Rheometer for measuring the flow properties of powders and granular materials

Abstract

The invention relates to a rheometer comprising of a container for receiving a material sample to be investigated, a shaft with a rotating body which is immersed into the material sample, and a container lid that moves in the axial direction of the shaft into the sample container to deliver consolidating stress to the material sample. The forces acting on the material sample due to the rotation of the rotating body and the motion of the container lid and the location of the sample lid are measured as consolidating stress and rotational strain are applied and removed from the material sample.

Claims

1. A rheometer for assessing characteristics of powders and granular materials, the rheometer comprising: a) a sample container for receiving a material sample to be investigated; b) a measuring shaft with a measuring rotating body, wherein said measuring rotating body and said sample container are rotatable relative to one another and said measuring rotating body is immersed into the material sample, wherein the measuring shaft and the measuring rotating body are rotated by a single drive unit; c) a container lid that fits inside said sample container without contacting said sample container and is in contact with the material sample, wherein the container lid comprises a passage to allow said measuring shaft to pass through and the container lid is prevented from rotating with said measuring shaft; d) a drive mechanism to cause a linear motion between the container lid and the sample container to apply stress and strain to the material sample; and e) a measuring unit outside of said sample container configured to evaluate measured values received from said measuring rotating body and the stress and strain applied to the material sample by the linear motion between the sample container and sample lid.

Description

BRIEF DESCRIPTION OF THE DRAWINGS

(1) FIG. 1 presents an isometric drawing of the preferred embodiment of the rheometer.

(2) FIG. 2 presents a drawing of the preferred embodiment of the rheometer.

(3) FIG. 3 presents a drawing of the preferred embodiment of the rheometer with the sample container lid in the measurement position.

DETAILED DESCRIPTION OF THE INVENTION

(4) The preferred embodiment of the invention is shown in FIG. 1, FIG. 2, and FIG. 3. The rheometer consists of a shaft drive unit 1, a shaft with a rotating body attached 3, a container lid 2 that is movable in the direction of the axis of the shaft 3, a sample material container 4, and a lid drive 5. The sample container 4 is partially filled with the material sample so the rotating body is immersed in the material sample when under consolidating stress. The container lid has dimensions so that it can move inside the sample container.

(5) At the start of an analysis the container lid 2 moves down to make contact with the material sample as in FIG. 3. The shaft and rotating body are then rotated to apply rotational strain to the sample. Depending on the analysis procedure, the vertical stress is increased or decreased by moving the container lid 2 down or up. In coordination with the container lid movement the shaft rotation speed can be increased, decreased, or stopped. During the analysis, a measuring unit is used to measure the forces acting on the material sample due to the rotation of the shaft and rotating body 3, the forces acting on the material sample due to the motion of the container lid 2, and the location of the container lid 2.

(6) Various analysis procedures can be used to simulate powder flowing through different industrial powder handling machines and storage units. These procedures include flowing the material sample then stopping the flow and applying a know consolidating stress to the material. Then the rotation of the measuring body is started again to determine the stress required to initiate flow in the material sample and if the sample flow is altered by exposure to stress. Another procedure would vary the consolidating stress on the sample material while the rotational strain is held at a known and fixed rate. Another procedure would hold the sample container lid at a fixed location and measure the change in stress on the sample container lid as the rotational speed is increased and decreased to determine the volumetric stress created by the rotational strain. The analysis procedures can be changed to alter the stress and strain paths on the samples to match specific industrial powder flow conditions.

(7) The drive units for the shaft and rotating body and sample container lid are shown only schematically but are known to persons skilled in the art. The measuring unit to measure the forces acting on the material sample due to the rotation of the rotating body and movement of the container lid and the location of the sample lid are not shown but are known to persons skilled in the art.