Patent Application
20230234083
This disclosure relates to atomizing viscous fluids, more particularly to atomizing two-part fluids using a filament extension atomizer.
Spraying or otherwise making a mist from highly viscous fluids presents several challenges. Viscous fluids do not flow easily and any process of breaking them up into particles has to overcome the inherent cohesiveness of the fluid.
One successful solution to this issue lies in filament extension atomizers (FEA) developed by PARC. In the most common of these atomizers, the system introduces the fluid to one or both surfaces of a pair of counter-rotating rollers or other diverging surfaces. As the surfaces come into contact, or near contact in a region called the nip, the fluid attaches to both surfaces. As the surfaces rotate away from each other, the fluid stretches between them, forming filaments. As the surfaces continue to move, the filaments burst into droplets.
Generally, the use of these atomizers involve a non-reactive fluid. The term ‘reactive” fluids generally involve at least two different components like an epoxy resin and a hardener, referred to here as a reactive system. Many challenges of trying to spray these fluids exist. To effectively react, the two fluids need to undergo sufficient mixing so the cross-linking agent can react more uniformly, and therefore form a more complete, uniform cross-linked material. Pre-mixing in a chamber, such as a reservoir or pump body, will not work well. The two fluids will react, resulting in clogging of the fluid dispenser as the cross-linking will cause blockages in the dispenser. The cross-linking may also make the dispenser difficult to clean as the fluids may stick to the chamber in which they mixed, even to the point of forming difficult to remove solids. Rapidly reacting fluids may become not sprayable at all.
According to aspects illustrated here, there is provided an apparatus includes a first belt having an external surface, a second belt having an external surface positioned with the external surface opposite to the external surface of the first belt, with a region in which the first belt and the second belt come in contact, a first set of guide devices arranged inside the first belt, a second set of guide devices inside the second belt, a first material dispenser positioned to allow a first material to be dispensed on the external surface at least one of the first and second belts, a second material dispenser positioned to allow a second material to be dispensed on the external surface at least one of the first and second belts, and a power source to cause at least one of the guide devices in at least one of the first set and the second set of guide devices to cause at least one of the first and second belts to move to cause the external surfaces of the first and second belts contact and then diverge away from each other so that at least one of the first material and the second material forms filaments that break up as the belts continue to diverge.
According to aspects illustrated here, there is provided a method of generating a spray of reactive materials includes dispensing a first material onto at least one of a first belt and a second belt, the first belt and the second belt arranged on a first set of guide devices and a second set of guide devices, dispensing a second material onto at least one of the first belt and the second belt, mixing the first material and the second material by moving the first belt and the second belt through a region in which the first belt and the second belt come in contact with each other to form a mixture, and causing the first belt and the second belt to diverge from each other forming filaments that break into a spray of droplets.
Generating sprays or mists from highly viscous materials presents several problems, mostly due to the ‘thickness,’ or resistance to flow of the material. The particles of the materials tend to have internal friction between layers of the fluid that flow at different rates, making them ‘sticky’ and hard to separate from other particles of the material. The terms “highly viscous” or “high viscosity” mean a viscosity of over 1 mPa-s (milliPascal-second).
The filament extension atomizer (FEA) technology developed at PARC emerged as a solution to this problem. FEA enables spraying of highly viscous formulations. Thin, low viscosity fluids, with or without a propellant, can be sprayed using pump or trigger sprayers. These methods do not work with higher viscosity fluids, but the FEA has had success in spraying these liquids.
Generally, FEA systems have diverging surfaces, such as a pair of counter rotating rollers. The two surfaces come into contact and then move away from each other. Typically, a fluid is applied to one or both of the surfaces. The surfaces move towards each other and come into contact, or near contact, then diverge from each other. During contact, the fluid sticks to the surfaces, and then as them move away from each other, the fluid forms filaments that stretch between the surfaces until the strain causes the filament to break up into droplets and form a spray.
The discussion here involves using an FEA system for reactive, fluids materials or systems. As used here, the term “reactive” means that a first material, when it comes in contact with a second material, causes a reaction in which the first material causes the second material to cross-link or otherwise change their composition. As used here, the term “cross-link” includes cross-linking, curing, or hardening. Materials that change their composition can include foaming materials that react to form a gas phase that creates voids in the material, materials that chemically react with each other, materials that cause properties such as pH to change, or materials that combine to form other alloys or copolymers. One should note that the first and second materials, individually, may comprise more than one material, such as a cross-linkable material and a buffering agent.
Cross-linkable materials comprise those materials that can form chemical bonds between different chains of atoms of a polymer or other complex molecule. Examples include but are not limited to, a material containing one or more of epoxy resin, silicone resin, or cross-linkable polymers. Examples of materials that can cause other materials to cross-link, referred to here as cross-linking agents, include epoxy hardeners, silicone hardeners, and polymer cross-linkers, such as boric acid.
