WO2010027947A2

WO2010027947A2 - Drainable degasser for molten materials

Info

Publication number: WO2010027947A2
Application number: PCT/US2009/055560
Authority: WO
Inventors: Dawid Smith
Original assignee: CAST SERVICES Inc
Current assignee: CAST SERVICES Inc
Priority date: 2008-09-02
Filing date: 2009-08-31
Publication date: 2010-03-11
Anticipated expiration: 2011-03-02
Also published as: WO2010027947A3

Abstract

An improved degasser, 10, for a liquid, 1, and preferably molten aluminum. The degasser has a liquid supply inlet, 12, for supplying a first volume of liquid to an inlet junction, 40. A degassing chamber, 18, has an entrance orifice, 11, for receiving the liquid and an exit orifice, 28, for discharging degassed liquid to an outlet junction, 42. A pump, 16, is between the inlet junction and the degassing chamber for pumping liquid from the inlet junction to the degassing chamber. The outlet junction is capable of receiving degassed liquid from the degassing chamber and directing a second volume to a liquid outlet and a third volume of liquid to a recirculating manifold, 30. A recirculating manifold transports the third volume to the inlet junction.

Description

DRAINABLE DEGASSER FOR MOLTEN MATERIALS

CROSS-REFERENCE TO RELATED APPLICATIONS

[0001] The present application claims priority to pending U.S. Provisional Application No. 61/093,569 filed 9/2/2008 which is incorporated herein by reference. BACKGROUND OF THE INVENTION

[0002] The present invention is directed to an improved degasser for molten materials. More particularly, the present invention is directed to an improved degasser for molten materials which is drainable and which has increased degassing capabilities .

[0003] Utilization of molten materials frequently includes a degassing step. The gas being removed is dependant on the molten material. In a particularly relevant application, molten aluminum is typically treated to remove dissolved hydrogen prior to casting thereby avoiding voids within the cast which result from hydrogen bubble formation during solidification. Other metals have similar issues and the present application can be utilized therein. Other non-limiting examples of undesirable gas entrainment are oxygen in water.

[0004] Removal of hydrogen from aluminum is a particularly challenging task due, in part, to the high temperature of molten aluminum and the desire to retain the aluminum at molten temperatures for as short a period of time as possible due to the energy requirements of maintaining the aluminum at melt temperature .

[0005] Hydrogen removal may involve some type of agitation coupled with a flow of a carrier gas. The removal of hydrogen in this manner is widely understood to be described by Sievert's Law which is not further described herein since this is a widely known concept. In general, the hydrogen is absorbed by a carrier gas and is therefore removed in a bubble of carrier gas. [0006] Rotors are typically utilized with carrier gas infusion to increase the surface area thereby facilitating, in the case of aluminum, the dissolution of hydrogen in argon. There is a myriad of art related to the specifics of bubbling and shearing and optimizations thereof. Regardless of the well advanced nature of this technique there is still a major deficiency in that the reaction chamber is typically an enlarged area within the flow system. For example, molten metal initially flows into a chamber which is below the normal flow of the molten metal. This is done to create a large volume within the degassing chamber. Molten metal then flows out of the degassing chamber by overflowing. Baffles and the like are typically utilized to insure adequate residence time within the degassing chamber. When an alloy change is required a sufficient amount of the second molten alloy must be passed through the degassing chamber to displace the previous alloy. This is highly wasteful and leads to a transition alloy casting which is necessarily scrapped.

[0007] A specific method for aluminum degassing is a vacuum degasser. This technique, exemplified in U.S. Patent No. 6,488,743, utilizes a vacuum to draw molten material upward into a chamber which is above the flow of the molten metal. In this case molten metal flows into, and out of, the bottom of the degassing chamber and is drawn upward to at least partially fill the chamber by vacuum. This technique requires a vacuum chamber and seals which inherently adds to manufacturing difficulties. Furthermore, when the chamber has to be cleaned the seals must be broken and reestablished which is labor intensive and adds to the expense associated with degassing. Due to the expense and labor issues it is not uncommon for the degassing operation to proceed well beyond the recommended cleaning frequency thereby allowing inferior aluminum and aluminum oxide to flow to the cast.

