i :1 n

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RADIO FREQUENCY DRYING OF

LATEX ADHESIVE ON CARPET

Final Report on EPRI RP 2782-05 December 1989

prepared by

Wallace W. Carr The School of Textile and Fiber Engineering

Georgia Institute of Technology Atlanta, Georgia 30332

Dr. K. R. Amarnath, EPRI Project Manager

(The'report contains no patentable inventions or discoveries.)

submitted to

Electric Power Research Institute 3412 Hillview Avenue

Palo Alto, California 94303

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NOTICE

This report was prepared by the organization(s) named below as an account of work sponsored by the Electric Power Research Institute, Inc. (EPRI). Neither EPRI, members of EPRI, the organization(s) named below, nor any person acting on their behalf: (a) makes any warranty, express or implied, with respect to the use of any information, apparatus, method, or process disclosed in this report or that such use may not infringe privately owned rights; or (b) assumes any liabilities with respect to the use of, or for damages resulting from the use of, any information, apparatus, method, or process disclosed in this report.

Prepared by the School of Textile and Fiber Engineering, Georgia Institute of Technology, Atlanta, Georgia

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EXECUTIVE SUMMARY

The feasibility of coupling a radio frequency (RF) oven Gith a conventional convection oven to dry latex adhesive backing on tufted nylon carpet has been studied. Four types of drying tests were conducted: convective heating only; RF heating only; RF preheating followed by convective heating; and convective heating followed by RF postheating. preheating and postheating appear to be feasible, but RF preheating has some advantages. It requires less floor space and lower initial capital investment and has a shorter simple payback period.

Both RF

iii

3 ACKNOWLEDGEMENTS

The support of Georgia Power Company's Technology Applications Center (TAG) is gratefully acknowledged. The project could not have been conducted without the use of the TAC's facilities. Special thanks are due to Gary L. Birdwell, TAC Manager, who has been closely involved in the project from its inception. Mr. Birdwell's support, suggestions and advise are gratefully acknowledged.

Mr. Jim Miller of Shaw Industries, Inc. has been extremely helpful throughout the project. His suggestions, advise and aid in procuring materials have been very valuable and are ackridwledged.

Special thanks are due to several individuals who have generously given their time, expertise and experience during the course of this investigation:

Mr. George Suhr, formerly of Reichhold Chemical Co. Mr.. Herman Caldwell, Gowin-Card, Inc. Mr. Mark Aeckerman, Shaw Industries, Inc. Mr. Philip Reynolds, RBI-Carpet Consultants

The author wishes to thank the student assistants who worked on the project. Mr. John Knox set up the equipment for the convection tests. Mr. Alan Deariso was primarily responsible for conducting the drying tests. Mr. Prashant Chawla carried out data analysis and was responsible for much of the economic evaluation.

Mr. Vance Mullis of the Georgia Power Company constructed a model for making the economic analysis. Mr. Mullis's work on the project is gratefully acknowledged.

Materials for the project were generously supplied by Shaw Industries,, Inc. and Reichhold Chemical Co. Their support is much appreciated.

., l,,^ _. .. __ ,.....,..... rl....,..._.l .=__... -l;i .-.. : ..,-. _.... ... , . .... .. . - - .

:1 -..

*\. ACKNOWLEDGEMENTS 7 '1

. The support of Georgia Power Company's Technology Applications Center (TAC) is gratefully acknowledged. The project could not have been conducted without the use of the TAC's facilities. Special thanks are due to Gary L. Birdwell, TAC Manager, who has been closely involved in the project from its inception. Mr. Birdwell's support, suggestions and advise are gratefully acknowledged.

Mr. Jim Miller of Shaw Industries, Inc. has been extremely helpful throughout the project. His suggestions, advise and aid in procuring materials have been very valuable and are 1 acknowledged. /'

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Special thanks,are due to several individuals who have generously given their tim,e, expertise and experience during the course. of this investigation:

Mr. George Suhr, formerly of Reichhold Chemical Co. Mr.. Herman Caldwell, Gowin-Card, Inc. Mr. Mark Aeckerman, Shaw Industries, Inc. '

Mr. Philip Reynolds, RBI-Carpet Consultants

The author wishes to thank the student assistants who worked on the project. the convection tests. Mr. Alan Deariso was primarily responsible for conducting the drying tests. Mr. Prashant Chawla carried.out data analysis and was responsible for much of the economic evaluation.

Mr. John Knox set up the equipment for

Mr. Vance Mullis of the Georgia Power Company constructed a model for making the economic analysis. the project is gratefully acknowledged.

Mr. Mullis's work on

Materials for the project were generously supplied by Shaw Industries,, Inc. and Reichhold Chemical Co. Their support is much appreciated.

-1 TABLE OF CONTENTS

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SECTION

E~CUTIVE SUMMARY ACKNOWLEDGEMENTS LIST OF TABLES LIST OF FIGURES

1 INTRODUCTION AND BACKGROUND 1.1 INTRODUCTION 1.2 OBJECTIVE 1.3 SCOPE OF WORK 1.4

1.5 SECONDARY ADHESIVE LAMINATION PROCESS 1.6 LOCATION OF RF OVEN IN RETROFITTING A

1.7 BRIEF LITERATURE REVIEW .

BRIEF DESCRIPTION OF TUFTED NYLON CARPET CARPET AND ITS PRODUCTION

SECONDARY BACKCOATING LINE

2 EXPERIMENTAL DETAILS 2.1 MATERIALS 2.2 EQUIPMENT 2.2.1 Convection Oven and Balance 2.2.2 Thermal Measurements 2.2.3. IBM Personal Computer 2.2.4 . Radio Frequency Oven 2.3 SAkPLE PREPARATION 2.4 DRYING, AND CURING TESTS

CARPET 2.5 HEAT-UP RATES OF COMPONENTS IN BACKED

3 TEST RESULTS AND DISCUSSION 3.1 INTRODUCTION 3.2 BASELINE TESTS 3.3 RF HEATING ONLY 3.4

3.5

3.6 QUALITY ASSESSMENT

3.8 CONCLUSIONS

RF PREHEATING FOLLOWED BY CONVECTIVE

CONVECTIVE HEATING FOLLOWED BY RF HEATING

POSTHEATING -

3.7 COMPONENT HEAT-UP RATES

PAGE

iii iv

vi i viii

1-1 1-1 1-1 1-1

1-2 1-4

1-4 1-8

2-1 2-1 2-1 2-1 2-4 2-4 '

2 - 4 2-4 2-6

2-6

3-1 3-1 3-1 3-1

3-7

3-7 3-16 3-16 3-17

d J

. TABLE OF CONTENTS (cont.)

4 ECONOMIC ANALYSIS 4 :I INTRODUCTION 4.2 CASES ANALYZED 4.3 THE ECONOMIC MODEL 4.3.1 Introduction 4.3.2 Assumptions 4.4 RESULTS AND DISCUSSION 4.4.1 Results 4.4.2 General Observations 4.4.3 Simple Payback 4.4.4 Economic Feasibility of Retrofitting

