sizing quench tanks - asm international

JUNE 2014 • VOLUME 2 • ISSUE 2

hts.asminternational.org

SIZING QUENCH TANKS

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FLOWMETER OVERVIEW

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www.IpsenUSA.com/AdvancedControls

ADVANCED MATERIALS & PROCESSES • JUNE 2014 37

JUNE 2014 • VOLUME 2 • ISSUE 2

Editorial Opportunities for HTPro in 2014The editorial focus for HTPro in 2014 reflects some key technologyareas wherein opportunities exist to lower manufacturing and pro-cessing costs, reduce energy consumption, and improve perform-ance of heat treated components through continual research and development.

September Surface EngineeringNovember Atmosphere/Vacuum Heat Treating

To contribute an article to one of these issues, please contact FrancesRichards at [email protected]. To advertise, pleasecontact Erik Klingerman at [email protected].

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ABOUT THE COVER:Hot furnace charge prior to immersion intoa quench bath. From “Houghton onQuenching,” Houghton International Inc.,Valley Forge, Pa., houghtonintl.com.

EDITOR Frances Richards

TECHNICAL ADVISORS Aymeric GoldsteinasStephen FeldbauerOlga Rowan

CONTRIBUTING EDITOR Ed Kubel

ART DIRECTOR Barbara L. Brody

PRODUCTION MANAGER Joanne Miller

NATIONAL SALES MANAGERErik KlingermanMaterials Park, Ohio440.338.5151 ext. 5574fax: [email protected]

HEAT TREATING SOCIETYEXECUTIVE COMMITTEERoger Alan Jones, PresidentThomas E. Clements,

Immediate Past PresidentStephen G. Kowalski, Vice PresidentMichael O’Toole, Executive Director

HTProÔ is published quarterly by ASM International®,9639 Kinsman Road, Materials Park, OH 44073,440.338.5151, asminternational.org. Vol. 2, No. 2. Copy-right© 2014 by ASM International®. All rights reserved.

The acceptance and publication of manuscripts in HTProdoes not imply that the editors or ASM International®

accept, approve, or endorse the data, opinions, and con-clusions of the authors. Although manuscripts publishedin HTPro are intended to have archival significance, au-thor’s data and interpretations are frequently insufficientto be directly translatable to specific design, production,testing, or performance applications without independ-ent examination and verification of their applicabilityand suitability by professionally qualified personnel.

SIZING QUENCH TANKS FOR BATCH IMMERSION QUENCHINGD. Scott MacKenzieA quench tank must contain sufficient fluid to quench the load without anexcessive rise in temperature of the quenching fluid.

APPLICATION NOTE

TOOL FOR ATMOSPHERIC CARBON POTENTIAL ANALYSISJim OakesAn atmosphere carbon potential analyzer provides a cost-effective way tomeasure carbon using a wire coil that functions in a way similar to usingshim stock.

OPERATIONAL PRINCIPLES OF FLOWMETERS: PART 1Daniel HerringFlow measurement is an increasingly important part of quality controlsystems in the heat treating industry.

DEPARTMENTS2 EDITORIAL2 HEAT TREATING SOCIETY NEWS4 CHTE UPDATE

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TABLE OF CONTENTS

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ADVANCED MATERIALS & PROCESSES • JUNE 201438

ASM to Lead Thermal Manufacturing Industries Advanced Technology Consortiumhermal manufacturing, consisting of heat treating, melting, and other process heating methods, is used in nearly everymanufacturing facility in the U.S. It affects the employment of an estimated 8.3 million Americans at more than 262,000companies, according to the U.S. Census Bureau. The Bureau says these companies (98% of which are small andmedium enterprises) produce $3.4 trillion in total value of annual shipments.

Advanced thermal manufacturing technologies potentially can improve the efficiency, productivity, and globalcompetitiveness of many U.S. materials manufacturing and value-added, end-user industries. However, technicalchallenges identified in previous roadmapping efforts (such as the Heat Treating Technology Road Map) are stillpreventing development and deployment of these technologies. The main reason is because these roadmaps weredeveloped independently from one another by different industries that rely on or supply thermal equipment andprocesses as a critical part of their operations. Understandably, these thermal manufacturing industries focusedprimarily on their specific areas of interest. As a result, there has been a lack of the necessary coordination andcritical mass needed to address the technical challenges facing these industries. In addition, there has been an in-complete transfer of available technologies to the small and medium enterprises that make up a large segment ofthe thermal manufacturing industries.

To address these issues, the proposed Thermal Manufacturing Industries Advanced Technology Consortium (TMIATC) will be formed to lead and coordinate a nationaleffort to develop and deploy advanced manufactur-ing technologies across the broad thermal manufac-turing community, including equipmentmanufacturers and end users. Specifically, TMI ATCwill lead the development of a comprehensive R&Droadmap that identifies common thermal manufac-turing needs across industries and solicits the inputfrom key stakeholders in highly interactive, action-oriented technology roadmapping workshops. Theresults of these sessions will identify advanced man-ufacturing technologies ready for implementation inthermal manufacturing industries as well as high-pri-ority areas for development. This 18-month processwill generate a final roadmap in the first year, and willthen begin to implement the recommendations dur-ing the remaining months.

