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.
- Accurate control of the depth of hardness and the hardness achieved.
- 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.
All progressive shaft 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. Typically these units will be vertical or horizontal and will feature rotation to ensure even heating around the periphery of the component.
The traverse mechanism will move either the coil and quench ring or the component itself at a controlled speed. Traverse speed will be variable to allow for shoulders and diameter changes and to help control the depth of hardness. Positional control will feature a shaft encoder and PLC with a HMI panel. Machine setting is recipe based and password protected to allow settings to be made and stored for a variety of parts.
- 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.
There are two principle approaches employed in shaft hardening systems:
- Vertical Traverse Systems - The vertical traverse system is used to pass the shaft through a single turn coil at a constant rate. Following the coil is the quench gallery which sprays quenchant onto the heated edge. This approach is often used for components with varying diameters or components with flanges such as axle shafts, drive shafts, turbo charger shafts, rolling mill rolls etc. The equipment can be configured as single or twin spindle dependant on the components to be processed and can be designed to handle any length of shaft. Using this approach either the component or the coil and quench can be moved. Components are loaded between centres or into specially designed cups and are rotated during processing to ensure even diametric heating and quenching. Positional control is normally by an encoder based system.
- Horizontal Traverse system - The horizontal traverse system can be used where the geometry of the component allows the parts to lay flat between the rollers of the machine. The system is often used for high volume production situations as the feed can easily be automated using a hopper or bar feed type arrangement it is also a very effective approach where long small diameter parts are to be processed. Components are supported on hardened rollers during processing, the rollers feature rotation to spin the component to ensure even diametric heating and quenching. Positional control is normally provided by a pusher mechanism with an encoder based system.
Induction Shaft Hardening - Case Study Horizontal Traverse system
Application - Power Tool Drive Shafts.
Component Details - Various diameter and length splined shafts. 10mm to 12 mm diameter 150mm to 250mm long.
Process Requirement - Harden 1 splined area to a depth of 1mm below root.
Induction Equipment - UT 111 200 30 kW 200kHz Ultra-Tec power unit.
Feed System - IHG11/2 Twin track horizontal pin feeder with low level hopper load.
The system features a specially designed twin track roller system to provide component rotation. Positional control of the pusher mechanism is via an encoder based system with operator interface via a HMI panel.
The control system utilises a menu based system to allow variable parameters including heat on, heat off, power and traverse speed to be set and stored under part number for rapid retrieval. Built into and forming the base is the quench collection system and al necessary pumps and filters.
Input to the system was via a hopper 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 30 /30 split air-blast cooler.
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