Countersunk Screw Curved Ribs Prevent Coating Damage
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Solution Overview
Problem
Existing countersunk screws for wood and plastic surfaces often damage the surface coatings of metal fittings and hinges due to their milling ribs, which are not designed to accommodate the oblique orientation and curvature required for efficient screwing without scratching the protective coatings.
Innovation Solution
The countersunk screw features curved, arc-shaped ribs that extend from the shank to the head, providing an oblique orientation to the direction of rotation, reducing screwing torque and ensuring the ribs do not have purely linear sections, with an increasing width from the head end to the shank end, and a conical contact surface that intersects with the surface at an angle of 80 to 100 degrees, ensuring stability and preventing damage to coatings.
Engineering Contradictions & Design Principles
Engineering Contradiction Analysis
1Ease of manufacture
If linear milling ribs are used on the countersunk head, then the head can be milled into the base material, but the ribs scratch off the protective coating on metal fittings and hinges
Solution Approach 1:
The patent applies curvature by forming the contact surfaces of the milling ribs on a conical surface rather than as linear features. The ribs are arranged radially outwardly on a conical surface with a specific semi-vertical angle, creating curved contact paths that prevent scratching of the protective coating while maintaining effective milling capability into the base material
2Object-affected harmful factors
If the milling ribs have full contact with the hinge surface, then coating damage is prevented, but screwing torque increases
Solution Approach 1:
The patent optimizes the geometric parameters of the milling ribs, specifically the semi-vertical angle of the conical surface and the radial outward arrangement of the ribs. These parameter changes create an optimal balance where the ribs maintain sufficient contact to protect the coating while minimizing friction and screwing torque through their specific angular configuration
3Force
If the ribs are curved in an S-shape with increasing width, then screwing torque is reduced and milling is improved, but manufacturing complexity increases
Solution Approach 1:
The S-shaped curved profile of the ribs with increasing width from head to shank creates optimized cutting edges that reduce screwing torque. The curvature allows the ribs to engage the material more efficiently during rotation, reducing resistance while the systematic geometric progression provides manufacturing regularity
Solution Approach 2:
The rib geometry varies locally along its length, with width increasing from the head end toward the shank end. This local variation in dimensions optimizes the cutting action at different stages of screwing while maintaining overall geometric regularity that facilitates manufacturing
Data Source
Figure 1~4
AI summary
The screw (10) has a tip (12) and a shaft (14) provided with a screw thread (16), and a head (20) comprising a conical portion (22) facing toward the tip, where the conical portion is provided with multiple circumferential distributed, outwardly projecting ribs (30) that are radially extended toward a head end. The ribs are viewable in a side view from the shaft. The ribs comprise radial abutment surfaces, which lie in a conical surface and form a mill edge at an edge-side in a pivoting direction, where the ribs exhibit a C-shaped portion or S- shaped portion.