The proposed structure of the consortium will facili-tate technology implementation and sustainability.TMI ATC will be led by ASM International through afederal grant. ASM, from its founding roots, and nowprimarily through its affiliate Heat Treating Society,is a leader in collecting and disseminating thermal-manufacturing information, and has many relation-ships with industrial companies.

The ASM Heat Treating Society has been involved forthe past 15 years in identifying and prioritizing keyinitiatives in heat treating-related areas of equipmentand hardware materials technology, processes andheat treated materials technology, and energy and en-vironment technology. This puts the society in aprime position to extend this work with the coopera-tion of other consortium participants.

Ed KubelContributing Editor

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2 TNew Face for

Heat Treating Society WebsiteThe Heat Treating Society (HTS) website joined the ASM Internationalwebsite on the new technology platform. What can you expect withthis new development?

One ID, One Password – If you login to the ASM website, you will au-tomatically be signed in ifyou navigate to the Affil-iate website (and vice-versa). One ID/emailaddress and one pass-word for the ASM andASM Affiliate websites.

Fast Checkout – Thenew, overhauled check-out process is designedafter well-known Inter-net commerce vendors.When you add a purchase to your shopping cart on your Affiliate web-site, you can also take advantage of adding products through the ASMwebsite “Store.” In addition, you can “Checkout as Guest,” which speedsup and minimizes the time to register on the website.

Find Content Easier –New ability to find content by Subject, ResourceType, Publication Date, and Author to find exactly what you are look-ing for to solve materials problems quickly and easily.

Easier Reading – Enlarged text adds to a simplified look and feel.

More Connections – Profile pictures can now be uploaded to theMember Directory, which can help with recognition at networkingevents.

Universal Content Management – One database, one version of theentire collection of ASM content.

It is an entirely new look and feel. Be sure to check it out!

http://hts.asminternational.org.



The winner of the 2014 HTS/Bodycote Best Paper inHeat Treating Award is a paper entitled “Developmentof Methodology to Improve Mechanical Properties of319 Al Alloy Engine Blocks through Cost-EffectiveHeat Treatment Optimization,” by Anthony Lom-bardi. Mr. Lombardi is a third year Ph.D. candidate inmechanical engineering at Ryerson University(Toronto) under the supervision of Dr. C. (Ravi)Ravindran, ASM President. Lombardi is the recipientof the prestigious NSERC Alexander Graham BellCanada Graduate Scholarship - Doctoral (CGS-D).The HTS/Bodycote award will be presented at the

ASM Leadership Awards Luncheon, Monday, Octo-ber 13, 2014, during MS&T in Pittsburgh.

The ASM Heat Treating Society established the BestPaper in Heat Treating Award in 1997 to recognize apaper that represents advancement in heat treatingtechnology, promotes heat treating in some substan-tial way, or represents a clear advancement in man-aging the business of heat treating. The awardincludes a plaque and $2500 cash prize endowed byBodycote Thermal Process-North America. Visit asminternational.org/hts to read the winning paper.

2014 HTS/Bodycote Best Paper in Heat Treating Awarded

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Winner of theHTS/Bodycote2014 BestPaper in HeatTreating Award,Anthony Lombardi.

Whether you are a seasoned professional or just be-ginning your career in the heat treating industry,HTS members are encouraged to become moredeeply involved in the society through committeemembership.

HTS committees capture key directional shifts inmember needs and translate those needs into actionitems for potential development. Their input andrecommendations enable the HTS Board of Direc-tors to establish effective policies, set meaningfulbudgets, and oversee society operations.

HTS Directors and committees meet on a regularbasis. As the eyes and ears of the HTS Board, societycommittees are invaluable for improving service toHTS members and customers. Volunteers areneeded to grow HTS permanent committees to meetthese objectives. The committees include:

HTS Awards and Nominations Committee, whosemission is to nominate candidates who are represen-tative of commercial and captive heat treaters; usersof heat treating; suppliers of materials and equip-ment; researchers, educators and government agen-cies involved in heat treating for the positions ofpresident, vice president, and members of the HeatTreating Society Board as well as the developmentand recommendation of awards to be given by theHeat Treating Society.

HTS Finance Committee, whose mission is to su-pervise the financial affairs of the Society under thedirection and with the approval of the HTS Board. Itreviews the financial plan of the Society and recom-mends it to the Board for action.

HTS Membership Committee, whose mission isto understand current, past, and potential HTSmember needs, refocusing efforts to provide im-proved member value. The committee is chargedwith understanding and interpreting memberneeds as well as achieving the financial contribu-tion for HTS.

HTS Technology and Programming Committee,whose mission is to develop programming and tech-nical information that provides practical, leading-edge global technology; and to foster the exchange,education, understanding, and exposure of technol-ogy within the heat treating industry.

HTS Research and Development Committee,which is charged to work with the heat treating com-munity, the Center for Heat Treating Excellence, andother research institutions, to identify, monitor, andprovide updates on worldwide research and technol-ogy development relevant to the industry.

HTS Education Committee,which is charged to re-search, develop, and support education programsthat best respond to the needs of the heat treatingindustry. The committee reviews courses and revisesthem as necessary, and develops new educationalservices related to heat treating.

To express your interest, or for more information,contact Sarina Pastoric at [email protected].

