CO.sub.2 cleaning system and method

• US 5,405,283 A
• Filed: 11/08/1993
• Issued: 04/11/1995
• Est. Priority Date: 11/08/1993
• Status: Expired due to Term

• Current Assignee: Visteon Global Technologies Incorporated (Visteon Corporation)
• Original Assignee: Ford Motor Company
• Inventors: Goenka, Lakhi N.
• Primary Examiner(s): Kisliuk, Bruce M.
• Assistant Examiner(s): MORGAN, EILEEN P
• Application Number:
  US08/148,222
• Time in Patent Office: 519 Days
• Field of Search: 51/317, 51/319, 51/320, 51/321, 51/426, 51/427, 51/428, 51/439, 451/36, 451/38, 451/39, 451/40, 451/89, 451/90, 451/91, 451/102
• US Class Current: 451/39
• CPC Class Codes: B08B 7/02 by distortion, beating, or vibration of the surface to be cleaned B08B7/0007 takes precedence
• CPC Class Codes: B24C 1/003 using material which dissolves or changes phase after the treatment, e.g. ice, CO2
• CPC Class Codes: B24C 3/322 for electrical components
• CPC Class Codes: B24C 5/04 Nozzles therefor nozzles in general B05B
• CPC Class Codes: B24C 7/0084 the abrasive material being fed in a mixture of liquid and gas B24C7/0038, B24C7/0076 take precedence; blasting medium with additives B24C11/005
• CPC Class Codes: H05K 3/26 Cleaning or polishing of the conductive pattern

Abstract

A nozzle expels liquid CO₂ through an orifice for converting the liquid into CO₂ snow. The nozzle is contained within an elongated cavity within a body which in turn is coupled to an exhaust nozzle for directing the CO₂ snow toward a workpiece. A mixing device is provided for receiving and mixing pressurized air at ambient temperature with liquid nitrogen for precooling the air and then directing the resulting mixture of gases into the cavity and toward the nozzle. In this manner, the precooled shop air will enhance the efficiency of the conversion of the liquid CO₂ into CO₂ snow particles.

Claims

1. An apparatus for cleaning a workpiece with abrasive CO₂ snow, comprising in combination:

a nozzle for receiving and expelling liquid CO₂ through an orifice sized for directly converting the liquid CO₂ into CO₂ snow,

a body defining a cavity therein, with said nozzle being coupled to said body for ejecting the CO₂ snow into said cavity,

an exhaust nozzle coupled to said body and said cavity therein for directing the CO₂ snow toward the workpiece, and

mixing means for receiving and mixing pressurized shop air at ambient temperature with liquid N₂ in portions for precooling the shop air to at least 0 degrees F., said mixing means being coupled to said body for directing the cooled shop air into said cavity for cooling the area adjacent to said orifice in said nozzle and for exhausting the CO₂ through said exhaust nozzle under pressure, whereby the cooled mixture of shop air and gaseous N₂ enhances the efficiency of the direct conversion of the liquid CO₂ into CO₂ snow particles.

2. The apparatus as described in claim 1 wherein said mixing means directs the resulting mixture of N₂ and shop air onto said nozzle near said orifice therein for creating turbulence within said cavity for improving the mixture and distribution of the CO₂ snow exiting said exhaust nozzle.

3. The apparatus as described in claim 1 wherein said mixing means directs the resulting mixture of N₂ and shop air onto said nozzle near said orifice therein for at least partially removing the latent heat generated by the conversion of liquid CO₂ into CO₂ snow.

4. The apparatus as described in claim 1 wherein the shape and cross-section of said exhaust nozzle maintains the pressure of the CO₂ and the mixture of shop air and N₂ therein to at least 40 psi, while exhausting the CO₂ snow toward the workpiece.

5. The apparatus as described in claim 1 wherein the pressure of the liquid CO₂ within said cavity defined within said nozzle is at least 200 psi.

6. The apparatus as described in claim 5 wherein the temperature of the liquid CO₂ within said cavity in said nozzle is less than 0°

F.

