1. Preface

Induction heattreatment has advantages of fast heating speed , energy saving, no oxidationdecarburization, non-pollution, high efficiency, etc. which are widely approvedby people in heat treatment field. So in recent decade it developed quickly.And such actual demand stimulated development of domestic induction heattreatment equipment. Taking “China’s FAW” in China as an example, it has morethan 100 set of induction heat treatment equipment which 50% appeared in recentdecade with almost 100% SCR MF and IGBT SF generators. Now in”FAW”52% ofhardening the parts of medium-duty truck with weight of 291.3kg useinduction heat treatment and this means induction heat treatment occupies halfapplication of heat treatment.

2. The situation ofearly induction heat treatment equipment in China

In the beginning of50’s with the construction of “FAW” and ”YTO” a batch of HF/MF heattreatment(20 sets in total) equipment were imported from the Soviet Union andalso a few similar equipment Czech. From then on Chinese knew induction heattreatment. In the end of 50’s some Chinese manufacturers developed HF and MFgenerators like Tianjin radio equipment factory and Beijing radio equipmentfactory developed electronic tube HF equipment, Xiangtan Electrical Machinery Factoryand Jinzhou Electrical Machinery Factory developed mechanical MF generator; Inthe middle of 60’s Tianjin industrial school of Labor bureau(renamed Tianjinthe ninth machine tool factory) started to make simple quenching machine who opened the ancient river of R&Dand manufacture induction heat treatment equipment in China.

3.The currentsituation and development of induction heat treatment generator in China

MF/HF generator isthe key device of induction heat treatment. At present in Chinese heattreatment industry except the oldest spark gap type HF generator the othergenerators are in use. Some of mechanical MF generator and tube generator arebackward but still is mainly applied in some regions or workshops. This articlewill introduce the advantage and disadvantage of all kinds of generators.

3.1.Mechanical MFgenerator

MechanicalMF generator was developed around 1920. At that time US BACHARACH INC firstlyapplied it to crankshaft neck quenching and it’s the first MF generator used inindustrial production. Its greatest advantage is durable and barely needsmaintainance except changing bearing every few years. And its disadvantage isfrequency is fixed and use range is limited, large occupation area , noisy,  high waterconsumption, low electrical efficiency(around 70%~75%).

3.2. Tube HFgenerator

Around 1930 Tube HFgenerator appeared. Its main advantage is easy tuning and use, despite highfrequency (later it had super frequency type) it has wide application range.His main disadvantage is low electrical efficiency (around 50%), high workingvoltage, poor security and for stand-alone device it has small power.

3.3 Thyristor MFgenerator

Thyristor MFgenerator is also called SCR MF generator which was successfully developed andused in large doses in 1970. In China it as successfully developed and used in80’s. In 90’s such generator is mature and some of its technical index hasreached international advanced level. The SCR MF generator for induction quenchingnormally has frequency 2.5~8kHZ . Compared to mechanical MF generator it has alot of advantages like: small size, less weight,;non-mechanical movement, lessnoise, easy to start and stop; available to automatically adjust and followfrequency according to part’s requirement to keep equipment running underhighest power factor; easy to install, special foundation not required; r asingle generator’s power can run at 1000kW with 90% electrical efficiency.

3.4. Transistor SF/HF generators

Transistor SF/ HFgenerators normally mean: (1)IGBT SF generator, MOSFET HF generator and SIT HFgenerator. Transistor SF/ HF generators were successfully developed in mid andlate of 70’s. In China they are developed successfully in 90’s. At present IGBTgenerator is mature and those generators made by Heatking has reachedinternational advanced level: frequency 8~50kHZ with 500kW power, frequency 50~100kHZwith 200kW power. Domestic MOSFET generator with 200kHZ frequency and 100kWpower. Dozens of SIT HF generators have been made in China but they graduallyretired due to short of spare parts. Because of disadvantage of small poweroversea manufacturers have stopped develop and make SIT generator. Theadvantage of transistor generator and of SCR generator is similar or close andthey can have hundreds of kHZ frequency.

4. Technical progressof hardening machine

For induction heattreatment hardening machine is important. In recent decade large motor companyand auto parts workshop has been purchasing reliable and advanced hardeningmachine which provided an important business opportunity of technologyimprovement for induction heat treatment equipment enterprises in China. Afterbig effort hardening machine had great progress and a large number of hardeningmachines like induction hardening machines for crankshaft, camshaft, axleshaft, knuckle, torsion bar, shock absorber bar made by Heatking reached theinternational advanced level. And the universal induction hardening machine of generalizedmanufacturers also had significant improvements in precision control and flexibility.The detailed technology progress of induction hardening machine in following:

4.1.Drive system

The drive system ofinduction hardening machine uses mechanical drive which includes a lot ofmodern ball screws and linear guides.

