US3621174A

US3621174A - Lubricative atmosphere for sealed switches

Info

Publication number: US3621174A
Application number: US770967A
Authority: US
Inventors: Robert A Holcomb
Original assignee: General Electric Co
Current assignee: Genicom Corp
Priority date: 1968-10-28
Filing date: 1968-10-28
Publication date: 1971-11-16
Anticipated expiration: 1988-11-16

Abstract

A controlled atmosphere containing a monocarbon compound selected from the group consisting of methanol, chloroform, methyl iodide and methylene chloride is introduced into cleaned hermetically sealed relays to provide lubrication of metal wear points. Reactive metal for the wear points is selected to induce polymerization of the compound to obtain a lubricative surface on the wear points. The compound must be noncarbonizing over the relay operating range.

Description

United States Patent Inventor Robert A. Holcomb Waynesboro, Va.

Appl. No. 770,967

Filed Oct. 28, 1968 Patented Nov. 16, 1971 Assignee General Electric Company LUBRICATIVE ATMOSPHERE FOR SEALED SWITCHES 17 Claims, 1 Drawing Fig.

U.S. Cl 200/168 G, 200/166 C, 252/372, 260/2 H, 260/2 R int. Cl H0lh 9/04 Field oi Search 200/ l 66 C. 166 0 56] References Cited UNITED STATES PATENTS 3,238,342 3/1966 Chaikin 200/ l 66 C Primary Examiner-H. 0. Jones AltomeysLawrence G. Norris, Michael Masnik, Stanley C.

Corwin, Frank L. Neuhauser, Oscar B. Waddell and Melvin M. Goldenberg ABSTRACT: A controlled atmosphere containing a monocarbon compound selected from the group consisting of methanol, chloroform, methyl iodide and methylene chloride is introduced into cleaned hermetically sealed relays to provide lubrication of metal wear points. Reactive metal for the wear points is selected to induce polymerization of the compound to obtain a lubricative surface on the wear points. The compound must be noncarbonizing over the relay operating range.

PATENTEUunv 16 I9?! INVHN'I'UR.

ROBE T A. HOLCOMB HIS AT ORNEY other surface films 1 LUBRICATIVE ATMOSPHERE FOR SEALED SWITCHES FIELD OF THE INVENTION This invention relates to the lubrication of clean metal contacting surfaces. More particularly, the invention relates to a controlled atmosphere for an enclosed switch capable of lubricating switch contacts and other metal wear points over the switch-operating range.

BACKGROUND OF THE INVENTION Sealed switches, such as relays which are built to meet the fail-safe requirements of operating in a space or aircraft environment, have over the years been made increasingly more reliable by the removal of lint, dust and other contaminants. It was thought that trouble-free switch operation would be obtained by such manufacturing procedures as assembly in clean rooms in a controlled relatively contaminant-free atmosphere, the parts making up the relay being chemically cleansed and degassed. It was found, however, that the contaminants provided some benefits and their removal contributed to the development of other switch failure conditions.

Ultraclean metal surfaces when brought into contact experience cold welding and mechanical adhesion due to the absence of sufficient lubrication. In addition to this, switch contacts when actuated are brought together so that surfaces rub. The rubbing action serves to wipe away any lubricative or that should remain after the chemical cleaning thus promoting the diffusion bonding, commonly referred to as cold welding. Since cold welding and mechanical bonding of the contacts to each other are greatly enhanced in atmospheres in which the contaminants have been removed, it was determined that the problem could be overcome by selectively adding a contaminant to the atmosphere capable of lubricating the relay contacts.

Certain compounds, when added to the relay atmosphere, polymerize in the presence of a reactive contact metal to form a lubricative coating on the metal surface. Unfortunately, the insertion of a compound into the atmosphere of a sealed relay can seriously augment the carbonization problem encountered in such devices. Carbonization, which occurs at the switch contacts, results from the thermal degradation of the compound in and around the electric are or sparks normally occurring between the contacts. With sufficient current, there is enough energy in the arc to blow or explode away these carbonaceous deposits. At lower current levels, however, the arc is sufficient to degrade the compound to form the carthese deposits from the contact area of the switch contacts.

Accordingly, it is an object of the present invention to provide a lubricant for the metal wear points of a switch which does not carbonize under switch-operating conditions.

Another object is to provide an atmosphere for a sealed switch including compound capable of lubricating metal wear points without carbonizing.

Another problem encountered with the lubrication of contacts and other metal surfaces in sealed switches is the time factor encountered when fonning a lubricant from the compound in the relay atmosphere. Normally, it is necessary for the relay to be operated several thousand times before polymerization of the compound takes place.

