Chapter 3 PREPARATION OF NONWOVEN, COMPOSITE SAMPLES & EXPERIMENTAL METHODS

Transcription

1 Chapter 3 PREPARATION OF NONWOVEN, COMPOSITE SAMPLES & EXPERIMENTAL METHODS

2 A study of noise control property has been made with jute nonwoven and also composite samples made from such nonwovens. The aim of this part of the study was to evaluate the physical and noise control properties of jute nonwoven as well as the composite samples by appropriate experimental methods. So, in this chapter, the following items are dealt with 1) The material used 2) The processing methods adopted for making of jute nonwoven samples and those of composite samples from selected jute nonwoven. 3) Characterisation of developed samples in terms of physical property as well as noise control property by using a simple low cost instrument indigenously developed in the laboratory 4) The statistical technique used for experimental design 3.1 Jute Nonwoven Fabric Production Nonwoven production process includes two steps i) fibre web formation, and ii) web bonding by needle punching. The jute fibres are found to vary widely in terms of quality, strength, fineness, presence of fibre defects and cost. The meshy inter-linked filament structure of jute reeds makes the process of manufacturing needle punched jute nonwoven different [136]. The process flow chart for jute nonwoven is given below: 43

3 Jute bale opening Selection Spreader (Application of oil-in-water emulsion) Jute processing for feeding into nonwoven line Piling and conditioning (24/36 hour under ambient condition) 1 st carding (Jute Breaker card) (Opening of fibre and sliver formation) 2 nd carding (Jute Finisher card) (Sliver blending) 3 rd carding (Jute nonwoven card) (formation of continuous length of fibre fleece Web Formation Camel -back cross lapper (Cross laying of fibre fleece) Needling (Needle punching unit) Web Bonding Winding of needle punched nonwovens (a) Jute Processing for Feeding into Nonwoven Line The raw jute strand (morah) of two different grade as mentioned in Table3.1 were mixed thoroughly for preparation of needle punched jute nonwoven fabrics. 44

4 Table 3.1 Fibre Mix (batch) for jute nonwoven Serial no. Grade Percentage Piling Time (hour) 1. TossaDaisee5 (TD 5) [73, 137] Semi Northern Tossa Daisee 5 (TD 5) Raw jute strands were passed through a jute spreader machine (S. G Industries, Howrah, West Bengal, India) with application of oil in water emulsion. Vegetable oil based oil in water emulsion was used to soften the raw jute fibre. Thereafter, emulsified jute spreader rolls were kept in covered condition as per standard method followed by jute mills [138]. The conditioned jute fibres were then successively processed through jute first carding (Breaker Card Model JF2, down striker, 3-pair, half circular) followed by second carding machine (Finisher card Mackie make up striker, 4 1 2pair full circular, single doffer) for discrete filament generation and formation of loosely held strand of jute fibres (with various length) commonly known as sliver, in roll form. The finisher card sliver rolls were fed to a nonwoven needle punching machine system for nonwoven fabric preparation. The needle punching nonwoven making system consists of (i) one finisher carding machine of Mackie make (ii) fibre fleece cross lapper for making fibrous web/sheet, (iii) needle punching and fabric take up rollers at the delivery end of M/s Fehrer Ltd. (b) Web Formation Web formation is the process that arranges the fibers or filaments into a sheet or web form. In the scope of this work, the carding method was used to form the web. The cross laid web was produced using camel back steep arm cross-lapper with required web weight per unit area aiming at to make 300 to 700 g/m 2 of the nonwoven fabric as shown in Figure

5 Figure 3.1 Schematic view of camel back steep arm cross-laying system A cross-lapper is a continuous web transfer machine that follows a card as part of an integrated web formation system. The fibrous web coming out of the card was fed to the inclined conveyor belt of the cross lapper which in turn feeds the web to successive horizontal conveyor belt. The web was layered from side to side onto a lower conveyor (also called feed lattice) to needle loom by means of the swinging conveyor. The feed lattice runs perpendicular to feed direction of fibre to the carding machine. The width of the fabric was governed by the swing of the swinging conveyor. The use of cross lapper changed the fibre orientation in the cross machine direction. The ratio of the speed of cross lapper and feed lattice was varied according to the mass and structure required for the ultimate nonwoven fabric [139]. In the present work the number of layers of card web was depending upon the desired final areal density of the fabric. The speed of the different parts of machine was measured using digital photo/contact type tachometer (DT-2236, Maker, Lab Equipment & Chemical) and other features are given in the Table

