Meter/Mix for Success
Progressive cavity pumps can provide precise, efficient dispensing for a variety of materials.
Finding the proper meter/mix and dispensing process is essential for the precise application of today’s epoxy-, silicone-, and urethane-based adhesives and sealants. Material manufacturers sell their formulations based on the benefits that they provide. They rely on their customers to accurately identify and apply formulations for potting/encapsulation or adhesion to perform a specific function. Customers select the material and manufacturer because of the benefits and capabilities that a specific formulation provides to their end product. In most cases, a customer selects the necessary chemistries for their application, and the materials manufacturer provides the correct formulation for that project.
From a dispensing point of view, the challenge is in supporting the expectations of customers and materials manufacturers—which is where the proper meter/mix/dispensing technology becomes critical. Ideally, systems need to deliver and blend the chemistries according to customer specifications, and should provide a means of delivery so the material is applied according to end user expectations.
Progressive Cavity Pumps
Most systems are engineered to accurately meter plural-
component adhesives and sealants, regardless of viscosity, and feature programmable ratios, dispense volumes, and flow rates. Dispense equipment is traditionally thought of as being configured with piston or metering rod displacement pumps or gear pumps. Both pump styles have been used in the past because of their specific delivery capability. However, both designs suffer from high wear rates when used for pumping moderately to highly filled or abrasive materials.
Progressive cavity (PC) pumps, on the other hand, provide an ideal vehicle for dispensing a variety of materials. Progressive cavity pumps feature an internal helix-shaped rotating element called the rotor and a double-helix-shaped stationary external element called the stator. The interference fit between rotor and stator creates a series of sealed cavities that are continually filled with material at the pump assembly inlet and gently move the material, relatively undisturbed, to the pump outlet. As a result, solid materials that are smaller than the cavity size can be dispensed effectively without damage to the materials or the pump. This makes the PC pump ideal for use with abrasive fillers without undue wear.
The amount of wear is equal to the size, makeup and percentage of filler present in the material over the pump’s lifespan. Fillers as fragile as glass micro-balloons or as destructive as sand can be successfully processed in a PC pump.
Ratios drift slightly when wear occurs, but this wear can be compensated for by a simple recalibration of the system. The life of the pump and continued uptime of the system in production is therefore extended. Conversely, if a seal on a piston or metering rod fails, the system is likely to break down and leak materials into the production area.
The consistently accurate precision dispensing of fluid media can be achieved with PC meter pumps, independent of media viscosity. PC pumps exhibit exceptional resistance to abrasive/filled content and chemically aggressive fluids. They are suited to transfer materials such as:
- Abrasive-filled polymers
- Microsphere-filled polymers
- Thixotropic materials
- Most anaerobic adhesives and sealants
- Silicones, epoxies, lubricants and polyurethanes
- Pastes, paints and gels
- Cosmetics and pharmaceuticals
- Food products
Suitable for single- or multi-component applications, PC pumps also provide many operational advantages, including constant volume at variable speeds, continuous flow, few moving parts, low maintenance and no cycle time delays for cavity recharge. Specific design features provide additional functional benefits. The cavities taper down toward their ends and overlap with their neighbors, essentially eliminating flow pulsation. No flow meter or check valves are required due to the PC pumps’ seal design.
The amount of material, dispense time, flow rate and ratio are all adjustable on a PC pump through a keypad with LCD interface. A microprocessor is programmed, at ratio, to turn the pumps for the selected dispense volume and can save a number of programs with different parameter settings for quick transfer between applications requiring different volumes of material. Highly accurate signal-to-action timing enables consistent deliveries of material. With the machine’s shot-size accuracy and range, adjustable flow rate, and consistent ratios, a repeatable process can be introduced into production. The systems should integrate into most commercially available robotic platforms.
The addition of flexible, digitally controlled meter/mix systems, built around a work station format, allows personnel to use the positive displacement pump technology that is ideal for medium- to high-volume dispensing requirements through proprietary microprocessor programming controls. These systems are capable of up to 40 stored dispense programs and offer the lowest maintenance requirements available in the industry, resulting in a lower cost of ownership compared to competitive systems.
Material Pre-Conditioning and Management
Material preparation is crucial for dispensing success. If materials are not conditioned properly, the material is in danger of acquiring air bubbles and inconsistent viscosities, along with settling and separation. Many dispensing problems occur due to poor material handling.
Filler settling, moisture absorption, and material viscosity cause inaccuracy and poor reliability in traditional dispense systems. Often, material handling is the least acknowledged critical aspect of a dispensing system. Material conditioning includes agitation, heating, degassing and desiccant drying.
Agitation is the stirring of the material prior to metering, mixing or dispensing. Agitation can occur continuously, at specific intervals or until the material reaches a specific viscosity level. Materials that incorporate filler require agitation to ensure the fillers do not settle.
If accuracy and repeatability are necessary to a dispensing application, some degree of material heating will most likely be needed. Heating material to a specific temperature ensures a consistent shot each time, removing environmental factors and varying viscosities.
Some materials act adversely when they are not properly degassed or de-aired. If the final product cannot contain any gas or air bubbles, the material must be de-gassed prior to dispensing. Degassing removes bubbles, entrapped air, and gas, and prevents blemishes in the materials.
A desiccant dryer or nitrogen blanket removes and guards against moisture from the dispensed material. The dry air is monitored so the desiccant dryer can be replaced when it reaches its limit. It is possible to easily swap the dryer while maintaining an uninterrupted drying process.
A Material Management Unit™ (MMU) can provide the vital material conditioning needed to ensure accurate, reliable and repeatable dispensing. MMUs are specifically designed to address material handling concerns and provide consistent delivery to a meter/mix/dispense system.
One of the principal advantages of an MMU is the ease of material supply exchange. Materials are typically supplied in cans, buckets, barrels or totes. The MMU’s design allows the user to swap containers without introducing air into the system. Air in supply lines is a major cause of off-ratio dispensing and shot size inaccuracy. Barrels can be disconnected and replaced without stopping production or requiring a de-airing of the dispense system. MMUs provide several key benefits:
- Full process control reduces manufacturing variables
- Reduces hazardous spills
- Reduces employee exposure to harmful fumes and fluids
- Reduces potential for injury from spills and lifting heavy material packaging
- Continuous process and device feedback
- Reduces variables caused by manual process control
- Reduces energy consumption from unnecessary continuous processing
Additional options that can help to enhance material management include material transfer pumps and progressive cavity transfer pumps. Material transfer pumps use integrated MMUs to easily convey material from one location to another. Exacting accuracy and low shear factors also make progressive cavity transfer pumps ideal for conveying material from one location to the next. PC pumps are designed with efficiency in mind; they use up to 99% of the material in the drum, thereby eliminating waste.
Ultimately, the performance of a meter/mix/dispense system is a driving factor in the success of any business that is reliant on accurate, controlled dispensing. When considering the options available in meter/mix/dispense systems, the benefits of the advanced capabilities of PC pump technology are clear—especially when combined with the use of a flexible and powerful material management system.
For more information, visit www.fluidresearch.com.
Progressive cavity pump benefits:
• Smooth, pulsation-free delivery of viscous products
• Delivery of filled materials with ease; ideal for shear-sensitive materials
• Reversible; no dripping or stringing
• Easy to disassemble, clean and maintain
• Extremely accurate metered flow
• Gentle on product
• Self-priming reliability