WO2019040702A1 - Extraction of laser generated air contaminates - Google Patents

Abstract

Effluent extraction for laser processing is disclosed, A pre-filter condenser unit extracts LGACs in an effluent stream. The effluent stream passes a serpentine path in the condenser. Condensate and particles are collected on rotatable blades. The blades are combed to remove collected materials for disposal.

Description

EXTRACTION OF LASER GENERATED AIR CONTAMINATES BACKGROUND OF THE INVENTION Field of the Invention

[001 ] The field of the invention is effluent fume extraction for laser processing. More particularly, the invention relates to air flow pre-filiering for laser-based surface cleaning and paint stripping.

Background of the invention

[002] Laser radiation has long been used in material processing applications that include cleaning and paint removal. Now, with high average power lasers and high power pulsed lasers, the field of applications are widening. These improved lasers allow for processing of a wider variety of materials as well as thicker materials. Some laser processed material can generate toxic chemicals and contaminates that need to be carefully collected and disposed of in appropriate safe sites. This special handling and disposal can be very expensive, and generally laser processing can limit disposal volumes when compared with liquid based stripping.

[003] In the laser ablation process the material comes off in hot gases and particles as so called Laser Generated Air Contaminates (LGACs). The LGACs are to be taken away with some form of a smoke evacuator that has filters to absorb and or condense the material. The air is filtered to the point that it can be safely returned to the room or outside while contaminates are collected for disposal. In some laser processing applications thick layers of material are laser processed and the LGACs effluent condenses quickly in fume exhaust nozzles and extraction hoses before reaching downstream filters. The extraction hoses can be several meters long and over the course of days or months of use, the hoses can fill up with the condensed toxic material

[004] It will be appreciated that frequent cleaning and or disposal and replacement of exhaust nozzles and hoses is costly and time consuming. Thus, improvements are needed for the extraction of effluent materials in laser material stripping BRIEF SUMMARY OF THE INVENTION

[005] In at least one embodiment of the present invention, a method of extracting LGACs from a laser processing site is provided. LGACs flow into an effluent extraction nozzle inlet, the air flow is modified to an annular cross section and directed along a serpentine path in a cylindrical condenser chamber. The serpentine path is formed by air spaces between adjacent blades in a stack of blades and by staggered openings in the blades that connect the air spaces. Effluent material condenses on one or more blades in the cylindrical condenser chamber, collected material is scraped off the blades by rotating the blades such that each blade passes between tines of a scraper comb, and scraped material is collected in a receptacle for disposal.

[006] The LGACs may be generated from high volume laser stripping, and the annular flow may be generated with a diffuser cone. The blade opening may be slots directing the air flow from a first air space on one side of a blade to a second airspace on a second side of the blade through one or more slots in the blade. A motor coupled to a drivetrain may rotate a blade mounting hub and the mounted blades. The scraper comb tines may be interdigitated with the stack of blades. Material may be vacuum extracted from the receptacle using a vacuum extraction port. The method may generate an outflow of pre-filtered air from the condenser chamber, filter the outflow, and return filtered air to the workspace. The serpentine path may be a branched network serpentine path.

[007] In other embodiments of the present invention, an LGACs extraction system is provided. An effluent inlet receives an air stream containing LGACs, a diffuser cone generates an annular effluent airflow, a condenser receives the annular air flow, directs the airflow along a serpentine path, condenses gases and collects particulate matter onto a stack of condenser blades, and scrapes the blades to remove condensed material which is received in a receptacle for removal. An outlet provides for pre-filtered effluent exiting from the condenser.

[008] The stack of condenser blades may be a stack of slotted blades fixed to a rotating blade hub with air spaces between adjacent pairs of blades. The slots may be oriented to provide a serpentine path through the condenser, and means may be provided for rotating the stack of blades through an interdigitated scraper comb. The system may include a vacuum extraction port. Each blade may have at least two slots. BRIEF DESCRIPTION OF THE DRAWINGS

[009] The above and other aspects, features and advantages of the disclosure will become more readily apparent with the aid of the following drawings, in which:

[010] Fig. 1 provides a view of an embodiment of the invention,

[01 1 ] Fig. 2 provides a cross sectional view of an embodiment of the invention.

[012] Fig. 3 provides a view of a stack of blades according to an embodiment of the invention.

DETAILED DESCRIPTION OF THE INVENTION

[013] In at least one embodiment of the present invention, a material approximately 1 mm thick is to be ablated with a laser over an area that can be several thousand square feet. However, even in ablation of small areas, we have found that laser ablated material is rapidly deposited in an unimproved fume exhaust nozzle and hose to the point that it blocks air flow. The blockage can be removed by mechanical scraping to restore good air flow, good effluent extraction, and to avoid site contamination from fume venting due to poor extraction air flow. For efficient laser processing, it is highly advantageous to limit or eliminate the need for clearing blockages. We have found that a novel extraction unit with a pre~filter condenser close to the extraction point effectively manages effluent condensation and reduces build up in the trailing vacuum extraction hoses that lead to the air filters and vacuum system.

[014] Referring now to FIG. 1 , the extraction unit includes nozzle inlet A, outlet B, condenser section C, and waist receptacle D. The waist receptacle may include a vacuum port E for convenient particulate extraction. The optional vacuum port E is a separate port from the air flow outlet B. E is used to remove debris resulting from pre-filtering, whereas B provides a flow path of pre~fiStered effluent to the downstream filters and vacuum system.

