WO2017064078A1

WO2017064078A1 - Tool for a cone-plate type rheometer and manufacturing process of such a tool

Info

Publication number: WO2017064078A1
Application number: PCT/EP2016/074373
Authority: WO
Inventors: Etienne GHIRINGHELLI; Jérémy PATARIN
Original assignee: Rheonova
Priority date: 2015-10-12
Filing date: 2016-10-11
Publication date: 2017-04-20

Abstract

Rheometer tool (10) having a conical surface (102), wherein said surface (102) comprises a plurality of protrusions (103) evenly distributed over the surface, wherein each protrusion (103) has a pyramidal shape and adjacent pyramidal protrusions (103) have one side of their respective base in common. The application also relates to a cone-plate type rheometer comprising such a tool and a process for manufacturing such a tool.

Description

TOOL FOR A CONE-PLATE TYPE RHEOMETER AND MANUFACTURING PROCESS OF SUCH A TOOL

FIELD OF THE INVENTION

The invention relates to a tool for a cone-plate type rheometer and a manufacturing process of such a tool.

BACKGROUND OF THE INVENTION

Measurement of rheological properties of a material can be made by introducing a sample of the material between two tools of a rheometer, each tool having a surface with a specific geometry, applying a controlled strain to the sample at one of the surfaces and measuring the torque response of the sample at the other surface and vice versa. Another common method is to apply a torque on one surface of the measuring geometry and measure the resulting strain.

To ensure the accuracy of the measured property, care is to be taken to avoid any slipping of the sample relative to the surfaces of the rheometer tools.

However, some materials, in particular gels or diphasic fluids, form depletion layers at the interface with the rheometer tool surface and thus deteriorate the accuracy of the measurement.

In order to address this problem, it is known to use rough surfaces (such as emery cloth or sandblasted material) rather than smooth ones.

However, this may not be sufficient to prevent slipping.

To that end, protrusions can be specifically provided on the surfaces in contact with the sample.

Document US 5,610,325 describes a parallel-plate rheometer comprising two parallel disc-shaped tools provided with various types of protrusions, having either a triangular, square or rounded cross-section.

Document US 7,249,523 describes a parallel-plate rheometer comprising two parallel disc-shaped tools provided with protrusions. These protrusions, which penetrate into the sample, are intended to immobilize the sample in regions located between the protrusions. However, in such case, the protrusions are in the form of a right square post, which could generate fracture of the sample and thus tearing of the material.

Document US 5,597,958 discloses a cone-plate rheometer comprising a plate and a conical tool provided with radial serrations.

Document US 7,475,592 discloses a parallel-plate or cone-plate rheometer comprising a plate and a conical tool provided with radial grooves. Each groove is intended to define a chamber for holding the sample. However, none of these configurations shows totally satisfactory for measuring the Theological properties of biological fluids. In particular, biological fluids are typically charged with particles and have a non-Newtonian behavior. BRIEF DESCRIPTION OF THE INVENTION

A goal of the invention is to provide a tool for a cone-plate type rheometer that allows more efficiently prevent slipping of a fluid sample without damaging it. In particular, said tool should avoid or at least minimize secondary flow of the sample during the test.

Accordingly, the invention provides a rheometer tool having a conical surface, characterized in that said surface comprises a plurality of protrusions evenly distributed over the surface, wherein each protrusion has a pyramidal shape and adjacent pyramidal protrusions have one side of their respective base in common.

By "evenly distributed" is meant in the present text that the distance between the bases of adjacent protrusions is null and that the protrusions have substantially the same height and substantially the same angle between their faces and their base.

According to an embodiment, the surface of the tool is frustoconical.

According to a preferred embodiment, each protrusion has four faces extending from the conical surface.

According to an embodiment, the projection of the base of each pyramidal protrusion in a plane perpendicular to the revolution axis of the conical surface is a square.

According to an embodiment, the pyramidal protrusions have a height ranging from 0.05 mm to 3 cm.

According to an embodiment, adjacent pyramidal protrusions have one side of their respective base in common.

