Oxygen probe is a commonly used sensor to control the atmosphere of heat treatment. It is a measuring probe to determine the oxygen partial pressure in the carbon-containing atmosphere. This method can indirectly measure the carbon potential of the atmosphere in the furnace. It uses the oxygen potential generated by the different oxygen concentrations on the inner and outer sides of zirconia at high temperature (> 650 ℃) to measure the oxygen content of the measured part.
Using high temperature zirconia as a solid dielectric, if the oxygen concentration on both sides of the dielectric is different at high temperature, an oxygen concentration battery will be formed. The potential generated by the concentration battery is related to the oxygen concentration on both sides. If the oxygen concentration on one side is fixed, it can be measured by measuring the concentration potential
Measure the oxygen content on the other side. An oxygen potential generated on both sides of the zirconia through the oxygen P1O1 outside the furnace and the oxygen P2O2 inside the furnace, and the absolute temperature of the measured atmosphere according to the Nernst formula: E = 1 / NF • RT • LnP1O1 / P2O2 (mv) expression.
There are many types of oxygen probes, but the overall structure is divided into two categories: integral and combined.
The integral structure is made of zirconia into a complete long tube, the reference gas path is in the tube, the electrode and the zirconia tube are sintered together to form a whole. Its advantages: good air tightness, small internal resistance, high and stable output signal strength, and good interchangeability of the probe. Disadvantages: easy to fall off or rupture due to vibration, and it is not easy to repair once damaged.
The combined RHO zirconia is generally made into spherical, flake and cone shape. Tighten with the aluminum oxide tube through the spring
The tight fitting zirconia head plays a sealing role. The electrode and the alumina tube are independent components, which are combined together to form a combined body. Its main features are: due to the improvement of probe processing accuracy, assembly accuracy and process technology, it has basically been able to achieve the advantages of the integral type. Since the aluminum oxide tube and the sheet-shaped or spherical sensor element are elastically crimped, the problem of earthquake resistance is solved, and it has the performance of resistance to sudden temperature changes and the problem of temperature resistance. The combined zirconia head, electrode, alumina tube and other components are independent and can be replaced arbitrarily, with strong regeneration ability. In recent years, combined probes have been deeply loved by users.
Use and maintenance
- When the oxygen probe is working in the furnace, clean reference air should be continuously introduced. The flow rate is 1 ~ 2L / min.
- The core part of the probe is a ceramic tube. When using it, avoid rapid cooling and hot heating as much as possible to prevent intense vibration and mechanical collision. If the oxygen probe must be withdrawn from the hot furnace, the speed of extraction or insertion should not exceed the speed of 600mm / min.
- Carbon deposition is an important cause of oxygen probe failure. In the initial carburization of the furnace pot (muffle furnace) or furnace brick (no muffle furnace), the carbon deposition is often very serious and the output potential of the oxygen probe is not high. At this time, the enrichment medium (kerosene, acetone) must be controlled , Propylene / Butane, etc.), the amount of intake should not be excessive. Otherwise, serious carbonization will occur on the oxygen probe, which will cause permanent damage to the oxygen probe. Control the flux of enriched media (kerosene, acetone, propylene / butane, etc.), do not set excessively high carbon potential, to prevent the carbon deposition of the oxygen probe.
- No muffle furnace is equipped with an oxygen probe when the furnace is pre-carburized after overhaul of a new or old furnace, and the oxygen probe is installed after the furnace is pre-infiltrated.
- The carbon burning device periodically burns the carbon for the oxygen probe. When the oxygen probe is working on the furnace, the recommended air flow rate is 5 ~ 9L / min, the carbon burning lasts 2min, and the carbon burning interval is 2 ~ 4h. The burnt carbon of the probe is harmless to the probe itself.
- The oxygen probe does not work below 700 ℃.