With RF Ovens

5 CONCLUSIONS AND RECOMMENDATIONS 5.1 CONCLUSIONS 5.2 RECOMMENDATIONS . .

4-1 4-1 4-1 4-3 4-3 4-4 4-5 4-5 4-5 4-11

, 4-11

5-1 5-1 5-1

1 LIST OF TABLES

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I

TABLE

2.1 WEIGHTS OF LATEX ADHESIVE APPLIED

3.1 EFFECT OF RF HEATING ON AVERAGE DRYING RATE IN THE CONVECTION OVEN

4.1 NET PRESENT VALUE (NPV) OF OPERATING COSTS FOR A 13-YEAR PERIOD

4.2 NET PRESENT VALUE OF OPERATING COSTS FOR A 13-YEAR PERIOD PER SQUARE YARD OF CARPET (NDV/YD2)

SPACE REQUIREMENT AND INITIAL CAPITAL EXPEND I TURE

4.3

4.4. ' SIMPLE PAYBACK PERIOD

PAGE

2-2

3-14

4 - 6

4-7

4-8

4 - 9

3

v i i

n LIST OF FIGURES

1 FIGURES PAGE

,1- 1 FOUR MAJOR COMPONENTS OF TUFTED CARPET 1-3

1-2 SECONDARY ADHESIVE LAMINATION LINE 1-5 ’\

17 1-3 SECONDARY ADHESIVE LAMINATION LINE WITH RF PREHEATING OVEN 1-6

1-4 SECONDARY ADHESIVE LAMINATION LINE WITH RF POSTHEATING OVEN 1-7 : I

2-1 CONVECTION OVEN AND BALANCE 2-3

3 2-2 STAGGERED THROUGH FIELD ELECTRODE CONFIGURATION USED FOR TESTS 2-5

:J 2-3 SET UP FOR HEATING IN AN RF FIELD 2-7

3 - 2 3-1

.3-2

MOISTURE CONTENT VERSUS DRYING TIME FOR BASELINE CONVECTION TESTS

LATEX TEMPERATURE VERSUS DRYING TIME

(0.78 kg/m2)

LATEX TEMPERATURE VERSUS DRYING TIME

(1.1 kg/m2>

- UNBACKED CARPET OF 23 oz/yd2

: UNBACKED CARPET OF 32 oz/yd2

3-3

3-3

3 -4

3-4

3-5

3-6

: I MOISTURE CONTENT VERSUS DRYING TIME FOR RF HEATING UNBACKED CARPET WEIGHT OF 23 oz/yd2 (0.78 kg/m2)

3-5

3-6

MOISTURE CONTENT VERSUS DRYING TIME

WEIGHT OF 32 oz/yd2 (1.1 kg/m2) FOR RF HEATING - UNBACKED CARPET

MOISTURE CONTENT VERSUS DRYING TIME FOR RF HEATING AND CONVECTIVE HEATING - UNBACKED CARPET WEIGHT OF 23 oz/yd (0.78 kg/m2) 3 3-8

3-7 MOISTURE CONTENT VERSUS DRYING TIME FOR RF HEATING AND CONVECTION HEATING

(1.1 kg/m2) - UNBACKED CARPET WEIGHT OF 32 oz/yd2

3-9

3-8

3-9

.\

3-10

3-11

3-12

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LATEX TEMPERATURE VERSUS DRYING TIME FOR RF HEATING - UNBACKED CARPET WEIGHT OF 23 oz/yd2 (0.78 kg;/m2) . 3-10

LATEX TEMPERATURE VERSUS DRYING TIME FOR RF HEATING - UNBACKED CARPET WEIGHT OF 32 oz/yd2 (1.1 kg/m2) 3-11

LATEX TEMPERATURE VERSUS DRYING TIME FOR RF HEATING - UNBACKED CARPET WEIGHT OF 23 oz/yd2 (0.78 kg/m2) 3-12

LATEX TEMPERATURE VERSUS DRYING TIME FOR RF HEATING AND CONVECTIVE HEATING - UNBACKED CARPET WEIGHT OF 32 (0 .78 kg/m2)

TEMPERATURE VERSUS TIME FOR RF FOLLOWED BY CONVECTIVE HEATING

oz/yd2 3-13

PREHEATING 3-15

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CHAPTER 1

INTRODUCTION AND BACKGROUND

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1.1 INTRODUCTION

Approximately half of the world's production of carpet is in the United States, and much of the U.S. carpet industry is concentrated in the northwestern part of Georgia. The carpet industry has a number of processes that could potentially utilize the electrotechnologies; however, little use of the electrotechnologies has been made. The investigation discussed in this report was conducted in an effort to make the carpet industry more aware of the electrotechnologies and to promote the utilization of radio frequency heating in carpet processing.

A study of the feasibility of utilizing a radio frequency (RF) oven in the drying and curing of latex adhesive backing on tufted nylon carpet was conducted. adheres the secondary backing. Drying and curing in the backcoating process was selected for study because it appeared to have potential for commercialization of RF drying technology. step in the backcoating operation often limits production speed. There are numerous backcoating machines that are running at relatively low speeds (in the neighborhood of 50 fpm) that cannot be increased by adding oven.lengths because floor space is limited [l]. Since RF ovens generally require much less floor space than convection ovens, increasing production speeds of dryer limited backcoaters via retrofitting with RF ovens was the focus of the investigation.

Latex adhesive holds the face yarns in place and

The drying and curing

1.2 OBJECTIVE

The objective of the study was to investigate the feasibility of coupling an RF oven with a conventional convection oven to dry latex adhesive backing on tufted nylon carpet. The effects of using an RF oven on process economics and carpet aesthetics were studied.

1.3 SCOPE OF WORK

The study was divided into four major tasks: establishing baseline operations of conventional backcoating operation, evaluating the technical feasibility of using-an RF oven in drying and curing latex backing, evaluating the economic feasibility of using an RF oven in the backcoating process and preparing a report summarizing the findings and conclusions of the investigation.

TASK 1. The initial task was to establish the baseline operating conditions of a conventional backcoating system so that the use of an RF oven in conjunction with the conventional system could be evaluated. The drying characteristics of latex-

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backed, t u f t ed nylon carpet was studied using a laboratory convection oven. on carpet w a s simulated-in the laboratory, and the backed carpet was dr ied using a convection oven. Moisture content (dry basis) versus drying t i m e curves were generated f o r two carpets selected with the a i d of J i m Miller of Shaw Industr ies , Inc. One of these was a low-weight carpet which is a high volume product. The other was a medium-weight carpet t ha t i s a l s o a high volume product. weights selected represent much of the carpet processed on backcoating machines.

The commercial application o f l a t ex backing

''

Thus, the two

TASK 2. The second task involved the evaluation o f the technical f e a s i b i l i t y of using an RF oven fo r drying and curing of latex backing. The ef fec ts of electrode configuration, ,operating conditions, l a tex consti tuents and carpet components were studied. Also, carpet properties and aes the t ics were assessed.

TASK 3. The t h i r d task involved making an economic analysis to es tab l i sh the f e a s i b i l i t y of using an RF oven i n drying and curing of l a t ex backing i n tuf ted nylon carpet. Economic analyses were made fo r several d i f fe ren t scenarios f o r modifying an exis t ing la tex backcoating system and f o r the i n s t a l l a t i o n of a new backcoating l i ne .

. .

TASK 4. The f i n a l task was the preparation of a report summarizing the findings and conclusions of the project .

1.4 BRIEF DESCRIPTIONS OF TUFTED NYLON CARPET AND ITS PRODUCTION

Tufted carpet 'used i n th i s investigation is shown schematically i n Figure 1.1. It consis ts o f four major components: primary backing, face yarns, adhesive layer and secondary backing.

Tufting bas ica l ly consis ts o f the inser t ion of a yarn through a substrate ca l led the primary backing. one s ide of the substrate t o the other s ide. the needle is retracted. punching the needle through the substrate , a row of t u f t s a re formed. Needles a re configured so t ha t rows of t u f t s a re produced simultaneously which a l lows wide carpets t o be produced f a i r l y rapidly.

A needle ca r r i e s the yarn f r o m The yarn i s held while

By moving the substrate and repeatedly

The yarns punched through the substrate form loops on the surface of the substrate . Thus the term loop p i l e is used t o describe the carpet. I n some cases, the loops a re clipped, and the term cut p i l e is used t o describe the carpet.

During tu f t ing , the yarns (referred t o as face yarns) a re inser ted through the primary backing, but a re not locked in . The yarns a re held i n place by a backcoating. The backcoating serves several functions including the following:

-...

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BACKING BACK1 NG

A

- . . . . - . - . . . . .

BACKING BACKING

FIGURE 1.1 FOUR MAJOR COMPONENTS OF TUFTED CARPET A) LOOPED PILE B) CUT PILE

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i

1. 2.

