CC BY
11
Ochilov Tulqin Ashurovich, Candidate of Technical Sciences, Associate Professor, Tashpulatov Salih Shukurovich, Doctor of Technical Sciences, Professor, Gadoev Nuriddin Ergashevich, Senior Lecturer,
Muhtarov Jurabek Reyimbergenovich, Doctor PhD., Senior Lecturer, Laysheva Elmira Talgatovna, Senior Lecturer,
Tashkent Institute of Textile and Light Industry E-mail: ssht61@mail.ru
KINETICS OF CHANGE IN FIBER STRENGTH AT STORAGE AND PROCESSING OF RAW COTTON ON TECHNOLOGICAL TRANSFERS
Abstract. The kinetics of important physic mechanical and technological characteristics of the fiber and raw cotton are considered: fiber and seed damage, fiber curliness of various degrees of maturity, weediness and the content of defects - which determine to a large extent the consumer value of the cotton plant. At the same time, the effect on time and storage conditions of cotton, the temperature of drying, industrial cotton varieties both on the main technological transitions of the cotton plant from riot to press and in general has been studied. The defining indicators of fiber spinning capacity are its length, strength, linear density (microneir) and color, and in recent years, with the introduction of new international standards for fiber and modern electronic systems for its certification, the consumer market is focusing on length, microneur and color.
Keywords. Damaged fiber and seed, crimp fiber, degree of maturity, clogging, the content of defects.
Fiber tenacity Pp one of the main characteristics of the static fiber estimating maximum load on the fiber during its uniaxial loading until failure in the weakest section. And, although the fibers in the yarn product and destroyed mainly by variable effort effect mainly cyclically repeated, and as a result of friction and wear, and is very rare for a single tensile characteristic specified limit values correlated with the fatigue strength and wear resistance of fibers. So often enough to make a difference Pp (b cH), to anticipate in general and other characteristics. This assessment fiber properties of materials science dates back to the evaluation of metals, building materials, plastics, characteristics are obtained under uniaxial deformation, and the test results apply to more complex three-dimensional voltage. Using one or the other theory of strength. Maximum normal stress, the biggest tangential stress, forming energy, etc. This approach to fiber justified by the fact that although the latter can be considered close to the flexible filament in fiber points of contact with the working bodies and with each other in the yarn , fabrics and knits in the filaments occur volumetric stress state. What has been said it has been proven in the works cited previously R. G. Mah-kamova, R. Z. Burnasheva et al., When the assessment of the
stress in the fiber, according to the energy theory of forming, matched strains, developing it under uniaxial break.
This raises the natural question in addition to modeling the kinetics of changes in fiber strength and the problem of an adequate assessment of the value of P.
Before turning to the analysis of tasks, note immediately that in recent years the textile prefer this assessment values Pp (Absolute), the relative strength of the fiber Pp(cH/tex), equal to the ratio of the first linear fiber density T
(1)
Pp
pp =—.
p t
b
This evaluation gives the relative characteristics ofthe fibers of the fortress; the value of y is sufficiently strong fibers mature fine cotton is 32-35 cN/tex, and in upland cotton cultivars 26-28 cN/tex. The values of this index below the given limits evidence of the weakness of fibers, their immaturity, which, unfortunately, is the case for almost all domestic and foreign advanced zoned selections grown in Uzbekistan. So many varieties of upland cotton, this figure does not exceed 16-19 cN/tex, with associated relatively low rate of harvesting cotton first choice, and industrial grades, and that proves developing subfilm technology of cotton sowing in the country, which share is
growing steadily and it gradually extends from Andizhan to the most regions of the republic. This method of seeding, as well as sowing of cotton by using seeds, allowed China to come out on top cotton producer, it was useful to Uzbekistan as one of the most northern zone of cotton cultivation.
Practice shows that these natural properties of the fibers do not remain constant over time and by changing the period of storage in a riot, after drying, cleaning of small, large litter, ginning, post-ginning cleaning and pressing. Such variation extends predominantly in the direction of decreasing transitions and all textile technology loosening and scutching, carding, in the manufacture of tapes, foreyarns and yarns, a knitted fabric and weaving and also in the finishing and in the manufacture of completed products.
The mechanism of these changes is similar to the kinetic law of destruction of cotton material, as described by equations for the characteristics of the material to withstand the specified limit on the number of cycles. Since different processes and corresponding fiber states these different indicators, it makes sense to talk about the different degrees of loss of fiber strength of individual technological transitions.
