US2751311A - Aluminizing - Google Patents

Description

June 19, 1956 L. B. ROSSEAU QLUMINIZING 4 Sheets-Sheet 1 Filed Sept. 28, 1954 x m a i 6 ATTORNEYS,

June 19, 1956 L. B. ROSSEAU ALUMINIZING 4 Sheets-Sheet 2 Filed Sept. 28, 1954 R m N m m ATTORNEYS.

June 19, 1956 B. ROSSEAU ALUMINIZING 4 Sheets-Sheet 4 Filed Sept. 28, 1954 INVENTOR. 6072 fifiassaau/ ATTORNEYS.

United States Patent ALUMINIZING Application September 28, 1954, Serial No. 458,821 4 Claims. (Cl. 117--52) The present invention relates to methods of selective aluminizing or otherwise coating steel or the like and selective aluminizing or other coating furnaces.

Very effective aluminizing processes have been developed which coat aluminum on ferrous metals by first cleaning the ferrous metals such as steel in a flux which is rectified by maintaining it in contact with a pool of molten aluminum and then dipping the articles in molten aluand Hanink, U. S. Patents 2,544,670 and 2, 544,671, Grange U. S. Patent 2,569,097 and article by Hanink and Boegehold, SAE Annual Meeting, Detroit, Mich., March 12, 1954.

It has been difficult in carrying out the process of aluminizing to control the depth of aluminum application to the articles being coated so as to permit selective aluminizing of part only of the article. while retaining other parts of the article free from aluminum coating.

The present invention is directed particularly to the technique of selective aluminizing and the apparatus by which aluminum can be coated only on certain predetermined parts of the article, omitting the aluminum coating from other parts.

The problem of selective aluminizing involves some difiiculties, because the fiux is most suitably heated by a submerged electrode furnace of the Hultgren type, and contact of the molten aluminum with the electrodes is to be avoided as it would cause a short circuit, but on the other hand it is necessary to maintain constant contact having a shallow pool of molten aluminum at the bottom, the molten aluminum in the pool being below the electrodes and being heated by heat conductivity from the flux. The aluminum is heavier than the flux commonly used and suggested by the literature, such as the patents and article referred to. Usually the molten aluminum at the bottom of the furnace chamber has a depth between a few inches and for example 18 inches.

The present invention is concerned with applying molten aluminum to restricted or limited areas only of the article being coated, and accomplishing this result in the same furnace in which the articles are desirably preheated, keeping the articles beneath the surface of the flux until after the completion of coating and detearing. The cost of the equipment is thus kept at a minimum while retaining flexibility in the operation. Excellent results are secured not only in respect to adherence over the limited areas coated, but also in regard to rapid removal of excess aluminum from the coated area and securing uniformity of coating thickness, since the fluxing salt is present immediately as the article emerges from the aluminum, and the inertia or shock and washing efiect by the salt when the article coated is withdrawn further assists in removing excess aluminum, which is received in the body of molten aluminum.

An example of the character of work which may be coated selectively is the seating portion of automotive intake and exhaust valves, while keeping the stem free from coating.

A purpose of the invention is to obtain uniform and adherent aluminum or other metal coatings on selective areas of steel and other ferrous alloys.

A further purpose is to coat selective areas to an accurate level while maintaining a flux coating on the aluminum bath.

A further purpose is to maintain the surfaces of the ferrous metal articles applied at the time of removal.

Further purposes appear in the specification and in the claims.

In the drawings I have chosen to illustrate one only of the numerous embodiments in which my invention may appear, selecting the forms shown from the standpoints of convenience in illustration, satisfactory operation and clear demonstration of the principles involved.

Figure l is a fragmentary diagrammatic top plan view of an aluminizing furnace according to the invention, eliminating the Work holding fixtures and the work.

Figure 2 is a fragmentary diagrammatic vertical section on the line 2-2 of Figure 1.

