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Straight Polarity - The machine will operate on straight polarity when the electrode holder cable is connected to the terminal marked NEGATIVE, ELECTRODE, or MINUS SIGN. The ground clamp is connected to the terminal marked POSITIVE, GROUND, WORK, or PLUS SIGN. If the machine is equipped with a polarity change switch, the switch should be in the position marked NORMAL, NEGATIVE, or STRAIGHT. Skip Welding - Skip welding is, as its name implies, welding intermittently. Each pass is applied as far from the last pass as possible. The unconnected beads are finally joined with another series of passes. This method is used on heat sensitive material to prevent a local build-up of heat. It is possible to keep a casting to a comhand-heat throughout the welding operation if this technique is used. Straight Beads - When the width of the weld deposit is approximately the same as the diameter of the electrode the beads are known as straight beads. This applies also to oxyacetylene torch welding. Beads deposited without weaving are called STRAGHT or STRINGER beads. Slag Removal - This is a term given to loosening and removing the slag adhering to the weld deposits. The deposit is struck with a chisel-shaped or pointed hammer and then brushed with a wire brush. This removes the slag and exposes the weld deposit. The slag forms a protective covering to prevent oxidation of deposits and should never be chipped or brushed until all signs of color have disappeared. Stress and Strain - Stress is the measurement of external forces applied to a material. Strain is the deformation of the material by the external force. Stress Relieving - The heating of a weldment to a temperature usually higher than 1050°F, but lower than the critical temperature range and holding at heat (called soaking) to allow stresses, residual from heating and cooling during welding, to be relieved. SCR - Silicon Controlled Rectifier. Used to change AC current to DC. Functions as an output control device for regulating the current/voltage and arc off-on ability. Secondary Power - Refers to the actual power output of a welding machine. This includes the load voltage while welding, measured at the output terminals and the current (amperage) flowing in the circuit outside the welding machine. Secondary amperage can be measured at any point along the secondary circuit. Sensitization - The changing of a stainless steel’s physical properties when being exposed to a temperature range of 800° – 1600° F, 427° – 870° C for a critical period of time. See also Carbide Precipitation. Sequencing - The control over all aspects of the weld. This would include the weld start, initial current, initial current time, upslope time, weld current level, weld current time, final slope, final current level and final current time. Shielded Metal Arc Welding (SMAW) - An arc welding process which melts and joins metals by heating them with an arc, between a covered metal electrode and the workpiece. Shielding gas is obtained from the electrodes outer coating, often called flux. Filler metal is primarily obtained from the electrodes core. Shielding Gas - Protective gas used to prevent atmospheric contamination of the weld pool. Single-Phase - When an electrical circuit produces only one alternating cycle within a 360° time span, it is a single-phase circuit. Slot Welding - A weld made by filling (or partially filling) an external hole (slot) in one member of a joint, fusing that member to another member. The hole (slot) may be completely enclosed, or it may be open at one end of the metal. Solenoid - An electrical device which either stops or permits the flow of gas used to shield the weld pool and arc or the flow of water used to cool a welding torch. Spatter - Metal particles blown away from the welding arc. These particles do not become part of the completed weld. Squarewave - The AC output of a power source that has the ability to rapidly switch between the positive and negative half cycles of alternating current. Advanced Squarewave is an enhanced version of this output waveform. Stabilizer - A device used in AC welding to assist re-ignition of the arc as current passes through the sine wave zero point. Straight Polarity - An old nonstandard term denoting electron flow from the electrode to the workpiece. Submerged Arc Welding (SAW) - A process by which metals are joined by an arc or arcs between a bare solid metal electrode or electrodes and the work. Shielding is supplied by a granular, fusible material usually brought to the work from a flux hopper. Filler metal comes from the electrode and sometimes from a second filler wire or strip. Safety Relief Device – A safety device usually incorporated in a cylinder valve and actuated by excessive pressure or temperature, or both, at predetermined limits to avoid failure of the pressure vessel. Self-Relieving (Self-Venting) – A feature incorporated in certain pressure reducing regulators which enables the unit to relieve the outlet pressure when adjusted in the decrease direction. Sensitizer – The ability of a chemical to cause a substantial proportion of exposed people or animals to develop an allergic reaction in normal tissue after repeated exposure to the chemical. Short Term Exposure Limit (STEL) – See “Threshold Limit Value – Short Term Exposure Limit.” SKIN – The “SKIN” designation, used with the terms TLV-TWA and OSHA-PEL, indicates that cutaneous absorption may contribute to the overall exposure. Solvent – A substance capable of dissolving another substance (solute) to form a uniformly dispersed mixture (solution) at the molecular or ionic size level. Span Gas – Gases which are used as a reference point to span an analyzer. Specific Gravity (Sp. Gr.) – The ratio of the weight of one substance compared to the weight of an equal volume of another substance which is used as a standard. Usually gases are compared to air (air = 1) while liquids and solids are compared to water (H2O = 1). Specific Heat – Amount of heat required to raise a unit mass of a substance one degree of temperature at either constant pressure (Cp) or constant volume (Cv). Specific Heat Ratio – The ratio of specific heat at constant pressure (Cp) to the specific heat at constant volume (Cv). Specific Volume (Sp. Vol.) – Volume occupied by a unit mass of a substance at a given temperature. It is usually expressed in cubic feet per pound or gallons per pound. Spring Housing – See “Bonnet.” Stainless Steel – Alloy steels containing high percentages of chromium, from less than 10% to more than 25%. Standard Temperature and Pressure (STP) – An internationally accepted reference base. Standard temperature is OOC. Standard pressure is one atmosphere or 14.6960 psia. Sublimation – The direct passage of a substance from solid to vapor without appearing in the intermediate (liquid) state. An example is solid carbon dioxide (dry ice) which vaporizes at room temperature. Sudden Release of Pressure Hazard – See “EPA Hazard Categories.”
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