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��� Drawing
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From a purely commercial viewpoint the drawframe is of little significance. it usually contributes less than 3% to the production costs of the yarn.
اهميت ماشين كشش •
به لحاظ اقتصادي
بر كيفيت محصول تأثيرگذاريبه لحاظ
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بر يكنواختي محصول تأثيرگذاريدالئل اهميت ماشين كشش به لحاظ
آخرين مرحله جهت حذف عيوب و افزايش يكنواختي در خط الياف كوتاه•
سرعت باالي توليد •
و ايجاد عيب، طول قابل توجهي از محصول تنظيماتدر صورت مناسب نبودن .معيوب خواهد گرديد
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Principles of Doubling
:كيلوتكس تنظيم شده اند 5ماشين كارد كه بر اساس توليد نمره 6ميانگين نمره فتيله : مثال
4.85 , 4.95 , 5.25 , 5.42 , 5.03 , 5.13
6با كشش الكني 6تغذيه به ماشين
5.15 , 5.10 , 5.09
5.05 , 4.95 , 5.12
6با كشش الكني 6تغذيه به ماشين
5.08
(6××××1=1) �������
(6××××6=36) �������
Purposes:Reduction of irregularty
Improvemrnt of mix or blend of fibers
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RS=The number of doubling
In practice usually R=2 or 3 is accepted as sufficient.
متري اندازه گيري مي شود، مثال قبل تأثير عمليات 1-5از آنجا كه نمره فتيله در طول هاي .را نشان مي دهدطول موج متوسط تا بلند هاي با نايكنواختيبر كاهش چندالكني
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فتيله سياه 3الياف شوندگيبر بهبود مخلوط چندالكنيبراي درك تأثير عمليات :اندال كني مورد استفاده قرار گرفته 6فتيله سفيد جهت انجام سه مرحله 3و
S=6
R=1
S=6
R=2
S=6
R=3
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Principles of Roller Drafting
(Ideal Draft)كشش ايده آل
.يك سيستم كششي با يك ناحيه كشش را در نظر بگيريدسطحي غلتك برابرسرعت 3 (B)فرض مي كنيم سرعت سطحي غلتك جلو
.باشد (A)عقب ) بر حسب گرم Mf(همچنين تمام الياف موجود در سازه داراي جرم يكسان
از سازه L1ليف در طول Nباشند و تعداد Lf=3 cm)(و طول يكسان .وجود داشته باشد
:برابر است با تكسبنابراين نمره ورودي به ناحيه كششي بر حسب
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غلتك گيراييدر كشش ايده آل هر ليف تا قبل از اينكه سرش به خط جلو برسد با سرعت غلتك عقب حركت مي كند چرا كه انتهاي آن
.توسط غلتك عقب گرفته شده است
برابر با (در اين حالت فواصل بين سرهاي الياف با يك ضريب يكسان لذا كشش ايده آل سبب افزايش . افزايش مي يابد) مقدار كشش
.گردد نميسازه نايكنواختي
:تعداد الياف در سطح مقطع ورودي و خروجي
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(Actual Draft)كشش واقعي
:در حالت واقعي تمام الياف.داراي طول يكسان نيستند •.اندبه طور مستقيم در سازه قرار نگرفته •.كامالً با هم موازي نيستند •
فاصله بين دو صفحه موازي در بر گيرنده ليف به طوري كه آن را قطع نكرده و عمود بر راستاي كلي سازه ليفي باشند
Fiber Extent:
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:اگر فاصله بين غلتك ها كوتاهتر از طول بلندترين ليف تنظيم شود •
•Fiber breakage
•Spewing
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(Drafting Waves)امواج كششي
بنابراين تنظيم فاصله بين غلتك هاي كششي به گونه اي است كه زماني ابتداي عقب غلتكهايجلو برسد كه انتهاي آن توسط غلتكهاي گيراييبلندترين ليف به خط
.رها شده باشد
الياف شناورFloating fibers
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مشكل الياف شناور؟
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(Drafting force)نيروي كششي
:نيروي كششي به عوامل زير بستگي دارد
وزن خطي دسته الياف -و مستقيم بودن الياف توازيدرجه -)مواجيت(خواص سطحي الياف -فاصله بين غلتك هاي كششي -
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Size of draft
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Input count
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Doubling
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Fiber straightness, parallelism,
fineness and length
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Roller setting
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تأثير عيوب ماشين
خارج از مركز بودن غلتك ها • �
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لغزش غلتك ها •
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At the drawing stage for carded yarns the material rarely
passes just one machine but usually two, arranged one after
the other and combined to form a group.
An exception is the rotor spinning mill, where often only one
passage is used or even none, i.e. the sliver is fed directly
from a high performance card, but equipped with an
integrated leveling device. Normally, processing in two
passages is necessary to fulfill requirements.
However, a second passage after the comber is superfluous,
since this does not produce any improvement in quality. On
the contrary, it usually adversely affects quality due to
excessive parallelization of the fibers. The drawframe used in this case, however, has then to be a leveling drawframe.
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Normal processing lines; 1. card; 2. drafting module for card;
3. drawframe; 4. combing preparation, 5. combing machine;
6. roving frame; 7. rotor spinning machine, 8. ring spinning machine
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����� � و���� ���Equalizing
Parallelizing
Blending
Dust removal
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One of the main tasks of the drawframe is improving evenness over the short, medium and – especially – long term .
Equalizing
The draft and the doublings often have the same value and are in the range of 6 (short fibers) to 8 (medium and long fibers). When processing pure comber noil in the rotor spinning mill, however, it is usually necessary to settle for a value of 4 or to use high-performance cards with integrated leveling devices instead of drawframes .