At the same time, cause the destruction of the fiber tensile stress concentrators are dangerous in its cross section. These may be biological and mechanical damage, overt and covert, in the absence of such a smallest cross-sectional area of the fiber. Therefore, if we assume that
n=n(an, N ,T), (2)
where the number of lesions n the number of mechanical influences function an, fiber properties N and T - the drying temperature, and the value of a function of maturity (grade) fiber, its humidity, conditions and cotton storage time, the analytical dependence of the strength can be written as Pp(an,N,T) = Po -AP(n), (3)
Where Po - the original value of the strength of the fiber prior to its processing in cotton gin plant; its value depends on the time and conditions of storage of cotton in rebellion, as well as industrial and breeding varieties of raw, being at the start of processing constant;
AP(n) - drop in strength due to fiber damage, and changes in drying temperature and humidity according to the raw (2).
Expression (3) can be represented in a somewhat different form, highlighting the separate value AP2 - Decrease of the degree of strength, which depends directly from the drying process cotton, and other changes presented in the form of magnitude AP1 , as a function of the degree of mechanical action and material properties. Then (6.3) can be written as Pp(an,N,T) = P0 -APl(anN) - AP2(T). (4) Moreover, in the formulas (3) and (4) under the influence refers to the loss of fiber strength dependence on humidity, cotton varieties not included explicitly in the ratio considered.
Let us analyze the right-hand sides of these relations.
Value P0 it corresponds to the initial strength of the fiber at the beginning of processing of cotton ginneries. Raw cotton, formed by the party on the breeding and commercial grade, type of collection, as well as belonging to the farmer or collective farm, may have a different background:
- without going through the drying and cleaning immediately transferred for processing; Cotton is mostly manual collection, assembled in favorable conditions and having a low standard moisture;
- Require pre-treatment, and drying; is predominantly cotton collection machine increased contamination, which is just to let the technology can not be cotton plants;
- Raw cotton of manual or machine collection, that passed precleaning separators, which requires pre-drying and cleaning;
- Raw cotton previous groups, riots or stockpiled in storage for a considerable period of time (from one to several months).
In the first case, the value Pom practically equal to the natural characteristics of raw cotton in the field, from the dropdown box; the potential loss of cotton strength for manual collection and transportation of a sufficiently small quantities can be neglected.
In two other cases, you should take into account the loss of the length of the spindle when the cotton harvest, field clearing patchwork, in a tumble dryer and cleaners Dry-cleaning shop procurement centers. Obviously, in this case, the loss of strength will be high, they can not be neglected, which is usually made of raw intermediate properties analysis.
A more complicated case of the latter, when raw cotton is one of the three previous options taken by the procurement centers or having some strength (Ie less natural) laid on the long-term storage. As a result of the biological processes of seed of life, as well as the destructive effects on the fiber storage medium, this figure varies in a complicated law, similar to one described above for the values in the kinetic model.
Let the time of bookmarks cotton for storage in light of these circumstances, the fiber had a strength P0'. Through time txp fiber strength acquired value Po changing on a complex law, which is a product of two exponential functions - one increasing (fiber maturation), decreasing another (depending on the storage density, cotton varieties). In the first case, in addition to the exponential parameters P0' is a constant P^ and the relaxation period T1, Second respectively PJ h T2. Value P^ and P" respectively indicate the possible extent of the growth of strength as a result of maturation and reduce it from destruction. The first value is associated with the biology of the plant, the second depends on the density of the rebellion, the presence of microorganisms on the surface of the
fiber, etc. The time constants Tl and T2 mean exponential rate of change, and, as previously shown, numerically equal to the intercept of the tangent to the exponential function at the initial point of the straight line parallel to the time axis, and which tends to the exhibitor. The smaller time constant value, the process is completed faster. After a time equal to three T1 or T2, exponential process ends at more than 95 percent.
Such a model can be written as
P =
VP;-(^-VPT )(i ->P+(JPi-VP7 )(i -
txp
e T)
txp
e ^
(5)
where, in addition to the above parameters P', P', P", txp, T1 and T2 by e denotes the value of nepperova (e = 2,71828).
From (5) we have for t = 0
po(0)=a/p;-^=p ' (6)
ie in cotton processing without storage, naturally, its initial strength fiber strength is supplied raw, and the effect on short-term storage of virtually no fiber strength.
If the cotton is stored for a long time, that is, when tp of (5) we have
P0(m) —ylPm ' P , (7)
the geometric mean value of the function P', P".
Usually P^ more P0', a PJ less P0',, so P0(w). It is in the range between these limit values and perhaps only a partial increase in the strength of the fiber in storage, and then only in a limited period of time, if T1 much less T2, T1 << T2.
