advancements in microwave heating technologyfast volumetric heating. dennis tool has fully...

an's desire to use andmanipulate materials hasdriven the need for indus-trial heating methods. In

the Iron Age, fire was used to melt, shapeand temper metals, and pottery was devel-oped for smelting, as well as cooking.Wood, peat and coal were the first energysources used to fire pottery, glass and met-als at elevated temperatures. Later, manlearned to harness oil, gas, solar, wind andnuclear power, and also developed electricheating processes including resistance,induction, infrared, and more recently,radio frequency. Each heating technologyoccupies a needed place, but there is stillroom for improvement in speed, efficiency,and delivering energy directly in to theworkpiece. Microwaves already are usedextensively in the mass-production foodindustry. The next step is the use ofmicrowave heating technology for indus-trial processes beyond cooking and drying.

In the late 1930s, the use of radio waveswas perceived as a method to heat noncon-ductive polar materials. The RF heater wasinvented and widely applied in conjunc-tion with dies and pressure to weld seamsin polar plastics. The use of RF technologyeventually expanded into automotive,industrial fabrics, packaging, stationaryproducts, inflatables, medical products andmany other product groups. Radio frequen-cy has certain limitations due to the needfor electrodes, high cavity voltages andcomplex power controls.

In the 1940s, Dr. Percy Spencer atRaytheon Corp. was experimenting with anew device called a magnetron for use inradar applications. Strangely, a chocolatebar in his pocket mysteriously melted dur-

IndustrialHeating.com – January 2005 43

This article provides a glimpse of the many potentially useful applications developed by microwave and materials experts.

Advancements in Microwave HeatingTechnologyReported by Ed Kubel, Editor, Industrial Heating

S p e c i a l F o c u s :

MICROWAVE HEATING

Fig. 1 Schematic (a) and photo (b) of vertical continuous batch furnace for sintering carbidecutting tools using microwaves

a) b

Aluminum-titanium-carbon powders during a self-propagating high-temperature synthesis(SHS) reaction initiated by microwave energy (2.45 GHz, 1,000W applied power). Courtesy ofVirginia Polytechnic Institute.

ing the testing. Dr. Spencer continuedexperimenting by popping corn and thenexploding in egg. Raytheon supported fur-ther research to develop and containmicrowaves generated from magnetrons forindustrial use and domestic cooking wenow enjoy. After 60 years of experimenta-tion, we know the best uses for microwavesin cooking, and accept that microwaves arenot great for every cooking need. A similarlesson is being learned in the industrialheating arena concerning microwave pro-cessing of materials. Industry must havesome understanding of how microwavesheat materials and what the limitations arebefore its potential can be tapped. With thehelp of universities, national laboratoriesand specialists, several companies high-lighted in this article are leading the way.

Commercializing microwave heatingThis article highlights processes available tothe market. The important players includemicrowave and furnace manufacturers, uni-versities, consultants, national laboratoriesand end users. Ceralink Inc. (Troy, N.Y.;www.ceralink.com), plays a unique role inworking to bridge the gaps and promotecommercialization, offering consulting andhands-on R&D as a partner, subcontractoror service. Dr. Holly Shulman, President ofCeralink, says collaboration between equip-ment manufacturers, scientists and industryis required to make the technology accessi-ble and affordable.

Cutting toolsUsing this approach, Dennis Tool Co.(Houston, Tex.) successfully developedand commercialized high -erformance car-

bide mining and drill bits. Company presi-dent Dr. Mahlon Dennis was aware ofresearch at Pennsylvania State Universityin 1995, recognizing that microwave sin-tering of carbide could offer improvedproperties, as well as benefits in processspeed and efficiency. Dennis contributedfunding and commercial direction to thestrong scientific and experimental founda-tion in the group led by Drs. DineshAgrawal and Rustum Roy at Penn State.The work resulted in several patentsincluding a system for microwave firing ina vertical continuous batch that usesprocess heat to preheat the incoming cru-cible load (stoke type heating). The fur-nace design overcomes complications ofheating large batches and offers excellentuniformity, speed and control. A schemat-ic and a photo of a commercial unit areshown in Figs. 1a and 1b.

One of the key decisions by DennisTool for successful commercialization was

to design and sell turnkey systems formicrowave sintering of carbide parts. Bymaking these microwave sintering sys-tems available to carbide and other man-ufacturers, production costs are decreasedand development costs are defrayed.Dennis Tool now uses these systems tomake their own products and they areexploring new products made possible byfast volumetric heating.

