Railcar Elastomeric Spring Radial Expansion Constraint
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Solution Overview
Problem
Conventional railcar draft gear elastomeric springs with thermoplastic polyester elastomers of durometer hardness between 40 and 45 on the Shore D scale face challenges in securing metal plates and preventing radial expansion, leading to poor performance and potential failure due to heat-generated radial expansion against the draft gear housing.
Innovation Solution
A cold-formed railcar spring design featuring a thermoplastic polyester elastomer preform with a central bore, compressed at least 30% of its initial length, and metal plates with radially spaced fasteners that interlock with the elastomer to prevent radial expansion, ensuring secure bonding and reduced friction against the housing.
Engineering Contradictions & Design Principles
Engineering Contradiction Analysis
1Strength
If thermoplastic polyester elastomer with durometer hardness between 40 and 45 is used to form the elastomeric spring, then the elastomer provides adequate flexibility and energy absorption, but the elastomer radially expands against the draft gear housing when compressed, leading to poor performance and potential failure
Solution Approach 1:
A constraining shell or film is applied to the elastomeric spring to prevent radial expansion while allowing the elastomer to maintain its flexibility and energy absorption properties. The shell confines the elastomer within specific radial boundaries, eliminating the harmful radial expansion against the draft gear housing.
Solution Approach 2:
The elastomeric spring is pre-compressed or pre-constrained during assembly to a height that limits its radial expansion potential before it is installed in the draft gear. This preliminary action prevents the elastomer from expanding against the housing during operation.
2Ease of manufacture
If metal plates are bonded to the elastomeric spring pad, then the spring structure is completed for draft gear assembly, but the bonding process is complex and bonding quality is inconsistent
Solution Approach 1:
The bonding process is replaced with a mechanical attachment system. Metal plates are secured to the elastomeric spring pad through mechanical means such as interlocking features, recesses, or physical engagement during compression, eliminating the need for adhesive bonding and its associated complexity and inconsistency.
3Strength
If the elastomeric preform is compressed at least 30% of its initial length, then the spring achieves proper density and energy absorption characteristics, but the compression process requires precise control and extended dwell time
Solution Approach 1:
The elastomeric preform is pre-compressed to a predetermined height during the molding or forming process before final assembly. This preliminary compression establishes the required density and energy absorption characteristics, eliminating or reducing the need for subsequent compression steps and associated dwell times.
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 solution enhances the durability and performance of railcar draft gear springs by maintaining secure metal plate attachment and limiting radial expansion, thereby improving energy absorption and dissipation capabilities while reducing the risk of spring failure.
Implementation Method 1
an elastomeric spring used to absorb, dissipate and return energy imparted to a railcar draft gear
Implementation Method 2
Each elastomeric spring includes an elastomeric pad having metal plates joined or bonded to opposite ends thereof
Implementation Method 3
upon being axially compressed at least 30% of the initial axial length thereof, the elastomer will permanently retain a substantial portion of the length reduction
Implementation Method 4
Each fastener has first and second generally parallel surfaces and a barb along a length thereof such that, upon axial compression of the preform, the fastener is pressed axially inward of one end of the preform such that the barb on the fastener mechanically interlocks with the elastomer of the preform
Implementation Method 5
the barb on the fastener mechanically interlocks with the elastomer of the preform whereby fastening the plate to one end of the preform
Data Source
AI summary
A cold formed railcar spring including a spring pad formed from a perform of thermoplastic polyester elastomer having a durometer hardness ranging between about 40 and about 45 on the Shore D scale and sandwiched between a pair of metal plates. Each metal plate has a generally centralized bore extending therethrough and includes a plurality of radially spaced mechanical fasteners formed as an integral part of each plate. Each fastener has first and second generally parallel surfaces and a barb extending from a side of the fastener such that, upon axial compression of the preform, the fastener is pressed axially inward of one end of the perform such that the barb on the fastener mechanically interlocks with the spring pad whereby securing the plate to the spring pad.