Noise Control in Textile Machineries

Indian Institute of Technology Delhi 1

Noise Control in Textile Machineries

Jagannath Sardar

(2008TTZ8165)

Submitted to

Prof. K. Gupta Department of Mechanical Engineering

Department of Textile Technology

Indian Institute of Technology Delhi New Delhi


Noise control in Textile Machineries: Contents: Page:

1. Introduction: ....…………………………………………… 1

2. Definitions and Background:…. …………………………. 3

2.1 Noise Control Principles………………………………... 4

2.2 Approach to Analysis of Problems……………………... 5

3. Analytical Survey of Noise Study in Textile Industry:....... 6

3.1 Spectrum Analysis………………….…………………… 9

3.2 Standards for noise abatement in industry...…………….. 10

3.3 The Machinery Directive………………………………… 10

4. Structure of Textile Industry:……………………………… 12

4.1. Machineries in Spinning and Noise emission..………….. 12

4.1.1. Existing mechanism of Noise control in Spinning..…. 14

4.2. Machineries in Fabric manufacturing and Noise emission... 18

4.2.1. Existing mechanism of Noise control

in Fabric Manufacturing……………………………… 23

5. Some ideas to control noise in textile machinery:..………… 24

5.1. Active Noise Control…………………..…………………… 25

5.2. Passive Noise Control…………………………….……….. 27

5.2.1. Primary function of Damping materials…………..…… 28

5.2.1.1Definition………………………..………………… 28

5.2.1.2 How does the damping material works……………. 29

5.2.2. Function of Barrier materials…………………..……….. 30

5.2.2.1 How does the barrier material works……………… 31

5.2.3. Function of Absorption materials……..…………………. 32

5.2.3.1. How does the absorption material works………….. 33

6. Conclusion:…………………………………………………….. 35

7. Reference:…….………………………………………………….. 37


Acknowledgement

I would like to show my high gratitude to our Respected Sir, Prof. Kshitij

Gupta, who has taken the course Design for Noise, Vibration and Harshness

and I have got a plenty of knowledge regarding Noise and Vibration from his

kind teaching. Before doing this course I have had least knowledge about Noise

and Vibration. Even I did not know the exact definition of sound as well as

Vibration.

I am also grateful to my entire classmates of this course. Specially, I am thankful

to Mr. Changadev Desai who has helped me to understand the course as well. I

am also thankful to Mr. Ajay, M.Tech final year student, who has taken care of

us during practical classes of the same course.


1. Introduction: Textile is one of the major economic Industries all over the world. In the field of noise

at the workplace, in spite of national regulations on noise at work in force for many

years, lots of people are still getting hearing losses due to machinery noise throughout

the world. In order to progress, there was a need for a policy enforcing noise reduction

at source at the design stage and allowing market forces to encourage less noisy

machinery being put on the market. This was made possible in Europe through a

specific European regulation [1]. In parallel to the strong action on noise reduction at

source at the design stage, a standardization programme developed at the European and

international levels on workplace noise in particular on designing low-noise workplaces,

designing means to reduce noise on the propagation path and measuring their

effectiveness.

Now a days the machine layout and operation pattern has been changed in textile

industry. Management of the industry are concerned to preserve floor space and

optimize production in both the natural and man-made fibres industries. Noise in the

mills and factories is increasing, and one of the main reasons is that in the face of keen

competition and already on a 24 h basis, machines are being operated at speeds higher

than ever before to increase production rates. This is possible to a great extent with the

man-made fibres; continuous threads can be produced and wound more quickly because

of their inherent strength and other advantageous properties compared with natural

fibres. As a direct result of the speed increase, out of balance forces and vibration

increase and more energy is released as sound [2] Due to the complex nature of Textile industry, versatile machineries are used in the field

of textile product. Different type of machineries produces different level of noise.

Generally workers are exposed in that level of sound during production. They have been

effecting by that sound at any instance.

OSHA (Occupational Safety and Health Act 1970) prescribed permissible exposures in

industries. These levels are shown in the table below (Table 1): [3]:


In a textile mill, minimum and maximum noise level can be achieved as 82.82 dBA and

102.3 dBA (approximately) respectively [4].

To prevent health hazards of the workers in that level of sound, different type of

techniques can be applied. But due to unconcerned and un educated workers, the

implementation of those techniques are partially failure. This is a challenging job to

prevent noise in textile industry as well as enlightening to the unconcerned workers and

administrative in Textile industry.

