Hearth Roll Pre-stretching for Annealing Furnace Creep
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Solution Overview
Problem
Conventional hearth rolls in annealing furnaces experience thermal deformation (creep) due to differing coefficients of linear expansion between the roll shaft and ceramic tube, leading to eccentric rotation, increased vibration, and frequent replacement, which hinders productivity and product quality.
Innovation Solution
A hearth roll apparatus with a ceramic tube and a roll shaft coupled to a tension generating unit that applies a tensile force to the roll shaft, minimizing thermal deformation by stretching it in the longitudinal direction and maintaining close contact between the roll shaft, ceramic tube, and tube fixing sleeve, preventing heat transfer and maintaining concentric rotation.
Engineering Contradictions & Design Principles
Engineering Contradiction Analysis
1Temperature
If the roll shaft is made from heat resistant steel to withstand high temperature, then the roll shaft can operate in the annealing furnace, but thermal deformation (creep) occurs due to the coefficient of linear expansion difference between the roll shaft and ceramic tube
Solution Approach 1:
The invention applies preliminary anti-action by pre-stretching the roll shaft before installation into the ceramic tube. This pre-applied tensile force creates an initial elongation that counteracts the thermal expansion that will occur during high-temperature operation, thereby preventing thermal deformation and maintaining dimensional stability throughout the service life of the roll shaft
Solution Approach 2:
The invention changes the physical parameter of the roll shaft by applying a controlled tensile force that permanently elongates the shaft. This parameter change (pre-stretching) modifies the initial length and stress state of the roll shaft so that when thermal expansion occurs at operating temperature, the net dimensional change is minimized, preventing contact gaps and eccentric rotation
2Ease of operation
If the roll shaft is allowed to rotate freely, then the hearth roll can feed the strip sheet, but eccentric rotation occurs due to thermal deformation, causing increased vibration and reduced reliability
Solution Approach 1:
By pre-stretching the roll shaft before installation, the invention creates a compensatory mechanism that prevents thermal deformation during operation. This ensures the roll shaft maintains its concentric position within the ceramic tube, allowing free rotation without eccentric movement, vibration, or contact with the tube wall, thereby maintaining both operational freedom and reliability
3Device complexity
If the roll shaft is not pre-stretched, then the structure is simpler, but thermal deformation causes gaps at contact portions, leading to heat transfer and reduced durability
Solution Approach 1:
The pre-stretching process is a simple one-step operation performed before installation, requiring no additional complex components or mechanisms. This preliminary action permanently sets the roll shaft in a pre-elongated state that compensates for thermal expansion, preventing gap formation, heat transfer, and premature failure, thereby extending apparatus life without significantly increasing structural complexity
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 reduces thermal deformation, extends the life of the apparatus, increases productivity by maintaining optimal line speed, and reduces replacement costs while enhancing product quality.
Implementation Method 1
a coil spring which stretches the roll shaft in the longitudinal direction by an elastic force
Implementation Method 2
the roll shaft is stretched in the longitudinal direction by the piston rod and piston, the movement of which is controlled by hydraulic or pneumatic pressure
Implementation Method 3
The grease G prevents external air from flowing into the annealing furnace in which hydrogen gas atmosphere is formed
Data Source
AI summary
A hearth roll apparatus for feeding a strip sheet in an annealing furnace is disclosed. The hearth roll apparatus includes a ceramic tube which is provided inside the annealing furnace to contactingly feed a strip sheet, a roll shaft which is coupled to a first end of the ceramic tube and extends across the annealing furnace through the ceramic tube, a tube fixing sleeve which is coupled to a second end of the ceramic tube and through which a portion of the roll shaft is inserted, and a tension generating unit which interlocks with the roll shaft and the tube fixing sleeve and supplies a tensile force for stretching the roll shaft in a longitudinal direction. Accordingly, thermal deformation like creep buy which the roll shaft is bent down is minimized, and a line speed of the strip sheet can be increased by high-speed rotation of the hearth roll.