4. to improve dimensional stability

to anchor the tufts in place to penetrate the yarn tufts and bind the filaments

4. 3. to adhere the secondary backing

1.5 SECONDARY ADHESIVE LAMINATION PROCESS

The& are several methods of backing carpet; however, most carpet is backed using a secondary backing. This was the process studied in the project discussed in this report. The secondary lamination process involves use of a latex to adhere a secondary backing to the underside of tufted carpet.

A secondary lamination line is shown schematically in Figure 1.2. Unbacked carpet is introduced on one end of the machine and is pulled through an applicator that applies a layer of latex adhesive to the back side of the carpet. The coated carpet is then brought in contact with a secondary backing which has a thin layer of adhesive applied to it. A tenter frame is used to transport the backed carpet through a convection oven which dries and cures the latex. are used to grip the carpet along its edges and hold it to predetermined dimensions during the drying and curing process. leaving the oven, the carpet is removed from the tenter frame and is transported using rollers.

Sharp metallic pins

After

Several other processes such as shearing, inspecting and packaging follow the backcoating operation. performed in line with the backcoating operation, but can be performed on a different process line.

1.6 LOCATION OF RF OVEN IN RETROFITTING A SECONDARY BACKCOATING LINE

These processes are sometimes

Determining the location of the RF oven in retrofitting a secondary backcoating line to give optimal results was one of the concerns of the study. The location of the RF oven is important because it can affect heating rate in the RF oven, size of oven required and possibly product quality. In locating the RF oven, the potential for arcing must be minimized. As mentioned in the previous section, the backed carpet is transported through the convection oven tenter frame to maintain the carpet‘s dimensional stability during drying and curing. If the tenter frame were used in an RF oven, the sharp metallic pins used to hold the edges of the carpet would probably cause corona discharge. Thus, if an RF oven is to be used, provisions to eliminate the corona discharge problem must be made.

Discussions with representatives of carpet manufacturers led to two approaches. The first is illustrated in Figure 1.3. The RF oven would be located between the pretenter and the tenter frames. carpet would have to reach the tenter frame before substantial curing of the latex occurred. However, it was felt that substantial preheating and some moisture removal could be carried out in the RF oven. The second approach, illustrated in Figure 1.4, is to use the RF oven to final dry the carpet after it has been dimensionally stabilized in the convection oven and removed from the tenter frame.

The

1 - 4

1

"J" BOX

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FIGURE 1 . 2 SECONDARY ADHESIVE LAMINATION LINE

3

%.

TRF PREHEATING

'

1 J

FIGURE 1.3

CONVECTION OVEN

ADHESIVE APPLICATOR PANS

SECONDARY A D H E S I V E L A M I N A T I O N L I N E W I T H R F P R E H E A T I N G OVEN

FIGURE 1.4 SECONDARY ADHESIVE POSTHEATING OVEN

LAMINATION LINE WITH RF

1 7

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One of the questions that the project has attempted to answer is which approach would be the best. backed carpet were studied to help answer this questions.

The drying characteristics of latex

1.7 BRIEF LITERATURE REVIEW

Metaxas et al. 12-51 have previously recognized carpet manufacturing as "an area for potential application of electrotechnologies. A number of potential areas for applying electrotechnologies were identified .by Metaxas; however, his work was primarily limited to microwave dryers. The major reason Metaxas selected microwave dryers over RF dryers was associated with corona discharge during processing with RF dryers. order to obtain dimensional stability, the carpet is transported through some of the processes using a tenter frame. pins are used to grip the carpet along its edges (selvage) to hold the carpet to predetermined dimensions during heating. The electric field at radio frequency would have to be substantially higher than those needed for microwave. during processing with RF ovens. For this reason, microwave dryers were selected over RF dryers for Metaxas studies.

In

Sharp metallic

The metallic pins might cause corona discharge

Although Metaxas et al. limited their investigation to microwave dryers;'Metaxas (51 recognized the possibility of using RF energy in parts of processes where the transport of carpet without using tenter pins might be feasible. For example, the use of an RF system installed at the end of the conventional hot air dryers to increase throughput was suggested. frequency system for this application might offer some operational and cost advantage over an equivalent microwave resonant equipment.

Another study [ 6 ] involving the use of microwave energy in the drying and curing of latex backing on carpet was reported in the early 1970's. times and product quality for microwave drying as compared to conventional hot air drying. The results indicated that drying times could be substantially reduced with no resultant loss of product quality .

Metaxas suggested that using a radio-

An experimental investigation was conducted to study drying

The use-of an RF oven in conjunction with a conventional convection oven for drying polyvinyl chloride and latex backing in a British carpet manufacturing facility was reported in the early 1970's [ 7 ] . By positioning the RF oven directly before the conventional dryer, an increase in production speed up to 50% was obtained.

J

CHAPTER 2

EXPERIMENTAL DETAILS

.\ 2.1 MATERIALS

The tests were conducted using two carpet weights selected with the

low-weight carpet referred to as FHA carpet. weighed approximately 23 oz/yd2 (0.78 kg/m2) and was a nylon looped pile carpet with a polypropylene primary backing. The other carpet selected was also a high-volume carpet and weighed approximately 32 oz/yd2 (1.1 kg/m2). This medium-weight carpet had a cut pile and a polypropylene primary backing. Shaw Industries, Inc.

The latex compound used for the test was supplied by Reichhold Chemical Co. of Dalton, Georgia. It contained a styrene-butadiene copolymer'which is the primary type of material used in the secondary lamination process. approximately 60:40. The latex compound also contained the following: calcium carbonate filler, surfactants, a sodium polyacrylate thickener and anti-.oxidants.

. aid of Jim Miller of Shaw Industries, Inc. One was a high-volume, $The unbacked carpet

Both types of carpet were supplied by

The ratio of styrene to butadiene was

The latex adhesive applied to the primary backing contained 82% total solids and 18% water and had a viscosity of approximately 16,000 centipoise. The skipcoat (adhesive applied to the secondary backing) contained 78% total solids and 22% water. It had a viscosity of approximately 12,000 centipoise. applied to the primary and secondary backings for the two weight carpets tested are given in Table 2.1.

The dry weights of latex adhesive

The two types. of secondary backing typically used with tufted nylon carpet are jute and polypropylene. approximately 5 . 7 oz/yd2 (0.19 kg/m2) , while the polypropylene backing weighed 3.0 oz/yd2 (0.10 kg/m2).

The jute backing weighed

2.2 EQUIPMENT AND INSTRUMENTATION

2 . 2 . 1 Convection Oven and Balance

The initial task involved establishing the baseline operating conditions of a conventional backcoating operation. For this, the variation of moisture content with time was needed. A system (see Figure 2.1) was set up for measuring the carpet's weight while it was drying in a convection oven. A Blue-M laboratory convection oven was modified for the convection tests. Sheet metal was used to reconfigure the inside of the oven so that the air would impinge on the latex backing. Four holes were made in the top of the oven, through which a basket for holding an ll-inch by ll-inch (0.28 m by

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4.

TABLE 2 . 1 WEIGHTS OF LATEX ADHESIVE APPLIED

.\

Unbacked Carpet Weight oz/yd2 (kg/yd2)

23 (0 :78)

32 (1.1) . .

Latex Compound Weight oz/yd2 ( k d v d 2 )

Adhesive Skip - c o a t Total Layer

1 8 . 9 5 . 9 24.8 (0.64) ( 0 . 2 0 ) ( 0 . 8 4 )

2 1 . 9 5 . 9 2 7 . 8 (0.74) (0 .20) ( 0 . 9 4 )

1

: I . ."

1

3

Convec t i o y Oven

FIGURE 2.1

Digital Balance \

- Rack To Hold

CONVECTION OVEN AND BALANCE

J

0 . 2 8 m) carpet sample was suspended. The basket was held in position by four rods that were attached to the top of a Fisher XT top loading balance.

