US3457097A - Method of coating ferrous metal with molten aluminum - Google Patents

Description

y 1969 SHIGERU YONEZAKI ETAL 3,457,097

METHOD OF COATING FERROUS METAL WITH MOLTEN ALUMINUM Filed Feb. 5, 1965 INVENTORS sweeu YONEZAKI uma oau Md enn l-H ASAKAWA p1. JMMM f PM ATTORNEYS United States Patent 3 457,097 METHOD OF COA'IIPiG FERROUS METAL WITH MOLTEN ALUMINUM Shigeru Yonezaki, Misao Obu, and Kenichi Asakawa, Kitakyushu, Japan, assignors to Yawata Iron & Steel Co., Ltd., Tokyo, Japan, a corporation of Japan Filed Feb. 3, 1965, Ser. No. 430,004 Claims priority, application Japan, Feb. 10, 1964, 39/6,793; Mar. 9, 1964, 39/12,924, 39/12,925, 39/ 12,926, 39/ 12,927

Int. Cl. B44d 1/34 US. Cl. 117-51 20 Claims ABSTRACT OF THE DISCLOSURE An improvement is provided in the method of coating a ferrous metal article with aluminum in which the surface of the metal article to be coated is previously reduced by means of reducing gas in a reducing zone and the article is then introduced into a molten bath of aluminum or alloy thereof while keeping the article out of contact with air. The improvement involves the steps of cooling the article after the reduction and pre-treating the surface of the article with a neutral or reducing carrier gas containing vapor of at least 1 of the following metals, nonmetals and compounds:

(A) elemental Bi, Sb, P-b, As, Se, P, Mg, Ca, Sr, Ba, Cd;

(B) fluorides of the alkali metals, K, Na, and Li;

(C) M00 K TiF and Na TiF and (D) halides of Si, P, Ti, Zr, V, Nb, Mo, Cr, Ta, W, Mn,

Pb, As, Bi, Sb and Se.

The pretreatment is effected prior to introducing the article into the molten aluminum coating bath.

This invention relates to a method of coating ferrous metal with molten aluminum, and particularly to an improved method of coating a ferrous metal article wherein the ferrous metal article to be treated is annealed for surface reduction and then introduced through a protective atmosphere into a bath of molten aluminum for coating.

When an aluminum coating is effected in a conventional apparatus as employed in a hot dip coating process such as the Sendzimir process, there inevitably arise various defects, such as partial absence of coating, pinholes, blisters, and deterioration of the thermal resistance and corrosion resistance of the coated metal article, and it has therefore been difficult to obtain products of good quality. To overcome these disadvantages, various improvements and attempts have been made heretofore. For example, the US Patent No. 3,051,587 disclosed an improved method of making vapor of metallic sodium circulate above the surface of the coating bath, or interlaying a bath of metal, such as molten lead, between the protective atmosphere and the molten aluminum bath, in order to avoid various defects that may be produced from the direct contact of the gas of the protective atmosphere with the molten aluminum bath.

The object of the present invention is also to provide a method for overcoming the above-mentioned disadvantages, and after numerous studies, the applicants have found that excellent wettability of steel strip with coating bath could be obtained by spraying a vapor of ele- "ice ments such as Bi, Sb, Pb, P, As, Se, or compounds such as fluorides of the alkali metals such as KF, NaF, LiF, oxides or fluorides such as M00 K TiF Na TiF halides of P, Si, Ti, Zr, v, Nb, Ta, Cr, Mo, w, Mn, Pb, As,

Bi, Se, Sb, metals of Group II of the Periodic System' such as Mg, Ca, Sr, Ba, Cd, or the like, onto the surface to be coated of the steel strip, during the cooling step after the reducing annealing step in aluminum coating by the Sendzimir process, and thus an excellent aluminum coated article having a continuous layer of alloy could be obtained,

The degreased steel strip is introduced into a reducing furnace so that reducing and annealing processes are conducted simultaneously therein, and after being cooled down to an appropriate temperature in a cooling zone, the strip is dipped in a coating bath. The applicants have found that, if the steel strip was first passed through the abovementioned vapor of metals or compound, just before entering the cooling zone or dipping in the coating bath, or was sprayed with vapor, on the surface to be coated so that the strip is treated with vapor, and then dipped in a coating bath containing aluminum or aluminum alloy, keeping the strip strictly out of contact with air, the abovementioned properties could easily be incorporated in the coated article.

