Dual-Thread Sheet Metal Screw to Reduce Filings and Gaps

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Solution Overview

Problem

Conventional self-tapping screws for thin iron sheets generate excessive iron filings and gaps during installation, leading to insufficient clamping force and screw instability.

Innovation Solution

A screw design featuring a shank with a straight rod portion and a tapered screw-in portion, including dual threads with identical anchor points and crest angles between 48-52 degrees, which minimizes crevice formation and enhances fastening force by distributing stress evenly.

Engineering Contradictions & Design Principles

VSEngineering Contradiction Analysis

1Ease of manufacture

If a conventional self-tapping screw is used to fasten thin iron sheets, then no pre-bored hole is needed, but excessive iron filings are generated and large gaps occur leading to insufficient clamping force

Engineering Contradiction:

Improveno pre-bored hole neededVSAvoidexcessive iron filings and large gaps

Core Design Contradiction:

Ease of manufactureVSObject-generated harmful factors

Solution Approach 1:

The screw thread is divided into two distinct segments: a first thread with larger pitch for initial hole formation and material removal, and a second thread with smaller pitch for final fastening and clamping. This segmentation allows the screw to perform both self-drilling and fastening functions effectively, reducing harmful iron filings while maintaining ease of installation without pre-bored holes.

Inventive Principle:

Principle #1Segmentation

Solution Approach 2:

Different portions of the screw thread have different geometrical properties optimized for specific functions. The first thread portion has larger pitch and depth for aggressive material removal, while the second thread portion has smaller pitch for precise fastening. This local differentiation of thread quality resolves the contradiction between easy installation and reduced harmful effects.

Inventive Principle:

Principle #3Local quality

2Strength

If the thread is screwed into the thin iron sheet for hole expansion, then fastening is achieved, but large gaps occur leading to screw shaking and insufficient clamping force

Engineering Contradiction:

Improvefastening forceVSAvoidscrew stability and clamping force

Core Design Contradiction:

StrengthVSStability of the object's composition

Solution Approach 1:

The fastening process is segmented into two stages: the first thread performs initial hole expansion and material displacement, while the second thread performs precise thread engagement and clamping. This segmentation ensures that the screw achieves both hole expansion and stable fastening without large gaps, eliminating screw shaking.

Inventive Principle:

Principle #1Segmentation

Solution Approach 2:

The first thread performs preliminary hole formation and material displacement before the second thread engages for final fastening. This preliminary action prepares the hole in a controlled manner, allowing the second thread to engage smoothly and create stable clamping force without large gaps that would cause screw shaking.

Inventive Principle:

Principle #10Preliminary action

3Device complexity

If a single thread design is used, then the screw structure is simple, but the screw causes fracture on thin iron sheets and generates many crevices

Engineering Contradiction:

Improvescrew structure simplicityVSAvoidcrevice generation and sheet integrity

Core Design Contradiction:

Device complexityVSManufacturing precision

Solution Approach 1:

The thread is segmented into two distinct threads with different geometrical characteristics. The first thread with larger pitch handles initial material removal with less stress concentration, while the second thread with smaller pitch provides precise fastening. This segmentation prevents sheet fracture and minimizes crevice generation while maintaining reasonable structural complexity.

Inventive Principle:

Principle #1Segmentation

Solution Approach 2:

The thread parameters (pitch, depth, angle) are changed between the first and second threads. The first thread has larger pitch and depth for gentle material displacement, while the second thread has smaller pitch for precise engagement. This parameter variation prevents sheet fracture and reduces crevice formation.

Inventive Principle:

Principle #35Parameter changes

Data Source

PatentEP3399200B1Screw for thin iron sheets

Publication Date: 2021.11.24 HUMBOLDT STATE UNIVERSITY

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AI summary

A screw (20) for thin iron sheets includes a shank (22), a first thread (38), and a second thread (40). The shank (22) includes a tapered screw-in portion (26), a head (24), and a straight rod portion (28) between the screw-in portion (26) and the head (24). The straight rod portion (28) features non-circular cross sections. The first and second threads (38, 40) are spirally developed on the outer circumference of the shank (22) and extend to the straight rod portion (28) from a tip (30) of the screw-in portion (26), respectively. The first thread (38) includes a plurality of first thread convolutions (42), and the second thread (40) includes a plurality of second thread convolutions (44) spaced from the first thread convolutions (42) of the first thread (38). Each of the first and second thread convolutions (42, 44) features a crest angle between 48 and 52 degrees.