2.2.2 Thermal Measurement

Two types of temperature measuring devices were used. thehocouples were used with an Omega Trendicator recorder for measurements inside the convection oven. A Luxtron 750 Fluoroptic Thermometry device which was designed for use in high frequency electric fields was used to record latex backing temperature during the RF and convection tests.

Iron-constantan

2.2.3 IBM Personal Commter

The Fisher XT top loading balance and the Luxtron Fluoroptic Thermometer were interfaced to an IBM personal computer using RS232 cables so that the variations of temperature and weight (during convection tests) with time could be recorded during tests.

2.2.4 Radio Freauencv Oven

The RF oven used for the tests was built by Strayfield International. It was a 20-KW unit operating at 27.1 MHZ. Three types of 24-inch- wide electrode configurations (flat plates, staggered through field and stray field) were used in preliminary tests, but the staggered through field was determined to be best suited for the latex drying and curing. The geometry of the staggered through field electrode used for the tests is illustrated in Figure 2.2. To ensure even exposure to-the electric field, the carpet samples were transported through the machine on a polypropylene conveyor belt driven by an electric motor.

2.3 SAMPLE PREPARATION

The primary steps in preparing the samples for drying and curing tests were as follows:

1.

2.

3 .

4.

5 .

After 11-inch (.28 m) by 11-inch (0.28 m) swatches of carpet and secondary backing were cut out, their weights were measured and recorded.

LatexGompound was prepared according to the instruction of Reichhold Chemical C o . , a major supplier of latex compound to carpet industry.

The Luxtron temperature probe was positioned in yarn loops on back of the carpet.

The proper the carpet

The carpet roller.

the

the

amounts of frothed adhesive were applied to the back of and secondary backing.

and the secondary backing were pressed together using a

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-1 1.25" DIA.

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FIGURE 2.2 STAGGERED THROUGH F I E L D ELECTRODE CONFIGURATION USED FOR T E S T S

.__ ' 1

3 7-5

1

3 6 . The uncured sample's weight was measured and recorded.

2.4 DRYING AND CURING TESTS

Four types of drying and curing tests were performed as follows:

1. Convective heating only ' 2 . RF heating only 3 . 4.

Preheating with RJ? oven followed by convective heating. Convective heating followed by RF postheating

The first set of tests was performed to establish a baseline for evaluating the effects of using an RF oven in the drying and curing process. These tests were performed simply to obtain information on how rapidly drying and curing could be achieved using the RF oven only. sets of tests were performed using the RF oven in conjunction with convective heating. attempt to establish advantages/disadvantages of the two proposed ways of utilizing RF heating the carpet backcoating process.

Carpet specimens of the two weights mentioned earlier were used in the tests. 'The backing weights applied were the standard weights used in industry and recommended by Reichhold Chemical Co. Although both jute and polypropylene secondary backings were tested, most of the tests were performed using jute.

The second set of tests used the RF oven only.

The third and fourth

Preheating and postheating tasks were run in an,

2 . 5 HEAT-UP RATES OF COMPONENTS IN BACKED CARPET

Latex-backe-d tufted nylon carpet contained a number of components. One of the concerns of the project was how these components heat up in RF field. properties of the components was not available, the RF oven was used to measure the tendency of the various components to heat up.

Since a test apparatus for measuring the dielectric

The set up shown schematically in Figure 2.3 was used to subject the various components to the RF field. A material was placed in the slot cut into a polyethylene plate which was then positioned between two electrodes in the RF oven. Voltage was applied to the electrodes, and the temperature of the material with respect to time was recorded.

Tests were run on several materials found in latex-backed, tufted nylon carpet including: water, nylon 6 6 filament yarn, nylon 66 spun yarn, nylon 6 filament yarn, nylon 6 spun yarn, polypropylene primary backing, polypropylene secondary backing, jute secondary backing, barium sulfate, and calcium carbonate.

, Slot For Holding Material .\ r-

\

AI u m inum El ec? rod e

Polyethylene Plate

. .

FIGURE 2.3 SET UP FOR HEATING IN AN RF FIELD

1 1

-.. CHAPTER 3

3 TEST .RESULTS AND DISCUSSION

1 -I :1 I ._ 1 -I 1.1 , ,

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.\ 3.1 INTRODUCTION

The r e s u l t s of the drying and curing t e s t s a re presented i n t h i s chapter. parameters monitored. Moisture Content (MC) i s calculated on a dry bas is f o r a l l of the data discussed i n the report . of MC after the drying and curing s tep is typical ly 5 % [ 9 , 111, based on t o t a l dry weight of backed carpet.

Moisture content and l a t ex temperature were the primary

The t a rge t value

3.2 BASELINE TESTS

Laboratory convection oven t e s t s were conducted t o serve a s a baseline f o r judging the e f f ec t s of RF heating on drying and curing. E f f o r t s were made t o obtain drying r a t e data on commercial drying systems f o r comparison with the laboratory r e su l t s . No source o f t h i s information w a s found; however, information on ta rge t moisture content following drying and curing and drying time were available. The t a rge t value o f moisture content is usually 5%. The dwell time i n commercial ovens i s typ ica l ly 120 seconds.

P l o t s o f MC versus time are shown i n Figure 3.1 fo r both carpet weights considered. The shapes o f the p lo ts indicate t h a t there is a shor t heat-up period, approximately 30 seconds, before maximum drying rate is reached. However, some drying does start almost immediately. Although the drying r a t e f a l l s off s l i g h t l y with drying time, it does not appreciably decrease u n t i l a f t e r the MC ta rge t value of 5% i s reached. Because the drying r a t e does not appreciably decrease as the carpet d r i e s out , there is not great advantage of f i n a l drying with RF heating t h a t is present with some materials.

Typical p lo t s of l a t ex temperature versus drying time a re shown i n Figure 3.2 f o r carpet weights of 23 and 32 oz/yd2 (0.78 and 1.1 kg/m2), respectively. apparently due t o var ia t ion i n probe location i n the la tex .

The curves change s l igh t ly from run t o run,

3.3 RF HEATING ONLY

The r e s u l t s of t e s t s using the RF oven a re shown i n Figures 3.3 - 3.8 RF heating lowered moisture content very rapidly t o 5%, as shown i n Figure 3.3. The RF drying times a re much shorter than the 210 seconds required f o r the laboratory convection oven (see Figures 3.4 and 3.5). They are a l s o much shorter than the 120 seconds typical ly needed i n commercial convection ovens.

n 7

11

.- I

1:

1c

5

0

MC% 23 OZ/SQ.YD. - MC% 32 OZ/SQ.YD.

I . . . . I , . . . I , ( , , I , , I . . , ,

0 50 100 150 200 250 300

TIME (SEC)

FIGURE 3.1 MOISTURE CONTENT VERSUS DRYING TIME FOR BASELINE CONVECTION TESTS

3 11

3

I "I

I1 .- "1 .

11 --I ."

n

-...

. . . . I . , . . I . . , , , , . . , , , , , I , , , , , , , , , / , ,

G G n

a

W Y

W

3 I- < U W eL z W I-

O ~ ~ " " " " " " " " " ' . " ' . ' . . I I I . , I . . , . 0 50 100 150 200 '250 300 350 4 0 0

TIME (SEC)

F I G U R E 3.2 LATEX TEMPERATURE VERSUS DRYING T I M E - UNBACKED CARPET WEIGHTS O F 23 AND 32 o z / y d 2

I- z W c z 0 0 u1 U 3 I-

0 5

s

I f

10

. *

5

0

I " " I ' 1 8 1 . I - . 1 ' . I . I . , I I

- Y MC Yo-RF ONLY- 23 OZ/SQ.YD. - MCYo -RF ONLY-32 OZ/SQ.YD.

l * . . I . . . , l , , , . , , . , , , I . , . .

1 0 1 5 20 25 30

TIME (SEC)

FIGURE 3 . 3 MOISTURE CONTENT VERSUS DRYING TIME FOR RF HEATING - UNBACKED CARPET WEIGHTS OF 23 AND 32 o z / y d 2

? "

4.