HTS Looking for Volunteers for Committees

Ferguson receivesIFHTSE Fellowship 2014 AwardDr. B. Lynn Ferguson, FASM, president, De-formation Control Technology Inc., Cleve-land, was honored at the 21st IFHTSECongress, recently held in Munich with anIFHTSE Fellowship 2014 Award.

The citation reads: In recognition of globallyacknowledged leadership in the development andpractical implementation of principles and practicesof mathematical modeling and their application tothe benefit and advancement of heat treatment in-dustry and surface engineering. Ferguson is a long-standing member of the ASM Heat Treating Society,and past member of HTS Board of Directors.


Heat treating companies spend a signifi-cant amount of time and money replacingfurnace parts and furnace fixtures. Extend-ing the service life of these componentsand reducing the time to heat them up and cool them downcould result in considerable savings. The Alloy Life Extension Proj-ect currently under way at the Center for Heat Treating Excellence(CHTE), Worcester Polytechnic Institute (WPI), is aimed at solvingthose problems.

The focus of the project is identifying and testing alloys and coat-ings that can improve the service life of parts like fans, burners,rollers, tubes and mesh belts, as well as fixtures like wire basketsthat carry the parts to be heat treated.

Researchers are also analyzing fixture design and material selectionto reduce the energy needed to repeatedly heat fixtures. The goalis to find alloys for use in the heat treating industry that will lasttwice as long as current materials, resulting in significant savings.

According to Rick Sisson, George F. Fuller professor of mechanicalengineering at WPI and director of CHTE, “Manufacturers are spend-ing lots of money for alloy fixtures that go into carburizing furnaces.The goal of this study is to explore options that will allow industryto work more efficiently, lessening fixture replacement costs, reduc-ing energy consumption, and improving product quality.”

The project has already produced some in-teresting findings. For example, the mainreason for alloy failure is excessive carbur-

ization, which causes furnace parts and fixtures to become brittleand easily fracture. Based on this information, a series of carburiza-tion-resistant alloys have been identified for commercial furnacetesting, including RA602CA, Inconel 625, and Stellite 250. Samples ofthese alloys are being tested at the facilities of CHTE member com-panies Sikorsky Aircraft and Bluewater Thermal Solutions.

Different alloys are being assessed for their resistance to oxidationand carburization at two Bluewater facilities in Illinois. Multiplesets of each alloy are run for different times in test furnaces, andone of each set is removed periodically to evaluate the extent ofalloy degradation. Based on visual inspection, samples are re-moved for metallographic characterization.

Another test being carried out at Bluewater is aimed at determin-ing whether an aluminized section of an industrial furnace meshbelt holds up better than regular mesh belts. Craig Zimmerman,technical director at Bluewater, explains, “Mesh belts last only ninemonths and they are extremely expensive to replace. We are hope-ful that this study will help us and everyone in the industry toidentify which materials can drive down costs. If we can make anyof the parts and fixtures last longer, it will be a huge savings.”


Improving the Service Life of Furnace Materials

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About CHTEThe CHTE collaborative is an alliance between the industrial sector and university researchers to address short-term and long-termneeds of the heat-treating industry. Membership in CHTE is unique because members have a voice in selecting quality research proj-ects that help them solve today’s business challenges.

Member research processResearch projects are member driven. Each research project has a focus group comprising members who provide an industrial per-spective. Members submit and vote on proposed ideas, and three to four projects are funded yearly. Companies also have the op-tion of funding a sole-sponsored project. In addition, members own royalty-free intellectual property rights to precompetitiveresearch, and are trained on all research technology and software updates.

CHTE also periodically undertakes large-scale projects funded by the federal government or foundations. These endeavors keep mem-bers informed about leading edge technology.

CHTE current research portfolioOther projects now in progress include:Nondestructive Testing for Hardness and Case Depth, Induction Tempering, Gas Quench Steel Hardenability, Enhancements to CHTEsoftware (CarbTool, CarboNitrideTool, and NitrideTool), and Cold Spray Nanomaterials (supported by ARL).

For more information about CHTE, its research projects, and member services, visit wpi.edu/+chte, call 508.831.5592, or email RickSisson at [email protected], or Diran Apelian at [email protected].

Furnace fixtures at various levels of degradation.

Part of the research is looking at ways to extend thelife of mesh belts so that companies don’t have toreplace them every nine months at significant expense.

Rick Sisson (right) and Anbo Wangwork together to identify ways toextend the life of alloy parts andfixtures. Mei Yang also contributedto the study.



www.inductoheat.com


The size of a batch immersion quenchtank depends on the dimensions of theworkload, as well as the allowable tem-perature rise. The temperature rise per-mitted is dependent on whether thequenchant is oil, water, or polymer.

In a batch operation, care should betaken to ensure that a sufficient amountof quenchant covers the top of the work-load. The physical dimensions of thetank should be large enough to ensurefull immersion of the quench load andfixtures, and, at the same time, shouldallow enough space for agitators and ma-nipulators. Depending on the size of theworkload, it is generally appropriate tohave at least 150–300 mm (6–12 in.) offluid over the top of the workload, andpreferably more.

When using hot quenching oils, it is nec-essary to make an allowance for thermalexpansion of the oil, either by makingprovision for an overflow system, or bymanual adjustment of the fluid level.

