Measuring and testing – Liquid analysis or analysis of the suspension of solids in a... – Viscosity
Patent
1991-06-03
1996-04-23
Williams, Hezron E.
Measuring and testing
Liquid analysis or analysis of the suspension of solids in a...
Viscosity
73 5439, 73815, 73846, G01N 1100
Patent
active
055092985
DESCRIPTION:
BRIEF SUMMARY
This invention is concerned with an apparatus and method suitable for use in measuring the characteristics of a sample, especially the flow characteristics of liquid or semi-solid materials, for example printing inks, greases, oils and the like.
In assessing the suitability of various materials for particular functions it is important to know the characteristics of the materials under a variety of conditions. To this end it has been proposed to subject samples of materials to be assessed to intermittent distorting forces to provide data relating to their liquid/solid behaviour. However, existing apparatus for determining the characteristics of such material samples have not been altogether satisfactory. Suitable known equipment has in many cases only been capable of operating at frequencies of up to 15 Hz. and whilst this has provided some useful data, the frequency is too low to give fully satisfactory data for many purposes--for example, an engine rotating at 6000 rpm is rotating at a frequency of 100 Hz. and it would therefore be useful to be readily able to test the characteristics of oils at frequencies at least up to this level. Known apparatus for measuring the characteristics of samples has consisted of two plates between which a sample to be tested is positioned in contact with both plates, one of the plates being oscillated or rotated around an axis perpendicular to the other plate (which is generally fixed) to measure torsional shear characteristics. The rotation of the plates round the axis does not give sufficiently revealing data in most instances, and commonly known apparatus in which the plate is oscillated has not been capable of oscillating at a frequency significantly in excess of 15 Hz because the mass (and therefore inertia) of the equipment necessary to achieve such an oscillation has restricted the frequency. One such known apparatus may use a relatively large electric motor including a shaft mounted on an armature, to which alternating current is applied at a suitable frequency thus to oscillate the shaft about its axis: such an oscillation is relatively free and uncontrolled and it is difficult to achieve very precise measurements at high frequencies using such apparatus. In this equipment the forces may be determined via the oscillating shaft or the fixed plate. In another known apparatus, the oscillation is effected using a mechanical linkage which provides a more precise control of the amplitude of oscillation but is relatively complex and still has limitations of frequency due to the inertia of the various parts. In such apparatus the force applied through the sample may be detected by means of a transducer in a support member by which the sample is supported. One apparatus of this general oscillating type, using a mechanically operated member, is described in patent GB-A-1365677.
One of the various objects of the present invention is to provide an improved apparatus suitable for use in measuring the characteristics of a sample.
In one aspect the invention may be considered to provide apparatus suitable for use in measuring the visco-elastic characteristics of a sample comprising a support member providing a flat support surface on which the sample may be positioned, a cover member providing a flat surface, means for adjusting the relative positions of the members whereby to bring a sample carried by the support surface into contact with the flat surface of the cover member and to adjust the spacing between the flat surfaces to a preselected distance, means for vibrating one of the members at one or more preselected frequencies, and means for detecting the behaviour of the sample. Said means for vibrating one of the members may vibrate the member at a single preselected frequency, or at a certain number of preselected frequencies simultaneously, for example two or preferably three or even more.
Preferably vibrating means of apparatus in accordance with the invention comprise a form of electrically driven oscillator for example a piezo-electric device; said vibrating means is pr
REFERENCES:
patent: 2865197 (1958-12-01), Penther et al.
patent: 3194064 (1965-07-01), Miles
patent: 4166381 (1979-09-01), Woo
Raha, S. An Apparatus to measure the dynamic viscoelasticity of Polymer melts. In. Journ. of Sci. Instr., Series 2, vol. 1, 1968 pp. 1109-1112.
Fruh, S. M., et al. Recoverable Shear Measurements in a Parallel Plate Rheometer. In AiChE Jour., vol. 16, No. 6, pp. 907-910, Nov. 1970.
Dynamic (Oscillatory)Measurements Without Sample Inertia Effects, Ferry, J. D., Visoelastic Properties of Polymers, Wiley, 1970.
Sinusoidal Shear Generator for Study of Viscoelasticity, Miles, D. O., Journal of Applied Physics, vol. 33, No. 4, 1962.
Roskos Joseph W.
Williams Hezron E.
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