The significant effects that will be obtained by the embodiment of the present invention are that, not only excellent aluminum coated steel strip that will not produce any defect such as coating gaps, pinholes, and blisters, can be obtained, but also that the coating operation will be easier and have an excellent operability and productivity.

In the drawings:

FIGURE 1 is a side view of the apparatus showing the aluminum coating line embodying the present invention.

FIGURE 2 is a side view of the apparatus in FIGURE 1 with vapor generating system installed outside the furnace, and

FIGURE 3 is a plan view of the apparatus with vapor spraying nozzles located on both sides of the steel strip.

The present invention will now be described in detail, taking for example the case of aluminum coating of steel strip.

A cold rolled or hot rolled steel strip in the form of coil is unrolled by uncoiler, and oils and other organic substances on the surface of the strip are removed by oxidizing combustion or cleaned by other suitable methods. The strip 1 so surface-cleaned, passes through shielded rolls 2, enters into reducing annealing furnace 3, and is heated therein to be annealed and subjected to reduction. It then enters into cooling zone 4, and after being cooled down to a certain temperature, it is introduced into final cooling zone 5, and, passing through hood 6, it is dipped in coating bath 7 Without coming into contact with air. Passing through the cooling zone 4 or at just above the coating bath 7 Within hood 6, the strip is treated with vapor of such elements as Bi, Sb, Pb, As, Se, fluorides of the alkali metals such as KF, NaF, LiF, oxides or fluorides such as M00 K TiF Na TiF halides of P, Si, Ti, Zr, V, Nb, Ta, Cr, Mo, Mn, W, Pb, As, Bi, Se, Sb, metals of Group II of the Periodic System such as Mg, Ca, Sr, Ba, Cd, sprayed from nozzles 13 onto the surface to be coated of the strip. Then it is introduced into the coating bath, passes over the pot rolls 8a, 8b, and is withdrawn from the bath. Nozzles 13 for spraying vapor are located at certain intervals on the upperside and underside of the strip (in front and behind the strip when the vapor is sprayed within hood 6 in order to uniformly spray vapor onto the surfaces to be coated. When the spraying of vapor from the upperside and underside (or front side and back side) of the strip subjects the strip to excessively large vibration due to the tension of the steel strip within the final cooling zone, the spraying device may be arranged in such a manner that the spraying of vapor can be effected from both sides of the strip, as shown in FIGURE 3. As for the position of nozzles 13, it may be slightly different depending on the type of vapor to be sprayed, but spraying effect is realized as long as a nozzle is located within the extent from cooling zone 4 to the surface of bath within hood 6, and better results can be obtained when, if possible, the nozzle is disposed in the cooling zone to effect the spraying of vapor therefrom.

Instead of spraying vapor on to the strip from abovementioned nozzles 13, the steel strip may be passed through vapor of the above-mentioned substances introduced in the passage of the steel strip 1, so that the sur face of the strip is treated with the vapor.

The vapor is then formed at 11a or 11b, carried by reducing gas, neutral gas, or inert gas injected from 10a or 10b, passed through heated conduit 12a or 12b into nozzles 13, and then is sprayed therefrom onto the surface of the steel strip 1. The spraying quantity of vapor is regulated by the flow of the carrier gas and the temperature of the vapor generating system 11a or 11b.

The apparatus shown in FIGURE 1 is one in which the heat of the reducing annealing furnace is utilized as source for generating vapor, and thereby the heating energy of the heating conduit 12a will also be economized. Chamber 11a is a vapor-generating system, in which suitable substance as above-described is charged and supplemented as it is consumed.

FIGURE 2 shows an example of the same apparatus with vapor generating system installed outside the furnace; in this case, a heating device is required.

It is also necessary to effect heating or heat retaining as required.

The metals or compounds used in this invention are those produced by heating the substances, which are listed below at the accompanying industrial vaporizing temperatures indicated by numerals. It is to be noted that the industrial vaporizing temperature referred to herein means the temperature of heating the vapor generating system in order to obtain a quantity of vapor necessary for carrying out the present invention.

(A) Elements such as Bi, Sb, Pb, 900 Q; As, Se, 400 C.; Violet P, 250 C.

(B) Fluorides of alkali metals such as K, Na, Li, higher than 900 C.

(C) Oxides or fluorides of alkali compounds such as M 900 C.; K TiF 700 C.; Na TiF 900 C.

