US2305758A - Coating of articles by cathode disintegration - Google Patents

Description

Dec. 22, 1942. a. BERGHAUS EI'AL COATING OF ARTICLES BY CATHODE DISINTEGRATION Filed April 22, 1938 3 Sheets-$11861; 1

w 'lBu Ina/anions Deb. 22, 1942. a; BERGHAUS arm.-

COATING OF ARTICLES BY GATHODE DISINTEGRATION Filed April 22, 1938 3 Sheets-Sheet 2 In vent S Dec. 22, 1942. a. BERGHALIS arm. 2,305,758

comma OF ARTICLES BY GATHODE msmwssnurou Filed April 22, 193 8 s Sheets-Sheet 3 3,3 hams M30. Khqmt I ventors Patented Dec. 22-, 1942 OFFICE V COATING OF ARTICLES BY CATHODE I DISINTEGRATION ,Bernhard 'Berghaus, Berlin-Lankwitz, and wuhelm Bnrkhardt, Berlln-Grunewald, Germany; vested in the Alien Property Custodian Application April 22, 1938, Serial No. 203,672

In Germany May 25, 1937 This invention relates to a method metallic articles by cathode disintegration and it consists mainly in that the article is continuously or intermittently connected up as acathode before or during the disintegration. The invention I makes it possible to provide metallic articles with layers of any desired thickness, with perfect texture and great adhesion. It is an advantage to disintegrate the cathode only intermittently. The

- article may carry cathode potential in the disintegration intervals. An alternating current voltage of any desired frequency may be applied as disintegration voltage between the article and the cathode. In order to be able to vary the intensity of the current applied to the article with the cathode potential, regulating means are inserted in the electric lead. When the disintegrating voltage is a direct current voltage or a rectified alternating voltage an adjustable re sistance may, for instance, be inserted in the electric lead to the article to which the cathode potential is applied.

when the disintegrating voltageis an alternating current voltage, a. rectifying valve is, for instance, inserted in the lead and connected in parallel with an adjustable resistance. The object of the rectifying valve is to allow the positive alternation to pass through without being weakened, in order to maintain the full current for the disintegration of the cathode material. The

' negative alternation on the other hand is stopped,

and the current is adjusted to the desired intensity by means of the variable resistance connected in parallel. Of course, use may be made of other methods of connection.

By suitably adjusting the current density, a

metal article to which the cathode potential is applied continuously or. intermittently may reach any desired temperature upto incandescence. The current density on the surface of the article is preferably chosen smaller than the current density on the surface of the cathode material tobe disintegrated.

The cathode material to be disintegrated is preferably disintegrated in an incandescentstate or from a crucible ina liquid state, the heating and melting being effected by the actual electric gas discharge. The pressure of the filling gas may vary between 5 and 0.001 millimeters of mercury, and the disintegration voltage is between 400 and 10,000. volts. In order to protect the insulation of the electric leads, which are constructed as a support for the cathode material to be disintegrated and the article to be coated, against detrimental heat and coating, the leads are pro- 4 Claims. (01.204-192) of coatin v and the leads no glow discharge can be produced.

The distance between the cathode to be disintegrated and the article to be coated may vary.

However, it is especially advantageous to choose the shortest possible distance; the same is given by the unhindered formation of the glow fringe around the article" and around the cathode material to be disintegrated.

By the method according to the present inventioncoatings can be provided on metallic articles of any form. The layers show throughout a uniform crystalline formation which holds together and they excel by their reliable adherence. For instance, layers of one-tenth of a millimetre thickness produced on ,metal sheets do not flake or crumble, even with a bending stress reaching the fracture point of the metal sheetfand they can be subsequently treated and polished.

The current to the article acting as cathode while being heated up is adjusted according to the sensitiveness of the article to heat. The current densities can be adjusted to values at which the articles are heated up to incandescent temperatures. The degree of the heating depends on the material of the, article and the coating material.

. The upper temperature limit is determined by the fusing point of the materials which are used.

In the case of intermittent disintegration and heating up of the article by its being connected up as a cathode between the periods of disinte gration the extent of the disintegration and the duration of the heating-up periods depend on the temperature it'is desired to impart to the article. Although it was to be assumed that the major part of the coated material will be removed again from the article brought to cathode potential during the disintegration, it was surprising to obtain in a short period of time 'a dense'reliable coating,

which was even more uniform on the surface of the article than is the case with the own cathode disintegration methods, in which the article is neutral or connected as an anode.

The current densities are so chosen that the current density of the article is smaller than on the cathode material to be disintegrated. For instance, a ratio of current densities of 1:30 has I vantage is obtained that, with different voltage on the cathode material to be disintegrated and on the article to be coated, the circuits can be regulated independently of one another. This connection'ofle'rs special advantages in the case of large total currents on the articles'to be coated, as compared with the current of the cathode to be disintegrated, since electric losses, as they v occur when use is made ofonly one source of voltage owing to the voltage differences between the article and the cathode, are avoided.

Apparatus for carrying out the invention is Fig; 1 is a section through an arrangement for coating articles by cathode disintegration in which a. source of continuous current serves as the disintegration voltage,

' the actual coating is started. During this period,

on the article 3, whereby thesurface of the arillustrated in the accompanying drawings wherei Fig. 2 is a section through another arrangement which a source of alternating current serves as the-source of the disintegration voltage, and

Fig. 3 is a section through a cathode disintegration arrangement in which separate sources of current are used for the disintegration of the cathode material and for the cathode cbnnection of the article to be coated respectively.