According to an embodiment, the angle between faces of adjacent pyramidal protrusions is comprised between 10 and 170°, for example 90°.

Advantageously, the tool may comprise a temperature regulation device configured to set the temperature of the conical surface to a temperature between -130 and +1100°C.

Another object of the invention is a cone-plate type rheometer comprising a rheometer tool as described above and a plate opposite to said rheometer tool, at least one of the rheometer tool and the plate being coupled to a rotor, the rheometer tool and the plate defining together a chamber for a fluid sample.

According to an embodiment, the surface of the plate facing the tool comprises a plurality of protrusions evenly distributed over the surface, wherein each protrusion has a pyramidal shape.

A further object of the invention is a method for measuring at least one Theological property of a fluid sample, characterized in that it comprises: - providing a cone-plate type rheometer as described above,

- introducing the sample in the chamber of said rheometer, such that the pyramidal protrusions penetrate into the sample,

- applying a rotational movement of the rheometer tool relative to the plate,

- measuring the response of the sample.

By "rheological property" is meant in the present text at least one of the following properties:

- Viscosity (depending on shear rate),

- Elastic modulus G' and viscous modulus G" in the linear regime (depending on the frequency),

- Elastic modulus and viscous modulus in the non-linear regime (depending on strain rate), value of strain at the end of linear regime, and moduli crossover parameters (strain rate and value of the moduli),

- Yield stress,

- Stress relaxation related parameters (relaxation modulus),

- Creep related parameters (compliance),

- Large Amplitude Oscillatory Strain (LAOS) related parameters (first Chebyshev modulus, second Chebyshev modulus, Stiffening ratio, Thickening ratio).

According to an embodiment, the fluid sample comprises a non-Newtonian fluid and/or a diphasic fluid.

In particular, the sample may comprise particles in suspension in a fluid and the height of the pyramidal protrusions is preferably at least ten times the size of the biggest particles.

A further object of the invention is a process for manufacturing a rheometer tool as described above. Said method comprises:

- providing a conical part intended to form the rheometer tool;

- milling the plurality of protrusions in the external surface of said part with a bur, the bur describing a hyperbolic path on said external surface.

Along said path the bur is preferably inclined with respect to the external surface of the conical part such that the pyramidal protrusions are normal to said surface.

Said milling process is advantageously carried out by a turning machine having at least five axes.

BRIEF DESCRIPTION OF THE DRAWINGS

Other features, embodiments and advantages of the invention will be apparent from the description that follows, based on the appended drawings wherein:

FIG. 1 is a schematic view of a cone-plate rheometer;

FIG. 2A is a sectional view of a rheometer tool according to the invention; FIG. 2B is a perspective view of the rheometer tool of FIG. 2A;

FIG. 3 is a schematic view showing paths of a bur for making the pyramidal protrusions on the rheometer tool;

FIG. 4 is a schematic drawing of the conical tool showing the trajectories of the bur;

FIG. 5 shows experimental results showing the shear stress as a function of the shear rate for different surface conditions of the cone-shaped tool.

It is to be noted that, in order to improve legibility of the drawings, the figures may be not to scale.

DETAILED DESCRIPTION OF EMBODIMENTS OF THE INVENTION

The invention applies to the measurement of rheological properties of any kind of fluid, including concentrated suspensions, polymers, soft gels, biological fluids, etc. In particular, the invention efficiently addresses the measurement of rheological properties of the fluids that have a strong sliding behavior.

FIG. 1 is a schematic cross sectional view of a cone-plate rheometer 1.

The rheometer comprises a cone-shaped tool 10 and a disc-shaped tool 20. The revolution axis of the tool 10 is perpendicular to the main surface of the tool 20.

The angle a' of the conical surface 102 of the cone-shaped tool relative to the normal to the revolution axis X of the conical surface is advantageously comprised between 0.2 and 4°, preferably between 0.5 and 4°.

