US2222157A - Alloy - Google Patents

Description

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enema Nov. 19, 1940 PATENT OFFICE ALLOY John Ruzicka, Brooklyn, N. Y., assignor to At lantic Zinc Works, Inc., Brooklyn, N. Y., a. corporation of New York- No Drawing. Application October 2, 1939, Serial No. 297,591

5 Claims.

This invention relates to a zinc base alloy and l permit smooth etching without the employment of much care and skill, and require additional time and materials in the etching process to avoid loss of detail and of quality in the image on the plate through rough etching.

Ulreater hardness and toughness in zinc plates would also be desirable to increase resistance to wear and deformation. For example, the image etched in relief on the plate may include halftone dots only about two thousandths of an inch in diameter and height. High pressures of printing or of molding stereotype mats from the etched zinc plate frequently compress and distort these fine dots, causing loss of detail; in the printed image. Similarly, printing and stereotype-mat moulding operations may distort the dots by wear dragonsblood powder used as an acid resist in the etching process. These beatings cause deterioration of several properties of zinc plates, to an extent depending upon the number, temperature and duration of the beatings.

Uneresult of the heatings is that the plate becomes soft and less resistant to distortion and size and, under extreme conditions-, crystals readily visible to the naked eye are formed: since adjacent crystals in a piece of metal generally etch at different rates of speed, an undesirable roughness of the etched surface is produced. Accompanying this crystal growth is a permanent "stretch of the plate as a whole. In the printing of colored matter, where two, three or more separate zinc plates are employed, it is necessary that the stretch of each of the zinc plates be as nearly alike as possible. Otherwise the four images, superimposed on each other during printing, will not register perfectly; and the prints do not accurately reproduce the relative dimensions of the original. However, slight differences in the beatings of the four plates always occur. To minimize the effect of these differences in heatings, it is obviously desirable to have an alloy with as little stretch as possible, even after extreme beatings.

another effect of heating is a loss of stiffness of the plate while hot. Some zinc plates, especially those containing only one alloying element in solid solution in the zinc, become so limp during the hot top burning-in at 600 F. that they bend under their own weight during the normal handling involved in the burning-in operation. When this occurs, it is a difficult and tirne-con sumi'ng operation to flatten the plate again, without damage to the etched surface, since the metal becomes harder and stiffer as it cools.

The composition of the zinc base is of importance, as excessive amounts of other elements lead to dihiculties in obtaining the desired results.

For example, the presence of an undue proportion of lead would be undesirable, particularly in the presence of cadmium. The lead is practically insoluble in zinc in the solid state; therefore, during freezing -of the molten lead-containing zinc, the lead separates out as a separate phase. Since the lead freezes at a lower temperature than zinc, the lead tends to segregate coarsely. To minimize this coarseness of segregation, extremely rapid freezing is necessary. The fastest freezing which is feasible in commercial production does not prevent coarse segregation of the lead in the interior oithe zinc casting. The lead does not etch as rapidly as the zinc. Therefore, lead causes etching roughness to a degree in direct proportion to the coarseness of the lead particles in the zinc. While iron increases the hardness and resistance to abrasion, as well as the re-crystallization temperature, the compound of iron and zinc is so hard as to cause excessive wear on a routing tool. Further, the iron tends to segregate at increasing rates from the mold face of the ingot or slab to its top surface, thus resulting in a difference in reistance to rte-crystallization of the two surfaces hit of the rolled metal and a resulting warping when the plate'is heated. The principal objects of the present alloy and the plates formed therefrom are to overcome the above difiiculties; to provide a zinc base alloy capable of being rolled or otherwise formed into plates or strips which etch smoother than zinc plates now in general use in the printing industries; to provide a zinc base alloy with greater resistance to compression-distortion; to provide a zinc'base alloy with greater resistance to the effects of heating, including deterioration in etching quality, permanentloss of hardness and toughness, permanent change in dimensions, and decrease in stiffness duringheating.

Further objects will be apparent from a consideration of the following description.

