8/12/2019 Study of Critical Factors Involved in Roving Quality1

1/6

Page

0

National Textile University

BSc. Textile Engineering

Yarn manufacturing

Course Code: YM-4011Semester: 7th

Section: AGroup: 3

Muhammad Farooq Kokab

10-NTU-031

Assignment

Study of Critical factors involved in Roving Quality

8/12/2019 Study of Critical Factors Involved in Roving Quality1

2/6

Study of Critical factors involved in Roving Quality

Page

1

Study of Critical factors involved in

Roving Quality1. Roving frame section

The input of roving frame is silver that comes from draw frame section where only parallel of

comber sliver. In roving section reduce the linear density of draw frame silver by drafting. After

reducing the linear density the silver is transfer into roving (a thin form of rope). This is first

stage where twist is inserted for making a yarn in spinning mill. The output of this section is

roving which is wind on a bobbin and this is suitable for further process. Here in this section

describes a clear view of roving section objectives and technical point, critical success factor,

preventive action and defects in the section.

1.1. Objectives

The main objective of roving frame are given below Drafting the draw frame sliver into roving. To insert the twist into the roving Winding the twisting roving on bobbin

2. Critical factors involved in Roving Quality

The following are the main point regarding to quality in Roving machine.

2.1. Roving Strength

Apart from the parameters, which decide sliver strength, the roving strength is additionally

dependent on the amount of twist inserted in the roving. The inter-dependence of twist and

strength in roving may be explained two effects. Either thefiber slip

orthey hold until the

tension becomes so high and then break. The amount of twist determines which of these

effects will occur. For small twist, parting is by fiber slippage at low tension. As the twist

increases, the strength also increases, but parting is still by slippage up to the point where the

strength is equal to the combined breaking strength of all the fibers in the cross section. This is

maximum strength; further increase in twist beyond this value means that the parting is by fibre

8/12/2019 Study of Critical Factors Involved in Roving Quality1

3/6

Study of Critical factors involved in Roving Quality

Page

2

breakage, but the strength does not increase and ultimately diminishes because of the increased

angle at which fibers are inclined to the axis.

2.2. Buffing

Buffing should be on time and after 20 days there should be buffing. If buffing is not done on

time then it will create problem in the yarn such as thick and thin places.

2.3. Smaller roving package-less hairiness

Yarn hairiness decreases with decrease in roving (doff) size, and yarn spun from front row of

roving bobbins is more hairy and variable as compare to that spun from back row of

rowing bobbins. It may be noted that though the trends are consistent yet the differences are

non-significant:2.4. Apron Spacing and Top-Roller Load

Spacer (distance strip) color also affects the quality of yarn. We should change the color

according to roving count. Control over the fibers in top arm drafting is

critically &dquo;

Reduction of apron spacing improves the control over the fibers, but settings below a certain

level lead to frequent drafting faults and therefore to more irregular yams. Drafting quality can

also be improved by increasing the pressure on top rollers, as this would help to reduce the

incidence of slippage of the material (under the rollers). Obviously, optimum apron spacing

would depend upon the top roller load.

Bottom and top apron also effect on quality in the form of thick and thin places produce.

2.5. Drafting Force

In a double apron drafting system, the drafting force increased with the size of the front

beard, i.e. with total draft, fibre length and speed of drafting. The drafting force is

decreased as break draft and apron-to-apron spacing increased. There was a difference in the

force when the roving was fed in the normal direction and then in the reverse, thus showing that

the effect of fibre hooking originated at the card still persists at the spinning frame. For good

8/12/2019 Study of Critical Factors Involved in Roving Quality1

4/6

Study of Critical factors involved in Roving Quality

Page

3

spin, a certain amount of fibre tension is necessary at the front draft zone. But an excessive

tension of the front beard will not always lead to optimum conditions. Further by measuring

the drafting force at the front draft zone, it was possible to detect the effect of fibre hooking

originated at the card. The force was higher when the majority of hooks were trailing.Further a certain amount of fibre tension is necessary in apron zone for optimum yarn

properties. Generally, high values of drafting force are associated with the best properties of

the spun yarn, but too high a fibre tension may lead to deterioration in yarn properties.