Dennis Tool has fully commercializedthe use of microwave sintered carbide forPDC substrates in oilfield drill bits, one ofthe company's primary businesses.Polycrystalline diamond compact (PDC orPCD) are used widely in both earth drillingand industrial machining applications. Thepart is formed by growing the diamondlayer onto a substrate of tungsten carbide athigh pressures and temperatures (106 psiand 2000˚C, or 6,894 MPa and 3630˚F).The abrasion and impact properties aredependent on both the diamond layer and

44 January 2005 – IndustrialHeating.com


MICROWAVE HEATING

Fig. 2 Microstructure of sintered WCo microwave sintered (left) having fine grain structure,overall uniformity and cobalt distribution; and microstructure of conventionally sinteredWCo (right) having several large grains, a rage of grain size and cobalt-rich areas; 1,500

How microwaves are producedThe term “microwave” is used to cover the portion of the electromagnetic

spectrum between 300 MHz and 300 GHz, which corresponds to wave-

lengths ranging from 1 meter to 1 millimeter. In practical terms, there are

certain frequencies that are allowed for industrial use.These are called ISM

(industrial, scientific and medical) frequencies for applications in those

areas as described in the following table.

Frequency, GHz Wavelength, cm

0.915 32.8

2.45 12.2

5.80 5.2

24.12 1.2

Kitchen microwaves operate at 2.45 GHz, while many large industrial sys-

tems use 915 MHz. The overwhelming majority of microwaves are pro-

duced by magnetrons. However, klystrons or gyrotrons are used to pro-

duce ultrahigh-frequency microwaves (millimeter waves).

Low-power magnetrons (2.45 GHz, 800 W) are inexpensive and rugged

devices (<$30 purchased in quantity). High power can be achieved by gang-

ing up low-power magnetrons, but this is cumbersome for large systems

beyond the drying stage. High-power 2.45 GHz magnetrons are available up

to 30 kW, while 915 MHz systems can be purchased in 60, 75 and 100 kW

units. A higher frequency 5.8 GHz magnetron has recently been made avail-

able, but not quite at mass production prices, while ultrahigh frequency 24-

30 GHz klystrons or gyrotrons are much more expensive technologies.

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MICROWAVE HEATING

the carbide substrate.The greatest advantage in using

microwaves in carbide sintering is theimproved microstructure, which translatesto better properties and better perform-ance. Microwave sintering promotes fastdensification, while minimizing graingrowth, diffusion, cobalt pooling and car-bon loss. Additives that minimize graingrowth (but cause mechanical degrada-

tion), such as TiC, TaC and free carbon,are not necessary when using microwavesinstead of conventional heating.

Figure 2 compares microstructures fromDennis Tool parts that were microwavedversus conventionally sintered. Significantimprovements in impact, abrasion and cor-rosion resistance are achieved using con-tinuous microwave sintering. Both hard-ness and fracture toughness increase,

which is attributed to the fine grain sizeand full crack-arresting behavior of unre-acted cobalt. Extensive laboratory and fieldtesting of parts convince Dennis Tool thatit has developed the next generation car-bide mining and drilling bits, with newproducts and applications on the horizon.New applications include cutting tools,dies, anvils, sleeves, bushings, nozzles,bearings and substrates. Some new materi-

How microwaves heatThe short explanation of microwave heating

is that materials heat up through internal fric-

tion when dielectric and magnetic loss

mechanisms respond in a microwave field.

One example is a charged impurity or vacan-

cy in a crystal lattice that switches places in

an alternating field. Friction is produced if the

ion cannot quite keep up with the field, while

no friction is produced if the ion cannot

move at all, or if it moves too easily.

There are many loss mechanisms that can

be activated in real materials related to crys-

tal structure, defects, bonding, surface, grain

boundaries, etc. One might think there

should be an optimum frequency for maxi-

mizing the friction for each mechanism, but

optimum frequency changes with tempera-

ture because certain movements become

easier as the material heats up.This produces

less friction in some cases and more friction

in other cases, such as where a defect was

frozen and couldn't previously contribute.

This behavior causes a peak in the dielectric

loss, which generally shifts to lower frequen-

cies at higher temperature. The selection of

an appropriate microwave frequency is criti-

cal to commercial success of the process.

Figure A shows several important relation-

ships for dielectric heating.

In conventional heating, all heat must be

transferred through the outer surface of the

material to the interior. Microwave heating

offers an important advantage of being able

to place energy directly into the volume of

the workpiece. This requires meeting certain

conditions where microwaves penetrate the

material enough to cause volumetric heat-

ing. Very little heating occurs if microwaves

are reflected or if they penetrate through

the material too easily. Table A shows some

penetration depths calculated from the

dielectric properties.

