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Description  |
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This invention relates to a method of making objects which may be later
inspected using X-ray techniques. In particular, this invention relates to
a marker which may be used to mark, in an unobtrusive manner, textile
substrates, yarns, or other objects for purposes of locating defects or
identifying components which would otherwise be difficult or impossible to
detect visually. The marks made by such marker may be readily detected
using conventional X-ray apparatus.
X-ray techniques are frequently used in applications where components which
are ordinarily hidden from view must be observed or inspected. For
example, airframe and aircraft engine manufacturers may use X-ray
techniques to detect structural flaws and confirm proper assembly of air
frames and aircraft engines. Generally, such inspections require some
means to identify or make visible principal elements within the X-ray
field of view, for example, the outline of a particular component or set
of components within the object to be inspected, or require some means to
draw attention on the X-ray image to a particular region of interest. It
is also frequently desirable to provide some means to allow identification
of the particular manufacturing batch or lot number or origin of
manufacture of one or more components hidden from direct view.
Presently, these objectives frequently have been met by use of a
radio-opaque metal marker or pointer made from, or perhaps painted with, a
radio-opaque material, or by use of adhesive-backed tape carrying a
radio-opaque substance, which has been placed on the part or parts of
interest. For example, small sections of adhesive-backed foil made
primarily of lead are commonly used for these purposes. Use of such foils
or other adhesive backed markers are not satisfactory for many
applications, especially where the adhesive used is not effective in
maintaining the position of the marker, or in cases where it is either
difficult or impossible to place a foil or tape on or in the desired
object, or to remove the marker after X-ray inspection has been completed.
Furthermore, such foils or tapes are expensive to manufacture, and can
comprise a potential health hazard, particularly if lead is involved.
It is contemplated that liquid inks or paints, to which radio-opaque
material has been added, may be used for the purpose of marking or
identifying objects under X-ray illumination. However, such liquids may
not be suitable for use with porous or semi-porous items (such as textile
products) because of the tendency of the liquid to migrate, via capillary
action or forces induced by the manufacturing process, into areas not
intended to be marked, and because of the need to allow such liquids to
dry before they contact other objects not intended to be marked. Also,
such liquids can create a potential health hazard if inhaled, in the form
of aerosols or vapors, during the application process.
The invention described herein provides a relatively safe, effective, and
convenient means to mark a wide variety of objects for which the
conventional techniques discussed above would be unsatisfactory. The
following description refers to the accompanying figures, in which
FIG. 1 depicts a crayon embodying the invention disclosed herein, and
FIG. 2 depicts a crayon used to mark a substrate containing textile yarns
in accordance with the invention disclosed herein.
In a preferred embodiment, a crayon or marking pencil 1 such as is depicted
in FIG. 1 comprised of a solid radio-opaque substance 3 such as finely
powered bismuth trioxide (Bi.sub.2 O.sub.3), uniformly dispersed within a
waxy medium 5 such as paraffin wax, is used as a marker to apply a mark to
the object to be inspected or marked. It is believed other heavy metal
containing compounds (such as an oxide, sulfide, sulfate, nitrate, etc.)
of bismuth, lead, cadmium, barium, or other suitable element having an
atomic number greater than about 56 may also be used, or may be preferred
in certain circumstances. The relative proportion of the dispersed
radio-opaque substance to the dispersing medium, the relative granularity
of the radio-opaque substance, the absolute amount of the radio-opaque
substance deposited, as well as other factors, will determine the visual
contrast observed on the X-ray image, while the extent to which the
dispersing medium rubs off and/or adheres to the object being marked, as
well as the color of any pigment or other coloring agent additionally
introduced into such medium, will determine the visual contrast generated
by the crayon. Certain radio-opaque substances contemplated herein, due to
their inherent color in the medium, may make the addition of additional
pigments or coloring agents unnecessary. Therefore, depending upon the
application, the crayon can make a mark which, while being quite prominent
when seen in an X-ray image, could be either prominent or unobtrusive to
the unaided eye when viewed under ordinary illumination, depending upon
the nature of the radio-opaque substance and whether an additional
coloring agent is used. It is contemplated that, optionally, the crayon
could contain, in addition to the radio-opaque substance, a suitable
conventional fluorescing composition which would provide enhanced contrast
when viewed under appropriate illumination, for example, ultraviolet
illumination.
It is contemplated that, while paraffin wax is a preferred dispersing
medium, any suitable wax-like, resin-like or rosin-like material having a
melting point over about 110.degree. F., and into which a suitable
radio-opaque substance may be dispersed, may be used. For example,
appropriate hydrocarbon waxes, polyethylene oxides, or low molecular
weight polyethylenes may be used. In some applications it may be difficult
or inconvenient to apply a mark which is sufficiently observable, either
because the mark is not sufficiently durable, or because of difficulty in
applying a sufficient quantity of marker material. For example, certain
applications may require that beeswax or various glues be employed as the
dispersing medium; these substances may be relatively hard, i.e., exhibit
high cohesion. If, for example, a relatively soft textile fabric is to be
marked with a material which can withstand the various dyeing and
finishing operations to which the fabric may be later subjected, it may be
necessary to use a dispersing medium which is relatively hard, and which
therefore may be rather difficult to transfer to the fabric without high
applicator pressure. In such cases, it is contemplated that a crayon
comprised of such dispersing medium may be applied by using an appropriate
solvent, or by using a heat source such as a heat gun or a device similar
to a conventional hot melt glue gun.
