12.3 Mathematical Model of High-Speed Pneumatic–
Hydraulic Composite Hammer
Based on the working principle and structural characteristics of the pneumatic–
hydraulic composite hammer, the dynamic mathematical model of the rising and
falling stages of the hammer body is established, which can be used as the basis for
the research and development of the new type of hydraulic hammer. Pneumatic–
hydraulic composite hammering technology can realize the function of pile hitting
with acceleration of more than 1G. The strike energy is related to the weight of
hammer, acceleration, gas pressure in nitrogen chamber of hydraulic cylinder,
maximum height of hammer, and resistance of oil return pipeline.
12.3.1 Overview
At present, the hammer theory research based on hydraulic and pneumatic technology is rare. This section mainly analyzes the hydraulic and pneumatic composite
hammer theory, mathematical model and basic characteristics of hydraulic hammer
based on hydraulic and pneumatic technology.
Figure 12.12 shows the schematic diagram of the hydraulic system of the
hydraulic–pneumatic acceleration compound hammer. A complete working cycle
of hydraulic–pneumatic compound hammer consists of three stages: the rising
stage, the descending stage and the pressure-retaining stage of the hammer body.
During the rising stage of the hammer body, the electromagnetic reversing valve 6
closes, the electromagnetic reversing valve 4 disconnects, the hydraulic pump 8 and
the high-pressure accumulator 7 simultaneously output the hydraulic oil, which is
supplied to the lower chamber of the cylinder through the electromagnetic reversing
valve 6 to push the piston and drive the hammer body 1 to achieve accelerated
lifting. At this time, the gas in the nitrogen chamber 5 at the upper end of the
hydraulic cylinder 2 is continuously compressed to store energy. During the
descending stage of hammer body, when the hammer body rises to the set stroke
height, the electromagnetic reversing valve 6 is disconnected, the electromagnetic
reversing valve 4 is closed, and the hammer body begins to descend. In the process
of hammer falling, the hydraulic oil in the lower chamber of the hydraulic cylinder
is returned to the oil tank through the electromagnetic reversing valve 4 and the
pipeline. The high-pressure nitrogen in the nitrogen chamber releases the stored
energy and accelerates the drop of the hammer due to the weight of the hammer.
When the hammer and the pile contact, it impacts the pile body and completes the
impact between the hammer and the pile. In the pressure-retaining stage, after
hitting the pile head, the hammer body uses aerodynamic force and gravity to
continue to exert pressure on the pile. During the descending stage of the hammer,
the hydraulic pump 8 simultaneously supplies hydraulic oil to the high-pressure
accumulator 7. Due to the long return pipeline and certain pressure loss, the
288
12 Pneumatic–Hydraulic Pile Driving Hammer
Hydraulic Composite Hammer
Based on the working principle and structural characteristics of the pneumatic–
hydraulic composite hammer, the dynamic mathematical model of the rising and
falling stages of the hammer body is established, which can be used as the basis for
the research and development of the new type of hydraulic hammer. Pneumatic–
hydraulic composite hammering technology can realize the function of pile hitting
with acceleration of more than 1G. The strike energy is related to the weight of
hammer, acceleration, gas pressure in nitrogen chamber of hydraulic cylinder,
maximum height of hammer, and resistance of oil return pipeline.
12.3.1 Overview
At present, the hammer theory research based on hydraulic and pneumatic technology is rare. This section mainly analyzes the hydraulic and pneumatic composite
hammer theory, mathematical model and basic characteristics of hydraulic hammer
based on hydraulic and pneumatic technology.
Figure 12.12 shows the schematic diagram of the hydraulic system of the
hydraulic–pneumatic acceleration compound hammer. A complete working cycle
of hydraulic–pneumatic compound hammer consists of three stages: the rising
stage, the descending stage and the pressure-retaining stage of the hammer body.
During the rising stage of the hammer body, the electromagnetic reversing valve 6
closes, the electromagnetic reversing valve 4 disconnects, the hydraulic pump 8 and
the high-pressure accumulator 7 simultaneously output the hydraulic oil, which is
supplied to the lower chamber of the cylinder through the electromagnetic reversing
valve 6 to push the piston and drive the hammer body 1 to achieve accelerated
lifting. At this time, the gas in the nitrogen chamber 5 at the upper end of the
hydraulic cylinder 2 is continuously compressed to store energy. During the
descending stage of hammer body, when the hammer body rises to the set stroke
height, the electromagnetic reversing valve 6 is disconnected, the electromagnetic
reversing valve 4 is closed, and the hammer body begins to descend. In the process
of hammer falling, the hydraulic oil in the lower chamber of the hydraulic cylinder
is returned to the oil tank through the electromagnetic reversing valve 4 and the
pipeline. The high-pressure nitrogen in the nitrogen chamber releases the stored
energy and accelerates the drop of the hammer due to the weight of the hammer.
When the hammer and the pile contact, it impacts the pile body and completes the
impact between the hammer and the pile. In the pressure-retaining stage, after
hitting the pile head, the hammer body uses aerodynamic force and gravity to
continue to exert pressure on the pile. During the descending stage of the hammer,
the hydraulic pump 8 simultaneously supplies hydraulic oil to the high-pressure
accumulator 7. Due to the long return pipeline and certain pressure loss, the
288
12 Pneumatic–Hydraulic Pile Driving Hammer