The high penetration depth of quartz indi-

cates that quartz glass will not couple well

(suscept) or heat at room temperature in a 2.45

GHz microwave field. However, it has been

demonstrated experimentally that quartz

glass couples and heats in the microwave field

at elevated temperatures. Unfortunately,

dielectric data is scarce at microwave frequen-

cies and elevated temperatures. The situation

is further complicated by the continual (some-

times exponential) change in dielectric prop-

erties with temperature, and a strong effect of

impurities, defects and surfaces. Direct

microwave heating tests are very valuable for

early stage feasibility, as well as measurement

of the dielectric properties in the appropriate

frequency and temperature regime.

In general, electrically insulating materials

do not couple or heat well from room tem-

perature at moderate frequencies, but do

couple and heat at higher temperatures or at

higher frequencies. For example, pure alumi-

na is microwave transparent at room temper-

ature using 2.45 GHz microwaves, but couples

from room temperature at 24-30 GHz.

Alumina begins to couple and heat more

effectively at 1000˚C (1830˚F) at 2.45 GHz and

becomes highly suscepting at 1500˚C

(2730˚F), which suggests that hybrid

microwave or millimeter-wave (gyrotron)

heating is required to fire alumina.

Semiconducting materials, such as silicon

carbide, usually heat well from room tempera-

ture at moderate frequencies. Conductive

materials such as metals should reflect

microwaves. However, heating of metals

(especially powder metals) has been observed

experimentally. There are many unanswered

questions concerning microwave heating,

such that theoretical explanations must catch

up with real life observations.

εr=εr’-iεr” Tan δ = εr” iεr”• Complex permittivity ➝ ability to

absorb and store energy

• Permittivity (εr”) ➝ penetration of microwaves

• Loss factor (εr”) ➝ store energy

• Loss tangent (Tan δ) ➝ Convert absorbed energy to HEAT

P = 2π f ε0 εr” E2

P = Volume energy density (W/m2)f = frequency (Hz)ε0 = permittivity of free spaceεr” = dielectric loss factorE = electric field strength (V/m)Power density ➝ heat

D = λ0 εr’1/2

2π εr”

D = penetration depthλ0 = wavelength in vacuumεr’ = permittivityεr” = dielectric loss factorPenetration depth

Fig. A Relationships for dielectricheating

Table A Microwave (2.45 GHz) penetration depths in some materials

Material Temperature, ˚C Penetration depth, cm

Water 25 1.5

Water 95 5.7

Ice 12 1,00

Wood 25 3-350

Hollow glass 25 35

Porcelain 25 56

Epoxy resin 25 4,100

Tefl on 25 9,200

Quartz glass 25 1,600

Note: very high penetration depths occur when the material does not couple or heat well in the micro-wave fi eld. Coupling often increases with temperature resulting in a decrease in penetration depth.


als include carbide diamond composites,functionally graded composites, nanocar-bides and nanocomposites.

Cutting tools are often an early provingground for new materials, since they aresmall, consumable and high-profit items,which usually do not cause catastrophicproblems if they fail. Silicon-nitride cut-ting tools were developed and commercial-ized, reaching a broad market in 2000through Valenite, a U.S. based cutting toolcompany recently bought by Sandvik.Three microwave-sintered grades are avail-able for machining, high speed turning andmilling of cast iron and machining of high-temperature alloys. As with carbides,Valenite claims microwave-sintered siliconnitride products have a finer grainmicrostructure with higher hardness andbetter fracture toughness than convention-ally processed material.

Metals processingA completely different approach of usingmicrowaves for heat is the generation ofon-demand plasma. Dana Corp. (Toledo,Ohio; www.dana.com), a manufacturer ofautomobile components, developed amethod for ultrarapid heat treating, coat-ing and brazing of metals. Dana's AtmoPlassystem uses microwaves to superheat plas-ma that surrounds the parts, and quickly

heats (temperatues up to 2000˚C) by con-duction. The process does not require theuse of a vacuum, as required in conven-tional systems. The cycle time for heattreating and coating is reduced by twothirds, and there is a net savings in bothtime and energy. Dr. Kumar from DanaCorp. explains that this method overcomes

the tendency of metals to arc in themicrowave field, while taking advantagesof the fast heating response of microwaves.

Dana Corp originally developed themicrowave plasma process to address aninternal bottleneck in a brazing step.Highly encouraging results also demon-strated a wider range of application in

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Fig. 3 Gear being processed usingAtomPlas method

Fig. 4 Heated gear using AtomPlas method



MICROWAVE HEATING

coating, sintering and heat treating. Danais currently evaluating its internal scale-up strategy, while looking for partners tocommercialize the AtmoPlas system. Thesystem is currently a batch process thatuses a refractory container or pod, whichholds the metal parts and the plasma(Figs. 3 and 4). The company plans toconvert this to a conveyor belt where podsare cycled and each pod receives individ-ual microwave plasma treatment.