It is accordingly another object of the present invention to provide a lubricative atmosphere for a switch of sufficient concentration to lubricate the switch contacts over the temperature range of operation without carbonizing and to minimize the polymerization incubative period.

Lubrication extends the mechanical life of metal wear points. At the same time, however, the lubricant when formed on switch contacts must not impede the contacts ability to conduct current. It is therefore a further object of the present invention to provide a lubricative polymer for metal wear points which does not impair electrical conductivity.

Because the switch contacts continue to remove the lubricant formed thereon by the repetitive wiping motion during operation, it is another object of the present invention to select a compound for the lubrication of switch contacts which will regeneratively produce the lubricative polymer under operating conditions.

In general, the invention is the recognition of the need for retaining the lubricative properties of contaminants in the relay atmosphere when the undesirable properties of the contaminants are removed. Considering the wide temperature range of relay operation and the different power requirements of various relay uses, the contaminant or contaminants retained or inserted for lubricating purposes must be capable of vaporizing over the temperature range and must not carbonize within the rated range of relay operation.

It has been found that these properties are presenthin monocarbon compounds, chloroform (CHCl methyl iodide (CH I), methylene chloride (CH- C1 etc. The monocarbon compound generally is capable of vaporizing over a typical 65 C. to +1 25 C. temperature operating range of the relay, has insuffcient carbon content to carbonize in the are at the contacts and will produce the lubricative surface on metal wear points necessary for their reliable operation in the presence of gold or other such reactive metal on these metal wear points. Because methanol, preferred for its ease in handling, absence of residue and noncorrosiveness, and and the other monocarbon compounds do not carbonize in the contact are even at relatively high concentrations. it is possible to increase concentration to reduce the polymerization incubation period without increasing carbonization propensity. Methanol, for example, at a concentration of 500 parts per million in a given relay at room temperature requires 16,000 contact operations before polymer lubrication begins. When the concentration is increased to 30,000 parts per million, only 6,000 operations are needed.

Other features and objects of the invention will become apparent from a further detailed discussion of the invention with reference to the attached drawing in which the FIGURE is a sectioned view of a relay showing the switch contacts and other metal wear points.

Referring now to the FIGURE, there is shown a cutaway portion of a relay, including the enclosure 11 and the base 14 which is sealed thereto. The seal between the base and the enclosure is a hermetic seal assuring an isolated atmosphere inside the enclosure. The electrical connector leads !2 are shown both inside and outside the relay with a hermetic glassto-metal seal 13 between the output leads l2 and the base plate 14.

Stationary contacts

15 and 16 are bonded to the frontmost electrical leads while movable contact 17 is bonded to the other electrical lead shown. Actuator 18, which may have a glass or other equivalent insulating tip 19 thereon, is moved by the armature 20 to bring the movable contact 17 into contact with stationary contact 16 at the point 16a.

Also shown in the FIGURE is the motor structure of the relay including the pole pieces 21, the magnetic core 24 and the coil 23 fonning the electromagnet which drives the armature 20 about pivot 22 causing the actuator 18 with its glass bead 19 to engage movable contact 17 to move it between the

stationary contacts

15 and 16. The FIGURE also shows the points of contact 170 and between the actuator bead l9 and the movable contact 17 and between the contacts l5, l6 and 17. It is at these points where cold welding and mechanical sticking and metal transfer is experienced in the absence of lubrication. Thus, lubrication at 17a, a glass-to-metal wear point, as well as 160, a metal-to-metal wear point, is equally desirable.

It should be noted that pivot 22 and the bearing surface in the supporting structure also form metal wear points capable of being lubricated if plated by or alloyed with a reactive metal, such as gold.

Switch contacts when making contact touch and rub one surface against the other before they again break contact. Without lubrication between the surfaces of the contacts, there is adhesion between the molecules of the metal surfaces such as methanol (CH OH),

such that metal transfer takes place. This transfer is often seen in the form of pitting, such as is common to the contact points of the ignition system in an automobile. The adhesion between surface metals is a form of diffusion bonding often called cold welding, where, if the return spring force of the movable contact, such as 17, is not sufiicient to overcome the attractive forces of the surface bonding, a permanent weld is experienced and the relay is rendered inoperative.