In this literature we will discuss about some approaches to make a pleasant working

environment not only for worker but also the beneficial for the management of the

Textile Sociaty.

Limiting Daily Exposure Time (h)

A-Weighted Sound Level Slow Response

(dBA) 8 90 6 92 4 95 3 97 2 100

1.5 102 1 105

0.5 110 Less Than 0.25 115

Table 1.1: Permissible daily noise exposure limits for industrial noise (OSHA)


2. Definitions and Background:

What is Noise? Noise is disagreeable or undesired sound by the recipient. In many

instances, noise is a relative definition of a sound since one person’s music may be

another person’s noise. It is difficult to give a very clear definition of an irritating noise.

Generally, noise is an unwanted sound, regardless of its intensity or duration [5].

Noise Pollution has been recognized as a major threat to human well being. Much

discussion and legislation has evolved in an attempt to recognize and combat the

problem of noise pollution. It has been recognized that noise, of sufficient intensity, can

damage hearing and be classified as a hazard. In combating the problem of noise

pollution it is necessary to use a means of measuring noise levels and a system of

classification. The decibel is a number which relates sound intensity or sound pressure.

When most people use the term decibel or discuss noise levels in decibels they are

referring to decibels as related to the “A-weighted” scale or, dBA [3].

The A-weighted scale parallels the sensitivity of the human ear and uses the lowest

audible sound that the human ear can detect as the reference point for determining the

decibel level of a noise. The reference intensities used above represent the threshold of

audibility where sound is just loud enough to be heard. At 140 decibels or more acute

pain is experienced. Some common noise values are as follows:

Ordinary conversation – 60 dBA

Heavy traffic – 80 dBA

Cocktail Party – 90 dBA

Moving subway train – 100 dBA

Riveting gun – 130 dBA

Hard rock band – 100 to 138 dBA

Jet plane heard at close range – 150 dBA

Any noise rating above 80 dBA produces physiological effects and any long term

exposures at much or above 90 or 100 decibels will cause permanent damage to a


person’s hearing. An increase of 10 dBA is a doubling of loudness with respect to the

human ear [5].

Noise generally consists of many tones with varying rates of vibration or frequency. The

frequency expressed in cycles per sound or hertz (HZ) usually is in the range of 20 to

20,000 cycles per second. The ear is not very responsive to very low or very high tones

as it is to the tones of medium frequency. The dBA scale matches the response of the

ear, and is therefore well suited for evaluating noise as it relates to human beings [6].

The noisy industrial machine can be viewed as a sound generator. The noise generated,

generally, will be made up of sound waves which encompass the spectrum of 125 cycles

per second to 8,000 cycles per second with a certain frequency band being dominant.

The noise emitted is either direct airborne sound or noise generated by mechanical

vibrations setting up vibrations in sheet metal panels or large solid areas.

Sound waves decrease in length as the frequency increases or, more simply, the

wavelength is inversely proportional to the frequency. Generally, it is easier to control

noise in the higher frequency bands than the lower frequency bands since it is difficult

to absorb sound which is made up of long wave lengths.

2.1 Noise Control Principles It is necessary to treat at least one element in the noise system if the perceived level of

noise is to be reduced. By reducing the noise level at the source or along the path, the

noise level at the receiver point of interest is accordingly reduced. Treating the receiver

in such a way as to minimize the sensitivity to high noise levels is another approach to

the general noise problem. Each element of the noise system has associated with its

treatment advantages and disadvantages.

Treatment of the noise source is the most effective approach to a localized noise

problem. The noise source treatment is often, however, the most difficult to properly

implement. Treatment would be accomplished by addition of noise control materials or

the re-design of the noise source. Addition of noise control materials could hinder the


process of the noise source in its primary functions. Redesign of the noise source may

be prohibitive based on the cost to redesign, develop and re-tool.

Treatment of the noise receiver is the least desirable approach since each receiver must

be treated individually. The addition of earplugs or earmuffs can encumber the receiver

to the extent of being impractical. Educating the receiver as to the source of the noise

and the purpose of the noise generating mechanism is another possibility. In any case

the degree of effectiveness of the treatment will vary since the range of subjective

reaction to noise varies from person to person.