Tank capacityA quench tank must contain sufficientfluid to quench the load without an ex-cessive rise in temperature of the

quenching fluid. In an uncooled tank,the quantity of quenchant required canbe calculated from the basic equation:

MmCpmDTm = MqCpqDTq

Where Mm is the mass of metal, Cpm isthe specific heat of the metal, DTm isthe decrease in temperature of themetal being quenched, Mq is the massof quenchaant, Cpq is the specific heatof the quenchant, and DTq is the in-crease in temperature of the quen-chant. Typical values for specific heatat 20°C (70°F) are:

Steel — 0.17 cal/g/C (0.17 Btu/lb/F)Aluminum — 0.23 cal/g/C

(0.23 Btu/lb/F)Quench Oil — 0.50 cal/g/C

(0.50 Btu/lb/F)Polymer Quenchant — 0.95 cal/g/C

(0.95 Btu/lb/F)Water — 1.0 cal/g/C (1.0 Btu/lb/F)

A general guideline for steel quenching(for a single quench) is that 10 liters ofoil is required for each kilogram of totalcharge weight (1 gal/lb). This rule ofthumb results in about a 40°C (70°F)temperature rise under nominal condi-tions, which is recommended to preventthe oil from reaching the flashpoint ofthe fluid. It is recommended that themaximum temperature during quench-ing using oils always should be at least55°C (100 °F) below the flash tempera-ture, which mitigates the potential for afire if a hung-up load occurs. This is il-lustrated in the following example:

Flash temperature of the oil:175°C (350°F)

Recommended temperature cushion: 55°C (100°F)

Temperature rise during quenching:40°C (70°F)

Maximum recommended operatingtemperature: 80°C (180°F)

However, with successive quenches,some form of cooling is necessary to pre-

vent the oil from overheating. The heatexchanger should be sized to recover theheat produced by the quenched loadwithin one heat treating cycle.

For example, in quenching 2270 kg (5000lb) of steel from 870°C (1600°F), a heattreater wants to remove the parts fromthe oil at 65°C (150°F). The “coldquench” oil used has a flash temperatureof 175°C (350°F) and operates at a tem-perature of 60°C (140°F). Based on theseprocess parameters, the maximum peaktemperature of the oil (considering theflash point of 175°C), would be 120°C(250°F). What should the minimum sizeof the quench tank be? Using the equa-tion given above:

MmCpmDTm = MqCpqDTqor

Mq = MmCpmDTm/CpqDTq

thereforeMq = 5000 lb (0.17 Btu/lb/F)

(1600 - 150F)/0.50 Btu/lb/F (110F)Mq = 22,409 lb (10,185 kg) oil

At a weight of 6.8 lb/gal (0.8 kg/liter), ap-proximately 3300 gal (12,500 liters) arerequired for these conditions. However,this temperature rise is a bit excessiveand could lead to premature oxidation ofthe oil. Alternatively, rearranging theequations using a fixed size quench tankallows solving for the temperature riseduring quenching.

Water and polymer quenchants have adifferent limitation on temperature. Thisis not related to safety, as with quenchoils, but effective cooling for water, andmaximum operating temperatures forpolymer quenching. For water, the max-imum temperature is 100°C (210°F).However, this limit is rarely used as thecost of make-up and cooling becomesexcessive. For polymer quenchants andwater used in quenching aluminum,aerospace standards specify a maximum

SIZING QUENCH TANKS FOR BATCH IMMERSION QUENCHING

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*Member of ASM International and Heat Treating Society.

A QUENCH TANK MUST CONTAIN SUFFICIENT FLUID TO QUENCH THE LOAD WITHOUT AN EXCESSIVE RISE IN TEMPERATURE OF THE QUENCHING FLUID.D. Scott MacKenzie,* FASM, Houghton International Inc., Valley Forge, Pa.

Hot charge ready to be quenched



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temperature rise of 5°C (10°F) with amaximum temperature of 45°C (110°F).For polymer quenchants, it is somewhatmore difficult. The maximum tempera-ture for polyalkylene glycol (PAG) quen-chants cannot exceed the cloud pointtemperature. This is between 60° and75°C (135° and 170°F) for most PAGquenchants, depending on the molecularweight of the polymer. It is also recom-mended that the maximum bulk temper-ature rise be at most 10°C (20°F) belowthe cloud point temperature. Polymerquenchants, besides being sensitive to ag-itation, are strongly affected by tempera-ture. The cooling rate decreasessignificantly with increasing temperature.Small temperature rises during quench-ing reduce variations in cooling rate andquench rate effectiveness. This also re-duces drag-out, produces more uniformquenching, and prolongs the life of thequenchant. Limiting the temperature risegreatly increases the quench tank size.

For PVP-type quenchants, there is nocloud point temperature. However, themaximum peak temperature is generallylimited to 65°C (150°F) or lower to pre-vent destructive oxidation of the quen-chant. This also reduces the amount ofdrag-out and chemical consumption inthe system.

As an example, consider the design of aquench tank containing Aqua-Quench3699, a hybrid polymer quenchant thatdoes not have a cloud point. Steel partswill be quenched from 1095° to 205°C(2000° to 400°F), with a maximum loadweight of 2270 kg (5000 lb). The quenchtank operates at 45°C (110°F) nominally.What volume of quenchant is requiredin gallons?