While Dana's system can be used to joinand braze materials having similar expan-sion properties, Technology InternationalInc. (TII, Kingwood, Tex.) developed andcommercialized a microwave process tobraze highly mismatched materials, such aslightweight armor combining silicon car-bide to titanium metal (Fig. 5). Themethod relies on the vastly different cou-pling (heating) characteristics of theceramic and metal in the microwave field.At the brazing temperature, the ceramic isseveral hundred degrees hotter than the

metal, which avoids high expansion andshrinkage of the metal. Bob Radtke of TIIsays the process must be performed quicklyto avoid heat transfer, which requires highpower and good microwave penetrationinto the ceramic. TII is currently workingto increase the brazing speed, which willallow an increase in the size of parts thatcan be brazed. Full production of largeparts will require the design and manufac-ture of specialized equipment.

The idea of using microwaves for melt-ing metal was introduced to the generalpublic through David Reid's web site in thelate 1990s. Reid developed a susceptingcrucible and began melting metal in akitchen microwave using a lost-wax castingmethod. This is a simple and highly effec-tive method for small batches. Accessories,such as crucibles and thermal insulation,can now be purchased from ResearchMicrowave Systems LLC (Alfred, N.Y.;www.thermwave.com) to use for meltingmetal in a kitchen microwave.

Fig. 5 Microwave process can braze dissimi-lar materials such as this part joining sili-con carbide to titanium alloy

Fig. 6 Large suscepting crucible is used atthe Y-12 National Security Complex tomelts a variety of metals using microwaves

Insulation

Crucible

Mold

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On a larger scale, Ed Ripley, at the Y-12National Security Complex (formally partof Oak Ridge National Laboratory; OakRidge, Tenn,; www.y12.doe.gov) was melt-ing hundreds of pounds of titanium, alu-minum, gold and silver using an idea simi-lar to that mentioned above; that is, a largesuscepting crucible in a microwave field(Fig. 6). Although metal is supposed toreflect microwaves, researchers at Y-12 andPenn State claim that the metal actuallybegins to absorb (couple) and heat directlyat approximately 3/4 of the melting tem-perature. Y-12 and Oak Ridge NationalLaboratory have extensive microwave facil-ities and have been developing microwavetechnology for more than 20 years. Ripleyexplains that several processes have justbeen declassified and are available forlicensing agreements. This includes amicrowave eutectic salt bath, with anoption to use a granular suscepting mediathat prevents hydrogen pick up. Oneadvantage of using microwaves is that thesalt bath can be heated quickly on demand,instead of being kept continuously molten.

Two companies have licensed the metal

melting technology from BWXT, Y-12'scommercialization arm. MicrowaveSynergy Inc. and MS Technology, bothlocated in the state of Tennessee are nowcompeting for the lead position in scale-upand commercialization of the Y-12microwave metal melting technology. Bothcompanies may have industrial partners,but are not disclosing specific information.

The technology involves the use ofmicrowave energy, special microwave-sus-ceptible materials and uniquely designedcrucibles and molds to melt and cast metalin a microwave chamber. This was origi-nally developed for melting depleted urani-um, a process that is currently being scaledup at Y-12. According to Stan Morrow ofMicrowave Synergy, microwave technolo-gy for metal melting saves energy, reducescycle time and improves metal quality. KenGivens, Vice President of BusinessDevelopment at MS Technology, adds thatone of the major benefits is versatility.Batches from 1 to hundreds of pounds canbe heated quickly and efficiently. Givenshas plans for international deployment ofthe microwave metal-melting technology

and has already entered into an agreementwith the Technical University of Munich(www.tu.muenchen.de) to install a demon-stration unit in their laboratory. MSTechnology is also designing a larger chambercapable of continuous melting of 2000 lb/hr.

It is not clear where this technology willfit as an industrial process. High-power2.45 GHz magnetrons are used, which arecostly. The size is currently limited by thebatch style design, with casting takingplace within the microwave cavity. Thistechnique may be best suited to castinghigh precision superalloys or titanium,rather than bulk commodity metals.

Another technology originating at Y-12with high commercial potential involvesthe use of microwave energy to diffusepowder metals into solid parts. One exam-ple is the chromizing of steel for surfacehardening. Chrome plating is a toxic, envi-ronmentally unfriendly process, and theFederal government is encouraging alter-natives. The microwave method avoids theuse of toxic chemicals and is achieved atatmospheric pressure and shorter times.This technology was licensed to Tesla, an

Commercial microwave processing has been a “chicken and egg” prob-

lem. Microwave equipment and furnace manufacturers have not seen

the market, making it difficult to justify expenditure in that direction,

while materials manufacturers have not had access to microwave heat-

ing equipment and could not easily find it on the market. Ceralink is

working on both sides of this dilemma, assisting the end users and

equipment manufacturers.

