Structural development process of ultra-high pressure sleeve forgings

2019-03-12 11:41:31 7

The ultra-high pressure sleeve forgings are mainly cylindrical containers, and the stress distribution is characterized by: the axial stress is the largest among the three principal stresses; the circumferential stress is distributed with the inner wall stress being the largest, and the wall thickness distribution is uneven, and the K value is larger. The more uneven the degree of unevenness (K is the ratio of the outer diameter to the inner diameter of the cylinder); when the pressure is applied, the inner wall will inevitably yield. According to the above stress characteristics, the ultra-high pressure sleeve forgings should not be designed to reduce the stress level under operating conditions simply by increasing the thickness and increasing the material strength, but should change the stress distribution from the structure. Ultra-high pressure sleeve forgings are generally designed with pre-stressed cylinders, liquid-supported cylinders (liquid-filled or direct external pressure), split cylinders, integrated cylinders, frame-wound wire structures, etc. The structural cylinders are used in industry.

The prestressed sleeve forging structure is to first generate a certain prestress to the cylinder during the manufacturing process, and partially offset the working stress by using a prestress which is opposite to the working stress direction. The specific structural types include multi-layer shrink sleeves, wire winding, tape winding, ferrules and self-reinforcing cylinders. Among them, the multi-layer hot-sleeve type is the earliest adopted structure, and the self-reinforcing cylinder body is used for making high-pressure polyethylene pipe type. The reactor can withstand a pressure of 320 MPa. However, the prestressed cylinder has a common disadvantage, that is, when the wall temperature exceeds 500 ° C or the service period is long, stress relaxation occurs, so that the prestress is greatly reduced or lost, and there is a large safety hazard in production.

The liquid-supported sleeve structure utilizes the pressure of the jacket liquid in the structure to apply an external pressure to the inner cylinder to replace the pre-stress of the inner cylinder, and the jacket pressure can be adjusted and controlled. In addition, by directly applying external pressure to the inner cylinder, the shear stress of the inner cylinder wall perpendicular to the radial plane can be minimized, the average circumferential stress becomes compressive stress, the fatigue strength is improved, and crack propagation is suppressed. Therefore, this type of ultra-high pressure container can be used for operating conditions exceeding 1000 MPa and above. However, the liquid-supported structure has the disadvantage that the structure is relatively complicated, and a set of controllable hydraulic system needs to be provided, and the pressure inside the jacket must be adjusted properly, otherwise the sleeve forgings may be unstable.

The split barrel structure is characterized by the maximum stress distribution of the circumferential stress on the inner wall surface of the cylinder. The cylinder is divided into 2-3 layers, and the sleeve with the largest stress is fan-shaped and the medium is only Inner surface contact (small gasket between the segments to prevent leakage of the contact surface), because the cross-section is discontinuous in the circumferential direction, no circumferential stress is generated on the split block, so that the maximum circumferential stress of the inner wall is eliminated. . The circumferential stress of the outer cylinder is only generated by the radial pressure of the fan block. As the radius of the force point increases, the circumferential stress value will be greatly reduced. The disadvantage of this structure is that the processing of the segment is high, and it is necessary to use a material with particularly strong compressive properties. If the gasket on the contact surface between the segments is leaked, the outer cylinder will be subjected to considerable circumferential stress.

The integrated cylinder structure combines a fan-shaped split sleeve, a liquid-filled jacket and a pre-stressed sleeve outer cylinder, which combines the advantages of the above three types, but the structure and manufacture are complicated. The structure can be used in operating conditions of 24000 MPa and 1500 °C.

The frame type winding structure is composed of two parts: a working cylinder and a frame. The winding body and the flat head are subjected to medium pressure. The frame is composed of two vertical columns and two semi-round beams, which are used to press the flat head and bear the shaft. Xiangli. The structure has the advantages of high strength, fatigue resistance, compact structure, simple manufacture, and the like, and can be used for hydrostatic extrusion of metal pressure forming, and the operating pressure and temperature can reach 1200 MPa and 1500 °C.

The development process of China's ultra-high pressure container sleeve forgings is similar to that of foreign countries. For equipment with working pressure of 100-300 MPa, most of the equipment is super-high-strength steel for single-layer forging or double-layer hot sleeve (recent multi-purpose hot sleeve); 300-800 MPa equipment, double or triple-layer hot jacket (low pressure) The continuous wire structure can be used; the equipment of 800-1000 MPa adopts three-layer hot sleeve plus self-reinforcing cylinder structure; the equipment of >1000 MPa adopts inner-layer splitting fan-shaped block structure.