Figure 3 is a fragmentary diagrammatic vertical transverse section on the line 3-3 of Figure 1.

Figure 4 is an end elevation looking in the direction of the line 44 in Figure 1.

Figure 5 is a fragmentary sectional perspective showing a suitable pusher bar arrangement.

Figure 6 is a diagrammatic side elevation of a suitable Work holding fixture.

Considering now the drawings in detail, the furnace of the present invention comprises a body 20 having a frame 21, an insulating layer 22 held by the frame, and a refractory lining 23 inside the insulating lining which forms a furnace chamber 24- suitably open at the top.

The furnace chamber contains a pool of molten aluminum 25 at the bottom and a body of molten flux 26 above the molten aluminum and extending to a point adjacent the top of the furnace.

Metallic electrodes 27 of the submerged salt bath heating type common in Suitable stirring means 32 is employed to agitate the molten flux.

Any suitable mechanism may be used advance the articles to The stems extend upwar The work supports desirably are suspended from headers 36 having bar engaging portions 37 which ride or slide on rails 38 which extend on either side longitudinally of the furnace and above the level of the electrodes.

The mechanism for advancing the work support here is shown as pusher bars 40 having dogs 41 pivoted thereon intermediate their ends at 42 and extending up at 43 above the rails in normal operating position. The dogs are overbalanced to restore to the position of Figure 5. The pusher bars suitably have rollers 44 which ride the bottom of the rails on a suitable box section and the dogs extend up through a slot 45 at the top of the box section. The pusher bars are reciprocated back and forth by fluid actuated cylinders 46 which move piston rods 47 pivotally connected at 48 to the pusher bars. As the pusher bars advance, the dogs move the work supports forward and as they retract, the dogs tilt under the next rearward work support until the dogs move behind it, and then the dogs rise to engage and advance it.

The work supports first bring the work beneath the flux at position 50, thus preheating the work to a suitable temperature. If only a certain portion is to be dipped, the preheating and fluxing may be limited only to this portion. In a typical example, a temperature of 1325 F. and a time of five minutes is used for preheating small parts beneath the flux.

The parts advance under pusher bar action through positions 51, 52, 53, 54 and finally positions 55 at the right in Figure 2. Beneath position 55 is located a con tainer 56 containing a pool of molten aluminum 57. The container is normally entirely below the flux and supported by a frame 58 from hanger arms 60 pivoted at 61 on a yoke 62 which at the other end is pivoted at 63 on a cross shaft 64 secured to the furnace frame. The yoke has a follower roller 65 on a lower surface intermediate its ends and the follower roller rides a cam 66 which reciprocates on guiding rollers 67 on a support 68. The cam is manipulated by a piston and rod combination 70 actuated by fluid cylinder 71. In operation, the first work support is lowered to position 50 by any suitable hoisting mechanism and is advanced to position 55 by repeated reciprocations of the pusher bars. In position 55 the work is poised above the molten aluminum bath 57 in the container 56. By forward motion of the cam 66 the yoke is raised and the container is raised until the molten aluminum, still below the level of the flux, dips the work to the predetermined level. In the case of the inlet and exhaust valves, this is preferably just enough to cover the seating portions. The temperature and time of immersion will be suitably regulated. In a particular example, the molten aluminum is maintained at 1300 to 1325 F. and the immersion time is preferably to seconds for the valves mentioned.

After the immersion is completed, the cam 66 is retracted and the molten aluminium drops below the level of the work, and the work immediately comes in contact with the flux. This is very desirable as it promotes detearing, since the flux tends to make the molten aluminum flow more readily. The drip time may suitably be seconds in a particular example, the flux being at 1325 F. Any drip is caught in the container 56.

It should be emphasized that the molten aluminum leaves contact with the work and the flux regains contact with the work without any air contact and the dripping continues without air contact, thus avoiding oxidation and interference with the coating adherence.

