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Historical Articles

November, 1952 issue of Plating

We are fortunate in being able to present the following review of papers presented at the recent International Conference at Dusseldorf, Germany attended by the author. Other Americans at the sessions were Mr. Carlson, Erie, Pa., representing the American Hot Dip Galvanizers Association, and Mr. Pearson of the Clifton Conduit Company, Baltimore.


INTERNATIONAL CONFERENCE ON HOT DIP GALVANIZING

ALLEN T. BALDWIN

AN INTERNATIONAL Conference on Hot Dip Galvanizing was held- at Dusseldorf, in Germany, from June 30 through July 4, 1952, which was attended by 180 delegates coming from Austria, Belgium, Denmark, France, Germany, Great Britain (including Northern Ireland and Eire), Holland, Italy, Norway, Sweden, Switzerland and the United States. This Conference was the second such meeting held by this group, the first having taken ace in Copenhagen in 1950. During the course of the Conference fourteen papers were presented and discussed extensively. In addition, the members had the privilege of visiting seven plants, one of which was a zinc smelter and the others were actively engaged in galvanizing tubes, structural steel and jobbing operations, wire and hollow ware and tanks. Several of the plants showed very recent construction or reconstruction and therefore were of much interest to those attending the Conference. The papers dealt with matters affecting the quality of the hot dip coating and numerous phases -of the construction and operation of the galvanizing shops themselves, including working conditions. The Zinc Development Association of Britain has taken the leading part in organizing these Conferences and carrying the burden of actual conduct of the meetings themselves in a very efficient and effective manner. The German Hot Dip Galvanizers Committee and Zinkberatung (Zinc Council) of Germany, made the arrangements for the local meetings and visits in and around Dusseldorf, which included visits for the ladies attending the Conference to points of interest to them. The Conference was ended by an excursion participated in by practically all members to Cologne and a boat ride along the Rhine.

The program opened with a series of three papers bearing on the conditions of the hot zinc coating which contributed to its ductility and to its adherence to the basis metal. These features are of outstanding importance to the galvanizers of sheet or strip steel.

In The Ductility of Hot Dip Galvanized Coatings, H. Bablik, Lecturer, Technical University, Vienna, is particularly concerned with the deep drawing characteristics of galvanized sheet steel which behaves as a compound body with an iron base and layers of zinc and zinc iron alloy. Tensile tests showed that the degree of possible crack-free deformation depended on the crystal orientation, cracks occurring in those crystals which are so oriented to the direction of the load that the normal stress in the plane of cleavage is exceeded. Since the deforming of the zinc layer results from the deforming of the iron base, experiments were conducted to measure the adhesion of the zinc to the iron base which showed that this adhesion is somewhat less in the presence of an iron zinc alloy layer than in its absence.

The Flaking of Hot Dipped Zinc Coatings, by M. L. Hughes, British Iron & Steel Research Association, discusses one of the results of unsatisfactory adhesion, namely, flaking or peeling. This author presented evidence to support his conclusion that flaking of itself could only occur when there was a three layer system, namely, the basis steel sheet, an alloy layer and the pure zinc layer. In the absence of this three layer system, cracking only might occur on distortion of the sheet. Flakes are said to consist of the pure zinc layer and alloy only. Under these circumstances any increase in the adhesion of the alloy layer to the basis steel would reduce the tendency to flaking. In general, freedom from flaking on sheets when being formed requires the creation of thinner total coating thicknesses.

The Effect of Aluminum and Iron on the Structure of Galvanized Coatings, by M. A. Haughton, British Non-Ferrous Metals Research Association, deals with one method of obtaining coatings of good adherence and freedom from flaking. Modern hot galvanizing methods for various reasons have led to the use of aluminum in the molten zinc baths in the order of 0.2 per cent or less, with the result that the alloy layers are very thin. Since the operation of galvanizing bath containing these quantities of aluminum have seemed to produce coatings of various types, this paper deals with the effect of iron dissolved in the zinc along with aluminum in an effort to explain some of the inconsistencies observed by others. Studies were made by using mixtures of zinc, iron and aluminum of quantities encountered in practice and melted in a graphite pot where the temperature was maintained at 450° C ±7° C (842° F ± 13° F). The effect of dipping time, as well as variations in the-iron and aluminum content, were observed metallographically and by weight loss. Part of the conclusions are that varying the iron content of a bath containing zinc only had no observable effect upon the metallographical structure of the coating or upon the rate of attack on the steel in the bath. The same conclusion applies to baths containing 0.05 per cent aluminum and various amounts of iron. In this case, the outer surface, however, is smoother and brighter. The addition of 0.1 per cent aluminum profoundly modifies the structure of the coating and the rate of attack on steel. With low iron content baths there is very little, if any, alloy layer. As the iron content rises there is an increasing tendency toward heavier attack of the steel and to the development of loose alloy layers. In baths saturated with iron the attack is of the rapid type. The addition of 0.2 per cent aluminum gives similar results but the protective film is thicker The whole picture suggests a critical unstable state where a slight change in conditions may completely reverse the effect of aluminum additions.

