The Importance of Vacuum Degas in

Adhesive Dispensing Equipment

 

Ashby Cross often incorporates a vacuum degas system in their meter, mix equipment. Vacuum degas can include each side of the adhesive or just a single side.

 

There are several reasons degas is incorporated into the design.  They include material sensitivity to moisture or air, wide ratios such as 100:7, viscosity, and application.

 

Many urethane’s are moisture sensitive and should be vacuum degassed in the tanks to eliminate the chance of crystal formation. Typically when the equipment is off-line a vacuum is applied to the tank to remove air then the tank is locked up under vacuum.

 

In applications with wide mix ratios it is always important to degas the resin (usually filled and high in viscosity). The catalyst is generally unfilled and thin which usually does not require vacuum degas. High viscosity, filled resins will compress during processing. This always leads to phasing; a term used to describe how the two materials exit the mix valve, and enter the static mixer, at different times. Each time the valve opens the resin could flow before the catalyst or the opposite. At this point the mix is off ratio. As static mixing is generally plug flow, the off-ratio adhesive makes its way down the static mixer and into the part. When soft spots occur in the finished product it is likely due to phasing from the machine.

All vacuum degas systems include an agitator that slowly rotates within the tank exposing all the material to the surface vacuum. In addition, high viscosity adhesives usually require heating to reduce viscosity which enhances vacuum degas.

 

Certain applications such as clear-coating, high voltage potting, casting, and vacuum chamber potting require air-free dispensing to prevent failure or cosmetic blemishes in the product.

In these cases both sides of the adhesive are vacuum degassed.

 

In applications where adhesive is dispensed within a vacuum chamber vacuum degassing of the adhesive to a level lower vacuum level than the vacuum chamber will eliminate splattering of the adhesive during dispensing.

 

 

Including a PLC to in the design of an adhesive dispenser adds a great deal of flexibility and reduces the overall cost of the system. As with most PLCs, added functionality is built in. With the standard system an operator generally controls the operation of the unit.

The Ashby Cross adhesive systems with Intelligent Dispensing combines volumetric shot size control, gel timer, multiple shot sequences, menu selectable programs, and maintenance features.  As an example, if a product requires several shots of different sizes the sequence of shots may be entered into the unit through the HMI. Each time the machine is activated the precise shot size is dispensed each time.

 

Timely maintenance of any two-part adhesive dispensing system is essential to the proper operation of the system. The Ashby Cross units provide feedback to the operator such as the number of times the dispense valve has been actuated and the number of overall cycles the metering section has completed. In addition, maintenance set points can be entered which alert the operator when they are reached.

 

A linear encoder accurately measures the distance the pistons in the metering cylinders travel and relate that information to shot size. Each shot is highly repeatable. The operator only needs to depress the foot pedal.

 

In terms of cost, the built in features provided with the PLC save thousands of dollars over a similar equipped machine with the same features added as options.

 

The Ashby Cross adhesive dispensing systems are accurate, require minimum setup, have no phasing of the adhesives seen in many dispensers, and are simple to operate.

 

Combine Intelligent Dispensing with years of application experience and thousands of field proven systems and you have the seamless reliable dispensing package.

 

Ashby Cross has added a PLC based control system to one of our most popular dispense systems.  The 1125 Variable Ratio piston metering system is an excellent bench-top meter, mix for light to medium production potting. The cylinders and rotary valve used to control flow are hardened which provides many maintenance free cycles especially when using abrasive fillers.

The PLC adds a lot of flexibility to the process. Standard features include a pot life (anti-gel) timer with alarm,  machine controlled shot size via built in encoder, a five shot selectable menu, cycle counters for both  the dispense head and metering section, and cycle set points which provide data for preventative maintenance.

In encoder mode, shot sizes range down to 0.3 cc with a +/- 1% repeatability. Maximum full charge volume is 160 cc at 1:1 ratio. The encoder also will sums the volume dispensed in each cycle and automatically refills the cylinders to avoid fractional shots.

