DE1060217B - Method and device for treating the surface of bodies of a metallic or other nature by means of an electric glow discharge - Google Patents

Description

FEDERAL REPUBLIC OF GERMANY

GERMAN

PATENT OFFICE

PATENT LETTER 1 060

ANME LDETAG:

NOTICE
THE REGISTRATION
AND ISSUE OF
EDITORIAL:

ISSUE OF
PATENT LETTERING:

DBP 1060217 kl. 48 b 11/20

INTERNAT. KL. C 23 C NOVEMBER 20, 1956

June 25, 1959

DECEMBER 10, 1959

agrees Oberein with an explanatory document

1060 217 (E 13254 VIII c / 4 »b)

'The present invention relates to a method for the surface treatment of bodies by means of an electric glow discharge through which the surface to be treated is reduced to a predetermined Temperature is brought. "..

In this type of process, the aim is usually to use the least amount of energy possible Bring surfaces to the prescribed temperature and during the process time on this Maintain temperature, since the cost of the treatment usually depends heavily on the energy consumption, especially with long processes. Accordingly, in such procedures, in general all measures taken to reduce heat losses through dissipation, radiation and cause convection. Above all, the treatment device is adequately insulated and. the heat loss of the treated body is reduced as much as possible.

In the case of a large number of such processes taking place on surfaces at a certain temperature, there would be on the one hand an intensification of the effects and, on the other hand, a shortening of the process duration is very desirable. However this cannot be achieved by increasing the energy expenditure, since the prescribed temperature the areas involved in the process must not be exceeded. The technology is accordingly endeavors in this area to find other ways to increase the effectiveness of such processes close.

30th

Surface treatment, for example, also belongs to the class of processes given above of metallic workpieces (nitriding, carburizing, cleaning, roughening, Oxycfiefen,! reducing, etc.). Metallurgical and chemical processes (smelting, dehydration, etc.) have already been taken under Use of electric glow discharges has been carried out with good success. Thermal carried out in this way Processes also have technological and qualitative advantages that change from case to case with regard to the products obtained, in general, the advantage of good economy.

Since the present methods are those with a predetermined temperature on the surfaces involved in the process, the energy conversion in the glow discharge must of course be based on the heat requirement of the bodies and substances concerned, which in turn is mainly due to dissipation and radiation losses and possibly by the Energy consumption of the * "chemical reactions. For example, when nitriding steel bodies by means of a glow discharge, an energy consumption of around 1.5 watts per cm ^{2 of} treated surface is required in order to achieve the most favorable temperature process and device

to treat the surface

of bodies of metallic or other

Nature by means of an electric

Glow discharge

Patented for:

Electrophysical Institute

Bernhard Berghaus,

Vaduz (Liechtenstein)

Claimed priority:
Switzerland from November 22, 1955

Hans Bucek, Zurich (Switzerland),
has been named as the inventor

of the steel body from 500 to 550 ° C.

It has already been assumed that with a higher energy conversion of the glow discharge the process duration or the quality of the products could be influenced favorably. But there the predetermined temperature the areas involved in the process must not be exceeded, was a possibility for this pulse-like mode of operation proposed. If the process in question is periodically alternating with high and low energy consumption, so is of course at the expense of the high-performance intervals Intervals a corresponding increase in energy is possible without the temporal mean value of the Energy and heat supply by the prescribed ' Temperature exceeds certain value. The processes using glow discharge pulses actually brought the expected benefits, but of course it is due to the temperature Mean value of the energy conversion only a limited increase in effectiveness can be achieved.

909 666 / Ϊ23

It has also already been proposed, in such thermal surface processes, by cooling the Workpieces to become independent of the temperature-related average energy consumption.

In contrast, the method according to the invention is characterized in that at least one Part of the surface to be treated dissipates a certain amount of heat by means of suitable cooling at the same time the energy supplied by the ion bombardment by such an amount of energy is increased so that the predetermined temperature is reached.

