FIELD OF THE INVENTION
The invention relates to a method to obtain unique electronic "signatures" of the
welding arc and to use them to estimate the chemical composition of the shielded
metal arc welding (SMAW) electrode coating. More particularly, the invention relates
to a novel method to determine the chemical composition electrode coating by
generating an electronic signature of an arc welding which eliminates the
disadvantage of prior art.
BACKGROUND OF THE INVENTION
In welding, Shielded metal arc welding plays a pivotal role. In this process, the
welding arc is established when a composite electrode (core wire + coating) melts
and establishes the welding arc using a power source. Several electrode coating types
such as rutile, cellulosic, basic coated and high efficiency iron powder types are
known to exist. In the commercial manufacture of electrodes, say for a given type pf
electrodes such a rutile type, may consist of dry mixtures of several chemical
compounds and minerals, deoxidizers, alloying elements and bound together onto the
core wire by use of water glass (sodium and or potassium silicates). Prior art methods
such as wet chemical analysis and even instrumental analysis suffer from several
infirmities when one attempts to do an analysis of chemical composition of the
electrode coatings. According to the prior art only elemental analysis is possible and
not the compound analysis, only crystalline materials can be analysed, need for
external and internal standards etc.

OBJECTS OF THE INVENTION
It is therefore an object of the invention to propose a novel method to determine the
chemical composition electrode coating by generating an electronic signature of an
arc welding which eliminates the disadvantage of prior art.
Another object of the invention is to propose a novel method to determine the
chemical composition electrode coating by generating an electronic signature of an
arc welding, which allows analysis of the arc behavior of coating electrodes.
SUMMARY OF THE INVENTION
Accordingly, there is provided a novel method to determine the chemical composition
electrode coating by generating an electronic signature of an arc welding. As per the
method of the disclosed invention, arc voltage -current signals are fed during a 20sec
arcing period of the SMAW arc to a computerized arc welding analyser. The output
from the analyser is in the form of a PDF (probability density function). This serves as
the signature of the arc which is a function of the chemical composition of the
coating, and this PDF distribution curve serves as the qualitative and quantitative
analysis of the coating composition.

A SMAW electrode whose coating has to be analysed is firstly connected to a power
source (AC/DC). An arc welding analyzer is also connected to the circuit. By using the
known hardware and software, the output data is collected for 20 sec from the arc
when the electrode burns and the arc are active. The resultant current and voltage
waveform is digitally converted into a probability density function (PDF) graph and it
is this PDF which serves as a signature of the welding electrode coating composition.
DETAILED DESCRIPTION OF A PREFERRED EMBODIMENT OF THE
INVENTION
A known data acquisition system was used to determine the electrical waveform
characteristics. Voltage was measured between the contact tip and the sample. These
points were considered as close to the arc as possible and represents the true arc
voltage. Current was measured using a Hall effect current sensor, and the wire feed
speed of the electrode was measured using a tachometer. The data acquisition
system gave waveforms of voltage and current vs. time, as well as statistical
histograms of voltage, current, and short-circuiting time. The histogram was
essentially a fingerprint of the weld, and quantified repeatability. To determine the
repeatability of weld parameters, identical welds were made and the histograms
superimposed on top of each other. Complex physical phenomena occur during the
arc transfer. The process appears dynamic, stochastic and non-linear. Various
sensors, such as electrical, optical or acoustical sensors are in use. Looking to the

robust and versatile application of a monitoring system, the electrical parameter
(welding voltage and current) can be seen as the most appropriate process
characterizing parameters. In the transient run of voltage and current, all process
information is stored, whereby disturbances can be recognized by variations of well-
known transient runs. Because of the complexity of these transients, the captured raw
data is further processed. An effective method can be seen in the application of
statistical methods to the non-deterministic stochastic welding process. The
description of a stochastic process is possible by means of probability density
distributions (PDDs) and class frequency distributions (CFDs). The definitions and
descriptions of both PDDs and CFDs, are known from the prior art non-patent
literature by Prof Rehfeldt. The PDDs and CFDs of welding voltage and current deliver
characteristic information of welding process behaviour.
In the first case, the above described system and process was used to obtain the
"signature" of a SMAW electrode coating. This is from a high efficiency 6.3 mm basic
coated low hydrogen SMAW electrode iron powder from a known manufacturer A.
From literature, it is seen that basic coated low hydrogen high efficiency electrodes
may contain a large number of materials such as calcite, fluorspar, and iron powder,
other slag formers and deoxidizers etc with silicate binders. The voltage and current
PDF curves are send to exhibit a characteristic shape. This may be taken as the
"signature" of the coating of electrode "A". (Graphs 1A and IB may be referred to).

COMPARISON OF A WITH B
It is seen that the shape of the voltage current PDF is very similar for this type of
electrode even though the formulations of coating of these electrodes are from two
different electrode manufacturers. Hence it is seen that on having the PDF of a given
master electrode, a person skilled in the art of electrode formuation development may
vary the ingredients of the formulation in such a way till a trial formulation "mimics"
the master PDF curve 100% (Graphs 3A and 3B may be referred to). This is the utility
of the novel method in analysing a coating formulation of SMAW electrodes.

WE CLAIM :
1. A novel method to determine the chemical composition electrode coating by
generating an electronic signature of an arc welding, comprising the steps
of:
(i) providing a known data acquisition system capable to determine the
electrical waveform characteristics;
(ii) measuring a voltage between the weldable article and contact trip of a
welding electrode which represents the true welding arc voltage;
(iii) measuring the welding arc current in a Hall effect current sensor;
(iv) measuring the wire feed speed of the electrode in a tachometer;
(v) feeding the measured values of voltage-current signals including wire-feed
speed to the data acquisition system which interalia outputs wave forms of
voltage and current corresponding to time including statistical histograms of
voltage, current and short circuiting time;

(vi) determining repeatability of weld parameters as provided by histograms of
step (v) by superimposing histograms ascertained for identical welds over
the histograms of step (v),
wherein the resultant current and voltage waveform is digitally converted to produce
a probability density function PDF graph, and wherein the PDF graph represents a
signature of the welding electrode coating composition.