In a preferred embodiment, the tool 10 is frustoconical. In other words, the conical surface 102 is truncated and the tool has a flat tip surface 101. The cone-shaped tool 10 is positioned relative to the disc-shaped tool 20 such that the virtual pointed tip 100 of the cone extends within the plane corresponding to the surface 200 of the tool 20.

The distance h_tr between the truncated tip 101 of the cone-shaped tool 10 and the disc-shaped tool 20 is typically comprised between 15 pm and 1 mm.

The radius R of the tools 10, 20 depend on the viscosity of the sample to be tested. The greater the viscosity, the smaller the radius of the tools. For example, the radius R is comprised between 5 and 150 mm.

Tools 10 and 20 may be made of a metal (e.g. stainless steel, Hastelloy™, titanium, etc.), a polymer and/or a ceramic.

According to an advantageous embodiment, the cone-shaped tool comprises a temperature regulation device (not shown) configured to set the temperature of the conical surface 102 to a temperature between -130 and +1100°C. To that end, a temperature sensor and Peltier elements may be arranged around the revolution axis of the tool 10. In use, a sample S for which rheological properties are to be measured is inserted between tools 10 and 20, the surfaces 102, 101 and 200 defining together a chamber for the sample.

At least one of the tools 10, 20 is coupled to a rotor (not shown).

According to an embodiment, the cone-shaped tool 10 is then caused to rotate at a given angular speed ω, the rotation axis X of the tool being the symmetry axis of the cone, whereas the disc-shaped tool 20 is fixed. The rotation of the cone-shaped tool 10 causes the application of a controlled strain to the sample, and the stress induced in the sample is measured on the disc-shaped tool 20.

However, this embodiment is not limitative and other configurations could be used without departing from the scope of the present invention. For example, the cone-shaped tool could be fixed whereas the disc-shape tool could be rotatable, and/or the strain could be applied at the disc-shaped tool whereas the stress could be measured at the cone- shaped tool.

As better seen on FIGS. 2A and 2B, the surface 102 of tool 10 is not smooth but comprises a plurality of protrusions 103 evenly distributed over said surface, each protrusion having a pyramidal shape.

Adjacent pyramidal protrusions 103 have one side of their respective base in common.

Although FIGS. 2A and 2B illustrate a preferred embodiment wherein each protrusion has a pyramidal shape with four faces extending from the conical surface 102, it is to be noted that the protrusions could also have only three faces or five faces or even a greater number of faces.

One can then define an internal conical surface that contains the sides of the base of the pyramids, and an external conical surface that contains the apices of the pyramids. Said internal and external conical surfaces have the same axis of revolution and the same angle; otherwise said, the generatrices of the internal and external conical surfaces are parallel to each other, the height of the protrusions being defined as the distance between said generatrices.

These protrusions have an effect of creating indentation into the sample and immobilizing the fluid with respect to the cone-shaped surface. In addition, when the fluid contains particles, the protrusions have an effect of trapping said particles and immobilizing them with respect to the cone-shaped surface.

In addition, the conical shape of the tool 10 provides a more regular shear stress. Thus, the cone-plane geometry of the rheometer according to the invention has a greater accuracy as compared to parallel-plate rheometers.

Although not illustrated, the surface 200 of the disc-shaped tool 20 may also be provided with protrusions similar to the ones of the cone-shaped tool 10. Thus, when one of tools 10, 20 provided with such protrusions is caused to rotate, the fluid is also caused to rotate at the same rotational speed, without slipping onto the respective tool.

Advantageously, the projection of the base of each pyramidal protrusion in a plane perpendicular to the revolution axis of the conical surface 102 is a square.

The height of the pyramidal protrusions depends on the sample to be measured. In general, said height ranges from 0.05 mm to 3 cm. The size of the pyramidal protrusions is limited to avoid creating secondary flows within the sample. In general, a height of 0.5 mm is sufficient for most of samples. However, if the sample comprises particles in suspension in a fluid, the height of the pyramidal protrusions is preferably at least ten times the size of the biggest particles.

In addition, the angle γ (see FIG. 2A) between faces of adjacent pyramidal protrusions 103 may be of 90°, more generally between 10 and 170°.

