Patent Application
20110135926
There are various uses for elongated flexible assemblies such as for elevator load bearing members or roping arrangements, drive belts for machines such as a passenger conveyor and handrails for passenger conveyors, for example. Such assemblies may be designed with a plurality of cords covered by a polyurethane jacket. For example, U.S. Pat. Nos. 6,295,799 and 6,739,433 show belts for use in suspending an elevator car and counterweight within an elevator system. An example passenger conveyor handrail construction is shown in U.S. Pat. No. 4,982,829. An example passenger conveyor drive belt is shown in U.S. Pat. No. 6,540,060.
One aspect of such assemblies is that they interact with other system components. The coefficient of friction between the jacket and the other system components typically is chosen to achieve satisfactory performance. For example, some friction is desired to achieve sufficient traction between elevator load bearing members and a traction sheave for controlling movement of the elevator car. The surface roughness on the sheave, the jacket or both is one factor that influences the coefficient of friction between them. Another factor is the chemical composition of the jacket material.
Handrails for passenger conveyors have other friction characteristic requirements. One side of the handrail slides along a guidance. That movement of the handrail preferably occurs with limited or no friction between the handrail and the guidance. The other side of the handrail provides a gripping surface for passengers riding on the conveyor. The gripping surface requires different friction characteristics. The gripping surface is often engaged by rollers used for driving the handrail. It is necessary in such arrangements to maintain a sufficient amount of friction between the handrail and the drive arrangement to achieve the desired movement.
Over time, the coefficient of friction between such components tends to change. The surface roughness, surface chemistry or both can change, for example. Surface contaminants may accumulate that need to be removed. Cleaning solvents or lubricants may be used during maintenance procedures. Any of these factors can alter the surface roughness, chemistry or both, which further increases the variability in friction characteristics of the components. Additional efforts are required to try to maintain desired friction characteristics. Even when known attempts are made, the results are not consistent or precise enough. Maintaining consistent friction properties is desirable for maintaining a desired level of performance, for example.
An exemplary assembly includes at least one elongated tension member. A jacket covers at least some of the tension member. The jacket comprises a polymer material including a friction stabilizer that facilitates maintaining a desired friction characteristic of at least an exterior surface on the jacket.
An exemplary method of making an assembly having at least one elongated tension member at least partially covered by a jacket includes mixing a friction stabilizer with a polymer base resin to provide a master batch of mixed material. The mixed material is then compounded with a base polymer material to yield a jacket material. The jacket material is then molded onto at least a portion of the tension member to form a desired shape of the jacket.
The various features and advantages of the disclosed examples will become apparent to those skilled in the art from the following detailed description. The drawings that accompany the detailed description can be briefly described as follows.
The load bearing assembly 26 supports the weight of the elevator car 22 and the counterweight 24 and facilitates movement of the elevator car 22 into desired positions by moving along sheaves 28 and 30. One of the sheaves will be a traction sheave that is moved by an elevator machine in a known manner to cause the desired movement and placement of the elevator car 22. In some instances, such as with flat belts, the traction sheave could comprise the shaft of the machine (i.e. not a separate component mounted to the shaft). The other sheave in this example is an idler sheave.
Another example is schematically shown in
The load on the example belt is carried by the tension members 32. The interaction between the jacket 34 and the sheaves 28, 30 requires a desired amount of friction to achieve sufficient traction, for example. Maintaining the desired coefficient of friction ensures consistent system performance. In each of the examples of
As shown in
The example of
Desired amounts of friction are useful to ensure a desired interaction between the drive belt 56 on the one hand and the drive sheave 54 or the step chain 58 on the other hand. In this example, the drive belt 56 includes a polymer jacket material with at least one friction stabilizer that facilitates maintaining a desired friction characteristic of at least an exterior surface on the jacket 34.
When a metal is used for the any of the example tension members 32, the metal material may be uncoated, coated, or plated with a protective metal. For example, a base ferrous metal may be coated or plated with zinc, tin or copper.
The friction stabilizer 62 is one of melamine-based, phosphate-based or both. Example friction stabilizers include non-halogen containing melamine salts. Some example melamine salt friction enhancers include melamine cyanurate and melamine-phosphate. Those examples are useful with a thermoplastic polyurethane jacket material.
Other example friction stabilizers include organic phosphates. One such example comprises hydrocarbon phosphate. Such a friction stabilizer is useful with jacket materials that comprise elastomeric alloys such as melt-processible rubbers.
The amount of friction stabilizer can be varied to achieve target friction characteristics. In one example, the amount of friction stabilizer mixed with the base polymer resin in the master batch mixer 66 is between 20% and 50% by weight. The resulting master batch of mixed material in this example is then compounded with a base polymer material 68 in a jacket material mixer 70. The resulting jacket material after the mixing at 70 may contain up to 20% by weight of the friction stabilizer. One example includes from 0.2% to 20% by weight of the friction stabilizer in the jacket material. In one example, the resulting polymer material in the jacket material mixer 70 comprises between about 0.2% and about 10% by weight of the friction stabilizer.
Referring to
Providing a melamine-based or phosphate-based friction stabilizer in an amount up to 20% by weight of the jacket polymer material increases the longevity of the friction characteristic of the jacket material. The friction stabilizer minimizes or prevents changes in the friction characteristic over time.
The presence of the friction stabilizer in at least one embodiment does not interfere with or adversely change other properties of the jacket material such as the flexibility of the base polymer material so that the jacket functions as desired for its particular application (e.g., is able to follow a guidance when the assembly comprises a passenger conveyor handrail, is able to transmit a sufficient drive force when the assembly comprises a drive member such as a belt or is able to wrap around sheaves and achieve sufficient traction for moving an elevator car when the assembly comprises an elevator load bearing member). Additionally, the ability to mold the jacket into a desired shape and to maintain good adhesion between the jacket 34 and the tension members 32 is not compromised. In fact, adhesion between the material of the jacket 34 and the tension members 32 is improved by the presence of the friction stabilizer in the jacket material.
The example friction stabilizers provide unexpectedly increased stability of friction characteristics of the jacket compared to a polymer jacket material with out one of them. In some examples, the adhesion strength is at least twice that which could be attained without the example friction stabilizers.
With the example friction stabilizers, the jacket of an assembly also has good thermal stability, hydrolytic stability, low hydrophilic characteristics and good compatibility to interact with other components such as an elevator sheave or a passenger conveyor step chain. The disclosed friction stabilizers also provide flame-retardant properties to the jacket material.
The preceding description is exemplary rather than limiting in nature. Variations and modifications to the disclosed examples may become apparent to those skilled in the art that do not necessarily depart from the essence of this invention. The scope of legal protection given to this invention can only be determined by studying the following claims.
| Filing Document | Filing Date | Country | Kind | 371c Date |
|---|---|---|---|---|
| PCT/US2008/073231 | 8/15/2008 | WO | 00 | 1/6/2011 |