In one embodiment of this invention such as depicted in FIG. 2, a crayon
containing a radio-opaque substance may be used by a textile inspector to
mark areas of a moving textile substrate 7 or substrate component (for
example, textured yarn) which contains an objectionable defect with a
small quantity of abraded crayon material 9. Depending upon the ultimate
end-use of the fabric, the defect detection protocol, the number of
allowed defects, as well as other factors, the crayon may be pigment
impregnated or tinted to a color which tends to maximize or minimize the
visual contrast of the marks.
It is customary in the textile industry to transport and store textile
fabrics during various stages of the manufacturing process either in the
form of large wound rolls of a continuous web of fabric, or in the form of
stacks of discrete sections of cut fabric. Manufactured yarn is also
stored in wound rolls prior to its fabrication into textile fabrics. In
either case, marks made during various inspection stages on all but the
outermost portion of the fabric rolls or stacks or yarn rolls are hidden
from view by the outer layers of fabric or yarn. Use of a radio-opaque
marking material to mark desired portions of the fabric or yarn prior to
winding on a roll, in conjunction with an appropriate conventional X-ray
device, allows observation of the number, size and position of marks
within the roll, which marks would otherwise be undetectable.
It is further contemplated that this technique may also be used to tag or
identify yarn, scrims, or other textile products which are integrated into
other products. For example, marks identifying the manufacturer may be
placed on the yarn, scrim material, etc. to be integrated into an
industrial belt or vehicle tire. Through the use of conventional X-ray
apparatus, such marking will allow identification of the manufacturer of
the yarn or scrim at any time during the life of the assembled belt or
tire.
EXAMPLE 1
A radio-opaque crayon was made by melting paraffin wax, and adding to the
melt approximately 35 percent (by weight) of lead (mono) oxide, PbO, in
fine powder form. The mixture was stirred continuously while the
temperature was lowered, so as to keep the dense lead compound uniformly
suspended in the paraffin dispersing medium. At a temperature of
approximately 110.degree.-120.degree. F., the mixture was soft and
pliable, and was shaped into a generally cylindrical crayon shape, and
then allowed to cool completely to room temperature. This same procedure
was also used to make crayons containing the same medium, i.e., paraffin,
but using powdered barium sulfate (BaSO.sub.4) in one case and using
powdered bismuth (tri)oxide (Bi.sub.2 O.sub.3) in the other, using the
same relative proportions. Thus, a total of three different crayon species
were made.
Small swatches of a woven textile fabric were marked using all three
crayons made as described above. The swatches so marked were then examined
using a conventional X-ray inspection machine having a video display,
using X-ray tube voltages ranging from 30 kilovolts to 90 kilovolts and
using X-ray tube plate currents ranging from 2 milliamperes to 30
milliamperes. The resulting X-ray images showed the marks easily; the
presence of the radio-opaque substances allowed a lower intensity of
X-rays to penetrate, as compared to the surrounding areas.
Swatches marked as described above were also placed between unmarked
fabric, thus hiding the marks from direct view. In this simulation, the
marks were not visible. Again, X-ray inspection techniques as described
above allowed an easy observation of the marks hidden within the
structure, due to the presence of the radio-opaque substances.
EXAMPLE 2
A radio-opaque crayon was made by melting paraffin wax, and adding to the
melt approximately 50% (by weight) finely divided bismuth (tri)oxide
(Bi.sub.2 O.sub.3). The mixture was stirred continuously while the
temperature was lowered, in order to assure relatively uniform dispersion
of the radio-opaque bismuth compound. At a temperature of approximately
110.degree.-120.degree. F., the mixture was soft and pliable, and was
shaped as in Example 1. The marking of small swatches was performed as in
Example 1, with similar results, except that enhanced contrast in the
X-ray image was noted. Because of the yellow color of bismuth trioxide in
the melt, visual contrast of marks made with this crayon on yellow
swatches was minimal, and the marks made on such substrate were quite
unobtrusive.
EXAMPLE 3
The procedures of Example 2 were followed, except that a small quantity
(about 1.5% by weight) of carbon black was added to the melt. The result
was a radio-opaque crayon capable of generating marks on light-colored
(e.g., yellow or white) fabric swatches which showed significantly
increased visual contrast compared with the crayon of Example 2.
Although the preferred embodiment of the invention has been described, it
is contemplated that changes may be made without departing from the scope
or spirit of the invention and it is desired that the invention be limited
only by the scope of the claims. For example, the relative proportion of
radio-opaque material to dispersing medium may be varied over a wide
range, limited primarily by the degree of X-ray contrast desired (higher
proportions yielding higher contrast) and the mechanical properties of the
crayon (proportions higher than a certain material-dependent threshold
yielding poorer mechanical stability).
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