To solve this, the maximum allowabletemperature rise must first be deter-mined. For this quenchant, the maximumtemperature is 65°C (150°F). Because thequench tank is operating at 150°F, thetemperature rise of the quenchant (ΔTq)

is 40°F (i.e., 150°–110°F). From the equa-tion above, and rearranging to determinethe mass of water required:

MmCpmDTm = MqCpqDTqor

Mq = MmCpmDTm/CpqDTq

thereforeMq = 5000 lb (0.17 Btu/lb/F) (1600)/0.95 Btu/lb/F (40F)Mq = 35,800 lb (16,270 kg)

polymer quenchant

A gallon of water weighs 8.33 lb/gal (1 kg/liter), so the number of gallons re-quired to quench 5000 lb of steel is 4296gal (16,260 liters). Temperature rise forpolymer and oil quenchants are shownin Figs. 1 and 2.

System temperature controlMaintaining the temperature of thequench bath is as important as the sizeof the quench tank, which requires ameans of temperature control.

Quenchant heating is achieved using sev-eral methods, including electrical resist-ance heating elements, gas- and oil-fired

radiant tubes, and waste heat from thefurnace exhausts. In some systems, thequenchant is heated by quenching a“dummy” hot load of parts. The energydensity of radiant tubes and electricalheating elements should not exceed 1.5W/cm2 (10 W/in.2). This prevents heatersfrom preferentially oxidizing the oil anddepleting the oxidation additive package.This energy density guideline should alsobe followed for polymer quenchants, withthe additional provision that maximumheater temperature should be about 70°C(160°F) to prevent exceeding the cloudpoint of the material. Heaters should alsobe interlocked with the agitation systemso they shut off if the agitation system isshut off or fails. The system should alsobe designed to make it impossible to turnon the heating system without the agita-tion operating.

Quenchant cooling. Various methods areavailable to cool quenchants including:

• Submerged water-cooling pipes• Cooling jackets• External water-cooled heat

exchangers• Forced air-cooled radiators • Refrigeration systems

Fig. 1 — Relationship of volume of oil quenchant and weight of quenched workload to prevent specific temperature rise of quench bath when quenched from 1600° to 140°F (870° to 60°C).

Fig. 2 — Relationship of volume of polymer quenchant and weight of quenched workload toprevent specific temperature rise of quench bath when quenched from 1600° to 140°F (870° to 60°C).

2500

2000

1500

1000

500

0

2500

2000

1500

1000

500

0

Weight of batch load

quenched, lb


quenched, lb

0 1000 2000 3000 4000 5000 6000 7000 8000Oil required in tank to limit bath temperature rise, gal

0 1000 2000 3000 4000 5000 6000 7000 8000Polymer required in tank to limit bath temperature rise, gal

1135

910

680

455

230

0

1135

910

680

455

230

0

Oil required in tank to limit bath temperature rise, liters0 3785 7570 11,355 15,140 18,925 22,710 26,495 30,280

Polymer required in tank to limit bath temperature rise, liters0 3785 7570 11,355 15,140 18,925 22,710 26,495 30,280


quenched, kg


quenched, kg

100°F 80°F 60°F 40°F Temperature rise(55°C) (45°C) (35°C) (20°C)

20°F (10°C)

50°F (25°C) 30°F (15°C)

40°F (20°C) 20°F (10°C) Temperature rise

10°F (5°C)



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Submerged water-cooling pipes and jack-ets are suitable only for small systems, andthere is always the risk of water contami-nation of oil quenchants, which should beavoided at all costs. Water contaminationof polymer quenchants is not critical. Ex-ternal water-cooled heat exchangers andair-cooled radiators are very efficient andwidely used for cooling large quenchingsystems. For oil quenchants, air-cooledheat exchangers are nearly always used inthe U.S. to prevent potential fires fromwater in quench oil. For polymer quen-chants, water and chillers are predomi-nately used. Air-cooled heat exchangersare generally limited to cool a quenchantto approximately 10°C (20°F) above ambi-ent temperature. Because most polymerquenchants should be used around roomtemperature, the use of chiller water orother means is mandated by temperatureand heat exchanger constraints.

To obtain maximum efficiency fromcooling systems, the direction of circula-tion should be such that hot quenchantis removed from the top of the tank andthen passed through the heat exchanger.Once cooled, the oil is returned to the

bottom of the tank. Generally, the heatexchanger should be sized to recover theheat within one quench cycle. The equa-tions above can be used to determinethe size of the heat exchanger:

Q = MmCpmDTm

where Q is the total heat that must beextracted from the quenchant. This isthe total heat given up by the quenchedmetal to the quenchant. To properly sizethe heat exchanger, the heat from theworkload should be completely recov-ered prior to the next load. For instance,assume that an integral quench furnaceis quenching an 1820 kg (4000 lb) chargeinto a 15,140 liter (4000 gal) quench tankat 60°C (140°F). The load is quenchedfrom a temperature of 870°C (1600°F)and extracted from the quench at 65°C(150°F). The cycle time from one loadquenching until the next load quenchingis 90 minutes. The heat exchanger mustrecover this heat from the quench oil toreturn the temperature of the quenchback to the original temperature of 60°C.Substituting and solving the equationgives:

Q = MmCpmDTm = 4000 (0.17) (1600 - 150) = 986,000 Btu

The heat exchanger must extract nearlyone million Btu from the oil in 90 min-utes to recover the oil temperature. Inother words, the heat exchanger mustbe rated for at least 660,000 Btu/hr (194kW). There also must be an adequatesafety factor to compensate for differ-ent heat treating cycles and ambientconditions.