Such a cone-shaped tool 10 is made by milling a conical part initially having a substantially smooth external surface using a bur. By "substantially smooth" is meant that the surface of conical part may present a certain roughness, depending on its manufacturing process. The surface of said conical part corresponds to the above- mentioned external conical surface.

FIG. 3 schematically illustrates the paths P of the bur on the conical part to create the protrusions shown in FIGS. 2A and 2B. FIG. 3 is directed to the creation of pyramidal protrusions with four faces but the skilled person would be able to determine suitable paths for a different number of faces.

Preferably, the bur has a cylindrical cross section with a conical tip such that in use, opposite parts of the bur generate in the conical part the sides of two adjacent protrusions. The tip of the bur defines the above-mentioned internal conical surface.

The paths P are typically arranged in a grid pattern onto the conical surface.

The angle of the bur with respect to the external surface of the conical part varies depending on the position of the bur relative to the conical part. In any case, the bur is oriented in a direction perpendicular to the surface of the conical part in the region that is being milled.

Such a process can be carried out by a turning machine having at least five axes. The equations describing the path of the bur can be defined as follows, referring to FIG. 4.

Ci is the internal conical surface, which corresponds to the base of the pyramidal protrusions formed by the bur.

Cext is the external conical surface, which corresponds to the surface of the tool before creating the protrusions. The axis of revolution of the conical surfaces Ci and Cext is z. Axes x and y are arranged so as to define with axis z an orthonormai coordinate system. The origin O of this system is the apex of the internal conical surface Ci. The apex of the external conical surface is denoted Ο'. a is the angle between the generatrix of the internal conical surface Ci (or of the external conical surface Cext) and axis z.

(Pn) is the set of trajectories of the bur tip along the internal conical surface (Ci) according to axis y. P1 is one of such trajectories. Λ^ is the normal to the surface in point M_p located on trajectory P1.

(Qm) is the set of trajectories of the bur tip along the internal conical surface (Cext) according to axis x. Q2 is one of such trajectories.

h is the height of the protrusions, corresponding to the distance between the internal and external conical surfaces.

Each point M_p* of a trajectory belonging to (Pn) is defined by the following coordinates in the (x, y, z)

Each point Nq_m of a trajectory belonging to (Qm) is defined by the following coordinates in the (x, y, z) coordinate system:

The angles Θ and β of the bur axis relative to x and y axes respectively in each point

M_p are defined by:

Θ =

The angles Θ and β of the bur axis relative to x and y axes respectively in each point are defined by:

2hmx sin a \

Θ = arccot (

V— ² + Vx² + 4h²m²sin²a. ^cot²a. (x² + 4h²m²sin²a tan a)

+ cot . (2x² + 4h²m²sin²a) wherein csca = 1/sina

The above equations define hyperbolic paths of the bur along the conical surface.

FIG. 5 shows experimental results showing the shear stress as a function of the shear rate for different surface conditions of the cone-shaped tool:

- the lozenge marks correspond to a tool with pyramical protrusions with four faces in accordance with the invention, wherein the angle a' of the conical surface was 2°, the height of the protrusions was 0.5 mm, with adjacent protrusions having one side of their respective base in common, and the radius R of the tool was 50 mm ;

- the light square marks correspond to a tool covered with a rough paper, wherein the dimensions of the tool (angle α', radius R) were the same as for the tool with pyramidal protrusions and the roughness of the paper was 0.5 mm RMS;

- the round marks correspond to a sandblasted conical tool, wherein the dimensions of the tool (angle α', radius R) were the same as for the tool with pyramidal protrusions;

- the triangular marks correspond to a tool with a smooth conical surface, wherein the dimensions of the tool (angle α', radius R) were the same as for the tool with pyramidal protrusions;

- the dark square marks correspond to a vane geometry. Vane geometry is a concentric cylinder rheometric tool composed of several blades (generally four) fixed on an axis. It is the standard way of measuring yield stress due to its elimination of serious wall-slip effects. For further details on such a tool, reference may be made to the review by Howard Anthony Barnes and Quoc Dzuy Nguyen, "Rotating vane rheometry— a review", J. Non-Newtonian Fluid Mech. 98 (2001) 1-14.

