precision dispensing webinar peter swanson & paul whitehead intertronics wednesday may 2, 2012...
TRANSCRIPT
Precision DispensingWebinar
Peter Swanson & Paul WhiteheadINTERTRONICS
Wednesday May 2, 2012
11:00 AM
You are familiar with dispensing!
Success! Failure!
Ideal application process
Pre-determined volume Applied to the same location
Accurately Repeatedly
Medical device manufacturingValidated repeatability
Micro-electronicsPrecision
But all engineers want to remove variability in their process
Material examples
Adhesives2 partsThermally or electrically conductive
Coatings Oils Inks Paint Greases Solder paste Enzymes or catalysts
Part of the design process
The process of material or adhesive specification must include consultation with manufacturing & processing engineers
How will it be dispensed/applied?Can it be dispensed/applied?
How the material is purchased makes a difference
Why use a dispensing system?
Measured amount No more, no less
Consistency & repeatability Fewer rejects
Speed Faster than a human
Removes skill factor Reduces waste & mess Health & safety
Reduced exposure to chemicals Operator fatigue, RSI
Can’t be done manually Precision, gaskets
Result?
Quality Economy Throughput
Factors affecting dispensing technique
Packaging 1 part, 2 part, multi-part
Mix ratio Viscosity Thixotropy Fillers
Abrasiveness Settling Compressibility
Behaviour with temperature Hot melt
Stability & reactivity Cure mechanism
Pot life or working life
Dispense pattern Corrosiveness
Metal parts Solvents
Seals? Hazards
Toxicity Flammability
2k – two or multi-part systems
Complex subject!
Time/pressure dispensing
Simple time/pressure dispensing from barrel (syringe) Few £100s Very popular
Control of time/pressure
Pressure of air pulse Time of air pulse Size of needle
Diameter of 0.25mm up 0.06 possible
Rheology of material
Suitable for manual use or as part of automation
Reasonably accurate +/- 1-10%? Digital timers
Issues with time/pressure
Air is compressible, liquid is not Repeated compression of air (pulsing) causes heat
Issues with time/pressure
Delay in dispense whilst waiting for air compression As barrel empties
Less liquid, more air More compression time needed Dot size decreases
Issues with time/pressure
Material viscosity can changeWith temperature
Pulsing Ambient temperature
With time Cure
Dispensing valves
Why use a dispensing valve?
Accuracy Remove the variable of air volume increase as the dispensing
barrel empties Mitigate the effects of temperature induced viscosity changes
Challenging materials Liquids with characteristics at the extremes
Cyanoacrylate adhesives(very low viscosity) Thermally conductive RTV silicone adhesives (very high viscosity)
Why use a dispensing valve?
Volume Largest dispensing barrel typically 55ml Dispensing cartridges available with a capacity of 400ml or more
Not suitable for handheld use? Barrels and cartridges need to be filled off-line, and changed
when empty. For higher daily volumes some form of larger reservoir is needed
Automation Valves can be fixtured to a robot and provide better stability than
a dispensing barrel
Valves – material feed
ReservoirPressurisedGravity feedExtrusion pumpCartridges and barrels
Valves - types
Pneumatic control most popular Robust Accurate Can be cycled quickly Often implemented at low cost
Pinch tube Diaphragm Spool Needle Poppet
and Spray!
Valves - operation
True volumetric dispensing
True, volumetric dispense has led to the development of valves which work on a “positive displacement” principle
1) Within the valve, a cavity of the desired volume is filled with the liquid, and then this volume is ejected – mechanically or pneumatically
2) Auger screw inside a tube which can be driven by a motor
These valves are usually specific to a limited range of deposit size or to certain viscosities
Positive displacement valve
Progressive cavity pump
Single-helix metal rotor and a double-helix hole in an elastomeric stator
Rotor seals against the stator, forming a series of spaces or pockets, which translate along as the rotor rotates, keeping their form and volume
Pumped material is moved inside the pockets Pockets are shaped such that they taper and overlap The output is
ContinuousEvenNon-pulsing
Progressive cavity pump
Endless-Piston-Principle®
Imagine a piston pushing on a liquid
Or several pistons in sequence
Make the piston thickness zero
Change the piston shape
A continuous or “endless” piston
Positive displacement dispensing
Flow rate is directly proportional to the rate of rotationCan be reversed
Volumetric output of the pump is directly proportional to the number of rotations
Due to the rotor/stator seal, input pressure has no effect on the pump
Able to pump at very low rates Low levels of shear are applied to the pumped fluid True positive displacement dispensing/dosing
Practical application
Controller allows programing of the motor Speed and number of rotations Dots or deposits of specific volumes, or
continuous beads Motor can be reversed briefly to prevent
stringing or dripping Dispensing needle is fitted to the end of
the pen using a standard luer fitting
Practical application
Once material characterised - desired volume can be selected on the controller
Dispensed regardless of material viscosity changes
Independent of ambient temperature Viscosities from water up to very high
viscosity pastesIncluding abrasive, filled or shear-sensitive
media Flow rates range from ~ 0.1 to 60
ml/minute Can be hand-held or fitted to automation
Capabilities
Highest precision of at least ± 1% and reproducibility over 99% of the medium
With automated handling Dispensing a bead is accomplished by setting one parameter -
the volume flow; matched to the speed of a robot or other automation, possible to dose coherent beads down to a width of 250 µm and at traverse speeds of up to 300 mm/s
Metering & mixing
Metering and mixing two component materials
Two pumps supply the components to a static mixing nozzle in the correct volumetric ratio
Contact dispensing
Practical limitationsSpeedVolume - 0.1 µl minimum?Release of material from needle
Have to touch material to receiving surface
Leads us to non-contact dispensingStamping or pin-transfer
Jetting dispense valves
Fast-pneumatic or piezo driven From ~1nL Up to ~1000Hz dispensing frequency Up to ~2,000,000 mPa.s viscosity
Material dependentValve technology used
A word on needles
Smooth flow for filled materials Avoids agglomerations Thin rigid metal construction Accuracy ID from 0.06mm to 1mm
Summary
Many applications are relatively simpleSingle partNot extreme viscosityNon-curing, only cure with outside energy or catalyst, long pot lifeNot hazardous, corrosiveModest outputs
Volumes, speeds
BUT many applications fall outside thisCan get quite complicatedConsult with both your material supplier and your dispensing
supplier
Our Products
Adhesives Dispensing Robotics UV & Light Curing
GasketsPottingSealants Metering & Mixing
Coatings Masking Cleaning