A Microwave Testing Center at Ceralink's new facility at Rensselaer

Technology Park near RPI in Troy, N.Y., provides a facility where companies

can explore the feasibility of using microwaves in their processes.

Ceralink has experience with microwave heating a wide range of materi-

als for melting, brazing, sintering, forming and calcining, as well as lower

temperature processes, such as binder burnout and drying. Commercially

available microwave equipment also is showcased at the center includ-

ing the CPI Autowave, CM Furnaces' Microwave Assist Electric furnace;

Research Microwave Systems' Thermwave; and the Milestone Ethos Plus

(Fig. B). Other equipment can be obtained, and assistance in equipment

set-up and testing is available. Ceralink also assists companies with

design, construction, and purchase of microwave systems.

Ceralink recently signed an agreement with C-Tech Innovations (UK),

formerly part of EA Technologies, to transfer microwave-assist hybrid

technology to furnace manufacturers in North America. Microwave-

assist furnaces are in commercial use in a specialized ceramics applica-

tion and in the mining industry. C-Tech and Ceralink are working to

design retrofits that enable standard and specialized gas and electric

furnaces to accept microwaves.

Ceralink focuses on commercialization, which means they collabo-

rate with all the involved parties from end users to equipment manu-

facturers, to research institutions. Ceralink acts as a central contact

point, benefiting all players and facilitating commercialization. For

example, Ceralink was instrumental in securing $5 million in funding

from DOE for Engelhard Corp. (Iselin, N.J.; www.engelhard.com) by find-

ing an appropriate university partner to develop a microwave process

for reclaiming precious metal catalysts from fuel cells. Another example,

is a company that is pursuing the use of microwaves for a metal melting

process. After demonstrating feasibility at the Microwave Testing

Center, it was suggested to use high power 915 MHz equipment, locat-

ed at Thermex Thermatron

(Louisville, Ky.; www.ther-

mex-thermatron.com).

Ceralink engineers built a

scale-up furnace that fit an

applicator at the Thermex

Thermatron facility and

ran tests on site. The tests

provided necessary data

for full scale up, including

energy and power require-

ments and evaluation of

furnace materials.

Fig. B. Microwave-related research isconducted at Ceralink's MicrowaveTesting Center

Bridging the R&D-commercialization gap



MICROWAVE HEATING

Australian based company, who is current-ly looking for commercialization partners.

Commercializing microwave heatingequipment Table 1 gives an overview of equipmentmanufacturers. Many companies that spe-cialize in microwave power will buildmicrowave heating systems to customerspecifications, and some will assist withdesign and processing issues.

Dennis Tool and Dana Corp both foundthe need to develop microwave systems toachieve their goals of improved parts andproductivity. Dennis Tool has become amicrowave furnace manufacturer, whileDana Corp will license technology to amanufacturing and marketing partner. Inproduction circumstances, the design ofmicrowave equipment must be stimulatedby the end users, and equipment manufac-turers need to be ready to understand andrespond to this new market. On the otherhand, equipment manufacturers canencourage this new microwave market bymaking standard research and productionsystems available.

Doug Parent, Marketing Director of CPI(Communications and Power Industries,Palo Alto, Calif.; www.cpii.com), formerlypart of Varian, recognized the need for ver-satile, microwave systems for process devel-opment and scale up. CPI manufacturersthe Autowave, a system that uses highpower magnetrons, a gas handling system,and PC workstation with Labview (Fig. 7)The Autowave can be fitted with a mag-netron, klystron (18 GHz) or gyrotron (28GHz, known as the Heatwave). Autowavescome in two chamber sizes designed foroptimum field uniformity. The system canbe used for research, scale-up, and/or pro-duction, but it is relatively expensive for

initial feasibility studies. Microwave-trans-parent refractory containers or caskets areused inside the chamber. This arrangementincreases the versatility and cuts down onpower requirements for small-scale tests.

In the past few years, Autowaves havebeen sold to universities and industrial com-panies mainly in Europe and the U.S. At itsMicrowave Testing Center, Ceralink hasbeen testing the Autowave since January2002. Ceralink's president, Dr. Shulman, isenthusiastic about the unit's reliability andwide range of uses, which includes sinteringmetals and ceramics, bending and melting

glass, brazing, chemical reactions, calcina-tion and a many other projects includingnanoceramic fabrication. Shulman says theAutowave is easy to operate and lends itselfto various fixture designs. CPI cannot dis-cuss specifics, but they have also suppliedmicrowave power for drying refractories inthe steel industry, heating chemical reactorsand plasma processing.

