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Dispensing Systems Can Pay for Themselves
Automated dispensing systems provide repeatable fill of potting and encapsulant materials under microprocessor control and following the instructions of simple programs.
By David Upton, Director of Marketing, FRC-Fluid Research Corp.
Adhesives and sealants based on epoxy, silicone, and urethane typically require precise formulations to be effective, and establishing the proper mix and dispensing process for those materials is critical to success. In fact, suppliers of those materials routinely sell their formulations based on the benefits they provide, and rely on their customers to properly identify and apply the proper combinations for their applications. For contract manufacturers and OEMs alike, developing and using an innovative material dispensing system is a key to reducing waste, labor, and material costs.
Potting and encapsulating are often performed on electronic circuits for environmental protection, as well as to guard against damage from shock, vibration, or even hard treatment. A circuit is just as frequently potted and encapsulated to protect its owner: to make it impossible to reverse-engineer a proprietary technology without damage by completely covering an electronic assembly in black epoxy resin.
Potting involves pouring a polymeric material that will harden into and over an electronic circuit, totally submersing the circuit board and its components. The outer shell or housing of the electronic device holds the potting compound in place until it hardens. For electronic devices or circuits that need protection from harsh conditions, such as moisture, high/low temperatures, and physical or electrical stress, circuits and components are usually protected with a two-part potting compound.
Encapsulation uses a mold and a polymeric material that will harden to protect electronic circuitry. The device or circuit to be protected is placed in the mold and the polymeric material is injected to completely fill the mold and surround the device or circuit. Once the material has hardened, the electronic device or circuit takes on the shape of the mold. While potting or encapsulation does add size or weight to a device or circuit, it also can add a great deal of protection. It can modify dielectric strength, dissipate heat, and allow a product to float in conjunction with waterproofing, while adding flexibility or rigidity to the product.
Programmable Material Handling
Potting and encapsulation are two of the more popular applications for the programmable multiple-component dispensing equipment developed and offered by FRC Fluid Research Corp. These two-part material dispensing systems must work with a wide range of materials and deliver repeatable and reliable results. Operators can quickly program the material ratio and flow rate as well as the quantity of the potting compound to be dispensed by using the dispensing system?s liquid-crystal-display (LCD) touch panel. Once programmed, a technician can place a circuit board or product under the dispensing machine?s static-mixing nozzle, and simply depress a foot switch to release the programmed amount of potting/encapsulant. The computer-based system allows fast setup, and operators can store and modify multiple flow rates, mix ratios, and even entire dispensing cycles. The optically encoded servo drives and microprocessor-controlled hardware are driven by trusted and proven FRC programming technology.
This microprocessor-controlled system can store as many as 40 different material fill programs, using a straightforward liquid-crystal-display (LCD) touch panel.
These two-step dispensing systems are designed to save labor as well as potting/encapsulant. After potting/encapsulant materials have been mixed in a static mixer, positive-shutoff valves prevent cured material from clogging the lines of a dispensing system, or being wasted. Because the systems employ a progressive-cavity pump design, valve wear, leakage, and the potential phasing errors that can plague piston-pump systems are eliminated. One alternative to the use of this type of automated, precision meter mix dispensing system is the use of labor-intensive procedures that require manual mixing and dispensing of the potting compound. Typically, a company performing potting or encapsulating of a circuit or device would acquire material in kits, such as a potting kit where the resin and catalyst must be mixed by hand. Once the materials are mixed, the potting compound is dispensed by hand into the target device or circuit, resulting in a good deal of wasted compound. The cost of these potting material kits can be high, added to the cost of the labor required for a manual operation, and it is easy to see how an automated dispensing system can pay for itself in about one year, depending upon its frequency of use. With such a machine, a company need not acquire potting compound in smaller kits, but can purchase materials in more cost-effective 55-gallon quantities.
How does an automated material dispensing system save so much in time and money and make such efficient use of the materials it handles? It is microprocessor controlled and allows for precise control over the parameters of each "fill" program. Parameters such as the amount of material, dispense time, flow rate, and material ratio can be adjusted using a keypad with LCD interface. The microprocessor controls the system?s pumps to dispense precisely the desired amounts of materials, in precisely the required ratios, with extremely accurate signal-to-action timing for consistent and repeatable deliveries of material. The microprocessor-controlled dispensing systems are designed for ready integration with most commercially available robotics systems.
Microprocessor control can bring programming power as well as consistency and precision to material dispensing systems. The FRC systems, for example, employ positive displacement pump technology ideal for medium to high volume dispensing requirements, but orchestrate that technology by means of proprietary microprocessor programming controls. These systems can store as many as 40 dispense programs. They are designed for low maintenance requirements, resulting in low cost of ownership. These automated dispensing systems are engineered to accurately meter multiple-component adhesives and sealants, regardless of viscosity.
Progressive Cavity Pumps
Traditionally, material dispensing equipment has been configured with piston or metering rod displacement pumps or gear pumps. These pumps offer very good delivery capabilities, but can suffer high wear rates when pumping moderately to highly filled or abrasive materials. In contrast, progressive cavity pumps can handle abrasive fillers without the wear of other pump types. Progressive cavity pumps use an internal helix-shaped rotating element called the rotor and a double-helix shaped stationary external element called the stator. The interference fit between the rotor and stator creates a series of sealed cavities. These cavities are continually filled with material at the pump assembly inlet, and gently move the material, relatively undisturbed, to the pump outlet. This approach allows a progressive cavity pump to be used with abrasive fillers without undue wear. This type of pump has also successfully handled fillers as fragile as glass microballoons without damage. When wear on a progressive cavity pump system occurs, material ratios will change slightly, but this wear can be compensated for by a simple system recalibration to extend the life of the pump and keep the material dispensing system in production. When the seal on one of those more "traditional" pump system fails, such as on a piston or metering rod, that system is likely to fail.
Automated dispensing systems that use progressive cavity metering pumps can handle a wide range of fluids precisely and reliably, independent of fluid viscosity. Progressive cavity pumps are dependable even with "difficult" potting/encapsulant materials, including abrasive/filled content and chemically aggressive fluids. Progressive cavity pumps can be used for single- and multiple-component applications and offer numerous advantages compared to other material pumps, including delivering constant volume at variable speeds, maintaining continuous flow, requiring few moving parts, low maintenance, and no cycle time delays for cavity recharge. In addition, their cavities taper down toward their ends and overlap with their neighbors, essentially eliminating flow pulsation. Due to the seal design of the progressive cavity pumps, they can be used without flow meter or check valves.
For companies with adequate potting/encapsulation requirements, an automated material dispensing system can help in saving labor, manpower, and even material costs compared to manual approaches. Furthermore, a material dispensing system under microprocessor control and using progressive cavity pumps can precisely and repeatedly control the amount of material that it dispenses, even when that material is abrasive in nature or comprised of aggressively reactive chemicals.
-Fluid Research Corp., 15775 Gateway Circle, Tustin, CA 92780
714-258-2350 fax: 714-258-2352 E-mail: firstname.lastname@example.org
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