It has been found that a zinc plate possessing the aforementioned desirable characteristics can be produced by alloying high grade zinc with small percentages of aluminum, nickel and magnesium. It is common knowledge that high grade zinc may be alloyed with small percentages of aluminum,-or any other one of several other 5 metals, to produce a. zinc plate having greater hardness and resistance to deformatiomand having smoother etching properties than the usual commercial-grade zinc plates; if in addition to the aluminum there is added nickel, or some other metal forming a hard compound with the 1 aluminum, a greater increase in hardness and toughness, and especially in wear resistance, is obtained. Nickel is preferable for this addition because it not only increases hardness, toughness and wear resistance, but also improves materially the resistance to the aforementioned effects of heating. From behavior of the metal, the nickel is probably present as an aluminum-nickel or an aluminum-nickel-zinc compound, and operates to give the alloy a greater resistance to abrasion without making it so hard generally or locally as to cause excessive wear of the routing However, the limiting percentage of nickel tool. is about 0.10 percent, and it is preferred to keep the proportion below 0.05 percent for plates which have to be routed. If in addition to the aluminum and nickel, a small percentage of magnesium is added, still further increases in hardness, toughness, stiffness and resistance to the effects 'of heating are obtained.

Although the relative percentages of the alloying ingredients may be varied, it has been found highly desirable if not essential for the production of commercially satisfactory plates, that the relative amounts of the alloying ingredients be" closely controlled and held below maximum limits. If this is not done, amounts of the elements in excess of such limits cause difficulties during the casting, rolling or polishing operations by which the plates are made, or during the photoengraving or printing operations of com- I mercial use of the plates. p

A satisfactory alloy is produced using a high grade zinc base containing less than 0.1% total of lead, cadmium and iron together, 'although other grades of z nc may be used. For a very high grade of metal according to the present invention, an electrolytic zinc can be employed, which contains as impurities from 0.01-0.015%

lead, com-0.002%- cadmium, and 0.001-0.002% 1 iron, with a total impurity of lead,'cadmium and iron of less than 0.02%. A greater quantity of impurity can be tolerated within the limits stated, but the final product does not have the superior quality of the preferred composition. To this zinc base is added 0.002-0.05% magnesium, 0.002- 010% nickel, and 0.05- 0.75% aluminum; preferably around 0.02% magnesium, 0.02% nickel, and 0.25% aluminum...

The capability of producing satisfactory alloys 5 cheaply and without the employment of the expensive aims of extremely high purity is note; worthy. It is found that the higher percentages of aluminum tend to increase the toughness of the alloy but to increase the price and difficulties 10 of preparing the master alloy: in particular, alloys containing from 0.5% of aluminum require much longer times for annealing, usually with the employment of higher temperatures to over come the greater segregation of aluminum by 15 formation of a cored structure during freezing, before rolling the plates from the ingots. Similarly, if the higher proportions of nickel are employed, a better abrasion resistance is obtained, but correspondingly with more wear upon rout- 20 ing tools and with greater difficulty in polishing the sheets; and such sheets are useful primarily for employments where routing and accurate mechanical working are not demanded. The proportion of magnesium should be carefully 25 controlled, as the higher proportions (above 0.03%, for example) lead to cracking of the edges during rolling, if extreme care is not employed in the reductions: .but such sheets have great toughness, and when sheets of such character are 30 particularly demanded, the higher percentages of magnesium can be effectively employed, with the utilization of higher rolling temperatures to overcome this greater tendency toward edgecracking.

A suitable method of incorporating the ingredients is as follows:

For easier and quicker solution of nickel and the aluminum in the zinc, each one is added as a separate master alloy which contains a relatively 40 high percentage of the alloying metal. This procedure is preferred, as it is difficult to effect a proper solution and mixture of both nickel and aluminum into the zinc base in-one operation: and the nickel and aluminum in a single master 45 alloy form,a high-melting compound which dissolves-with difliculty during the dilution with further zinc. Further, it has been found practically impossible to obtain a master alloy containing say 20 to 25 percent of aluminum and 2 5 to 3 percent of nickel, even upon heating at 1600 degrees F. for six hours beneath a covering of flux; whereas separate master alloys of such concentrations individually can be prepared at 1200 degrees F. in four hours. Simple master alloys, 65 containing lesser proportions and capable of easy preparation, contain too little of nickel and aluminum to be practical in commercial employment. A master alloy containing 20-25% aluminum and a master alloy containing 2-3% nickel 60 have been found to be' the most convenient. After the alloying metals of the master alloy are completely dissolved, each master alloy is cast into thin plates which can be easily broken.

