FOAM GENERATING APPARATUS

Abstract: A mixture of air and liquid is introduced to a premixer (12) comprising a cylindrical casing housing a plurality of convoluted elements arranged end-to-end along the longitu­ dinal axis of the casing. The air/liquid blend exiting the premixer is introduced to a static foamer (14) which is identical to the premixer except that it additionally contains a porous bed of spherical beads which fill the space between the convoluted elements and the casing.

Description: FOAM GENERATING APPARATUS It is well recognized that wet processing in the textile industry is a major source of energy consumption. With the advent of high energy costs, the concern as to the availability of oil and natural gas, considerable effort has been expended in reducing energy usage for wet processing techniques such as bleaching, dyeing, printing and finishing. A technology, which has developed as a result of energy conservation research in the textile field, involves the use of foams for wet processing. By foaming techniques, the amount of liquid applied to the textiles is reduced substantially thereby greatly lowering the amount of energy required to dry the product. Not only is there a saving of energy, but foaming also permits increased productivity and a variety of other advantages. A most important consideration in foam technology is the production of foam having uniform properties such as density, viscosity, stability and bubble size. Such uniformity is particularly. critical when dyeing with foam since variations in.the foam's physical properties will produce an unacceptable result readily apparent to the observer. One type of device for producing foam is a socalled "static foamer". Such a device operates on the principle that when air and a liquid/soap solution are forced together through a porous medium, such as beads, screens or the like, a small bubble dispersion (i.e. foam) is produced. Static foamers are well known. For example, US-A-2,090,727 discloses an arrangement in which liquid and gas are delivered under pressure to a chamber containing a mass of balls of noncorrosive material, such as glass, which causes an intimate mixture of the liquid and gas to produce foam composed of small bubbles of gas. Further examples of arrangements in which a liquid-gas mixture is passed through spherical beads to produce a foam are disclosed in US-A-4,038,037 and US-A-4,061,001. An example of a disclosure of a known type of static foamer in which a mixture of liquid and gas is passed through a type of screen is US-A-4,207,202. In this patent specification, an expanded metal strip serves as the porous material for causing the liquid and gas supplied thereto to be intermixed to generate foam. Although the concept of a static foamer employing a bed of porous material is known, the present invention provides for the mixing of liquid and air in a manner which achieves an improved level of uniformity. An appreciation of this improvement can be obtained by considering the problems involved in producing foam with a static foamer. The combination of air and liquid (water) to produce foam basically is a heterogeneous system The addition of a surfactant to the liquid serves only to stabilize the air phase in the liquid phase as a bubble but does nothing to ensure that the air/liquid ratio is constant throughout the foam dispersion. Therefore, uniformity of the foam requires proper flow dynamics as the air/liquid mixture passes through the foamer. The present invention constitutes a structural arrangement in which the air and liquid are introduced to apparatus which controls the flow of the materials in such a manner that an extremely uniform foam is produced. In accordance with the invention, a foam generating apparatus comprises a premixer for producing a blend of air and liquid, the premixer including a first cylindrical casing having a plurality of convoluted elements arranged therein in end-to-end relationship and extending longitudinally of the casing; a static foamer including a second cylindrical casing within which is disposed a further plurality of convoluted elements arranged in end-to-end relationship and extending longitudinally of the casing, and a bed of spherical beads occupying the space between the elements and the casing; and means for joining the premixer to one end of the second casing for supplying the blend to the foamer for passage through the beads to develop a homogeneous dispersion of the air and liquid which is discharged from the opposite end of the second casing. The premixer combines the air and liquid in a continuous, predictable manner. On introduction of this mixture into the static foamer, the combined effects of the convoluted elements and the spherical beads are to divide and radially mix the developing foam flow to prevent air-liquid concentration gradients across the diameter of the foamer. The result is a foam of excellent uniformity, even when the foam has a high air-to-liquid ratio (frequently called a "blow-ratio"). The invention will be described in detail with respect to the accompanying drawings, wherein: Figure 1 diagrammatically illustrates the basic components of a foam generating apparatus according to the invention; Figure 2 is a perspective view, partially in section, illustrating details of the premixer portion of the apparatus shown in Figure 1; and, Figure 3 is a sectional view of the static foamer portion of the apparatus shown in Figure 1. Referring to Figure 1 of the drawings, a source of liquid under pressure is illustrated as a pump 10 which directs the liquid (a mixture of water and a surfactant) to a premixer 12. Pressurized air is supplied by suitable connections to opposite sides of the path of liquid flow immediately upstream of the premixer. The air/liquid blend passes through the premixer 12 and then is directed by conventional couplers in an in-line fashion to a static foamer 14. Within foamer 14, the blend is further mixed to produce a foam discharge for supplying a suitable foam applicator (not shown). The details of the premixer 12 cart be appreciated with reference to Figure 2. The premixer is a commercially available device known as a Kenics KM0D-60 sold by the Kenics Corporation, a division of Chemineer, Inc. of Dayton, Ohio. It comprises a cylindrical casing 16 suitably threaded at its ends so as to permit its connection to the liquid/air supply. Within casing 16, a plurality of convoluted elements 18 art provided. Each of these elements comprises a rectaelgular piece of metal to which a 1800 twist has been imparted. The elements are arranged end-to-end to extend in line along the longitudinal axis of casing 16; Adjacent ends of the elements are oriented at 90 t--with respect to one another, as can be appreciated frclVn Figure 2. A premixer of the type just descried mixes the air and liquid in a continuous predictab3 manner. The elements 18 create uniform flow dynamics which help prevent surging or pulsating of the feed components which, in other types of premixers, produces variations in the uniformity of the air/liquid blend, particularly as they occur along the direction of flow of the blend from the premixer. An additional characteristic of the present premixer 12 is that it is essentially a free-flow system having no nozzle effect, baffle plate or the like such as are found in other types of premixers. Accordingly, air/liquid flows can occur over a large range with minimal back pressure. The static foamer 14 is similar in construction to the premixer 12. The casing 20 of the foamer is of larger diameter than casing 16. Additionally, the casing 20 is provided with flanges 22 at its ends which cooperate in conventional fashion with flanges 24 provided on the adaptors 26 and 28 at opposite ends of casing 20. However, the most significant difference between premixer 12 and the foamer 14 is that the latter further includes a porous bed comprising spherical beads 30 occupying the spacing between the convoluted elements 32 and casing 20. Preferably, these beads have a diameter of approximately 1.4 mm. In order to retain the beads within the foamer, screens 34 are provided between the flanges at opposite ends of the casing 20. The beads 30 provide the porosity for generating foam from the air/liquid blend supplied to the foamer in a direction along the foamers longitudinal axis. The convoluted mixing elements 32 produce a rotational circulation of the developing foam around the elements' hydraulic centres, thus causing radial mixing. This type of mixing is essential to preventing air/liquid gradients between the materials close to the centre of casing 20 and that adjacent the casing's interior wall. The elements 32 split the flow according to the number of elements present in the foamer. In a typical foamer 14, four mixing elements are utilized. This produces 16 flow splits inasmuch as the disclosed foamer operates in accordance with the formula that the number of splits equals 2n, where n is the number of elements employed. Utilizing the apparatus which has been described, a foam is produced having uniform, predictable and reproducible density, viscosity, stability and bubble size properties.

