Arc: sequence of stationary charges. Arcs have a destructive effect.

Anomalous discharge: discharge that precedes a voltaic arc.

Antioxidant: additive added to the fluid to slow down its deterioration by stopping the formation of the oxygenated acid compounds.

Average working current Aa: arithmetical mean working in the Gap area.

Contamination: pollution condition in the Gap due to the residues of eroded material as well as the residues of thermal degradation of the dielectric fluid.

Crater: cavity generated on the surface by a series of discharges.  

Deionization: delay in discharging – in the Gap area – between the electrode tool and electrode piece to the “non conductor” status after each discharge.

Dielectric: non conductive fluid of electricity during the ignition delay “td” where both the electrode tool and electrode piece are immersed and where discharges are developed.  

Discharge: actual passage of current in the Gap during a pulse.

Discharge energy: it is the Energy of every single discharge measured in mJ.

Discharge voltage Va: average voltage applied to the Gap extremes during discharge.

Electrode: it currently stands for the electrode tool.

Flash point: it is the temperature at which the heated dielectric fluid under controlled conditions inside a normalized piece of equipment forms a mixture of hydrocarbon-air vapors that ignite when an ignition source is applied.

Gap: space between electrode tool and electrode piece. It is subdivided into:

  • Side Gap, “electrode-piece” space parallel to the axis of vertical feeding.
  • Frontal Gap, electrode-piece space not parallel to the axis of vertical feeding.

Hydrocarbons: they represent the very large family of substances chemically made up of “Carbon and Hydrogen”.

Ignition delay td: time between the instant where the voltage is applied to the electrodes in the Gap area and the start of discharge.

Injection: circulation of the dielectric fluid in the Gap area created by a pressure higher than the atmospheric one.

Interval time “to”: time between two pulses. It is required to allow the Gap to cool down.

Ionization: instant immediately preceding the current passage (before the end of the third phase) during which the Gap is made a conductor by the electrode feeding under the effect of the electrode-piece voltage difference.

Machining stability: condition in which the machining is performed. Machining stability is deemed to be good when the machining goes on smoothly without any phenomena of short circuit and ignition delay.

Neutralization (No. of…) TBN: it is expressed with the equivalent number of milligrams of potassium hydroxide (KOH). It represents the amount of acid – expressed as equivalent mg of potassium hydroxide – required to neutralize all the basic constituents found in one gram of the fluid sample to be examined.  

Peak current of the Aw discharge: the highest current value in Gap during discharge. It is regulated with the intensity level.

Polarity: pole to which the electrode-tool is connected. For instance, polarity is positive if the electrode tool is connected to the positive pole.

Pollution: refer to contamination.

Pulse frequency: number of pulses per second.

Pulse time “ti”: duration of the voltage pulse applied to the electrodes. It equals the sum of the discharge time “te” and ignition delay time “td”.

Removal speed: material removed while being machined in mm3/min. 

Short circuit: situation occurring in case of a direct electrical contact between the electrode tool and the electrode piece.

Suction: circulation of the dielectric fluid in the Gap area created by a pressure less than the atmospheric one.

Total acidity (TNA): it is expressed by the number of milligrams of potassium hydroxide required to neutralize the acid substances found in the fluid under examination.

Vn pulse: voltage step applied to the electrode-piece.

Vacuum voltage Vn: voltage applied to the Gap extremes before the discharge ignition.

Viscosity: it is the physical quantity that measures the resistance (internal friction) opposed by a fluid to the forces that tend to make it flow. It is measured and expressed under specific temperature conditions with conventional units according to the assessment method used to determine it. The most widespread unit of measurement is the cSt (centiStoke), referred to preset temperatures (20°C for the low boiling such as dielectric fluids and solvents, 40°C for lubricants). 

Wear: removal of material at the electrode end.

  • frontal wear measured in mm at the electrode end.
  • linear wear, height on which a dimensional reduction of the electrode tool can be detected;
  • volumetric wear %, ratio between:

Volume removed from the electrode   

________________________________  x100

Volume removed from the piece

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