Measuring and testing – Liquid analysis or analysis of the suspension of solids in a... – Viscosity
Patent
1997-04-28
1998-06-30
Brock, Michael
Measuring and testing
Liquid analysis or analysis of the suspension of solids in a...
Viscosity
73 5432, G01N 1114
Patent
active
057737126
DESCRIPTION:
BRIEF SUMMARY
BACKGROUND OF THE INVENTION
This invention concerns a method for measuring the viscosity of a liquid, wherein a rotary measuring head is introduced into the liquid, and the torque exerted on the measuring head is sensed. The invention further relates to a viscosimeter for implementing this method, said meter comprising a driving motor, which is provided with a torque sensor and is adapted to rotate a measuring head that is insertable into a liquid.
DESCRIPTION OF THE PRIOR ART
In many industrial processes, the viscosity of the liquids involved is of decisive importance to the practicability. A typical case is the production of glass containers, in which a liquid (here, of course, melted glass) is, in carefully adjusted batches, fed from a furnace through so-called feeder channels into a machine for blowing glass bottles. In spite of the fact that the viscosity of the melted glass is vital to the size and shape of the batches, as well as to the plasticity of the melted glass in the glass-blowing operation, no actual measurement of the viscosity of the melted glass is performed today. Instead, one confines oneself to determining the viscosity indirectly by sensing the temperature of the melted glass, optionally in combination with monitoring of the shape of the batch of melted glass cut off.
In an ongoing process, such a solution mostly yields satisfactory results, but in particular at start-up after an intermission or upon an alteration of e.g. the sort of glass (i.e. color or quality), an initial wastage of some size can hardly be avoided.
One reason for the absence of viscosity metering in today's production of glass containers, for instance, despite the obvious advantages offered by such metering, is that the prior-art measuring methods and viscosimeters are not suited for this purpose.
Amongst the prior-art viscosimeters, rotational viscosimeters are especially notable. The rotational viscosimeters comprise a motor which rotates a measuring head intended to be introduced in a given fashion into the liquid whose viscosity is to be determined. The viscosity is then actually determined by sensing the torque to which the measuring head is exposed when rotating in the liquid.
If reliable results are to be obtained, the rotational speed and the depth of introduction of the measuring head into the liquid have to be known, since these parameters naturally affect the torque, and hence the measurement results. Also, the position of the measuring head when introduced into the liquid has to be well-defined, since e.g. the side walls of the vessel holding the liquid also affect the torque. In the following, this effect will be referred to as the edge effect.
In a feeder channel of the type mentioned previously, it is not, however, possible to reliably determine either the depth of introduction of the measuring head or its position, partly because the analysed melted glass is in continuous movement, and partly because the melted glass gradually wears down the walls of the feeder channel, such that the flow conditions in the feeder channel undergo continuous change.
Quite apart from their limited practicability, the prior-art rotational viscosimeters are distinguished by the fact that much attention has to be given to the quality and the calibration of the torque meter (the offset of the torque meter has to be known), since but one value of the torque is obtained per measuring site for determining the viscosity.
SUMMARY OF THE INVENTION
In view of the failings of the prior art, a principal object of this invention is to provide a viscosity-measuring method obviating the drawbacks of the known methods, as well as a simple viscosimeter intended for the implementation of this method.
According to the invention, this object is achieved by a method which is of the type stated by way of introduction and which is characterised in that the measuring head is rotated at a substantially constant speed, that the torque is sensed at two depths of introduction of the measuring head into the liquid, and that the viscosity of
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Derwent's Abstract, No. G2039 D/27, Abstract of SU 761,882, Sep. 7, 1980.
Arvidsson Thomas
St.ang.hl Pierre
Brock Michael
Glasforskningsinstitutet
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