With all the variety of the hydraulic hammer
models produced, only a few principal schemes of the hydraulic drive exist. The most prevalent is a scheme, which is applied by the majority of foreign manufacturers. The hydraulic hammer striker
is at the same time the operating cylinder
piston, and has two tail rods of different diameters d1 and d2 as a rule. The "Lower" rod d1, which strikes the instrument by its threshold, has larger diameter. The operating cylinder chamber, formed around the “lower” rod, is an idle stroke chamber, i.e. provides the striker movement outby the tool, or idle stroke. At startup of the hammer this chamber is constantly under the pressure of hydraulic fluid during the entire operation cycle. The cylinder chamber, formed around the “upper” rod (operating stroke chamber) has larger surface area than the idle stroke chamber, and alternately connected both to the drain line (acceleration upward), and to the pressure line (braking action before the “upper” top dead point and acceleration downwards). The alternate connection of the operating stroke chamber with the drain and pressure lines is conducted by the two-position slide hydraulic valve
with the striker in the cylinder positional feedback. The signals to the slide valve switching are set to the slide valve pilot chamber when the piston passes by the corresponding grooves in the cylinder. When loading the striker, its piston at a certain position opens the control channel, and the slide valve connects its pilot chamber with the pressure line, thus ensuring it’s switching to the operating stroke position. At the end of the operating stroke, just before the strike, the piston by its groove connects the slide valve control chamber with the drain line, providing the slide valve switching to the striker loading position. The hydraulic hammer slide hydraulic valve
constructively has the operating stringcourses of different diameters, so that the hydraulic fluid pressure constantly operates upon one of its thresholds, while the opposite one is under the pressure only during the striker braking action and operating stroke phases.
The above-described hydraulic hammer principal scheme is implemented in various models by the different design and layout decisions. For example, the hammer hydraulic valve may be embedded directly into the hammer shell or be attached to the latter as an individual module. The axis of the slide valve may be placed parallel or perpendicular to the hammer axis.
The slide hydraulic valve construction can be implemented in the form of a solid bar with grooves or can have a tubular structure. The slide valve pilot chambers can be formed by the difference between the diameters of its journal parts or in the form of individual plungers. The hammer operating cylinder can be embedded in the casing shell or constructively implemented in the form of the cylinder barrel, mounted in the casing shell. Guide sleeves, in which the piston rods are moved, can be performed separately from the cylinder or having one of them attached to the barrel or the hammer casing shell. Hydraulic accumulators can be set on the casing shell flank surface or in alignment with it.
Butt- to- butt design of the hydraulic valve or setting the operating cylinder in a barrel allows to simplify the hydraulic lines commutation internal system, to optimize their shape and sizes, to simplify the individual components manufacturing technology, and to increase the repairability of the product, but on the other hand requires applying of additional seal components. Monolithic hydraulic module without barrel with the embedded hydraulic valve allows reducing the total number of components and seals, but complicates the manufacturing technology and reduces the repairability of the hammer. Ultimately, the layout and design solution is determined by the technological capabilities and preferences of developers and manufacturers of the hydraulic hammers, as well as the possibility of patenting the individual design solutions.
As a variation of the described above principal scheme is the design solution, when the striker rods d1 and d2 are performed of the same diameter (for example, in some hydraulic hammers models of NPK Japanese company). In this case the hydraulic fluid, supplied by the pump, is accumulated at the striker braking action phase and during the entire operating stroke, while the hydraulic accumulator discharges at the phase of the striker acceleration "upwards". This engineering solution provides practically constant striking energy of the hammer provided that the hydraulic pump output varies over a wide range, but requires installation of the hydraulic accumulators with larger shunting volume. In such cases the line-operated hydraulic accumulators are installed exterior to the hammer at the excavator operating equipment.
The advantages of the above described principal scheme are rather simple manipulation of the striker movement and absence of hydraulic fluid drainage during the striker operating stroke, when its speed reaches the maximum values. The increased rate of the hydraulic fluid flow in the drain line during the striker movement "upwards" is compensated by applying of pipes with sufficiently large cross-section in a drain line, or by installing in a drain line of own low-pressure hydraulic accumulator.
