By R. Nemenyi

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6 the vacuum required for the heat treatment of some metals and alloys is indicated. 6 D E G R E E OF VACUUM REQUIRED FOR THE H E A T TREATMENT OF VARIOUS MATERIALS Material to be heat-treated Vacuum (torr) Copper Nickel Alloyed tool steel and highspeed steel Heat-resistant steel Molybdenum, tungsten Niobium, tantalum Beryllium Stainless steel ltolO" 1 lO' 1 1(Γ4ο1(Γ 2 lO^toKT 2 1(T4 io- 5 lO"7 l(T 3 tolO- 5 46 Inert-gas Atmospheres and Vacuum The data for nickel would indicate that a pressure of 10 - 1 torr would prevent oxidation during vacuum heat treatment, this corresponds to the equilibrium partial pressure for the Ni-N : O system at over 1400°C, the value for p0n being 10" 7 torr at 1000°C.

The main phases of prepared nitrogen-base or monogas production are: burning of the combustible base gas with a slight deficiency of air to give a very lean exogas; conversion of the CO content of the resulting atmosphere to carbon dioxide; removal of carbon dioxide formed during Prepared Nitrogen-base or Monogas Generators 59 F I G . 1 COMPOSITION OF PREPARED CONTROLLED ATMOSPHERES PLOTTED vs. THE AIR FACTOR USED IN THEIR PRODUCTION. The combustion limit, at about 5% (CO + H 2 ), is marked combustion and subsequent conversion and finally removal of moisture or drying to the desired dew point.

0°C, — 10°C or -40°C, a drying unit is used. If the base gas contains sulphur, a sulphur-removal unit is also needed. When the cooling water has a high free oxygen content, an oxygen-removal unit should be employed. Drying can be effected by an absorption dryer or by a so-called pressure dryer. In Fig. (30) The base gas and air enter the flow meters (3) through valve (1) and filter (2) respectively. After being mixed in the mixing unit (4) the gas passes to the retort (5). Leaving the retort the gas enters the cooler (6) cooled by water (7).

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