Research Microwave Systems (RMS) isaddressing a different need by providingmicrowave accessories such as susceptors,thermal packages and crucibles, as well asthe Thermwave, a low-cost microwave.

Table 1 Microwave Equipment Manufacturers

Microwave Furnace Manufacturers Specialty Web Address

Advanced Manufacturing Technology

Industrial microwave heating consultants www.amtmicrowave.com

CEM Corporation Microwave digestion systems www.cem.com

CM Furnaces Microwave + electric hybrid furnaces www.cmfurnaces.com

Cober-Muegge Microwave vulcanization, equipment www.cobermuegge.com

Communications and Power Industries

Microwave heating systems and equipment www.cpii.com

C-Tech Innovations/ Ceralink Design and build microwave hybrid furnaces and other mw furnaces www.ceralink.com

Dennis Tool Continuous Microwave Sintering Furnace

Ferrite Components, Inc. microwave tempering and cooking systems www.ferriteinc.com

Gerling Applied Engineering Microwave systems and equipment www.2450mhz.com

Harper International Microwave Rotary Calciner www.harperintl.com

Harrop Industries Microwave gas hybrid furnace www.harropusa.com

Industrial Microwave Systems, Inc. (US)

Microwave systems continuous planar, cylindrical www.industrialmicrowave.com

Industrial Microwave Systems, Inc. (UK)

Continuous Microwave Furnaces and equipment www.industrial-microwave-systems.com

Linn High Therm GmbH Dual frequency microwave furnace www.linn.de

Manitou Systems Inc. Microwave and RF plasma systems www.manitousys.com

Microdry Corp. Industrial microwave systems www.microdry.com

Milestone S.R.L. Microwave systems digestion and analysis www.milestonesci.com

Mino Yogyo Co. Ltd. Microwave hybrid furnaces www.mino-ceramic.co.jp

O-I-Corporation Microwave digestion systems www.oico.com

Panasonic Microwave pottery kiln

Personal Chemistry Microwave system organic synthesis, biochemistry www.personalchemistry.com

PSC RF heating systems and microwave equipment www.pscrfheat.com

Puschner-Microwave Power Systems Microwave furnace, dryers, www.pueschner.com

Radatherm Pty Ltd Microwave sintering furnaces www.radatherm.com.au

Research Microwave Systems, LLC Laboratory microwave systems, accessories www.thermwave.com

Takasago Industry Co Microwave batch and microwave elevator kiln www.takasago-inc.co.jp

Thermex-Thermatron, Inc. High power, high frequency MW and RF heaters www.thermex-thermatron.com

Fig. 7 Autowave microwave system thatuses high-power magnetrons, a gas han-dling system and PC workstation


The Thermwave can be used for manytypes of materials, including organic andinorganics, in processes such as drying,chemical reactions, annealing and firing.The Thermwave works with an inexpen-sive controller and shielded thermocouple.RMS is currently developing a unit withmore microwave power and is expandingits line of accessories to include susceptingcrucibles and low-cost insulation packages.The greatest pull for these systems has beenfrom research institutes in Europe, Korea,Malaysia and India.

Bernie Krieger of Cober Electronics Inc.(Norwalk, Conn.) developed a commercialmicrowave process based on the needs of anexternal end user. Cober specializes inmicrowave equipment and has been explor-ing the market for microwave heating formore than 20 years. Cober hit on a winningcombination for vulcanizing rubber, whichuses microwaves and hot air. Krieger had tounderstand the needs of his customer, andovercome the urge to focus only on sellingmicrowave equipment. The need was for acomplete functioning system to vulcanizerubber with better quality and in a shortertime, eliminating messy and costly steps,and have a good payback on the invest-ment. Today, Cober's system has changedthe face of the rubber vulcanizing industry.

Other microwave equipment manufac-turers also work with their customers todesign and build systems for heating.

Thermex Thermatron (Louisville, Ky.)builds sophisticated high power microwaveequipment, and have become adept at test-ing its customers products using equipmentin house. The company is an importantsource of industrial 915-MHz generators.Thermex Thermatron is proud of its engi-neering and stands behind its products, ofreal significance when setting up 100-kWpower units. Ferrite Inc. (Hudson, N.H.)also supplies high-power systems, but hastraditionally focused on the food industry.Now the company is looking toward pro-cessing other materials at higher tempera-ture. CPI is probably the most sophisticatedin precision engineering, which is what ittakes to produce a traveling wave tube likea gyrotron. CPI works with Ceralink andother consultants, effectively combiningmaterials, heating and microwave expertiseto address its customers' needs. GerlingApplied Engineering Inc. (GAE, Modesto,Calif.) is also highly reliable in the supportof its microwave heating products.