In general, for (as already mentioned earlier) the fact that cotton ripening in rebellion can not be overestimated - a long cotton storage inevitably leads to some reduction in strength, especially in the lower layers of rebellion that we studied experimentally and will be given a few below.
From (5) it is also clear that in the absence of one of these events - the prevailing role is played by the second - ripening or degradation of the fibers.
So in case of equality P0', and P', ie Stowing ripe cotton
under txp ^ <x value Po is ^P'P', those. fiber strength is inevitably reduced.
Conversely, if it were possible to eliminate degradation of the fiber at the same time its ripening, the P0(m) would equal ypP(0, and hardening it happened.
It was pointed out that the decrease in the fiber strength is closely related to his injury on technological transitions depends on the number and size of mechanical and fiber properties that are affected by drying temperature, time and conditions for cotton storage in a riot, and represents some kinetic
m
function of type, mostly non-linear extent —.
P
In the previous section of the paper when considering damage kinetics and tortuosity cotton compare these parameters was performed as a comparative diagrams for six measuring points - from riot (0) prior to compression (5) in different sections of the values of cotton varieties, time and storage density riot two dryer coolant temperature levels.
In such diagrams is possible to recreate the necessary dependence of these parameters on the degree of exposure to raw cotton, but rather speculative. There is no question of function, functional dependence is out of the question, as a continuous variable value is not plotted on the x-axis, and only the technological transition number.
To obtain the functional dependency is not desirable to have the serial number of the physical process, but a continuous value. This acts as the technological line of cotton plants, the mechanical effects of cotton in these processes, allowing you to go off the charts according to the curves - in this case, type Pp(an).
But these dependences are not sufficiently smooth, as provided in section 3 of the assessment of each technological transition on the degree of exposure approximate and varies depending on cotton varieties and, most importantly, apply in varying degrees to the entire population of the fibers.
So obviously, at a variable step position on the horizontal axis of the measuring points in some cases, possible local breaks depending, in particular a sharp length reduction (relative) in the individual drying conditions, especially low grades, as well as ginning, when the maximum load experienced by all, without exception, seeds separated from the fiber.
More will be smooth curve Pp, and AP, if the delay on the x-axis is not simply the sum of normalized mechanical influences and their dependency to the characteristics, different for each junction. However, to perform this transformation is not yet possible to sufficiently correct for variations of the values depending on the processing conditions. The reverse task of smoothing the curve Pp technically it is easy to
perform, but it is not entirely correct, because of the random nature of the sample average values.
In the latter case, both these functions would be of a direct
TH t
or (— = 1), a parabolic curve (— > 1). In this case represents
P P
one of the curves of the analyzed models of the kinetics of fiber fracture, although not completely coincide with those for damage and crimping.
Select from the AP to separate the value of the temperature change in strength, presenting (3) in the form (4). To do this, there are two reasons: the first is that the effect of temperature relatively short time and can lead to irreversible fiber properties, which are accounted using the kinetic parameter in future technology transition is difficult and does not reveal
the essence of the process. And second, the change will allow to reveal the essence of the problem is not on the mechanical and physical level, and to a large extent solve the problem give the inner meaning, and not only the kinetic and statistical.
Here are just a general model of the phenomenon, based on the equations S.N.Zhurkova. Equation binds time (durability) to fracture fibers voltage, attached thereto, provided its complete destruction
kT
(8)
where to - constant, close to the period of the thermal vibrations of the atoms (10-12-10-13 c); Uo - the activation energy of a mechanical break ties; Y - coefficient depending on the fiber structure and takes into account the heterogeneity of the distribution of stresses on the fiber and microregions molecular chains; K - Boltzmann constant.
This equation is valid for a wide range ofvoltage variations and temperature T, K.E.Perepelkin applied to the study of tensile strength fiber strands in accordance with GOST 3274.1-72 standard dynamometer using LH-3M, replacing Y on Y1 - structurally sensitive factor, characterized by, on the grounds that the gap fiber does not occur simultaneously.
Logarithm (8) based on this model allows you to define the breaking stress:
* Uo kT t a = —--In—.
Yi Yi To
And fibers voltage condition is equality unit Bailey criterion
(10)
Jo r[a(r)]
where o from t - Voltage dependence on time. This dependence has been identified by us in the study of the process of breaking pendulum dynamometer fiber scheme is simple. Its essence is that the ends of the fibers are wound onto eyelets radius load torque arm, rejected at break at an angle a . Here m - pendulum mass, R - distance from the center of rotation to the center of gravity, and - the acceleration of gravity.