For the four first tools, the corresponding disc-shaped tool had a smooth surface. For each type of tool, the fluid sample was Carbopol® 2984 which is an acrylic acid homopolymer, with a concentration of 0.8 % by weight, and having a visco-plastic behavior with a flow threshold of 62.7 Pa.

FIG. 5 clearly shows that the surface condition that provides the measured shear stress closest to the shear stress measured using the vane geometry (which is considered to be the most accurate value of the shear stress since this geometry avoids wall-slip) is the conical surface having pyramidal protrusions in accordance with the invention. This effect is especially significant at low shear rates, where the wall-slip effects affect more strongly the measured shear stress. REFERENCES

US 5,610,325

US 7,249,523

US 5,597,958

US 7,475,592

Howard Anthony Barnes, Quoc Dzuy Nguyen, Rotating vane rheometry -Newtonian Fluid Mech. 98 (2001 ) 1-14

Claims

1. Rheometer tool (10) having a conical surface (102), characterized in that said surface (102) comprises a plurality of protrusions (103) evenly distributed over the surface, wherein each protrusion (103) has a pyramidal shape and adjacent pyramidal protrusions (103) have one side of their respective base in common.

2. Rheometer tool according to claim 1 , characterized in that the surface (102) is frustoconical.

3. Rheometer tool according to one of claims 1 to 2, characterized in that each protrusion (103) has four faces extending from the conical surface ( 02).

4. Rheometer tool according to claim 3, wherein the projection of the base of each pyramidal protrusion in a plane perpendicular to the revolution axis of the conical surface (102) is a square.

5. Rheometer tool according to one of claims 1 to 4, characterized in that the pyramidal protrusions (103) have a height (h) ranging from 0.05 mm to 3 cm.

6. Rheometer tool according to one of claims 1 to 6, characterized in that the angle (γ) between faces of adjacent pyramidal protrusions (103) ranges from 10 to 170°.

7. Rheometer tool according to one of claims 1 to 6 characterized in that it comprises a temperature regulation device configured to set the temperature of the conical surface to a temperature between -130 and +1100°C.

8. Cone-plate type rheometer (1) comprising a rheometer tool (10) according to one of claims 1 to 7 and a plate (20) opposite to said rheometer tool, at least one of the rheometer tool and the plate being coupled to a rotor, the rheometer tool and the plate defining together a chamber for a fluid sample (S).

9. Cone-plate type rheometer according to claim 8, wherein the surface (200) of the plate (20) facing the tool (10) comprises a plurality of protrusions evenly distributed over the surface, wherein each protrusion has a pyramidal shape with four faces.

10. Method for measuring at least one rheological property of a fluid sample, characterized in that it comprises: - providing a cone-plate type rheometer (1) according to claim 8 or claim 9,

- introducing the sample (S) in the chamber of said rheometer, such that the pyramidal protrusions penetrate into the sample,

- applying a rotational movement of the rheometer tool (10) relative to the plate (20), - measuring the response of the sample.

11. Method according to claim 10, characterized in that the fluid sample comprises a non-Newtonian fluid and/or a diphasic fluid.

12. Method according to one of claim 10 or claim 11 , wherein the sample comprises particles in suspension in a fluid and the height of the pyramidal protrusions is at least ten times the size of the biggest particles.

13. Process for manufacturing a rheometer tool (10) according to one of claims 1 to 7, characterized in that it comprises:

- providing a conical part intended to form the rheometer tool (10);

- milling the plurality of protrusions (103) in the external surface (102) of said part with a bur (2), the bur describing a hyperbolic path on said external surface (102).

14. Process according to claim 13, characterized in that along said path the bur (2) is inclined with respect to the external surface (102) of the conical part such that the pyramidal protrusions (103) are normal to said surface.