Discussion on the design of the hydraulic press wi

Discussion on the design of large bore hexahedral hydraulic press

φ 460 bore, 6 × The hexahedral hydraulic press with tonnage above 15mn has entered the mainstream of the market. At present, the hexahedral hydraulic press with various structures on the market is in normal operation. Over the years, the experience in use and manufacturing has imperceptibly changed the performance requirements of the hexahedral hydraulic press. Larger bearing capacity, lower component damage rate, more practical and accurate electrical and hydraulic control system are becoming the design standards of excellent hexahedral hydraulic press, which are required by diamond manufacturers and implemented by professional manufacturers

combined with the experience of the design and use of six sided hydraulic press over the years, the following design ideas are put forward for discussion with peers

1. About the design of the main engine

as the main bearing component, the hinge beam adopts the bottom structure design, which has become the consensus of the industry. At present, the mainstream six side hydraulic press with a total investment of $27.54 million adopts this structure. For many years, the high fracture rate of hinge beam lugs has been a headache for manufacturers, and also worried about users. In addition to the influence of design size, material and other factors, the cost of only charging parts related to casting and processing technology are also factors that cannot be ignored

the author believes that to effectively reduce the high fracture rate of the ear piece, we should pay attention to the following aspects in the design:

a, reasonably design the tensile strength limit value of the hinge beam ear piece, that is, the determination of the safety factor of the component. Due to the existence of many unmeasurable conditions such as casting parts, alternating stress, casting heat treatment conditions, it is very difficult to determine the safety factor accurately and reasonably. Taking ZG35CrMo as the material and quenching and tempering treatment as an example, from the design examples and application of several specifications of press, it can be concluded that it is safe that the tensile strength limit of ear section at full load is not higher than 16kgf/mm2

b. The currently known casting process of hinge beam is to reserve the casting pin hole and then boring. Due to the improper hole casting process, it is easy to cause the enrichment of casting defects at this position. The main reason for the fracture at this position is the internal defects that still exist after the finished product. If this casting process is changed, the defects of the original process will be eliminated by removing the reserved holes and directly casting the flat plate, and using the special mold to drill and mill the pin holes during rough machining

c, there is a reasonable size matching relationship between the thickness of the lug and the diameter of the pin hole of the hinge beam

Figure 1 is the shear bending moment diagram of the pin bar. According to this stress diagram, it can be seen that the pin bar is in a complex stress state, and the pin bar strain accompanying the stress will directly affect the stress of the ear piece in contact with it. Due to the difference in the thickness of the ear piece and the bearing capacity of the pin bar, the strain of the pin bar due to stress is different in each section, which makes the actual stress state of each ear piece of the hinge beam uneven, and the stress state of the middle ear piece of the three ears is particularly bad. By reasonably designing the thickness of each ear piece and the diameter of the pin hole, this uneven force can be reduced, especially between the three ears. The reasonable design of these sizes can weaken the actual uneven force of each ear piece and effectively reduce the fracture probability of the ear piece. Practice has also proved that there is an ideal matching relationship between the size of the pin hole and the thickness of the ear piece

Figure 1

d. The cracking of the working cylinder is another major loss of the six sided hydraulic press. Regardless of the structure of the working cylinder, from the design of the hinge beam alone, the reasonable design of the wall thickness of the hinge beam and the matching clearance with the working cylinder is an important factor for whether the working cylinder can be effectively protected, which is also the reason why some press manufacturers use the "gapless cylinder". The design and determination of these dimensions should be based on the relevant strength theory

another vulnerable key component of the host is the working cylinder. At present, the structure of working cylinder can be roughly divided into integrated type and combined type. Through the theoretical stress analysis and the observation of the actual damaged parts, the cracking stress is bending stress, which is consistent with the phenomenon that the cracking position is often at the arc transition between the cylinder wall and the cylinder bottom. The reasonably designed combined structure working cylinder can avoid the existence of bending stress, so as to eliminate the tendency of cracking. At the same time, the ultra-high pressure static seal adopts pre compressed metal hollow O-rings or radially concentric rubber O-rings and retaining rings. This self tightening static seal structure has the characteristics of automatically compensating the contact pressure of the seal ring with the change of oil pressure, making the seal reliable

2. About the hydraulic control system

as a large-scale equipment used in industrial production, the design of the hydraulic system of the hexahedral hydraulic press should be based on the principle of simplicity, practicality and accurate function trade-off, cooperate with the industrial PLC control system, and fully meet the requirements of the diamond synthesis process

at present, the mainstream hydraulic system principle comes from the design of ds-029 hexahedral hydraulic press. From the current use situation, this hydraulic system has the following disadvantages:

a. Due to the use of imported throttling method to adjust the synchronization of six cylinder pistons, it is easy to produce the phenomenon of synchronization instability, and in the stage of connecting overpressure, this synchronous control is in an invalid state, and the pistons of each working cylinder actually go their own way. This will affect the state distribution of pressure field in the large synthetic cavity

b. It is easy to produce pressure sudden change and hydraulic shock in the process of action program conversion, such as in the stage of liquid filling to overpressure and pressure relief to return. This will affect the adjustment result of piston positioning

c. There are many connection points in the pipeline of the ultra-high pressure system, and the tee and connecting valves are complex. The failure rate is high, and leakage is easy to occur, which greatly increases the maintenance workload of the press

in view of the above shortcomings, an improved hydraulic system design scheme is proposed, and the schematic diagram is shown in Figure 2:

Figure 2

the main improvement parts are:

A, using the outlet throttling method to control the forming shrinkage: 0.4-0.7% six cylinder piston synchronization, which fundamentally solves the problem of synchronous control failure in the overpressure action program, and the six piston back pressure advances, and the action is more stable

b. Adopt the principle of six cylinder full connection, and control the piston action of each cylinder through the solenoid valve of six cylinders. This design greatly reduces the high-pressure leakage points, and reduces the pressure abrupt change and hydraulic shock phenomenon in the action conversion

c. Adopt multi-stage overflow valve to control the pressure of return, pressure relief and safety stages, and simplify the oil circuit system

d. adopt multi-stage electromagnetic unloading circuit, taking into account the stability and efficiency of the pressure relief process

e, the pressure is controlled by the electromagnetic proportional valve, and the pressure is truly realized. The force curve is successfully used in the fields of electronics, national defense and military industry, aerospace, petroleum and petrochemical, textile manufacturing, machinery production and so on, so as to improve the pressure field in the synthetic cavity. This method is superior to the current popular frequency conversion pressure compensation and pressure maintaining method: not only the pressure maintaining process is controlled, but also the pressure increasing process is within the control range. (end)