DE19815233A1 - Process for vacuum carburizing under treatment gas - Google Patents

Abstract

In a process for vacuum carburizing under treatment gas, in which steel is carburized in a rough vacuum at gas pressures of up to about 20 mbar using propane (C¶3¶H¶8¶) as a carbon donor at a temperature of about 250 ° C., the propane Hydrogen gas (H¶2¶) mixed in a ratio of about 1: 1 to about 1: 2 (excess hydrogen), the extraction of the decomposition products of the propane taking place via a pumping station connected to the treatment chamber.

Description

The invention relates to a method for vacuum maufkohlung under treatment gas in the steel in a rough vacuum at gas pressures up to about 20 mbar un using propane (C ₃ H ₈ ) as carbon donor is carburized at a temperature of about 950 ° C.

It is already a process for heat treatment, in particular carburization, of metallic workpieces in a furnace at high temperatures and in a gas atmosphere in which the associated gas atmosphere is achieved by reacting a hydrocarbon gas, in particular natural gas or propane, with another elemental oxygen contained medium, in particular air, is known (DE 43 43 927), this implementation being supported, if necessary, by a generator or catalytic converter device in or carried out in the furnace, and in addition depending on the atmosphere, an enrichment agent for suitable adjustment of the carbon level is supplied, at least during a section of the heat treatment at least partially instead of the elementary (unbound), oxygen-containing medium carbon dioxide (CO ₂ ) is used for the formation of atmospheres, the carbon dioxide being converted into a treatment gas atmosphere re suitable amount instead of the correspondingly mined supplied oxygen-containing medium is fed directly to the respective reaction unit or to the furnace.

Furthermore, a process for gas carburizing iron workpieces in a carburizing atmosphere containing hydrogen (H ₂ ) and carbon monoxide (CO) is known at temperatures of 800 to 1050 ° C. (DE 41 10 361), in which a carburizing atmosphere over substantial time phases of the carburizing with a CO-to-H ₂ ratio of greater than ½ is maintained in that a circulation of carburizing atmosphere from the carburizing chamber is carried out via a gas separation system with feed-back of the CO-containing fraction into the carburizing room, and if necessary , is strengthened by parallel, suitable addition of CO from an independent CO source or that this is accomplished solely by suitable addition of CO from an independent CO source.

Finally, a vacuum oven for heating is known treatment of a batch (DE 34 16 902) with a lockable steel container and one in one  inner heating chamber located heater and with a gas blower and a gas guide direction for generating a circulation flow through the heating chamber, the heating chamber under off Close of the gas blower is closable.

The object of the present invention is to achieve reasons, a particularly simple procedure for opening to create coal with the inexpensive propane as Carbon dispenser is used and ins special pollution of the system and the Suction pump through condensed decomposition products of propane is avoided.

According to the invention, this object is achieved by that the propane hydrogen gas in a ratio from 1: 1 to about 1: 2 is added, whereby sucking off the decomposition products of the propane via one connected to the treatment chamber Pumping station takes place.

The invention allows a wide variety of designs opportunities. Below are some Experiments described that the determination of the gün Most mixing ratio of propane to what concern hydrogen gas.

For the purpose of the trials, a targeted process gas extraction from graphite tube into the hard felt wall similar to the treatment chamber of a vacuum furnace introduced according to DE 34 16 902. Wei Then there was a gas inlet into the gas outlet pipe installed through which another gas is let in  can be sen. At the gas outlet was a 240 × 240 mm large steel sheet attached to the boiler wall brings to the tar precipitation at this point to condense. The sheet was used with every attempt exchanged. Through a visual assessment of the A rating was determined for tar condensation.

During the tests, propane was used by two suppliers used. Differentiate between the two types of propane yourself in the propane content.

Analysis of the gas types, figures in vol.%

The gas from B corresponds approximately to the propane from Hispano Suiza.

To the effect of hydrogen on tar formation and checking the carburization has been done on some Try hydrogen directly in the gas outlet pipe or together with the propane directly into the Heating chamber initiated. In addition, the propane amount varies.  

The 3 min. Gas inlet / 1 min. Gas outlet cycle at max. 20 mbar par tial pressure selected.

During the tests, the temperature was still in the gas outlet pipe and on the condensation plate measured.

Batches for the test series

Either a small batch consisting of:
33 gears with outside diameter 170 mm, diameter 50 mm, h 40 mm, A 0.078 m ² , total surface 2.5 m ² .

These parts were all already carburized and were used again and again in the experiments.

Or used a large batch consisting of:
300 ball cages with outside diameter 70 mm, diameter 58 mm, h 36 mm, A 0.017 m ² , total surface area 5 m ² .

