The application of pressure compensated variable pumps in HPHT Hydraulic Cubic Press machines primarily lies in their ability to meet the higher demands for pressure control and compensation in modern diamond synthesis processes, significantly enhancing production efficiency and product quality.
Here is a detailed explanation of its application in HPHT Hydraulic Cubic Press machines:
Replacing Traditional Pump Types and Adapting to Diversified Processes
The HPHT Hydraulic Cubic Press machine has a history of over 40 years of development and application in China. For a long time, the hydraulic system of six-sided top hydraulic presses has consistently used SCY series axial piston pumps as the power source.
However, SCY series axial piston pumps primarily provide a constant flow, resulting in a constant system pressurization speed. This step-wise curve is inconsistent with improved diamond synthesis processes.
In recent years, with the improvement of synthesis technology and the diversification of HPHT Hydraulic Cubic Press machine applications, such as the synthesis of fine diamond particles, diamond composite sheets (PCD), cBN, etc., there is a need for a pressurization method that matches their growth curve.
Pressure compensated variable pumps precisely meet this demand, becoming an effective way to replace SCY series axial piston pumps.
Working Principle and Matching with Synthesis Process
The unique aspect of the pressure compensated variable pump is that its output flow decreases as the working pressure increases, which is precisely what modern diamond synthesis processes require.
The main body of the oil pump (refer to Figure 1 in source) is driven by a transmission shaft, causing the cylinder block to rotate. The plungers are pressed against the variable head (or swash plate) by a central spring. This causes the plungers to reciprocate as the cylinder block rotates, completing the oil suction and oil pressure actions.
When the spring force is greater than the hydraulic thrust acting on the annular area at the lower end of the servo piston, the oil pushes the variable piston downwards, increasing the pump's flow. Conversely, when the oil pressure is greater than the spring force, the servo piston moves upwards, blocking the channel, causing the oil in the chamber to be unloaded. At this point, the variable piston moves up, the swash plate angle decreases, and thus the pump's flow decreases.
This design ensures that the pump's outlet flow changes approximately according to a constant power curve within a certain range.
Actual Application Effects and Advantages
Provides a curve that matches new diamond synthesis processes: The pressure compensated variable pump can achieve a pressure curve that matches new diamond synthesis processes, ensuring that the synthesis process meets requirements.
Improves work efficiency:
During the piston's idle forward stroke and rapid return stroke, the pressure compensated variable pump operates in a no-load large flow output state, which accelerates the piston's speed during these two work steps.
This overcomes the defect of constant oil supply by the original SCY series axial piston pump, reducing the piston's unnecessary travel time.
According to calculations, in the same working time, using a pressure compensated variable pump results in two more pieces of diamond synthesized per shift on average compared to using an SCY series axial piston pump.
Improves product quality: The quality of synthesized diamond is generally improved by 5% compared to when using SCY series axial piston pumps.
Application Example (Φ500mm Press Machine)
For example, when synthesizing Φ34.5mm cavity diamonds on a Φ500mm press machine, the pressurization ratio of the press's intensifier is 1∶7.7.
The diamond synthesis parameters are set as: temperature delivery pressure 45MPa, first stop pressure 60MPa, and final pressure 75MPa. It is also required that the overpressure speed begins to slow down after the first stop pressure.
Pump adjustment method:
First, adjust the limit screw to the maximum position, then adjust the spring sleeve.
When the system pressure is observed to be 7.8MPa, lock the spring sleeve.
Then, screw the limit screw to the position where the final pressure is 75MPa and the system pressure is 12MPa.
Through such adjustments, the pressurization speed during synthesis will operate according to the desired process curve (Figure 2 in source).
Preparation and Precautions Before Use
Noise issue: Besides misalignment of the coupling and motor, attention must be paid to the matching of the oil outlet pipe and connector body inner diameter with the oil pump flow. When the motor is unloaded, the oil output of the pressure compensated variable pump is at full flow. Therefore, the inner diameter of the oil outlet pipe and connector body must have sufficient space to accommodate the full flow of oil. Otherwise, an excessively small inner diameter will create fluid resistance, leading to severe vibration of the oil pipe and pump noise.
Pump body overheating issue: If an excessively small connector body or oil outlet pipe inner diameter causes a large amount of lubricating oil from the pump's swash plate to be trapped in the oil chamber instead of being discharged from the drain port, it will lead to pump body overheating. Serious consequences include increased oil temperature, affecting the sealing effect of the main machine.
Solution: Effective oil drainage is necessary. The screw plug at the bottom of the pump body can also be turned into an oil drainage channel through the connector body, thereby completely solving the pump overheating problem through multi-channel oil drainage.
In summary, the pressure compensated variable pump, through its unique flow-pressure matching characteristics and efficient operating mode, greatly enhances the performance of HPHT Hydraulic Cubic Press machines in the synthesis of artificial diamonds and other superhard materials, holding significant value for promotion and application.