From the equation of equilibrium of the pendulum
P ■ r = mgR sin^, (11)
at a small angle a , when a = sin a, we have
Pr
a = -
(9)
Rmg
(12)
As for the time t clip falls at a distance i and the pendulum is deflected by an angle a ,the value of the fiber deformation amount
i = ur = m, (13)
where - clamp lowering speed. From the last two formulas have the value of fiber tension
p _ uRmg
(14)
At a time when the fiber is stretched by uniaxial tension, between the stress and effort of the link is the cross sectional area of the fibers, ie,
P = aS. (15)
After the reforms, taking into account these relations have a record function of voltage, which can be reduced, denoting complex value, and includes
uRmg
и
r 2S
■ CT.
(16)
After simple transformations we can obtain the dependence in a slightly different form
т[а(т)] = т0exp(U ~!cr) = T0 exp(A + Вт), (17) kT
где A = , В = . kT kT
Substituting from (17) into (10), we obtain the criterion Bailey equation for the unknown quantity that is being allowed a relatively unknown, takes the form
T =-! £n(-BroeA +1). Bo
(18)
Substituting the last equation in the stress function, we have the expression
' in(1 - BreA)
* U kT a = —--In
Yi Yi
Bt„
(19)
clearly showing that the temperature increases fiber strength decreases linearly.
Formula (19) it is easy to rewrite the value of the breaking load, directly under study:
in(1 - BroeA)"
= US - m tn
Yi Yi Let us analyze the formu
Bt0
a (20). Firstly, it makes
(20)
sense
that, since negative numbers do not have the logarithm (with a positive basis - 2.71828). We expand the logarithm of the specified power series convergent with the rapidly decreasing terms, allowing limited only to two senior members of the decomposition
A2
(21)
^ д , (BroeA )2
ln( 1 - BreA ) = -(BreA +-
).
Substituting this formula in (20), we have a simple expression
US kTS"
P =
A + ln( 1 + ) 2
(22)
Yi Yi
Repeatedly expanding the logarithm of expression (22) in a row, containing the first two terms of the expansion
Mi + ^Br^eA ) = BTieA + ( ^ )2i. 2 2 2 2
(23)
and substituting (23) into (22), we finally have an analytic function
function.
Pp =
US SkT
Yi Yi
A + B^eA + BZ! 2 8
(24)
Recall that the accepted shorthand and includes in both cases indicated temperature and, if you deploy (24) based on these values; we obtain a structurally bulky, but an explicit function. We will not give it in full, and give in short form, convenient for analysis:
aL a 03
Pp = a0eT (1 + TeT ), (25)
where a0 ,a1,a2,a3 - constant coefficients.
The obtained ratios indicate complex influence of temperature on the strength of the fiber, and its growth is reduction in strength with increasing temperature. It is in these moments, when the fiber is warming up the coolant, its strength is low. And when the individual fibers are applied tensile load, or contacts, the latter may be destroyed, to receive mechanical damage and largely losing valuable quality - crimp.
This phenomenon as mentioned above, takes into account the kinetic model of changes in fiber properties, also it is revealed the essence of the process, its physics. One does not contradict the other.
Note that the direct influence of temperature on the subsequent behavior of the fiber has almost no, really, high temperatures can lead to irreversible changes in the outer layer of paraffin, to some extent, cotton cellulose. The main thing is that
the fibers are damaged when heated in the drying drum at a subsequent mechanical effects continue to develop and indirectly affects the temperature to reduce the strength of the remaining technological transitions cotton plants - spinning, weaving, etc.
Conclusions
1. Reduction of fiber strength is closely related to his injury on technological transitions depends on the number and size of mechanical and fiber properties that are affected by drying temperature, time and conditions of storage of cotton in a riot, and is a certain kinetic feature.
2. It has been experimentally proved that the fact that cotton ripening in rebellion can not be overestimated - a long cotton storage inevitably leads to some reduction in strength, especially in the lower layers of rebellion.
3. A kinetic model of changes in fiber properties also it is revealed the essence of the process, its physics.
4. These relations indicate complex influence of temperature on the strength of the fiber, and its growth is reduction in strength with increasing temperature. It is in these moments, when the fiber is warming up the coolant, its strength is low. And when the individual fibers are applied tensile load, or contacts, the latter may be destroyed, to receive mechanical damage and largely losing valuable quality-crimp.
References:
1. Hadzhinova M. A. Investigation of the Properties and cotton fiber structure during drying. - Tashkent: Fan 1966.
2. O'zDst 633-95. Cotton. Methods of determining the length.
3. Muratov A., Gesos K. F., Sharapova R. Z. Comparative electron microscopic study of the supramolecular structure of some cotton fibers varieties // Cytology and Genetics. 1983. - No. 5. - P. 18-23.