[0008] There has been an ongoing desire for an improved degassing operation which avoids those problems associated with the prior art. Such an improved degassing operation is provided herein .

SUMMARY OF THE INVENTION

[0009] It is an object of the present invention to provide an improved degasser.

[0010] It is a particular object of the present invention to provide a degasser which is particularly suitable for use in removing hydrogen from molten aluminum.

[0011] A particular feature of the present invention is the minimal loss of material between changes from one molten material to another.

[0012] An advantage offered by the present invention is simplicity of design which greatly enhances operability and functionality. [0013] These and other advantages, as will be realized, are provided in a degasser for a liquid. The degasser has a liquid supply inlet for supplying a first volume of liquid to an inlet junction. A degassing chamber has an entrance orifice for receiving the liquid and an exit orifice for discharging degassed liquid to an outlet junction. A pump is between the inlet junction and the degassing chamber for pumping liquid from the inlet junction to the degassing chamber. The outlet junction is capable of receiving degassed liquid from the degassing chamber and directing a second volume to a liquid outlet and a third volume of liquid to a recirculating manifold.

A recirculating manifold transports the third volume to the outlet junction.

[0014] Yet another embodiment is provided in a method for degassing a liquid. The method includes the steps of: supplying a first volume of liquid to an inlet junction; pumping the first volume of liquid and a second volume of liquid into a degassing chamber; removing gas from the liquid in the degassing chamber; passing a third volume of liquid from the degassing chamber to an outlet junction; separating the third volume into a fourth volume and second volume; passing the fourth volume out of the degasser; and passing the second volume to the inlet junction. BRIEF DESCRIPTION OF FIGURES

[0015] Fig. 1 is a cross-sectional schematic representation of an embodiment of the invention. [0016] Fig. 2 is a flow diagram illustrating the invention. DETAILED DESCRIPTION

[0017] The present invention is specific to a degasser and method for degassing a liquid or molten material . The invention will be described with reference to the various figures included herein without limit thereto. In the various figures similar elements will be numbered accordingly.

[0018] The invention will be described with reference to Fig. 1. In Fig. 1 a degasser, generally represented at 10, is illustrated in cross-sectional schematic view during steady state use. The degasser, 10, comprises an inlet, 12, and outlet, 14. The inlet receives liquid, 1, with dissolved gas therein. The outlet discharges degassed liquid. The formation and treatment prior to the inlet and after the outlet is not limited herein. In an exemplary embodiment the inlet is in flow communication with a reservoir, holding furnace, casting furnace or the like which provides liquid, such as molten aluminum, and the outlet is in flow communication with a launder wherein degassed liquid, preferably molten aluminum, is transported for subsequent use such as casting. [0019] Generally, material flow is from the inlet, through a degassing chamber and then towards the outlet with a portion of the flow towards the outlet being diverted back toward the inlet as will be more fully described herein. Within the degassing chamber the flow is predominantly impeded by a baffle as will be more fully described herein.

[0020] A pump, 16, which is in flow communication between the inlet, 12, and entrance orifice, 11, of a degassing chamber, 18, receives the liquid, or molten material, and pumps a higher volume of liquid than that received from the inlet. The degassing chamber, 18, contains a large volume of molten material thereby providing a sufficient residence time for the molten material to insure that adequate degassing occurs. At least one baffle, 20, is provided within the degassing chamber to insure adequate residence time. It is preferred to have a secondary passage, 22, such as a hole or slot, at the lower extent of the baffle to allow draining but the secondary passage should be sufficiently small to only allow a flow volume which is less than the flow volume of the inlet and outlet. In other words, the secondary passage is sufficiently large to allow the degassing chamber to be drained but not sufficiently large to defeat the function of the baffles. The baffle may separate the degassing chamber into zones, however, this is not necessary. For the purposes of illustration the degassing chamber is segmented into two zones with each having a degassing facilitator such as an agitator and/or bubbler which will be described further. The number of zones, bubblers and agitators is not limited herein. [0021] While in the degasser the gases within the liquid are persuaded by a degassing facilitator to escape by any method known in the art preferably selected from some combination of vacuum, agitation and bubbling. Within the degassing chamber is at least one optional, but preferred, agitator, 24, with a rotation mechanism, 25, attached thereto. An agitator increases the shear of the molten material thereby increasing the contact between a carrier gas and dissolved gas to be removed. Also within the degassing chamber is at least one optional, but preferred bubbler, 26. The bubbler provides at least one gas to the molten material. If the baffles create distinct zones with the only flow between zones being due to molten material flowing over the baffle it is most preferred to have at least one agitator and at least one bubbler in each zone. The bubbler may enter the molten material from the bottom, top or a side. In one embodiment the bubbler and agitator are combined as an integral unit, 60, with the bubbles exiting an orifice in a portion of the agitator or agitator shaft. In one embodiment the bubbles may be arranged in counter- flow with the material being degassed.