6 Table3.2 Features of nonwoven machine used for making of porous absorbing jute nonwoven Specification/Description Carding Machine (Needle Loom Line Card) Roller and clearer type with 2 pairs of Worker and Stripper Roller. Cylinder 146 rpm Doffer 11.5 rpm Feed Roller 3.0 rpm Width of the web coming out of the card 1.80m Cross lapper type Steep arm camel back type Delivery roller speed of needle loom at 3 2, 2.5 and 3 m/min different punch density Number of Regular Barb needles (9 barb ) on 1616 needle board Number of needle board 2 Arrangement of needle Diagonal track Width of needle punched nonwoven fabric 2.00 m produced from the needle loom Needle Gauge 18 (c) Web Bonding by Needle Punching The carded jute web was fed on a feed lattice to pass into the needle loom between the stripper plate and the bed plate, which contain holes of 1 / th 4 inch ( 6 mm) diameter that match the needle arrangement in the needle board.the fibre web was needled during the down movement of the needle board from up side as shown in Figure 3.2. Figure 3.2 Schematic view of Needle punching process 47

7 For production of fifteen numbers jute based needlepunched nonwoven fabrics, threepunch density values were used viz. 14, 19 and 24 p/cm 2. These values were achieved by changing the delivery speed of the needle loom at three equidistant levels of 2 m/min, 2.5 m/min and 3 m/min using the following equation. Punch Density (PD)=.. 10 punch/cm [140,141] (3.1) where a=total number of needles per 1 m of working width [m -1 ] f= Frequency of needle board [s -1 ] p= Number of passage through needle loom v= Velocity of web [m.s -1 ] The depth of needle penetration was set at 7 mm, 9 mm and11 mm by lowering down the bed plate Evaluation of Material Characteristics of Jute Nonwoven Jute fibre was tested for its diameter, while jute nonwoven fabrics were evaluated in terms of mass per unit area (areal density), thickness, bulk density air permeability, porosity, tortuosity, breaking strength and transmission loss. The fibre and fabric samples were conditioned for 72 hours maintaining 20±2 o C and 65±2% relative humidity prior to each test [142]. Characterisation methods followed for nonwoven jute are given in Table

8 Table 3.3 Characterisation of jute nonwoven Property Standard method Instrument used Number of sample tested Fibre diameter Projection 50 microscope, Digi Vision NX Areal Density ASTM D 37776/D37776M-09a Sana ST-20 5 [143] Electronic Balance Thickness ASTM D [144] MAG Electronic thickness tester 25 Bulk Density Air resistance Fabric Porosity Tortuosity Breaking Strength at Machine direction (MD) and Cross direction (CD) Transmission loss Calculated Calculated based on air flow value measured by ASTM D [145] Calculated Calculated ASTM D [146] Prolific Air- Permeability Tester Zwick Tensile Tester Model Z010 Instrument developed (a) Fibre diameter (d) Diameter of the fibre was measured, assuming the cylindrical form of the longitudinal fibre, with a projection microscope make Paramount Digi Vision NX with 30 magnification. The test results were presented in Table 4.9 (b) Mass per Unit Area (Areal Density) (G A ) Mass per unit area values of nonwoven jute was measured in accordance with ASTM D 37776/D37776M-09a standard test method for mass per unit area (weight) of fabric 49

9 using electronic balance with accuracy of 1g, make Sana- India, model, ST-20. The average results were tabulated in Table 4.1 (c)thickness (t) Thickness of nonwoven jute was measured as per ASTM D under pressure of 4.14 kpa in an electronic thickness tester (make, MAG-India). Average thickness values were given in Table 4.1. (d) Bulk Density ( ) The bulk density of the nonwoven fabric was calculated using the following equation. h / Bulk density = (3.2) h. The results were shown in Table 4.1 (e) Air flow Resistivity ( ) Air permeability of nonwoven jute was tested using an Air Permeability' tester (make, Prolific- India). The volume of air in cubic centimetre passed through 10 cm 2 circular area of fabric per second under a pressure differential of 20 mm of water head was measured following ASTM D The airflow resistivity ( ) was calculated based on following formula and tabulated in Table 4.2 [41, 45] = (3.3) where P= Static pressure differential between both faces of the sample, dyne/cm 2 (10-1 Pa) c= Air velocity, cm/s, t= Thickness of sample, cm 50

