Rheometer

Abstract

A rheometer for determining and/or monitoring the flow behavior of viscous fluids, in particular plastic melts and plastic solutions, includes a housing, in which at least one substantially rectilinear channel is formed between an inlet opening and an outlet opening, the channel having a rectangular cross section, and a plurality of pressure measuring devices which are arranged along the channel, wherein the channel is provided over its length with a cyclically narrowing and widening cross section.

Claims

1. A rheometer for determining and/or monitoring the flow behavior of viscous fluids, in particular plastic melts and plastic solutions, having a housing in which at least one substantially rectilinear channel is formed between an inlet opening and an outlet opening, wherein the channel has a rectangular cross section, and having multiple pressure measurement devices which are arranged along the channel, wherein the channel is provided over its length with a cyclically narrowing and widening cross section, wherein two channels which are parallel to one another and which are separated from one another by means of at least one web are formed, wherein the web forms, together with a housing wall, a gap, and wherein, in relation to a respective channel length, the narrowing and widening cross sections of parallel channels are different from one another.

2. The rheometer according to claim 1, wherein the web has a profiled top edge.

3. The rheometer according to claim 1, wherein the narrowing and widening cross section of the channel is formed by a profiled channel wall.

4. The rheometer according to claim 3, wherein the channel wall is, in cross section, of sinusoidal, trapezoidal or sawtooth-like form.

5. The rheometer according to claim 1, wherein the channel wall has multiple narrowing and widening cross sections over its length.

6. The rheometer according to claim 1, wherein the channel has a width B which satisfies the equation B5 H, where H is defined as the height of the channel.

7. The rheometer according to claim 1, wherein the channel has, over its length, between one and fifteen narrowing and widening cross sections.

8. The rheometer according to claim 1, wherein the web is formed so as to be detachable.

9. The rheometer according to claim 6, wherein B10 H.

10. The rheometer according to claim 7, wherein there are equal numbers of the narrowing and widening cross sections.

Description

BRIEF DESCRIPTION OF THE DRAWING

(1) The invention will be described below on the basis of exemplary embodiments in conjunction with the drawing. In the figures:

(2) FIG. 1 shows a perspective partial view of a first exemplary embodiment of the rheometer according to the invention,

(3) FIG. 2 shows a sectional view of the rheometer shown in FIG. 1,

(4) FIG. 3 shows a perspective illustration which is analogous to FIG. 1,

(5) FIGS. 4a to 4c show simplified cross-sectional shapes of the web according to the invention,

(6) FIG. 5 shows a simplified plan of the illustration according to FIG. 1, and

(7) FIGS. 6 to 8 show examples of different profilings of the channel wall.

DETAILED DESCRIPTION OF THE INVENTION

(8) FIG. 1 shows an exemplary embodiment of a rheometer according to the invention in the open state. In this regard, FIG. 2 shows a sectional view for the purpose of explanation. The rheometer has a housing 1 in which two channels 4 which are parallel to one another are formed. These are separated from one another by a web 8 which may be formed so as to be detachable. The web 8 has a top edge 10 which forms a spacing to the inner wall of a cover plate 12. This gives rise to a gap 9 (see in particular FIG. 2 and FIGS. 4a to 4c).

(9) As FIG. 1 shows, the housing is provided with an inflow distributor 13, which distributes an inflowing fluid mass to inlet openings 2 of the two parallel channels 4. The fluid thus flows through the channels 4 and exits through outlet openings 3. For clarification, the arrangement is illustrated again in FIG. 5, FIG. 5 also shows an additional pump 14 which may be provided for conveying the fluid.

(10) In the region of the channels, pressure measurement devices 5 are provided, as illustrated in FIG. 5. Additionally, it is also possible for temperature measurement devices (not shown) to be provided.

(11) As can be seen in particular in FIGS. 1 to 3, the channels 4 each have different channel cross sections. For a constant width B of the channels, this thus leads to a variable height H of the respective channel or of the effective channel cross section resulting from the width B and the height H.

