HK1020036B - Molybdenum alloy elevator safety brakes - Google Patents

Description

Molybdenum alloy elevator safety brake

The present invention relates generally to a safety brake system for slowing or stopping a vertically traveling object, such as an elevator car, in an overspeed condition. More specifically, the present invention relates to a safety brake system for slowing or stopping an elevator car having a molybdenum alloy friction surface.

A typical safety brake system mounted on an elevator car includes a pair of wedge-shaped brake shoes having generally flat friction surfaces. The flat friction surfaces are typically provided at opposite sides of the guide post portion of a T-shaped guide rail that is supported on the elevator hoistway wall. The two wedge-shaped brake shoes are driven by a governor mechanism which causes the wedge-shaped brake shoes to move along an adjacent guide shoe which in turn causes the friction surfaces of the two brake shoes and the guide rail to contact each other to slow or stop the car.

In a typical safety braking system, the wedges can carry up to about 56,000 pounds (250,000 newtons) of normal force, which is through a force of 7 inches²8000 pounds/inch applied to the surface²Obtained under pressure of (0.0045 m)²55,000 kpa pressure) over the area of (a). Using a cast iron friction gauge having a nominal coefficient of friction of about 0.15 when moving relative to the rail at a speed of about 6 m/sFace, a force of 56,000 pounds (250,000 newtons) acting on a wedge-shaped structure produces a friction force of about 11,200 pounds (50,000 newtons) on the friction surface of the wedge-shaped structure. In a conventional elevator car design using cast iron friction surfaces, there are four friction surfaces that produce a total potential braking force of about 45,000 pounds (200,000 newtons).

When constructing a very tall building, it becomes necessary to service high speed, heavy duty elevators (typically 4 to 8 m/s, and here 12.5 m/s) between the various floors of the building. Such elevators have a load capacity of up to about 16,000 kg. The safety braking requirements of such elevators are also increased. It has been determined that in such modern elevator cars requiring high speed and heavy loads, ordinary gray cast iron cannot be used as a stable friction material because of its excessive wear causing brake failure and its high frictional heat causing a reduction in the coefficient of friction. Therefore, there is a need to manufacture the safety brake shoe of an elevator using another friction material having low wear and stable high friction to meet the needs of a high-speed, heavy-duty elevator installed in a high-rise building.

It is an object of the invention to provide an elevator safety brake for stopping an elevator car.

Another object of the invention is to provide a reliable elevator safety brake with a stable high coefficient of friction and low wear for use in high-speed, heavy-duty elevators.

The above objects are achieved with an elevator brake system having a brake shoe formed from a base and a friction surface fixed to the base for contacting a surface of an elevator guide rail. At least a portion of the friction surface is formed of an alloy material including about 99.4% by weight molybdenum, 0.5% by weight titanium, and 0.1% by weight zirconium. The safety brake is provided with an actuator which presses the friction material of the brake shoe against the guide rail surface to stop the elevator car.

The accompanying drawings, which are not drawn to scale, include:

fig. 1 is a simplified schematic diagram of an elevator safety braking system having two wedge-shaped friction structures located on opposite sides of a guide rail;

fig. 2 is a simple schematic view of an elevator safety brake having a molybdenum alloy friction plate on the rail-facing surface of the brake shoe base;

fig. 3 is a simplified schematic illustration of the elevator safety brake of the embodiment of fig. 2 additionally including a transverse opening formed therein;

FIG. 4 is a simplified schematic illustration of another embodiment of the present invention showing a set of molybdenum alloy friction plates secured to the rail facing surface of the brake shoe base;

FIG. 5 is a simplified cross-sectional view taken along line 5-5 of FIG. 4, illustrating the connection of the friction plates by a flexible material;

FIG. 6 is a simplified schematic illustration of a molybdenum alloy friction material secured to a brake shoe base in a set of strips;

FIG. 7 is a simplified partial cross-sectional view of a molybdenum alloy friction material secured to a brake shoe base by a set of plate-retained fasteners;

fig. 8 is a simplified perspective view of a fastener.