(D) Halides of nonmetals and metals such as Si, P, Ti, Zr, V, Nb, Mo, Cr, Ta, W, Mn, Pb, As, Sb, Bi, Se.

PCl 60 C. Si Cl 58 C. TiF 150 C. ZrF 600 C. NbF 100 C. TaF 90 C. VF 200 C. CrCl 850 C. MoCl 200 C. WCl 270 C. MnCl 700 C. PbF 860 C. SbCl 50 C. BiCl 240 C. SeCl 80 C. AsCl C.

(B) Group H metals such as Mg, 700 C.; Ba, 950 C.; Ca, 900 C.; Cd, 450 0.; Sr, 850 C.

The industrial vaporizing temperatures of the various compounds and metals for generating vapor used in the present invention vary over a wide range from lower temperature to higher temperature as listed above, but, in

any case, satisfactory coating state will be obtained when the steel strip is treated with vapor heated to these vaporizing temperatures at a region between the cooling zone and the coating bath.

The industrial vaporizing temperatures of the various metals or compounds used to generate vapor in the present invention are such as listed above, but, in actual coating process, these temperatures vary naturally according to line speed or width of the strip.

The metals or compounds for generating vapor which are shown separately in 5 groups from A to E are, of course, effective when they are used solely or in combination of two or more in the same group, but an acceptable result may be expected also when one or more of the substances of different groups are used in proper combination by mixing. In such case where more than two of the substances are mixed, vapor can be generated by the same vapor generating system, but it can also be generated in separate vapor generating systems and sprayed onto the surface to be coated of the strip.

Examples carrying out the present invention in molten aluminum coating will now be described.

EXAMPLE 1 A coil of cold rolled steel strip of mm. width is coated with aluminum at a speed of 3 m./min. The strip is previously cleaned of grease on its surface by burning to achieve oxidation in an oxidizing furnace, and then introduced into a reducing annealing furnace, the atmosphere of which consists of A.X gas (A.X gas, employed in the present example and in the following examples, consists of H 75%, N 25% w./W.). The strip is heated for about 1 minute to 800-950 0, being thus reduced and annealed sufiiciently. Then, it is introduced into the cooling zone, cooled therein in reducing atmosphere down to coating bath temperature (about 650 C.), and then introduced into the coating bath. At this time, the surface to be coated is treated, immediately before entering into coating bath, with vapor of ZrF In this case, the temperature to generate vapor of ZrF was kept constant at 600 C., and N gas at 4 liters/min. was used as vapor carrier gas.

The aluminum coated strip thus obtained had continuous layer of alloy, and the coating gaps, pinholes were extremely few, in comparison with strip untreated.

EXAMPLE 2 A coil of cold rolled steel strip of 90 mm. width is coated with aluminum at a speed of 4 m./min. The strip is previously cleaned of grease on its surface by burning to achieve oxidation in an oxidizing furnace, and then introduced into a reducing annealing furnace, the atmosphere of which consists of AX gas. The strip is heated for about 1 minute to 800950 C., being thus reduced and annealed sufiiciently. Then, it is introduced into the cooling zone, cooled therein in reducing atmosphere down to coating bath temperature (about 700 C.), and then introduced into the coating bath. At this time, the surface to be coated is treated, immediately before entering into coating bath, with vapor of K TiF In this case, the temperature to generate vapor of K TiF was kept constant at 700 C., and N gas at 5 liters/min. was used as vapor carrier gas.

The coating of the thus-obtained coated strip is continuous, being essentially free of coating gaps, and pinholes are extremely few in comparison with untreated strip.

EXAMPLE 3 A coil of cold rolled steel strip having 90 mm. width is coated with aluminum at a speed of 4 m./min. The strip is previously cleaned of grease on its surface by burning to achieve oxidation in an oxidizing furnace, and then introduced into a reducing annealing furnace, the atmosphere of which consists of A.X gas. The strip is heated for about 1 minute to 800-950 0., being thus reduced and annealed sufliciently. Then, it is introduced into the cooling zone, cooled therein in reducing atmosphere down to coating bath temperature (about 650 C.), and then introduced into the coating bath. At this time, the surface to be coated is treated, being sprayed from both sides in the central portion of the hood, with vapor of KF.

In this case, the temperature to generate vapor of KF was kept constant at 950 C., and A.X gas at 5 liters/ min. was used as vapor carrier gas.

