An Improved Process and Preparation for Coating Iron or Steel.
Year: 1898

page_text: Date of Application, 17th May, 1898-Accepted, 23rd July, 1898
[Communicated from abroad by WILLIAM JOHN WILDER, of West Chicago, in
the State of Illinois, United States of North America, Manufacturer.]
An Improved Process and Preparation for Coating Iron or Steel.
I, WILLIAM PHILLIPS THOMPSON, F.C.S., M.I.M.E., of the Agency for Foreign
Patent Solicitors, 322, High Holborn, in the County of Middlesex, 6, Lord Street,
Liverpool, and 6, Bank Street, Manchester, both in the County of Lancaster,
Lower Temple Street, Birmingham, in the County of Warwick, Civil Engineer,
do hereby declare the nature of this invention and in what manner the same
is to be performed, to be particularly described and ascertained in and by the
following statement:
-
As is well known, galvanized iron and steel, though of great value, and used
in immense quantities in the industrial arts, have several serious defects. Among
these are the unevenness of the coating; its brittleness; the weakness of its
attachment to its base; its liability to be detached by the rusting of the base
beneath it; its tendency to crack and flake off when the base is bent at a sharp
angle or doubled back; its liability to be detached from its base and destroyed
by expansion and contraction; and its inability to resist the corrosive action of
sulphur and gases usually present as impurities in the air of large cities.
The chief objects of my invention are first to provide an article of plated metal
which while possessing the virtues of galvanized iron and steel, will be free
from their defects, and at the same time cheap enough to enable it to compete
with, and displace them for all purposes for which they have heretofore been
used, and second to provide a process for producing the desired product.
In manufacturing my improved plated metal I preferably proceed in the
manner hereinafter described. For the coating I prepare or have prepared an
alloy whose preferred composition is substantially as follows:
84 per cent. by weight of zinc.
14 per cent. by weight of tin.
15 per cent. by weight of lead.
5 per cent. by weight of aluminum.
The specified proportions though considered the best are not essential, nor is
it essential to use all of the metals mentioned.
The proportion of tin may be reduced as low as about six per cent. or on the
other hand increased to ninety per cent. of the whole, and what is subtracted
from or added to the weight of the tin used may be added to or subtracted from
the weight of the zinc, so as to leave the joint weight of the zinc and tin about
the same as in the formula. Where, however, the proportion of tin used is

page_text: reduced, the heat used in preparing the alloy and in applying it to sheets coated
therewith, has to be increased, and where the proportion of tin used is as low as
six per cent. the heat which has to be used is so great as to endanger the zine
contained in the alloy as well as the pot in which it is melted and moreover the
results are not so good even where the other metals are not injured, as they are
where the preferred proportion of tin is used. The objection to increasing the
proportion of tin used is that it involves an increase in the cost of the finished
sheets without materially improving their coating.
Lead is not an essential element of the alloy. It is used in order to give it
great fluidity when melted and so as to enable it to flow more freely and smoothly
over the surface of a sheet being coated than the alloy does where lead is omitted,
and its value is rather in the process of coating than in the coating when formed.
Where less than one and a half per cent. of lead is used the fluidity of the mixture
is correspondingly diminished but even where none at all is used good results
may still be secured by using more care and skill, than would otherwise be
called for. The proportion of lead used may be increased to 2.5 per cent, without
materially affecting the value of the alloy but if substantially more than that
is used the surplus does not combine with the other metals used but sinks to
the bottom of the melting pot. In doing this it carries other metal with it and
causes an undesirable waste.
Where the proportion of lead in the alloy is increased, the weight of either
the zinc or tin or both, may be decreased by subtracting from one or both,
enough metal to compensate for the lead added.
Aluminum is of great value in the alloy, in improving its appearance and in
assisting a coating formed of it, to form a union with its base and resist the
action of sulphur and gases.
+
The proportion of aluminum used may be reduced as low as one eighth of
one per cent. of the alloy, but the results are not so good in that case as where
the preferred proportion is used. So also the proportion of aluminum used may
be increased to 75 of one per cent. but if substantially more than that amount is
mixed with the other metals the surplus aluminum will not combine with them
but will rise to the surface of the mixture and should be skimmed off. The
more perfectly combined the elements of the alloy are, the better it will answer
as a coating.
In making the alloy the metals should preferably be melted together in the
usual way and kept in the molten state and stirred occasionally until they are
perfectly combined. This generally occupies from thirty-six to forty-eight
hours and I prefer to keep the elements of the alloy in the melted state and
stir them occasionally for the latter period.
In practice I have prepared the alloy in the pot used in coating the sheets
and have used the alloy as formed without allowing. it to cool but as will be
evident the alloy may be either used as soon as made or allowed to harden and
afterwards re-melted. Where, however, the alloy is allowed to cool slowly the
constituent metals tend to separate, and when melted have to be re-united which
occupies some hours. In making the alloy the heat used should be sufficient
to melt all the metals which enter into it, and not high enough to destroy or
materially injure either of them.
The alloy when made may be used while in a molten state as a bath for coat-
ing iron and steel just as melted zinc is commonly used in making what is com-
monly termed galvanized iron or steel and the coating may be applied by dipping
the sheets or other articles to be coated into the molten bath and then with-
drawing them or by passing them through the bath, according to either of the
methods used by galvanizers. I prefer to keep the bath at a temperature be-
tween 600 and 900 degrees Fah. The necessary heat depends largely upon the
amount of tin used. Where as little as six per cent. of tin is used I prefer
900 degrees, but where the preferred proportion of tin is used (14 per cent.) I
prefer to keep the bath between six and seven hundred degrees Fah. I seldom