1 li I

'5 1 3

. I ' 1 i,. I L I 'I .-

3 1 9

I f

10

5

0 I . . . 1 . . . . l * . . , I , , , , I * , . , I , , , , , , , , , , 1 0 50 100 150 200 250 300 350 400

TIME (SEC)

FIGURE 3.4 MOISTURE CONTENT VERSUS DRYING TIME FOR RF HEATING AND CONVECTIVE HEATING - UNBACKED CARPET WEIGHT OF 23 o z / y d 2 (0.78 kg/m2)

15

10 I- z W t- z . ' 0 0 W U 3 I-

H g s

0

5% DRYING TARGET

t

1

0 50 100 150 200 250 300 350 400

TIME (SEC)

FIGURE 3.5 MOISTURE CONTENT VERSUS DRYING TIME FOR RF HEATING AND CONVECTION HEATING - UNBACKED CARPET WEIGHT OF 32 o z / y d 2 (1.1 kg/m2)

'- 1

s

1

The variations of latex temperature with drying time are plotted in Figure 3 . 6 . Latex temperature for RF heating increased much faster than for convective heating, as illustrated in Figure 3.7 and 3.8. The latex temperature increased to 100°C in approximately 15 to 20 seconds for RF heating while it took between 300 and 320 seconds for convective heating.

3 . 4 'RF PREHEATING FOLLOWED BY CONVECTIVE HEATING

4.

The results of tests using the RF oven to preheat before the convection oven are shown in Figures 3.9 - 3.11. The backed carpet was preheated in the RF oven and immediately moved to the convection oven. was a delay of 30 to 60 seconds. before and after the RF oven so that the change in MC could be calculated. The MC plots are made as though there was no time delay. The'temperature plots show that the latex temperature did drop during transportation of the carpet from one oven to the other, as illustrated in Figure 3.9.

Although the relocation was done as quickly as possible, there The carpet weight was measured

Moisture content versus drying time for the two carpet weights is p1otted.h Figures 3.10 and 3.11 for preheating times in the RF oven of 2, 4 , and 6 seconds. The wet latex absorbs RF energy rapidly, and the moisture content drops even for two seconds of preheating. short (approximately 34 seconds) heat-up period before maximum drying rate is reached (as was seen with only convective heating) appears to be eliminated by RF heating. drying rate (see Table 3.1) in the convection oven. This is probably due to moisture migrating to the latex surface when RF heating is used, resulting in higher drying rates.

The

The preheating increased the average

' As can be seen in Figures 3.10 and 3.11, the drying times in the convection oven to reach the target MC of 5% decreased as residence time in RF oven is increased, as would be expected. The decrease in required residence time in a convection oven of fixed length would obviously mean that process speed could be increased. If process speed were to be increased from 50 to 75 fpm (15 to 23 mpm), then required residence time in the convection oven would have to be reduced by two thirds. from 50 to 100 fpm (15 to 30 mpm) would require a decrease in residence time by one half. The data for 23 oz/yd2 (0.78 kg/m2) carpet were used to estimate the RF preheating times of 2 and 3 seconds to reduce required residence time in the oven by the factor of two thirds and one half, respectively. These estimated RF preheating times were used in the economic analysis presented in Chapter 4.

Similarly increasing backcoater line speed

3 . 5 CONVECTIVE HEATING FOLLOWED BY RF POSTHEATING 4

The results of tests using the RF oven to final dry and cure after the backed carpet has been in the convection oven are illustrated in Figure 3.12. Since the RF oven follows the convection oven, RF postheating cannot affect the convective drying curve the way RF preheating does. Also, since the convective drying rate does not appreciably decrease until the MC target value of 5% is reached, there

w U => l- a U W n I w I-

FIGURE

0 5 1 0 15 20 25 30

TIME (SEC)

3.6 LATEX TEMPERATURE VERSUS DRYING TIME FOR RF HEATING - UNBACKED CARPET WEIGHTS OF 23 AND 32 oz /yd2

I

I. '1 13 .s -1 1

I. ' I I

w III 3 l-

U W

a

. .

120

-

-

TEMP. 23 OZ/SQ.YD. - TEMP.- RF ONLY-23 OZ/SQ.YD. J

.

0 ' " ~ ' " . ~ ~ " ~ . ~ " ~ ~ ' " " ' ' ~ ' ~ 1 , . , . 1 . . I I

0 5 0 100 150 200 250 300 350 400

TIME (SEC)

FIGURE 3.7 LATEX TEMPERATURE VERSUS DRYING TIME FOR RF HEATING AND CONVECTIVE HEATING - UNBACKED CARPET WEIGHT OF 23'oz/yd2 (0.78 kg/m2)

3

n

4

1 1

" _ '1 .1 3

3

h

0

E n Y

W oc => I-

u s ' n r W I-

140

120

100

' 80

60

40

20

i I y TEMP. -CONV. OVEN -32 0USQ.YD. I - TEMP.- RF ONLY-32 0USQ.YD.

1 I . . . , I . . . . I , . , . , , , , * 1 , I , I . , 1 . , . .

0 50 100 150 200 250 300 350 400

TIME (SEC)

FIGURE 3 . 8 LATEX TEMPERATURE VERSUS DRYING TIME FOR R F HEATING AND CONVECTIVE HEATING - UNBACKED CARPET WEIGHT O F 32 oz/yd2 (1.1 kg/m2)

3

J

I

TEMPERATURE (DEG. C)

E m

I . . ~~ i . . . . , - . . . * . .

-...

1

I

"1 _.

-I I

". ' 1 .I

1 3

MC 96 -2 SEC RF + CO FIN. - MC % 4 SEC RF+ CO FIN.

MC % -6 SEC RF +CO FIN.

5% DRYING TARGET

0 50 100 150 200 25 0 300

TIME (SEC)

FIGURE 3.10 MOISTURE CONTENT VERSUS DRYING TIME FOR RF PREHEATING AND FINAL DRYING WITH CONVECTION OVEN - UNBACKED CARPET WEIGHT OF 23 oz/yd2 (0.78 kg/m2)

s

-'I '-1

. I I .II

. I

- - MC% 4 SEC RF PREHEATING

MC % 6 SEC RF PREHEATING

5% DRYING TARGET ........................

0 50 100 150 200 250 300

TIME (SEC)

111 FIGURE 3.11 MOISTURE CONTENT VERSUS DRYING TIME FOR RF PREHEATING AND FINAL DRYING WITH - _-- CONVECTION OVEN - UNBACKED CARPET. WEIGHT OF 32 oz /yd2 (1.1 kg/m2)

J

-2

TABLE 3.1 EFFECT OF RF HEATING ON AVERAGE DRYING RATE IN THE CONVECTION OVEN .\

RF Preheating Time

(SI

0

2

4

6

. I

1

Average Drying Rate In The Convection Oven (0 .Ol%/s)

23 oz/yd2 32 oz/yd2 camet carDet

4.1 3.6

5.2 4.0

6.2 4.0

4.7 4.0

-1

1 15

10

. .

5

0

i 1

I

Y MC% 120 SEC CO + 1 OSEC RF

MC% 140 SEC CO + 10 SEC RF

MWo 160 SEC CO +10 SEC RF

- - MC% 190 SEC CO +10 SEC RF

0 5 0 . 100 150 200 250 300

TIME (SEC)

FIGURE 3.12 MOISTURE CONTENT VERSUS DRYING TIME FOR CONVECTION DRYING FOLLOWED BY RF POSTHEATING - UNBACKED CARPET WEIGHT OF 23 oz/yd2 (0.78 kg/mz)

r-j -..

s

J

13

IJ 3 f 1 J

is no great advantage of final drying with RF heating that is present with some materials. However, in commerical ovens there is some variability in drying, resulting in wet spots in the latex. The ~

tendency to have wet spots can limit process speed. A potential advantage of using RF postheating, not investigated in this project, is moisture leveling. If RF postheating can rapidly dry the wet spots, increase in process speed beyond those calculated in this repdrt may be obtainable.