[015] Extraction air flow is drawn into the unit at the nozzle inlet which may be for example a 3" diameter inlet port. Now referring to FIG. 2, to facilitate laminar flow toward the condenser, a diffuser cone F coaxial with the axis of the inlet may direct air flow from a circular cross section at the inlet to an annular cross section at the condenser with flow directed away from a central hub in the condenser. The outer diameter of the nozzle may increase in diameter to the annulus outer diameter to maintain laminar airflow to the condenser. [016] The condenser section receives the annular flow and provides a long flow path that allows sufficient time for the gases to cool. The flow path for the hot gases and particles follows a serpentine path formed inside a cylindrical condenser chamber and condensed gasses and particles collect inside the unit. The serpentine path flows through a stacked series of rotatable disk shaped circular blades and intervening air spaces of blade assembly G, The serpentine path may be a branched serpentine path network with multiple flow paths branching and recombining from a first set of blade openings in a first blade to multiple flows in an intervening air space and to a second set of blade openings in a second blade, A drive motor is coupled at drive train I to the blade assembly through a rotatable mounting hub to rotate the blades about the axis of the cylindrical chamber. As the blades rotate, each blade passes between tines of a scraper comb H, and a portion of the collected particles and condensate are removed from the blades. The profile of the scraper comb is interdigitated with the blades and air spaces. The material scraped from the blades is collected in a waste receptacle, for example the material drops into a removable bin for vacuum extraction.

[017] Now referring to FIG. 3, each blade has one or more opening to direct the flow through the disk from one air space to the next along the serpentine path within the condenser chamber, For example, blade J has slots at 0, 90, 180 and 270 degrees and blade K has slots at 45, 135, 225 and 315 degrees such that a serpentine path is formed at L, The edges of blades are in close proximity to the cylindrical chamber inner wall limiting flow from air space to air space at the disk diameter. The slots may extend radially through the blades from the rotation axis toward the chamber wall in at least one embodiment, the slots extend from a rotatable hub to the edge of the circular blade. The slots may extend partially between the hub and the chamber wall. From one blade to the next blade, the slots are staggered such that the flow path is serpentine. As the effluent stream follows the serpentine path, material is extracted from the stream as it collects on the blades.

[018] In this way, debris collected in the extraction unit minimizes the exposure of downstream filtering hardware to potential blockage and extraction flow is maintained to limit exposure of the worksite to on an overflow of LGACs. It will be appreciated that different arrangements of blade openings can be used to creating a serpentine path such that condensation and collection of contaminates is provided. The invention is not limited to any particular arrangement of openings such as the blade slots in the example above.

[029] In at least one embodiment, the blades are rotated continuously and this allows the exhaust system to operate continuously at optimal efficiency while maximizing the time between hose replacement. In other embodiments, the blades are rotated periodically.

[020] Those skilled in the art will recognize or be able to ascertain using no more than routine experimentation many equivalents to the specific embodiments of the invention described herein. The disclosed schematics can be used with any laser processing system, but the impetus for the presently disclosed structure lies in laser-based paint stripping. It is therefore to be understood that the foregoing embodiments are presented by way of example only and that within the scope of the appended claims and equivalents thereto, the invention may be practiced otherwise than as specifically described. The present disclosure is directed to each individual feature, system, material and/or method described herein. In addition, any combination of two or more such features, systems, materials and/or methods, if such features, systems, materials andior methods are not mutually inconsistent, is included within the scope of the present invention.

Claims

1. A method of extracting LGACs from a laser processing site comprising,

generating an air flow of LGACs into an effluent extraction nozzle inlet,

modifying the air flow to an annular cross section,

directing the airflow along a serpentine path in a cylindrical condenser chamber, the serpentine path formed by air spaces between adjacent blades in a stack of blades and by staggered openings in the blades that connect the air spaces,

condensing effluent material on one or more blades in the cylindrical condenser chamber, scraping collected material off the blades by rotating the blades such that each blade passes between tines of a scraper comb, and

collecting scraped material in a receptacle for disposal.

2. The method as in claim 1 , wherein the LGACs are a byproduct of high volume laser stripping of a thick material layer of 1 mm or more from a substrate, over at least 1 square meter of area.

3. The method as in claim 1 , wherein the LGACs are a byproduct of a volume of at least 10 liters of laser stripped material from a single workpiece.

4. The method as in claim 1 , wherein modifying the air flow to an annular cross section comprises modifying the air flow with a diffuser cone.

5. The method as in claim 1 , wherein the blade openings are slots.

6. The method as in claim 1 , wherein directing the air flow comprises directing the air flow from a first air space on one side of a blade to a second airspace on a second side of the blade through one or more slots in the blade.

7. The method as in claim 1 , wherein rotating the blades comprises rotating a blade mounting hub with a drivetrain that is coupled to a motor.

8. The method as in claim 1 , wherein the tines of the scraper comb are interdigitated with the stack of blades.

9. The method as in claim 1 , former comprising vacuum extracting material from the receptacle using vacuum extraction port.

10. The method as in claim 1 , Further comprising generating an outflow of pre-filiered air from the condenser chamber, filtering the outflow, and returning filtered air to the workspace.

11. The method as in claim 1 , wherein the serpentine path is a branched network serpentine path.

12. An LGACs extraction system comprising,

an effluent inlet configured to receive an air stream containing LGACs,

a diffuser cone configured to generate an annular effluent airflow,

a condenser configured to receive the annular air flow, direct the airflow along a serpentine path, condense gases and collect particulate matter onto a stack of condenser blades, and scrape the blades to remove condensed material,

a receptacle configured to receive the removed condensed material, and

an outlet for pre-filtered effluent exiting from the condenser.

13. The system as in claim 12 wherein the stack of condenser blades comprises a stack of slotted blades fixed to a rotating blade hub, respective air spaces between adjacent pairs of blades, the slots oriented to provide a serpentine path through the condenser, and means for rotating the stack of blades through an interdigitated scraper comb.

14, The system as in claim 12 further comprising a vacuum extraction port.

5, The system as in claim 12 further comprising a downstream air filter and vacuum system.