Two Stage Waterjet and Abrasive Jet Catcher

This invention pertains to catchers for high pressure waterjets and abrasive laden waterjets.

Waterjet cutters have been in use for the last decade to cut a wide variety of materials. Such a cutter commonly utilizes a source of high pressure liquid such as a hydraulic intensifier, a conduit system and a nozzle. Such a system is described in U.S. Pat. No. 4,435,902. One element of such a device is a catcher to absorb the energy of the cutting after the work is done. A typical catcher is a tube filled with a liquid.

Entraining abrasive particles in ultra-high pressure (over 20,000 psi.) waterjets has vastly improved cutting performance. Though still in the development stages, the abrasive-waterjet cutting techinque has already displayed its advantages over conventional methods in several special applications. It is now possible to effectively cut many materials that could not be cut with waterjets alone, including metals, ceramics, glass, etc.

To develop the market potential of this technique, it is necessary to reduce or eliminate a few critical limitations which prevent it from being widely adopted by the industry. One of the most severe limitations is lack of equipment portability. Other limitations include the lack of an efficient system to catch water and spent abrasives, and the high noise level associated with the breakup of the abrasive-waterjet stream.

Abrasive particles are highly destructive, even after cutting through hard materials. Currently, the energy of the abrasive-waterjet is dissipated in a water tank at least 2 feet deep. Shallower vessels have proved ineffective, because a stationary abrasive-waterjet can easily cut through 0.25" steel plate at the bottom of a 15" water column. Thus, an X-Y table requires a tank large enough to cover the maximum cutting area. The bulky tank restricts maneuverability, which is a prerequisite for robotic and many factory applications. Further, the action of the abrasive-water jet churns the water and abrasives in the catcher/tank, increasing spillage. Also, frequent cleaning of the catcher/tank is necessary to remove used abrasives and residues that accumulate during cutting. Aside from these problems, the tank itself serves as a reesonator that radiates noise. It is extremely difficult to incorporate an effective noise suppression device into such a system.

The following criterion have been established to describe a catcher for waterjets and abrasive-laden waterjets:

1. Adequate protection to the wall and bottom of the catcher

2. Minimal size and weight for portability and maneuverability

3. Minimal vibration to facilitate accurate cutting performance

4. Facilitate discharge of water and abrasives to a hopper for ease of removal and clean up

5. An effective noise suppression device to protect operators

An attempt has been made to use a 24" long tube catcher filled with water alone. However, this length may be unacceptable for many factory applications, especially robotic operations, and the water column is inadequate unless a carbide plug is used to protect the bottom of the catcher. In cutting operations the deflection of the abrasive-waterjet causes severe damage to the tube wall. The longer the catcher, the more vulnerable is the side wall. A wear-resistant liner such as a carbide sleeve for the tube catcher inner wall would be quite expensive.

The invention provides a simple catcher for waterjets and abrasive-laden waterjets that both reduces noise and slows the jet and which is characterized by a relatively long life.

The catcher includes several parts. First, an entry section minimizes noise escape and vibration. Second, a damping section utilizes the flow of liquids to reduce wear on the catcher and minimizes the size of the catcher, next, a noise reducing section markedly reduces the noise generated by the jet, and finally, an exit section facilitates discharge of water and abrasives.

FIG. 1 is a section front elevation view of the invention.

FIG. 2 is a section front elevation view of the entry section of the FIG. 1 embodiment.

FIG. 3 is a section front elevation view of a second embodiment of the damping section of the invention.

FIG. 4 is a section front elevation view of a third embodiment of the damping section of the invention.

FIG. 1 is a section elevation view of the invention. A high pressure waterjet or abrasive waterjet from a jet cutting apparatus such as described in our U.S. Pat. No. 4,216,906 enters the entry section 2 of the invention. Entry Section 2 includes an inlet 3 of reduced diameter which allows passage of jet 1 but retards emission of sound. The jet then proceeds into the damping section 4 of the invention. When jet 1 enters inlet 3 air is also sucked into the catcher due to the aspiration principle. Damping section 4 includes a fluid filled chamber 6 which is preferably cylindrical in cross section. The end 7 of section opposite inlet 3 is closed by a cap 8. Cap 8 is protected by a plug 9 of wear-resistant material such as a metallic or non-metallic carbide (WC, SiC or ceramic (AL.sub.2 O.sub.3)). As jet 1 enters the fluid in chamber 6 it flows toward plug 9 until its kinetic energy is spent. The only outlet from chamber 4 is an outlet 11 placed between inlet 3 and plug 9 and preferably closer to inlet 3. No outlet from inlet 3 is possible due to entrance of fluid jet 1 and asperated air. The spent fluid is thus forced to flow upward toward outlet 11 in opposition to jet 1. This return flow is indicated by arrows 12. The return flow aids in absorbing the kinetic energy of jet 1. Upon exit from damping section 4 fluid flow proceeds down a passage 13 into the noise reducing section 14 of the invention. The fluid flow at this point includes liquid, air and solid particles. Section 14 is preferably a hollow cylinder with a inlet tube 16 extending nearly to one end 17 and an outlet section 18 at the other end. The dimensions of chamber 14 are chosen to maximize sound absorption. In operation, section 14 is filled with fluid with inlet tube 13 outlet 19 always below liquid level. The exiting liquid and air must thus pass through liquid which further reduces noise escaping through the outlet section 18. Fluid and air finally flow through outlet section 18 to a hopper (not shown) to allow separation of fluid, abrasive and air.

FIG. 2 is a detail section elevation view of the entry section of the FIG. 1 embodiment. It is often the case that 1 the path of a water jet (not shown) is displaced from the vertical into positions 1a or 1b. This deflection is more noticeable when cutting thick materials and is inherent to the cutting process. Also, this displacement may be due to a misaligned jewel in the jet-forming nozzle or an off center jet-forming orifice in the jewel. This could result in collision of jet 1 with entry inlet 3 resulting in erosion of inlet 3 and its ultimate destruction. To allow for this possibility, inlet 3 is provided with alignment means 21. Alignment means 21 in this embodiment includes a round ring 22 with a spherical outer surface 23 attached to entry inlet 3 and an annulus 24 with a mating surface 26. Alignment means 21 thus allows adjustment of the entry section to allow for offset jets. Alternative means of alignment would be apparent to a person skilled in catcher construction.

FIG. 3 is a section elevation view of a second embodiment of the invention. This embodiment is identical to the FIG. 1 embodiment except for the addition of a converging diverging surface 31 to the interior of damping section 4. The entry, noise reduction and exit section (not shown) are identical to the FIG. 1 embodiment. Surface 31 is preferably constructed of a wear resistant material such as a metallic carbide. The return flow 12 is forced to increase its velocity in the vicinity of the throat 32 of surface 31. The increased velocity return flow acts to brake jet 1's velocity and absorb energy in less space than in the FIG. 1 embodiment. This allows damping chamber 4 to be made shorter than the FIG. 1 embodiment. A shorter catcher is particularly useful for mobile cutter applications.

FIG. 4 is a section elevation view of a third embodiment of the damping section of the catcher. In this embodiment the parts and function are identical to the FIG. 3 embodiment except that surface 41 is constructed from a plurality of rings 42. The rings have different inside diameters to form a throat area 43 analogous to area 32 in FIG. 3. Rings 42 may be metallic in a water jet catcher or could be ceramic or a metallic carbide if the jet is abrasive laden. Rings 42 are cheaper to fabricate than a carbide liner.

The embodiments shown are exemplary only the invention being defined solely by the attached claims.