The results plotted in Figure 3.12 shows that RF postheating does rapidly dry the carpet. However, since much of the moisture has been removed by the convection oven, the drying rate is lower in RF postheating than RF preheating. larger than RF preheating ovens.

Thus, RF postheating ovens must be

The data for 23 oz/yd2 (0.78 kg/m2) carpet were used to estimate the RF postheating times of 8 and 11 seconds needed to allow increasing backcoater line speed from 50 fpm (15 mpm) to 75 and 100 fpm (23 and 30 mpm), respectively. analysis discussed in Chapter 4 .

3.6 QUAFITY ASSESSMENT

The estimated times were used in the economic

. .

Carpet samples were tested for quality according to standard testing procedur.es for commercial carpets. bundle wrap, tuft bind strength and delamination. There was no appreciable difference between the baseline samples and the samples cured using RF to preheat and postheat. differences for the samples dried and cured using RF heating only. The delamination strength of the RF heating only was significantly lower than for the other samples. measurement af the bonding strengths of the latex compound between the primary and secondary backings. The secondary backing did not adhere very well for the RF'heating only. This may have been due to moisture migrating to the surface which depressed the surface latex temperature which would reduce curing of the latex in contact with the secondary backing.

The samples were also visually inspected to evaluate appearance and feel. test samples.

The three tests performed were

However, there were some

The delamination test is a

There were no apparent differences between the baseline and

3.7 COMPONENT HEAT-UP RATES

When the RF heat-up tests were performed, none of the backed nylon carpet components heated up rapidly in RF field except water. However, when either the barite or the calcium carbonate was mixed with water, heat-up rate was much faster than for tap water. Apparently, the minerals dissolve in the water and increase ionic conduction.

n -1 3 . 8 CONCLUSIONS

4

1 . '1 ._

'$ '1

4. The following conclusions were drawn from the tests results:

1. Both RF preheating and postheating can rapidly reduce the moisture content in latex-backed carpet.

"kF preheating has an advantage since it eliminates the short "heat-up" period (before maximum drying rate is reached) associated with convective drying.

Because the convective drying rate does not decrease significantly over the drying cycle down to 5 % moisture content, there is no great advantage of final drying with RF heating that is present with some materials.

2.

3 .

4. RF preheating requires a shorter exposure time in the RF field than the RF postheating. Thus, RF preheating requires a shorter oven length.

The component primarily responsible for the heat-up of the latex- backed carpet is water. Dissolved minerals in the water increase the 'heat-up rate appreciably over that of tap water.

5 .

6 . RF preheating and postheating do not affect product quality.

7. Both RF preheating and postheating appear to be technically feasible, but RF preheating has some advantages over RF postheating.

J

C W T E R 4

-4 ECONOMIC ANALYSIS .

4.1 INTRODUCTION

An analysis was made to evaluate the economic feasibility of using an RF oven in drying and curing of latex backing on tufted nylon carpet. The focus of the study has been to increase the production of dryer- limited backcoaters by retrofitting them with RF ovens. Several ways of increasing backcoating production were considered so that the relative merits of retrofitting with an RF oven could be assessed.

The scenario for the economic analysis is as follows. to increase its carpet backcoating capabilities. old backcoater that is capable of operating up to 100 fpm. (30 mpm); however, the convection drying and curing oven is limiting the operational speed to 50 fpm (15 mpm). increased by increasing oven length, but floor space is limited. The company is interested in increasing its backcoating capabilities by incorporating an RF oven in the existing backcoating line.

A company needs It currently has an

The production speed could be

4.2 CASES ANALYZED

Several scenarios for increasing the production speed were considered, as described below.

Case 1: New Backcoating Line Operating at 100 fpm (30 mpm) With Convection Oven

A new machine with production speed of 100 fpm (30 mpm) would be installed. The backcoater plus oven would have a length of 400 ft (122 m) and a width of 25 ft (7.6 m). The gas-fired convection oven consists of 12 modules and has a length of 140 ft ( 4 3 m). This option is viable only if a new backcoating facility can be considered and approximately 1.5 million dollars are available for backcoater, land and building.

Case 2: New Backcoating Line Operating at 100 fpm (30 mpm) With 1000- - kw RF oven

A new machi’ne with production speed of 100 fpm (30 mpm) would be installed. The backcoater and RF oven would have a length of 300 ft (91 m) and a width of 25 ft (7.6 m ) . The 1000 kw, RF oven has a length of 30 ft (9.1 m ) . This option is viable only if a new backcoating facility can be considered and approximately 1.6 million dollars are available for the backcoater, land and building.

-1

Case 3:

Case 4:

Case 5:

Case 6:

Case 7:

Retrofit With Preheating 330-kw RF Oven to Increase Process Speed to 100 fpm (30 mpm)

A preheating 330-kw oven would be located between the pretenter and the tenter frames as shown schematically in Figure 1.3. 10 ft (3.0 m) positioned in the line without major machine modifications and without lengthening the line. increased from 50 fpm (15 mpm) to 100 fpm (30 mpm). The capital expenditure in this case is estimated to be $414,000.00.

The RF oven would have a length of approximately It is assumed that the RF oven could be

Process speed would be

Retrofit With Additional Six Convection-Oven Modules to Increase Process Speed to 100 fpm (30 mpm)

The existing convection oven would be extended by adding six convection-oven modules. (21 m) of space is available for the additional oven length. Process speed would be increased from 50 fpm (15 mpm) to 100 fpm (30 mpm). The capital expenditure in this case is estimated to be $396,000.00.

This aption is viable only if 70 ft

Retrofit By Replacing Existing Oven with New Twelve-Module Convection Oven to Increase Process Speed to 100 fpm (30 mpm)

The existing convection oven would be replaced with a new twelve-module convection oven. Since the new oven is longer than the old one, an additional 50-foot (15-m) long space would be needed for the new oven. Process speed would be increased from 50 fpm (15 mpm) to 100 fpm (30 mpm). capital expenditure in this case is estimated to be $792,000.00.

The

Retrofit With Postheating 370-kw RF Oven to Increase Process Speed to 100 fpm (30 mpm)

A postheating 370-kw RF oven would be located after the convection oven as shown schematically in Figure 1.4. The RF oven would have a length of approximately 22 ft (6.7 m). Process speed would be increased from 50 fpm (15 mpm) to 100 fpm (30 mpm). The capital expenditure in this case is estimated to be $496,000.00.

Retrofit With Preheating 200-kw RF Oven to Increase Process Speed to 75 fpm (23 mpm)

A preheating 200-kw oven would be located between the pretenter and the tenter frames as shown schematically in Figure 1.3. 7.5 ft (2.3 m). It is assumed that the RF oven could be positioned in the line without major machine modifications and

The RF oven would have a length of approximately

J

-...

Case 8:

Case 9 :

Case 10:

without lengthening the line. Process speed increased from 50 fpm (15 mpm) to 75 fpm (30

would be mpm). The

capital expenditure- in this- case is estimated to be $324,000.00.

Retrofit With Additional Three Convection-Oven Modules to Increase Process Speed to 75 fpm (23 mpm)

The existing convection oven would be extended by adding three new convection-oven modules. This option is viable only if 35 ft (11 m) of space is available for the additional oven length. Process speed would be increased from 50 fpm (15 mpm) to 75 fpm (23 mpm). The capital expenditure in this case is estimated to be $198,000.00.

Retrofit By Replacing Existing Oven With New Nine-Module Convection Oven to Increase Process Speed to 75 fpm (30 mpm)

The existing convection oven would be replaced with new nine- module convection oven. old one, an additional 12-foot (15-m) long space would be needed for the new oven. Process speed would be increased 'from 50 fpm (15 mpm) to 75 fpm (23 mpm) . expenditure in this case is estimated to be $594,000.00.

Since the new oven is longer than the

The capital

Retrofit With Postheating 220-kw RF Oven to Increase Process Speed to 75 fpm (23 mpm).