Fig. 1 is a simplified schematic diagram of a known elevator safety brake system to which the present invention may be applied. The braking system 10 includes a pair of actuators 12 attached to a car 14 on opposite sides of a guide rail 16 supported in an elevator hoistway (not shown). The actuator 12 is formed in part by a wedge-shaped guide shoe 18 which is movably located in a bracket 20 in a direction substantially perpendicular to the guide rail 16. The guide shoe 18 is pressed against the guide rail 16 by a spring 22. The guide shoe 18 has an inclined support surface 24. The wedge brake shoe 25 with the base 26 is provided with an inclined wedge surface28 which is complementary to the inclined support surface 24 of the guide shoe 18. The brake shoe 25 is further provided with a surface 30 facing the track. The brake shoe 25 is located between the guide shoe 18 and the guide rail 16. A brake pad 32 with a high friction material is secured to the rail facing surface 30 of the brake shoe base 26. A roller assembly comprising a set of rollers 34 is located between the inclined support surface 24 of the guide shoe 18 and the complementary inclined sprag surface 28 of the brake shoe 25. The rollers 34 provide a low friction contact between the adjacent complementary inclined surfaces 24 and 28 of the guide shoe 18 and brake shoe 25, respectively. The guide shoe 18 is acted upon by a spring 22 with a force F directed towards the guide rail 16_NAnd is pressed against the brake shoe 25 by the roller 34.

In an emergency situation requiring operation of braking system 10, force F directed toward elevator car 14_AActing on the base 26 of the wedge-shaped brake shoe 25, this causes the shoe 25 to move towards the elevator car 14. In general, force F_AApplied by a rope, cable or mechanical linkage connected to a governor (not shown). The complementary inclined surfaces 24 and 28 of the guide shoe 18 and brake shoe base 26, respectively, cause the brake shoe 25 to move toward the guide rail 16 until the brake shoe 32 contacts the guide rail 16. As is known to those skilled in the art, the normal force F exerted by the leaf 32 by the spring 22_NActing on the guide rail 16. By normal force F_NThe magnitude of the braking force generated is substantially directly related to the coefficient of friction mu between the high friction material used for the brake pads 32 and the rail material 16_kIs in direct proportion. When braking occurs, heat can build up on brake pads 32, which can detrimentally alter the coefficient of friction μ between the brake pad material and the rail material_k. If the heat becomes high enough for a given material, the hardness is substantially reduced and the high friction material is also deformed or melted, which in turn can cause the brake to fail.

In the prior art, the brake pad 32 used in the brake system 10 has a friction surface formed of gray cast iron. However, gray cast iron is suitable for low-speed, light-load conditions, and does not work as a stable friction material at high-speed, heavy-load conditions. In view of the deficiencies of gray cast iron in this application, it has been found that gray cast iron, which is used as the high friction material for the brake pad 32, can be replaced by a molybdenum alloy. The brake pad according to the invention with molybdenum alloy, which will be described in more detail below, can be operated as required when the elevator is operated at speeds up to 10 m/s and a load of 16000 kg. Brake pads made in accordance with the present invention have also been found to have significant mechanical toughness, thermal shock resistance, negligible wear rate relative to rail steel, and a sufficient coefficient of friction relative to rail steel.

A30 mm diameter plate made of No.364 titanium-zirconium-molybdenum (TZM) molybdenum alloy comprising about 99.4% by weight molybdenum, 0.5% by weight titanium, 0.1% by weight zirconium was secured to a steel substrate to form a 30mm test piece in accordance with American Society for Testing and Materials (ASTM) Standard B387-90, with a chamfer provided on the edge of the molybdenum alloy material. The test piece was applied with a normal force of 11,000 newtons against a rotating 2 meter diameter disc, which is used to mimic the emergency braking on the surface of a typical steel hoistway guide rail under heavy load, high speed conditions. A friction of approximately 6,000 newtons is generated, which indicates that the material has a nominal coefficient of friction with the rail steel of approximately 0.4, which is 1.5 times that of a typical 30-grade grey cast iron. The TZM molybdenum alloy pieces showed very little wear, about 1% of that exhibited by conventional 30-grade gray cast iron. The rail damage caused by this molybdenum alloy was the same as that caused by 30-grade grey cast iron. The material was simulated in all rail cases (clean rail, rusted rail, oiled rail, wet rail and rough rail).