The coating of the thus-obtained coated strip is continuous, being essentially free of coating gaps, and pinholes are extremely few in comparison with untreated strip.

EXAMPLE 4 A coil of cold rolled steel strip of 90 mm. width is coated with aluminum at a speed of 4 tn/min. The strip is previously cleaned of grease on its surface by burning to achieve oxidation in an oxidizing furnace, and then introduced into a reducing annealing furnace, the atmosphere of which consists of A.X gas. The strip is heated for about 1 minute to 800950 C., being thus reduced and annealed sufficiently. Then, it is introduced into the cooling zone, cooled therein in reducing atmosphere down to coating bath temperature (about 670 C.), and then introduced into the coating bath. At this time, the surface to be coated is treated, in the final cooling zone, with vapor of Bi.

In this case, the temperature to generate vapor of Bi was kept constant at 930 C., and A.X gas at 4 liters/ min. was used as vapor carrier gas.

The coating of the thus-obtained coated strip is continuous, being essentially free of coating gaps, and pinholes are extremely few in comparison with untreated strip.

EXAMPLE 5 A coil of cold rolled steel strip of 90 mm. width is coated with aluminum at a speed of 4 m./min. The strip is previously cleaned of grease on its surface by burning to achieve oxidation in an oxidizing furnace, and then introduced into a reducing annealing furnace, the atmosphere of which consists of A.X gas. The strip is heated for about 1 minute to 800-950" C., being thus reduced and annealed sufiiciently. Then, it is introduced into the cooling zone, cooled therein in reducing atmosphere down to coating bath temperature (about 650 C.), and then introduced into the coating bath. At this time, the surface to be coated is treated, in the final cooling zone, with vapor of Mg.

In this case, the temperature to generate vapor of Mg was kept constant at 700 C., and A.X gas at 5 liters/ min. was used as vapor carrier gas.

The coating of the thus-obtained coated strip is continuous, being essentially free of coating gaps, and pinholes are extremely few in comparison with untreated strip.

EXAMPLE 6 A coil of cold rolled steel strip of 90 mm. width is coated with aluminum at a speed of 4 m./min. The strip is previously cleaned of grease on its surface by burning to achieve oxidation in an oxidizing furnace, and then introduced into a reducing annealing furnace, the atmosphere of which consists of A.X gas. The strip is heated for about 1 minute to BOO-950 C., being thus reduced and annealed sufficiently. Then, it is introduced into the cooling zone, cooled therein in reducing atmosphere down to coating bath temperature (about 650 C.), and then introduced into the coating bath. At this time, the surface to be coated is treated, in cooling zone, with vapor of Bi and KP.

In this case, the temperature to generate vapor of Bi and KP was kept constant at 930 C. (Bi; KF 900 C.), and N gas at 5 liters/min. respectively, was used as vapor carrier gas.

The coating of the thus-obtained coated strip is continuous, being essentially free of coating gaps, and pinholes are extremely few in comparison with untreated strip.

EXAMPLE 7 A coil of cold rolled steel strip of mm. width is coated with aluminum at a speed of 2 m./min. The strip is previously cleaned of grease on its surface by burning to achieve oxidation in an oxidizing furnace, and then introduced into a reducing annealing furnace, the atmosphere of which consists of A.X gas. The strip is heated for about 2 minutes to 800950 C., being thus reduced and annealed sufficiently. Then, it is introduced into the cooling zone, cooled therein in reducing atmosphere down to coating bath temperature (about 700 C.), and then introduced into the coating bath. At this time, the surface to be coated is treated, immediately before entering into the coating bath, with vapor of Sb.

In this case, the temperature to generate vapor of Sb was kept constant at 900 C., and N gas at 5 liters/min. was used as vapor carrier gas.

The coating of the thus-obtained coated strip is continuous being essentially free of coating gaps, and pinholes are extremely few in comparison with untreated strip.

EXAMPLE 8 A coil of cold rolled steel strip of mm. width is coated with aluminum at a speed of 3 m./min. The strip is previously cleaned of grease on its surface by burning to achieve oxidation in an oxidizing furnace, and then introduced into a reducing annealing furnace, the atmosphere of which consists of A.X gas. The strip is heated for about 1 minute to SOD-950 C., being thus reduced and annealed sufiiciently. Then, it is introduced into the cooling zone, cooled therein in reducing atmosphere down to coating bath temperature (about 660 C.), and then introduced into the coating bath. At this time, the surface to be coated is treated, in the cooling zone, with vapor of NagTiFs.