Treatment of the noise path is conceptually the simplest and therefore the most common

approach to a localized noise problem. The approach is to place material in the path of

the noise (generally between the noise source and the noise receiver) so that the level of

noise at the receiver is reduced. The application of materials is often oversimplified,

however, leading to ineffective and/or inefficient use of materials. Also the air paths are

typically addressed while the structural paths are often overlooked. Finally, the design

of the treatments developed without consideration of assembly procedures can lead to

installation errors, which compromise the purpose of the treatment.

2.2 Approach to Analysis of Problems As pointed out earlier, the end recipient of noise is the human ear. An expedient

solution to a noise problem comes through the use of earplugs or other ear protection.

Legislation has taken the position that hearing protection of this nature will not be

tolerated if effective means for controlling noise at the source exists. The first step in

quieting a noisy environment is to clearly identify the problem.

An ideal starting point is to obtain the dBA levels emitted at various frequency bands.

This should also be done at several positions around the machinery. This can be done

with a simple sound level meter, however, with more sophisticated equipment, more

detailed data can be compiled regarding the frequency characteristics and nature of the

sound source.


3. Analytical Survey of Noise Study in Textile Industry: Occupational Noise exposure has been linked with a range of negative health effects by

various researchers. The resulting injury of occupational hearing loss is also a well

recognized and global problem. To protect workers from hearing damage due to noise

exposure and other related health effects, a vast store of knowledge has been

accumulated till date about its nature, etiology and time course. There is still ignorance,

amongst majority of people working in industries in developing and third world

countries including India about ill effects of exposure to high values of noise.

Equivalent sound pressure level Leq has given in various sections of a plant with the

help of a digital sound level meter. The noise spectrum has been evaluated with the

help of 1/3 octave filter set. A cross sectional study involving 112 workers exposed to

different levels of occupational noise has been conducted [4].

Meliksah ERTEM et al [7]. shows the comparison of the mean hearing threshold levels

(dB) of control subjects with carpet mill and cotton textile factory workers. 4000 Hz

notch was plotted in carpet mill and cotton textile workers audiograms in the figure 1.

Fig. 1 Mean hearing levels (dB) at different frequencies.

The results of the study establish the fact that noise level in certain sections of the plants

i.e Loom Shed, Spinning, Ring Frame, TFO Area is more than the acceptable limit of 90


dBA for 8 h exposure stipulated by OSHA. The noise level in other sections like

carding, blow room, combing etc., although is less than 90 dB(A), but is quite higher

than limits used for assessment of noise for community response. Octave band analysis

of the noise shows the presence of high sound level in 4,000 Hz frequency range, which

can be a major reason for causing occupational hearing loss. The results of the

interview questionnaire which included a number of parameters reveal the following; (i)

only 29% workers are aware about the effects of noise on health (ii) 28% workers are

using ear protectors (iii) the satisfaction with the working environment is related to

noise level, as workers exposed to comparatively less noise level report better

satisfaction (iv) 70% of the workers reported that high noise level causes speech

interference (v) 42% workers report the noise to be annoying. The study thus

demonstrates the presence of gross occupational noise exposure in both the plants and

the author believes that occupational noise exposure and the related effects in India is a

widespread problem.

The equivalent A-weighted sound pressure level LAeq has been calculated using the

equation:

The details of the Leq values of noise to which the workers are exposed in various work

areas in a textile mill is shown in the Table 2 and Table 3 below:


Madbuli H. Noweir et al. [8] has shown, the dBA means of Leq, Max (SPL) and Min

(SPL) of the surveyed factories are in Table 4. The most used and possibly, the most

meaningful parameter, the Leq has varying degree of variance, ranging from 1.5 dBA2

(Hygienic Paper Products Co.) to 5.9 dBA2 (Nasr Printing Factory). Factories with

smaller variance of Leq could be treated with general noise control and reduction

techniques. However, factories with high variation may have hot spots which would

need individual noise control at the sources in addition to any general measures.

Table 4


3.1 Spectrum Analysis

The octave band analysis of the noise in various work areas shows the presence of

high sound level in 4000 Hz. Figure 2 and 3 shows the octave band analysis of sound

spectrum in Ring Frame and loom shed respectively. The high level of sound present in

this frequency region can be a major reason for causing noise induced occupational

hearing loss.