Expedient arrangements for carrying out the method according to the invention are shown in FIG. 1 to 4.

jf Fig. 1 shows a longitudinal section through a recipient for glow discharge treatment of hollow shafts;

2 shows a diagram with some examples of the hardening depth profile in nitrided steel parts;

3 and 4 show longitudinal sections of further devices for glow discharge treatment of workpieces.

In order to implement the present process, most of them must be carried out on an industrial scale Thermal processes to be carried out, of course, leave the principle that heat losses are kept as small as possible in the interests of the economic viability of the process in question should. As is well known, z. B. in the known thermal gas nitriding of steel bodies Great importance is attached to good thermal insulation of the nitriding chambers, especially when it is electrical heated chambers. Likewise, in the case of the known glow discharge processes, for example in the surface treatment of workpieces in a glow discharge vessel under negative pressure, usually one or more bare sheet metal cylinders connected in series to reduce heat losses arranged as a radiation reflector around the workpiece and a noticeable heat dissipation via the Suspension and holding means avoided as far as possible.

In contrast to this general principle for thermal processes, the proposed The most effective heat dissipation possible from the surfaces involved in the process, i.e. if possible, a cooling of the same is provided. To then a prescribed temperature of the concerned To be able to achieve areas, the energy supply to the same must of course be increased accordingly will. This increase the heat supply on the one hand and the better heat dissipation on the other hand an increased energy expenditure on each surface element of the surfaces involved in the process. It is precisely this effect that is desirable, although the increase in energy apparently only serves to heat the Coolant is used and a deterioration in economic efficiency is to be feared.

But it has surprisingly turned out -7- at least in the cases examined so far -, that the greater energy expenditure a corresponding reduction in the required process duration in each case has the consequence, so that the total energy consumption remains approximately the same for hieiv. But that's natural Significant technical progress was achieved through the gain in time alone, apart from that at the same time resulting improvement in the utilization of the respective facility to carry out the relevant Process. Apart from the time savings, it is primarily the higher treatment intensity that makes it possible in all cases examined so far, the production of better quality products.

The \ ^r orliegende method has been tested experimentally with a device according to FIG. 1.

The workpiece to be treated on the outside 1 / the z. B. to be metallized or nitrided is from Metal vessel 2 is electrically insulated and stands as one electrode of a counter-electrode concentrically surrounding it 3 opposite. Both electrodes are insulated from current inlets leading through the vessel wall 4 connected. The voltage of the is between the workpiece 1 and the counter electrode 3 Power source 5, for example 500 volts, through soft, at a gas pressure of 1 to 20 mm Hg in the vessel, an electrical glow discharge occurs between these parts of different potential. The energy expenditure this discharge is largely concentrated in the immediate vicinity of the cathode itself forming glow seam and cathode drop space. When operating with direct current, the negative pole must be the Voltage source 5 lie on workpiece 1. However, alternating current of normal frequency (50 Hz) can also be used. be used.

The hollow shaft 1 is here internally cooled by an insulating material, e.g. Porcelain, draining coolant, e.g. B. oil. Through the valve 8 on the inflow line 6 made of insulating material the coolant flow can be shut off and regulated. Also the double-walled discharge vessel 2 is expediently cooled by an inflowing via the pipe socket 9 and out of the Pipe socket 10 outflowing coolant. The inside of the vessel is on the part of the vacuum pump 11 via the Suction line 12 held at a desired negative pressure. Via the valve 13 and the line 14 can the. For the present process intended gas are introduced into the interior of the vessel. The surface temperature of the workpiece 1 to be treated is via a hole 15 in the counter electrode 3 and a Window 16 in the vessel wall 2 monitored by means of a radiation pyrometer 17.

