In active method, noise coevals from machines can be reduced by modulating quiver and clash. It is a good established fact that metallic gear to metallic gear agreement produces more noise compared to polymeric cogwheel, therefore polymeric cogwheels are more suited and are recommended. Generally polyurethane, polyester, polyamide polymers are used for this intent. As revolving parts of the machine for illustration, spindles, cogwheels, grouch shaft etc. bring forth more quiver, these parts could be replaced by polymeric stuffs.
Besides, proper and regular care and overhauling of machines besides play an of import function in cut downing and maintaining low noise degrees.
4.2 Passive Noise Control
A muffling stuff ( isolator ) is used to cut down the quiver of power loom. The damping stuffs are in the signifier of resilient tablet made of gum elastic, neoprene, cork or plastic. The isolation systems may be placed as shown in Fig. 4.2-
Figure: 4.2 Position of isolators in foundation
See a instance when the power loom of mass M1 is placed on a foundation block of mass M2. The spring K1 represents the foundation dirt and spring K2 is an insulating spring which is placed between multitudes M1s and M2, in order to minimise the transmittal of quivers from the land to the equipment. If the land is subjected to a periodic supplanting given by Z0 wickedness I‰t. The equipment of gesture may be written as ( Saran, 2006 ) ,
m11 + K1Z1 – K2 ( Z2 -Z1 ) = K1 Z0 wickedness I‰t aˆ¦aˆ¦4.1
or m22 + K2 ( Z2 -Z1 ) = 0 aˆ¦aˆ¦4.2
The value of maximal amplitude of gesture are given by,
A Z1 = K1 Z0 aˆ¦aˆ¦4.3
A Z2 = K1 Z0 aˆ¦aˆ¦4.4
The displacement transmissibility of machine ( TD ) is defined as the ratio of displacement amplitude of mass M2 to the displacement amplitude of stiff support. Then,
TD = = aˆ¦aˆ¦4.5
or TD = aˆ¦aˆ¦4.6
where, Aµm = = mass ratio
a1 = ; a2 =
= ; =
If is taken as allowable amplitude, and Z0 is the applied dynamic supplanting, so the ratio of is known. For this value, a2 can be determined which in bend will give the stiffness of the isolator spring, i.e. K2.
4.2.2 Enveloping the noise beginning
Noise is transmitted by quiver. Hence the belongings of the enclose must be such that it should non vibrate when a sound moving ridge hits its surface ; otherwise the enclosure itself can go a noise beginning. Since quiver is reciprocally related to the mass of the stuff, in the usage of enclosures. By the mass jurisprudence, an ideal enclosure is the heavy enclosure ( stuffs of high denseness ) .
Let us see that the noise coming from the power loom workshop is reduced by seting the looms in an ideal enclosure of masonry block of solid dense concrete 4 inch ( 10 centimeter ) midst.
The strength transmittal loss may be given as:
TL = 20 log I?lI? – 47.4 aˆ¦aˆ¦4.7
Where I?l = country denseness of divider
I? = frequence
The denseness of masonry block of solid dense concrete 10 centimeter midst = 110 lb/ft3
= 1849.6 kg/m3
I?l = 36.67 lb/ft2 = 36.67 ( 0.454 )
= 179.22 kg/m2
TL500 = 20 log ( 179.22 ) ( 500 ) – 47.4 = 51.6 dubnium
dubnium transmitted = 87 – 51.65 = 35.35 dubnium
4.2.3 Using Double foliage wall
A dual foliage wall can execute better than a individual foliage wall of similar mass because the sound has to go through through two barriers. If the two foliages are non connected to each other, the insularity values of the two foliages are frequently connected by ties or strands, and the full insularity can non be achieved. Even where the two foliages are isolated from each other, the full benefit can merely be obtained above a certain frequence that depends on the pit breadth. This is because the air in the pit behaves like a spring linking the foliages together, and causes a resonance at the mass-spring-mass frequence. Below this frequence, the two foliages behave more like an tantamount individual foliage.
Making the pit width broad can cut down the mass-spring-mass frequence, as in the instance of
sound insulating secondary glazing. The mass-spring-mass frequence ( F0 ) may be estimated from the undermentioned equation:
F0 = 59.6 aˆ¦aˆ¦4.8
M1 and M2 = the surface multitudes of two foliages in kg/m2 & A ; d = pit breadth in meters ( m )
Decrease in mass-spring-mass frequence ( F0 ) , barred the air in the pit to do resonance.
4.2.4 Screening of quiver by the usage of unfastened trenches
188.8.131.52 Active Screening
Screening of quiver is done near the beginning of quiver. Fig.4.3 shows a round trench of radius R and deepness H which surrounds the machine foundation that is the beginning of perturbation. Barken ( 1962 ) mentioned that the decrease in quiver amplitude occurs merely when the trench dimensions are sufficiently big compared with the moving ridge length of surface moving ridges generated by the beginning of perturbation. The deepness of trench varied from 150 millimeters to 600 millimeters and radius R of annulate trench varied from 150 millimeters to 300 millimeters.
Figure: 4.3 Vibration testing utilizing a round trench environing the beginning of vibration-Active showing ( Woods, 1968 )
Wood ( 1968 ) has introduced a term amplitude decrease factor which is defined as:
ARF = amplitude decrease factor
The dimensions of the trench are expressed in non-dimensional signifiers by spliting H and R by the moving ridge length I»R of Rayleigh moving ridges, I»R is obtained by finding the figure of moving ridges ( N ) happening at a distance ten from the beginning ( I»R = x/n ) .