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Parallelizing
To obtain an optimal value for strength in the yarn characteristics, the fibers must be arranged parallel in the fiber strand. It is fulfilled by means of the draft.
The value of the draft must be adapted to the material, i.e. to several fiber parameters, mainly :
•the staple length ;•the mass of the fibers ;•the volume of the strand ;•the degree of order (parallel disposition )
It will be clear that the draft cannot be high on a machine directly following the card (if possible, not above 8), but thereafter can increase from machine to machine
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•compensation of raw material variations
•production of blended yarns (cotton/synthetic or synthetic/synthetic blends)
For example, to obtain a 67:33 blend, four slivers of one
component and two of the other are fed to the drawframe. Of course, these slivers must have the same hank.
Blending �
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Dust is steadily becoming a greater problem both in processing and for the personnel involved .
Dust removal can only be carried out to a significant degree when there are high levels of fiber/fiber or fiber/metal friction.On high-performance drawframes equipped with appropriate suction systems, more than 80% of the incoming dust is extracted .
Dust removal
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Operating principle
Sectional view of a drawframe
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���� Creel
:قفسه بايد به گونه اي باشد كه
• false drafts are avoided• the machine stops immediately when a sliver break occurs ;• sliver breaks can be dealt with easily, comfortably and safely .
A guiding device for feeding the slivers into the drafting arrangement
positively driven roller above each can
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• simple, uncomplicated construction;
• stable design with smooth running of the rollers (centricity);
• a mode of operation producing a high-quality product even
at high running speeds;
• high degree of flexibility, i.e. suitability for all raw materials, fiber lengths, sliver hanks, etc., that might be
processed in the short staple spinning mill;
���� ����� قلب دستگاه چندالكني و مؤثرترين قسمت آن بر كيفيت فتيله
:نيازمندي هاي يك سيستم كششي مناسب
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•optimal control over the movement of the fibers during
the drafting operation;
• high precision of both operation and adjustment;
• rapid and simple adjustability of roller spacings and
draft levels;
• ease of maintenance and cleaning;
• optimal ergonomic design.
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In all types of drafting arrangement, the factors
that affect the draft are:
Factors dependent upon the fiber material:
mass of fiber in the strand cross section;
degree of order of the fibers (parallel disposition);
shape of the cross section of the fiber strand;
compactness of the fiber strand;
adhesion between the fibers dependent upon
surface structure,
crimp,
spin finish,
compression of the strand;
fiber length;
evenness of distribution of fiber lengths (staple form);
existing twist in the fiber strand.
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Factors dependent upon the drafting
arrangement:
diameter of the rollers;
hardness of the top rollers;
pressure exerted by the top rollers;
surface characteristics of the top rollers;
fluting of the bottom rollers;
type and form of fiber guiding devices, such as
pressure rods, pin bars, aprons, condenser etc.;
clamping distances (roller settings);
level of draft;
distribution of draft between the various drafting
zones
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The coiler speed is too low if the coil diameter is round but wavy and
the diameter of the sliver column is too large (2) A sliver column too
large touches the entire inside wall of the can (1). �
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The coiler speed is too high if the diameter of coil A is out of round (the
coil develops a tip pointing to the wall of the can ; the radius of the coil
is too small (1)), if the coil diameter "a" is not consistently equal and if
the sliver column is too small (2) (clearance to wall of the can more than
5 mm) (1).
Note:Higher delivery speeds increase the diameter of the sliver
column. Lower delivery speeds reduce the diameter of the sliver column.
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Changing the can table speed alters the distance "a" between two sliver coils "A."
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Dimension "a" must be sufficiently large so that no sliver damage,
such as folded fibers or sliver ears occur when the sliver is pulled from the can.
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Autoleveling
(Closed-loop autoleveling)
(Open-loop autoleveling)
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Tongue-and-groove sensor
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Trützschler AUTO DRAFT?
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Mechanical draft should be selected properly in autoleveler
drawframes. To decide about the mechanical draft, drawframe
should be run with autoleveler switched off. If the sliver
weight is correct, then the mechanical draft selected is
correct. Otherwise, the gears should be changed so that the
sliver is weight is as per the requirement without autolevler.
If the feed variation indicated in the A% is continuously
showing more than -5% or +5%, then the mechanical draft
selected is not correct.
If the mechanical draft selected is correct, then the indication
in A% display of sliver fed should be between -5% red lamp
and 0% green lamp or +5% red lamp and 0% green lamp. In
other words, green lamp(0% variation indication) should be on
at least for 80% of the running time.
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To meet the present quality requirements , finisher
drawframeshould be an autoleveler drawframe. �
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Two important parameters for Quality Leveling:
Leveling action point ( time of correction)
Leveling intensity
Leveling intensity indicates the amount of correction. i.e.
if 12% variation is fed to the drawframe the draft should
vary 12% , so that the sliver weight is constant.
Time of correction indicates that if a thick place is sensed
at scanning roller, the correction should take place exactly
when this thick place reaches the correction point (leveling
point)
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Most of the modern autolevelers can correct 25% feed
variation. It is a general practice to feed 12% varition
both in plus and minus side to check A%. This is called as
Sliver test.
If no of sliver fed to drawframe is N, Check the output
sliver weight with "N", "N+1", "N-1" slivers. Then:
A% = ((g/m(N-1) - g/m(N))/ g/m(N) ) x 100
A% = ((g/m(N+1) - g/m(N))/ g/m(N)) x 100
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