When the apparatus is started up, the coolant flow through the hollow shaft 1 is expediently shut off by means of the valve 8 and a so-called start-up process is carried out. Only after the final discharge state and the prescribed temperature of the hollow shaft surface, indicated by the measuring device 17, have been reached at the end of the start-up process, the valve 8 for the internal cooling of the hollow shaft 1 is slowly opened. The slow drop in temperature that occurs at the surface of the hollow shaft is monitored on the measuring device 17 and, to a corresponding extent, the energy expenditure in the. Glow discharge increased, be it by increasing the gas pressure in the vessel 2 or by increasing the voltage difference between the hollow shaft 1 and the counter electrode 3. The coolant flow is increased with a steady increase in energy expenditure in order to maintain the prescribed surface temperature until the desired energy density is reached Watt per cm ² surface of the hollow shaft 1 is reached. If desired, an automatic program control, monitored and influenced by the radiation pyrometer 17, can of course also be provided for this increase in heat dissipation and increase in energy.

A nitriding process carried out in an analogous manner on steel bodies with the composition 0.3 C, 0.4 Mn, 2.5 Cr, 0.6Mo resulted in a treatment

temperature of 520 ° C during a process time of 48 hours in a nitrogen-containing atmosphere of 10 mm Hg and an increase in the energy density due to the rapid heat dissipation to 1.3 times the value, a greater penetration depth and an improvement in hardness by 5 Rockwell compared to an uncooled treatment same duration. The examination of the depth profile of the surface hardness showed that the hardness depth curve can be significantly influenced by this increased energy flow on the surface of the workpiece. Fig. 2 shows a generated without cooling and increase in energy case depth curve A and, for comparison, obtained with the same steel and of the handling case depth curve B. By suitable selection of gas pressure and energy expenditure, the course of the case depth curve affect B and aligned, for example, the curve C .

By this experimental observation is thus proven that with an increase in energy expenditure on the treated surfaces ¹ body despite unchanged retention of the prevailing surface temperature influencing the resulting herein by diffused nitrogen "finished surface zone is obtained. On the one hand, the process time for generating a certain depth of penetration of the diffused substance is shortened, which represents a significant advance compared to the diffusion methods generally used up to now, because the diffusion rate at a certain surface temperature was previously considered to be uninfluenced. On the other hand, the quality of the surface zone created by diffusion is different from that of the nitride layers that result without an increase in energy, both in terms of surface hardness and in terms of the hardness depth profile and mechanical properties such as splinter resistance, ductility, porosity and volume change.

While so far with such nitriding processes in a steel with given alloy components The hardening depth profile can only be influenced by suitable pretreatment by the nitriding temperature and the duration of treatment was possible, the structure and the Properties of the resulting surface zone when using the optimal temperature by choice the energy conversion on the surfaces involved in the process can be influenced in the desired manner. Of course, with a planned, as yet unknown steel alloy - as is the case with other metallurgical Processes usual - by means of a few test pieces, those with different amounts of energy of the surface and properties of the surface zone resulting from different surface temperatures to determine experimentally depending on the treatment time, in order to then produce workpieces from this To be able to refine steel accordingly. But the results obtained are clearly reproducible, and a one-time series of tests then provides a recipe for creating surfaces with predetermined ones Properties.

Finally, it should be mentioned that with the method described, such as experimental results show ^ along the refined steel surface on the surfaces involved in the process a much higher uniformity the structure is achievable than was previously possible. For example, the fluctuations hardness values for such nitrided surfaces are at least 50% lower than usual.

