WO2007004895A1

WO2007004895A1 - Rheometer

Info

Publication number: WO2007004895A1
Application number: PCT/NO2006/000255
Authority: WO
Inventors: Carlos Salas Bringas; Willy K. Jeksrud
Original assignee: Universitetet For Miljø Og Biovitenskap; JEKSRUD, Reidun, Pedersen
Priority date: 2005-07-04
Filing date: 2006-07-03
Publication date: 2007-01-11
Also published as: NO323243B1; NO20053273D0

Abstract

The invention describes an apparatus and system for determining properties in compositions. More specifically, the invention describes a novel on-line rheometer and die tester for determining rheological characteristics of solid-liquid materials.

Description

RHEOMETER Introduction

The present invention relates to an apparatus and system for determining properties in compositions. More specifically, the invention describes an on-line rheometer and die tester for determining rheological characteristics of solid-liquid materials.

Background and prior art

Rheological testing equipment and methods are used for determining properties of compositions. These properties include viscosity. The viscosity is defined as the quotient of the shear stress and the shearing speed. In Newtonian fluids the viscosity is a function of pressure and temperature, while in non-Newtonian fluids the viscosity depends additionally on the shearing speed.

By determining the viscosity it is possible to quantify changes in flowing compositions with regard to time. By monitoring the changes over time, one can adjust the composition of the flowing media in order to achieve optimum flowing characteristics.

Determining rheological characteristics can be performed off-line or on-line. Offline measuring was typically used in early rheological testing, and conducted in a laboratory after taking samples from a flowing composition. In recent years, on-line rheological measuring has become an important feature in controlling and optimizing the characteristics of flowing material in a process.

There are different types of rheometers operating after different principles. The rheometer according to the present invention comprises a rotational rheometer having a cylindrical shearing gap. The rheometer is intended for an on-line operation involving flowing substances.

US-4077251 describes a rheometer belonging to the same category as the invention. More specifically it describes a rotary viscosimeter of a modified Couette-type for continuous measurements of the viscosity of non-Newtonian fluids. The fluid to be tested is shorn in an annular gap between concentric cylinders in circumferential direction. In order to bring about an axial flow through the annulus, the geometry of one of the cylinders is modified such that a small axial pressure gradient is formed. The modification consists of small grooves while the main part of the cylinder surface remains unchanged. The main focus is to be able to take samples of the flow without essentially affecting the main flow.

The present invention takes rheometers to a new level by providing an on-line rheometer with a die tester (ORDT). The rheometer is fitted with a headed shaft with helical flights assembled in a vertical position to measure the rheological characteristics and process parameters on-line.

The torque from the helical headed shaft is used to measure the mean shear stress and the rotational speed is used to measure the mean shear rate.

As said, the rheometer also comprises a changeable die making it possible to relate the rheological measurements with the die profile activity. A single die may contain more than one orifice.

A rheometer according to the present invention enables the ability to measure high viscous materials having particles like fibers. Use of a changeable die together with power consumption measurements, allows the comparison between the rheological values with processing parameters. The ORDT is provided with a feeder enabling it to capture solid-liquid materials from the process stream in an on-line configuration. Several benefits are achieved. Economical benefits of the incorporation of a new tool for quality control with potential to be used for a control process (automation).

Research institutions will receive the benefits of the incorporation of new industrial instrument where the scientific measurements values are closely related with the production values. There is a constant worldwide demand for better product quality regulations for monitoring processes. The present invention will meet this demand and bring the on-line rheometer measuring a step forward.

Summary of the invention The present invention describes an on-line rheometer and die tester. More specifically, the invention describes a rheometer for on-line measuring of properties of compositions, comprising a rotary shaft with helical flights housed in a barrel with an upper and lower end, where the shaft runs from the bottom of the barrel and up through the top of the barrel wherein the shaft is suspended in a bearing, and where the upper part of the shaft is connected to a motor, and where the rheometer further comprises a die with an orifice in the lower end of the barrel, and an inlet feeder pipe in the upper end of the barrel, allowing to relate rheological measurement with flow characteristics of the composition entering the feeder pipe and exiting through the die. The invention also comprises a system for on-line measuring of properties of compositions by using a rheometer described above, and further comprising means for controlling speed of the motor, measuring speed of the motor, measuring torque exerted on the motor, measuring temperature and pressure, collecting the measured values, data processing, and presenting the properties of the compositions to a user.

