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Metering, Mixing and Dispensing Adhesives: Automated v Manual Equipment

Once a two-component adhesive has been identified as the solution to an application, the next step is to evaluate the most suitable method of dispensing it, taking into consideration factors such as cost, accuracy, efficiency, productivity and the elimination of waste.

In this month’s blog post we examine the differences between automated and manual meter, mixing and dispensing equipment and which applications they are best suited to.

 

Overview

Manufacturers are seeking ever more robust and cost-effective solutions when facing challenges in bonding, potting, and form-in-place gaskets. As a result, two-part fluids are increasingly being specified to provide higher quality, consistency and endurance.

The requirement for quality and performance during the working life of a product extends not only to durable goods, but also to consumer products that have a life expectancy of just a few years —and where competition is fierce. As a result, multiple compound fluids that can provide superior controlled performance are being selected by many industrial sectors.

The diversity of industrial activity requires a similarly broad range of automation options. For example an automated meter/mix solution will consider the necessary output and fluid characteristics and dispensing the final mixed fluid will take into account positioning accuracy, flow rate, volume consistency, repeatability and the appropriate safety precautions.

As a rule, two-part fluids require an automated process whenever possible. Due to their nature, this type of material must be carefully mixed following the manufacturer’s recommendations – any deviation will result in probable catastrophic failure or degradation of the product’s integrity and performance over its intended life. If an automated solution is considered too costly, or its relevancy is in question, the manual meter/mix of the fluid is no less critical than the conditions applied with an automated system.

 

Low-Volume Manual Meter/Mix Operations

At a minimum, low-volume manual mixing of fluids should be limited to prefilled and separated cartridges or burst-bag kits that can adequately mix the fluid components. Two-part cartridges are preferred, as they use an internal mixing rod and blending head that thoroughly mix the two components in the correct ratio. The mixed fluid can be dispensed directly from the cartridge using a manual gun or a time-shot dispensing system.

Burst-bag kits separating the two fluid components require a careful manual mixing process, and any instructions that are provided with the kit should be strictly followed. Once the two components are mixed, the fluid is poured into a cartridge or syringe, and dispensed using a time-shot dispense system. This is a less favourable method than using a cartridge kit, as air can be introduced in the pouring process.

 

Low- and Moderate-Volume Meter/Mix Automation

Bench-mounted meter/mix/dispense stations such as the DP200-1 and the DP400-1 from Fisnar, provide a solution for automating low to moderate volume dispensing. These machines are viable alternatives to fully-automatic bulk metering and mix systems, providing the fluid components are available in a dual cartridge. The cartridge package is inserted into a dual-cylinder pneumatic ram, which is mounted onto a tower to become a dispensing station and the rams are profiled to suit the ratio of the cartridge (e.g., 2:1, 4:1, etc.). Final mixing is then performed by a static mixer. The system is usually foot-pedal controlled, but control options include a digital shot timer, air logic and pinch-tube valve installation. Dual cartridges of 200 ml and 400 ml can also be accommodated.

Low-volume applications can require highly accurate positioning and precise volume control. A common installation would involve an automated robot equipped with a valve head and static mixer fed from a metering system. In miniature semiconductor and surface-mount component processes, pre-mixed syringes are used to dispense into the confined spaces between components.

For automated, low-volume, micro-shot applications, a meter/mix system that includes cartridge reservoirs can be mounted on a robot, though the system must be installed on a machine that is capable of handling the necessary load.

A number of applications in durable goods, such as the defence and transport sectors, require sophisticated fluid conditioning and process monitoring. Metering and mixing solutions in these sectors are dictated by rigorous standards and require careful planning and custom proposals.

 

High-Volume Meter/Mix Automation

High-volume, two-part metering and mixing require an automated and systemized solution. The dispensing process can be manual or automatic. Consideration should be given to fluid storage, fluid delivery, and the possible installation of level alarms and sensors. The dispensing method is determined by decisions similar to those in low-volume dispensing, including positioning accuracy and volume control.

 

Fluid Supply Options

Automated production and low-cycle, high-volume dispensing requires a sufficient fluid supply that is available at all times. The appropriate fluid supply to the metering system is determined by the type of fluid containers available, container size, viscosity, and conditioning specified by the manufacturer’s technical data sheet (TDS). The fluid supply options will include direct delivery from supplier containers, gravity and pressure-assisted reservoirs, or secondary holding tanks.

Medium- to high-viscosity fluid is commonly supplied in 3kg and 20 litre pails or 200 litre drums. Extruder-pump systems are used to deliver the fluid directly to the metering pumps or to secondary holding tanks that are controlled by sensors.

Fluid conditioning processes (e.g., thermal management, environmental control, agitation and de-gassing) are possible. Low- and high-level triggers in fully automatic systems ensure an adequate supply of fluid. Low- and high-level sensors in non-automatic supply systems can signal when to change a container or refill a reservoir.

