Improving Carpet Through-Air Drying by Means of Increased Air Permeability

Textile Research Journal, Aug 2002
by Lee, H Stephen, Carr, Wallace W, LaRoche, Jason K

ABSTRACT

Air permeability is an important parameter in through-air drying of unbacked tufted carpet. The primary backing of tufted carpet is the dominant parameter determining carpet air permeability. Carpets of identical construction are tufted using woven and nonwoven primary backings, and the effects of primary backing type on air permeability and drying are studied. The carpet tufted with the nonwoven backing has significantly higher air permeability and significantly lower drying time for a constant pressure drop drying process.

Through-air (through-flow) dryers are widely used for drying unbacked tufted carpets after the dyeing process. For a given blower configuration, the velocity of the air flowing through the carpet depends on its air permeability, which is a measure of how easily air flows through a unit area of porous material for a given pressure drop. Since the air permeability of the carpet increases at a given fan configuration, the airflow rate increases (see Figure 1), increasing the drying rate.

In previous work [4], we studied the effects of several process and construction parameters on air permeability of unbacked tufted carpet and developed a model predicting pressure drop over the carpet versus apparent velocity. The carpet was divided into two sections: the pile yam section and the primary backing section. Over 80% of the pressure drop over the carpet was due to the primary backing section.

Since the primary backing section was the main resistance to airflow in that work, the focus of the research reported here is to increase the air permeability of this section, and thus improve the drying process. The primary backing used in the previous research [4] was limited to woven polypropylene fabric. In this study, we compare the performance of nonwoven and woven backings. Carpets of identical construction are tufted using the two primary backing materials, and air permeabilities are measured with a modified Frazier air permeability tester (FAPT). We also conduct drying studies with a laboratory through-air dryer (LTAD).

Samples (7 cm in diameter) were used in the modified FAPT. The edge of the sample area was first marked on unbacked tufted carpet, and the tufts outside the circular area were removed, leaving only primary backing in this region. Then a 9 cm diameter sample was cut with scissors, and strong adhesive tape was applied over the untufted region to make it impermeable to airflow.

Samples (30.5 cm in diameter) were used in the LTAD. The edge of the circular sample area was first marked on unbacked tufted carpet, and the tufts outside the circular area were removed. Then, a 34.5 cm diameter sample was cut with scissors, and strong adhesive tape was applied to the untufted region to make it impermeable to airflow and to allow a sample holder to tightly clamp the carpet sample. Carpet samples were placed in a 30.5 cm internal diameter, aluminum binding hoop. For the drying study, the bound carpet sample was soaked in room temperature water. Then, to obtain a moisture regain of about 50%, the sample was vacuumed with a 1.5 hp shop-vac, first on the face side and then on the back.

Air permeability tests were conducted with the FAPT based on the Standard Test Method for Air Permeability of Textile Fabrics, ASTM Test Method D 737-75 [1]. In addition to the 1.27 cm (0.5 inch) water pressure drop specified by the test method, air permeability was measured for pressure drops ranging from 1.27 to 8.89 cm (0.5 to 3.5 inches) water, which are typically used in industrial dryers. Five specimens were selected from different regions of the carpet, and the data were averaged. The average pressure drop was plotted versus apparent velocity.

The following procedure was used to monitor the drying process in the LTA: Tests were performed after setting the flow conditions of pressure drop and air temperature with a dry carpet sample in the LTAD. Once the LTAD reached equilibrium conditions, the settings were held constant, and airflow was then diverted through a bypass duct while the test sample was inserted into the test section. Airflow was then re-routed through the test sample, and the data acquisition program was initiated to monitor the testing process and record the data. Since the sample was much bigger than that in the FAPT tests, variability from sample to sample was smaller and fewer repetitions were needed. Three specimens were tested in each test, and the drying results were averaged.

