Note: Descriptions are shown in the official language in which they were submitted.
~0~ 5~
BACKGROUND OF THE INVENT ION
1 Field of the Invention
This invention relates t~ a marking composition for
hot metal articles, especially iron or steel articles, and relates
also to a method of applying the marking composition to the sur-
faces of such articles.
2. Description of the Prior ~rt
-
The conventional way to mark a hot steel article is by
writing by hand on the surface with a chalk stylus or waxy crayon
that melts at high temperatures and leaves a permanent mark. The
- marking of a hot article in this manner is unsatisfactory because
of the proximity of the person marking to the article in parti-
cular on account of the high temperature and the attendant dangers
to health which can lead to fatigue, inattentiveness and wrong
markings. Because the work is monotonous the risk of errors is in-
creased. When markings are absent, an ingot, bloom or slab is not
identifiable and is therefore declassified which involves a signi-
ficant economic loss. Also the labour costs are high with such a
method.
~apanese patent publication No. 65.08019 proposes the use
of a ceramic material as a marking for hot steel, and suggests
spraying the material onto the surface, specifically with reference
to an aqueous solution of ZnS04 (Example 1) and a slip containing
; sodium silicate, boric acid, anhydrous chromic oxide and 49% water
(Example 2). The use of a powder i~ mentioned in passing. A glaz-
ing of the material appears to be aimed at, to produce a glassy
layer which in fact will tend to break during subsequent rolling of
the steel in the mill. The use of wet materials is also disadvanta-
geous, since the steam produced on contact with the hot metal
- 2 - ~
-: :
1~3'^~
removes a large amount of the useful material.
U~S~Ao patent No. 3~296,6~9 disclo-qes the uqe of an
aluminium paint for marking metal, specifically suggesting the
application of a paint containing ,20% aluminium flakes in a r~sin
varnish by a brush. Spraying is suggested as an alternative. The
purpose of the aluminium is to provide a detectable zone of dif-
ferent temperature on the hot steel article.
SUMMARY OF THE I~lVENT ION
.
It is an object o~ the invention to provide a marking
matesial for hot metal, especially steel, which adheres reliably and
sufficiently tenaciously to survive subsequent treatment.
It is another objoct to provide a marking material which
is suitable fo~ application in a manner which permits the operator
to be a sufficient distance from the article for safety.
It is yet another object to provide a marking material
which can be applied by means of simple equipment which suffers
little wear and requires little maintenance.
~- According to this invention there is provided a marking
` composition for hot metal articles which is a dry powder suitable
for application to a hot metal surface in dry powder form and con-
sists of at least three components, which are a pigment, aluminium
and an adhesion agent, the aluminium being provided to act as a re-
ducing agent to rleduce oxide on the hot metal surface, and the ad-
hesion agent being effective to cause adhesion at a temperature
which is not lower than 200C. The materials selected should be
recistant- as necessary to the temperature of the surface to which
they are to be applied. The minim~m temperature of effectiveness
! of the adhesion agent may be well above 200C; for instance the
~ temperature of the metal may be 1200C.
- -~0~ S4
In the case ~f iron or ~teel surfaces, the alwminium
powder serves to reduce the primary rollin~ oxide of iron, thereby
preventing or minimizing ~ubsequent flaking of~ of the mark with
underlying rust.
It is of particular importance that the material is dry
when applied. The carrier gas used to spray it onto the metal
surface is desirably very dry also, and if compre~sed air is used
it is desirably pre-conditioned to be dry and dust-free.
Requirements which may be set for a marking powder are
that it should not be poisonous and that it should not contain pre-
dominantly volatile components. Reguirements which may be set for
the mark obtained are that when the article is both hot and cold the
contrast and visibility of the mark should be good and further that
the mark ~hould not come off during after-rolling. The mark should
not contain compounds detrimental to the steel; it should be tem-
perature resistant in the event of subsequent thermal after-treatment
and it should not disappear during storage or transport in the open
air. These re~uirements can be met by materials embodying the in-
vention.
Preferably the aluminium powder is more than 50% by weight
of the marking material and preferably also it has a maximum grain
size of not more than 60o microns.
The preferred pigment is TiO2, though other known suitable
pigments may be employed, for instance chromium oxide, though it
suffers the disadvantage of being poisonous.