A number of two-part fluids used in automatic metering and mixing require automatic or manual flushing of the system periodically. Personnel safety and relevant procedures need to be followed when working with and discarding hazardous materials.

Depending on the fluid and the process, the conditioning and control of the fluid can extend to the metering system, hoses and mix head. Conditioning requirements are generally installed on large-scale systems and also require heavy-duty robots for automated dispensing.

 

Variations in Meter/Mix Machines

A variety of metering and mixing technologies are available. They include piston-pump, gear-pump, solid rod and progressive-cavity machines, all of which provide volumetric metering with a high level of accuracy and repeatability.

Piston-pump technology is the most common and less costly solution for high-viscosity fluids requiring high pressure. However, the technology is not tolerant to fluids containing solid content, since particulate can become trapped within the seals, eventually causing damage to the integrity and performance of the machine. In a few cases, the frequent maintenance schedule required can be tolerated.

Single-acting, fixed-ratio, piston-pump machines are recommended over variable-ratio models. The reasons include, but are not limited to, prevention of contamination, ease of set-up, calibration and cost.

The single-acting metering principle in a piston-pump machine configures the two metering pumps for an exact ratio. Fluid is drawn into the cylinder when the pump rod retracts to its recharge position and is dispensed as the pump rod displaces the fluid. A single-acting, piston-pump machine like the Fluid Research LC50FR needs to recharge at the end of a pump cycle. This is an important consideration in automatic dispensing.

An alternative to a single-acting model is a double-acting system, which is primarily used to provide continuous metering by dual-rod, reciprocating piston pumps. Double-acting systems also reduce the frequency of recharge, thereby extending the life of the pump seals.

Progressive-cavity pump technology is an efficient solution for fluids with a high content of solids and abrasive fillers, such as silica or aluminium. The system uses a rotor/stator design to meter, mix and dispense high-viscosity fluid. They are also continuous in operation and therefore pulse free.

Low-pressure, gear-pump metering systems are widely used for low- to medium-viscosity fluids. These pumps provide pulse-free, continuous dispensing. In general, gear pumps cannot be used with fluids containing abrasive fillers. The machines operate when fluid enters the pump under pressure. As the gear rotates, fluid is sealed between the spur-mesh contacts and thereby flows around the perimeter of the gear-pump housing. In this manner, the fluid is volumetrically controlled and delivered to the dispensing valve head.

 

Mixing Options for Two-Part Fluids

A static mixer is the most commonly used mixing method. This plastic mixer comprises an outside tube and inner mixing elements. The metered fluid is fed to a dispensing valve head with a static mixer attached. Two valves within the valve head are opened simultaneously, thereby allowing the two fluids to enter the mixer under pressure. The correct number of mixing elements is required in a static mixer to properly and efficiently mix the metered fluid. The fluid supplier should be consulted to determine the optimal static mixer for a specific application.

Another mixing method is to use a dynamic mixer, which can be described as a dispense valve head with a rotating mechanical blender. A dynamic mixer is usually only necessary when there is a wide disparity in the mix ratio. Dynamic mixing is costly and usually requires a fluid-flushing circuit. A compromise may be to use a disposable rotary static mixer that may provide more thorough mixing than obtained from a standard static mixer.

Shop static mixers. 

Automated Dispensing

Bench-mounted fluid dispensers are an option when dispensing pre-mixed fluid from a syringe or cartridge. Two important factors need to be considered: the working life of the mixed material, and the increasing air space as the fluid level decreases within the syringe or cartridge. Both of these variables affect the accuracy of the dispensed shot. Costly compensatory and mechanical dispensers are available, but they need careful monitoring and adjustments. Valve controllers that are similar to fluid dispensers can provide a four-way, timed signal to a valve head for automatic dispensing.

Any automatic metering and mix system can be interfaced to a stand-alone, batch-production dispensing robot or integrated into an in-line conveyor facility. In an automatic dispensing application, the metering system is in a steady state of readiness to receive a signal from the robot, which carries the remote mixing valve head. The robot controls the dispense path and also controls the volume by controlling the speed. In the case of potting and encapsulation, the metering system can also control the volume, but the process is always a union between the robot and the metering machine.

Other factors in dispensing a shot or a bead are the mixer orifice and the size of the dispensing needle, if one is used. The common method of controlling a small bead is to use a pinch-tube valve at the end of a static mixer. The components of a pinch-tube valve are disposable.

Automated dispensing robots with multiple axes are available with a range of working platforms selected for the application. Most common is a three-axis machine, in either a gantry or cantilever design. Selective compliance assembly robot arms (SCARAs) can carry heavy loads and perform within a greater range of axes. These installations can be seen in large-scale industrial assembly. Smaller robots with three or four axes can handle syringes and cartridges containing pre-mixed fluids, such as pre-mixed and frozen materials.