The field trials of Woods ( 1968 ) therefore correspond to
= 0.222 – 0.910 and = 0.222 – 1.82
For satisfactory showing of quivers, Wood ( 1968 ) recommended that ARF should be less than or equal to 0.25. The decisions made on the footing of this survey to maintain ARF a‰¤ 0.25 are:
For full circle trenches ( I? = 360o ) , a minimal value of = 0.6 is required. The zone screened in this instance extended to a distance of atleast 10 wave lengths ( 10 I»R ) from the beginning of perturbation.
For partial circle trenches ( 90o & lt ; I? & lt ; 360o ) , the screened zone was defined as an country outside the trench widening to at least 10 wave lengths ( 10 I»R ) from the beginning and bounded on the sides by radial lines from the Centre of beginning through points 45o from the terminals of trench. In this instance besides, a minimal value of = 0.6 is required.
Partial circle trenches with I? & lt ; 90o, effectual showing of quiver is non achived.
Trench breadth is non an of import parametric quantity.
184.108.40.206 Passive Screening
Wood ( 1968 ) has besides performed field trials to analyze the effectivity of unfastened trenches in inactive showing as shown in Fig. 4.4.
Figure: 4.4 Vibration testing utilizing a consecutive trench-Passive showing ( Woods, 1968 )
A typical layout of these trials consists of two quiver exciters and one trench of size scopes from 100 millimeters x 300 millimeters x 300 mm deep to 2440 millimeter ten 3050 millimeter ten 1220 mm deep.
The values of varied from 0.444 to 3.64 and from 2.22 to 9.10. It was assumed in these trials that the zones screened by the trench would be symmetrical about the 0o line.
For satisfactory showing, Wood ( 1968 ) recommended that ARF should be less than or equal to 0.25 in a semi-circular zone of radius ( 1/2 ) L behind the trench. The decisions made on the footing of this survey to maintain ARF a‰¤ 0.25 are:
should be atleast 1.33
To keep the same grade of showing, the least country of the trench in the perpendicular way ( i.e. LH = AT ) , should be as follows:
= 2.5 at = 2.0
and = 6.0 at = 7.0
Trench breadth had practically no influence on the effectivity of showing.
This shall be more effectual, if there are several looms inside a power loom based fabric industry.
4.2.5 Design of Active and Passive Screening
220.127.116.11 Design of Active Screening
Normal runing frequence of a power loom = 100-960 revolutions per minute
( Beginning: Paraniri Industries 2009 )
Let us plan for revolutions per minute = 960
Operating frequence of power loom in footings of Hz = = 16
Rayleigh wave speed VR = 140 m/s ( assumed )
Therefore, wavelength = I»R = = = 8.75 m
Depth of trench for active showing H = 0.6 I»R = 5.25 m
18.104.22.168 Design of Passive Screening
Depth of trench for inactive isolator is given by H = 1.33 I»R = 11.63 m
Let the trench is provided at a distance of 20 m
= = 2.28
= 2.28, = 2.5 + = 2.696
Length of trench = = 17.74 m
4.3 Other methods of Noise Reduction
Following steps may be taken for an effectual control on noise pollution.
Proper designing of edifices and workshops: Proper designing of doors and Windowss of a room can assist in cut downing the noise to a much greater extent. The sound travels through really thin clefts between the door and wall. The infinite between the jamb and frame may be packed with sound absorbing stuff. In instance of Windowss, the transmittal loss additions as the thickness of glass additions, while in instance of doors, the transmittal loss additions as the weight of door additions. Glazed Windowss with dual or ternary window glasss of glass provide the first-class sound insularity. The air infinite at the borders of such window glasss can be filled with sound absorbing stuff.
The noise pollution can besides be controlled by utilizing drifting floors and suspended ceilings. Suitable sound absorbing stuffs such as hair felt, acoustical tiles, perforated plyboard and assorted porous stuffs are available to be fixed on walls, floors and ceilings in order to cut down the noise degree.
Using ear protective AIDSs: The workers working in power loom based fabric industries holding noisy machineries, should be provided with the ear protection AIDSs such as soft plastic and gum elastic ear stoppers, earphones etc. Stuffing of cotton balls in the ear, covering of ears with custodies under noise conditions, being off from the beginning of noise are some personal protection steps.
Use of constructing codifications: Certain codifications should be enforced which require sound proofing in the building of industries, edifices and flats. Cities should be planned in such a manner that industrial noise and main roads are separated from the residential countries. In USA edifice codifications have been enforced harmonizing to which all freshly constructed edifices are required to hold sound proofing mechanisms.
By flora screen: Trees absorbs and dissipate sound energy and act as a buffer zone. Plants and trees should be planted along main roads, streets and near industrial countries. Assorted trees minimize noise by 5-10 dubnium. Ashok, Neem, and Tamarind are good for this intent. In metropolitan metropoliss green belt flora and unfastened infinite may hold great value in sound soaking up
Following recommendations were issued by West Bengal Pollution Control Board for power loom workshops runing in the residential countries:
The outer walls of the suites should be dual walled with at least six ( 6 ) inches infinite in between.
Such null infinite to be filled with proverb dust.
Inside of the wall should be covered with thermocol bed ( minimal 1 inch thickness ) .
Room should be holding false ceiling made up of straw boards or boards manufactured from jute sticks.
All the doors of the room should be swing doors.
The room should hold equal airing agreement.