Normally, when two metal surfaces are rubbed together, there is enough lubricant on the surface of the metals so that the metals slide easily over one another. However, when the metal surfaces have been cleaned so that lubrication is removed, as has been stated above, the problems of cold welding and mechanical sticking are realized. While it is desirable to lubricate the contact surfaces to eliminate the bonding of the surfaces together, the lubricant must be one that will not carbonize in the are between the contacts when the switch is operated at high current levels. The carbonaceous deposit on the contacts drastically raises the resistivity thereof so that the relay begins to limit current flow in the circuit.

The lubricative material on the contact surfaces should be thick enough to physically prevent the degree of metal contact needed for surface bonding while at the same time soft enough to permit sufficient contact to establish electrical continuity between the contacts. Thus, the lubricative substance on the contact surface preferably is unctuous in nature, greasy enough to permit contact slide without the transfer of metal, and yet oily or thin enough to permit electrical contact to be established, thereby not interfering with the electrical conductivity of the contacts.

it has been found that the desired unctuous lubricant can be formed on the metal contacts by insertion of an compound into the sealed atmosphere of the relay. in the presence of the reactive metal plating, such as gold, on the contact's surface, the compound when in sufficient concentration polymerizes to form an unctuous lubricant thereon. Many compounds were found to be undesirable, however, because when introduced into the relay atmosphere in sufficient concentration to produce the desirable polymer, they carbonized in the arc produced at the contacts under certain operating conditions. Benzene (C H for example, will polymerize at a concentration of lO parts per million and carbonizes above 20 parts per million. Thus, only a very narrow useful range is obtained, requiring exact control.

Another problem with the selection of the compound to be used is the incubation period for the formation of the polymer. For any given concentration, some minimum number of mechanical operations of the contacting surfaces is required to start the polymerization action. The minimum number of mechanical operations is inversely proportional to concentration. Since lubrication is lacking during the incubation period, the extent of the incubation period is directly determinative of the possible failure of the relay. If the incubation period is long enough, cold welding or mechanical bonding or metal transfer through the reactive metal surface can occur before the lubricant is formed. Therefore, it is desirable to have sufficient concentration of the compound in the atmosphere to greatly shorten the incubation period since polymer formation rate is a direct function of the concentration of the compound. Thus, for example, ethanol (C H OH), which will produce a polymer at the low concentration of 50 parts per million but carbonizes above 600 parts per million will have a long incubation period if the concentration is kept below the 600 parts per million where carbonization occurs. Far greater concentrations than 600 parts per million are necessary to minimize the incubation period. Also, because temperature change directly affects concentration of the compound in the relay atmosphere, the compound selected must be capable of lubricating over a wide range of concentration without carbonizing.

Monocarbon compounds provide the answer. Monocarbons have been found to be noncarbonaceous over the operating range of the relays tested in concentrations as high as 50,000

parts per million, while at the same time forming a polymer with as small a concentration as 50 parts per million. Because carbonization is not experienced with monocarbons over a concentration change of 1,000 to 1, it is possible to increase the concentration sufficiently to reduce the incubation period for the forming of the polymer thereby reducing contact wear during the incubation period and eliminating the likelihood of mechanical bonding or cold welding during this period. Monocarbon compounds which have provided lubrication over the wide concentration range mentioned above are methanol (CH OH), methyl iodide (CH -,l), chloroform (Cl-lCl and methylene chloride (CH CI- It can be appreciated that the selection of the lubricative component of the atmosphere of an enclosed switch is critical. The component must be capable of lubricating metal wear points over the operating temperature range of the switch. ln some applications this range may extend from 65 C. to +l25 C. Thus, the lubricative must be capable of vaporizing at the lowest temperatures and must not dissociate at the highest temperatures. The lubricative component must be capable of forming a preferably unctuous polymer in the catalytic presence of reactive metal and must not carbonize when in concentrations sufficient to minimize the incubative period for polymerization. in addition, the additive to the relay atmosphere must be capable of reforming the polymer at the metal wear points as the lubricant is pushed aside exposing the reactive metal. The compound selected to meet these requirements can be an additive to an inert gas atmosphere, such as nitrogen, or can comprise the entire atmosphere of the enclosed switch.

The addition of a selected compound to the atmosphere of an enclosed switch, while being a significant step in the method of improving the operability of an enclosed switch, is but one of the several steps necessary for improved switch operation through lubrication. The method comprises removing substantially all contaminants from the switch. The metal of the parts of the switch for which lubrication is desired must be selected to be reactive with the lubricative atmosphere. Prior to sealing the switch, it must be charged or back filled with a controlled atmosphere which may consist of the vapor itself or the vapor in atmosphere with an inert fill gas. Once the enclosure for the switch is sealed with the atmosphere contained therein or even prior to sealing and in the presence of the desired atmosphere, the switch is operated for the incubative period necessary to polymerize the compound in the presence of the reactive contact metal to form the lubricative surface on the metal. The method of improving switch opera tion includes adding sufiicient concentration of the compound to reduce the incubation period to a minimum. ln addition, the temperature of the switch atmosphere is increased thereby increasing the concentration of the compound in the atmosphere to reduce the incubation period. increased concentration, both by added quantity and by increased temperature, can be employed to reduce the incubation period.

