Abstract: The present invention relates to a process for preparing a metal-chelate retarder by a sol-gel method. The method comprises the following steps: weighing calcium nitrate tetrahydrate, aluminum nitrate nonahydrate and ferric nitrate nonahydrate according to a certain mass ratio and adding them into deionized water; placing the mixed solution on a magnetic stirrer and stirring the mixed solution evenly; adding citric acid monohydrate or gluconic acid, ethylene glycol or glycerol, and placing the mixed solution into a water bath to react to obtain the metal-chelate retarder. The process of the present invention has a reliable principle, overcomes the defects of long production period, complex preparation and the like of the existing retarders, has the advantages of simple process operation, cheap and easily available raw materials, and short production period.

Abstract: A multi-level sliding sleeve including an outer cylinder, an inner sliding sleeve, a combined ball socket, a guider, an expander, an upper gland, a lower gland, and a ball. The outer cylinder includes internal threads in an upper end and external threads in a lower end, and the outer cylinder including an external wall including a plurality of drainage holes along the peripheral direction. The inner sliding sleeve is mounted to an inner wall of the outer cylinder through shear pins. The inner sliding sleeve includes a plurality of square holes in the middle along the peripheral direction, each of which is equipped with a ball socket inside. The ball sockets combine together to form a combined ball socket. The combined ball socket is equipped with the guider in the upper end and the expander in the lower end.

Abstract: A multi-level sliding sleeve including an outer cylinder, an inner sliding sleeve, a combined ball socket, a guider, an expander, an upper gland, a lower gland, and a ball. The outer cylinder includes internal threads in an upper end and external threads in a lower end, and the outer cylinder including an external wall including a plurality of drainage holes along the peripheral direction. The inner sliding sleeve is mounted to an inner wall of the outer cylinder through shear pins. The inner sliding sleeve includes a plurality of square holes in the middle along the peripheral direction, each of which is equipped with a ball socket inside. The ball sockets combine together to form a combined ball socket. The combined ball socket is equipped with the guider in the upper end and the expander in the lower end.