Fireproof Door Latch Assembly with Melting Safety Pin
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Solution Overview
Problem
Fireproof door locks face challenges in maintaining the closed position during a fire due to latch bolt deformation, risking fire and smoke expansion when the door is opened.
Innovation Solution
A latch assembly with a base, movable latch bolt, link, follower plate, and safety pins with a melting point lower than the main components, which aligns safety pins with positioning holes to prevent the latch from unlatching during a fire, ensuring the door remains closed.
Engineering Contradictions & Design Principles
Engineering Contradiction Analysis
1Ease of operation
If the latch bolt is made movable to allow door opening, then the ease of operation is improved, but the reliability is worsened because the latch bolt may deform due to high temperature and move to the unlatching position
Solution Approach 1:
A safety pin is introduced as an intermediary component between the latch bolt and the positioning hole. The safety pin acts as a mediator that physically blocks the latch bolt from moving into the unlatching position during fire, while allowing normal operation under normal conditions. The safety pin is made of low-melting-point material that melts when exposed to fire heat, at which point it releases the latch bolt to allow door opening.
Solution Approach 2:
The invention changes the physical state of the safety pin from solid to liquid through phase transition when exposed to high temperature. The safety pin is made of material with melting point between 60°C and 150°C, which is lower than the operating temperature during fire. This parameter change (melting) causes the safety pin to lose its blocking function, allowing the latch bolt to move freely and the door to be opened during fire emergency.
2Reliability
If the engagement holes are always aligned with positioning holes, then the reliability is improved by preventing unlatching, but the ease of operation is worsened because the door cannot be opened when needed
Solution Approach 1:
The safety pin is designed to be dynamically responsive to temperature changes. Under normal conditions, the safety pin remains in the blocking position, preventing the engagement holes from aligning with the positioning holes and thus preventing accidental unlatching. When exposed to fire heat, the safety pin melts and changes position, allowing the latch bolt to move and the door to be opened. This dynamic behavior automatically adapts the latch system's reliability and operability based on environmental conditions.
Solution Approach 2:
The safety pin utilizes phase transition (melting) as the mechanism to switch between two functional states: blocking state under normal conditions and non-blocking state during fire. The safety pin is made of low-melting-point material that transitions from solid to liquid when exposed to fire heat, causing it to collapse or melt away from the blocking position, thereby allowing the latch bolt to move into the unlatching position and the door to be opened.
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 latch assembly effectively retains the top and bottom latches in the latching position during a fire, preventing fire and smoke expansion by ensuring the door remains closed.
Implementation Method 1
A safety pin is received in the sleeve and includes a shank extending through a stop of the sleeve. The stop is located between a head of the safety pin and an inner periphery of the sleeve. The safety pin has a melting point between 60°C and 150°C, which is lower than a melting point of the stop and lower than a melting point of the sleeve.
Data Source
AI summary
A latch assembly includes a base having two sidewalls each having a positioning hole. A follower plate includes two sidewalls each having an engagement hole that is aligned with the positioning holes when the latch is in a latching position and that is not aligned with the positioning holes when the latch is in an unlatching position. Two sleeves are mounted between the sidewalls of the follower plate. An end of each sleeve is received in the engagement hole of one of the sidewalls of the follower plate. A stop having a low melting point is received in each sleeve to retain a safety pin in the sleeve. When the stops melt due to heat of a fire while the latch is in the latching position, the safety pins are moved by a spring into the positioning holes of the base to retain the latch in the latching position.