10 (f) Porosity( ) and Tortuosity (h) The porosity was calculated by using equation 3.4 [40, 147] taking jute fibre density 1.3g/cm 3 [148] Porosity =1 (3.4) Where, = bulk density of nonwoven jute and = bulk density of constituent fibre The empirical model for determination of tortuosity was determined by Archie s law [149]. The value for nonwoven jute fabric was calculated using the following expression [40]. Tortuosity (h)= (3.5) Average values of porosity and tortuosity were given in Table 4.2 (g) Breaking Strength Tensile testing of the jute nonwoven along and across machine direction was carried out using Zwick Tensile Tester (Model Z010) as recommended in ASTM D using 75 mm gauge length and 25 mm test width at a test speed of 300 mm/min. The results were tabulated in Table 4.12 (h) Transmission Loss (TL) The acoustical parameter of the nonwoven jute was tested at central frequency of 1/3 octave band on an instrument developed for this work described in section 3.4. Transmission loss (TL) is the ratio of sound energy incident on nonwoven jute to that which is transmitted through it, expressed in decibels (BS 2750: 1980). It is 10 times the logarithm to the base 10 of the reciprocal of the sound transmission coefficient [56-60] of the material. The transmission loss was derived from the following equation 51

11 Transmission Loss (TL) = (3.6) where, D = db measured using digital sound meter when the material is removed and D = db measured by digital sound meter when the sound wave strikes the sample present in front of db meter. The results of 15 jute nonwoven at 7 different frequency were presented in Table Jute Nonwoven Polyester Composite (CJ) There are several different jute composite formation methods available today [84-86]. In this work, Resin Transfer Moulding i.e. RTM (Machine Make: Phoenix of series 2012) method was used to form the composite. In the process, fibre preform i.e. jute nonwoven was packed into a mould cavity as reinforcement that had the shape of the square laminate of mm 2. The mould was then closed and clamped. Resin solution comprised general purpose polyester resin, catalyst (methyl ethyl ketone peroxide) and accelerator (cobalt nitrate) were then pumped into the mould under pressure displacing the air at the edges, until the mould was filled for making composite. Properties of the resin and formulation of resin mix are given in Table 3.4 Table 3.4 Properties of general purpose unsaturated polyester resin and formulation of resin mix Quantity 1. Matrix (Unsaturated polyester resin) from Strong Bond Polyseal Pvt. Ltd, India. 3/4/5 times of jute nonwoven Appearance Yellow transparent Specific Gravity at 25 C 1.12 Viscosity at 30 C (measured in 485 cpoise Brookfield RVDT-1) Acid Value 22 Volatile Content 36% Gel time at 30 C 8.15 min 2. Catalyst (Methyl ethyl ketone) from Amber Chemicals, India. 2 % solution 1% of resin 3. Accelerator (Cobalt nitrate ) from Amber Chemicals, India. 2% solution 1% of resin 52

12 The photograph of resin transfer moulding machine is given in Figure 3.3. Pressure gauge Resin mix tank Inlet tube Figure 3.3 Photograph of Resin Transfer moulding machine 3.2.1Resin Transfer Moulding (RTM) The operational sequence of RTM process is presented below. Preform layup Closing of Mould Resin Injection Curing De-moulding 53

13 (a)preform Layup The preform jute nonwoven was placed separately in the female part of the mould. The number of jute nonwoven layers were fixed in accordance to the target thickness (L T ) of jute composite and changed from 1 to 4. This part of the mould was guarded by black colour rubber seal for prevention of the resin over flowing from the side at the time of injection as shown in Figure 3.4. Rest pad Rubber seal Figure 3.4 Photograph of jute nonwoven layup on female part of mould (b) Closing of Mould This step was taken place through the placing of male part on female part of mould followed by closing and clamping of mould with jute nonwoven preform. The male part of the mould was placed on the rest pad (flange) of the female part at the time of matching as shown in Figure

14 Figure 3.5 Photograph of matching of male and female part of the mould Figure 3.6 Photograph of tightening of bolt for closing of the mould The mould was closed by tightening of bolts and nuts (Figure 3.6) (c) Resin Injection The resin mix was injected into the mould through vents at one side replacing the air entrapped within the preform, by way of vents of other side and continued till the resin came out of the vent on the other side. The position of injection and overflow vent were shown in Figure 3.7. The resin was injected using a positive gradient pressure of 238 kpa (35 psi) through the vent. The treatment was done at room temperature. The desired resin 55