[0022] The degassing chamber has an outlet orifice, 28, which allows a sufficient volume of molten material to pass there through to insure adequate flow through the outlet, 14, and through a recirculating manifold, 30. The outlet orifice in the bottom of the chamber is preferably no higher than parallel to the bottom of the degassing chamber to allow for drainage of the chamber. The recirculating manifold allows a portion of the degassed material to be redirected to a location upstream of the pump and therefore in position to be passed back through the degassing chamber thereby greatly improving the quality of molten material without a significant increase in the footprint of the degasser. Valves, 50, are preferably provided in various sections to allow portions of the degassing chamber to be flow isolated from other sections. It is also preferred to include filters prior to the final cast. The filters may be incorporated into the degassing chamber if desired and, most preferably, at an entrance or exit port.

[0023] A single degasser can be utilized independently or multiple degassers can be used either in parallel or in series. [0024] As would be understood from the description herein the pump, 16, must have the capability of pumping a sufficient amount of material to maintain a flow through the outlet and through the recycle manifold. A schematic flow diagram at steady state is illustrated in Fig. 2. In Fig. 2 the Volume In (V_1n) is that volume which is supplied to the degasser. The Volume Out (V_out) is that volume which is discharged as degassed liquid. It is most preferable that V_1n and V_out are approximately equal such that the volume within the degasser remains relatively constant at steady state. The inlet and the recirculating manifold meet at an inlet junction, 40, and from the inlet junction to the pump and chamber, 41, the volume of molten material flowing is the sum of V_1n and the Recycle Volume (V_r) . Similarly, the outlet and recirculating manifold meet at an outlet junction, 42. Between the outlet junction and the chamber, 41, the volume of molten material flowing is the sum of V_out and V_r which is also approximately the sum of V_1n and V₁.. To initiate flow the outlet is sealed and the recirculating manifold is optionally sealed thereby allowing at least the degassing chamber and preferably at least a portion of the recirculating manifold to fill. Once a sufficient volume is obtained in the degassing chamber and recirculating manifold the flow through the outlet is allowed to proceed. [0025] By way of non-limiting example, with reference to Fig. 2, a volume of material supplied to the degasser (V_1n) would be 453.6 Kg/min (1000 lb/min) . The pump would pump at 453.6 Kg/min (1000 lb/min) with the degasser closed to allow the degasser to fill. A particularly suitable pump is a lifting pump available as the Mini HF Launder Transfer Pump from Molten Metal Equipment Innovations of Middlefield, Ohio. In one embodiment at least a portion of the recirculating manifold could be filled by allowing liquid to flow in from the inlet junction side even though this is counter to the flow at steady state. For the purposes of discussion a recycle volume (V_r) of 226 Kg/min (500 lb/min) is considered. Once the degasser is filled to an acceptable volume the degasser would be opened to allow any remainder of the recirculating manifold to fill. At the point where the degasser and recirculating manifold are filled the pump speed would be increased to 680.4 Kg/min (1500 lb/min) thereby allowing 453.6 Kg/min (1000 lb/min)to exit (V_out) the degasser and 226 Kg/min (500 lb/min) (V_r) to recirculate back to a position prior to the pump.