ConclusionsThis brief article describes the basics ofsizing quench tanks for immersionquenching and offers a methodology forsizing the temperature-control system. Itis recommended to contact your quen-chant supplier or heat-exchanger supplierfor more detailed, precise determinationsfor specific applications. HTPRO

For more information: D. Scott MacKen-sie is research scientist – metallurgy,Houghton International Inc., Valley Forge,PA 19482, 610.666.4007, [email protected], houghtonintl.com.


www.TiniusOlsen.com


APPLICATION NOTE

TOOL FOR ATMOSPHERIC CARBON POTENTIAL ANALYSISA question frequently asked by heattreaters is: “What is the actual carbon inmy furnace?” There are many tools forcontinuous atmosphere monitoring, ver-ification, and troubleshooting. They ad-dress standard heat treating practicesand industry requirements, such asAMS or CQI-9, to ensure continuouscontrol and periodic verification of thefurnace atmosphere used for the heattreatment process.

Heat treaters regularly seek ways to pre-vent and reduce rework and scrap loadsby implementing procedures and toolsto make sure the heat treating processmeets customer expectations and spec-ifications. One process parameter re-quirement is to ensure consistentatmosphere carbon content. Measuringcarbon absorption into steel is com-monly done to verify atmosphere consis-tency. Super Systems’s CAT-100 instru-ment is an atmosphere carbon potentialanalyzer that provides a cost-effectiveway to measure carbon using a wire coilthat functions in a way similar to usingshim stock.

Working principlesThe CAT-100 measures carbon poten-tial in a positive-pressure atmosphere.The value is determined by measuringspecific properties of a steel wire coil in-serted into an atmosphere made up of acarbon-bearing gas for a predefinedtime. The concept behind the instru-ment is similar to that behind the com-pany’s Shim Port method. Both usemetal pieces “soaked” in a carbon-con-taining atmosphere as the basis for car-bon analysis. Two important differencesbetween the instrument testing methodand the shim-stock method are the timerequired to generate a carbon-potentialreading and the cost associated with themeasuring instruments.

CAT-100 is capable of providing on-sitecarbon-potential measurement in lessthan one hour, while the shim-stockmethod requires specialized equipmentthat many heat treaters do not have on

site. This requireshaving an off-sitelaboratory measurethe shim stock,adding several daysto the process. Wirecoils are availablefor use with theCAT-100, and in-strument calibra-tion is relatively easy.

Carbon potential meas-urement using the CAT-100 is based onthe carbon content of the wire coil aftersoaking in the furnace, which is meas-ured by analyzing changes in the metal-lurgical properties of the coil. Forexample, metallurgical changes causedby carbon diffusing into the coil affect itselectrical resistance. Measurements aremade on the coil after removing it fromthe furnace (at ambient temperature).Measurement accuracy is dependent onthe coil temperature.

Measured carbon potential is also de-pendent on changes in surface metalproperties. The steel surface eventuallyreaches equilibrium with a given gascomposition and furnace temperature.Electrical resistance is directly propor-tional to the amount of carbon presentin the fine-wire coil. Using the baselineelectrical resistance and carbon contentfor the untreated wire, the additionand/or depletion of carbon in the heattreated wire can be accurately measured.The instrument provides a direct read-ing of percent carbon without the influ-ence of gas composition.

The measurement can be influenced bynitrogen absorption into the coil fromthe furnace atmosphere. Because this results in erroneous readings, the instru-ment should not be used for carbonitrid-ing processes.

Operating procedureThe instrument must be calibrated foruse with a specific wire coil. The reasonis that different lots of coils could have

different carbon content,and the presoak carbon content of thecoil is crucial for accurate carbon poten-tial measurement. Before the testingprocess begins, the furnace atmospheremust be verified as suitable for a coilsoak. Furnace temperature should begenerally uniform before the coil is in-troduced to the atmosphere, and shouldnot change greatly during the soak. Aspecial insertion rod is used to place thecoil into the furnace atmosphere; it mustnot be inserted within a furnace chargeor in a basket. The coil soaks in the at-mosphere about 30 to 40 minutes de-pending on the temperature, and isremoved after the soak is completed.

When the coil cools sufficiently(quenching must not be used), it is at-tached to testing posts on the instru-ment and a carbon potential value isdisplayed after about 30 seconds. Read-ings can be stored in the instrument’s in-ternal memory and can be downloadedto a computer using included software.Following proper procedures, carbon-potential readings are accurate and re-peatable. The CAT-100 is designed toprovide results within 0.03% of the car-bon in an atmosphere containing 0.1 to1.3% carbon (the effective testing rangeof the instrument). HTPRO

For more information: Jim Oakes is vicepresident, Business Development, SuperSystems Inc., 7205 Edington Dr., Cincinnati,OH 45249, 513.772.0060, email: [email protected], supersystems.com.

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The CAT-100 provides accurate, repeatable furnace atmosphere carbon-potential readings.