Observations on the Attack of Molten Zinc on Iron by Dr. R. Haarmann, Rheinische Rohrenwerke. He reports experiences with the attack of molten zinc on steel, with particular reference to what takes place in the steel kettle holding the molten zinc. This paper is intended to publish observations on interesting experiences that generally have led to unsatisfactory service life of the steel container. He discusses the effect of temperature, irregular heat application and the composition of the steel from which the kettle has been made, as well as the composition of the zinc bath itself. The attack on the kettle structure may be such as to cause large flakes to form and separate from the basis metal or pits may appear of various types. One factor of some importance in this field is the attack of the molten zinc on the grain boundaries of the steel, as well as the direct dissolving of the steel itself. The paper is accompanied by extensive micrographs and other data bearing on this problem.

The Potential Behaviour of the Iron-Zinc Alloy Layer of Galvanized Steel in Various Hot Aqueous Solutions by R. C. Weast, Department of Chemistry and Chemical Engineering, Case Institute of Technology, Cleveland, Ohio. This paper is a report of studies carried out in the laboratories of the Case Institute of Technology, in Cleveland, Ohio, on the conditions influencing corrosion of the hot galvanized coating. The studies include the potential behaviour of the zinc-iron alloy to observe if those factors known to influence the potential behaviour of zinc have a corresponding effect on the alloy layer. The effect on the alloy layer is complicated by many factors including the variation of zinc and alloy potential with solution composition, differential aeration cell effects, and relative corrosion and pitting effects. This study led to the following conclusions:

(1) The alloy layer of galvanized steel is cathodic to steel and zinc in a variety of waters whose chemical composition falls within the range of those commonly encountered in domestic supplies.

(2) The potential of the alloy becomes more cathodic as the temperature of the water is increased from 20° to 70° C (68° to 158° F).

(3) Solutions which cause the potential of zinc to become more cathodic with respect to iron also cause the potential of the alloy layer to behave in a like manner.

(4) The alloy potential becomes more anodic as the dissolved oxygen concentration in the water is reduced below the saturation value.

(5) Low concentrations of elements such as lead, tin, aluminum, and cadmium commonly found in commercial zinc do not make the resultant galvanized object as cathodic as does the iron-zinc alloy formed during normal galvanizing.

(6) The alloy potential is apparently sensitive to minor changes in the concentration of the corroding solution.

A Galvanizer’s Views on Bath Heating and Operation by E. McI. Wilson, Henry Hope and Sons, Ltd., England, was the first of a group of papers dealing with operations and equipment. Mr. Wilson presents a very complete picture of the factors involved in ,the selection and operation of the galvanizing kettle. This major piece of equipment is probably the most costly single piece and the place where there are great opportunities for inefficiencies to develop in the operation of the plants. He discusses the types of fuel, the methods of applying the heat, giving specific data on BTU requirements for various conditions of operation. This paper should be of practical value not only to those seeking to enter the field but to ‘those who already have shops of their own. An illustration of the care the author has taken to develop the important details is his illustration of the fact that a given plant if operated on a 3-shift 5-day week will only use 55 per cent of the amount of heat per ton galvanized that the same installation would use if operated with a single shift for 5 days. A study of the proper hours of use of the installation is shown to be most important. Likewise, he goes into detail to show the effect of changing dimensions of the kettle so that the perimeter of the surface area is kept as low as possible, to secure economy in use of fuel.

Top Heated Galvanizing Bath at Virsbo, Sweden by N. Thoren, Engineer, Wirsbo Brak Akt., Virsbo, is the story of a special installation which has beep operating successfully in. Virsbo, Sweden, for over two years. ‘ This installation consists of a container built of firebrick and has no steel walls coming in contact with the molten zinc. The heat is supplied by direct radiation from electrical resistors mounted over part of the top surface of the bath. This method of construction eliminates the question of burning holes through the steel bath walls with resultant losses, and eliminates the creation of dross by attack of the zinc on the steel container and provides a simple and trouble-free method of re-heating the zinc bath after there have been idle periods when the metal has been allowed to freeze. There are size limitations that are determined partly by the energy that can be radiated per square foot of the zinc surface. This development provides an attractive method of establishing a zinc bath for many uses. The heat requirement for actual operation of the kettle will vary from as low as 50 KW per ton to 100 KW per ton, depending in part on the relation of weight to surface of objects being galvanized.