A postheating 220-kw RF oven would be located after the convection oven as shown schematically in Figure 1.4. oven would have a length of approximately 14 ft. (4.2 m). Process speed would be increased from 50 fpm (15 mpm) to 75 fpm (30 mpm). The capital expenditure in this case is estimated to be $396,000.00.

The RF

4.3 THE ECONOMIC MODEL

4.3.1 Introduction

An economic model analysis using Lotus 1-2-3, computer software, was developed to compare the approaches discussed in Section 4.2 for increasing backcoating productivity. were calculated for the different cases. Operating expenses included depreciation of equipment and building, labor costs, fuel costs (electricity and gas) and maintenance costs. Net present value (NPV) of operating expenses over a 13-year period was used as the parameter to compare the different approaches for increasing backcoating productivity.

After-tax operating expenses

The model took into consideration wage inflation and escalation of gas and electricity prices. because it gives the maximum tax advantage. present value (PV) and cumulative present value, called net present value (NPV) of the operating expenses for thirteen years.

A five-year depreciation period was used The model calculates

Since the

J

1 7 -I 3 -.I 11 \-I '-1 '3 -1 -1 . I

'-1 L n

.1 II 13 3 3 J

-.. cost of electricity rates (4, 5 , and 6C

does vary with locations, three electricity price per kwh) were considered.

The model does not address several factors that could be important in selecting a method of increasing backcoating productivity such as: down time required for the modification, design time and cost and other consulting and miscellaneous fees. not "include these factors, it should give a good indication of the economic viability of the approaches considered.

Even though the model does

4.3.2 ASSumDtiOnS

Several assumptions were made in the economic model. calculations and estimations were necessary in making the model. These are briefly described below:

Also,

1.

2.

3 .

4.

5.

6 .

7.

8.

9.

10.

11.

12.

The unbacked carpet to be processed weighs 23 oz/yd2 (0.78 kg/m2) and is 12-ft (3.7-m) wide.

The operational speed of the old backcoater is 50 fpm (15 mpm) *

. I

The old backcoater has a 90-ft (27 m) long oven, consisting of 8 modules.

The price of land in an'industrial area (Dalton, Georgia) was $10,000 per 44,000 square ft. (4,088 square m) [I].

The building construction price was assumed to be $10 per . square ft. ($108 per square mj [l] . New convection-oven modules are available at a cost of $60,000 each. Each module is approximately 11.7 ft ( 3 . 6 ) long. Twelve (12) modules are capable of drying and curing the latex backing at a process speed of 100 fpm (30 mpm) [2].

The cost of a backcoating machine without any type of oven was $580,000 [2].

The capacity of the RF oven needed was estimated from results in Chapter 3 and information provided by Gowin-Card, Inc. on gas-fired oven performance in drying latex backed carpet.

The physical size and cost of the RF ovens were estimated using reference 9.

The RF ovens were assumed to use indirect, gas-fired heat to help remove evaporated water from the RF oven.

The electricity and gas requirements of the RF oven were estimated using reference 9.

An annual depreciation rate on equipment of 20% for five years was assumed.

. . .

13.

14.

15.

161

17.

. 18.

19.

20.

21.

The building depreciation period was 30 years.

The electricity price escalation was based on Georgia Power Company's (GPC's) future projections.

The initial gas price was assumed to be $ 5 per million BTU.

The gas price escalation was based on Whorton Econometric Forecasting Associates (WEFA) projection.

The labor cost inflation rate was assumed to be 5 % annually.

The backcoating line requires two operators and nine other workers per shift. while the others make $7.50 per hour (1).

Installation and commissioning cost for all equipment was assumed to be 10% of total equipment cost.

Maintenance cost of any equipment was assumed to be 10% of installed equipment cost.

The operators are paid $ 9 . 5 0 per hour

.The backcoater is operated 6,000 hours per year.

4.4 RESULTS AND DISCUSSION

,4.4.1 Results

The results of the economic analysis are summarized in Tables 4.1 and 4.2. The net present values (NPV) of operating costs for a thirteen year period'are shown in Table 4.1. different for different cases, net present value per square yard (NW/yd2) of carpet produced is a better parameter for comparison. is summarized in Table 4.2.

Since production rates are

It

Space requirements and capital expenditures for each case are summarized in Table 4.3. which cases are viable for a particular company's situation.

In many instances, these factors may limit

4.4.2 General Observations

The following general observations from the results of the economic analysis can be made.

1. All ten cases for increasing productivity have lower NPV/yd2 than the unmodified backcoating line. existing line to run at 100 fpm (30 mpm) have lower NPV/yd2 and substantially lower capital expenditure requirements than the t w o cases for completely new lines with process speed of 100 fpm (30

The four'cases for modifying the

mpm) *

2. Comparing modifications using RF ovens with those using convection oven modules to increase process speed to 100 fpm (30 mpm) indicates the following:

TABLE 4.1 NET PRESENT VALUE (NPV) OF OPERATING COSTS FOR A 13-YEAR PERIOD

.\

Case - 1

2

3

4

5

6 .

7

8

9

10

11'

. .

Net Present Value (NPV) ( $ 1

Electricity Rate cc.c/kwh sc/kwh 6C&h

5,254,301 5,348,479 5,442,656

6,990,992 7,612,877 8,234 ;762

4,858,787

4,335,715

4,685,724

' 4,951', 294

. .

4,238,943.

3,818,346

4,129,069

4,344,158

3,831,553

5,093,719

4,429,892

4,779,901

5,203,287

4,386,778

3,888,979

4,229,702

4,508,627

3,878,685

a Unmodified 50 fpm Backcoating Line

n r

5,328,650

4,524,070

4,874,079

5,455,279 .

' 4,534,612

3,959,612

4,300,335

4,673,096

3,925 , 816

n 7

-...

TABLE 4.2 NET PRESENT VALUE OF OPERATING COSTS FOR A 13-YEAR PERIOD PER SQUARE YARD OF CARPET (NDV/YD2)

.\

13

._ $1 'I ..

II . J . '1 -.

..I

Net Present Value Per Square Yard

Case

1

2

3

4

5

. 6 .

7

8

9 .

10

lla

4cflcwh

0.84

1.12

0.78

0.69

0.75

0.79

0.91

0.82

0.89

0.93

1.23

Electricity Rate sc/kwh

0.86

1.22

0.82

0.71

0.77

0.83 '

0.94

0.83

0.90

0.96

1.24

6 C /kwh

0.87

1.32

0.82

0.73

0.78

0.87

0.97

0.85

0.92

1.00

1.26

a. Unmodified 50 fpm Backcoating Line

4 - 7

4.

4

1 ' I

TABLE 4 . 3 SPACE REQUIREMENT AND INITIAL CAPITAL EXPENDITURE

Space -\

Process Brief Requirement Speed Description f t

Case f D m of Case j m l

1 100

2 100

3 100 . .

4 100

5 100

6 ' . 100

7 7 5

8 7 5

9 7 5

10 75

New Machine With CO 400a 1

New Machine With RFO 300a ( 9 1 )

Retrof i t With RF Pre- lob heater ( 3 . 0 )

Retrof i t With Addition- 7 0 a1 CO Modules ( 2 1 )

R e t r o f i t by replacing 47 Old CO With New CO

Ret rof i t With RF Post- 22

( 1 4 )

heater ( 6 . 7 )

R e t r o f i t With Preheater 7 . 5b ( 8 . 3 )

Retrof i t With Addition- 36 a1 CO Modules (11)

Retrof i t By Replacing 1 2 Old CO With New CO ( 3 - 7 )

Retrof i t With RF Post- 14 heater ( 4 . 3 )

Capital Expenditures

1 , 5 3 4 , 0 0 0

1 5 8 4 , 2 4 5

414,315

3 9 6 , 0 0 0

792 , 000

496 , 733

'323 758

1 9 8 000

594 , 000

3 9 6 , 4 0 0

Note: CO denotes Convection Oven RFO

a

b

denotes- RF Oven

Length o f backcoater plus oven

O n some backcoating l i n e s , the preheating RF oven probably can be f i t t e d i n without extending the l i n e .