15 to material uptake ratio of 3:1, 4:1 and 5:1 controlled the nominal fibre weight fraction at 25, 20, and 17 percent respectively as mentioned in Table Overflow vent Injection vent (d) Curing Figure 3.7 Photo graph of injection vent and over flow vent After filling of the mould, composites were cured at ambient temperature for 3 to 4 hour depending on the target thickness of the product. (e) Demoulding The samples were removed from the mould after curing Evaluation of Material Characteristics of Jute Nonwoven Composite Jute composite samples were characterised in terms of mass per unit area, thickness, tensile strength, flexural strength, impact strength and transmission loss. Samples were subjected to conditioning in 20 0 ±2C and 65±2% relative humidity for 48 hours prior to each test. Characterisation methods of composite are described in Table

16 Table 3.5Characterisation of jute composite Property Standard method Instrument Number of test Thickness Slide calliper (Make,Mitutoyo-Japan) 5 Weight Orpat-India Make Electronic Balance 5 Bulk Density Calculated Void Content Calculated Tensile Strength ASTM D [150] Universal Tensile Tester (Blue Star-India make) 5 Flexural Strength ASTM D [151] Izod Impact Strength Scanning Electron Microscopy Transmission Loss ASTM D [152] Universal Tensile Tester (Blue Star-India make) Izod Impact Strength tester (Blue Star-India make) JEOL Scanning Electron Microscope (Model: JSM 6360 Instrument developed for this work (a) Thickness (L) Thickness of the samples in mm was measured with the help of digital slide calliper with accuracy of 0.01 mm. The measured values were tabulated in Table (b) Mass per unit area (m) Sample weight in kg of size mm 2 each was measured by the Orpat India electronic balance. On basis of this weight, the mass per unit area of composite sample in in kg/m 2 was evaluated and represented in Table

17 (c) Bulk Density ( and ) Actual bulk density ( ) of each sample was calculated in g/cm 3 on the basis of its measured weight and thickness. The theoretical bulk density( ) of the composite samples was obtained using the following equation = (1 + ) 10 (1 ) where = Theoretical bulk Density (g/cm 3 ) G A = Areal density of nonwoven fabric (g/m 2 ) R M = Ratio of Material to Resin take-up = compaction factor t = thickness of jute nonwoven layer The results of actual and theoretical bulk density were tabulated in Table (3.7) (d) Void Content (V %) Void content of the composite was determined using following relation [153] and the data was given in Table (%) = Void content 100 (3.8) Where is the theoretical density, calculated according to the equation 3.7. is the actual density calculated from measured weight. (e) Tensile Strength Tensile property of the composite specimens was carried out using an UTM (Universal Testing Machine, Blue Star-India make), as per the ASTM-D using 50 mm gauge length and 6 mm test width at a cross head speed of 5mm/min. The gripped ends were tabbed with a rubber pad to protect the specimen from being crushed by the grips. Average tenacity values in mpa were given in Table

18 Tenacity (MPa) = ( ) ( ) (3.9) (f) Flexural Strength Three-point bending test was also done using an UTM (Universal Testing Machine) Blue Star-India Make according to ASTM D at a crosshead speed of 1.7 mm/min, with sample dimensions of 20 L 15 mm 2 and support span of 16 L mm where L is the thickness of the specimen. The following relationships were used to evaluate the flexural strength ( ) Flexural strength= The values of flexural strength in mpa were tabulated in Table 4.15 (3.10) (g) Impact strength The impact strength was evaluated in IZOD-type cantilever beam impact tester following the ASTM standard (D ). An average of five tests was taken and given in Table (h)transmission Loss (TL) The acoustical parameter of the jute nonwoven based composite material was tested on an instrument developed in laboratory for this work. The noise control property of composite was evaluated in terms of Transmission Loss (TL). The transmission loss in db was derived from the equation 3.6 discussed earlier in this chapter and presented in Table 4.16 Transmission Loss= D D (3.6) where, D = db measured by digital sound meter when the there is no material infornt of meter 59