OPERATIONAL PRINCIPLES OF FLOWMETERSONCE A “SET IT AND FORGET IT” TECHNOLOGY, FLOW MEASUREMENT IS AN INCREASINGLY IMPORTANTPART OF QUALITY CONTROL SYSTEMS IN THE HEAT TREATING INDUSTRY.

Daniel H. Herring*, The Herring Group Inc., Elmhurst, Ill.

In most heat treating applications, im-portant flowmeter selection criteria in-clude reliability, accuracy, ruggedness,ease of calibration, and ease of mainte-nance. Given the high accuracy and re-liability of today’s instruments, userscan run their processes more econom-ically. This article discusses the mostcommonly used flow measurement in-struments and compares their operat-ing principles (Table 1).

Types of flowmetersFlowmeters typically measure either vol-umetric or mass flow. Volumetric flowmeasurement looks at the flow of a givenvolume of the medium over time (e.g.,ft3/h). This technology uses either me-chanical flow rate indication or elec-tronic output (Fig. 1).

Mass flow measurement looks at theflow of a given mass over time (e.g.,lb/h). Industrial thermal mass flowme-ters are often equipped with electronicoutput (Fig. 2). Conversions betweenthe two measurements can be made ifthe pressure, temperature, and specificgravity of the flowing medium areknown.

Flowmeters can be further subdividedinto several general types. Of these,variable-area and thermal-massflowmeters are most often used in heattreating applications:• Variable area: Fluid flow rate is measured as the flowing medium passes through a tapered tube. The position of a float, piston, or vane placed in the flow path changes as higher flows open a larger area to pass the fluid, providing a direct visual indication of flow rate.

• Differential pressure: Calculating a fluid flow rate from the pressure loss across a pipe restriction is the most commonly used flow measurement technique in industrial applications. The pressure drops through these

devices are well understood, and a wide variety of configurations are available, each having specific strengths and weaknesses. Variations on the theme of differential pressure flow measurement include the use of pitot tubes.

• Mechanical: In these instruments, flow is measured either by passing isolated, known volumes of a fluid (gas or liquid) through a series of gears or chambers (positive-displacement type) or via a spinning turbine or rotor. Measurements using a positive-displacement flowmeter are obtained by counting the number of passed isolated volumes.

• Electronic: Magnetic, vortex, and ultrasonic devices are available, all of which have either no moving parts or vibrating elements and are relatively nonintrusive.

• Thermal mass: In contrast to volumetric flow devices, thermal mass flowmeters are essentially immune to changes in gas temperature and pressure. Because measurements can be very accurate and repeatable, these devices are used in critical flow measurement applications.

Variable-area typesVariable-area flowmeters are simple,versatile devices that operate at a rela-tively constant pressure drop and meas-ure the flow of liquids, gases, and steam.The popularity of this type of flowmeterin the heat treating shop is their direct-view design, where flow is indicated me-chanically, which makes it easy tounderstand the operating principle. Sev-eral different designs of variable-areaflowmeters are used throughout theheat-treating industry (Fig. 3).

*Member of ASM International


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Fig. 2 — Typical mass flowmeter. Courtesyof MKS Instruments.

Fig. 1 — Typical volumetricflowmeter. Courtesy of Atmosphere Engineering Inc.



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Rotameter typesThe glass or plastic rotameter (Fig. 3a),is the most widely used because of itslow cost, low pressure drop, relativelywide range, linear visual flow indica-tion, and simplicity of operation. Topass through the tapered tube, fluidflow must raise the float. The greaterthe flow rate, the higher the float islifted. In liquid service, the float risesdue to a combination of the liquid’sbuoyancy and its velocity. With gases,buoyancy is negligible, so the float re-sponds mostly to velocity.

The float moves up and down in pro-portion to the fluid flow rate and theannular area between the float and thetube wall. As the float rises, the size ofthe annular opening increases. As thearea increases, the differential pressureacross the float decreases. The floatreaches a stable position when the up-ward force exerted by the flowing fluidequals the weight of the float. Thus,every float position corresponds to aspecific flow rate for a particular fluid’sdensity and viscosity.

TABLE 1 — COMMONLY USED FLOW MEASUREMENT INSTRUMENTS BY TYPE

Industrial Disassembly Sensitivity to Robust flowmeter type Style Manufacturer (a) without repiping dirty fluids spare parts

Variable area, Metal tube Waukee Engineering Co. Inc. Yes Moderate Delicateincluding rotameters

Metal cylinder Meter Equipment Mfg. Inc. Yes Low Moderatetube

Glass or plastic Fisher-Porter No Sensitive Moderatetube Brooks Instrument

King Instrument Co.Dwyer Instruments Inc.

Key Instruments

Vane type Universal Flow Monitors Inc. No Moderate ModerateErdco Engineering Corp.Orange Research Inc.

Moving orifice Hedland, Div. No Moderate RobustRacine Federated Inc.

Piston Insite (Universal Flow No Moderate Delicate(with spring) Monitors Inc.)

Differential pressure/ Orifice Lambda Square Inc. No Moderate RobustOrifice Flowell Corp.

Venturi Flowell Corp. No Moderate RobustFox Valve Development Corp.

Turbine/Impeller Rotary impeller Roots (BNC Industrial Co. Ltd.) No Sensitive ModerateTokicoTechno Ltd.