These parts were all not carburized and were exchanged again and again after the attempt, so always a batch with non-carbonized parts.  

Results

The tar condensation on the sheet was visu assessed and divided into groups.

Description of the experiments Trial No. 1

Batch:
small batch of carbonized parts 2.5 m ² without C-sample.

Treatment procedure:
Heating 930 C / vacuum / 40 min.
Hold 930 C / vacuum / 25 min.
Vac. Coals 930 C / 40 min.
without diffusion
Cooling: 2 bar N ₂
(Nitrogen cooling).

Fumigation:
Propane from A 13 l / min.
in heating chamber.

Rating condensation sheet:
The entire sheet is covered with tar, especially at the point where the exhaust gas hits.

Trial No. 2

Batch:
small batch of carbonized parts 2.5 m ² without C-sample.

Treatment procedure:
Heating 930 C / conv. Heating / 60 min.
Hold 930 C / vacuum / 20 min.
with trial H ₂ inlet
Vac. Coals 930 C / 40 min.
without diffusion
Cooling: 2 bar N ₂
(Nitrogen cooling).

Fumigation:
Propane from A 13 l / min. in heating chamber plus 10.5 l / min. Hydrogen in gas outlet pipe.

Rating condensation sheet:
The entire sheet is covered with tar, especially at the point where the exhaust gas hits. Soot particles can also be seen at the point of impact.

Trial No. 3

Batch:
large batch with new parts 5-6 m ² , approx. 280 shift sleeves.

Treatment procedure:
Heating 960 C / conv. Heating / 90 min.
Hold 960 C / vacuum / 40 min.
Vac. Coals 960 C / 16 min.
Diffusion 960 C / 14 min.
Lower: 880 C / 30 min.
Cooling: 2 bar N ₂
(Nitrogen).

Fumigation:
Propane from A 17 l / min. in heating chamber.

Rating condensation sheet:
Tar topping only at the gas contact point, approx. 70% of the surface clean without tar topping.

Experiment No. 4

Batch:
small batch of carbonized parts 2.5 m ² with C-sample.

Treatment procedure:
Heating 930 C / conv. Heating / 60 min.
Hold 930 C / vacuum / 15 min.
Vac. Coals 930 C / 40 min.
Diffusion 930 C / 55 min.
Cooling: 2 bar N ₂
(Nitrogen).

Fumigation:
Propane from B 13 l / min. in heating chamber plus hydrogen 13 l / min. in the heating chamber.

Rating condensation sheet:
Total sheet thinly covered with tar. At the point where the exhaust gas hits, the tar covering is slightly thicker.

Carburizing effect:
Normal correspond to the treatment. AT (0.35% C) = 0.6 mm and rim C = 0.77%. Tested on a test bolt.

Trial No. 5

Batch:
large batch of new parts 5 m ² with 4 C samples.

Treatment procedure:
Heating 930 C / conv. Heating / 60 min.
Hold 930 C / vacuum / 30 min.
Vac. Coals 930 C / 40 min.
Diffusion 930 C / 60 min.
Cooling: 2 bar N ₂
(Nitrogen).

Fumigation:
Propane from A 4 l / min. in heating chamber plus 13 l / min.
in heating chamber.

Rating condensation sheet:
The entire sheet is without tar covering.

Carburizing effect:
The 2 C samples at the batch edge show a normal coaling result corresponding to the treatment. AT (0.35% C) 0.68mm and Rand-C 0.81-0.83%.

The 2 C samples inside the batch show one reduced carburization. AT (0.35% C) 0.42-0.53 mm and Rand-C 0.42-0.50%.  

Summary:
The formation of tar depends on the surface of the batch and its efforts to absorb carbon. With large batches, tar formation is clearly lower.

Hydrogen has a significant impact, provided that Hydrogen directly into the heating system with the propane is always admitted. Hydrogen in the gas outlet pipe has no significant influence. The Koh However, the effect of lungs is greatly reduced Propane after.

It has also been found that the tar condensation does not depend solely on the temperature hangs. The condensed on the condensation sheet Tar as well as on the boiler wall. The sheet had a temperature of 200-300 ° C and that Boiler wall approx. 60 ° C. Tar condenses preferentially at points of impact in the hot gas outlet pipe in Form of soot, but also preferred on the deflector len.

Claims (1)

Process for vacuum carburizing under treatment gas, in which steel is carburized in a rough vacuum with gas up to about 20 mbar using propane (C ₃ H ₈ ) as carbon donor at a temperature of about 250 ° C, characterized in that the propane Hydrogen gas (H ₂ ) is mixed in a ratio of about 1: 1 to about 1: 2 (excess hydrogen), the extraction of the decomposition products of the propane via a pumping station connected to the treatment chamber.