19 D =db measured by digital sound meter when the sound wave strikes the sample present in front of db meter. (i) Scanning Electron Microscopy The surface morphology of samples was examined at 17kV using JEOL Scanning Electron Microscope (Model: JSM 6360), by preparing the sample with Gold-Palladium alloy coating. 3.3 Experimental Plan for Preparation of Jute Nonwoven and Jute Composite Jute Nonwoven A 3-factor, 3-level Box-Behnken design [154,155] has been used to derive a second order polynomial equation and construct contour plots to predict responses. In this analysis the independent variables selected were, areal density of fibre web feed to needle loom (G), punch density (PD, punch/cm 2 ) (PD) and Depth of needle penetration (DP, mm). Fifteen jute nonwoven fabric were prepared and evaluated for prediction of non-acoustical and acoustical property of needle punched jute nonwoven fabric. Design details, coded value of the level of each process parameter (G, PD, DP) and experimental are given in Table 3.6, 3.7 and 3.8 respectively. Table 3.6 Details of design used Design Number 1 Number of factor 3 Design Matrix ± 1 ± 1 0 Number of point Total Sample 15 0 ± 1 0 ± ± 1 ±

20 Table 3.7 Input material and Machine parameters used in making Jute Based Nonwoven Variables in process parameters Web Area Density (g/m 2 ) (G) Coded Value (X 1 ) Punch Density (punches/ cm 2 ) (PD) Coded Value (X 2 ) Needle Penetration (mm) (DP) Coded Value (X 3 ) 300 (-1) 14 (-1) 7 (-1) Level Used Coded value ( ) 500 (0) 19 (0) 9 (0) 700 (1) 24 (1) 11 (1) Table 3.8The experimental plan along with actual level of variables for three factor design Coded value Nominal Sample No. areal PD DP X 1 X 2 X 3 Density(G) Areal Density-Weight input Material in g/m 2, PD-Punch Density in Punches/cm 2, DP-Depth of needle penetration in mm Jute Composite (a) Selection of Jute Nonwoven for Making Jute Nonwoven Polyester Composite (CJ) The selection of jute nonwoven under investigation in making composite was made on the basis of three criteria in sequence of following parameters: 1) high strength from 61

21 Table ) relative high transmission loss (TL) at 3150 Hz from Table 3.4 and 3) consequential higher productivity in terms of PD from the Table 3.4 in each category of areal density namely 300, 500 and 700 g/m 2. The detail method is given in Annexure I. The results of breaking load and transmission loss were obtained after characterisation of all the 15 jute nonwoven samples and details are given in the Table 3.9. Table 3.9 Particulars of selected jute nonwoven for composite Sample Number Actual areal Density (g/m 2 ) Depth of Needle penetration (mm) Punch Density (p/cm 2 ) (Delivery Speed of needle Loom m/min) Breaking load (N) CD/MD Transmission loss (db) (2.5) / (2.5) 216.3/ (2.5) / (b) Experimental Plan of Making Jute Composite (CJ) The target thickness (L T ) of jute composite depends on the number (n) and thickness (t) of nonwoven jute layer used to produce the final structure. The mass/weight of composite sample depends on the actual areal density (G A ) of jute nonwoven and resin to material uptake ratio (R M ). The bulk density of the composite depends on the following parameters: 1) Nonwoven fabric with actual areal density G A (g/m 2 ) 2) Resin to material uptake ratio R M 3) The target thickness of sound insulating Barrier material L T mm 4) The number of jute nonwoven layer( n) 5) Thickness of individual jute nonwoven layer t mm 6) Initial stack thickness (n t) (as shown in the Figure 3.8). The amount of mass concentration in 1 square metre of final structure is (1 + ) g. The total initial thickness (stack thickness) of the preform within the mould before resin 62

22 injection is n t, and converted to a target thickness of L T mm (Here n t L T ) The theoretical bulk density ( ) in g/cm 3 be represented by equation 3.11 = (1 + ) 10 3 (3.11) Figure 3.8 Stacking of n numbers of jute nonwoven sheets The stacked thickness (n t mm) of the preform with n number of jute nonwoven sheet placed on the mould was compressed under a pressure of 238 kpa. The composite laminate was produced with a target thickness of L T mm. A new parameter was introduced i.e., compaction factor (C f ) which can be expressed by the following equations 3.12 a) and b) based on the Figure 3.8. The factor comprises process parameter like target thickness of laminate, thickness of single nonwoven jute layer and number of nonwoven jute layer. = = 1 = (1 ) (3.12a) (3.12b) From the above equation it is clear that compression of stacked nonwoven in terms of compactor ( ) increases with the denominator i.e. more number of the preform layers are compressed for a fixed target thickness (L T ) and vice versa. The bulk density expression represented by equation 3.7 earlier in this chapter is thus obtained 63

