Print Head Shear Section Prevents Nozzle Clogging
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Solution Overview
Problem
Highly filled suspension fluids used in printing technologies often clog nozzles due to bridge formation and particle agglomeration, leading to interruptions and reduced yield, as existing solutions like filtration are not practical and do not fully address the issue.
Innovation Solution
Increasing the shear rate within the flow path before the nozzle outlet using a return flow path to break up particle agglomerations, thereby preventing bridge formation and clogging, while maintaining larger flow path dimensions and controlling the flow rate through the nozzle outlets.
Engineering Contradictions & Design Principles
Engineering Contradiction Analysis
1Reliability
If the nozzle outlet diameter is increased to prevent clogging, then particle bridge formation is reduced, but droplet size increases and flow rate through the nozzle increases
Solution Approach 1:
The flow path is segmented into a supply channel and a return channel that are spatially separated. The supply channel delivers suspension fluid to the nozzle outlet, while the return channel removes excess fluid downstream. This segmentation allows independent optimization of each channel's dimensions and flow characteristics, enabling prevention of clogging in the supply channel while maintaining precise droplet control at the nozzle outlet.
Solution Approach 2:
The invention transitions from a single-channel flow path to a dual-channel flow path configuration. By adding the return channel as a separate dimensional pathway, the system can control flow rate and shear rate independently from nozzle outlet dimensions, resolving the contradiction between clogging prevention and droplet size control.
2Reliability
If a filter is used to remove large particles, then clogging is reduced, but the system requires frequent cleaning or replacement and adds complexity
Solution Approach 1:
The invention extracts the harmful function of filtration (physical barrier removal) and replaces it with a beneficial hydrodynamic function (shear-induced particle separation). By taking out the filter component entirely and using flow path design to achieve particle management, the system eliminates maintenance requirements while maintaining clogging prevention.
Solution Approach 2:
The mechanical filtration system is replaced with a hydrodynamic system using controlled shear flow. Instead of using a physical filter to remove particles, the invention uses fluid mechanics (shear forces in the supply channel) to prevent particle agglomeration and bridge formation, thereby preventing clogging without mechanical filtration.
3Productivity
If the flow rate through the nozzle is increased to maintain droplet ejection, then printing productivity improves, but particle agglomeration and bridge formation increase
Solution Approach 1:
The return channel is positioned downstream of the nozzle outlet to remove excess suspension fluid after it has passed through the nozzle. This preliminary removal of excess fluid prevents particle agglomeration and bridge formation before they can occur at the nozzle outlet, enabling high flow rates without clogging.
Solution Approach 2:
The return channel acts as an intermediary element between the nozzle outlet and the collection point. It mediates the flow by selectively removing excess suspension fluid that has passed through the nozzle, thereby controlling the effective flow rate through the nozzle while maintaining high overall system productivity.
Applied Scientific Principles
This section explains which scientific principles are used to turn an abstract innovation direction into a practical engineering solution.
Function Achieved in This Case
This approach effectively prevents nozzle clogging by breaking up agglomerations with sufficient shear forces, ensuring stable droplet flow and reducing maintenance interruptions, allowing for reliable printing of suspension fluids with varying particle sizes.
Implementation Method 1
a supply pump (5) for establishing a flow within the flow path
Implementation Method 2
an actuator (7) for imparting pressure fluctuations on the suspension fluid at the one or more nozzle outlets for generating one or more droplets therefrom
Implementation Method 3
a return channel (33) for allowing excess fluid not ejected from the nozzle to flow away from the one or more nozzle outlets
Data Source
Figure 1
Figure 2A
Figure 2B
AI summary
The invention is directed at a print head for printing a suspension fluid. The print head comprises a nozzle having one or more nozzle outlets for allowing the suspension fluid to be ejected from the nozzle, a flow path including a supply channel for supplying the suspension fluid to the one or more nozzle outlets, and a supply pump for establishing a flow within the flow path. The nozzle further comprises an actuator for imparting pressure fluctuations on the suspension fluid at the one or more nozzle outlets for generating a stream of droplets therefrom. The flow path further comprises a shear section for locally increasing the shear rate at least at a location in the flow path upstream of the one or more nozzle outlets. The flow path further includes a return channel for allowing excess fluid not ejected from the nozzle to flow away from the one or more nozzle outlets. The shear section is configured to locally increase the shear rate to be larger than a shear rate obtained near at least one of the one or more nozzle outlets. The invention is further directed at a printing apparatus, a method of printing, and a method of manufacturing a print head.