(12) The different profilings of the lower wall according to FIG. 1 of the channels 4 can be seen from the sectional view in FIG. 2. This also shows in a clarifying manner in particular the gap 9 which is formed between the top edge 10 and the cover plate 12. It is self-evident that the fluid mass flowing through has different pressures depending on the respective channel cross section, which pressures thus also lead a different flow transfer behavior through the gap 9.

(13) The profiling of the wall of the channel 4 thus forms minima and maxima, as shown in FIG. 3. In this regard, FIGS. 6 to 8 show different possible profilings. According to FIG. 6, the profiling is, as also illustrated in FIGS. 1 and 3, realized in a sinusoidal manner, while FIGS. 7 and 8 show a trapezoidal or sawtooth-like profile. It can be seen from this that, in relation to the flow direction, which is from the left according to the arrow in FIGS. 6 to 8, a relatively slow increase in the reduction of the channel cross section occurs, this being associated with a relatively slow pressure increase. Following the maximum, with the smallest channel cross section, a relatively rapid increase in cross section occurs according to FIGS. 7 and 8.

(14) In the exemplary embodiments shown, the entire length of the respective channel may be between 100 mm and 400 mm. The width B of the channel may be between 15 and 40 mm, while the smallest height, at a maximum of the structuring of the channel wall (FIG. 3), may be 0.6 to 2.0 mm. The maximum height, at a minimum profiling, may be between 3.0 and 8.0 mm, as also illustrated in FIG. 6. Depending on the geometries to be investigated or monitored and the respective properties of the fluid, alternate switching of between one and fifteen maxima and one and fifteen minima of the channel cross section over the entire length of the channel is possible according to the invention. It is preferable for these narrowing cross sections 6 and widening cross sections 7 (see FIG. 2) to be formed in each case so as to alternate in adjacent channels, with the result that a pressure maximum prevails in one channel, while, at the same run length, a pressure minimum is formed in the other channel.

(15) FIGS. 4a to 4c show different profilings of the top edge 10 of the web 8. While FIG. 4a forms a rectangular shape with a planar top edge 6 for the formation of the gap 9, the top edge 10 according to FIG. 4b is hyperbolically rounded. It is also possible for a wave-like structuring of the top edge to be provided over the width of the web. FIG. 4c shows a further variant in which an upper and a lower web are used, with the gap 9 being able to be situated in the central region of the web. As explained, it is also possible to shape the web 8 in a variable manner over its length, with the result that extensional flow processes can be generated via the web too.

(16) The rheometer may be used in different installation positions in order to carry out a practical simulation or monitoring of the processes of a plasticizing unit or of a screw.

(17) The rheometer according to the invention thus allows an experimental screw simulation, in particular for the experimental determination of the pressure-throughput behavior. Since no drag flow is generated in the wave rheometer according to the invention, it is possible to investigate the pressure flow behavior of the fluid in a manner decoupled from drag flows. This allows a simpler interpretation of the measurement data and of the associated physical processes. By way of suitable temperature control, it is also possible to provide the feeding of the fluid in an only partially plasticized state in order to experimentally record and analyze the melting behavior. Overall, the rheometer allows the extensional flow behavior of the fluids to be investigated. One particularly important aspect of the invention is to monitor an ongoing production process by means of the rheometer in order to be able to respond to changes in the properties of the fluid. It is self-evident that use may be made of the wave rheometer for the process monitoring of a wide variety of fluid types and fluid processing machines, that is to say also for processes without plasticization.

LIST OF REFERENCE SIGNS

(18) 1 Housing 2 Inlet opening 3 Outlet opening 4 Channel 5 Pressure/temperature measurement device 6 Narrowing cross section 7 Widening cross section 8 Web 9 Gap 10 Top edge 11 Channel wall 12 Cover plate 13 Inflow behavior 14 Pump