Exposure to continuous and extensive noise at a level higher than 85 dBA may lead to

hearing loss. Continuous hearing loss differs from person to person with the level,

frequency and duration of the noise exposed [9.]. Negative effects of noise on human

beings are generally of a physiological and psychological nature. Hearing losses are the

most common effects among the physiological ones. It is possible to classify the effects

of noise on ears in three groups: acoustic trauma, temporary hearing losses and

permanent hearing loss [10]. Blood pressure increases, heart beat accelerations,

appearance of muscle reflexes, sleeping disorders may be considered among the other

physiological effects. The psychological effects of noise are more common compared to

the psychological ones and they can be seen in the forms of annoyance, stress, anger

and concentration disorders as well as difficulties in resting and perception [11, 12, 13].

3


A great majority of people working in industry are exposed to noise. Therefore, in this

study, the effects of noise on human beings have been investigated with respect to the

level of noise they are exposed to [14] assembly procedures can lead to installation

errors, which compromise the purpose of the treatment.

3.2 Standards for noise abatement in industry

In the field of noise at the workplace, in spite of national regulations on noise at work in

force for many years, lots of people are still getting hearing losses due to machinery

noise in Europe as well as throughout the world. In order to progress, there was a need

for a policy enforcing noise reduction at source at the design stage and allowing market

forces to encourage less noisy machinery being put on the market. This was made

possible in Europe through a specific European regulation.

In parallel to the strong action on noise reduction at source at the design stage, a

standardization programme developed at the European and international levels on

workplace noise in particular on designing low-noise workplaces, designing means to

reduce noise on the propagation path and measuring their effectiveness.

3.3 The Machinery Directive

A major new approach directive is Directive 89/392/EC (first published in 1989,

subsequently amended and renumbered in 1998 as 98/37/EC), so-called “Machinery

Directive”.

Three types of standards, so-called type A, type B and type C standards, are elaborated

to accompany this directive. Type A is for standards covering basic safety concepts,

type B standards covering horizontal issues (e.g. noise emission measurement in

general) applicable to a large number of machinery and type C standards concerning

safety aspects (including hazards due to noise emission) of single types of machinery

[1].


Figure 4 illustrates the essential role of standards in the current strategy for reducing

noise in industry.

Fig. 4 Global strategy for noise abatement in industry


4. Structure of Textile Industry: A composite industry of Textile can be described as in the Structure of four types of

categories as Spinning mill, Weaving mill, Dyeing mill and Composite mill. In spinning

mill, only the yarns are produced using different type of twisting and pre processing

machines. In weaving mill, the yarn comes from the spinning section. First, the yarn

goes to the winding section to make the bigger packages to manufacturing the fabrics.

In weaving section, different types of looms are used for producing different categories

of fabrics according to the requirements of market demands. Similarly, in the dyeing

mill, they only make the fabric dyed and printed and finished.

In the composite mill, all three types of sections, which are mentioned above, are

involved. Some composite mill produce garments in further process.

The structure of a specialized composite mill has shown below:

Fig.5. Structure of a typical composite mill

4.1. Machineries in Spinning and Noise emission

In the spinning section, various machineries are used in the pre-spinning process as well

as twisting process. In pre-spinning process, generally Carding, Combing, Drawing and


Draw twisting or Roving machines are used to produce twisted roves or slivers. For all

the operations, pneumatic pressure compressors are required. Those machines are

emitted noise in different levels. An US patent has reveals some features which takes

place to control noise in air jet spinning machinery [ 15].

After pre-processing, roves or slivers are used to manufacture yarns. In this section, as

per the end use, different types of spinning machines are used such as ring spinning,

rotor spinning DREF machines etc.

According to the speed of the machines, the emissions of sound levels are different in

different machineries. In the twisting zones, the rotor speed is maximum compare to

other spinning machines. The rotor speed is approximately 120000 rpm and the opening

roller speed is 5000-6000 rpm. Most of the sound emits due to the high speed of rotor.

Similarly, the speed of the spindle of Ring spinning approximately 20000 rpm and in

draw twisting machine, the speed of the spindle approximately 14000 rpm.

The approximate emissions of sound levels in spinning machineries are given in the

table 5.

Table 5

Name of the MachinesMax. Sound Level

(dBA)(apprx.)

Blow Room 82-84.8

Carding 86.2-89.2

Combing 84.5

Drawing 85

Roving 88-95.5

Ring Spinning 99.5-100.2

Rotor Spinning 102-104

DREF Spinning 89.9


4.1.1. Existing mechanism of Noise control in Spinning

There are many kind of machines are existing in the spinning or any field of operations.

