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.

Torrey Hills Technologies Hengli brand furnace win silver award!

(SAN DIEGO, CA, Aug. 5, 2014)   – Torrey Hills Technologies, LLC (THT) and Hengli Eletek, Co. Ltd  were jointly named as a Silver winner in Most Innovative Product of the Year in the Enterprise category of Best in Biz Awards 2014 International, for inventing a volatile organic compound (VOC) removal / thermal oxidizing system. Best in Biz Awards are the only independent business awards program judged by members of the press and industry analysts. Other winners of this prestigious award include Toshiba, Dell, BlackBerry, Epson, Lenovo, and more. For a full list of gold, silver and bronze winners in Best in Biz Awards 2014 International, visit: http://intl.bestinbizawards.com/intl-2014-winners.

 

Concerned about the negative impacts of modern manufacturing on environment, the Hengli/THT team designed a ground-breaking VOC removal system for their model AST belt furnace. Connected to the furnace exhaust, the VOC removal system eliminates VOC emissions before reaching outside air. Widely used in electronics manufacturing as solvents that are dried on a belt dryer and exhausted into the air, VOCs are one of the top causes for smog. The electronics manufacturing process contributes a significant portion of VOCs to air pollution, yet THT and Hengli are the first to achieve a green solution that allows VOCs to be oxidized into CO2 before being released into the ambient air.

“It was a pleasure to collaborate with Hengli on this important solution," said Ken Kuang, President and CEO of THT. “We are honored to be named as Silver winner for the 2014 Best in Biz Awards, and we are confident about the positive impact of this technology on environment.”

Torrey Hills Technologies, LLC ( http://www.torreyhillstech.com , http://www.beltfurnaces.com ) is a leader in developing and delivering quality yet affordable equipment and supplies for multiple industries. Since its establishment, the company has expanded its business from microelectronics packaging components to large-scale furnace equipment for semiconductor packaging, circuit board assembly, advanced materials processing and solar cell manufacturing. Headquartered in San Diego, Calif., the company now has customers located around the world in North America, South America, Europe, Asia, and Australia.

Hengli Eletek Co., Ltd. was founded in 1992 with the mission to become a leading supplier of thermal processing solutions to the global electronics and materials markets. Hengli products have been highly appreciated by customers from more than 20 countries located in North America, South America, Europe, Asia, and Australia.

Best in Biz Awards recognizes top companies, teams, executives and products for their business success as judged by established members of the press and industry analysts. Best in Biz Awards honors are conferred in three separate programs: North America, EMEA, and International. For more information, please visit the official web site: http://www.bestinbizawards.com.

Manufacturing Solar Cells - Assembly & Packaging

By Ken Kuang, Joyce Zhang and Bill Ishii, Torrey Hills Technologies, LLC, San Diego, CA 

The trend in packaging has shown a serious shift: attendance at assembly and packaging conferences has been dwindling over the past few years whereas solar power shows have increased in popularity. More and more electronics assembly and packaging companies are appearing at solar expos. There are significant opportunities for electronics engineers in the rapidly expanding solar business.

Solar cells are derived from the 1839 discovery of the photovoltaic effect by French physicist A. E. Becquerel. However, it was not until 1883 that the first solar cell was built by Charles Fritts, who coated the semiconductor selenium with an extremely thin layer of gold to form the junctions. The device was only about 1 percent efficient. A Russian physicist named Aleksandr Stoletov then built the first solar cell based on the outer photoelectric effect (discovered by Heinrich Hertz earlier in 1887). Also, Albert Einstein explained the photoelectric effect in 1905 for which he received the Nobel Prize in Physics in 1921. Finally, Russell Ohl, who worked on the series of advances that would lead to the transistor, developed and patented the junction semiconductor solar cell in 1946. 

Modern solar cells can be described as the co-existence of three different generations: crystalline silicon, thin film, and  dye. Along with the development of solar cells, there has also been a parallel development of solar cell manufacturing technologies. Assembly and packaging engineers have played a significant role in developing these manufacturing techniques, creating incredible potentials in every generation of the solar business.


First Generation

Elemental or crystalline silicon is the principal component of most semiconductor devices, most importantly integrated circuits or microchips. Silicon's ability to remain a semiconductor at higher temperatures has made it a highly attractive raw material for solar panels. Silicon's abundance, however, does not ease the challenges of harvesting and processing it into a usable material for microchips and silicon panels. At least three standard manufacturing processes mean that there are technical opportunities for assembly and packaging engineers.

1. Phosphorus diffusion. There are two main layers that are essential to the solar cell's function. One is a p-type layer, which means that the wafers are boron doped, and an n-type layer created by introducing phosphorus. The silicon wafer usually already starts off by already being doped with boron. In order to form the n-type layer, phosphorus has to be introduced to the wafer at high temperatures of around 870°C for 15-30 minutes in order for it to penetrate the wafer. The excess n-type material is then chemically removed.

These diffusion processes are usually performed through the use of a batch tube furnace or an in-line continuous furnace. According to BTU, detailed cost of ownership models have shown that in-line diffusion can deliver per wafer costs of as low as one third the cost of a batch diffusion furnace. The basic furnace construction and process are very similar to the process steps used by packaging engineers.

2. Silicon wafer metallization.Electrical contacts are formed through squeezing a metal paste through mesh screens to create a metal grid. This metal paste (usually Ag or Al) needs to be dried so that subsequent layers can be screen-printed using the same method. As a last step, the wafer is heated in a continuous firing furnace at temperatures ranging from 780 to 900°C. This completes the metallization process, removes solvent and binder, and forms electrical contacts. Metallization is the most critical step. The challenge of reducing wafer thickness for higher efficiency has created stringent requirements for both the equipment and the process itself.

