. Factors affecting nozzle wear

1.1 Material factors of the nozzle itself

At present, the materials commonly used to manufacture jet nozzles are mainly tool steel, ceramics, cemented carbide, artificial gems, diamond and so on. The micro-structure, hardness, toughness and other physical and mechanical properties of the material have important effects on its wear resistance.

1.2 Internal flow channel structure shape and geometric parameters.

Through the simulation of different types of nozzles, the author found that in the hydraulic sandblasting jet system, the constant variable speed nozzle is better than the streamlined nozzle, the streamlined nozzle is better than the conical nozzle, and the conical nozzle is better than the conical nozzle. The outlet diameter of the nozzle is generally determined by the flow rate and pressure of the jet. When the flow rate is unchanged, if the outlet diameter is reduced, the pressure and flow rate will become larger, which will increase the impact kinetic energy of the sand particles and increase the wear of the outlet section. Increasing the diameter of the jet nozzle will also increase the mass wear, but at this time the internal surface loss is reduced, so the best nozzle diameter should be selected. The results are obtained by numerical simulation of nozzle flow field with different contraction angles.

To sum up, for conical nozzle, the smaller the contraction Angle, the more stable the flow, the less turbulent dissipation, and the less wear to the nozzle. The straight cylindrical section of the nozzle plays the role of rectification, and its length-diameter ratio refers to the ratio of the length of the cylinder section of the nozzle to the diameter of the outlet, which is an important parameter affecting wear. Increasing the length of the nozzle can reduce the wear rate of the outlet, because the path of the wear curve to the outlet is extended. The inlet angle of the nozzle has a direct effect on the wear of the inner flow passage. When the inlet contraction angle decreases, the outlet wear rate decreases linearly.

1.3 Inner surface roughness

The micro-convex surface of the inner wall of the nozzle produces great impact resistance to the sand-blasting jet. The impact of sand particles on the protruding part of the bulge causes the surface micro-crack expansion and accelerates the abrasive wear of the nozzle. Therefore, reducing the roughness of the inner wall helps to reduce friction.

1.4 Influence of sand blasting

Quartz sand and garnet are often used in hydraulic sandblasting fracturing. The erosion of the sand on the nozzle material is the main cause of wear, so the type, shape, particle size and hardness of the sand have a great influence on the wear of the nozzle.