The invention is further defined in the enclosed dependent set of claims.

Detailed description of the invention

To help understand the present invention, a detailed description is given with reference to the drawing where:

Figure 1 shows the principle of how the inventive ORDT works, and

Figures 2a to 2c shows the different parts comprised in a preferred embodiment of an apparatus according to the invention.

Figure 1 shows the principle of how the inventive ORDT works. The main elements of the ORDT comprises a barrel 10 in a vertical position with an upper and lower end, housing a vertical shaft 11 connected to a motor 1 with variable speed in the upper end, and with a head including helical flights at the lower end. The motor can be hydraulic, DC, AC with or without gear. In the lower end of the barrel 10, a changeable die 9 is attached.

The vertical shaft 11 rotates relative frictionless due to a bearing 2 located in the upper part of the barrel 10. The function of the rheometer will now be described. Material to be investigated is fed into a feeder pipe 12 allowing the material to flow into the barrel 10 and causing the shaft 11 to rotate due to the torque exerted on the headed shaft 11. A temperature sensor 13 is connected to the feeder pipe 12.

The motor 1 is connected to means for measuring the speed 15 (related to mean shear rate) of the shaft 11, and the torque 16 (related to the mean shear stress). It is further connected to a speed controller 14, and means for measuring temperature (18, 19) and pressure (20). The measured values are collected in a datataker 21, and sent to a signal processor 22 for instance located in a PC 23.

A gradual deceleration of the headed shaft 11 gives a relation between shear stress and shear rate over different degrees of shear, and therefore gives the characteristics of the material in study, e.g. viscosity and which type of fluid (Newtonian or non- Newtonian).

Measurements of the viscoelastic properties of solid-liquid material are possible in two different ways using the same procedure in the ORDT, i.e. stopping the helical headed shaft 11 from a high speed and either observing the residual torque (related to the mean shear stress), or observing the residual pressure (P2) before the die 9. It is possible to determine the melting point of the material by varying the temperature through external heat exchanger 3 and 6, while keeping an equal pressure until the material starts to flow through the die.

In order to characterize the steady state of the material, temperature measurements Tl and T2 are performed for the incoming and outcoming material.

The function of the changeable die 9 is to be able to study how different die profiles influence the material flow, and the influence of the rheological values on power consumption together with the flow characteristics (Newtonian or non-Newtonian). A single die can have different orifices and/or one or more venturies for comparing different flow characteristics.

The function of the ORDT is based on a mechanical principle by performing a constant measurement of power consumption of the motor 1 for comparing different raw materials according to the energy costs for processing (mechanical energy).

As mentioned, the ORDT has a heat exchanger 6 for the die section. It also has controlled heat exchanger 3 for the barrel 10, and one heater 7 for calibration purposes in a circulation path 8. The die 9 section and barrel 10 can also be cooled down with the heat exchangers 6, 3.

For calibration purposes, the ORDT is fitted with a circulation path 8. This makes it possible to have a closed loop for adjusting and calibration purposes. Pressure and temperature measurements are placed just before the die 9, and they are used for the die testing function as well.

The physical configuration of the ORDT allows the capturing of small portions of solid-liquid material through the feeder pipe 12 for on-line and off-line use.

Figure 2 a) shows cooling 39 for main motor 1 which is connected to a gear box 38. A feeder pipe 12 feeds the rheometer with the material to be monitored and controlled, one heat exchanger 3 is located on the barrel 10, and another heat exchanger 6 is located on the die 9.