One suitable adhesion agent is a waxy chalk in powder
form, particularly that available under the Trade Name "Bowax"
This however suffers from the disadvantage that it contains talc
(Mg3Si4010(0H)2) which is thoug}tto be injurious to the respiratory
.
organs. Another suitable adhesi~n agent is anhydrous silicic
acid (SiO2). Most preferred, however, is the bonding clay ~entonite,
in dry form, with a low magnesium content, e.g. less than 5%.
According to the invention in another aspect, there is pro-
vided a method of applying marking composition to the surface of a
hot metal article, wherein the composition is a composition of the
invention as described above and is applied in dry condition by
means of a carrier gas jet.
The composition and method of the invention can be employed
not only in the marking of steel in the form for instance of hot
ingots, blooms, slabs and plates, but also with equally good re-
sults in the marking of iron, e.g. hot cast iron casting moulds
(coquilles) and casting plates.
BRIEF DESCRIPTION 0~ THE DRAWINGS
A preferred embodiment of the method of the invention is
illustrated by way of non-limitative cxample in the accompanying
drawing, in which the single figure i9 a diagrammatic view of a con-
ventional spray gun modified for carrying out the method.
Referring to the drawing, a hot steel ingot 1 to be marked
is shown diagrammatically, moving below the output nozzle 2 of a dry
spray gun 3 from which emerges a carrier gas jet 4 carrying the dry
marking powder onto the hot ingot 1.
The hand-operated spray gun 3 is of a conventional type;
examples are the ~ype GB flock gun of The DeVillbiss Company,
Toledo, ~hio, United States of America and the Type Ecco 40 gun of
- the Atlas Copco Tools AB. No protec~ion is sought for the gun per
se. The gun is modified by the provision of a longer delivery pipe
5 which extends from a mixing vessel ~ to the nozzle 2. A suitable
-- nozzle size is 3 mm.
.
tj~
Compressed air, preconditioned to render it dust-free and
dryJ is supplied through a hose 7 which is connected to a nipple 8
to a ~ore 9 in the handle 10 of the gun 3. A trigger lever 11
operates the main operating valve 12 which is in the bore 9. A
needle valve 13 permits adjustment of the pressure of the air.
Typically, the pressure in the hose 7 may be 6 atmospheres, and i9
reduced to 0.2 - 1 atmosphere by the valve 13.
The handle 10 i8 fixed to a cap 14 for the vessel 6 and the
bore 9 is extended to within the ves~el 6 by a tube 15 having an
off-centre end, so that the air emerging from it sets up a vortex
which whirls up the marking powder 16 contained in the vessel. Thus
the powder is entrained in the air stream which passes into the de-
livery conduit 5 through the cap 14. A highly constant concentra-
tion of powder in the air jet can be achieved in this way.
The length of the extended delivery conduit 5 is in this
embodiment about 2.5 metres, so that the operator's hand can be
that distance from the hot metal surface. The nozzle is preferably
at about 5 cm. from the hot surface.
EXAMPLES OF THE INVENTION
Some preferred marking compositions embodying the in-
vention are given in the following examples.
- 6 -
~v~ s~
Component Grain Size Parts by
weiqht
. .
Example 1
Ti2 ~3~ ; <5~ 2
Al <600~ 8
; Dry "Bowax" <37~ 5
Example 2
Ti2 >3~ ; <5~ 4
Al <600~ 16
Dry SiO2 <40~ 5
10 ExamPle ~
2 ~3~ ; ~5~ 2
Al <600~ 8
Dry Bentonite containing
; 2.5% Mg by weight ~75~ 5
Each of these powders were applied to a steel surface
having a temperature of 1200C by means of the conventional hand-
held powder ~pray having a lengthened delivery conduit illustrated
in the drawing, so that the operator's hand was at least 250 cm~
from the metal surface. Compressed air was supplied at a pressure
of 6 atmospheres reduced to 0.2 - 1 atmosphere before entering the
vessel 6 containing the powder. The nozzle of the gun wa~ moved
at about 5 cm. from the hot surface. Satisfactory marking was
achieved in each case. The marks adhered immediately and securely
and showed high resistance to subsequent treatment of the steel.
While the invention has been illustrated above by re-
; ference to the preferred method and several preferred examples, it
will be understood by those skilled in the art that various changes
may be made without departing from the -spirit and scope of the in-
vention and it is intended to cover all such changes and modifi-
cations by the appended claims.
7 --
~. .
.
