RU2192629C2 - Device for evaluating flow characteristics of polymeric materials - Google Patents

Abstract

FIELD: analyzing polymeric material flow characteristics. SUBSTANCE: device used for analyzing tensile polymeric-material flow in the course of recovery such as single-axis extension of jet to produce fibers or film by extrusion has housing with removable cover, support, draw plate made of porous penetrating material, lubricating duct, lubricating cavity, and sealing ring. EFFECT: enhanced precision of investigation results. 1 dwg

Description

 The invention relates to techniques for testing polymeric materials, in particular highly viscous liquids, and can be used to analyze the flow of polymeric material under tension during processing, for example, with uniaxial stretching of a jet to produce fibers or film by extrusion.

 A device is known [Akutin M.S., Prokunin A.N., Proskurina N.G. and others. On the stretching of polymer melts with a constant strain rate // Mechanics of Polymers, 1977, 2, p. 353-356), including a grip for attaching the sample from one end, rigidly connected to a measuring force unit, and gears into the gap of which the sample is drawn by the other end. The principle of operation of the device is based on fixing the longitudinal force during tension of a cylindrical specimen made of a polymer material.

 The disadvantages of this device are: the difficulty of mounting a cylindrical sample in the grip; a narrow circle of test media, limited to those materials from which a cylindrical sample can be formed.

 The closest in technical essence to the proposed invention is an elastomer comprising a chamber with a hole through which the test material is pressed through at a constant speed, and a sensor created in the pressure chamber [A. Perevertov et al. // Plastics, 1969, 1, from. 69] (prototype). The elastomer allows you to determine the length of time the material is in a viscous-fluid state at a given temperature and flow resistance.

 The disadvantage of this device is that it does not provide complete slippage of the material at the boundary, and therefore, a uniform tensile velocity along the channel, which affects the accuracy of the results of studies of the tensile flow of polymer materials.

 The problem to which the invention is directed is to increase the accuracy of the results of studies of the tensile flow of polymeric materials.

где х - координата, направленная вдоль оси фильеры;
l - длина фильеры;

R₀, R₁ - начальный и конечный радиусы внутреннего канала.The problem is solved due to the fact that in the device for determining the rheological properties of polymeric materials, comprising a housing with a removable cover, a support and a die installed therein, the die is made of porous penetrating material and has a special profile defined by the formula

where x is the coordinate directed along the axis of the die;
l is the length of the die;

R ₀ , R ₁ - the initial and final radii of the internal channel.

 This device allows you to study the rheological behavior of polymeric materials under uniaxial tension, to determine the rheological constants of the tensile flow by forcing the material under study through a special profile die.

Течение рассмотрим в цилиндрической системе координат х, r, φ. Считаем, что на границе обеспечивается полное проскальзывание материала. В этом случае для решения задачи можно применить гипотезу плоских сечений, т.е.Consider the motion of an incompressible medium in a die whose profile is given by the formula

We consider the flow in a cylindrical coordinate system x, r, φ. We believe that complete slippage of the material is ensured at the boundary. In this case, to solve the problem, we can apply the hypothesis of flat sections, i.e.

где V_x - скорость в сечении х. Из условия постоянства расхода материала через любое сечение получаем соотношение
V_x•π•R²(x) = V₀•π•R $\genfrac{}{}{0ex}{}{\text{2}}{\text{0}}$ , (2)
где V₀ - скорость течения материала на входе в фильеру.

where V _x is the velocity in section x. From the condition of constant consumption of material through any section, we obtain the ratio
V _x • π • R ² (x) = V ₀ • π • R $\genfrac{}{}{0ex}{}{\text{2}}{\text{0}}$ , (2)
where V ₀ is the velocity of the material at the entrance to the die.

Радиальную компоненту скорости течения V_r находим из условия несжимаемости [Ильюшин А.А. Механика сплошной среды. - М.: изд-во МГУ, 1971, 245 с.] .In view of (1), from relation (2) we obtain the velocity component V _x

The radial component of the flow velocity V _{r is} found from the incompressibility condition [Ilyushin A.A. Continuum mechanics. - M .: publishing house of Moscow State University, 1971, 245 p.].

тогда

По соотношениям (3) и (4) определяются компоненты тензора скоростей деформации:

Из выражения (5) видно, что в таком течении отсутствуют девиаторные составляющие тензора скоростей, следовательно, полимерный материал в фильере испытывает одноосное растяжение вдоль оси со скоростью, зависящей от усилия продавливания и коэффициента экструзии, равного отношению радиусов входного и выходного сечений.

then

By relations (3) and (4), the components of the strain rate tensor are determined:

It can be seen from expression (5) that in this flow there are no deviator components of the velocity tensor, therefore, the polymer material in the die experiences uniaxial tension along the axis with a speed depending on the forcing force and extrusion coefficient equal to the ratio of the radii of the input and output sections.

 The simple form of the strain rate tensor (5) is due to the choice of a special die profile and the condition for slipping on the boundary. The latter is ensured by penetration of the lubricant supplied under pressure through the porous walls of the die. The porosity of the material is determined by the formula [Belov S. Century. Porous metals in mechanical engineering. - M.: Mechanical Engineering, 1987, p. 12].

P = V _P / V _T ,
where V _P - the volume of voids of the porous body; V _T - full body volume.

 Experiments on the use of liquid lubricants in the extrusion of thermoplastics with forming channels of various porosities showed that a stable extrusion process with a lubricating film takes place in the range of porosities P = 0.18-0.3. With an increase in porosity P> 0.3, the destruction of the extrudate is observed due to the increased supply of lubricant to the channel. The decrease in porosity P <0.18 due to the increased hydraulic resistance of the microchannels of the porous material is accompanied by a two to three-fold increase in the pressure of the supplied lubricant.

 The drawing schematically shows a device for determining the rheological properties of polymeric materials.

 A device for determining the rheological properties of polymeric materials comprises a housing 1 with a removable cover 2, a support 3, a die of penetrating porous material 4, a lubricating channel 5, a lubricating cavity 6, sealing rings 7 and 8.

 The proposed device operates as follows. The housing 1 is filled with the studied polymer material, the cover 2 is mounted, which connects the housing with a movable reverse plate. Lubricant under pressure is supplied through the lubricating channel 5 to the lubricating cavity 6, penetrates through the pores of the die into the internal channel and creates a separation lubricant film between the die and the polymer material to be studied over the entire surface of the channel. At the same time, the first extrusion speed is turned on, the force of forcing the material through the die with a channel of a special shape is recorded. Then the magnitude of the speed changes and the dependence of the pressure on the extrusion speed is determined, which allows to determine the rheological properties of the material.

 This device allows you to investigate the rheological properties of polymeric materials as a result of measuring the force of punching through the die with a certain speed with complete slippage at the border; determine rheological parameters for various types of media (Newtonian fluid, power-law fluid, non-linearly viscous fluid, a medium with linear viscoelasticity); ensure complete slippage of the material at the boundary to study the tensile flow of polymeric materials; conduct rheological studies on small volumes of material.

Claims (1)

A device for determining the rheological properties of polymeric materials, comprising a housing with a removable cover, a support and a die installed in it, characterized in that the die is made of porous penetrating material and has a special profile defined by the formula

where x is the coordinate directed along the axis of the die;
l is the length of the die;

R ₀ , R ₁ - the initial and final radii of the internal channel.