A method developed to determine bubble size distribution in flowing foam is targeted to foam application to fabrics, one of the minimum application techniques for applying chemicals to webs in very small volumes of water. Bubble size distribution is known to determine vital properties of the foam, such as viscosity, stability, and draining. The investigations described here reveal that bubble size distribution also affects the uniformity of the textile substrate. A measuring system incorporating a video camera was set up to study flowing foam. An image processing algorithm and analysis program were developed to determine bubble size distribution, and this method was then compared with one where bubbles were measured individually with photographs. The correlation between the methods was close. The image processing method was used to determine bubble size distributions of various foams. The effects of foam density, residence time of foam in the transport pipe, mixer speed and time-dependent effects on bubble size distribution were demonstrated. The study revealed that foam can be applied uniformly to a cotton web using a closed system in which application of moisture and bubble size distribution vary. However, uniformity deteriorates when foam with a non-uniform bubble distribution is used.In the textile finishing industry, foamed solutions are used to apply chemicals to fabric. The main advantages of this minimum application technique are due to the volume increase of the medium to be applied as a result of air-inclusion [ 1 ] . This means that chemicals can be applied to a large area in a controlled manner, using relatively small volumes of liquid. Another advantage is that less energy is needed to dry the web after treatment. In some cases, the quality of the treated material is higher than that obtained with traditional finishing techniques.In most applications, the foam should undergo minimal changes during transport, but break down in a short time when it interacts with the fabric so that the liquid can be absorbed by the fabric. In practice, under certain conditions, the foam itself may penetrate partly into the web because the lamellae, the spaces between the bubbles, are not drained quickly enough. It appears that the properties of the cloth fibers have an important effect on this. These factors affect the final distribution of the applied liquid through the thickness of the substrate [7], which may impede the foam application process, but also provides options to apply dyes and other chemicals by methods that cannot be used with a foulard. For example, the two sides of the web could be treated with different finishes.Foam is produced in a mixer in which liquid and gas are mixed by the shear forces between rotors and stators. Foam is an unstable medium, which is subject to physical and physicochemical changes that break it down from the instant it leaves the mixer. To be able to control the application process, the condition of the foam has to be known during its production, transport, and application.One ...
The viscous transport of foam through capillary systems can be described by a so-called power law. With flow of foam through a stationary substrate a relationship between pressure and foam flow can be found in which a number of geometrical parameters and rheological constants play a part. This model may be extended to the application of foam to moving fabrics in closed systems. As long as the liquor absorption plays a subordinate role during application, the model described explains the behaviour observed, within the limits of experimental error. The model can be considered as a useful basis for further study.
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