Contactless dosing

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The non-contact dosage (also: Jetten ; contactless dosing ) is a dose at which a abdosierte, contiguous amount of liquid free - flying towards the destination - that is completely detached from the metering.

characterization

For highly productive, industrial applications and “ Industry 4.0 ”, “jetting” became the term for contactless dispensing, as it implies speed, flying and impulsive throwing.

Essential for the productive applicability of jetting is the repeatable, residue-free detachment of a defined amount of liquid from the dosing opening, as well as the defined movement impulse of the free-flying amount of liquid .

When jetting, the dosing device (dosing valve ) “flies over” the target and, at the appropriate point in time, releases a quantity of liquid which, based on its total impulse and z. B. gravity reaches the destination freely flying.

Typical flight heights of the dosing opening above the target location are more in the millimeter than in the centimeter range, since spherical forces, internal impulses, heat transfer or other reactions with the environment change the shape and properties of the dosing quantity in the flight phase.

Dispensing quantities are typically between 3 nl and 0.5 ml, with a focus on around 10 µl.

The "jetting" method, which is widespread in joining technology , should not be confused with the spraying liquid delivery, often referred to as "jet dosing", for coating surfaces, which is only due to the process technology and also takes place without touching the target object.

Advantages of jetting over contact dosing

  • fewer positioning processes (no height adjustment, no thread breaking movement)
  • faster dosing sequences
  • no carry-over of dosing material
  • smaller dosing quantities possible
  • less maintenance (cleaning)
  • better process definition

Technical requirements of jetting

Due to the necessary kinematic impulse of the dosage and the environmental impact in the flight phase, specific issues arise when jetting:

  • avoidable, more common phenomena :
    • Residual adhesions at the dosing opening, accumulation and change in the detachment behavior (due to change in momentum) up to clogging
    • “Satellite formation” due to delayed partial detachments in the area of ​​the dosing opening
    • "Satellite formation" and / or atomization through internal impulse gradients of the " drops " and their " spherical forces "
    • dynamic changes in shape up to division during flight (e.g. bone or torus shape formation )
    • Splashing from impact at the target location
    • Changes in temperature and viscosity change u. a. the fluid dynamics
  • Requirements for the dispensing mechanism :
    • Application-specific definable opening, passage and especially closing kinetics
    • The smaller the individual dispensing quantity (“dot”), the more important the kinematic impulse component generated when closing is for proper detachment from the dosing opening
    • Highly viscous or strongly adhesive liquids or pastes require strong closing impulses for detachment
  • necessary process parameters to be mastered :

Dosing mechanisms

Mostly pressurized ball seat valves, the ball lock of which is actuated by pneumatic, electromagnetic, electro-pneumatic or piezoelectric actuators , the latter achieving the highest power density and metering frequencies in the kilohertz range and extremely steep switching edges.

Jetting metering valves can be viewed as special cases of a metering pump , as active displacement is used at least in the droplet detachment phase .

Application method

With the leading dosing systems, the amount per dosage can be varied online using the ball lock. It is far greater possible than with well-known printer heads , which could only deliver identical individual quantities. Since the variation of the dispensing amount shows complex effects on the release behavior and dispensing result and is not mastered by simple dispensing devices, various application methods have become established:

  • Standardized individual dosing per destination without quantity modulation
  • Cumulation of standardized individual doses per destination
  • Individualized individual dosing with quantity modulation for each destination

application areas

  • Due to the clean, stable and service-friendly process properties, typically highly productive series production tasks are served by jetting, especially in the manufacture of consumer products such as smartphones or disposable packaging. Liquid and paste-like functional materials from the electronics industry, including adhesives, are mostly jetted .
  • Jetting is a key function for reliable material application in the context of " Industry 4.0 ", e.g. B. in binder jetting (also 3D printing) or additive manufacturing .