ENGINEERING

Precision Nozzels
Subrex fluid delivery systems are engineered to dispense a measured amount of fluid onto a work-piece in a precise manner. The last point of interaction by the system with the fluid before extrication is the portion of the system that engineers at Subrex have focused their attention on.

Nozzles, needles or tips as they are known and commonly referred to in the industry are designed to straighten, constrict and direct fluid flow to discrete locations on a work-piece. This aspect of the delivery system is often the most overlooked and can be the difference between success and failure of a robotic or automated process to dispense fluids with consistent accuracy and high productivity.

Components are specifically designed and manufactured to optimize system performance that impact conditions upstream. Upstream conditions are dictated by the required flow-rate through the exit aperture of the nozzle, viscosity of the liquid and the pressure required to overcome resistance of the liquid to movement. Movement can be influenced through manipulation of viscosity by the addition or removal of thermal energy from the liquid through the system.

Design details of the body of the nozzle, needle or tip and exit aperture can have a substantial impact in terms of resistance to flow. More pressure is required to achieve the desired flow-rate when the output exhibits high resistance to flow from abrupt transitions between sections and restrictive aperture sizes required for the desired deposit placement. High-pressure requirements force the main upstream system component, the pump, to do more work to achieve the pressure necessary for fluid movement. The result is decreased accuracy and increased variation in the deposit volume. A correctly designed nozzle should not impede flow to the extent that an unnecessarily large pressure delta is caused by fluid flow through the nozzle.

Subrex products are based on engineering derived from extensive simulation and testing and are inherently designed for superior fluid delivery component. Workable design variance are subjected to iterative simulations to ensure compliance with established standards before components are manufactured.
dispensing nozzles

Nozzle offset distance comparison

The illustration simulates the relative distance from the chip that exists in the fluid deposit between a conventional needle and a thin wall nozzle. Thickness of the thin wall nozzle is about 0.002 inch. Subrex nozzles are produced to a run out tolerance of less than 0.002 inch to further enhance placement precision of the fluid deposit.


Relative Thermal Performance Comparison of Component Construction Materials

The chart shows the approximate thermal performance between various materials used in construction of nozzles and needles relative to each other. Thin wall nozzles are primarily constructed from copper alloys. Nozzles can efficiently transfer heat into or out of the fluid to manipulate the viscosity of the fluid. Some applications require heat to reduce viscosity, others can benefit from removal of heat to increase viscosity. Manipulation of temperature can be a useful tool for process optimization.


Flow comparison nozzle to cannula

The graphic representation above illustrates the superior advantage in flow rate Subrex thin wall nozzle technology has in comparison to competitive nozzle designs. Short and long cannulae are ¼ inch and ½ inch respectively. Comparison was made using the same fluid with equivalent pressure and time. Effective flow rate difference is dramatic between components.

The Subrex advantage increases as the nozzle size decreases. Thin wall nozzle technology performance is enhanced as wall size becomes a sizable percentage of the nozzles total projected area in smaller nozzles. Wall thickness is varied as a function of pressure acting against the walls at a specific diameter to achieve the largest aperture possible while minimizing deflection for a given pressure.

Traditional medical gage tubing is based on a standard that is a function of the outside diameter dimension. Standard gage Subrex nozzles comply with this standard. A larger inside diameter for an equivalent outside diameter, generous transitions between sections, smooth walls and monolithic design all work in concert to enhance performance.


Thin wall technology nozzle (tt) in comparison to plan of record needle (por)


This graph shows the dramatic reduction in flow rate variance that occurs on a positive displacement pump when Subrex Thin Wall Nozzles are used. Both components are 20 gage. The POR is a short, machined cannula style needle. Difference in width of the two curves illustrates the disparity by the distance between the tolerance limits for 99% of the population with 95% confidence. Reduction in flow rate variance is approximately 510% or over five times less in comparison to the POR. This demonstrates the superior repeatability of the Subrex nozzle at achieving the desired flow rate.

Significant reduction in backpressure reduces deflection of fluid path components and work energy requirements. Target flow rate is realized more rapidly due to reduced resistance to flow in the path. Fluid deposits are more precise when dispense time is short.



Back pressure between subrex 19 gage nozzle and 18 gage machined ¼ inch long cannula

Pressure measured at 65 mg/s flow rate for high filler content under fill epoxy. Cannula peak pressure delta is more than 80% greater in comparison to the Subrex nozzle at the same flow rate.

Start and stop of deposit is crisp with the Subrex nozzle. Pressure is almost vertical rising and almost vertical falling to 10psi with only slight curvature past that point as pressure returns to zero for the Subrex nozzle. Pressure remains relatively constant once steady state flow is achieved.

Cannula style needle pressure rise continues to increase although at less dramatic slope for the entire duration of the dispense time. Pressure never comes close to reaching a steady state response.

Subrex nozzle pressure profile represents a low peak pressure combined with rapid rise and fall from transient to steady state pressure. This reduction in amplitude of the pressure pulse for thin and viscous fluids is a desirable attribute to have in a nozzle. The rapid decay of pressure in response to termination of flow in Subrex nozzles reduces unwanted bolus volume.

Cannula pressure profile continues to decay for a substantially longer period of time after flow termination, pushing out additional bolus volume onto the work-piece. Drastic measures are necessary upstream to force compensation at the cannula to alleviate undesirable affects.