Measuring and testing – Testing impact delivering device – Pile driving hammer
Reexamination Certificate
1999-01-22
2001-01-09
Noori, Max (Department: 2855)
Measuring and testing
Testing impact delivering device
Pile driving hammer
Reexamination Certificate
active
06170317
ABSTRACT:
The invention relates to an arrangement for detecting a need for maintaining a hydraulic breaking apparatus, the hydraulic breaking apparatus comprising means for supplying hydraulic pressure into and removing it from the breaking apparatus, a percussion piston that reciprocates due to the action of the hydraulic pressure, and a tool whose upper end is subjected to an impact delivered by the percussion piston during the breaking, and measuring means for measuring at least one parameter describing the loading of the breaking apparatus.
Hydraulic breaking apparatuses, which in the present application refer to hydraulically driven percussion hammers, are used to break relatively hard materials, such as stones, concrete, asphalt etc. Such percussion hammers comprise a percussion piston, which performs a reciprocating movement due to the action of the hydraulic fluid and which is arranged to deliver an impact at the upper end of a tool placed against the surface to be broken. When the percussion piston hits the upper end of the tool at a high speed, it causes a great force effect at the tool, whereafter the surface against which the tool is placed will break or the tool will penetrate into the material to be broken. If the surface to be broken is especially hard, the tool bounces back from the surface due to the impact.
Hydraulic breaking apparatuses, such as percussion hammers and the like, require maintenance as any other technical devices. The purpose of maintenance is to ensure that the percussion hammer operates effectively during the entire expected lifetime of the hammer. If maintenance operations are not carried out regularly, the apparatus will be subject to repeated failures and premature wearing and, eventually, it will be discarded earlier than usual. Recurrent failures cause not only considerable repair costs but also breaks in the normal productive use, which in turn increases the expenses substantially. Also, the apparatus might become substantially less safe if the required maintenance operations are not carried out or if they are timed incorrectly. Maintenance is even more important when considering the harsh conditions in which percussion hammers are typically used.
Maintenance operations are usually carried out at predetermined intervals according to an advance plan drawn up by the manufacturer. The plan usually requires that maintenance operations are carried out based on operating hour limits determined empirically or through calculation, or based on the time that has passed since the previous maintenance operation. It is common to determine a maximum maintenance interval based on calendar time, since for example lubricants become ineffective in time even if the apparatus is not used at all. On the other hand, the presently used maintenance interval that is based on operating hours is always more or less an average value, since there are differences between individual apparatuses as regards their facilities, for example, and more importantly, the conditions, manner and frequency of use of the apparatuses also vary considerably. The latter facts are taken into account to some extent by devising different maintenance programmes; there are different programmes for example for excavation operations and for demolishing buildings. Also, the frequency of failures may vary greatly depending on the operator of the apparatus.
The manufacturers usually determine the maintenance intervals of a percussion hammer according to the operating hours of the basic machine, such as an excavator or some other corresponding carrier. However, this is a rather uncertain method since the use of the basic machine is not comparable as such to the operating hours of the percussion hammer, but the ratio between the operating hours of the basic machine and the percussion hammer may vary greatly, even from 10 to 90%, depending on the breaking operation to be carried out. Further, determining the maintenance interval in this manner has the disadvantage that it is not possible to take into account the actual strain caused by impacts of different magnitude on the percussion hammer. When the object to be broken breaks under the tool of the breaking apparatus or when the tool is able to penetrate into the material to be broken, a return pulse that is reflected from the object to be broken is considerably weaker than when the object is hard and makes the tool bounce back due to the recoil. When the tool hits a hard spot, the strain imposed on the breaking apparatus is considerably greater since the tool is subjected to greater resistance. Such great strains are rather harmful to the durability of the apparatus in the long run and they increase substantially the need for maintenance of the percussion hammer. Unfortunately, with the present methods it is not possible to take into account this fact in any way. Further, it is not presently possible to detect incipient serious damages in the structure of the percussion hammer before it is too late, whereupon the percussion hammer may already be damaged so badly that it cannot be repaired before the damage is detected in the next maintenance operation carried out according to the operating hours of the basic machine.
The purpose of the present invention is to provide a better arrangement for detecting a need for maintaining a percussion hammer than previously, taking into account the loading caused by the actual use of the percussion hammer and the subsequent need for maintenance.
The arrangement according to the invention is characterized in that it comprises an independently operating indicator which is placed in connection with the breaking apparatus, which indicator is specific for each apparatus, and which is arranged to indicate visually, for example by means of LED lamps, that the parameter measured with the measuring means provided in connection with the indicator has exceeded the limit value determined in advance for maintenance.
The basic idea of the invention is that the loading of the breaking apparatus is measured continuously with at least one sensor. The sensor is arranged to measure at least one preselected parameter, which describes the loading imposed on the structure of the percussion hammer by the impacts delivered by the percussion piston. The object is not to actually measure the loading or condition of an individual component, but to measure the loading imposed on the entire breaking apparatus. The essential idea of a preferred embodiment of the invention is to measure the number of actual impacts delivered by the percussion hammer and to indicate a need for maintenance of the apparatus when a predetermined number of impacts have been delivered. Further, the basic idea of another embodiment of the invention is to measure the magnitude of a desired parameter and to set for the measuring value a predetermined limit which is exceeded when an impact that is significant for the loading of the breaking apparatus and for the need for maintenance has been delivered. By means of the invention, such impacts exceeding a certain loading limit are registered, and when an empirically determined or calculated loading level or accumulated load is reached, the apparatus is considered to require maintenance. Such impacts with a great loading effect are considerably more significant for the wearing and breakage of the breaking apparatus than normal blows. Further, the basic idea of a third preferred embodiment of the invention is that the loading data measured with measuring sensors is analyzed more accurately in order that permanent changes occurring in the percussion hammer can be detected. Such permanent changes in the measurement results indicate that the components of the breaking apparatus are worn or that one or several of the components are being damaged or have already become damaged. With such monitoring it is possible to carry out maintenance operations in the form of proactive maintenance, and the occurrence of total damage in the breaking apparatus is also prevented.
The invention has the advantage that maintenance operations are carrie
Juuri Kauko
Ojala Eero
Oksman Mika
Noori Max
Smith-Hill and Bedell
Tamrock Oy
LandOfFree
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