Volumetric dispensing

High-precision volumetric dispensing

Volumetric dispensing systems are both mechanically defined and numerically controlled to precisely control the volume and rate of material dispensed. This is different from time-pressure systems in which the dose volume can fluctuate depending on many variables such temperature, viscosity, time i.e. pot life, air volume and system pressures.

mta offers two primary technologies for volumetric dispensing, reciprocating piston pumps and continuous flow progressive cavity pumps. Between the two technologies, we can provide solutions for a broad range of materials; mono- or two-component materials, in a variety of dispensing processes including adhesive bonding, sealing, potting and conformal coating.

Reciprocating piston pump volumetric dispensing

The piston pump has a charging stroke in which material moves into the pump (illustration 2) and a dosing stroke in which material is metered out (illustration 4). Between charging and dosing, the piston rotates to open and close the corresponding ports (illustrations 1 and 3). The dose stroke is numerically controlled making the volume and flow rate extremely accurate and repeatable. After leaving the piston pump, the material can proceed directly to a dispensing needle or a mixing chamber. Read below for more information on the dynamic mixing chamber.

The metering pumps are made of low-wear ceramic material.  Several bore sizes are available to provide a range of volumes. The smallest version can dispense volumes as low as 0.1mm³ with high precision and repeatability.  

Dispensing heads that use reciprocating pumps include the mono-component numerical volumetric dispenser (NVD), the two-component numerical volumetric dispenser (NBD), the mini mono-component numerical volumetric dispenser (mini-NVD) and the mini two-component numerical volumetric dispenser (mini-NBD). The primary limitation of reciprocating pumps is they cannot continuously dose shots larger than the volume of the pump cavity. This is one reason we also offer continuous-flow progressive cavity pumps.

Continous flow volumetric displacement

Continuous flow volumetric displacement pumps use a rotor with one or more helical windings that rotates eccentrically in an elastomer stator. The eccentric movement of the rotor creates a series of cavities that continuously push the material through the pump. The cavities’ complex geometry provides a consistent volume at any phase of rotation, so the flow does not pulsate. 

The precise flow rate is directly controlled by the motor speed. This precision allows the continuous flow dispenser (CFD) to apply long beads with consistent diameters throughout complex contours.

We designed the CFD to be mechanically and chemically compatible with a broad range of materials. It works with low-viscosity, high-viscosity and filled materials.  The rotors, stators and pump housings are available in a range of materials, so we can find combinations suitable for various applications. We even offer inert materials for pharmaceutical and medical applications.

After leaving the continuous pump, the material can either proceed directly to a dispensing needle, static mixing tube or dynamic mixing chamber. Read below for more information on the dynamic mixing chamber.

Two-component material mixing

When applications require two-component materials, mta uses separate pumps for the resin and hardener components before mixing. This applies to the piston and continuous pumping technologies. Since we use individual pumps for each material, we can precisely control the mixing ratio with high repeatability.

After the pumps meter the materials, the resin and hardener move separately into a dynamic mixing chamber. A rotating mixing blade mixes the materials inside the chamber. As with the pumps, the blade’s speed and number of rotations are also numerically controlled.  This provides the correct number of folds without damaging the material.  

Dynamically mixing the material provides two significant advantages over static mixing tubes. First, we can size the mixing chamber according to the shot size – not the number of folds. Hence, the chamber can be much smaller than static mixing tubes. Second, the reaction does not begin until the material is ready to be dosed maximizing the pot life.

As a result, very little residual material reacts between doses and the pot life is maximized. This means mta’s dynamic mixing systems can dose much smaller volumes of material than are possible with static mixing tubes.