Shop Automated Dispensing here. 

Final Thoughts

To conclude, both automated and manual dispensing and meter mix equipment have a valuable purpose to serve and are able to meet user’s two-component dispensing requirements. However the choice of which is better, is very much down to the kind of application in question as well as the purchaser’s budget and expectations. Our technical team welcome any questions that readers may have on this subject. Simply send an email to: infoeurope@ellsworth.com.

 

Boost productivity on your production line with effective repackaging.

More and improved packaging options are available today for two-part chemistries than ever before, including side-by-side cartridges for extrusion or spray, dual syringes, syringe kits, jar kits, twin pouches, barrier kits, injection kits, and premixed and frozen syringes and cartridges. The demand for packing down from totes, drums and pails into smaller units such as gallons, quarts and pint kits also still exists. If material modification is required, such as colour change, viscosity change, or the addition of conductive fillers or spacer beads, it is an advantage to have this accomplished as part of the repack process.

 

Side-by-Side Cartridges

One of the most popular package types, side-by-side cartridges is the equivalent to a mini Meter / Mix system without the capital expenditure and maintenance associated with the more advanced system. The same style of disposable mixer nozzle used with MM/D equipment is even used with dual cartridges, making it an effective and low cost solution.

The most common extrusion-style cartridge sizes include 50, 75, 100, 150, 200, 300, 375, 400, 450, 600, 900 and 1,500 ml though other less common options are available. Formula mix ratio requirements dictate the actual size options applicable for repack. The more common compatible volumetric mix ratios include 1:1, 2:1; 3:1, 4:1 and 10:1. A 3:2 mix ratio is also available in the 50-ml cartridge.

As for dispensing, both pneumatic and manual applicators are used to dispense material. Pneumatic is the best choice if it is practical at the point of use since it assures a homogenous blend when dispensing out of the mixer nozzle.

A newer growth area for side-by-side cartridges is spray coatings. The ability to apply to apply coatings in remote areas is a great advantage. Repairs can be made and on-site applications can be made without the need for cumbersome spray equipment. The only requirement of this technology is that an air source is available for the applicator.

Cartridges sizes are similar to those listed previously, however in this case larger size cartridges are more practical. Popular standard sizes include 1,500 (1:1 ratio), 1,125 (2:1 ratio), 1,000 (3:1 ratio) and 940 ml (4:1 ratio). One of the greatest benefits of these coatings is that they can accommodate a variety of viscosities. For fine tuning, one or both sides may be thinned out or thickened to ensure the two parts blend and coat effectively. If material modification is required, it is a bonus if the repackager has the ability to perform these services prior to repacking the coating into the cartridges.

Side-by-side cartridges do have some limitations, for example they can only accommodate certain mix ratios and they are not recommended for formulas that have fillers that settle quickly. With that said, measures can be taken to offset these potential problems – such as cold-temperature storage, periodic rotation of inventoried cartridges and shaking prior to use.

For a compatible formula, these cartridges are among the most efficient delivery systems. There is minimal waste and no air is introduced by the mixer nozzle during dispensing. The entire mass of material does not have to be used, as in other systems. It is possible to use these cartridges for multiple applications over time, with only the disposable mixer nozzle needing to be replaced when it is time to continue use.

 

Dual Syringes

Dual syringes are similar to side-by-side cartridges, but the key difference is that they hold a smaller quantity of material, while a manual plunger is used to dispense the material. Dual Syringes have fewer options for volumetric mix ratios (e.g., 1:1, 2:1, 4:1 and 10:1) and sizes range from 2.5 to 30 ml total.

Static mixer nozzles are an option with certain dual syringes. Manual plunger dispensing through a mixer is not always practical, especially with thicker materials in a larger syringe. However, many applications do use mixer nozzles. Dual syringes are often used for repair, touch up jobs and in-field kits and test samples can help to determine the viability of the package.

 

Barrier and Injection Kits

Barrier and injection kits are available in a number of sizes including 2.5, 6 and 8 oz, as well as a one tenth gallon and 20 oz. The barrier kit has an internal foil partition that keeps the resin and catalyst separated. Mixing is accomplished by removing the external tape at the foil partition and stroking clockwise with a mixer rod/internal propeller for 60-80 strokes. This can be done manually or with auto-mixers.

The injection kit has the catalyst in the mixing rod, so no barrier is necessary. The mix ratio determines the style of kit to be used; 1:1 up to 10:1 ratios require the barrier style, while 10:1 and upwards are better suited to the injection style. In cases where the application is borderline, the injection kit is the better choice because it is easier to use. To blend material, a ram rod is used to move the catalyst into the cartridge, and the mixing process is the same as the barrier kit. Dispensing is then accomplished with a manual or pneumatic applicator.

