Elevator Tension Member with Thermoplastic Polyurethane Elastomer Jacket
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Solution Overview
Problem
Elevator tension members with high tensile, fine steel filaments face issues such as increased pressure and wear due to smaller diameters, sensitivity to transverse stresses, and different friction behavior, which are not adequately addressed by prior art technologies, particularly in the absence of a machine room.
Innovation Solution
A polymer-coated elevator tension member using thermoplastic polyurethane elastomers with specific thermal properties, such as a glass transition temperature of the hard crystalline phase above 90°C, to enhance fatigue life and friction behavior, thereby improving the overall performance and reducing wear.
Engineering Contradictions & Design Principles
Engineering Contradiction Analysis
1Volume of moving object
If fine, high tensile steel filaments are used to reduce tension member diameter, then the breaking load requirement can be met with smaller diameter (5mm or thinner), but the pressure between steel cord and sheave increases inversely proportional to the product of sheave diameter and steel cord diameter
Solution Approach 1:
A polymer jacket is introduced as an intermediary layer between the fine steel filaments and the sheave. This jacket distributes the contact pressure over a larger area, reducing the peak pressure on the steel cords while maintaining the compact diameter. The polymer material acts as a mediator that transforms the concentrated point contact into a distributed line contact.
Solution Approach 2:
The tension member is constructed as a composite structure combining fine high-tensile steel filaments with a polymer jacket. The steel provides the necessary breaking load strength while the polymer provides pressure distribution and friction control. This composite approach allows simultaneous optimization of both diameter and pressure characteristics.
2Volume of moving object
If fine, high tensile steel filaments are used, then the diameter of drive sheave can be reduced (30 times or even 25 times rope diameter), but fine filaments are more sensitive to transversal stresses and contact stresses increase at filament contact points
Solution Approach 1:
The polymer jacket serves as a protective intermediary that shields the fine steel filaments from direct transversal stresses and contact stresses. It absorbs and distributes these harmful stresses, preventing them from concentrating on the fragile filament surfaces.
Solution Approach 2:
The polymer jacket acts as a flexible protective shell that envelops the steel filaments. This thin film structure provides mechanical protection against transversal stresses while maintaining the flexibility needed for elevator operation. The shell distributes localized stresses over a broader area.
3Volume of moving object
If fine, high tensile steel filaments with higher hardness are used, then breaking load is achieved with smaller diameter, but the wear between sheave and steel rope completely changes and friction behavior is different (lower) due to hardness difference and reduced contact surface area
Solution Approach 1:
The friction and wear characteristics are modified by changing the surface material parameter from hard steel to softer polymer. The polymer jacket provides a different coefficient of friction that ensures reliable traction on the sheave while reducing wear through its self-lubricating properties and ability to conform to surface irregularities.
Solution Approach 2:
The composite structure combines the high-strength steel core with a polymer outer layer that has optimized friction and wear properties. This allows the inner steel to provide breaking load strength while the outer polymer layer handles the friction and wear interactions with the sheave.
4Stress or pressure
If polymer jacket is used to encase steel cords, then pressure is cushioned and distributed, and inter-filament transversal stresses are alleviated, but a good adhesion between polymer and steel cords is crucial due to shear stress induced during acceleration and deceleration
Solution Approach 1:
The mechanical adhesion between polymer and steel is enhanced by introducing chemical bonding mechanisms. Surface treatments or coupling agents create chemical bonds at the interface, supplementing the mechanical interlocking and ensuring reliable stress transfer during dynamic operation.
Applied Scientific Principles
This section explains which scientific principles are used to turn an abstract innovation direction into a practical engineering solution.
Function Achieved in This Case
The polymer-coated tension member exhibits improved fatigue life and friction properties, significantly increasing the bending stiffness of the elevator tension member, with the polymer jacket contributing more than 80% to the total stiffness, and extending the operational life by selecting TPEs with optimal thermal properties.
Implementation Method 1
a good adhesion between the polymer and the steel cords is crucial. The polymer jacket therefore becomes a part of the tension member that has an influence on many use parameters of the tension member
Implementation Method 2
a good adhesion between the polymer and the steel cords is crucial
Implementation Method 3
the polymer jacket cushions and distributes the pressure on the steel cords at the drive sheave
Implementation Method 4
the polymer jacket cushions and distributes the pressure on the steel cords at the drive sheave
Implementation Method 5
thermoplastic polyurethane elastomers are best suited for this application, particularly for their resistance to wear, moisture and heat
Implementation Method 6
it has a glass transition temperature of the hard crystalline phase that is higher than 90°C
Data Source
AI summary
An elevator tension member is presented that has one or more steel cords as strength members that are encased in a jacket of thermoplastic polyurethane elastomer. The thermoplastic polyurethane elastomer is selected on the basis of its thermal properties in that the glass transition temperature of the hard phase (Tg HS) is above 90° C. In preferential embodiments that thermoplastic polyurethane elastomer has a crystallisation temperature (Tg) that is at least 20° C. higher than Tg HS. In other preferential embodiments the sum of Tg HS and Tc is higher than 200° C. Such thermoplastic polyurethane elastomers exhibit an unexpected increase in useful lifetime when compared to conventionally used polyurethanes. Moreover the invention provides a simple method to select an appropriate thermoplastic polyurethane elastomer.