Another exemplary embodiment of an apparatus for carrying out the method in the case of surface treatment the inner wall of tubes by means of a glow discharge is shown in FIG. 3 in schematic representation. Here is a removable one on the outer jacket of the pipe 20 to be treated Cooling device attached, which consists, for example, of the cooling cylinder 21, the end walls of which 22 and 23 each have a hole suitable for the pipe 20

ίο own and against this with the elastic seals 24 and 25 are sealed. In this way, an annular space 26 is created around the pipe 20 through which a liquid or gaseous coolant can flow via the inlet or outlet line 27 and 28, respectively. the Both mouths of the tube 20 protrude from the cooling cylinder 21 in a dome-like extension inside, which by the sealing caps 29, which are fastened in a gas-tight manner on the end walls 22 and 23 and 30 are formed. The two dome-like extensions are through the bore of the tube 20 connected to one another and together form the glow discharge space. Extends through tube 20 a hollow counter electrode 31, which by means of the Insulators 32 and 33 'is passed through the caps 29 and 30, respectively. This hollow electrode 31 is connected to one pole of the voltage source 34, the other pole to the cooling cylinder 21 and is in communication with the pipe 20 via the connecting line 35. Via lines 36 and 37 the intended treatment gas is introduced into the gas discharge space or pumped out of the same.

During operation, a glow discharge arises between the inner wall of the tube 20 and the hollow electrode 31, which, when the tube 20 is at least temporarily operating as a cathode, heats its inner wall. As a result of the cooling of the pipe 20 by the coolant in space 26, the heat is rapidly dissipated from the pipe involved in the process ^:

inner wall, so that the energy conversion of the glow discharge increases and the application of energy the inner wall can be increased. The hollow electrode 31 can also be cooled from the inside by a flow of liquid or gas. This is For example, it is recommended for AC operation to avoid excessive heating of the then temporarily to avoid a hollow electrode acting as a cathode. But also with direct current operation with one as anode working hollow electrode, its cooling, can be advantageous in order to reduce the temperature caused by the inner wall of the pipe Dissipate heat.

The measures to be provided according to the present method for the rapid dissipation of heat from the Of course, surfaces involved in the process by no means always require a coolant flow as in the Embodiments according to FIGS. 1 and 3. In particular for smaller workpieces, the cooling due to strong heat dissipation or heat radiation are sufficient. Such an embodiment for the Surface treatment of the inner wall of a metal sleeve 40 is shown schematically in FIG. 4

- Playback omitting all less important ones Details. For rapid heat dissipation, the sleeve 40 lh is attached to a solid metal block 41 here good heat conduction, for example made of copper, which has a corresponding, precisely fitting bore 42. the The mouth of the sleeve 40 faces a discharge space 43, which is connected to the insulating ring 44 by a Block 41 is electrically insulated, but hood 45 fastened in a gas-tight manner is complete. In this hood is

by means of the insulator 46, an electrode rod 47 is attached in a gas-tight manner, which protrudes into the sleeve 40 and outside the hood 45 with one pole of a voltage source 48, on which the metal block 41 The other pole of the voltage source 48 is connected to the metal hood 45.

A negative pressure gas atmosphere of a few millimeters Hg is generated in a suitable manner in space 43 and a DC voltage of 400 to 1000 volts is used, so when the hood 45 is used as the anode works, a glow discharge with a tight on the inner wall of the sleeve 40 and the outside of the Stick electrode 47 located glowing edge, although these two parts are at the same negative potential condition. By a suitably selected diameter of the rod electrode 47 and the corresponding gas pressure in space 43 it can be achieved that these cathodic glow fringes and thus the associated Touch cathode drop spaces, which experience has shown to a significant increase in the energy density leads in the interior of the sleeve (so-called hollow cathode effect). Due to the large mass of the metal block 41, the amount of heat generated on the inner wall of the sleeve 40 in this way is quickly dissipated. Normally, the strong radiation achieved as a result of the large outer surface of the block 41 is sufficient Air cooling from, a temperature rise of the inner wall of the sleeve 40 over the prescribed Worth to prevent. Otherwise, of course, additional liquid or gas cooling can be used of block 41 are provided.

The described heating of the sleeve 40 by means of the hollow cathode effect is "in this apparatus can be effectively influenced by regulating the gas pressure in space 43 and can be well controlled in this way will. The desired effect can be achieved with a DC voltage source as well as with Achieve the use of an AC voltage source.