The work is now preferably subjected to shock (including vibration) as it is withdrawn. This is desirably accomplished by an automatic hoisting mechanism which is provided with a hook 72 that engages the bar 36 and raises the work at a velocity not less than 10 feet per minute, and preferably greater. The jolt as the hook engages is desirably abrupt. This has the efiect of removing adidtional molten aluminum by inertia eifect and by the washing of the coated article in the molten flux as it is withdrawn.

The coated article is then suitably processed, a desirable sequence being cooling in an air blast for two seconds, air cooling to 800 F. or less in three to four minutes, washing in water to remove excess flux for 45 seconds, followed by a brightening dip, a hot rinse and an oil dip for corrosion protection of uncoated surfaces.

The depth of immersion in the aluminum is conveniently controlled where selective dipping is being performed by any suitable means, desirably using hand wheel 73 turning in bearing 74 carrying screw 75 which engages nut portion 76 on the bottom of slide 77 which is guided on guide 78 and carries the entire cam, cam support and piston assembly forward to compensate for exhaustion of molten aluminum in the bath 57. The hand wheel is suitably turned when inspection of the work indicates it should be dipped deeper. When it is desired to replenish the molten aluminum, aluminum is poured into the container 57 suitably to till it, any excess entering the pool 25 at the bottom of the furnace. The adjustment at wheel 73 is then reset to zero and the operation continued allowing for further exhaustion.

In view of my invention and disclosure variations and modifications to meet individual whim or particular need will doubtless become evident to others skilled in the art, to obtain all or part of the benefits of my invention without copying the method and structure shown, and I, therefore, claim all such insofar as they fall within the reasonable spirit and scope of my claims.

Having thus described my invention what I claim as new and desire to secure by Letters Patent is:

l. The method of selectively aluminizing, which comprises maintaining a bath of molten flux, maintaining a body of molten aluminum beneath the flux and in contact therewith to rectify the flux, immersing metal articles to be aluminized beneath the flux, maintaining a second body of molten aluminum beneath the flux, relatively raising the second body of molten aluminum until it surrounds at least a portion of the metallic articles to be aluminized while maintaining the second body of molten aluminum at all times beneath the level of the flux and then relatively lowering the second body of molten aluminum with respect to the metallic articles being coated and reestablishing instantaneous contact of flux with the articles which have been coated.

2. The method according to claim 1, in which only the lower portions of the articles are immersed beneath the second body of molten aluminum.

3. The method according to claim 1, in which the articles are rapidly moved upward out of the flux to wash off excess aluminum by the flux.

4. The method according to claim 1, in which the articles are moved out of the flux and are concurrently subjected to shock.

References Cited in the file of this patent UNITED STATES PATENTS cum

Claims (1)

1. THE METHOD OF SELECTIVELY ALUMINIZING, WHICH COMPRISES MAINTAINING A BATH OF MOLTEN FLUX, MAINTAINING A BODY OF MOLTEN ALUMINUM BENEATH THE FLUX AND IN CONTACT THEREWITH TO RECTIFY THE FLUX, IMMERSING METAL ARTICLES TO BE ALUMINIZED BENEATH THE FLUX, MAINTAINING A SECOND BODY OF MOLTEN ALUMINUM BENEATH THE FLUX, REALTIVELY RAISING THE SECOND BODY OF MOLTEN ALUMINUM UNTIL IT SURROUNDS AT LEAST A PORTION OF THE METALLIC ARTICLES TO BE ALUMINIZED WHILE MAINTAINING THE SECOND BODY OF MOLTEN ALUMINUM AT ALL TIMES BENEATH THE LEVEL OF THE FLUX AND THEN RELATIVELY LOWERING THE SECOND BODY OF MOLTEN ALUMINUM WITH RESPECT TO THE METALLIC ARTICLES BEING COATED AND REESTABLISHING INSTANTANEOUS CONTACT OF FLUX WITH THE ARTICLES WHICH HAVE BEEN COATED.

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