Referring to Figure l, i is the cathode disintegration chamber which can be evacuated, 2 is the cathode to be disintegrated and 3 the article to be coated, which is for instance of metal. The

for coating articlesby cathode disintegration in cathode disintegration chamber comprises a base 4 and a removable upper housing part 5. The cathode holder 6 is arranged in an insulated manner in the base 4 and is surrounded by a screen 1 which is spaced from the holder. A filling gas, such as argon, hydrogen, nitrogen, helium, or the like, may also be supplied through the base I. which may be provided with a short connecting pipe leading to the vacuum pump.- The metal holder 8 for the article is. mounted in an insulated manner in the upper part 5 and issurrounded by a screen 3 which is spaced from the metal holder 8, in which space a glow discharge cannot take place, the screen being connected through a switch i0 and a protecting resistance 4 i i to the positive pole of a source l2 of continuous current,,or a source for rectified alternating current. The negative pole of the, source of continuous current may be connected through a switch l3 to the cathode holder 6 and through a switch i4 and an adjustable resistance l5 to the article holder in any desired sequence. The screen 9 of the article holder may be connected through a conductor l8 and a switch H to the wall of the chamber, or through a conductor l8 and switch is over the base 0 to the screen I of the cathode holder, if necessary.

The operation of the apparatusdescribed is as follows:

The article 3 is connected to the source of current l2 through the switch ll and adjustable resistance l5, by means of'which the current can be so adjusted that the current flowing through the article I will attain any desired temperature, even the temperature of incandescence, before ticle is made rough and is cleaned, so that, dur ing the subsequent metal coating period of the article when the switch i3 is closed, the cathode 2 is disintegrated and the metal serving for the coating of the article 3 is deposited thereon Normally the switch I4 is open during the coating period, but it may also be left closed, more particularly when the article 3 to be coated is to be additionally heated during the coating. A few minutes will suflice for the preliminary cathodic treatment of the article. Referring 'to Figure 2 l is the cathode disintegration chamber, 2 the cathode to be disintegrated and 3 the metallic article to be coated.

The coated disintegration chamber consists of abase 4 and an upper part 5. The cathode holder 6 is mounted in an insulated manner in the base 4 and is surrounded by a screen I. The metallic article holder 8 is mounted in an insulated manner in the upper part 5 and is surrounded by a screen 9, which may be connected through a switch l0 and a rectifying valve 20 for the negative alternation over a change-over switch 2| to the one pole of a high voltage alternating current transformer 22. The transformer may be connected with its other pole over a'change-over switch 23 and an adjustable resistance 24* which is shunted by a. rectifying valve 25 for the negative alternation to the article holder and, therefore, to the article. By means of the circuit containing the resistance connected in shunt with the rectifier 25, a small alternating current can pass through in both directions.- In that case the rectifier 25 allows onlythe anodic alternation to pass through. Alternatively, the transformer may be connected with one pole through the switch 23 to a conductor 26, which leads through -a rectifying valve for the negative alternation to the screen of the article holder, and by means of the change-over switch 2| the other pole of the transformer may be connected to the cathode holder 6 and thus to the cathode to be disintegrated. The screen 9 6} the article holder may be connected through the conductor l6 and switch I! to the wall of the chamber, or through the conductor l3 and switch I! over the base I to the screen 'I- of the cathode holder, if re- .quired. The individual switches may be actuated in any desired sequence.

The operation of the apparatus shown in Figure 2 is similar to that described with reference the switch 23, we get the preliminary cathodic treatment or the article. With the switch 23 connecmd to the conductor II and switch 2| connected to the cathode holder 8 and thus to the cathode 2, we get the required circuits for the actual coating process with the articledisconnected from the source of current.

In Fig. 3 the apparatus for carrying out the invention diil'ers irom that shown in Fig. 1 merely in this, that a source I! of voltage is provided for the. disintegration of the cathode 2, which is connected through a resistance 21 and a switch It tothe cathode 2, and through a second source of voltage 28 to the article 3 over the switch It and the resistance It.

What we claim is:

1. A method of coating metal articles by cathode disintegration within a metal housing having a cathode tobe disintegrated therein insulated with respect to the housing and the article to be coated arranged within and insulated with respect to the housing which comprises, impressing -a voltage across the article and the housing with the article connected as a cathode to create a glow discharge within the housing heating the article, and impressing a'voltage across the oathode to be disintegrated and the housing to disintegrate particles therefrom onto the article so as to coat the same.

2. A method or coating a metallic article which comprises, supporting the article in an insulated manner within a sealed housing having a cathode therein, adjusting the pressure within the housing'to support a glow discharge and cathode disintegration therein, impressing a voltage across the housing and the article with the article being negative with respect to the housing to create a glow discharge within the housing heating the article, and impressing a voltage across the cathode and the housing with the cathode being negative with respect to the article for disintegrating particles from the cathode onto the heated article. i

3. A method of coating a metallic article which comprises, supporting the article within a sealed housing having a cathode therein, adjusting the pressure within the housing to support a glow discharge and cathode disintegration therein, impressing a voltage across the housing and the article with the article being negative with respect to the housing tocreate a negative glow discharge around the article heating the article, and disintegrating particles from said cathode onto the heated article with the cathode being negative with respect to said article.

4. A method of coating a metallic article which .from the cathode onto the heated article.

BERGHAUS. WILHELM BURKHARD'I.

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