The principle advantages of induction edge hardening over traditional methods such as flame hardening are as follows:
- Precise control over the hearted zone leading to reduced distortion.
- Significantly reduced energy costs due to the efficiency of the induction heating process.
- Health and safety due to the removal of naked flames and pressurised gas storage systems from the process.
- Easily repeated results and de-skilled setting and operating procedures.
- Better quality product due to reduced scaling and better quality control due to the predictable nature of the process.
- Reduced scrap due to reliability and repeatability of process.
There are two principle approaches employed in edge hardening systems:
- Traverse Systems - The traverse system is used to pass the edge of the component through a short coil at a constant rate. Following the coil is the quench gallery which sprays quenchant onto the heated edge. This approach is typically used for long straight components such as lawn mower bottom blades, paper knives, leather knives, etc. the system can be configured in the vertical plane or the horizontal plane and either the component or the coil and quench can be moved.
- Single Shot - The method of quenching will be dictated by the hardness pattern. It will normally feature a spray of some kind but can in some cases simply be a bulk tank into which the component is dropped or placed once heated. Quench mediums are typically water based and often feature polymer additives to either accelerate of retard the quenching effect.
All edge hardening systems feature the same principle elements as follows:
- An Induction Power Unit - The power and frequency of this unit is selected based on a variety of parameters including throughput, component thickness and the desired hardness pattern.
- A Mechanical Handling System - The type of handling system will be dictated by the components to be processed, the throughput required and customer preferences and requirements.
- Quench System - The method of quenching will be dictated by the hardness pattern. It will normally feature a spray of some kind but can in some cases simply be a bulk tank into which the component is dropped or placed once heated. Quench mediums are typically water based and often feature polymer additives to either accelerate of retard the quenching effect.
- Cooling System - The cooling system will normally be a split type where the cooling water for the generator is on one circuit and the quench is cooled on a separate circuit. Typically air blast coolers, refrigeration chillers and water to water cooler are utilised subject to climatic conditions and local requirements.
Induction Edge Hardening - Case Study Traverse System
Application - Lawn Mower Bottom Blade.
Component Details - 3mm thick 300mm to 450mm in length.
Process Requirement - Harden one edge to a depth of 10mm in 30 seconds.
Induction Equipment - UT 111 200 12 Kw 200KHz Ultra-Tec power unit.
Feed System - IHG 11 HLMBH 22 Horizontal traversing conveyor complete with 30 minute capacity auto load magazine.
The system features a specially designed and tooled conveyor with a variable speed drive. Built into and forming the base is the quench collection system and al necessary pumps and filters.
Input to the system was via a stripper type magazine with 30 minute capacity. The system featured PLC control with a recipe based setting system utilising a Mitsubishi HMI with error trapping on all critical parameters. Work coils and quench gallery IWC 12 /12 split air-blast cooler.
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