23 by replacing in equation = (1+ ) 10 3 (1 ) (3.7) = Theoretical bulk Density (g/cm 3 ) G A = Actual areal density of nonwoven fabric (g/m 2 ) R M = Ratio of Material to Resin take-up = compaction factor t =thickness of jute nonwoven layer Theoretically, it is possible to produce jute composite for noise control within a compaction factor range of (commonly achievable for glass fabric based composite) depending on the restriction imposed for target thickness value of the laminates. This ranges between 4 to 12 mm. All 81 combinations (3 3 3 ) of the sample were tried but only 27 jute composites were practically possible to produce using three jute nonwovens (sample 6, sample 15 and sample 8) by resin transfer moulding method. Details are given in Annexure II. The experimental design for making composite is given in Table

24 Table 3.10Experimental Design for Making Composite Laminate Resin to material uptake ratio Areal density of nonwoven jute fabric (G A ) (g/m 2 ) Thickness of nonwoven jute layer (t) (mm) Target Thickness Composite (L T) (mm) Thickness of CJ Composite (L) (mm) Number of nonwoven jute layer (n) Development of Instrumental Setup Principle of Instrument In the present study, a simple instrument was developed to measure noise control behaviour of material within specified zone of Hz. The instrument is portable, cheaper and allows the direct acoustical comparison between the samples tested under the same condition. It is also capable of measuring the noise control behaviour of both porous absorbing material and rigid material. The measurement technique essentially 65

25 depends on amount of sound energy transmitted through the sample when placed in the path of sound. When the sound wave from source (A) propagated without the sample (C) in the path of the sound wave, a sound detector (B) positioned on the opposite side of sound source senses the incident energy as shown in Figure3.9a) A B Figure 3.9 a) Sound wave from source (A) propagated without the sample sensed by the sound detector (B) A C B Figure 3.9 b) Sound wave from source (A) propagated with the sample (C) in the path of the sound wave to a sound detector (B) The detector displays the db which is the 10 times of common logarithm of the ratio of incident energy to the reference as expressed in equation Incident sound energy level(d ) =10 log 10 ( ) db (3.14) where, 66

26 E i = Incident energy and the standard reference value of E 0 is J With the sample in the path of sound energy the detector measures the db corresponding to 10 times the common logarithm of the ratio of the transmitted energy to the reference. Transmitted sound energy level ( ) =10 log 10 ( ) db (3.15) where, E t = Transmitted energy and the standard reference value of E 0 is J The difference of incident and transmitted energy can be expressed as Difference = ( ) (3.6) =10 log 10 ( )- 10 log 10 ( )db =10 log 10 ( ) =10 log 10 ( ) = 10 = TL The difference is the TL i.e. Transmission Loss also referred in equation 2.25 in the Chapter 2, where τ is transmission coefficient Description of Instruments The schematic diagram of the transmission loss measuring experimental setup developed under the scope of this research work is depicted in Figure This device consists of six components: a) Function signal generator b) Variable signal Amplifier c) Sound source (loud speaker) d) Sound chamber e) Sound detector(digital sound meter) f) Material sample holder. 67

27 Loud speaker Variable signal Amplifier Figure 3.10 Schematic diagram of Transmission Loss measuring set up Figure 3.11 represents photograph of the Transmission Loss measuring instrumental set up. Figure 3.11 photograph of Transmission Loss measuring instrumental set up Figure 3.12 shows the top view of the box carrying sound chamber and the photograph in the inset depicts the position of sample on sample holder. 68

28 Figure 3.12 photograph of Transmission Loss measuring instrumental set up showing sample fixing (a) Function Signal Generator The signal generator MTQ 2002generates Sine wave within a Frequency Range, 1 Hz to 20 khz with 01 Hz to 20 Hz Sensitivity and Amplitude range, 20 db to 40 db and is shown in Figure Figure 3.13 Photograph of Signal generator 69