This hollow cathode effect can also be used on predetermined surface areas the surfaces involved in the process to bring about a higher energy turnover.

In the present process, the increased energy density of the glow discharge causes the as a cathode working surface a more intensive ion bombardment, both the middle kinetic energy as well as the number of gas ions impacting per unit of time increase. Except the resulting stronger heating of the metal surface - the one caused by rapid heat dissipation to the coolant is precisely compensated - there is possibly also a deeper penetration into that outermost layers of the lattice structure of the body and a quantitatively larger supply of atomic Gas at the boundary layer has an influence.

However, it should be expressly mentioned that some initial studies on the effect of the increased Heat transfer in the case of radiant heating of metal objects for surface treatment is an advantageous one Effect of the greater flow of energy through the surfaces involved in the process on the acceleration and quality of the process concerned. Even the application of strong Heat impulses are of influence here.

The present method is of course not limited to the surface treatment of metallic and other bodies, but all can be subjected to the present method, on the surface ¹ of solid and liquid material masses or layers takes place processes.

.8th

Claims (17)

PATENT APPROACH E: 1. Process for treating the surface of bodies of a metallic or other nature by means of an electric glow discharge, through which the surface to be treated is reduced to a predetermined Temperature is brought, characterized in that at least part of the surface to be treated dissipated a predetermined amount of heat by means of suitable cooling and at the same time the energy supplied by the ion bombardment by one such an amount of energy is increased that the predetermined temperature is achieved. · 2. The method according to claim 1, characterized in that the gas pressure in the discharge vessel is increased to increase the discharge energy will. 3. The method according to claim 1, characterized in that the operating voltage of the gas discharge to increase the discharge energy is increased. 4. The method according to claim 1, characterized in that the diffused per unit of time Amount of substance is increased by the increase in energy. 5. The method according to claim 1, characterized in that by choosing the increase in energy and energy flow, the depth distribution of the diffused substance is influenced. 6. The method according to claim 1. for nitriding the surface of steel bodies, characterized in that the to achieve a after Degree of hardness and hardness depth profile predetermined nitriding by the required process time Increase in energy density is reduced. 7. The method according to claim 6, characterized in that the hardness depth profile by choice the energy density of the glow discharge is influenced. 8. The method according to claim 1, characterized in that by suitable design of the to be treated body facing surfaces of other components as large as possible of the Heat radiation from the surfaces involved in the process is absorbed. 9. The method according to claim 1, characterized in that of those involved in the process Areas only a predetermined area is operated with increased energy supply. 10. / Device for performing the method according to claim 1, characterized by Means for accelerating the dissipation of heat from the surfaces involved in the process. 11. The device according to claim 10 for the surface treatment of bodies in a negative pressure atmosphere in a discharge vessel by means of an electric glow discharge, the bodies forming an electrode, characterized by means of supply. one . Coolant flow to those areas of the body that are not are involved in the process. 12. The device according to claim 11, characterized by an electrically non-conductive Medium as a coolant and through lines of this medium designed to be insulating Body. 13. \ ferfahren according to claim 11 for the treatment the outside of hollow bodies, characterized by means for passing a Coolant flow through the cavity. 14. The device according to claim II for the treatment the inside of a cavity of a body, characterized by means for cooling the outside of the body. 15. The device according to claim 14 for the treatment of the inner wall of pipes, characterized by a removable cooling device surrounding the pipe. 16. The device according to claim 15, characterized by a coaxially arranged in the tube Inner conductor, which in turn is also designed as a tube and for the passage of a coolant flow is set up. 17. The device according to claim 14 for the treatment of the inner wall of sleeve-like shaped, relatively small workpieces, characterized by the workpiece for the most part enclosing metal block in good thermal contact with its outer surfaces good thermal conductivity. 1 sheet of drawings O 909 558/258 6.59 (909 666/323 12.59)