A pressure sensor 4 is located near the die 9. The rheometer is provided with a bracket 30 for fastening of the rheometer in a vertical position. A load cell 29 is further provided for torque measurements at the top of the vertical shaft 11.

A ring 37 is provided for holding an arm 36 for torque measurement. Item 35 is a proximeter for speed measurement of the motor 1.

Figure 2 b) shows the power input of the force cooling 31, and item 32 shows the

AC motor power input. A temperature sensor 13 is located on the feeder pipe 12. A DC motor 33 is connected to a feeder screw 35. The temperature sensor 5 is located near the die 9.

Figure 2 c) shows the coupling 25 for the AC motor which is connected to the vertical shaft 11 (with helical flights). A bearing 2 preferably made to hold an axial load is located in the upper part of the shaft 11. A feeder screw 35 is located inside the feeder pipe 12 for driving the material to investigate forward. Item 28 indicates the base for the rheometer. The rest of the reference numbers are described above.

Examples of use For feed/food processors the viscosity is important because it will physically affect the end products (texture and brightness), and indicates the degree of starch gelatinization, as well as when proteins coagulates or unfold (denaturizing process), viscoelasticity is related with the expansion and shrinkage phenomena of a pelleted product. On the other hand, the mechanical principle of the ORDT allows a direct interpretation between the physical characteristics of the raw materials with their process-ability and power consumption at different temperatures and shearing environments. The pseudoplasticity characterization (shear thinning behavior) enables its interpretation and incorporation into the die profile activity and is as well a useful tool for processors to decide which die to use for a particular recipe to increase the physical quantity of end products.

Fields using the present invention are among others: research institutions, feed producers, food producers, control process and automation companies, and other industries working with solid-liquid materials.

Claims

1. A rheometer for on-line measuring of properties of compositions, comprising a rotary shaft (11) with helical flights housed in a barrel (10) with an upper and lower end, where the shaft (11) runs from the bottom of the barrel (10) and up through the top of the barrel (10) wherein the shaft is suspended in a bearing (2), and where the upper part of the shaft (11) is connected to a motor (1), and where the rheometer is characterized in that it further comprises a die (9) with an orifice in the lower end of the barrel (10), and an inlet feeder pipe (12) in the upper end of the barrel (10), allowing to relate rheological measurement with flow characteristics of the composition entering the feeder pipe (12) and exiting through the die (9).

2. A rheometer according to claim 1, characterized in that the upper part of the shaft (11) is connected to a motor (1) with variable speed.

3. A rheometer according to claim 1, characterized in that the barrel (10) and die (9) comprise means for controlled heating (3, 6).

4. A rheometer according to claim 1, characterized in that the barrel (10) and die (9) comprise means for controlled cooling (3, 6).

5. A rheometer according to claim ^characterized in that the inlet feeder pipe (12) comprises means for measuring temperature (Tl).

6. A rheometer according to claim 1, characterized in that the barrel

(10) comprises means for measuring temperature and pressure (T2, P2).

7. A rheometer according to claim 1, characterized in that the die (9) is changeable.

8. A rheometer according to claim 1, characterized in that the die (9) contains more that one orifice and/or venturies.

9. A rheometer according to claim 1, characterized in that the outlet from the die (9) is connected to the upper part of the barrel (10) for creating a circulation path for calibration purposes and off-line use.

10. A rheometer according to claim 9, characterized in that the circulation path comprises controlled heating.

11. A system for on-line measuring of properties of compositions, characterized in using a rheometer according to claim 1 , and further comprising means for:

- controlling speed (14) of the motor (1),

- measuring speed (15) of the motor,

- measuring torque (16) exerted on the motor, - measuring temperature (18, 19) and pressure (20),

- collecting the measured values in a datataker (21),

- data processing (23),

- presenting the properties of the compositions to a user (24).

12. A system according to claim 11, characterized in that a sensor for measuring temperature (Tl) is located at the inlet feeder pipe (12), and sensors for measuring temperature (T2) and pressure (P2) are located near the die (9).