29 (b) Variable Signal Amplifier The Sine wave from MTQ 2002 is fed to the variable signal generator. The signals were regulated by adjusting the gain of variable signal generator shown in Figure 3.14 Variable signal amplifier Figure 3.14 Photograph of Variable signal amplifier (c) Sound Source (Loud Speaker) The loud Speaker-Model LS 40 in a frequency range of 50 Hz to 5000 Hz with 100 mm diameter to fit the opening end of sound chamber is shown in the Figure The diameter of the speaker was selected on the basis of diameter of the tube. Figure 3.15 Photograph of sound chamber fitted with loud speaker 70

30 (d) Sound Chamber The sound chamber was a discontinuous poly vinyl chloride tube of 100 mm diameter. The discontinuous tube consists of two parts, one attached to sound source and the other to sound detector. The two parts of the discontinuous tube were screwed with each other against a solid wall of 25 mm thickness as shown in Figure3.16. The solid wall carried the sample to be tested. The thickness of the tube wall was 5 mm i.e. 5% of the tube diameter to prevent vibrations during emission of sound energy as per the recommendation [156]. The inside wall of the tube is covered with sound absorbing lining, thus providing enough mass and surface to reduce losses from the walls of the tube even at the lower frequency. The entire assembly comprises 520 mm long discontinuous tube and the solid wall at the junction of two parts was placed in a box of dimension mm 3.This arrangement divided the box into two sections. Mineral wool was placed in the space between box wall and the discontinuous tube. It helped in reducing the cross nodes that might be generated by the loudspeaker especially at higher frequencies [156]. Figure 3.16 Photograph showing discontinuous tube of two parts The tube was long enough to eliminate the effect of non-plane wave. The sample was needed to be placed at distance equal to thrice of tube diameter i.e. at 300 mm from the sound source and same was followed in the construction of the instrument. The distance 71

31 between the source and the detector probe was chosen to allow a space of times of the wavelength ( 0.05λ) at the lowest required frequency of measurement [65, 157]. The lowest frequency used in the present study was 50 Hz with maximum wavelength of 6800 mm. The minimum distance requirement between the sound source and detector was 340 mm. The length of the tube thus selected was maintained at 520 mm ensuring condition of plane wave [65, 156]. (e) Sound Detector The probe of the sound detector was attached to the inner wall of the tube at opposite side of the sound source. The probe of the sound detector received the sound energy and the display unit outside the box showed the value in db (Figure 3.17). The working range of digital display is within 130 db to 30 db with accuracy 0.01 db. The probe of sound detector was520 mm apart from sound source and conserved law of the space requirement and allowed the testing of sheet like materials Figure 3.17 Photograph of sound detector display unit 72

32 (f) Sample Holder The box consisted of two sections, with a partition wall, used as sample holder. The partition wall was of 25 mm thickness with a central circular hole of diameter 100 mm for screwing the discontinuous tube. The sample holder was placed in the box through a slot cut at the inner side of the box and able to accommodate the sample of thickness between 3 to 12 mm. The sample was secured tightly on the holder by means of annular ring clamp attached to the part of the discontinuous tube on detector side. The circular portion (7850 mm 2 ) of rectangular sample was exposed to the sound energy Operation At first the material to be tested was mounted on sample holder, placed in the sound path. The sine signals from frequency generator were sent to the sound loudspeaker producing sound waves. The sound wave was propagated through the sound chamber passing through the sample material and sensed by the sound detector placed in the right section of the discontinuous tube. The transmission loss was determined by the difference of db value recorded by the digital display of sound detector without and with sample on sample holder using equation Calibration The instrument was calibrated against a standard 6 mm thick glass sheet used as glass pane in building construction for noise control with Transmission Loss of 36 db at 4000 Hz [157]. The calibration of instrument was carried out following four steps mentioned below a) The power source of the function generator is switched on, and the sine signal of 4000 Hz was set by pressing the range key. Signal was then feed to the variable function amplifier. 73

33 b) When there was no sample between source and sound detector the initial reading of 100 db was adjusted on digital display unit of sound detector by the knob of the variable signal amplifier shown in Figure Adjusting knob of variable signal amplifier Figure 3.18 Photograph indicating the adjusting knob of the variable signal amplifier c) In next step the 6 mm glass sheet was placed on the sample holder. d) The transmission loss of 36 db ( db) at 4000 Hz was set by adjusting the knob of variable signal amplifier. 74