The magnesium is added to the zinc directly 65 and, to minimize the loss of magnesium; by oxidation, it is added only a few minutes before the alloy is cast. a

Example A charge of 1000 pounds of electrolytic zinc of the aforesaid analysis was first melted in an electric induction furnace. After melting and reaching a temperature of 800-900 F., 10 pounds of a master alloy composed of 9.8 pounds of zinc and 75 0.2 pound of nickel were added; at the same time 110 pounds of a second master alloy containing 7.5 pounds of zinc and 2.5 pounds of aluminum were added. The molten metal was then held at BOO-900 F. until the nickel and aluminum were completely dissolved, rapid and uniform distribution of these metals throughout the bath being accomplished by a continuous stirring action. 91 grams of magnesium were then added, and a few minutes later the pot was skimmed. The molten alloy was then poured into iron molds and permitted to solidify. By analysis this alloy contained 0.25% aluminum, 0.02% nickel and 0.018% magnesium. The ingots or slabs were then rolled as usual to the thickness customary for etching plates, and were polished. These plates show a hardness in excess of 30-31 (Scleroscope) and 80 (Rockwell). They etch as rapidly and much smoother than the usual commercial zinc plates, and show particular excellence after annealing. The annealing process does not lead to warping and the grain size remains from to A of that of the usual zincs. The stretching after 15 minutes of heating at 600 F., for example, is around 0.0025 inch per inch. The material is very tough and permits moulding of at least a thousand or more stereotype mats before excessive wear: the wear in all cases of commercial employment has not been sufiicient to indicate the number of mats which can be prepared. The etching properties are far superior to those of the commercial zinc plates containing lead, cadmium and iron, and correspond to those of hard zincs now on the market. The sheets are stiller, especially when hot, than even zinc alloys comparable in other properties.

The following tabulation shows the advantage of the proposed alloy over other zinc base alloys employed for like purposes and over the common sort engravers zinc.

Composition Alloy Rockwell hardness Stretch Alloy r Annealed 4 min. at 600 F.

As rolled I 100 kg. load, W diam. ball. load applied for ten seconds.

Not tested for particular specimens.

3 Samples annealed for 4 min. at 600 F.. then quenched. followed by 16 anncalings of 1 minute each, each annealing followed by quenching in cold water. This simulates extreme burning-in conditions for a fhottop pjlatc receiving 5 etching bites and heated themuxrmum proiablo temperature which is reached commerdaily in "burning-in tho dragonsblood acid-rcsist.

Commercial trials of the above alloys, have yielded the following results:

A l ltchitiiilg Hot Ntgmbter of y smoo rec y ness mess mats Good Good Poor 50. Verygood. Good Over 1,000. Verygood. Poor Over 1,000.

l Diiiicult to grind and rout.

Thus, although the individual alloying elements each furnish certain properties, all are necessary to yield all the desired properties and their combinede'fiect is greater than merely the adding together of their individual effects.

When the proportions of impurities such as lead, cadmium and iron are higher, and with less than 0.1% of the total, the material still retains its hot stiffness, hardness, resistance to, stretch and to wear, but usually the smoothness of the etching decreases, and there is greater resistance to routing operations.

It is to be understood that the above discussion is only for the purpose of illustration and that various changes and modifications may be made without departing from the scope of the invention.

I claim:

1. A zinc alloy consisting of 0.005 to 0.10% nickel, 0.05 to 0.75% aluminum, 0.002 to 0.10%. magnesium. and the balance zinc containing as a total less than 0.1% of iron, lead and cadmium.

2. A zinc alloy consisting of substantially 0.02% nickel, substantially 0.25% aluminum, substantially 0.02% magnesium, and the balance zinc containing as a total less than 0.1% of iron, lead and cadmium.

3. A zinc alloy for printing and stereotypemat-moulding plates and having qualities of hardness and toughness and resistance to deformation while hot. consisting of 0.005 to 0.10% nickel, 0.05to 0.75% aluminum, 0.002 to 0.10% magnesium, and the balance zinc containing as a total not substantially exceeding 0.02% of iron,

lead and cadmium.

4. A zinc alloy for printing and stereotypemat-moulding plates and having qualities of hardness and toughness and resistance to deformation while hot, consisting of substantially 0.02% nickel, substantially 0.25% aluminum, substantially 0.02% magnesium. and the balance zinc containing less than 0.015% lead, 0.002% cadmium, and 0.002% iron.

5. The process of forming a zinc base alloy containing aluminum and nickel, which comprises preparing a first master alloy of high grade zinc containing 20 to 25% of aluminum and a second master alloy of high grade zinc containing 2 to 3% of nickel, melting a charge of zinc containing a total of less than 0.1% of iron, lead and cadmium, introducing and stirring portions of the master alloys into the molten charge until the same cc'ntains .005 to 0.10% nickel and 0.05 to 0.75% aluminum, adding magnesium to a percenta e f 0.002 to 0.10%, and pouring the charge before substantial oxidation of the magnesium occurs.

JOHN RUZICKA.