[0026] It is preferable to reduce the hydrogen level in aluminum to no more than 0.15 ml/lOOg of aluminum. It is more preferable to reduce the hydrogen level in aluminum to no more than 0.06 ml/lOOg.

[0027] The present invention is particularly suitable for use with liquids comprising aluminum such as aluminum alloys. The present invention is also particularly suitable for liquids comprising water.

[0028] For the purposes of the present invention bubbler gas is categorized as either a reactive gas or a carrier gas. [0029] Reactive gases chemically react with a molten material or an impurity therein to the benefit of the molten material. Chlorine gas, for example, may be used in molten aluminum to react with Group IA and Group HA materials to form chlorides which is excluded typically by skimming. [0030] A carrier gas removes a material by dissolution. Argon, helium, krypton, xenon and nitrogen are mentioned as suitable carrier gases for hydrogen in molten aluminum. Argon or nitrogen are particularly preferred since hydrogen is dissolved therein and removed in bubbles of carrier gas from the molten aluminum. [0031] The invention has been described with particular reference to the preferred embodiments without limit thereto. One of skill in the art would readily appreciate additional embodiments and alterations which are not specifically set forth but which are within the scope of the invention as more specifically set forth in the claims appended hereto.

Claims

Claimed i s :

1. A degasser for a liquid comprising: a liquid supply inlet for supplying a first volume of liquid to an inlet junction; a degassing chamber comprising an entrance orifice for receiving said liquid and an exit orifice for discharging degassed liquid to an outlet junction; a pump between said inlet junction and said degassing chamber for pumping liquid from said inlet junction to said degassing chamber; wherein said outlet junction is capable of receiving degassed liquid from said degassing chamber and directing a second volume to a liquid outlet and a third volume of liquid to a recirculating manifold; and wherein said recirculating manifold transports said third volume to said inlet junction.

2. The degasser for a liquid of claim 1 wherein said first volume and said second volume are the same .

3. The degasser for a liquid of claim 1 wherein said degassing chamber further comprises at least one baffle.

4. The degasser for a liquid of claim 3 wherein said baffle comprises a secondary passage.

5. The degasser for a liquid of claim 1 wherein said degassing chamber further comprises an agitator.

6. The degasser for a liquid of claim 5 wherein said degassing chamber further comprises a bubbler.

7. The degasser for a liquid of claim 6 wherein said agitator and said bubbler are integral .

8. The degasser for a liquid of claim 1 wherein said degassing chamber further comprises a bubbler.

9. The degasser for a liquid of claim 8 wherein said bubbler injects at least one gas into said liquid wherein said gas is selected from a reactive gas and a carrier gas.

10. The degasser for a liquid of claim 9 wherein said carrier gas is selected from the group consisting of argon, helium, krypton, xenon and nitrogen.

11. The degasser for a liquid of claim 1 wherein said liquid comprises aluminum.

12. The degasser for a liquid of claim 1 wherein said liquid comprises water.

13. A method for degassing a liquid comprising: supplying a first volume of said liquid to an inlet junction; pumping said first volume of said liquid and a second volume of said liquid into a degassing chamber,- removing gas from said liquid in said degassing chamber,- passing a third volume of said liquid from said degassing chamber to an outlet junction; separating said third volume into a fourth volume and said second volume; passing said fourth volume out of said degasser; and passing said second volume to said inlet junction.

14. The method for degassing a liquid of claim 13 wherein said first volume and said fourth volume are the same.

15. The method for degassing a liquid of claim 13 wherein said degassing chamber further comprises a baffle.

16. The method for degassing a liquid of claim 13 wherein said degassing chamber further comprises an agitator.

17. The method for degassing a liquid of claim 13 wherein said degassing chamber further comprises a bubbler.

18. The method for degassing a liquid of claim 17 wherein said bubbler injects at least one gas into said liquid wherein said gas is selected from a reactive gas and a carrier gas.

19. The method for degassing a liquid of claim 13 wherein said liquid comprises aluminum.

20. The method for degassing a liquid of claim 13 wherein said liquid comprises water.