And the result that each operation has its own noise emission spectrum. Below, in the

figure, shown the noise spectrum for different process in textile sector

Fig. 6 Noise spectra of five processes 1. Staple fibre cutter, 2. Spinning, 3.

DrawTwisting, 4. Weaving, 5. Winding.

It is very difficult to control huge amount of noise in direct approach. Ear protector

could be a solution to prevent hazardous effect direct to the human physic as well as

psychology. But there are objection from hygiene, safety and comfort consideration.

The solution then is to reduce noise level in active approach. The active approach is to

overhauling and maintenance periodically that reduce the noise at source. A necessary

step to noise reduction at source is a detailed knowledge of the source mechanisms,

transmission path and noise radiating surface [2].

A typical diagram of a drawtwister has shown in the fig. 7.


Fig. 7. Diagram of a drawtwister

From the fig. 8 we have seen that the loudest narrow band sound is produced from the

spindle and bobbin zones.

Fig 8. SPL of Drawbox and Bobbin


A spindle diagram has shown in the fig. 9. The noise source can be control by the detail

study of the material and mounting mechanism of the spindle. Generally, spindle and

ball-bearing are produced by the metal, which produce more noise. It is possible to

change the material, metal to polymeric one.

Fig. 9. Spindle Use of Polyurethane gear, flexibly mounted gears, redesigned headstock and various

vibration isolation of parts, the noise contours change and the levels are reduced to meet

the recommended levels at the operator’s position. Some noise reduction techniques on

the draw-roll assembly has shown in (Fig 10). One approach used a polyurethane

bonded bush between the gear and the shaft. It reduced the overall noise level of one

shaft assembly by 7-8 dB. Another trial was made substituting a copper-manganese

alloy shaft for the steel shaft. The use of this material not only introduced its high

damping properties but also lowered the shaft critical below the running range. The


result of using the copper-manganese shaft was to reduce the overall noise level by 4.5

dB.

Fig.10 Treated draw roll.

In the figure 11 octave band levels for the modified machine are compared to the

average drawtwist noise and a deafness risk criterion n.r.85. There is a reduction of

noise from 128 sones to 77 sones, i.e. a reduction in loudness od 40%. These noise

levels are for the modified machine running with full bobbins at spindle and drawroll

speeds higher by 11% and 20% respectively than the maximum production speeds

commonly used [16].


Fig. 11 Octave band levels at centre of machine for modified drawtwist machine. 1.

Average drawtwist noise, 2. Modified machine noise, 3. n.r. 85 criterion

4.2. Machineries in Fabric manufacturing and Noise emission

As earlier discussion we have seen, various machineries are being used in fabric

manufacturing section, such as different type of Winding machine, Looms and knitting

machines. In winding zone, TFO (Two for one Twist), Doubling, Cheese winding, cone

winding, Precision winding machines are being used. And it is obvious that all the

machines are produced different levels of noise.

Similarly, different types of looms are used as per the requirement of fabric

construction. Now a day’s most preferable looms are shuttle less automatic looms.

Production of this type of loom is higher. It means the speed of the loom is higher and it

is understood that the loom produce higher level of noise.

The approximate emissions of sound levels in Fabric manufacturing are given in the

table 6.


Table 6

Name of the MachinesMax. Sound Level

(dBA)(apprx.)

TFO 100

Doubling 92-95.5

Cheese Wing 93

Cone winding 92

Precision Winding 91-92

Shuttle Loom 99-100

Shuttle less Loom 100-105

Air jet Loom 110

Water jet Loom 96-99

The noise source of winding machine is almost similar to that of spinning machineries.

In case of TFO, the noise generates due to the revolution of the spindle in the spindle

chamber. The whole assembly of spindle and chamber vibrates due to it high revolution.

The maximum spindle speed is 16000 RPM [17] And the outcome of the result is high

amplitude narrowband noise [fig. 12]. Another major source of noise is gearing

arrangement in the gearbox.


Fig. 12. TFO Spindle chamber arrangement.

Similarly, in Loom shed, there are many types of looms are use and it is obvious that all

different looms have different speed according to their production rate and frequency.

Due to the different sped and mechanism, the looms are produced different levels of

noise. Like, Air jet looms produce higher level of noise compare other looms (table 6).

In the figure 13 a typical Air jet loom has shown. Basically Air nozzle produces much

noise in this loom. Not only air nozzles, reed of the looms are produced high noise when

it strikes on the base plate of the reeds.