Increased concentration of the compound vapor in the atmosphere by raised temperature is realized in the typical relay as shown in the FIGURE since the insulative material used in the construction of the relay coil acts as a sponge absorbing large amounts of the compound material. Thus, with raising the temperature, the compound is desorbed into the atmosphere thereby greatly increasing the vapor pressure or concentration of the vapor in the atmosphere. The effect of temperature on the concentration of the compound in the relay atmosphere is less pronounced where the compound is added to a sealed chamber around the contacts themselves. Here there is no highly sorptive material such as the coil insulation present and, as it is well known, the pressure of the enclosed atmosphere increases only slightly with temperature compared with the pronounced change in a sorptive system. Because the relay chamber, including the coil and its insulative material, is basically a sorptive system, it is necessary that the compound used is capable of producing effective lubrication over a wide concentration range.

in a highly concentrated atmosphere to reduce the incubation period. Later, for sealed operation, a much lower concentration compound can be used. Also, the compound can be inserted in the enclosure in at least three different ways. These gas to result in the desired total amount; or after evacuation, insert a liquid compound which evaporates inside the enclosure.

In the absence of a need to reduce the incubation period for polymer formation, as for example, where the polymer is formed prior to sealing, the required concentration of compound in the switch atmosphere is that amount sufiicient to sustain polymer presence at the metal wear points.

Another variation of the method of forming the lubricant is to form the polymer separately from the parts desired to be lubricated and then coat these parts. The lubricant thus mechanically added can be supported by the lubricative atmosphere of the switch enclosure.

While a particular method, some of its variants and particular compounds have been pointed out as being suitable for producing the lubrication of metal wear points in an enclosed switch, it is intended that the foregoing description should be taken as an illustration of the requirements for lubrication of metal wear points and the necessary conditions and requirements of the system for such lubrication. it is therefore intended that the scope of the invention be only limited by the language and intent of the appended claims.

What is claimed and desired to be secured by Letters Patent of the United States is:

1. In a sealed switch comprising reaction producing metal wear points, a controlled atmosphere including a monocarbon compound selectedfrom the group consisting of methanol, chloroform, methyl iodide and methylene chloride of sufficient concentration for regeneratively producing a lubricative polymer at said switch metal wear points over at least a portion of the temperature range of switch operation without carbonizing.

2. A sealed switch as recited in claim 1 wherein said reaction producing metal is gold and said compound will react in the presence of said gold wear points to form said lubricative polymer.

3. A sealed switch as recited in claim 2 wherein said controlled atmosphere includes a fill gas.

4. A sealed switch as recited in claim 3 wherein said fill gas is substantially inert.

5. A sealed switch as recited in claim 4 wherein said compound is a liquid and is capable of vaporizing over the temperature range of switch operation.

6. A sealed switch as recited in claim 5 wherein said compound is a liquid and is capable of vaporizing over the typical -65 C. to +1 25 C. temperature range of switch operation.

7. A sealed switch as recited in claim 5 wherein the reaction of said compound is repetitive with switch operation, such that said lubricative surface reforms as surface metal of said gold wear points is exposed.

8. A sealed switch as recited in claim 7 wherein the lubricative polymer formed by said compound is unctuous.

9. A method for improving the operability of reaction producing rubbing parts of a sealed switch comprising cleaning the parts to remove contaminants,

surrounding the parts with a controlled atmosphere including a monocarbon compound selected from the group consisting of methanol, chloroform, methyl iodide and methylene chloride, and

operating said switch in said controlled atmosphere for the incubative period necessary for said compound to react in the presence of said reaction lproducing parts and the rubbing of said parts to fonn a ubncatrve surface on the metal wear points of said parts.

10. The method recited in claim 9 wherein said compound is selected to provide lubrication without carbonization over at least a portion of the temperature range of switch operation. a

11. The method recited in claim 10 wherein the amount of compound is selected to be sufficient to minimize the incubation period without increasing carbonization propensity.

