Influence of belt furnace on engine valve heat treatment
What is an engine valve?Fig 1 shows typical engine valves. Engine valves are essential parts for engine functioning. They
are located in the cylinder head and can be classified into intake valves and exhaust valves. The
intake valves bring in air/fuel into chamber for combustion and the exhaust valves let exhaust
out after burning. The open and close of valves are decided by the cylinder piston positions. A
detailed explanation by Marshall Brain on how engine works can be found at
http://auto.howstuffworks.com/engine4.htm.
Fig 1. Typical engine valves (Courtesy of online picture http://www.plxsport.com/atv-partsvalvetrain-wiseco-titanium-intake-valve-suzuki-ltr-450?att_id=0)
Engine valves heat treatment description
The working conditions of engine valves are severe. Doug Kaufman states that intake valves
typically run at the range of 800F—1000F (427C-538C) while exhaust valves typically run at
1200F—1450F (649C-788C), due to the temperature difference of intake gas and exhaust.
Besides high temperature, valve also experiences cyclic loading. A valve can open and close
dozens of times per second.
Because of the high working temperature and strength required in such conditions, heat
resistant steels are often used. Besides proper material selection, proper heat treatment is
essential in manufacturing high performance engine valves. It is vital to create the desired
properties like strength, wear resistance, toughness, fatigue strength, hardness and
microstructure.
Normal heat treating methods include annealing, normalizing, tempering and hardening. To
decide a specific heat treatment process, alloy phase diagram (Fig. 2) is the fundamental tool.
Fig 2.Fe-C phase diagram (Courtesy of online source http://www.calphad.com/iron-carbon.html)
A typical heat treating process for VAZ PASSENGER CARS engine valves was published in.
Metallovedenie i Termicheskaya Obrabotka Metallov, No. 10, pp. 6- 9, 1996. Several major
steps in the heat treatment process for inlet valves includes:
1) Preliminary heat treatment, annealing to around 700C for 3—4 hours to obtain
Spheroidized pearlite with certain hardness.
2) Stabilizing annealing. Hold 2-3 hours at 600 - 620°C to release stress and eliminate
warping issues that might occurred in other process
For outlet valves the heat treatment process is a little different because of the quality
requirement difference between inlet and outlet valves.
HSK fast firing furnace for engine valve heat treatment
The HSK series fast fire furnace heats from ambient to 1050C in approximately 40 minutes and is
designed to sustain continuous on/off heating and cooling cycles resulting from alternating
periods of production and non-use. It features an ultra-clean low-mass refractory heating
chamber equipped with FEC (Fully Enclosed Coil) heaters formed into ceramic insulation panels.
With the use of advanced insulation materials, lower thermal capacity enables the furnace to
warm up and cool down very quickly and lose less heat to the environment.
To prevent valves from falling off the belt, a hearth plate with walls can be incorporated within the
furnace. The belt would travel through the furnace on a metal hearth plate with side walls, which would
prevent products from falling off the belt.
Appendix I shows the brief technical details of a HSK fast firing furnace.
APPENDIX I
Technical Specification for Model HSK Series Conveyor Furnace
Main Characteristics
Specification HSK2505-0611
Rated Temperature 1,050 deg. C
Belt Width 250mm/10"
Above Belt Clearance 50mm/2.0"
Specification HSK2505-0611
Heating Length 2700 mm/106.3"
Cooling Length 1240 mm/48.8"
Control Zones 6
Conveyor Speed 30-200mm(1.2"-8")/min
Overall System Width 1200 mm/47.2"
Overall System Length 6905 mm/272"
Overall System Height 1350mm/53"
Typical Temp. Uniformity +/-3 deg. C
Net Weight 1,200kg
Power
AC 220-480V, 3 phase, 5 wire, 50/60 Hz, 42 kW
Power draw at normal operating conditions: <15kw p="">
References
[1]. Kiyoshi FUNATANI. HEAT TREATMENT OF AUTOMOTIVE COMPONENTS: CURRENT
STATUS AND FUTURE TRENDS. Trans. Indian Inst. Met.Vol.57, No. 4, August 2004, pp.
381-396
[2]. Doug Kaufman. Understanding Valve Design and Alloys
[3]. IIT BOMBAY. Design for heat treatment, online presentation
[4]. A. N. Cherdantsev, A. N. Makar'ev, V. P. Akhant'ev, I. N. Kaplina. Technology for heat
treatment of engine valves of VAZ passenger cars. Metallovedenie i Termicheskaya
Obrabotka Metallov, No. 10, pp. 6- 9, 1996.
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