Another one original principal scheme of the hydraulic hammer
drive is a scheme, which is applied into the home-produced hydraulic hammers
of the GPM-120
A special feature of this scheme is that the striker, while moving "upwards", is tightly attached to the other component, which is at the same time a gas accumulator piston, with the diameter D, which is larger than the striker rod diameter d. At the home position the chamber between the striker thresholds and the hydraulic accumulator piston is connected to the drain line. The difference between the diameters of the hydraulic accumulator and striker pistons creates the site, on which the pump line pressure operates, and that causes the striker movement "upwards" and the gas compression in the pneumatic accumulator. After moving the striker at the preset value h the chamber between the striker thresholds and the hydraulic accumulator piston is connected to the pressure line through the striker radial and axial grooves, and the two mating parts are connected to the pressure line, and then the two mating parts are disconnected. Now, the whole striker threshold is under the fluid pressure, the magnitude of which is determined by the gas pressure value in the accumulator. The striker slows down and starts to accelerate towards the tool. Just prior to strike the operating cylinder is connected to the drain line, the pressure in the hydraulic system drops, the piston of the accumulator under the action of the gas pressure connects to the striker again and the operation cycles are repeated. The advantages of this scheme are the ultimate simplicity of construction, minimum of moving components, absence of special hydraulic valve, high technological effectiveness and thus the low cost of the product. The disadvantages of the scheme are the significant pressure differentials in the various phases of the hammer operation cycle, inefficient use of the toolcarrier pump power, presence of the grooves for the hydraulic fluid passage in the striker, which are the stress concentrators.
There is another one principal scheme, which is applied only into the home-produced hydraulic hammers of the SP-62, D-550, D-600 and D-450 models.
In this scheme both the striker and the operating cylinder piston are implemented as the separate components, connected together by means of the resilient joint. The operating cylinder constitutes the cylinder of double action, i.e. its operating chambers are alternately connected to the pressure and drain lines, and the piston movement reversing is ensured by means of the two-position slide hydraulic valve with the piston position feedback. At the home position the hydraulic valve slide under the action of a spring placed under its threshold is set into the position, which provides the operating cylinder rod end connection (of the idle stroke chamber) to the pressure line, and the piston end to the drain line. At startup of the pump output flow, the piston accelerates "upwards", forcing fluid from the piston end into the drain line. After moving at a prescribed distance the piston blocks the drain holes in the cylinder barrel, the pressure above the piston increases, effects on the slide valve threshold and transfers the latter into the operating stroke position, i.e. connects the piston end with the pressure line, and the rod end with the drain line. The piston slows down and starts to accelerate towards the tool. Just prior to strike the piston opens the groove, which connects the piston end to the drain line through the holding valve 6. As a result, the pressure inside the piston end and above the slide valve threshold drops to a level, at which the spring switches the slide valve into the striker starting position. The striker strikes the instrument, and then the hammer operation cycle is repeated. The design feature of the hammers, constructed under this principal scheme, is utilizing a line-operated accumulator in the construction of the hydraulic hammer, which uses gas as a resilient element instead of the hydraulic system fluid. This accumulator represents a pressure multiplier, the piston end of which is constantly connected to the pressure line, with the rod end connected to the drain line. The accumulator piston rod enters into the insular cavity 4, formed in the hydraulic unit casing shell, and filled with the hydraulic fluid, which is the hydraulic system oil. When the hammer is operating, the pressure arises in this insular cavity, and its magnitude is so many times higher than in the hammer pressure line, as the accumulator piston area larger than the area of its rod. The magnitude of this pressure reaches 50 ... 80 MPa. Under such pressures an enclosed volume of mineral oil is compressed by 4.5 ... 5%, and in the process of setting the striker into the home position during its braking action before the “upper” top dead point, the accumulator piston end accumulates the volume of fluid under operating pressure, which is necessary and sufficient to implement the striker operating stroke. To replenish the amount of "the liquid spring" due to possible leakages there is a holding valve in the accumulator piston. Such accumulator does not require any recharges during the hammer operational use. The described above principal scheme of the hammer is most efficient for the medium and heavy models of hydraulic hammers
, since it allows using the heavy load strikers with the small size of the operating cylinder. The small size of the operating piston reduces the volumes of the internal oil flow-over, and the small diameter of the rod seal components reduces its price. The larger striker mass at the equal striking energy, in comparison with the hydraulic hammers
, designed by others principal schemes, allows to reach the larger impact impulse magnitude, which is numerically equal to mv, and the high efficiency coefficient of the strike; thereby this increases productivity, in particular at the destruction of adhesive materials, such as frozen grounds.
Article writer: Candidate of Science (Engineering).
Dmitrevich Yurii Vladimirovich
Company Limited "Traditciya-K"