AU3739693A - Safety gear for lift cars - Google Patents

Description

SAFETY GEAR FOR LIFT CARS This invention relates to safety gear for lift cars.

Lift cars for conveying people and goods from one level to another level in a multi-storey building are provided with safety gear to stop the lift car in the event of a failure which may be as severe as a broken cable in which the lift car will drop under the influence of gravity, or overspeeding of the lift machine which will cause the lift to rise or descend more quickly than is desired. The safety gear conventionally comprises a mechanism which senses the fault condition and which causes a gib or, as it is sometimes called, a wedge to move into contact with a lift guide rail to provide, by friction, a braking force to retard and stop lift movement.

Conventional gibs are made from cast iron and include a surface which abuts the lift guide rail in the event of the safety gear being actuated to retard and stop a lift car. Although fault conditions which require operation of the safety gear are not common occurrences, when it is necessary for the safety gear to operate to retard and stop a lift car both the gib and the guide rail are damaged. The gib can therefore require replacement and the guide rail must be cleaned in order to remove material from it which is transferred from the surface of the gib to the guide rail during frictional contact of the gib with the guide rail. Unless the material is removed from the guide rail a lift car being guided by the guide rail will be buffeted and a poor quality ride will be produced.

Replacement of the gib is expensive and both the need to replace the entire gib and the need to clean the guide rail also results in substantial down time for the lift which may be over and above that required to repair the fault which caused the emergency condition requiring actuation of the safety gear.

Furthermore, many old lifts which are provided with safety gear of the type described above are now being modernized and as a result the weight of the lift car is being increased. Some old safety gear used with old lift cars are not sufficient to retard and stop the modernized lift car with the result that additional safety gear must be added in order to meet safety requirements. The speed at which modern lifts and, for that matter, upgraded old lifts may be required to operate is up to seven meters per second and the weight of the lift cars can be up to six tonne. The braking pressure which is required can be in the order of 40 MPa. I"- order to provide a braking force which is sufficient to retard and stop a lift car the conventional thinking has been to require a heavy and solid braking surface on the gib and for this reason a surface of the cast iron gib has been used as the brake surface thereby providing a cast iron brake surface.

We have surprisingly found that use of a softer brake lining in safety gear for lift cars provides unexpected good retardation and stopping characteristics as well as other unexpected results and advantages.

The invention may therefore be said to reside in safety gear for a lift car, including: a gib for movement into contact with a lift guide rail for retarding and stopping the lift car in an emergency situation, said gib supporting a brake lining for engaging said rail, said brake lining being formed from a material which is relatively soft compared to cast iron.

The invention also provides a gib for a lift safety gear, comprising a gib body for movement into contact with a lift guide rail for retarding and stopping the lift car in an emergency situation, said gib supporting a brake lining for engaging said rail, said brake lining being formed from a material which is relatively soft compared to cast iron.

We have surprisingly found that the use of a softer brake lining in safety gear for lift cars provides a more constant retardation than the use of a conventional cast iron gib and more than adequately stops a lift car in an emergency situation. This is contrary to the conventional thinking which has suggested that at the high weights and pressures required of safety gear in lift cars soft brake linings would simply not work and would melt awa thereby providing no retardation and causing the lift car to plummet to the ground in the event of a worst scenario failure.

Furthermore, we have surprising found that the us of the softer material does not wear as much as expected an since the safety gear of a lift car only operates in an emergency situation which occurs rarely the safety gear of the present invention has an adequate lifetime.

Furthermore, we have surprisingly found that when the softer brake lining is used the guide rail of the lift car is not damaged and no substantial deposits of brake lining material are transferred to the lift car guide rail. Thus, it is not necessary to clean the guide rail to the same extent after actuation of the safety gear in an emergency situation.

Furtherstill, because the gib included in the present invention has the lining when the lining does wear it is not necessary to replace the entire gib but merely to replace the lining and this therefore decreases the cost involved with repair of the safety equipment.

Furtherstill, because of the much better than expected retardation and stopping qualities, conventional safety equipment for old lifts has been found to be adequate when only the gib having a softer brake lining is utilized in it and therefore when old lift cars are increased in weight during modernization it will not be necessary to add a further safety gear at great expense but merely to modify the existing safety gear to include a gib having the softer brake lining. Preferably the brake lining is formed on an insert which includes a pad for supporting the brake lining and a recess is formed in said gib for receiving said pad to thereby secure the brake lining to the gib. Alternatively, the brake lining may be a single piece coupled to the gib. Preferably the brake lining is formed from a bronze alloy brake material.

Preferably the insert is formed from steel.

A preferred embodiment of the invention will be described, by way of example, with reference to the accompanying drawings in which:

Figure 1 is a plan view of a gib used in safety gear for a lift car according to the preferred embodiment of the invention;

Figure 2 is a side view of the gib including an insert according to the preferred embodiment;

Figure 3 is a plan view of the insert according to the preferred embodiment of the invention;

Figure 4 is a side view of the insert of figure 3; Figure 5 is a view along the line V-V of figure 3;

Figure 6 is a graph showing a test result for a conventional safety gear; and

Figure 7 is a graph showing a test result according to the preferred embodiment of the invention.

