Meter mix equipment is an integral technology to most companies that use two or more part adhesives. This equipment ensures proper mixing in the proper ratios, which is key to the sensitive chemistries of modern adhesives. With a need that extends across industries, types of equipment vary greatly from manual desktop units that dispense from handheld nozzles to full automated machines that are integrated into in-line manufacturing processes. All of these systems consist of two essential parts - the metering apparatus and the mixing apparatus.
Types of Metering
There are a number of different types of equipment for metering and driving adhesive components through a system. Each has distinct advantages and is used under particular conditions.
Piston Pump - Piston pump systems are among the most common systems used. They work with a reciprocating piston alternately filling the pump cavity and then pushing out fluid. They are excellent for dispensing tightly controlled amounts of adhesive for precise applications. Highly filled adhesives can wear to the piston and seals, so are usually not used.
Gear Pump - Gear pump systems are another popular option for metering - here components are pushed through a set of rotating gears which accurately meter the flow. Their advantage is that the system pumps continuously - ideal for low and medium-viscosity fluids that need continuous flow. In general, they cannot be used with highly filled adhesives.
"Each method of mixing and meters has its advantages and disadvantages - in most cases, a system is custom-tailored to each process."
Solid Rod - Solid rod displacement pumps work similarly to piston pumps, dispensing a precise amount of adhesive, ideal for adhesive shots that require tight tolerances. These systems are well-suited to highly filled adhesives since there are fewer moving parts or seals to experience wear.
Progressive Cavity - Progressive cavity pumps usually work with an auger or other rotor/stator design to meter and dispense. These systems are also ideal for shear sensitive and/or highly filled adhesives, and can handle high-viscosity fluids. They offer continuous flow like gear pumps.
Types of Mixing
Once the adhesive parts have been properly metered, they must be mixed thoroughly and completely. This is achieved with either static or dynamic mixers, of which there are a number of different types.
Static Mixers - This method of mixing involved pushing the metered parts of an adhesive through a specialized nozzle under pressure. The inside of the nozzle contains a variety of different pieces which adequately combine the parts. Different nozzles are made for varying viscosities, mix ratios and types of adhesives. Disposable nozzles have become popular, as cleanup is easier and the expense is minimal.
Dynamic Mixers - Dynamic mixers involved powered moving parts which actively mix the metered adhesive. They are more costly to run and maintain, and usually require flushing after use, but are sometimes required when there is a very high mix ratio or specialty mixing is required. Many foam chemistries such as silicone and urethane require the additional mixing a dynamic mix head provides.
Each method of mixing and meters has its advantages and disadvantages - in most cases, a system is custom-tailored to each process. Designers take into account the type of material being mixed, necessary flow rate and properties and mix requirements, among other factors, to determine what type of setup makes the most sense. Systems can range from under $10,000 to over $500,000 depending on complexity and integration.
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