page_text: use less than seven per cent. of tin and when I use that proportion I obtain good
results by keeping the bath at a temperature between seven and eight hundred
degrees Fah. I generally use the higher heat. All that is essential however,
is to keep the alloy fully melted on the one hand, and on the other, to avoid
increasing the temperature of the bath high enough to injure either of the
constituent metals.
The alloy above described may be applied as a coating to either iron or steel
but in the manufacture of plated sheets I prefer to use sheet steel as a base.
Before introducing the sheets or other articles into the bath they should be
thoroughly cleansed preferably in a suitable pickle, after the manner usual in
galvanizing. If the sheets or other articles have any acid adhering to them
when withdrawn from the pickle it should preferably be thoroughly removed
therefrom before they are coated. The sheets or other articles when coated should
preferably be perfectly free from either rust or acid.
After cleansing the sheets or other articles they should have a suitable flux
applied to their surfaces. Either of the fluxes used by tin platers will answer.
It may be applied in the manner in which fluxes are usually applied in making
galvanized iron and steel, or in any other manner known in the art of plating
iron and steel.
After receiving a suitable flux the sheets or other articles to be coated may be
introduced into the bath of molten alloy and withdrawn therefrom according
to either of the methods now in use in plating with zinc, or in any other suitable
manner. Where either iron or steel is treated in this way, the heat of the bath
appears to alloy that portion of the coating next the base with the metal of the
base. The union between them is perfect and cannot be affected either by expan-
sion and contraction or bending the finished article. The coating is as flexible
as the coated base, and so tough and tenacious that sheet steel or iron can be
worked up into articles of manufacture as well after coating as before, in which
it differs radically from galvanized iron and steel. As is well known, most articles
of galvanized iron or steel are coated with zinc after they are made.
My improved coating is far superior to zinc in texture and appearance. The
texture of the coating in its preferred form is fine, smooth and homogeneous
and in appearance it resembles aluminum. In its power of resisting corrosive
agents my plated metal is far superior to either galvanized iron or steel and I
judge from exhaustive tests that it is 'more durable than tin plate and superior
to it for many purposes. It may be heated red hot without injury to the coating
and is superior to either galvanized iron or steel for making household utensils.
For roofing and all other architectural sheet metal work my sheets are superior
to any other plated sheet metal with which I am acquainted.
I do not wish to be confined when my claims are construed, to an alloy con-
taining lead, except where it is specified; or to one in which the metals entering
into it are combined in the preferred proportions herein before specified, and
where I specify zinc, tin and aluminum as contained in the coating, I do not
wish to be understood as excluding all other metals. Lead, for instance, may
either be combined with the zinc, tin and aluminum or entirely omitted as has
been hereinbefore explained.
Having now particularly described and ascertained the nature of my said
invention and in what manner the same is to be performed, I declare that what
I claim is:
1. An improved flexible tenacious coating for iron or steel consisting of an
alloy of aluminium tin and zinc with or without lead and prepared as and in the
proportions substantially as hereinbefore set forth.
2. The improved process for coating iron or steel, consisting essentially in
preparing a molten bath of an alloy containing aluminium tin and zinc, with
or without lead cleansing iron or steel and applying a suitable flux; and after

page_text: applying the flux introducing said iron or steel into and withdrawing it from the
bath, substantially as described.
W. P. THOMPSON & Co.,
322, High Holborn, London, W.C.,
Patent Agents for the Applicant.