Results and Discussion

We conducted air permeability tests for the two untufted primary backings and the two tufted carpets prepared from each backing. We also performed an additional test for the carpet with nonwoven backing, sheared to a pile height of 2.5 mm. In Figure 3, apparent velocity is plotted versus pressure drop for these samples. For a given pressure drop, the apparent velocity of air flowing through the woven backing is much lower than that through the nonwoven backing. Tufting yams through the woven primary backing result in a carpet with higher air permeability than the untufted woven backing. On the other hand, tufting yams through nonwoven backing result in a carpet with lower air permeability than the untufted nonwoven backing. Tufting has different effects on air permeability because the structures of the backings are different. The woven primary backing is a very tight structure produced from tape yams. The warp and weft yarns cover 100% of the surface area of the woven primary backing, resulting in low porosity and air permeability. Tufting creates holes in the woven primary backing, increasing porosity and thus air permeability. On the other hand, the nonwoven primary backing is very permeable. Tufted yams in the nonwoven primary backing decrease the porosity of this region, and as a result, air permeability is lower. For carpets with identical construction parameters except the primary backings, the carpet with the nonwoven backing has much higher air permeability than the carpet with the woven backing.

Even though the air permeability of the nonwoven backing is much higher than for the woven backing, the primary backing section is still the main resistance to air flow. As shown in Figure 3, reducing the pile height from 9.5 to 2.5 mm decreased the pressure drop over the carpet, but the effect relative to the backing type was small.

We used Equation 3, which includes both viscous and inertial terms to describe the airflow through the unbacked tufted carpet, to fit the data in Figure 3 and to obtain the values of the overall inertial resistance and viscous resistance coefficients for the two carpets. We calculated the values of A^sub PYS^ and B^sub PYS^ for the PYS of the carpet with nonwoven backing using Equation 9. Since the pile yam sections of the two carpets were identical, we also used these values of A^sub PYS^ and B^sub PYS^ for the carpet with woven backing. Then we calculated the values of the overall inertial resistance and viscous resistance coefficients for the PBS of the two carpets using Equation 10. The results are summarized in Table I. Using these values and data for other carpets with woven backings from reference 4, we calculated air permeability at various apparent velocities using Equation 12. The results are shown in Figure 4 for the primary backing sections of the carpets with nonwoven and woven backings. It is apparent that air permeability of the PBS for the carpet with nonwoven backing is much higher than air permeabilities of the PBs for the carpets with woven primary backings of different weft densities.

To illustrate the effect of increased carpet air permeability on through-air drying, carpets with nonwoven and woven backings were dried at a constant pressure drop over the carpet of 1.27 cm H^sub 2^ 0 and an air temperature of 116degC. Figure 5 shows moisture regain as a function of drying time for the two carpets with identical construction parameters and initial moisture regain. The carpet with nonwoven backing dried much faster than the carpet with woven backing. We expected this since the apparent velocity used for drying the carpet with nonwoven backing is much higher than that for drying the carpet with woven backing, as shown in Figure 5. At a moisture regain of 5%, the drying time for the carpet with nonwoven backing is about one half that for the carpet with woven backing. Thus, primary backing type has a significant effect on drying. If air permeability of the PBS can be increased without affecting carpet quality, drying productivity can be significantly increased.

Conclusions

Air permeability is an important parameter in through air drying of unbacked tufted carpet, affecting drying time for a constant pressure drop process. The air permeability of the nonwoven primary backing section is significantly higher than for that of the woven backing section, but the primary backing section is still the main resistance to airflow through the carpet. For a constant pressure drop through-air drying process, the drying time for the carpet with the nonwoven backing is about 50% that for the carpet with the woven backing.

ACKNOWLEDGMENTS

This work was supported by the National Textile Center. We are grateful to Dr. Morton Reed of Milliken Carpet, Dr. David Gentry of Amoco Fabric & Fibers Co., and Mr. David Wright of Queen Carpet Corp. for many helpful discussions and for providing samples.

This paper was presented at The 2000 International Mechanical Engineering Congress & Exposition, Textile Engineering Division.