 4.2. Speed andlocation control

Main drive uses servoNC which can make stable travelling speed, correct location, high repeatabilityand realize real-time speed change; work-piece rotation uses frequencyconversion adjustment and can choose different RPM. The servo NC hassimple structure and reliable operation.

4.3. Sequence controland display

A lot ofNC devices are used to realize machine action sequence control with highcontrol precision ,to storage processing parameters of hundreds of parts and torecord the number of processed parts. Also these NC devices can monitorreal-time running of equipment and be online with alarm device to stopequipment in case of breakdown. The data restored in NC device can be pulled upand displayed. Some simple hardening machines also use PLC control to realize intellectualizationof low level.

4.4.Rust, water andsteam preventing measure for hardening machine

Rust-preventingmeasure for hardening machine

For machine the existenceof water and steam is inevitable which can lead to unavoidable rusting forwater tank and moving parts of machine. And rusty parts is the fault source ofmachine. The rust-preventing measure is using stainless material like:stainless steel for water tank, ball screw, apex and its sleeve use stainlesssteel, using material 1Cr18Ni9Ti 、2Cr13 or 3Cr13 or brass.

Water- preventingmeasure for hardening machine

It’s normal to havewater splash during hardening machine running. However splash of quenchant notonly affects civilized production but also worker’s operation. The mainprevention measure is to install protection door which is made of stainlesssteel plate, PMMA, brass guide and nylon bearing. For machine with hardeningtransformer which moves up and down should put stainless steel water-proofcurtain. During machine running steam appears and also lampblack while part’swashing not sufficient. In some foreign-funded enterprises plant is airtightand it’s not allowed to distribute steam and lampblack. In that case should addcover above fore-trench of machine and waste condensator to condense steam andlampblack into liquid to discharge or add oil mist collector.

4.5. 3D fineregulating device and inductor quick-change-connection technology of hardeningtransformer

Hardening transformeris placed in 3D movable platform and it can moves up and down, left and right,back and forth 50mm to meet adjustment requirement of hardening location.Inductor quick-change technology includes 2 parts: (1) quick-change-connection devicebetween inductor and hardening transformer and its fastening should be fast,reliable and safety for large electric current; (2) quick connection ofwater-cooling pipe and quenchant pipe for inductor, water-cooling pipe andquenchant pipe are connected by quick-change adapter to realize quick andreliable operation. Now in China brass adapters are used.

5. Energy monitoringdevice

Energy monitoringdevice is not a necessary part of induction heat treatment equipment. Butnormally famous oversea induction heating equipment manufacturers use thisdevice. It can guarantee the consistency of heating quality andhardening quality for part under bad voltage. Heatking already successfullydeveloped energy monitor technology and used it widely. In a large auto axlefactory with big network voltage fluctuation we did following experiment: at9:00 AM the voltage was 350 V, 380 V at 4:00 PM,400 V at 10:00 PM, 440 V at 2PM, in above 4 periods we picked up randomly 1 PCS of axle separately and didsampling on 3 specific locations(spline, neck and flange corner) to check thesurface hardness and depth case. It turned out that the testing result oncorresponding locations of those 4 axles is basically the same. The workingprinciple of energy monitor is : Via process test to determine how much energydemand (kWs) of each type of work-piece from beginning to hardening temperatureand to set this energy value, the heating time will be prolonged automaticallyupon low voltage and be shortened upon high voltage to keep constant heatingenergy. When hardening energy reaches set point the machine will stop heatingautomatically to ensure the consistency of heating quality andhardening quality.

6.The end

Since the reform and opening up, especiallyin nearly a decade China’s induction heat treatment equipment technology hadgreat progress. And Heatking’s product with better cost performance alreadyreached or is closed to the international advanced level of similar products.We can only say that domestic induction heat treatment equipment almost meetrequirement of our induction heat treatment industry. We are surprised to findthat private enterprise is main force of induction heat treatment (equipment)technology’s development in China. Heatking has already successfully developeda serial key technology like thyristor MF generator, IGBT SF generator, MOSFETHF generator, crankshaft fillet quenching, auto CV joint quenching, corrugatorroll quenching, etc. technology. We have reason to believe that relying on ourown wisdom we can help to make China’s induction heat treatment technologyreach advanced international level.