12. The method recited in claim 10 further including raising the temperature of said controlled atmosphere to increase the concentration of said compound in said controlled atmosphere to minimize the incubation period without increasing carbonization propensity.

13. A sealed switch comprising relatively movable metal contacts having at least one reaction-producing metal surface,

actuator means coupled to said contacts for causing said contacts to make and break electrical connection,

motor means coupled to said actuator means for driving said actuator means, and

a controlled atmosphere including a monocarbon compound selected from the group consisting of methanol, chloroform, methyl iodide and methylene chloride and of sufficient concentration for reacting in the presence of said reaction-producing metal surface for regeneratively producing a lubricative polymer for lubricating said contacts during making and breaking thereof.

14. A sealed switch as recited in claim 13 wherein a of said contacts is gold, said monocarbon compound polymerizing in the presence of the gold at the points of rubbing contact in the course of making and breaking of electrical connections to form a lubricative surface thereon.

15. A sealed switch comprising metal contacts having at least one reaction-producing metal surface,

actuator means operatively connected to said contacts for causing said contacts to make and break electrical connection,

motor means operatively connected for driving said actuator means; and

a monocarbon compound selected from the group consisting of methanol, chloroform, methyl iodide and methylene chloride which does not carbonize the contacts in the presence of electrical arcing during making and breaking of said contacts and which regeneratively forms a lubricative solid reaction product in the presence of said contacts at the points of rubbing in the course of making and breaking of electrical connections.

16. A sealed switch comprising a plurality of wear points, said wear points including contacts and actuator means for causing said contacts to make and break electrical connections, at least one rubbing surface of each of said wear points having a reaction-producting metal surface, motor means operatively connected for driving said actuator means, a controlled atmosphere for preserving switch life comprising a monocarbon compound selected from the group consisting of methanol, chloroform, methyl iodide and methylene chloride of sufficient concentration to react in the presence of the reaction-producing metal of said surfaces upon the rubbing of said surfaces of said wear points to form a lubricate surface thereon without carbonizing.

17. A sealed switch as recited in claim 16 wherein the metal of said reaction-producing metal surfaces is gold, and said monocarbon compound reacting upon rubbing of said surfaces of said wear points in the catalytic presence of gold in at least one surface of said wear points to form said lubricative surface.

portion

Claims

1. In a sealed switch comprising reAction producing metal wear points, a controlled atmosphere including a monocarbon compound selected from the group consisting of methanol, chloroform, methyl iodide and methylene chloride of sufficient concentration for regeneratively producing a lubricative polymer at said switch metal wear points over at least a portion of the temperature range of switch operation without carbonizing.

6. A sealed switch as recited in claim 5 wherein said compound is a liquid and is capable of vaporizing over the typical -65* C. to +125* C. temperature range of switch operation.

9. A method for improving the operability of reaction producing rubbing parts of a sealed switch comprising cleaning the parts to remove contaminants, surrounding the parts with a controlled atmosphere including a monocarbon compound selected from the group consisting of methanol, chloroform, methyl iodide and methylene chloride, and operating said switch in said controlled atmosphere for the incubative period necessary for said compound to react in the presence of said reaction producing parts and the rubbing of said parts to form a lubricative surface on the metal wear points of said parts.

10. The method recited in claim 9 wherein said compound is selected to provide lubrication without carbonization over at least a portion of the temperature range of switch operation.

13. A sealed switch comprising relatively movable metal contacts having at least one reaction-producing metal surface, actuator means coupled to said contacts for causing said contacts to make and break electrical connection, motor means coupled to said actuator means for driving said actuator means, and a controlled atmosphere including a monocarbon compound selected from the group consisting of methanol, chloroform, methyl iodide and methylene chloride and of sufficient concentration for reacting in the presence of said reaction-producing metal surface for regeneratively producing a lubricative polymer for lubricating said contacts during making and breaking thereof.

14. A sealed switch as recited in claim 13 wherein a portion of said contacts is gold, said monocarbon compound polymerizing in the presence of the gold at the points of rubbing contact in the course of making and breaking of electrical connections to form a lubricative surface thereon.

15. A sealed switch comprising metal contacts having at least one reaction-producing metal surface, actuator means operatively connected to said contacts for causing said contacts to make and break electrical connection, motor means operatively connected for driving said actuator means; and a monocarbon cOmpound selected from the group consisting of methanol, chloroform, methyl iodide and methylene chloride which does not carbonize the contacts in the presence of electrical arcing during making and breaking of said contacts and which regeneratively forms a lubricative solid reaction product in the presence of said contacts at the points of rubbing in the course of making and breaking of electrical connections.