.. .

1

TABLE 4.4 SIMPLE PAYBACK PERIOD

Simple Brief Capital Payback Description Operating Yearly Expenditure Period

- CAse of Case costs Savings Is1. (years 1 '7 1

2

3

4

5

6

7

8

9

10

11

New Machine With

New Machine With RFO

Retrofit With RF Preheater

0.0174

0.0244

0.0195

0.0164

377,974

109,174

297,334

416,374

397,174

285,814

141,120

218,880

198,720

126 , 720

- -

1,534,000

'1,584,245

4.1

14.5 11 414,315 1.4

Retrofit With Additional 40 Modules

396,000 1.0

-1 Retrofit BY Replacing Old CO With New CO

0.0169 792,000 2.0

'-1 Retrofit With RF Postheater

.O. 0198 496 , 733

323,758

1.7

. -1 2.3 Retrofit 'With Preheater '

0.0223

._ 1 Retrofit With Additional CO Modules

0.0196 198 , 000

594,000

396 , 400

- -

0.9

3.0 13 - 0.0203 Re tro f i t By

Replacing Old CO With New CO

Retrofit With RF Pos theater

0.0228

0 i 0272

3.1

- - :I Existing Back- coating Line

3 3

1

a. The RF ovens require substantially less floor space. '1

-.. .- I b. The capital expenditures associated with RF ovens are slightly higher than those for retrofitting by adding convection oven modules, but are much lower than that for replacing the old convection oven with new convection oven modules.

'E. The values of NPV/yd2 for the RF oven modifications are slightly higher than for modifications using convection oven modules, but are appreciably lower than for the existing modified oven.

The RF oven modifications are more sensitive to increasing electricity rates, but perhaps less sensitive than might be expected. This is due to the substantial part of operating costs being associated with labor.

d.

3. The four cases involving modifications to increase process speed to 100 fpm (30 mpm) have lower NPV/yd2 than the similar cases to increase process speed to 75 fpm (23 mpm). This is not surprising since productivity is increased while labor costs remain constant. Increasing process speed to 100 fpm (30 mpm) versus 75 fpm (23 mpm) 'requires substantial increase in required floor space and capital expenditure for the modifications using convection oven modules. The increases associated with retrofitting with RF ovens is much less.

4 . Comparing modifications using RF with those using convection oven modules to increase process speed to 75 fpm (23 mpm) indicates the following:

a.

b.

The RF ovens require less floor space.

The expenditures associated with RF ovens are higher than for retrofitting by adding convection oven modules, but are much lower than that for replacing the old convection' oven with new convection oven modules.

The values of NPV/yd2 for the RF oven modifications are slightly higher than those for modifications using convection oven modules, but are appreciably lower than that for the existing unmodified oven.

c.

d. The RF oven modifications are more sensitive to increasing electricity rates. The sensitivity may be less than expected because labor costs represent a substantial part of operating costs.

5. When similar scenarios are considered, floor space, capital expenditure and NPV/yd2 are lower for RF preheating than RF postheating.

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4 . 4 . 3 S i m D l e Payback

The analysis presented i n the previous ections is somewhat complicated and de ta i led and may not meet the needs of those who prefer a simpler approach t o evaluating the economic f e a s i b i l i t y of using an RF oven i n drying of la tex adhesive on carpets. payback analysis of the capi ta l investment i n the ten cases discussed earl-ier was made. weight of 23 oz/yd2. rate of $5.00 per mill ion BTU were assumed.

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For t ha t reason, a simple

The analysis was made f o r carpet with an unbacked An e l e c t r i c i t y r a t e o f 5 cents per kwh and gas 7

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I n the analysis , the t i m e required f o r the savings i n operating c o s t t o payback the c a p i t a l investment w a s calculated. Operating cos ts include, labor , maintenance, and fue l costs (gas and e l e c t r i c i t y ) . The differences i n the operating costs of the ten cases and operating cos t of the ex is t ing , unmodified backcoating l i n e were calculated on a per square yard of carpet basis . The differences represent the savings i n operating costs per square yard of carpet produced. yearly savings were calculated by multiplying the savings per square yard by yearly production.

Simple payback period w a s obtained by dividing the t o t a l i n i t i a l investment by the yearly savings. The r e su l t s fo r the ten cases a re tabulated i n Table 4 . 4 . involving RF ovens ranged from 1.4 t o 3.1 years. The r e su l t s indicate simple payback period is shorter f o r RF preheating than f o r RF postheating. Also, it is shorter fo r the RF modifications increasing process speed t o 100 fpm than t o 75 fpm.

The

The simple payback period f o r the four cases

4 . 4 . 4 Economic Feas ib i l i ty of Retrofittiniz with RF Ovens

The primary reason f o r making the economic analysis was t o evaluate the economic f e a s i b i l i t y of increasing the process speed of dryer- l imited, space-limited, backcoating l i n e s v i a r e t r o f i t t i n g with an RF oven. feas ib le t o u t i l i z e RF ovens t o r e t r o f i t backcoaters. Both RF preheating and RF postheating appear t o be economically feas ib le , but RF preheating has some advantage over RF postheating.

The r e s u l t s of the analysis indicate tha t i t is economically

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CHAPTER 5

CONCLUSIONS AND RECOMMENDATIONS

.\ 5.1 CONCLUSIONS

Coupling an RF oven with a conventional convection oven to dry latex adhesive backing on tufted nylon carpet appears to be feasible. Although both RF preheating and postheating appear to be feasible, RF preheating has some advantages over RF postheating. are: it eliminates the "heat-up" period (before maximum drying rate is reached) associated with convective drying; it requires a smaller oven length; and it has a shorter simple payback period.

The advantages 13'

5 .2 RECOMMENDATIONS

It is doubtful that RF heating in carpet processes will be utilized on a significant scale until a full scale demonstration is conducted to convince*the carpet industry of the viability of the technology. It is recommended that EPRI put together a consortium of carpet manufacturers to share the cost of the demonstration. After the first unit is successfully demonstrated, the owner of the plant in which the demonstration is conducted can be required to pay for the unit.

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REFERENCES

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2.

3.

4.

' 5 .

6 .

7.

8.

9.

10.

11.

Miller, J., Private Communication, Shaw Industries, Inc., September 1988.

Gohel, H. P. and Metaxas, A.C., "Microwave Drying of Nylon Tufted Carpets I. Dielectric Property and Q Measurements," Proceeding (MPI Conference) Ottawa, June 1978.

Metaxas, A.C. and Meredith, R. "Microwave Drying of Nylon Tufted Carpets 11. TE,, Resonant Cavity, " J. Microwave Power 13(4), 315-320, 1978.

Electrical Characterization of a Modified

Holme, J. and Metaxas, A.C., "Microwave Drying of Nylon Carpets, I11 Field Trails," J. Microwave Power, 14 (4), pp 367-382, 1978.

Metaxas, A.C., "The Future of Electrical Techniques in the Production of printed Tufted Carpets," J. Microwave Power, 16 (l), pp 43-55, 1981.

Small, H., Hatcher, J. D., and Lyons, D. W., "Microwave Drying of Latex Carpet Backing," J. of Microwave Power, 7 (1). pp 29-34, 1972.

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Haley, N. A., "Dielectric Heating Can Speed Carpet Backing," Modern Textiles, Vol 54 ( S ) , 1973.

Reynolds, P. , Private Communication, RBI. International, September 1989.

Caldwell, H., Private Communication, Gowin-Card, Inc., August 1989.

Sanio, M. R. and Schmidt, P. S., "Cost Estimation For Industrial Dielectric Heating Systems," EPRI Report on Contract RP 2893-01, February 1989.

Laughridge, B., Private Communication, Reichhold Chemical Co., August 1989.

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