Mandrel Bar Seizure Resistance via Pre-Rolling Scale
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Solution Overview
Problem
Existing mandrel bars face challenges with seizure during rolling of high-alloy steel, leading to reduced service life and increased manufacturing costs, as they are prone to friction, roughening, and cracking, especially when dealing with high-alloy steel like 13% chromium steel.
Innovation Solution
A mandrel bar surface treatment method involving heat treatment to develop a scale on the mandrel bar, followed by rolling ordinary steel with 8% or less chromium for at least 50 passes to prevent metal exposure and enhance seizure resistance, allowing the mandrel bar to effectively roll both high-alloy and ordinary steel without seizures.
Engineering Contradictions & Design Principles
Engineering Contradiction Analysis
1Quantity of substance
If a mandrel bar is used for rolling high-alloy steel, then the demand for high-alloy steel pipes is met, but seizure occurs on the mandrel bar due to high deformation resistance and difficulty in forming oxidized scale
Solution Approach 1:
The mandrel bar is pre-treated by rolling ordinary steel containing 8% or less chromium for at least 50 passes before rolling high-alloy steel. This preliminary action forms a stable oxide scale layer on the mandrel bar surface that prevents seizure during subsequent high-alloy steel rolling operations.
Solution Approach 2:
The invention changes the chemical composition parameter of the steel being rolled as a preprocessing step. By rolling ordinary steel (8% or less chromium) before high-alloy steel, the oxide scale formation conditions are optimized to create a seizure-resistant surface layer on the mandrel bar.
2Ease of operation
If lubricant is applied to the mandrel bar surface during rolling, then lubrication is improved, but seizure cannot be avoided altogether and oscillations occur during rolling
Solution Approach 1:
Instead of using lubricant as the intermediary between mandrel bar and steel, the invention uses an oxide scale layer formed by rolling ordinary steel as the intermediary. This scale layer acts as a more effective mediator that prevents direct metal-to-metal contact and seizure during high-alloy steel rolling.
3Strength
If the mandrel bar surface is polished and quenched and tempered, then hardness is adjusted and scale is developed, but the surface still undergoes harsh sliding friction resulting in roughening and cracking
Solution Approach 1:
The mandrel bar undergoes a preliminary rolling process with ordinary steel before actual production. This preliminary action conditions the surface by forming a protective oxide scale that reduces subsequent friction and prevents roughening and cracking during high-alloy steel rolling, thereby extending service life.
4Quantity of substance
If seizure occurs on the mandrel bar, then rolling of high-alloy steel is achieved, but axial streaking flaws occur on the inner surface of the hollow shell requiring large amounts of time and money to repair
Solution Approach 1:
The invention applies preliminary anti-action by rolling ordinary steel for at least 50 passes before rolling high-alloy steel. This creates a protective oxide scale layer that prevents seizure and the resulting axial streaking flaws, eliminating the need for costly and time-consuming repairs.
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 method significantly improves seizure resistance and extends the service life of the mandrel bar, enabling durable rolling of high-alloy steel, such as 13% chromium steel, while reducing tool replacement needs and manufacturing costs.
Implementation Method 1
subjecting a heat treatment to develop a scale on the mandrel bar
Implementation Method 2
the mandrel bar undergoes harsh sliding friction against the inner surface of the shell
Data Source
AI summary
A method for surface treating a mandrel bar used for hot rolling of high-alloy seamless steel pipe is provided. The method includes heat treating the mandrel bar to develop a scale, and after heat treatment, rolling ordinary steel comprising 8% or less of chromium for at least 50 passes. This achieves a mandrel bar for rolling high-alloy steel possessing both durability and superior resistance to seizure.