3. Solar module assembly. Solar module assembly usually involves soldering cells together to produce a 36-cell string (or longer) and laminating it between toughened glass on the top and a polymeric backing sheet on the bottom. Frames are usually applied to allow for mounting in the field, or the laminates may be separately integrated into a mounting system for a specific application such as integration into a building. The basic process is very similar to the SMT process assembly that packaging engineers are already familiar with, albeit on a larger scale. The packaging industry's lean manufacturing methodology can be applied directly to solar module assembly.

Second Generation 

Second generation solar cell, also known as thin-film solar cell (TFSC) or thin-film photovoltaic cell (TFPV), is made by depositing one or more thin layers (thin films) of photovoltaic material on a substrate. The most advanced second-generation thin film materials in use today are amorphous silicon (aSi), cadmium telluride (CdTe), and copper indium gallium selenide (CIGS). The thickness range of such a layer is wide and varies from a few nanometers to tens of micrometers. Is thin-film now the way to go? There are certainly many good reasons for moving to thin films for the solar cell manufacturing process.

1. Thin film deposition. Copper indium gallium selenide (CIGS) is used for the thin film active layers in CIGS solar cells, commonly formed using sputter deposition. During this vacuum-based process, a plasma of electrons and ions is created from inert argon gas. These ions dislodge atoms from the surface of a crystalline material which is then deposited to form an extremely thin coating on a substrate. Depositing thin film by sputtering is the same process used in semiconductor manufacture and in packaging.

2. Thin film annealing. After sputtering, the thin film needs to be annealed to achieve optimum results. It is also possible to inject additional chemicals during the annealing process. An annealing furnace is similar to the brazing furnace commonly used in packaging industries. The muffle is typically made of SUS 316L material to ensure good corrosion resistance for the thin film solar panel's corrosive environment. A typical belt furnace can anneal up to 600 x 1200mm (23.6 x 47.2-in.) thin film solar panels after thin film deposition.

3. Metallization. Like its first generation cousin, the manufacture of thin film solar cells need Al or Ag screen printing metallization, originally invented for the thick film process. Such metallization pastes or inks can be used on both rigid (glass, silicon) and flexible (polyimide, polyester, stainless steel) substrates. The metallization can be accomplished through either thermal curing or firing.

The electrochemical dye solar cell was invented in 1988 by Professor Graetzel of Lausanne Polytechnique, in Switzerland. The "Graetzel" dye cell uses dye molecules adsorbed in nanocrystalline oxide semiconductors, such as TiO_2, to collect sunlight. Dye cells employ relatively inexpensive materials such as glass, Titania powder, and carbon powder.

Graetzel's cell is composed of a porous layer of titanium dioxide nanoparticles, covered with a molecular dye that absorbs sunlight, like the chlorophyll does in green leaves. The titanium dioxide is immersed in an electrolyte solution, above which is a platinum-based catalyst. As in a conventional alkaline battery, an anode (the titanium dioxide) and a cathode (the platinum) are placed on either side of a liquid conductor (the electrolyte). Sunlight passes through the cathode and the conductor, and then withdraws electrons from the anode, at the bottom of the cell. These electrons travel through a wire from the anode to the cathode, creating an electrical current.

 
Similar to Semiconductors

The basic dye cell manufacturing steps also resemble the approaches taken by the semiconductor and packaging industry. For example, a screen printer is typically used to apply titania and other layers to the Transparent Conductive Optical (TCG or TCO) glass. Nanocrystalline TiO₂ pastes are screen printed onto the TCO glass, then dried and fired in a continuous belt furnace. The sintering process allows the titanium dioxide nanocrystals to partially "melt" together, in order to ensure electrical contact and mechanical adhesion on the glass. All these furnaces are typically modified from standard thick film furnaces.

After dye staining and anode side application of proprietary current collectors, platinum catalyst is obtained by using the Pt-Catalyst T/SP product which can either be squeegee printed or screen-printed using a polyester mesh of 90. The solar cell needs to be dried at 100°C for 10 minutes before being fired at 400°C for 30 minutes. During the assembly, sealing and filling processes, TCO glass with the completed Titania layer is mated to the cathode current collector, protective glass plate, sealed, busbar attached to the cell and then the cell is filled with electrolyte. Custom designed, fully automated and efficient cell assembly, sealing and electrolyte filling machine sets are required for these production steps.

At one time, Torrey Hills Technologies sold in-line continuous furnaces mostly for thick film and brazing applications. Several years ago, in response to the growing demands of the solar manufacturing industry, the company's engineers reinvented the original technology and adjusted it to different types of solar cell processing. A critical step in solar cell manufacturing is metallization through screen printing. By changing the specifications of thick film drying and firing furnaces, the company stepped comfortably into the solar cell market.

Solar technologies have created compelling technical challenges and business opportunities for assembly and packaging engineers. The traditional thick film, thermal treatment and assembly techniques play key roles in solar cell manufacturing. Many skill sets possessed by electronics engineers can be easily reinvented and applied to the solar cell industry. 

 Contact: Torrey Hills Technologies, LLC

6370 Lusk Blvd., Suite F111, San Diego, CA 92121 

858-558-6666 fax: 858-630-3383

 E-mail: info@torreyhillstech.com 

Web: http://www.torreyhillstech.com