Fig 13. Air jet Loom

In the Shuttle loom, most sound generates due to the movement of the shuttle. During

Weft insertion takes place through the Warp shed, shuttle caries the weft thread and it

strikes to the end of the shuttle path called sley end (fig 14.). Shuttle nose strikes on the

solid material and make noise in a high level.

In this occasion, there have a active control arrangement take place. At the end of the

shuttle path there have a buffer, which is made by rubber. The rubber buffer consume

kinetic energy of the shuttle and indirectly protects the noise.


But there have no such type of arrangement to control noise in the reeds section.

According to the pattern of the fabrics, the reeds are acting up and down. Due to this

movement of the reeds a huge noise emits from the loom. When reeds moved down, it

strikes metallic parts inside the loom. Not only has this event, the friction between reeds

and slot of the reeds emitted noise in each movement. A typical reed has shown in the

figure 15.

Fig. 15. Reed

Fig. 14. Shuttle Loom and Shuttle


4.2.1. Existing mechanism of Noise control in Fabric Manufacturing

An air jet loom makes cloth using compressed air to insert the weft into the warp. The

weft is inserted into the warp by the rocking motion of the sley, sword, reed, and

rocking shaft. By reducing the vibration produced by the rocking motion of this non-

balanced load, Toyota Industries has successfully improved the workplace environment

of its customers’ weaving mills. Some model of air jet loom was designed to optimize

the cross-sectional shape of the sley, the weight of which was reduced by 20% [18].

In addition, the material of the sword was changed and by perfecting its placement of

ribs using computer analysis, it was possible to lighten and harden the sword. By

attaching the balance weight to the rocking shaft, the load was reduced. As a result,

vibration was greatly decreased by reducing the dynamic load on the floor by 20%.

As earlier discussion, a conventional loom has changed very little since the industrial

revolution[19] Much of the noise arises from the impact and general clatter of the

shuttles, picking arms and harness. The spectrum is mainly high frequency and the

sources are difficult to eliminate, mainly because impact is inherent in the process.

Noise control of shuttle and picking arm noise in the jute industry [20] can reduced a

loom by up to 10 dB. This can has been achieved by replacing metallic picking points

and picking cones with polyethylene parts [21]. Nylon driving pinions and nylon bushes

have been used in lieu of cast iron. Figure 16 has shown the different sound level in

Shuttle and water jet looms [2]


Fig. 16. Noise comparison, 1.Shuttle loom (205ppm) 2.Water Jet Loom (400ppm)

5. Some ideas to control noise in textile machinery: It has already been discussed that controlling noise is challenging job in textile

machinery. There have so many barriers to control noise or to protect health hazards of

workers.

In this text we will discuss the probable controlling system of induced noise from textile

machineries.

Noise control in textile machinery can be classified in two broad sections. One is active

and another is passive control. Probable noise control system in textile machineries has

shown in the flow chart in figure 17.


Fig. 17. Control Flow chart

5.1. Active Noise Control

According to the flow chart, it is possible to control of noise that emits from the

machineries by two ways. In active system, directly we can control the noise bye

controlling the machine itself. Generally the noise generates from the machine due to its

unwanted vibrations in various levels of frequencies and material to material friction

[22].

If we are able to control that unwanted vibration friction as well, to some extent we can

control the noise directly. Machine vibration can be controlled by three ways; first, we

can control by proper balancing the machines,

There are two main types of balancing machines, hard-bearing and soft-bearing. The

difference between them, however, is in the suspension and not the bearings. In a hard-


bearing machine, balancing is done at a frequency lower than the resonance frequency

[Figure 18] of the suspension [23].

Fig. 18. Resonance frequency

In a soft-bearing machine, balancing is done at a frequency higher than the resonance

frequency of the suspension. Both types of machines have various advantages and

disadvantages. A hard-bearing machine is generally more flexible and can handle pieces

with greatly varying weights, because hard-bearing machines are measuring centrifugal

forces and require only a one-time calibration. Only five geometric dimensions need to

be fed into the measuring unit and the machine is ready for use. Therefore, it works very

well for low- and middle-size volume production and in repair workshops. A soft-

bearing machine is not so flexible in respect of amount of rotor weight to be balanced.