With reference to figure 1 a gib 10 for safety gear for a lift car is shown. The safety gear is of conventional design and operation and therefore the safety gear apart from the gib is not shown in the drawings. The gib 10 according to the preferred embodiment of the invention is also of conventional design except that the surface of the gib which, when the gib is in use, is to be adjacent a lift guide rail is provided with a recess 12 which has end walls 14 and 16. The side 18 of the gib opposite the recess 12 is at an angle typically of about 4 degrees so that the gib is in the form of a wedge which upon actuation will wedge and self-lock itself against the guide rail of the lift car to create a braking force. An insert 20 is provided in the recess 12 and comprises a pad 22 of steel material and a brake'lining 24 of braking material softer than cast iron and preferably of a bronze alloy braking material. Alternatively, the insert may be formed entirely from lining material to form a insert of brake lining material which is in one piece.

As is best shown in figures 3 to 5, pad 22 of the insert 20 is provided with a cut-out 26 defined by end wall portion 28 and a wall portion 30. The pad 22 also has an end wall 34. The pad 22 is provided with a slot 36 for receiving the brake lining 24 and as is best shown in figur 3, the braking lining 24 has rounded ends 38 which match th shape of the slot 36.

The brake lining 24, pad 22 and gib 10 are provided with openings 40 for receiving screws (not shown) so that the brake lining, pad and gib can be securely fastened together.

The screws (not shown) are adapted to hold the brake lining 24 and pad 22 to the gib 10 until it is assembled in the safety equipment. hen assembled in the safety equipment the gib is relatively close but spaced from the guide rail until the safety gear comes into operation and therefore the insert 20 cannot move out of the recess 12 in a direction transverse to the longitudinal axis of the gib 10. The wall portion 28 and the wall portions 34 of the pad 20 abut the walls 14 and 16 respectively of the recess 12 and abutment of those wall portions prevents movement of the insert 20 in the direction of the longitudinal axis of the gib 10 to thereby securely hold the insert to the gib.

As is best shown in figure 5, a spacer material 42 can be provided between the brake lining 24 and the pad 22 if desired. Preferably the gib 10 is made from cast iron as is conventional and a conventional cast iron gib is merely machined to provide the recess 12. However the gib could also be formed from spheroidal graphite cast iron. The pad 22 is formed from steel and the brake lining 24 is preferably of a bronze alloy brake material. Most preferably the brake lining is about 89.8% copper, 5.2% tin and 4.9% graphite and is a sintered alloy. The hardness is preferably in the range 80 to 85 HRB (100) and most preferably 82.1 HRB (100). Figures 6 and 7 show graphs illustrating the results of the preferred embodiment of the present invention as compared to conventional braking gear.

Figures 6 and 7 show test mass speed versus time. The test was performed with safety gear with standard cast iron gibs and a test mass of 6,486 kg. The test mass was allowed to freefall until a speed of 6 meters per second was reached. At this point the safety gear was engaged. The speed continued to increase to 6.5 meters per second and at that stage a second safety gear was engaged. Both safety gears acting simultaneously brought the mass to rest. This test result shows that the single safety gear with conventional cast iron gibs did not retard the large test mass of 6,486 kg. In figure 6 region 1 is the freefall region, region 2 shows the first test gear acting on its own and region 3 shows both the first and second safety gears operating to decelerate and stop the car.

Figure 7 shows a result of the same tes t except that the gibs in the first safety gear are provided with brake linings according to the preferred embodiment which are formed from bronze alloy. In this test the safety gear decelerated the car and stopped it. Region 1 in figure 7 shows freefall and region 2 shows the safety gear engaged and decelerating the car to a standstill.

It should also be noted in figure 7 that the deceleration is substantially linear providing a smooth and even retardation of the car until it comes to rest. Since modifications within the spirit and scope of the invention may readily be effected by persons skilled within the art, it is to be understood that this invention is not limited to the particular embodiment described by way of example hereinabove.

Claims (10)

THE CLAIMS DEFINING THE INVENTION ARE AS FOLLOWS:

1. Safety gear for a lift car, including: a gib for movement into contact with a lift guide rail for retarding and stopping the lift car in an emergency situation, said gib supporting a brake lining for engaging said rail, said brake lining being formed from a material which is relatively soft compared to cast iron.

2. The safety gear of claim 1, wherein the brake lining is formed on an insert which includes a pad for supporting the brake lining and a recess is formed in said gib for receiving said pad to thereby secure the brake lining to the gib.

3. The safety gear of claim 1 or claim 2, wherein the brake lining is formed from a bronze alloy brake materia .

4. The safety gear of claim 2, wherein the insert is formed from steel.

5. The safety gear of claim 1 wherein the brake lining is a sintered alloy having 89.8% copper, 5.2% tin and 4.9% carbon in the form of graphite and a hardness of 80 to 85 HRB (100) .

6. A gib for a lift safety gear, comprising a gib body for movement into contact with a lift guide rail for retarding and stopping the lift car in an emergency situation, said gib supporting a brake lining for engaging said rail, said brake lining being formed from a material which is relatively soft compared to cast iron.

7. A gib according to claim 6, wherein the brake lining is formed on an insert which includes a pad for supporting the brake lining and a recess is formed in said gib for receiving said pad to thereby secure the brake lining to the gib.

8. A gib according to claim 6 or claim 7, wherein the brake lining is formed from a bronze alloy brake material.

9. A gib according to claim 7, wherein the insert is formed from steel.

10. A gib according to claim 6 wherein the brake lining is a sintered alloy having 89.8% copper, 5.2% tin and 4.9% carbon in the. form of graphite and a hardness of 80 to 85 HRB (100) .