2.6. Roving Twist and Ring Frame break draft

o As for as roving twist is concerned fibre to fibre frictional force is more important thanother properties like fibre torsional and bending rigidities. The slight twist imparted to the

fibres in the roving also causes increased normal force, which should enhance the number

of fibre contacts and cause fibre frictional forces. Increase in roving twist increases the

inter-fibre friction due to more contact area, which creates problem during drafting and

ultimately deteriorates the yarn quality. Increase in roving twist multiplier (TM) increases

the inter-fibre friction due to more inter-fibre contact force and it causes problem during

drafting in ring frame and ultimately deteriorates yarn quality. We haveconcluded thatthe yarn irregularity and total imperfections increase with the increase in fibre-to-fibre

friction.o Roving with higher twist gives better speed frame efficiency and large bobbin

sizes. Higher twist roving does not affect creel stretch in ring frame. However, it givesundesirable faults in drafting zones. Lower twist roving gives better the draft

performance due to less fibre - fibre friction.o The break draft in Ring Frame depends on the twist in the feed roving hank. High twist

roving could not be sufficiently drafted in the back roller zone of ring frame, resulting in

thick places in the spun yarn. Increase in the break draft ratio will frequently cause a

drafting wave, resulting in serious thick and thin places in the spun yarn. When the break

draft increases, the yarn imperfection also increases and they further state the yarn

imperfection increases due to the increasing roving twist multiplier for same yarn count.

8/12/2019 Study of Critical Factors Involved in Roving Quality1

5/6

Study of Critical factors involved in Roving Quality

Page

4

2.7. Behavior of Hooks in Roving Process

The relationship between the total amount of hooks in sliver and roving for cotton is linear.

Therefore, it is sufficient to analyze hooks in sliver prior to roving as basis for evaluating the

effects on roving and yarn properties. While converting sliver into roving, the draft(approximately 8) should reduce the amount of hooks. However, while measuring hooks by

Lindsley techniques, the twist in the roving is not removed, and this hides or masks the true

reduction in the amount of hooks caused by the roving draft.

Further, in general the irregularities added at the speed frame are not influenced by the feed

direction of the hooks in the feed sliver especially for coarse roving. But it acquires significant

importance as the roving is made finer. Feed the hooks as leading results in more

irregularities in the case of finer roving.

3. Following are the defects and causes to destroy the roving quality:

3.1. Improper Roving tension

Roving tension is directly related to machine. The roving tension depends upon delivery rate and

the difference between flyer speed and bobbin. For preventive action we should keep the

delivery length and the speed difference constant then the tension in this case will be ideal.

The level of roving tension is an important factor with regard to the performance of the machine.

With a modern drive system, it is possible to install a roving tension control system on the

machine. For this purpose a control unit consisting of sensor and microprocessor checks roving

tension between drafting unit and flyer top on two positions per machine and adjusts the tension

accordingly. This ensures high roving uniformity and prevents false drafting. Such a tensionmonitoring device is produced, for instance, by the ROJ Company.

3.2. Improper handling of material

Roving material is very sensitive regarding to quality point of view. It is necessary to take care of

material. The material should be handled in such a way that fine dust must not affect the

material. It must be avoided touching because of its sensitivity. Fresh material should be used for

next process. This material should not be keep for long time. If it will be kept for long time then

8/12/2019 Study of Critical Factors Involved in Roving Quality1

6/6

Study of Critical factors involved in Roving Quality

Page

5

it will create variation. C.V% increases if material is not used. Supervisor must treat its worker in

a proper way so that handling of material should be according to policy of mill.

3.3. Improper piecing in roving

Supervisor should train his workers in a proper way. If end breakage is disturbed then its

treatment should be proper. If piecing will not be proper then it will affect the next process.

3.4. Roving breakage

This problem is caused due to maintenance problem. Maintenance required machine stoppage

but it is against the production. To enhance the quality of product, the machine maintenance is

the chief requirement. For the proper solution of roving breakage, speed of machine, trained

operator and proper management should be must otherwise it create sever problems in ring

section.

4. References

Akshay Kumar, S M Ishtiaquea & K R Salhotra M S Senthil Kannan, Impact of differentstages of spinning process on fibre orientation and properties of ring, rotor and air-jet

yarns: Part 1 Measurements of fibre orientation parameters and effect of preparatory

processes on fibre orientation and properties, Indian Journal of Fibre & Textile Research

Vol. 33, December 2008, pp. 451-467 http://www.indiantextilejournal.com/articles/FAdetails.asp?id=2128 Rieter spinning Manual, Vol.3 https://sites.google.com/site/spinningtextile/hair1 http://www.textileschool.com/School/Spinning/Roving.aspx How to minimize the defects rate of final product in textile plant by the implementation

of DMAIC tool of Six Sigma. Program: Master of Industrial Engineering-Quality and

Environmental Management Final Degree Thesis 15 Ects, 2009-10 Sweden Thesis Nr.

17/2010, School of Engineering

http://www.indiantextilejournal.com/articles/FAdetails.asp?id=2128http://www.indiantextilejournal.com/articles/FAdetails.asp?id=2128https://sites.google.com/site/spinningtextile/hair1https://sites.google.com/site/spinningtextile/hair1http://www.textileschool.com/School/Spinning/Roving.aspxhttp://www.textileschool.com/School/Spinning/Roving.aspxhttp://www.textileschool.com/School/Spinning/Roving.aspxhttps://sites.google.com/site/spinningtextile/hair1http://www.indiantextilejournal.com/articles/FAdetails.asp?id=2128