The hydraulic tension pre-tightening uses the hydraulic pressure to stretch the bolt to a predetermined elongation through a special tensioner, so that the nut can be tightened without load, and the pre-tightening force of the bolt can be accurately ensured. The pre-tightening method of the above four bolts is actually analyzed from the stress condition of the bolts. There are only two kinds of them: one is to tighten the nut with a mechanical and hydraulic wrench, and the screw is inclined by the spiral sliding surface to make the bolt elongate; and the electric heating and hydraulic stretching The pre-tightening method is to use the thermal expansion force and the hydraulic pressure to extend the bolt, and then easily turn the nut. When the external factor is removed, the pre-tightening bolt is in an elastic deformation state. The difference between the two is that during the pre-tightening process, the thread is always subjected to tensile stress and torsional shear stress much higher than in the working state, while the latter is separated in the two stages of elongation and contraction. The threads are not subject to any additional stresses during operation. It can be seen that the method of using the torque wrench or the fixed torque wrench to control the pre-tightening force is simple and convenient, but the accuracy is poor. The pre-tightening torque is greatly affected by the friction force during the pre-tightening process, and is not suitable for large-scale Bolted joints. Therefore, in recent years, the method of measuring the elongation of the bolt is usually used to control the pre-tightening force of the bolt, and the elongation can be calculated according to the predetermined value of the pre-tightening force. For the large-diameter bolt, the heating or hydraulic stretching pre-tightening method is adopted. Perform so that the bolts reach the desired preload. Generally speaking, in the early bolt pre-tightening, the mechanical method was purely manpower and felt. With the step-by-step improvement of the pre-tightening force, the torque wrench, the labor-saving wrench, the hydraulic wrench and the electric heating method were gradually developed. , hydraulic stretching method. At present, the main principle of pre-tightening of bolts is that ordinary bolts are usually required to be mechanically tightened by mechanical force and mechanical force. Torque wrenches or labor-saving wrenches are required for bolts with torque requirements, and bolts with strict requirements for torque or bolt elongation are required. According to the specific situation, the electric heating method or the hydraulic stretching method is used for pre-tightening control. In the use process of Shenyang Pump Co., Ltd., the early use tends to be electric heating, and nowadays it tends to hydraulic stretching method. There are many pumps that do not have such conditions. For example, early single-shell boiler feed pumps and petrochemical hydro-pumps have larger bolt diameters and more compact space. Only general-purpose wrenches can be used. Today's high-pressure boiler feed pumps for generator sets The double-shell structural bolts are usually between the two, the number of bolts is between, the diameter of the pump cylinder is larger, the space is relatively large, the hydraulic stretching method is used to compare the precision of the domestically produced pump, and the foreign early adopts the electric heating method, and the foreign The hydraulic stretching method is often used for pre-tightening. Hydraulic stretching method for bolt pre-tightening, usually by high-pressure hydraulic manual piston pump with high-pressure oil meter and transition joint, three-way pass, as well as five-way, high-pressure oil hose, quick joint, bolt-specific hydraulic stretching Composition. When the bolt is pre-tensioned, it is generally pre-tensioned with two or four bolts symmetrically, and the two screws are symmetrically used at the same time. Micro vacuum pumps are a series of brushed and brushless DC motor-driven pumps, which can be customized according to specific performance requirements. The miniature vacuum Diaphragm pump has large flow and long life. Applicable to various medical, environmental protection, chemical, biological engineering and other instruments and equipment. Ultra-small size, supports a variety of motors. Maintenance-free and long service life. Mini vacuum pump,Vacuum pump,Vacuum diaphragm pump,Micro air pump Changzhou Yuanwang Fluid Technology Co., Ltd. , https://www.ywfluid.com
Briefly describe the bolts in the pump unit
The spring nut is an ideal force-uniform threaded nut, that is, a semi-circular or belt thread groove is cut in the nut and the screw, and a coil spring with a circular or rectangular cross section is used as a medium for axial load. Errors, whether due to pitch or other reasons, can transfer the load well to every turn of the force. The pre-tightening control and the selection of special tools have proved that the proper selection of large pre-tightening force is beneficial to the reliability of the threaded joint and the improvement of the fatigue strength of the joint; however, the excessive pre-tightening force will lead to the whole joint. The increased size of the structure also causes the coupling to be broken or broken due to excessive preload during assembly. Therefore, the control of the preload force becomes extremely important during assembly. There are several methods for pre-tightening the bolt/screw during assembly. The mechanical method uses a normal wrench to use manpower or casing. For more accurate pre-tightening force, a torque wrench can be used, but this kind of torque wrench is usually only used for nuts smaller than ", and this method is only used under the general conditions when the pre-tightening force is not precisely required. This method is a big step forward compared to the mechanical tightening method, but the scope of application is not large, it is suitable for smaller diameter bolts, and it is cumbersome for large bolts. The electric heating method is preloaded with electric heating. Method Before pre-tightening the bolt, usually the nut is directly heated by the flame, and then penetrated into the hole of the coupling member and tightened with a nut; or the hole is drilled in the center of the bolt, and the steam heating bolt is passed, but the two methods cannot obtain accurate pre-tightening. The electric heating method is better than the flame and steam heating method, and is also easy to control. There are two ways to use the electric heating method, one is similar to the electric induction coil heating and the flame heating, and needs to be assembled after heating; The other is to insert the resistance wire into the pre-machined hole of the bolt. The heating rod is made of silicon carbide as a protective sleeve, and the heating element with the resistance wire is built therein. Pieces, the power is relatively small, the heating time is also relatively long, usually heating the bolts, will also be heated by the coupling, thereby reducing the pre-tightening effect.