Diffusion-Bonded Bolted Assemblies for High-Temperature Torque Retention

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Solution Overview

Problem

High energy x-ray tubes face material degradation due to thermal stresses from backscattered electrons, leading to reduced operating life and potential seal failure between the window and envelope, necessitating a secure and high-temperature-resistant fastening solution for the heat shield.

Innovation Solution

A fastening assembly using refractory metals or superalloys with diffusion bonding between bolts and washers, allowing secure attachment of a heat shield to the collector at temperatures exceeding 500°C, ensuring mechanical stability and torque retention while minimizing contamination of the vacuum environment.

Engineering Contradictions & Design Principles

VSEngineering Contradiction Analysis

1Strength

If conventional fastening methods are used to secure the heat shield, then the assembly can be easily installed and removed, but the fastening strength and torque retention deteriorate at high temperatures exceeding 500°C

Engineering Contradiction:

Improvefastening strengthVSAvoidoperating temperature

Core Design Contradiction:

StrengthVSTemperature

Solution Approach 1:

The patent applies diffusion bonding to change the physical-chemical state of the joint between fastener and washer. By heating the assembly to temperatures exceeding 500°C during assembly, atomic diffusion occurs at the contact interface, creating a metallurgical bond that maintains fastening strength at high operating temperatures where conventional mechanical fastening would fail

Inventive Principle:

Principle #35Parameter changes

Solution Approach 2:

The patent employs a composite fastening system combining mechanical fastening elements (bolt, washer, nut) with a diffusion-bonded joint. The diffusion bond creates a composite structure where the fastener and washer become metallurgically integrated, providing both the mechanical advantages of discrete components and the thermal stability of a bonded joint

Inventive Principle:

Principle #40Composite materials

2Reliability

If diffusion bonding is used to secure the fastener to the washer, then torque retention at high temperatures is improved, but the complexity of the manufacturing process increases

Engineering Contradiction:

Improvetorque retentionVSAvoidmanufacturing process

Core Design Contradiction:

ReliabilityVSEase of manufacture

Solution Approach 1:

The patent merges the assembly process with the diffusion bonding process. The heat treatment required for diffusion bonding is combined with the assembly operation itself, so that the fastener and washer are joined permanently during the assembly stage. This eliminates separate bonding operations and integrates multiple functions into a single manufacturing step

Inventive Principle:

Principle #5Merging (Combining)

Solution Approach 2:

The diffusion bonding process is performed as a preliminary action during assembly, creating a permanent bond before the component enters service. By establishing the metallurgical bond during manufacturing rather than during operation, the patent ensures reliable torque retention at high temperatures without requiring additional maintenance or reinforcement steps

Inventive Principle:

Principle #10Preliminary action

3Strength

If refractory metals or superalloys are used for the fastener, then high-temperature strength is improved, but the cost of materials and manufacturing increases

Engineering Contradiction:

Improvehigh-temperature strengthVSAvoidmanufacturing cost

Core Design Contradiction:

StrengthVSEase of manufacture

Solution Approach 1:

The patent applies refractory metals or superalloys specifically to the fastener components (bolt, washer, nut) that require high-temperature strength, rather than using these expensive materials throughout the entire heat shield assembly. The diffusion bonding process is applied locally at the fastener-washer interface, concentrating the expensive materials and processing only where mechanically critical

Inventive Principle:

Principle #3Local quality

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 effectively secures the heat shield, reducing thermal stresses on the x-ray window, enhancing the operational life of the x-ray tube by maintaining a stable vacuum and preventing contamination, while allowing for controlled removal of bolts for potential rework.

Implementation Method 1

The upper surface of the washer forms diffusion bonds with the underside of the head of the fastener when the washer and the fastener are held in contact at temperatures in excess of 500° C.

Methodology Applied

Scientific EffectDiffusion bonding: Diffusion Welding

Implementation Method 2

A heat shield may be secured to a portion of the x-ray tube to shield the window from backscattered electrons

Methodology Applied

Scientific EffectThermal stress absorption: Heat Sink

Data Source

PatentUS9494181B2High temperature secondary torque retention for bolted assemblies

Publication Date: 2016.11.15 GE PRECISION HEALTHCARE LLC

AI summary

A fastening assembly includes a fastener having a head with an underside and an elongated shaft extending therefrom. The fastener constructed of at least one of a refractory metal and a superalloy. A washer includes a body with an upper surface and an opposing lower surface which defines opening portion for receiving the elongated shaft of the fastener therethrough. The upper surface of the washer forms diffusion bonds with the underside of the head of the fastener when the washer and the fastener are held in contact at temperatures in excess of 500° C.