7. The apparatus as described in claim 1 wherein the length to diameter ratio of said cavity is greater than 10.

8. The apparatus as described in claim 1 wherein the CO₂ snow is mixed with shop air and gaseous N₂ and CO₂ passing out of the exhaust nozzle in the approximate ration of 5 to 1 by mass.

9. A method for cleaning a workpiece with abrasive CO₂ snow, comprising the steps of:

receiving CO₂ in a liquid form at a first pressure and temperature,

passing the liquid CO₂ through an orifice in a nozzle for directly converting at least a portion of the liquid CO₂ into CO₂ snow,

collecting the CO₂ now within an elongated cavity for enhancing the coagulation of the CO₂ snow into snow particles and then passing the CO₂ snow and snow particles through an exhaust nozzle having a contour for directing the flow toward the workpiece,

mixing shop air, at ambient temperature and a pressure of less than 100 psi, with liquid N₂ for cooling the resulting gaseous mixture, and

injecting the cooled mixture of shop air and N₂ into the elongated cavity adjacent the nozzle for improving the conversion efficiency of the liquid CO₂ into snow particles by decreasing the temperature adjacent to the nozzle, and for exhausting the snow particles under pressure through said exhaust nozzle.

10. The method as described in claim 9 wherein the injecting step includes the additional step of directing the mixture of shop air and N₂ onto an area of the nozzle operatively adjacent to the orifice therein for removing latent heat resulting from the flashing of the CO₂ from liquid to snow.

11. The method as described in claim 9 wherein the step of passing the CO₂ snow and gas mixture through the exhaust nozzle further includes the step of accelerating the mixture to a speed of at least Mach 1.0.

12. The method as described in claim 9 further including the step of generating a mixture of exhausted CO₂ gas and snow in the approximate ratio of 0.4 to 1 by mass.

13. An apparatus for cleaning a workpiece with abrasive CO₂ snow, comprising in combination:

a nozzle for receiving and expelling liquid CO₂ through an orifice sized for directly converting the liquid CO₂ into CO₂ snow,

a body defining an elongated cavity therein, with said nozzle being coupled to said body for ejecting the CO₂ snow into said elongated cavity,

an exhaust nozzle coupled into said elongated cavity of said body for directing the CO₂ snow from said elongated cavity toward the workpiece, and

first means coupled to said body for receiving and directing pressurized air at a known temperature into said elongated cavity in the area adjacent to said orifice in said nozzle for enhancing the conversion efficiency of generating the CO₂ snow, for enhancing the coagulation of the CO₂ snow into larger CO₂ snow particles within said elongated cavity, and for exhausting under pressure the CO₂ snow and particles out through said exhaust nozzle,

whereby the pressurized air enhances the efficiency of generating the CO₂ snow particles.

14. The apparatus as described in claim 13 wherein said elongated cavity has a length to diameter ratio of greater than 10.

15. The apparatus as described in claim 14 wherein said first means includes mixing means for receiving and mixing liquid. N₂ from a source thereof with the pressurized air and directing the resulting precooled mixture into said elongated cavity adjacent said nozzle and said orifices therein for creating turbulence within said elongated cavity for improving the mixture and coagulation of the snow exiting said exhaust nozzle.

16. The apparatus as described in claim 13 wherein said mixing means directs the resulting mixture of N₂ and shop air onto said nozzle near said orifices therein for at least partially removing the latent heat generated by the conversion of liquid CO₂ into snow.

17. A method for cleaning a workpiece with abrasive CO₂ snow, comprising the steps of:

receiving liquid CO₂ at a first pressure and temperature,

passing the liquid CO₂ through an orifice in a nozzle for directly converting at least a portion of the CO₂ from the liquid phase into CO₂ snow,

coagulating the CO₂ snow within an elongated cavity to form CO₂ snow particles,

passing the CO₂ snow and CO₂ snow particles through an exhaust nozzle having a contour for directing the flow toward the workpiece,

injecting shop air into the elongated cavity adjacent the nozzle for agitating the CO₂ snow to enhance coagulation of the CO₂ snow particles, and for exhausting under pressure the CO₂ snow particles through the exhaust nozzle.