Available options include heating and vacuum degassing, wide range of tanks with or without agitation, remote, hand-held snuff-back mix/dispense gun.

Ashby Cross has manufactured adhesive dispensing equipment for over 35  years. We welcome your dispensing questions – post them in the comments, use our Contact page, or call us at 978-463-0202

 

Potting thousands of small components with a 2-part silicone required an automated adhesive dispensing system integrated with a table-top robot.

The complexity of the dispensing required multiple passes at different flow rates then a final pass to level the adhesive.

The adhesive dispensing system used was a GP8O  gear metering system with vacuum degas capability in the reservoirs. The gear metering provided accurate ratio while the vacuum degas stripped air from the adhesive in the tanks.

When metering two adhesives at the design ratio it is important the two fluids react the same to the applied force. If compression occurs in the metering the ratio will not be accurate.

Programming of the robot is intuitive and done with a teach pendant. No actual code or dimensions are needed.

Almost any potting application can be automated with the wide range of tables available. Either gear metering or piston metering systems can be incorporated into a complete, automated dispensing system.

The versatility of the system permits the potting of different products.

 

Ashby Cross has manufactured adhesive dispensing equipment for over 35  years. We welcome your dispensing questions – post them in the comments, use our Contact page, or call us at 978-463-0202

Selecting adhesive dispensing equipment – Gear vs. Piston metering

Adhesive dispensing equipment is purchased for many reasons, but mostly, like with other capital expenditures, it’s purchased to, reduce waste, increase productivity, yield greater product reliability, eliminate workers exposure to chemicals, reduce adhesive costs in some instances, and generally result in greater profits.
Additionally, an increase in production can sometimes force companies into the purchase because the mix-by-hand method is no longer adequate to maintain production.

Our responsibility at Ashby Cross is to ensure the customer’s needs are met in designing an adhesive dispensing system that will meet their application.

There are a number of considerations in the design. The primary one is the adhesive that will be processed. This drives the type of metering we would select.

A short primer on metering systems

Gear and cylinder/piston are the two most widely used metering devices available when designing adhesive dispensing equipment.  Each is very precise and will accurately proportion the adhesive.
We would consider such things as viscosity, specific gravity, temperature, fillers, filler type, and ratio when deciding which type of metering to use.
The nature of gear pumps, very tight tolerances with rotating parts, does not lend itself to processing highly filled or abrasive fillers in the adhesive. In this instance we would opt for the cylinder/piston metering with abrasion resistant seals.

In either case, the basic system design makes use of two proportioning devices (gear pump or cylinder/piston). Gear pumps are defined by their specific output per revolution, for instance, 3 cc per revolution. Using an example of a 2:1 by volume ratio material we would combine a 3cc/rev. with a 6cc/rev. pump and rotate them at the same speed. The output would be 2:1 by volume.
We can also vary the relative speed of the gear pumps to achieve the desired ratio. For instance combine two 3cc/rev. pumps and rotate one half as fast as the other.

Ratios of 100:100 through 100:7 by volume (continuously through the range) can be achieved by combining different pump sizes and relative speeds.

The benefits of a gear metering system include.

•   Few moving parts
•   Variable flow rates
•   Self bleeding.
•   Adjustable ratio

Cylinder/piston systems offer a broader application range as they can be used in heavily filled, abrasive applications as well as unfilled applications. Viscosity can range from thin to a million or more cps.

Ratio, in the fixed ratio machines, is achieved through the relative volumes of the two cylinders.
For the same 2:1 ratio adhesive example we used above the resin cylinder would have a volume twice that of the catalyst cylinder. The typical Ashby Cross system is pneumatically and hydraulically driven. The hydraulic drive is provided by the adhesive which enters the machine at elevated pressure.

The pneumatic drive is an air cylinder that works in conjunction with the hydraulic pressure.

Ashby Cross has manufactured adhesive dispensing equipment for over 35  years. We welcome your dispensing questions – post them in the comments, use our Contact page, or call us at 978-463-0202