In this case, the temperature to generate vapor of Na TiF was kept constant at 900 C., and A.X gas at 6 liters/ min. was used as vapor carrier gas.

The coating of the thus-obtained coated strip is continuous, being essentially free of coating gaps, and pinholes are extremely few in comparison with untreated strip.

EXAMPLE 9 A coil of cold rolled steel strip of 90 mm. width is coated with aluminum at a speed of 4 m./min. The strip is previously cleaned of grease on its surface by burning to achieve oxidation in an oxidizing furnace, and then introduced into a reducing annealing furnace, the atmosphere of which consists of A.X gas. The strip is heated for about 1 minute to 800-950 C., being thus reduced and annealed sufficiently. Then, it is introduced into the cooling zone, cooled therein in reducing atmosphere down to coating bath temperature (about 650 C.), and then introduced into the coating bath. At this time, the surface to be coated is treated, in the hood, with vapor of TiF In this case, the temperature to generate vapor of TiF was kept constant at C., and N gas at 5 liters/min. was used as vapor carrier gas.

The coating of the thus-obtained coated strip is continuous, being essentially free of coating gaps, and pinholes are exeremely few in comparison with untreated strip.

EXAMPLE 10 A coil of cold rolled steel strip of 90 mm. width is coated with aluminum at a speed of 4 m./min. The strip is previously cleaned of grease on its surface by burning to achieve oxidation in an oxidizing furnace, and then introduced into a reducing annealing furnace, the atmosphere of which consists of A.X. gas. The strip is heated for about 1 minute to 800950 C., being thus reduced 7 and annealed sufiiciently. Then, it is introduced into the cooling zone, cooled therein in reducing atmosphere down to coating bath temperature (about 670 C.), and then introduced into the coating bath. At this time, the surface to be coated is treated, immediately before entering into the coating bath, with vapor of NaF.

In this case, the temperature to generate vapor of NaF was kept constant at 930 C., and A.X gas at 6 liters/min. was used as vapor carrier gas.

The coating of the thus-obtained coated strip is continuous, being essentially free of coating gaps, and pinholes are extremely few in comparison with untreated strip.

EXAMPLE 11 A coil of cold rolled steel strip of 90 mm. width is coated with aluminum at a speed of 4 m./min. The strip is previously cleaned of grease on its surface by burning to achieve oxidation in an oxidizing furnace, and then introduced into a reducing annealing furnace, the atmosphere of which consists of A.X gas. The strip is heated for about 1 minute to 800-950 0., being thus reduced and annealed sufficiently. Then, it is introduced into the cooling zone, cooled therein in reducing atmosphere down to coating bath temperature (about 670 C.), and then introduced into the coating bath. At this time, the surface to be coated is treated, in the final cooling zone, with vapor of M In this case, the temperature to generate vapor of M00 was kept constant at 900 C., and N gas at 5 liters/min. was used as vapor carrier gas.

The coating of the thus-obtained coated strip is continuous, being essentially free of coating gaps, and pinholes are extremely few in comparison with untreated strip.

EXAMPLE 12 A coil of cold rolled steel strip of 90 mm. width is coated with aluminum at a speed of 3 m./min. The strip is previously cleaned of grease on its surface by burning to achieve oxidation in an oxidizing furnace, and then introduced into a reducing annealing furnace, the atmosphere of which consists of A.X gas. The strip is heated for about 1 minute to BOO-950 0., being thus reduced and annealed sufiiciently. Then, it is introduced into the cooling zone, cooled therein in reducing atmosphere down to coating bath temperature (about 700 C.) and then introduced into the coating bath. At this time, the surface to be coated is treated, in cooling zone, with vapor of CICI In this case, the temperature to generate vapor of CrCl tinuous, being essentially free of coating gaps, and pinholes are extremely few in comparison with untreated strip.

EXAMPLE 13 A coil of cold rolled steel strip of 90 mm. width is coated with aluminum at a speed of 4 m./min. The strip is previously cleaned of grease on its surface by burning to achieve oxidation in -an oxidizing furnace, and then introduced into a reducing annealing furnace, the atmosphere of which consists of A.X gas. The strip is heated for about 1 minute to 800-950 C., being thus reduced and annealed sufficiently. Then, it is introduced into the cooling zone, cooled therein in reducing atmosphere down to coating bath temperature (about 670 C.), and then introduced into the coating bath. At this time, the surface to be coated is treated, in the hood, with vapor of Cd.