As shown in fig. 2, the friction surface of this brake may be in the form of a plate 32 secured to the base 26. As shown in fig. 3, the friction surface may be formed in a shape that is processed into a checkered pattern. Referring to fig. 4 and 5, the friction surface may also be formed of a set of plates 38 of TZM alloy. The tabs 38 may be secured directly to the base 26 by mechanical fasteners (not shown) or by other means, and the tabs 38 may also be secured to the base 26 by a flexible material spacer (compliant material interface)40, the flexible material spacer 40 being resilient to movement of the alloy friction material relative to the base 26 and allowing a large number of tabs to contact the rail surface without the rail-facing surface of the brake shoe base 26 being in full contact with the rail. The flexible material used in the present invention includes a heat-resistant rubber-like material such as heat-resistant silicon. The individual panels 32, one or more sheets 38 may have a cross-hatch pattern (not shown) machined therein.

Referring to fig. 6, the friction surface may also be formed from a set of long sheets (pins)42 of alloy material that are positioned substantially transverse to the direction of relative movement between the friction surface and the rail surface. In most cases, these long pieces are positioned horizontally in the elevator system, but this is not essential. The long flap 42 may also be secured to the base 26 by flexible material spacers in the manner shown for flap 38. The flexible material spacer may flex back the movement of the tab 42 relative to the base 26.

Referring to fig. 7 and 8, in yet another embodiment, the friction surface may be formed by a set of fasteners 46 made of an alloy material, the fasteners 46 having a head 48 and a stem 50. Each head 48 of the set of fasteners 46 is coupled to the base 26 by a fastening plate 52, the fastening plate 52 having a set of openings 54 through which the stems 50 pass.

It will be understood from the above description that several embodiments of the safety brake system for stopping an elevator according to the invention have been described. The molybdenum alloy used therein provides a high coefficient of friction, which has the advantage that low normal forces and small, light springs and safety devices can be used. It should be understood that the embodiments described herein are merely illustrative of the spirit of the invention. Many modifications may be made by one of ordinary skill in the art without departing from the spirit and scope of the invention. Accordingly, the invention is to be defined by the appended claims and their reasonable interpretation.

Claims (11)

1. An elevator safety brake for stopping an elevator car, comprising:

a brake shoe having a base and a friction surface secured to the base for contacting a surface of an elevator guide rail, wherein: at least a portion of the friction surface is formed of an alloy material comprising 99.4% by weight of molybdenum, 0.5% by weight of titanium, 0.1% by weight of zirconium; and:

means for pressing the friction material of the brake shoe against the guide rail surface to stop the elevator car.

2. The elevator safety brake of claim 1, characterized in that: the friction surface is a plate fixed to the base.

3. The elevator safety brake of claim 2, characterized in that: the strip has a cross-hatch pattern machined therein.

4. The elevator safety brake of claim 1, characterized in that: the friction surface comprises a set of plates made of an alloy material.

5. The elevator safety brake of claim 4, characterized in that: at least one of the sheets has a cross-hatch pattern machined therein.

6. The elevator safety brake of claim 4, characterized in that: at least one of the flaps is secured to the base by a flexible material that can spring back upon movement of the flap relative to the base.

7. The elevator safety brake of claim 6, characterized in that: the flexible material is a heat resistant rubber material.

8. The elevator safety brake of claim 1, characterized in that: the friction surface comprises a set of elongated pieces of an alloy material, which are placed transversely to the direction of relative movement between the friction surface and the guide surface.

9. The elevator safety brake of claim 8, characterized in that: at least one of the elongate pieces is secured to the base by a flexible material that can spring back upon movement of the elongate piece relative to the base.

10. The elevator safety brake of claim 9, wherein: the flexible material is a heat resistant rubber material.

11. The elevator safety brake of claim 1, characterized in that: the friction surface comprises a set of fasteners formed of an alloy material, the fasteners having a head and a stem, the heads of the set of fasteners being secured to the base by a securing plate having a set of openings through which the stems extend.