In Germany, Linn High Therm GmbH(Eschenfelden) manufactures both labora-tory and industrial microwave heatingequipment including high temperature sys-tems. Linn High Therm has a unique com-bination of furnace expertise, knowledge ofmicrowave systems and background inmaterial science. Mr. Malte Moeller statesthat the new high-temperature processesare one bright future for microwave heat-

ing, but by far not the only one. Almostdaily the company gets inquiries aboutmicrowave drying or heating applicationsthat nobody has ever thought about before.Although many of these processes cannotbe realized due to economic or technologi-cal difficulties, this shows that microwavelow-temperature processes are by far not atthe end of their development potential. Infact, microwave drying is rapidly beingincorporated in to ceramic processes,including filters, substrates, honeycombstructures, industrial insulators, thermalinsulation and whitewares (Fig. 8).

Japan has taken a strong position on thecommercialization of microwave furnaces.Takasago Industry Co. Ltd. (Toki-city,Japan), a large kiln manufacturer is nowmanufacturing and selling microwave assistkilns in Japan. This is a patented C-TechInnovation technology. Examples aregiven in Fig. 9. Mino Yogyo Co. Ltd.(Mizunami, Japan), one of Takasago's com-petitors, is also offering microwave fur-naces (Fig. 10). Both companies have builtlarge scale production kilns, but it is notknown how many have been sold or exact-ly which industries they are targeting.They have demonstrated firing whitewaresand large alumina parts (Fig. 11 and 12),but it is likely they are also looking to otherhigh-technology industries.

Furnace manufacturers in the U.S. havebeen slow in the uptake, but are beginning

Fig. 8 Furnace made by Linn High Therm for microwavedrying of ceramics

Fig. 9 Microwave-assist gas kiln (left) and hybrid microwave roller hearth (right)from Takasago Industry Co. in Japan

Fig. 10 Hybrid microwave gas kiln (left) and pure microwave continuous kiln(right) from Mino Yogyo Co. in Japan



MICROWAVE HEATING

to take an interest in microwave systems.CM Furnaces worked with Ceralink and C-Tech to build a hybrid microwave-assistelectric furnace (Fig. 13). The basic furnaceis one of its standard products in the 1700laboratory series, which was retrofitted witha GAE 2-kW, 2.45-GHz generator. Thistype of furnace and other microwave-assistlaboratory furnaces will be commerciallyavailable soon. Microwave-assist gas kilnswill be available through Harrop Industries(Columbus, Ohio), also using technologyfrom C-Tech Innovations made availableby Ceralink. Any North American furnacecompany can work with Ceralink to devel-op its microwave assist product lines for adesign fee and a small royalty on sales.Harper International (Lancaster, N.Y.) hasteamed up with microwave company Frickeand Malle in Germany to bring microwaveexpertise to their furnace manufacturingcapabilities. Harper has also licensedmicrowave rotary calcine technology and ismaking this commercially available.

The use of large microwave furnaces willprobably have growing pains. The end usermay explore the willingness of the furnacemanufacturer to share some of this devel-opment cost. The furnace manufacturerswill need microwave experts on site to bemost effective in building microwave fur-naces. It is a good idea to find out the qual-ifications of the team designing and build-ing the system. Hiring a knowledgeableconsultant to understand the manufactur-er's microwave furnace capabilities, couldalso save time and money.

Microwave heating expertsThe recently held Fourth World Congresson Microwave and Radio FrequencyApplications (7-12 Nov. 2004) in Austin,Tex., brought together the world's leadingexperts in microwave technology. Thenext major event where one can meet thiscast of researchers will be at the Ampereconference in Modena, Italy 13-15 Sept.2005. Many experts can be found in thecommercial arena (some of these personshave already been discussed), and manyother technical experts can be found atresearch institutions.

An important group resides at BayreuthUniversity (Bayreuth, Germany; www.uni-bayreuth.de) led by Dr. Monica Willert-Porada. This group works closely withindustry and has developed an interestingapproach to support commercialization.Dr. Willert Porada founded in 1997, a non-profit organization, InVerTec, housed atthe Center for Excellence of NewMaterials at Bayreuth. InVerTec's missionis to impart knowledge, coordinate andtransact R&D initiatives in the field ofcombined electrothermal processes andassist with scale-up on the basis of theirown research work.

The current focus of their project workincludes using microwaves for roasting ofores, heat treatment of glass, detoxificationof filter dusts and slags for the metal indus-try and decontamination of asbestos con-taining wastes. According to a spokesper-son for InVerTec: “At our pilot plant sta-tions, most reactor and oven types can be

implemented in microwave heating andcombined heating procedures. In order toprove planning reliability for scale-up, weoffer the possibility to do experiments atthe microwave frequency of 915 MHz andthe common microwave frequency of 2.45GHz.” InVerTec's equipment includes amicrowave rotary kiln, microwave fluidizedbed reactor (Fig. 14), microwave with inertgas, and a 915-MHz single-mode reactor.

