Do I need a belt furnace for BBQ?--3 Reasons Not to Use a Belt Furnace

The yummy picture was taken last Friday. My colleagues and I cooked BBQ lunch together. Though we deal with belt furnace everyday, we used two batch ovens. Our reason is a belt furnace does not have a sauce dispenser inside!

Unlike BBQ, more and more manufactures are changing from batch production to continuous production. In furnace application industry, this corresponds to changing from batch furnaces to belt furnaces. Though this is the trend, there are reasons not to do so.

1. A belt furnace is expensive

Good point. But you can increase productivity and save labor cost by implementing continuous production.

2. A belt furnace takes up much space

That is true. Some big belt furnace can be over 100ft long. Not every facility can hold such a long tool. One can use multiple shorter furnaces instead of a big one---each furnace runs at lower belt speed and smaller productivity, but adding up contributions of each furnace will get the expected productivity. Multiple smaller furnaces also improves redundancy—even one of the furnaces needs maintenance, other furnaces can keep the production going on.

3. My product is so heavy that the belt loading capacity is exceeded.

Very practical question. Though we can use reinforced belt with loading capacity over 25 lb/ft2, some products are much heavier. Pusher kiln may be a good option for continues production for super heavy products.

What is your reason to say "Yes" or "No" to continuous production in heat treatment process? How do you like the idea of a BBQ belt furnace?

Interested in a belt furnace, see more at http://www.beltfurnaces.com/

More Hydrogen, Less Oxidization?

One of our atmosphere furnace users recently consulted us regarding the surface brightness of the SS products. The user found the SS product surface had oxidization and then increased H2 flow rate expecting to solve the oxidization, but turned out the oxidization issue was not getting better. It is a little confusing. “More H2, less oxidization”, should not it be true?

H2 is a common reducing atmosphere. It has been used in applications like annealing, brazing and etc. According to our experience, H2 plays an important role in achieving bright surface finish for metals like SS, silver and etc. In brazing, H2 has the effect to improve the wettability by removing the oxidization surface of the melting filler material.

However, it is not always true that more H2 equals less oxidization. Here is why.

•  H2 source can contain impurities like water, oxygen.
•   H2 can react with oxidizations on the metal belt surface and produce H2O. Then the H2O can react with the SS product in the furnace, causing SS oxidization. In this case, H2 acts like a carrier that transfer the oxygen element from metal belt oxidization layer to the SS product.

Knowing why more H2 may not be beneficial, what can we do to eliminate product oxidization? Here is our suggestions.

• Choose high purity gas. Dew point of the gas needs to be below -50C for SS bright surface finish. When necessary, use gas purifier before connecting the gas to the furnace
• Adjust flow rate of N2 to help lower down the O2 level in the furnace chamber. For gas cost and safety concerns, it is recommended to choose N2 as the major gas to control O2 level.
•   Maintain clean operation of the furnace belt. Using in-line ultrasonic belt cleaner is a good option. 

After several trials, our furnace user was happy to get the bright surface finish.

Have you encountered oxidization issues when using a belt furnace? How do you solve it? Welcome sharing your ideas with me  song@torreyhillstech.com

More about furnaces please check http://www.beltfurnaces.com/

Influence of belt furnace on engine valve heat treatment

http://www.beltfurnaces.com/doc/Engine_Valve_white_paper.pdf

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.