Perhaps the greatest benefit of barrier and injection kits is that there are no mix ratio restrictions, as there are with side-by-side cartridges. Users are also guaranteed maximum output since the mixing process redistributes filler that may have settled in the cartridge. While barrier and injection kits were initially used for aerospace and airframe applications, many different industries also now use them.

 

Two-Component Pouches

Made of a laminate film or foil for solvent- or moisture-sensitive materials, two-component pouches can be used for almost any mix ratio. Pouches come in two styles: burstable and clipped. The burstable style, which is the most widely used, has a burst seal dividing it at a location that creates the target mix ratio. Parts A and B are packed into the respective sides, and heat sealing creates the closure of the pouch. One end of the pouch is rolled up until the burst breaks, forcing the material into the other side, essentially creating a pouch with one cavity. The pouch should be repeatedly run over the edge of a table or workbench until parts A and B are completely blended. To dispense blended material, a corner is snipped off and the material is squeezed out.

A new generation of burst pouches includes a spout with a needle adapter option. This pouch has a second burst located just below the spout. With this style pouch, no snipping is required. The blended material is used to break the second burst, and it is then dispensed out of the spout or needle.

In a clipped pouch, the pouch is folded over a rod at the desired location, and a clip is put in place to secure the barrier. The two sides are filled and sealed, and the clip and rod are removed to create a one-cavity pouch. The remaining steps are the same as for the burstable pouch.

Two-component pouches are ideal for field kits, touch up work or other small jobs whereas larger pouches are used for applications at outdoor installation jobsites. No applicators are needed to use this package format however not all materials work well in this format. As with all repackaging, it is best to obtain samples in order to perform a full evaluation.

 

Premixed and Frozen Syringes

Premixed and frozen (PMF) is a practical packaging solution ideal for when the end user requires perfectly blended and air-free material applied to the target part with no in-house processing. In PMF packaging solutions, both the blending and container are built-in benefits. PMF is an excellent packaging option for small, repeatable dot applications by performed by automated dispensing/robotics. It is also often used with basic pneumatic table top dispensers. It is also a very good option for expensive materials, such as silver-filled epoxies. When properly used, PMF eliminates all but the smallest amount of waste.

The PMF process consists of blending batches of two-part material, vacuum degassing and filling into syringes. Centrifuging of the syringes may be used to remove air entrapment that can occur during syringe packaging. The syringes are then placed in a dry ice bath to flash-freeze, which stops the curing process. Syringes are shipped on dry ice via overnight delivery service to ensure they remain frozen during transit. Upon arrival, the syringes must be unpacked from dry ice and placed into a -40 freezer. The most common size freezer is 5 cu Ft and costs roughly £2000.

For this type of technology, packaging costs are sensitive to the working life of the formula involved. Quick-curing materials require small batch blending to ensure a minimal amount of time passes before the syringes are packed and brought down to frozen temperature. PMF is most suited to longer work life formulas since the batch sizes can be larger. This type of package requires the initial expense for a freezer, as well as additional freight costs related to overnight delivery service. For some applications, however, the PMF packaging solution’s benefits and quality assurance often outweigh those costs.

Interested in our Custom Repacking Service? Contact us here.  

We welcome any questions you may have regarding these repackaging options and will be happy to discuss your application in detail.

Ellsworth Adhesives provides custom adhesive packaging solutions through our partner company Kitpackers. Learn more about their products and services at: http://www.kitpackerseurope.com/

Hello and thank you for stopping by to check out our new blog!

This new Ellsworth Adhesives blog will serve as a platform to showcase our expertise in the adhesive field and has been created very much with you, the reader in mind.

Managing Director John Henderson comments “At Ellsworth Adhesives we are proud of our expertise in adhesive materials. Our technical team has excellent product knowledge and we wanted to share this intelligence with a wider audience. The creation of the new Ellsworth Adhesives blog provides the perfect platform to achieve this objective and we hope that readers will enjoy our monthly posts.”

As a distributor of adhesive materials and adhesive dispensing equipment, we represents all of the adhesive industry’s top brands including Dymax, Henkel Loctite, Dow Corning, Lord and Metcal. Each of the brands has a different focus area – for example Dymax specialise in UV Curing materials and equipment, while Dow Corning is known for its silicone solutions. With such a wide ranging product portfolio, our technical team therefore has a broad spectrum of technical knowledge to share.

Topics to be covered on the blog in forthcoming months include Adhesives for the electronics industry, Metering, mixing & dispensing Adhesives, A guide to selecting the correct encapsulant and finally a look at Developments in two component adhesives. In line with the reader focus of our blog, we would love to hear from you about the kinds of topics you would like us to address in future posts. Please email your suggestions to our Marketing Coordinator, Michelle Duncan: mduncan@ellsworth.com.

We hope you enjoy our very first blog post on two component adhesive packaging!