Claims: CLAIMS 1. A foam generating apparatus comprising a premixer (12) for producing a blend of air and liquid, the premixer including a first cylindrical casing (16) having a plurality of convoluted elements (18) arranged therein in end-to-end relationship and extending longitudinally of Uie casing; a static foamer (14) including a second cylindrical casing (20) within which is disposed a further plurality of convoluted elements (32) arranged in end-to-end relationship and extending longitudinally of the casing, and a bed of spherical beads (30) occupying the space between the elements and the casing, and means for joining the premixer to one end of the second casing (20) for supplying the blend to the foamer (14) for passage through the bads (30) to develop a homogeneous dispersion of the air and liquid which is discharged from the opposite end of the second casing. 2. Apparatus according to claim 1, wherein the air and liquid is supplied to an end of the premixer casing in a flow direction extending along the longitudinal axis of the casing (Figure 2). 3. Apparatus according to claim 1 or claim 2, wherein each of the convoluted elements (18,32) comprises a rectangular piece having a twist of approximately 1800 imparted thereto, and wherein adjacent ends of the pieces are oriented in angular offset relationship with respect to one another. 4. Apparatus according to claim 3, wherein the adjacent ends are oriented at approximately 900 with respect to one another.

Inventors: PACIFICI, JOSEPH A.
Applicants: WEST POINT-PEPPERELL, INC.
Application year: 1982
Main classification: D06B19
IPC codes: D06B19, B01F13, B01F5, B01F3