Office Chair Column Joint With Metal-Plastic Load-Bearing Socket

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Solution Overview

Problem

Existing office chair connecting structures between the column and seating portion are costly due to material and manufacturing processes, and lack sufficient structural integrity for intensive use, often requiring self-lubricating sockets and complex assembly operations.

Innovation Solution

A connecting structure formed by injection moulding plastic with glass fibre reinforcement and a pressed sheet metal frusto-conical socket, eliminating the need for additional components and providing enhanced structural integrity through internal ribs and a quick-coupling mechanism, allowing direct load transfer and simplified assembly.

Engineering Contradictions & Design Principles

VSEngineering Contradiction Analysis

1Strength

If traditional die-casting aluminium is used for box support, then structural integrity is achieved, but manufacturing cost increases due to material cost, die-casting operations, and finishing operations

Engineering Contradiction:

Improvestructural integrityVSAvoidmanufacturing cost

Core Design Contradiction:

StrengthVSEase of manufacture

Solution Approach 1:

The patent uses a composite structure combining plastic material for the box support with an inserted metal conical component. This allows the plastic to provide the main structural form while the metal insertion provides the required strength for intensive use, avoiding the high costs of pure metal die-casting and finishing operations.

Inventive Principle:

Principle #40Composite materials

2Reliability

If self-lubricating sockets are used in metal structure, then seizure and jamming are prevented, but manufacturing cost increases

Engineering Contradiction:

Improveprevention of seizure and jammingVSAvoidmanufacturing cost

Core Design Contradiction:

ReliabilityVSEase of manufacture

Solution Approach 1:

The plastic material itself provides the self-lubricating property through its inherent low friction characteristics. The plastic seats and rotation holes in the plastic box support eliminate the need for separate self-lubricating socket components, reducing part count and manufacturing cost while maintaining reliability.

Inventive Principle:

Principle #25Self-service

3Strength

If welding operations are used for steel sockets, then structural strength is achieved, but manufacturing cost increases due to welding and painting operations

Engineering Contradiction:

Improvestructural strengthVSAvoidmanufacturing cost

Core Design Contradiction:

StrengthVSEase of manufacture

Solution Approach 1:

The patent combines the box support structure with the mounting features directly in the plastic injection molding process. The plastic box support integrates the seats for passage pins and the overall structure, eliminating the need for separate welded steel socket components and subsequent painting operations.

Inventive Principle:

Principle #5Merging (Combining)

4Ease of manufacture

If integral plastic structure is used, then manufacturing cost is reduced, but structural characteristics become insufficient for intensive product use

Engineering Contradiction:

Improvemanufacturing costVSAvoidstructural characteristics for intensive use

Core Design Contradiction:

Ease of manufactureVSStrength

Solution Approach 1:

Inventive Principle:

Principle #40Composite materials

5Strength

If conical component is obtained by lathe turning or from tube, then connection structure is achieved, but manufacturing cost increases

Engineering Contradiction:

Improveconnection structureVSAvoidmanufacturing cost

Core Design Contradiction:

StrengthVSEase of manufacture

Solution Approach 1:

The conical component is pre-formed by pressing sheet metal into the desired conical shape with integrated flange and reinforcement features, then inserted into the plastic box support during injection molding. This preliminary forming of the metal component allows for cost-effective manufacturing while ensuring proper fit and structural connection.

Inventive Principle:

Principle #10Preliminary action

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 reduces production costs, enhances structural reliability, and simplifies the manufacturing process while ensuring compliance with regulatory tests, offering a cost-effective and robust connecting system for office chairs.

Implementation Method 1

The box support is formed by injection moulding plastic material, preferably polyamide filled with glass fibre

Methodology Applied

Scientific EffectInjection moulding:

Implementation Method 2

allowing direct load transfer and simplified assembly

Methodology Applied

Scientific EffectLoad transfer: Mechanical Force

Implementation Method 3

The structure is provided internally with a plurality of reinforcement ribs which connect the frusto-conical part of the metal portion to the side walls in order to stiffen the structure

Methodology Applied

Scientific EffectGeometric reinforcement: Geometry

Data Source

PatentEP2421408B1Process for forming a connecting structure between the column and seating portion of an office chair, and a structure obtained by said process

Publication Date: 2013.03.06 IMARC SPA

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AI summary

A method for forming connecting structures between the column and seating portion for office chairs, characterised by: - forming a frusto-conical portion (8) provided with a flange (24, 26, 28) by cold-pressing a portion of sheet metal, - inserting said flanged portion into a mould (32) reproducing the shape of the structure, - injecting plastic material into the mould in such a manner as to incorporate the flanged portion (24, 26, 28) of said frusto-conical portion (8) into the plastic material.