Brakes – Elements – Shoes
Reexamination Certificate
2001-09-06
2003-12-30
Lavinder, Jack (Department: 3683)
Brakes
Elements
Shoes
C188S25100R, C188S25100R, C264S029100
Reexamination Certificate
active
06668985
ABSTRACT:
BACKGROUND OF THE INVENTION
The present invention relates to a safety device for elevators with at least one elevator guide rail, securely installed in the elevator shaft and a brake part, comprising at least one friction element with at least one friction surface that can be pressed against the guide rail to decelerate the elevator, with the friction material of the friction element comprising a fiber-reinforced, ceramic composite material containing silicon carbide and carbon fibers as reinforcing components, as well as a procedure for producing such a friction element.
A safety device of the described type or a brake shoe for an emergency stop device for elevators is shown in the U.S. Pat. No. 5,964,320.
Passenger elevators for apartment blocks, observation towers, etc. must contain an independent emergency brake or emergency brake means in addition to the operational brake. Such an emergency brake is designed as a safety stop, which in case of an emergency, i.e. when the elevator car exceeds a specified maximum speed, stops the car by pressing friction linings against the guide rails in the elevator shaft after a delay that is acceptable to passengers in the car and securely holds the car in the stopped, stationary position.
Modern buildings are built increasingly higher, to fully utilize the ground and space available, in particular, in cities. In order to be able to reach the individual floors in such high-rise buildings within a reasonable time, full use is made of maximum permissible speeds of up to 1500 meters per minute. This means that the kinetic energy to be absorbed in case of an emergency, during the deceleration of the car, also increases in line with increasing speeds so that the friction linings of the emergency brakes—functioning as linear brakes—are exposed to extreme loading. Conventional metal friction linings for emergency brake devices in elevators are not able to withstand such an extreme loading, during which temperatures of up to 1000° C. can be generated. Such conventional friction linings as described, for instance, in British published application GB 2 274 827, have a friction surface structure that contains a graphite phase, a steadite phase, a cementite phase and a perlite phase.
In order to meet increasing requirements, ceramic brake linings with silicon nitride as their main component, have been suggested for emergency elevator brakes in recent times.
The U.S. Pat. No. 5,503,257 shows an elevator safety device comprising ceramic brake parts, with the ceramic material consisting of aluminum oxide, silicon nitride or zirconic oxide.
Even such ceramic brake linings or respective brake shoes containing such linings, are pushed to their limit in order to provide a safe function, as during the sudden locking of the brake shoes on the metal guide rails, the inherent brittleness and sensitivity to impact of these ceramics can cause the linings to brake as a result of mechanical overstressing or thermal shock.
The described ceramic brake parts made of aluminum oxide, silicon nitride or zirconic oxide have a smaller dimension than the support plate and are engaged or glued in the retaining elements of the support plate. Due to the ceramic brake parts and the metallic support plate having different expansion behaviors, it must be anticipated that the brake parts will be distorted or loosened at high friction surface temperatures. This may potentially cause the failure of the entire brake device as a result of sheared off or broken off brake parts. Brake parts with larger surface dimensions (i.e. plate-shaped brake parts) can not be used due to their inadequate damage tolerance during the arising bending load.
The U.S. Pat. No. 5,964,320 suggests a brake body for emergency elevator brakes, comprising a braking surface and a multitude of brake parts that are embedded in and protruding over the brake area. These protruding brake parts are made from a composite material, containing a ceramic base material, consisting of the group silicon nitride or titanium boride, sialone and silicon carbide that does not comprise less than 10 weight percent of at least one ceramic material selected from the group that consists of silicon carbide whiskers and silicon carbide platelets. As these brake shoes or friction linings include minimum parts of SiC whiskers (acicular fibers up to a few &mgr;m “micrometers” in length) or SiC platelets (plate-shaped parts at micrometer scale), the ceramics are somewhat strengthened and a small improvement in fracture resistance is achieved. In addition, these brake parts can contain 10 to 55 volume percent of long SiC, Si3N4, C or tungsten fibers, which are, however, in this case arranged vertical to the lining surface. The fibers do, however, only provide a very low level of reinforcement. Whisker and platelet particles are respirable due to their small size and can, when given off as a result of wear and braking abrasion, also be inhaled by humans. Whiskers and platelets are consequently no longer used today due to their toxicity and their use is illegal in most countries.
SUMMARY OF THE INVENTION
Based on the prior art described above, the present invention has the task to further develop a safety device for elevators of the type described above in such a way that the requirements for emergency devices of elevators reaching the maximum permissible speed of up to 1500 meters per minute (equal to 25 m/s) and temperatures in excess of 1000° C. at the emergency brake device, when cars are stopped during emergencies, are fulfilled.
The task is solved by a safety device of the type described above, in which the friction element composite material contains a matrix of silicon carbide (SiC) and carbon (C) and the reinforcing component being formed preferably exclusively from carbon fibers with a minimum length of 10 mm and the volume content of carbon fibers in the friction element lying between 30% and 70%. Such a safety device is, in particular, characterized by 10 mm long or longer carbon fibers reinforcing the friction element; whisker or platelet reinforcing components are thus not required so that during emergency braking, no hazardous abraded dust is generated. The carbon fibers forming the reinforcement component are embedded in a matrix consisting of silicon carbide and carbon. The volume content of carbon fibers in the friction element between 30% and 70% guarantees an sufficiently high break and thermal shock resistance, with a lower volume content of carbon fibers being preferable, where extremely low rates of wear and a high thermal conductivity are to be achieved, whilst a high volume content of carbon fibers should be used, where particularly stringent requirements are made with regard to the mechanical stability of the composite material.
The amount of carbon fibers in the friction element is determined by the required mechanical stability and thermal shock resistance, improving with increasing fiber content. A minimum content of silicon carbide is required for generating adequate friction and wear resistance. Lower volume contents of carbon fibers are preferable in case of moderate driving speeds or where the friction linings can have a respective thickness. High fiber contents should be used, where extreme driving speeds are to be achieved or, where for space reasons, the friction linings must be extremely thin.
In a preferred embodiment, the carbon fibers are arranged as stacked layers of woven and/or knitted fabrics in the friction elements; in this case, the carbon fibers are at least arranged in the area of the friction surface in such a way that they run parallel to it. This fiber arrangement allows the bending moments, generated during the abrupt impact of the linings onto the guide rail during emergencies and when holding the car during standstill with extremely high surface pressures of up to 100/Mpa, to be absorbed. As a result of, in particular, this measure, also large-surface linings can be produced as a single piece, i.e. replacing the multitude of individual, smaller friction elements.
Due to the high fractur
Krenkel Walter
Renz Ralph
Inventio AG
Lavinder Jack
MacMillan Sobanski & Todd LLC
Sy Mariano
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