Literature Cited:

1. ASTM D737-75, Standard Test Method for Air Permeability of Textile Fabrics.

2. Ghali, K., Jones, B., and Tracy, Experimental Techniques for Measuring Parameters Describing Wetting and Wicking in Fabrics, Textile Res. 164, 106-111 (1994).

3. Igwe, G. J. I., Design of a Simple Gas and Solid Filtration Apparatus, Textile Res. J. 58, 280-285 (1988).

4. Lee, H. S., Carr, W. W., Beckham, H. W., and Wepfer, W. J., Factors Influencing the Air Flow Through Unbacked Tufted Carpet, Textile Res. J. 70, 876-885 (2000).

5. Lee, H. S., Study of the Industrial Through-Air Drying Process for Tufted Carpet, Doctoral thesis, Georgia Institute of Technology, Atlanta, GA, 2000.

6. Nossar, M. S., Chaikin, M., and Datyner, A., High Intensity Drying of Textile Fibers, Part I: The Nature of The Flow of Air Through Beds of Drying Fibers, J. Textile Inst. 64, 594-600 (1973).

7. Rainard, L. W., Air Permeability of Fabrics I, Textile Res. J. 16, 473-480 (1946).

8. Rainard, L. W., Air Permeability of Fabrics II, Textile Res. J. 17, 167-170 (1947).

9. Wehner, J. A., Miller, B., and Rebenfeld, L., Moisture Induced Changes in Fabric Structure as Evidenced by Air Permeability Measurements, Textile Res. J. 57, 247-256 (1987).

Manuscript received June 27, 2001; accepted January 16, 2002.

H. STEPHEN LEE, WALLACE W. CARR, AND JASON K. LAROCHE

School of Textile & Fiber Engineering, Georgia Institute of Technology, Atlanta, Georgia 30332, U.S.A.

Copyright Textile Research Institute Aug 2002
Provided by ProQuest Information and Learning Company. All rights Reserved

 

 

Design Issue:

This experiment assessed the air permeability (how easily air flows through a material) of different types of carpet primary backings before and after tufting to improve the carpet drying process during manufacturing.
How fast a carpet dries is partly determined by the permeability of its primary backing.
After tufted carpets are dyed, through-flow air dryers are used to dry the carpeting.

Design Criteria:

Be aware that carpeting with woven primary backing allows more air to travel though it than carpet with nonwoven primary backing.

Key Concepts:

Carpets can be tufted (a dense clump of yarn attached at the base) using either woven or nonwoven primary backings. This backing helps determine the airflow and permeability of the carpet.
Woven backings had higher air permeability and were able to absorb more fluids when tufted due to the creation of small holes created during the tufting process. Woven carpet backing was less permeable before tufting.
Tufting reduced the size of the holes present in the nonwoven backing, therefore making the backing less permeable than when it was untufted.

Research Method:

Air permeability tests were conducted on identical nylon carpet samples (woven untufted, woven tufted, nonwoven untufted, and nonwoven tufted) using a modified Frazier air permeability tester and a laboratory through-air dryer.
Carpet samples were wetted using room temperature water, and then vacuumed with a Shop-vac on both sides to reach the desired saturation level.
Five sections of the carpet samples (7 cm in diameter) were tested using a Frazier air permeability tester. Additional carpet samples (30.5 cm diameter) were tested using a laboratory through-air dryer.
Results of the permeability tests were averaged. Mathematical models of air permeability were evaluated using experimental data and regression.

Commentary:

The method for choosing the carpet manufacturer and the five sections of carpet was not explained. The authors included step-by-step equations and regressions to explain the testing process and models used.

Author(s): H. Stephen Lee, Wallace W. Carr, and Jason K. LaRoche, School of Textile & Fiber Engineering, Georgia Institute of Technology, Atlanta, Georgia
Article Title:Improving Carpet Through-Air Drying by Means of Increased Air Permeability
Publisher: Textile Research Institute
Publication: Textile Research Journal
Publication Type: Refereed Journal
Date of Publication: 2002
Funder/Sponsor: National Textile Center
ISSN: 0040-5175
Volume: 72
Issue: 8
Pages: 681-685