Another highly visible group is located atPennsylvania State University (UniversityPark, Pa.; www.psu.edu), in the MaterialsResearch Institute. Led by Drs. DineshAgrawal and Rustum Roy, this group hasbeen a pioneer in the field of microwaveprocess research since 1984. In the 1980s,their focus was on sintering and synthesizingceramics, such as alumina, zirconia, zincoxide, hydroxyapatitie, zeolites, mullite andsilica. In the 1990s the focus shifted todeveloping microwave processes for electro-ceramics such PZT barium titanate, relax-ors, and transparent ceramics.

Innovators at Penn State, like RustumRoy, have never been restrained by con-ventionality, so when the idea ofmicrowave sintering powder metalsoccurred, they proceeded with experimentsand found this a highly effective method.Work in the area of microwave sinteringcarbides caught the attention of MahlonDennis and is now fully commercialized atDennis Tool Co.

Penn State recently hosted a meetingwith over 40 companies to launch theMicrowave Powder Processing Consortium.

Fig. 12 Large alumina parts produced usingmicrowave processing

D=600 mmt=30 mm

Processing time:24 hours (70˚C/H)

Energy comsumption484 kWh/batch

Energy cost$65/batch

(1/6 to gas kiln)

Fig. 11 Microwave-fired tableware

Fig. 13 Hybrid microwave-assist electric fur-nace developed by CM Furnaces, Ceralinkand C-Tech

The theme was to organize a consortiumthat would use Penn State's equipmentand knowledge base to develop mutuallyrelevant microwave technology at ashared cost. Matthew Smith, from PennState's Intellectual Property Office, alsodiscussed the technology transfer andlicensing of patents involving microwaveprocessing from their pool of developedintellectual property.

Since moving from the University ofFlorida in 2001, Dr. David Clark andresearch faculty member Diane Folz havebuilt the Microwave Processing ResearchFacility at Virgina Polytechnic Institute'sDepartment of Materials Science andEngineering (Blacksburg, Va.; www.vt.edu).The laboratory is equipped to performresearch using microwave energy rangingfrom 2-18 GHz with power levels from 200W to 6.4 kW. Current microwave researchfocuses on waste remediation and recy-cling, nanomaterial synthesis, formation ofglass-ceramics, sterilization, and medicaltreatment technologies.

Diane Folz explains that one of the mostinteresting uses for microwaves is selectiveheating of specific components within astructure. It was this characteristic that ledthe group to investigate microwave recy-cling and waste remediation. Graduate stu-dent Rebecca Schulz, in work funded byWestinghouse Savannah River Co., demon-strated a microwave process for recycling

precious metals from electronic circuitry,while also treating the off gases that result-ed in the combustion process. The workresulted in several patents on the processand design of microwave hardware. Aschematic of the system is shown in Fig. 15.

Dr. Jim Hwang is leading an effort tocommercialize a technology that his groupdeveloped at Michigan TechnologicalUniversity (Houghton, Mich.; www.mtu.edu). Microwaves are used to assist steel-making in an electric arc furnace (EAF).The viability of the technology lies in thefact that iron ore and carbon are excellentmicrowave absorbers. Prototype equipmentfor the new technology is located inHwang's lab and consists of modified elec-tric arc furnace with an auxiliarymicrowave heating system. A charge ofiron oxide, coal and limestone is loadedinto the chamber and microwave energy isintroduced. The charge absorbs microwave

energy to the point of coal ignition. Theexothermic reaction of carbon oxidationfurther increases the temperature. The EAFelectrodes then descend to provide electricarcing energy, producing molten steel andslag. Design modifications to the chamberwill allow continuous mode operation. IH


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powders, SHS, klystron, gyrotron, microwave

field, microwave frequency.

Fig. 14 Microwave fluidized-bed reactor atInVerTec at the Center for Excellence atUniversität Bayreuth, Bayreuth, Germany

Fig. 15 Schematic of microwave hardware used to recycle precious metals from electroniccircuitry developed at Virginia Polytechnic Institute

Processed offgas

Offgas treatment tube (refractory)

Suscepting material

Upper treatment chamber

Refractory material

Combustion exhaust tube (metal)

Lower treatment chamber and Metals collection system

Suscepter

Refractory material

Crucible

Incoming waste stream

Flow meter

Forced air flowRemotely located electronics and personnel

advancements in microwave heating technologyfast volumetric heating. dennis tool has fully...

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