The Galvanizing of Cast Iron by W. Montgomery, F. Braby & Co., Ltd., Glasgow, discusses the handling of an important line of products which galvanizers are called upon to galvanize. The problems in this field have to do with the creation of suitable zinc coatings that are smooth and adherent, and to have a low dross formation. The industry experience in this field is one of constant attention to the formation of dross which is higher in relation to the work done with steel objects. It is pointed out that the micro constituents of the casting which can influence the galvanizing action are graphite, carbide and silicoferrite. The writer concludes that silico-ferrite reacts more vigorously with zinc than pure ferrite. He concludes that only two procedures can be recommended of practical value to the general galvanizer. Shot blasting as a preparatory treatment gives the best results but this must be followed by a short acid dip and then the casting should be passed through a suitable flux blanket. The other recommended method is to follow an acid pickling with washing and dipping in a flux bath and there is an indication that a combination of these two recommended methods produces the best results, whether dealing with grey castings or malleable castings.

Flux Techniques and Hot Galvanizing Economies by A. T. Baldwin, Hanson-VanWinkle-Munning Company, U. S. A., is a resume of experiences gained with the use of the No. 20 zinc ammonium chloride type of flux in the United States during the past twenty years, showing that the processes developed with the use of this material in preparing work to be galvanized have been definite contributors to improvement in quality and lowering of costs in many fields.
Working Conditions in Job Galvanizing Plants by H. T. Eatwell is a report covering the steps that G. A. Harvey & Co., Ltd., of London, have taken in the creation of modern working conditions in their shops in that city. The article deals with floor construction, lighting, ventilation, heating, mechanical handling, galvanizing and pickling baths, and those facilities which provide comfort and health to the workers, such as washing facilities, etc. As a consequence, this article would be very important to those contemplating entering this field of manufacture.

The Economics of Galvanizing by F. C. Braby, F. Braby & Co., Ltd., is a discussion of the place materials, heating, labor, overhead, administrative and selling expense, enter into the cost of the hot galvanizing operation in England. This, of necessity, not only considers the costs of the materials but the ways in which to control losses and to salvage values from by products. It would appear that the cost of the zinc itself lies between 50 per cent and 70 per cent of the total cost, while acids vary from 1 per cent to 8 per cent, flux about 1 per cent, heating about 5 per cent, and labor varies from 6 per cent to 25 per cent.
Some Notes on the Recovery of Zinc from Galvanizers’ Ash by N. B. Rutherford, British Non-Ferrous Metals Research Association, reviews various methods of separating the granules of metallic zinc, which generally occur in the zinc ashes removed from the hot metal during the course of operation in the shop. About 60 per cent of the zinc melted leaves the shops in Great Britain as coating on the work and the balance of the zinc melted is converted to ash or dross and some of this zinc can be recovered in a suitable metallic form for further use. This brings up the question of the cost of recovery and this paper discusses the various methods that have been in use by galvanizers and leads to a recommendation of the use of a steel cylinder with an open bottom suspended in a remote corner of the galvanizing kettle. The ashes, as accumulated, are placed in this cylinder and are stirred into the surface of the molten zinc. This method recovers about 80 per cent of the metallic zinc present, with a minimum use of labor. This degree of recovery is only exceeded by the expenditure of a great deal more labor by other methods.

The Treatment of Pickle Liquors by A. R. L. Chivers, Zinc Development Association, Britain, discusses the composition of waste pickle liquors and methods of recovery. In the case of hydrochloric acid, which is used very broadly in England and on the Continent, there seems to be little to do other than neutralize to create a solution which can safely be discarded into a sewer or river. There are only limited possibilities of by-product recovery. With sulphuric acid, however, which is being used in galvanizing shops working on single products, such as sheets or tubes, recovery systems dealing with salvaging ferrous sulphate and returning the purified acid to the pickle system, are being used successfully. Illustrations of equipment for this purpose are given along with statistics of operation so that this subject matter should be of interest in connection with stream pollution problems in this country.

Trends in Hot Dip Galvanizing by R. W. Bailey, Zinc Development Association, Britain, is in part a summary of the impressions gained by the O. E. E. C Galvanizing Mission No. 78 of European galvanizers in the United States in the Fall of 1951. The papers presented at this Conference also disclose the trends in all fields of galvanizing. He points out that the United Kingdom and European galvanizing industries are compelled to make themselves efficient and competitive and, from the writer’s experience, this conclusion is in line with the facts, particularly as was demonstrated by the broad interest displayed by the members of the Conference in all the activities of the Conference.


 



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