The preparation of a soft-bearing machine for individual rotor types is more time


consuming, because it needs to be calibrated for every individual part. It is very suitable

for high-production volume and high-precision balancing tasks. Hard- and soft-bearing

machines can be automated to remove weight automatically, such as by drilling or

milling, but hard-bearing machines are more robust. Both machine principles can be

integrated into a production line and loaded by a robot arm or gantry, requiring very

little human control. Soft-bearing machines are also generally more expensive because

of the higher complexity in the design and manufacturing.

Secondly, proper material selection for vibrating parts and in which parts material to

material frictions takes place; as an example metallic gear arrangements. For our

experience, it is visible that metallic gear to metallic gear arrangement produces more

noise compare to polymeric gear. Although, there have many advantages as well as

disadvantages for polymeric gear arrangements. However, in account of control of

noise, polymeric gears are more suitable rather than metallic one. Generally

polyurethane, polyester, polyamide polymers are used for this purpose. It is known that

where the rotational movements takes place in the machine parts, the vibration occurs

more, as an example spindles, gears, crank shaft etc. those parts can be replaced by

polymeric materials instead of metallic one.

On the other hand, noise can be reduced by keeping control the noise source. That

means, overhauling is important to reduce noise. Periodically lubrication is required in

the zone of gears to gear arrangement, ball-bearing and other rotational parts. For all the

machines overhauling duration and indication of lubrication is mentioned [24].

5.2. Passive Noise Control

The passive noise control system is nothing but the control after emission of noise.

Emitted noise can be controlled by two ways; one is to making casing around the noise

source and another is hearing protection. Many cases in textile machineries casing

arrangement is difficult because of the production front. Generally, the production front


in textile machineries is kept open to doffing conveniently after preparation of final

products for spinning as well as weaving. It is easy to casing the gearbox effectively.

Casing arrangement will be discussed as the following ways:

Casing arrangement can be prepared by three ways; using damping material, barrier

materials and absorptive materials. In both the cases the aim is to control vibration.

Details discussions about those materials are given below.

5.2.1. Primary function of Damping materials

A damping material is used to reduce the vibration level in a vibrating system. The

terms damping and deadening have long been used to describe the effects of general

noise control measures. The topic taken up here is vibration damping as opposed to

sound absorption, sound transmission loss or vibration isolation [25].

5.2.1.1Definition

Damping is the reduction of kinetic energy present in a system through transformation

into another form of energy. The efficiency of damping present is evaluated by

determining the system’s loss factor. The dimensionless loss factor (η) is defined as:

UW

ff

TD

Qd

n

n

ππη

221

0

0 =∆

===

Where,

Q = System damping factor

D0 = Total energy dissipated in the system as the result of damping for one cycle

T0 = Total vibration energy of the system

fn = Undampted resonant frequency (Hz)

∆fn = Half power bandwidth (Hz)

Wd = Energy dissipated from the system

U = Max. energy stored in the system


Half power bandwidth is shown in the figure 19.

Fig. 19. Half power bandwidth

5.2.1.2 How does the damping material works

The damping materials generally reduce the vibration amplitude by generating heat

energy. Viscoelastic dampers are adhered to the vibration surface. This materials

generates heat when it undergoes deformation. By optimizing a material’s stiffness and

internal losses, the damping performance can be optimized.

It should be noted that the addition of damping material changes the stiffness to mass

ratio of the system and accordingly, the resonances of system are affected.

The damping performance of the viscoelastic material can be improved by spacing the

material from the sheet metal. These applications take advantage of the extensional

deformation of the damping material. By placing the viscoelastic material between two

relatively inelastic materials, the viscoelastic material experiences shear deformation

(figure 20). This also results in improved damping performance. Because of the

different mechanisms of inducing deformation in the damping material, a material that

performs well as a free layer may not perform as well as a constrained layer and vice

versa.


Fig. 20. Different damping applications

5.2.2. Function of Barrier materials

A barrier material also reduces the amplitude of sound waves propagating in a certain

direction. The barrier material interferes with sound waves as they propagate away from

the sound source. The portion of the sound energy which continues to propagate along

the original path is then of significantly lower amplitude than the original wave.

In the figure 21, it has been that how the barrier material works.