In a FEA system using two counter rotating rollers the contact area between the rollers is small. In a reactive system, this means that a reactive material spends little time in contact with the other fluid before it is atomized. Since a mixing of these two fluids can take time, the small contact area reduces the ability to increase the contact time without slowing the roller speeds down to a point where spray quality or output is decreased. Furthermore it can be difficult to increase the contact area and time between the two rollers by increasing the size of the rollers since increasing the size of the rollers only has a small impact on the contact area and greatly increases the size of the overall system.
In order to address concerns with using two roller to create filaments, two belts are used to create both a contact area and the diverging surface for the creation of FEA spray. Using belts as the diverging surfaces allows a system to be created with a smaller footprint, but with a large contact area to encourage mixing of the two fluids to form a reactive solution. This allows compact FEA systems with a long contact area, but still capable of running at high surface speeds to create filaments that breakup and meet output demands from an application.
In the case of using belts as the diverging surfaces, the rollers or other guide devices take on a different role than being the diverging surfaces themselves. This separates the guide devices from being the diverging surfaces. As used here, the term “guide device” means any device that moves, or just directs, the belts. The guide devices may cause the belts to move, such as powered rollers, including those mounted on a shaft, connected to motors that cause the rollers to spin. Examples include rollers, and rollers with sprockets. The belt could be a timing belt. These then in turn cause the belt to move. Other types of guide devices may take the form of more passive devices, such as rollers that only move because the belt causes the rollers to spin, or even as simple as a pin or other structure that merely directs the belt in a particular direction.
Guide devices can take a wide range of shapes and configurations. They can be smooth rollers that are mounted on a shaft. The shaft is configured to a bearing system that allows the roller and shaft assembly to freely rotate. Guide devices such as rollers can also be configured so that there is a bearing between the roller and a fixed shaft, this is commonly known as an idler. In addition to smooth rollers, the guide device can be a toothed gear or other substantially circular shape with features to contain and guide a belt. In addition to substantially circular roller-like shapes, rigid shapes that a belt is allowed to freely glide over or past can be used to create geometries not otherwise realizable with circular features. These shapes may include triangular, rectangular, square, etc. Stationary, or passive, guide devices can include features that help constrain motion of the belt in a direction other than the linear velocity of the belt. This can include guide rails, pins, or grooves. Additionally, the guides can be eccentrically mounted around an axis of rotation so that as the belt moves through and around the device the belt moves against the opposing belt.
These materials then mix in that region. The guide devices are arranged to form areas of high pressure such as 20, and areas of low pressure such as 22. These alternating regions assist with the mixing of the materials to form a mixture. As the belts move, as shown in the figure they would both move left to right, and then diverge. Their divergence causes the mixture to form filaments 30, that will eventually break up into droplets such as 32. This is discussed in one more issued patents, such as U.S. Pat. No. 9,962,673, “Methods and Systems for Creating Aerosols,” issued May 8, 2018, and its related cases.
Using belts in place of a single pair of counter rotating rollers allows for adjustments that would not otherwise be possible. The system controller could move the guide devices to extend the length of the region in which the surfaces are in contact. In addition, the controller may control the speed, or pressure, of the belts to control the amount of time the materials mix. Generally, the controller 24 manages the operation of the dispensers 26 and 28, and the guide devices that move the belts. The controller may control any number of guide devices from one to all. Controlling one of the guide devices may cause one of the belts to move, which, because of the friction between the belts may cause the other belt to move. A power source, such as a battery, AC power from the grid, etc., provides the impetus to the guide device or devices the move the belts, possibly by a motor or other drive.
Other configurations of the belts and guide devices are also possible, and may take up less space.
In the embodiment of
Other method of enhancing mixing may involve other differences in the belts, in addition to moving them at different speeds. As shown in
Other variations of guide devices, belts and their shapes are of course possible.
This embodiment includes a harvesting air flow. While not shown in previous embodiments, any of the other embodiments may include harvesting air flows. The harvesting air flows flow in the directions shown by arrows 110 and 112. The harvesting air flows direct the droplets in a predetermined direction. While shown flowing in a particular direction as in
In this manner, using belts instead rollers provides better mixing, and more opportunities to control the rate and length of the mixing region. This overcomes the issues with mixing materials in a reactive system, while also overcoming issues with viscosity.
All features disclosed in the specification, including the claims, abstract, and drawings, and all the steps in any method or process disclosed, may be combined in any combination, except combinations where at least some of such features and/or steps are mutually exclusive. Each feature disclosed in the specification, including the claims, abstract, and drawings, can be replaced by alternative features serving the same, equivalent, or similar purpose, unless expressly stated otherwise.
It will be appreciated that variants of the above-disclosed and other features and functions, or alternatives thereof, may be combined into many other different systems or applications. Various presently unforeseen or unanticipated alternatives, modifications, variations, or improvements therein may be subsequently made by those skilled in the art which are also intended to be encompassed by the following claims.
