DE885266C - Treatment of contacts or electrodes of electrical DC switching and control devices - Google Patents

Description

Treatment of contacts or electrodes of electrical DC switching and control units When separating metallic contacts, in particular, arises between the contacts on the stalk at which contact was last canceled was a small metal bridge or bead, which when the contacts finally open tears off at the warmest point. The temperature distribution depends on the direction of the current with dependent, so that the bridge is not exactly in the middle, but closer to that tears off a contact or electrode. When interrupting direct current occurs as a result, there is a gradual migration of contact material between the electrodes (a so-called fine hike). This creates. on one electrode Elevations and depressions on the counter electrode, mostly on a single one Steals whose location cannot be determined in advance, but depends and depends on chance which, as a result, shows the dreaded pin formation after a short time. The result is then usually uncertain and also fluctuating with regard to the point in time Making contact and finally a relatively faster wear of the contacts.

This has a particularly disruptive effect on switching devices, relays or controllers where it is important to ensure that .the contact carriers are at the moment : the contact separation or a precisely defined distance when switched off take from each other, as well as those where it is important that the contact separation to a takes place exactly at a fixed point in time. -In such cases arise from the fine migration or dk pen formation errors, which are often also caused by the most precise guidance of the contacts cannot be prevented.

It is known that certain contact materials or alloys of the Fine hike or subject to pen formation only to a small extent. The usage Such materials are not appropriate in all cases, especially often also various other properties of the contact building materials, e.g. B. their conductivity, Contact resistance, erosion resistance, behavior with regard to oxide formation etc. must be taken into account.

According to the invention, contacts are obtained that are significant in this regard Have better properties by applying a pretreatment to the contacts or electrodes are exposed, whereby they. with alternating polarity of currents of a certain Height are claimed, in particular interrupt such currents.

The invention is based on the idea that when the polarity is frequently changed, the migration of the contact building materials always goes back and forth between the contacts, while the work surface, the contacts or electrodes are remelted and smoothed. The reconnection process following the individual interruptions also has a beneficial effect on the formation of the contacts, namely due to the hammer effect, which is considerable, especially when the contacts strike at high speed, and the mostly unavoidable bouncing processes in some cases also cause high local heating at the contact points. Relatively large working surfaces are then formed at the contacts, which are precisely worked into one another. The contact is made again and again at different locations of these surfaces, so that the formation of pins is delayed. Contacts according to the invention also have the advantage that there are no irregularities whatsoever, as they are otherwise caused by the deposition of finely divided metal particles, especially when switching small currents. Such deposits of metal vapor on the electrodes, which can be traced back to the evaporation of the bridge building material -siin, d, form a finely divided, spongy -metal bog that sticks very firmly to the electrodes at night. Due to the strong electrostatic fields at the first moment the contacts are opened, their building material is clumped together and thus contributes to a substantial but uneven lengthening of the metal bridges. This creates scatter in the separation of contacts, the contact carriers, which have unpleasant consequences, especially when controlling sensitive circuits through such relays or regulators. By means of an aftertreatment according to the invention, in particular with small currents, for example. between 0.5 and 1 amp; A metal bog of this type that has arisen on metal contacts can largely be regressed within a short time.

During .pretreatment it is advisable to make sure that the Current value at which the interruption takes place, always for both current directions same. is great. The current value itself is expediently chosen higher than this for the later use of the contacts is envisaged. It can also It can be advantageous to have contacts that show considerable irregularities after a long period of operation. show how to restore it to a usable state through such a treatment. For the treatment of the contacts (formation) alternating current or direct current can be used can be used, whereby .by a suitable switchover: it is ensured that the current direction is changed with each interruption process.

Contacts that are intended for higher currents are used in the Pretreatment expedient currents of alternating polarity from 0.5 to about 5 amperes get abandoned. In this way, the electrodes are completely melted reached at their last touching points, so .that migration of the contact building materials is prevented or reduced. Thus, by remelting the contact surface both the elevations and depressions resulting from the fine migration as well as removed the metal moor. Such contact treatment or processing can therefore be referred to as forming the contact surface. By forming in this way can thus contacts that z. B. not after a long period of operation with direct current only strong contact building material migration, but also irregularities as a result of the show mentioned different long separation paths, z. B. by simple AC circuit as good as new again. The formation can be advantageous, however can also be applied to completely new contacts, thus ensuring a careful Polishing. Of the contact surfaces or. The sometimes applied incorporation of the contacts becomes superfluous under power.

The treatment of the contacts can either be done by frequent use of alternating current or chopped direct current of different directions or their sign directly changing DC voltage.

The electrical machining of the contact surfaces can be expedient made by switching the operating circuit to the machining circuit will.

The invention is for any contacts electrical switching and Control devices, especially for small currents of the order of a few amperes or fractions of an ampere, so z. B. for relays, controllers, etc., especially suitable.

Claims (1)

PATENT CLAIMS: i. Treatment of contacts or electrodes. electrical DC switching and control devices, in particular relays, for prevention the Migration of the contact building material, characterized in that the contacts or electrodes electrical currents of alternating polarity are exposed, so that the work surface , the contacts or electrodes are remelted and smoothed. Handling of contacts at or electrodes according to claim i, characterized by the use of alternating current. 3. Treatment of contacts or electrodes according to claim i, characterized by the use of direct voltage that changes its sign directly or chopped Direct current in different directions. d .. treatment of contacts or electrodes, n according to claim i and z, characterized in that the electrical machining of the Contact surfaces by currents of 0.5 to about 5 amperes at a contact voltage takes place below io volts. Treatment of contacts or electrodes according to claim i and 3, characterized in that with DC voltage devices the work surfaces , the contacts b-zw. Electrodes to avoid switching direct currents resulting from changes in the contact surface (elevations and depressions) Currents of alternating polarity of 0.5 to 5 amperes are claimed. 6. Treatment according to claim i to 5, characterized in that the electrical machining of the Contact surfaces by switching the operating circuit to the machining circuit is made.