Fig. 21. Noise incident on a barrier material


A barrier material, which reduces sound energy as the sound wave is transmitted

through the material. The measure of a material’s effectiveness as a transmission loss as

earlier discussion. Transmission loss is the fraction of energy dissipated as a result of

sound being transmitted through the material. Transmission loss is measured in decibels

as:

TL = 10log10 5.2.2.1 How does the barrier material works

As the sound wave interacts with the barrier material, the mass of the material opposes

the wave motion of the air molecules, thus causing a reflection of some portion of the

sound energy. A fraction of the energy is absorbed and dissipated as heat due to the

internal damping of the material. The remaining energy is converted to sound energy on

the side of the barrier material opposite the impinging sound wave.

The transmission loss (TL) of a material is principally determined by the mass of the

material. At low frequencies the material’s stiffness and mass determine the TL. At high

frequencies the material stiffness, damping and the mass determine the TL. For

frequencies where the TL is essentially mass controlled, the TL by 6 dB for most

frequencies.

The effectiveness of the barrier is dependent on its ability to sufficiently interfere with

the sound wave. The barrier must have effective dimensions much greater than the

wavelength of the sound to have significant influence on the sound level.

The material should be impervious with respect to air. Holes in the barrier affects its

performance. They significantly reduce the effective dimensions of the barrier and they

allow for air pressure communication directly through the barrier material. Thus

reduction the potential acoustic value of the barrier.

Incident sound intensity (Ii) Transmitted sound intensity (It)


5.2.3. Function of Absorption materials

Sound absorption materials reduce the acoustic energy of a sound wave as the wave

passes through the material. They are commonly used to often the acoustic environment

of an enclosed volume by reducing the amplitude of reflected sound waves. The benefit

of the absorption material is multiplied by applying the material to a reflective surface

since the sound is made to pass through the absorption material more than once.

In the figure 22 a absorption material has shown.

Fig.22. Noise incident on an absorption material

For a sound absorption material applied to an acoustically reflective surface, sound

energy incident (Ii) on the material is partially absorbed by the material (Ia) and the

remaining sound energy is reflected (Ir). The sound absorption capability of a material is

expressed in terms of the sound absorption coefficient; α the sound absorption

coefficient is defined as:

α =

The absorption coefficient can have values between 0 and 1.

Acoustic energy absorbed by a surface (Ia=Ii-Ir) Acoustic energy incident on a surface (Ii)


5.2.3.1. How does the absorption material works

In order for a material to have good sound absorption performance, the material has to

be a porous or fibrous one. Sound waves propagate into the material and loss energy by

viscous dissipation. Sound waves inside the material also caused the fibres to rub

against each other, thereby producing heat energy and dissipation sound energy.

The absorption characteristics of a material are a function of frequency. Performance

generally increases with an increase in frequency. As a rule of thumb, the material

thickness should be a quarter of the wavelength (λ) of the sound wave to be effective.

Therefore, material thickness is an important determinant of absorption performance. It

has shown in the figure 23.

Fig.23. Random incidence sound absorption for

Polyurethane foam of various thicknesses.


So, from the above discussion, it is proved that the noise induce from textile

machineries can be controlled by designing some special features in a particular place of

a specified noisy part.

Some cases when machines are not in controlled for emission of noise, the workers of

supervising authority can have ear protector. Using ear protector, to some extent, noise

hazards can be controlled for human health.


6. Conclusion: For the textile, industry control of noise emission from the textile machineries is a

challenging job. Some of the cases noise control has been taking place in few industries.

Most of the textile industry in India, they are unable to implement the noise control

system. To understand for noise control it is experienced that the controlling systems

not only reduce the noise at source to acceptable levels, but also reduces the energy

consumption in to some extent and at the same time leads to a better design of the

machines too. For example, polymeric gear-gear arrangement or polymeric spindle

consumes less energy compare to metallic one for the same r.p.m., it means that less

energy consumption can leads to give higher speed as well as higher production.

In this occasion, we have seen that it is possible to reduce emission of noise as well as

control of noise when human health is concerned. There have number of possible

procedure to control noise. We have also seen that the control can be achieved by two

ways, such as Active and Passive control. There have different features for those control

system.

For active control, our aim is to reduce vibration and friction in situ of the noise parts by

replacing materials as well as parts configurations. In this case, rotational metallic parts

can be replaced by polymeric where noise comes out due to friction.

For passive control, we want to reduce the noise level which has already been emitted

from the source. There are some procedures to control the noise. The noise source can

be covered fully of the cover can be treated by different process such as using damping,

barrier and absorption materials. Some cases ear protectors are used to prevent noise

hazards.


7. References:

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