In this case, the temperature to generate vapor of Cd was kept constant at 460 C., and A.X gas at 4 liters/ min. was used as vapor carrier gas.

The coating of the thus-obtained coated strip is continuous, being essentially free of coating gaps, and pinholes are extremely few in comparison with untreated strip.

What is claimed is:

1. In a method of coating a ferrous metal article with aluminum, wherein the surface of said metal article to be coated is previously reduced by means of reducing gas in a reducing zone and said article is then introduced into a molten bath of aluminum or alloy thereof while keeping said article out of contact with air, the improvement comprising the steps of cooling said article after said reduction, and pretreating said surface with an agent consisting essentially of a neutral or reducing carrier gas containing vapor of at least one of the following:

(A) elemental Bi, Sb, Pb, As, Se, P, Mg, Ca, Cr, Sr,

Ba, Cd;

(B) fluorides of the alkali metals, K, Na, and Li;

M003, and NazTiFfi; and

(D) halides of Si, P, Ti, Zr, V, Nb, Cr, Ta, Mn, Pb,

As, Bi, Sb and Se,

prior to introducing the thus-treated article into the molten aluminum coating bath whereby the surface of the ferrous metal article is provided with a continuous aluminum-containing coating which is essentially free from pinholes and blisters.

2. The improvement according to claim 1, wherein the reduction is effected concomitantly with annealing, the article is strip ferrous metal, and the vapor pretreatment is effected by applying the vapor containing carrier gas onto the surfaces to be coated, the said application being effected in a final cooling zone following the reducing annealing step.

3. The improvement according to claim 1, wherein the article is strip ferrous metal, and the vapor pretreatment is effected by passing said strip through vapor containing carrier gas atmosphere provided intermediate (a) a cooling zone into which the strip passes after the reducing annealing step and (b) the surface of the coating bath.

4. The improvement according to claim 1, wherein the reduction is effected concomitantly with annealing, the article is strip ferrous metal, and the vapor pretreatment is effected by spraying the vapor containing carrier gas as at least one spray onto the surfaces to be coated, the said spraying being effected in a final cooling zone following the reducing annealing step.

5. The improvement according to claim 1, wherein the vapor pretreatment is effected by spraying the vapor containing carrier gas at an angle from both sides of the article.

6. The improvement according to claim 1, wherein the vapor is generated in a vaporizing zone disposed within the reducing zone and the vapor is entrained by said reducing gas to the point of application thereto to the surfaces being pretreated.

7. The improvement according to claim 1, wherein the vapor is generated in a vaporizing zone disposed exteriorly of the reducing zone.

8. The improvement according to claim 2, wherein the vapor is zirconium tetrafluoride vapor.

9. The improvement according to claim 2, the vapor is potassium hexafluorotitanate vapor.

10. The improvement according to claim 2, the vapor is potassium fluoride vapor.

11. The improvement according to claim 2, the vapor is bismuth vapor.

12. The improvement according to claim 2, the vapor is magnesium vapor.

13. The improvement according to claim 2, wherein the vapor is bismuth and potassium fluoride vapor.

14. The improvement according to claim 2, wherein the vapor is antimony vapor.

15. The improvement according to claim 2, wherein the vapor is sodium hexafluorotitanate vapor.

16. The improvement according to claim 2, wherein the vapor is titanium tetrafluoride vapor.

wherein wherein wherein wherein 17. The improvement according to claim 2, wherein the vapor is sodium fluoride vapor.

18. The improvement according to claim 2, wherein the vapor is molybdenum trioxide vapor.

19. The improvement according to claim 2, wherein the vapor is chromium dichloride vapor.

20. The improvement according to claim 2, wherein the vapor is cadmium vapor.

References Cited UNITED STATES PATENTS 1,761,850 6/1930 Smith. 2,046,031 6 6/ 1936 Rodriguez 1175 1 2,437,919 3/ 1948 Oganowski.

Alferiefi 117-51 Graham. Lundin.

Knapp 11751 Teshi ma et a1. 1 1751 Coburn 11751 Whitfield et a1. Logan 11751 Bernick et a1 117-51 ALFRED L. LEAVITT, Primary Examiner U.S. C1. X.R.

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