Turbine Hoffer Flow Controls Inc. No Sensitive DelicateSponsler Inc.

Great Plains Industries Inc.

Thermal mass Thermal mass Sierra Instruments Inc. No Sensitive DelicateMKS InstrumentsBrooks Instrument

(a) Not all-inclusive

Features and advantagesAdvantages of variable-area flowmeters include:• Mechanical flow measurement with just a single moving part, ensuring measurement reliability• Application versatility and availability of a variety of construction materials, inlet and outlet sizes, and types• Easy installation with generally no straight pipe requirements• Low pressure drops• Linear scales, allowing easy flow measurement interpretation• Electronic output availability, preserving the mechanical flow measurement

Advantages of tapered-tube rotameters include:• Low instrument cost (when glass or plastic metering tube is used)• Can be used for very low flow rates

Advantages of slotted-cylinder flowmeters include:• Flow measurement accuracy determined by the precision of the slot manufacturing operation; good flow range of 25:1 results• Instrument specifications can be changed by field replacement of the slotted tube and float without having to re-pipe the flowmeter vessel• Ability to handle high flows and pressures• Improved immunity to pulsating flows, with no minimum backpressure

Limitations common to both tapered-tube and slotted-cylinder variable-areaflowmeters include the requirement of vertical mounting aand the fact that theycontain moving parts.



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This is why it is necessary to size the ro-tameter for each application. Whensized correctly, flow rate can be deter-mined by matching the float position toa calibrated scale on the outside of theinstrument. Many rotameters comewith a built-in valve to manually adjustflow. Several shapes of floats are avail-able for various applications.

Both glass and metal rotameters areavailable. Glass and plastic rotameterscost less and are more accurate thanmetal tapered-tube rotameters (Fig. 3b),but may not be able to provide the dura-bility and reliability needed in a manufac-turing environment. Metal rotametersare reliable, but the machined taperedtube limits the flow measurement range(turndown). Another limitation is thatmetal rotameters typically have brass oraluminum bodies, which can make themunsuitable for use in certain gases (am-monia, for example).

Slotted-cylinder typesThe flowmeter most commonly used inthe process industries substitutes a slot-ted cylinder for the tapered tube (Fig.3c). Compared with a metal rotameter,a greater selection of construction ma-terials and a flow turndown of at least25:1 (vs. 3.6:1) are provided.

The lower portion of the float is a pistonthat can “plug” the slot in the cylinderwall. The float rises until enough of theslot has opened to create equilibriumbetween the two upward-acting flowforces and the single downward-actingforce. As for rotameters, when in thisequilibrium position, float height is pro-portional to flow rate. The basic equa-tions for tapered tube and slottedcylinder flowmeters are similar, withtheir flowmeter coefficients (K factors)accounting for any differences.

Flowmeter accessoriesRegardless of the design of variable-areaflowmeters, flow measurement is takenat some equilibrium point where thefluid flow force is balanced by an oppos-ing force exerted by a “flow element”(such as a float). Either the force of grav-ity or a spring is used to return the flowelement to its resting position when theflow lessens. Gravity-operated flowme-ters (Fig. 3a–c) must be installed in avertical position, while vane or spring-operated devices (Fig. 3d–f ) can bemounted in any position.

Some variable-area flowmeters can beprovided with position sensors andtransmitters (pneumatic, electronic, dig-ital, and fiber optic) for connecting to re-

mote displays or controls. Most flowme-ters have only flow alarm output signals,although some provide a continuous sig-nal that represents the flow rate.

A variable-area flowmeter or rotameteris typically provided with calibrationdata and a direct-reading scale for air orwater (or both). To size a meter for otherservice, the actual flow must be con-verted to a standard flow. Instrumentmanufacturers use different standardflow units. For liquids, the standard flowis the water equivalent in gal/min at 70ºFand 10 psi (20ºC, 69 kPa); for gases, it isthe air equivalent in standard cubic feetper minute (scfm) at 70ºF and atmos-pheric pressure. Tables listing standardwater and/or air equivalent values areavailable from flowmeter manufactur-ers, who also might provide slide rules,nomographs, and computer software forflowmeter sizing. HTPRO

Look for Part 2 of this article in the Sep-tember 2014 issue of HTPro covering se-lection basics, sizing, mass flowmeteroverview, and FAQs about flowmeters.

For more information: Daniel H. Herring(The Heat Treat Doctor) is president, The Herring Group Inc., P.O. Box 884,Elmhurst, IL 60126-0884, 630.834.3017, dher r ing@heat- t reat-doc tor.com,heat-treat-doctor.com.

Fig. 3 — Variable-area flowmeters: (a) glass/plastic tapered tube rotameter, (b) metal tapered tube rotameter, (c) slotted metal cylinder, (d) vane type, (e) piston meter with spring-loaded orifice piston over a tapered plug, and (f) tapered tube with spring.

Flow

P2D Tube

D Float

g

P1

Flow

(a)

Flow

P2D Tube

D Float

g

P1

Flow

Indicator

(b)

Indicator

Slot

g P2

Open slot length Flow

P1

Flow(c)

P1 Vane P2

Flow Flowg

(d)

Moving orifice

Metering coneP1 P2

F spring

Flow Flow

(e)

P1 P2F spring

Flow Flow

(f)



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