GB2144669A

GB2144669A - Cleaning electrical contacts

Info

Publication number: GB2144669A
Application number: GB08234822A
Authority: GB
Inventors: Rudolf August Herbert Heinecke
Original assignee: Standard Telephone and Cables PLC
Current assignee: STC PLC
Priority date: 1982-12-07
Filing date: 1982-12-07
Publication date: 1985-03-13
Also published as: GB2144669B

Abstract

The contacts of a switch or relay are cleaned by exposure to a localised low pressure jet of an ionised plasma. Typically the plasma contains hydrogen, oxygen, sulphur hexafluoride, or mixtures thereof. The plasma may also include a noble gas, e.g. argon. <IMAGE>

Description

SPECIFICATION Cleaning Electrical Contacts This invention relates to techniques for cleaning electrical contacts for relays and switches and to apparatus for effecting such cleaning.

A problem experienced with all relays and switches is that of deteriation of the contacts with use. After a large number of operations the contact resistance may increase to an unacceptably high value thus limiting the useful life of the switch device. It has been found that one of the factors leading to high contact resistance is lack of cleanliness during initial assembly of the device. In an attempt to extend the useful contact lifetime it has become common practice to subject relay and switch contacts to some form of cleaning process. Typically the contacts are washed with an organic solvent and/or water and are then dried prior to assembly.

Whilst such techniques have been reasonably successful in prolonging contact lifetime it has been found that traces of insoluble matter may still remain on the contact surface and cause subsequent deterioration.

A particular problem with some relays is that the contacts require cleaning after assembly of the device. Alternatively it is sometimes desirable to clear the contacts of a relay after a period of service.

Clearly in such situations the use of wet chemical techniques is precluded.

The object of the present invention is to minimise or to overcome these disadvantages.

According to one aspect of the invention there is provided a process for cleaning electrical contacts, the process comprising subjecting the contact to a localised low pressure jet of an ionized plasma.

According to another aspect of the invention there is provided a contact cleaning apparatus, including a vacuum chamber, means for supplying one or more gases to said vacuum chamber, and means for including a localised plasma with said gas and adjacent the contacts of a switch or relay disposed within the chamber.

We have found that the use of a localised plasma provides effective contact cleaning without detriment to the remainder of a switch or relay in which the contact is mounted.

An embodiment of the invention will now be described with reference to the accompanying drawing in which the single figure is a schematic diagram of a contact cleaning apparatus.

Referring to the drawing the apparatus includes a vacuum chamber 11 in which devices 12 to be cleaned are mounted. The chamber is sealed via a gasket 13 to an earthed conductive plate 14 which plate has openings 15 from the evacuation of the chamber via pump 16. The plate 14 has a further opening 17 provided with an insulating bush 171 which bush receives a conductive tube 18 whereby gas fed into the chamber is directed at the contacts of a relay or switch 12. Advantageously the tube 18 leads into a manifold (not shown) having a plurality of outlets one for each device 12 disposed in the chamber 11.

Gases or gas mixtures are supplied to the tube 18 via an insulating tube section 181 from a gas manifold 182 comprising an array of flowmeters 183 and gas valves 184. A main control valve 185 may be used to isolate the manifold 182 during initial evacuation of the chamber 11.

A plasma may be included in the chamber by the application of radio frequency power from a generator 19 via an external electrode 20 mounted on the upper part of the chamber 11, which electrode provides capacitive coupling to the gas within the chamber. Advantageously the generator imped- ance is matched to that of the chamber via a matching transformer 21. Typically we employ radio frequencies in the range 0.1 to 80 MHz and an estimated input power of 10 to 100 watts, but these valves are not critical to the process.

The function of the tube 18 is to restrict the plasma to a region adjacent the tube outlet into the chamber 11, i.e. to the immediate region of the contacts of a switch or relay 12 disposed at the tube outlet. In this way plasma induced damage to the main body of the switch or relay is avoided.

To effect cleaning a switch or relay is placed in the chamber 11 such that its contacts are adjacent the outlet of the tube 18. The chamber is sealed and evacuated to a pressure below 0.1 torr. A gas or gas mixture is then bled into the chamber via the tube 18 to maintain a dynamic pressure of 0.3 to 20 torr. The generator is switched on to supply radio frequency power to the chamber thereby inducing a slow discharge or plasma. We have found that using the arrangement described the plasma is confined to a region adjacent the gas inlet to the chamber, i.e. adjacent the end of the tube 18. This localised plasma is of sufficient intensity to effect contact cleaning but, as it is restricted to the contact region, it does not damage the remaining portions of the switch or relay. This localisation of the plasma can be enhanced by earthing the contacts being treated.Also means may be provided for switching the contacts during treatment.

Typically the contacts are exposed to the plasma for a period of 10 to 120 seconds, this period depending on the nominal input power employed.

After treatment has been completed the generator is switched off and the chamber is backfilled to atmosphere pressure with air. The switches or relays can then be removed and, advantageously, provided with a hermetic seal around the contact region.

A variety of gases may be employed in the cleaning process. Typically we employ hydrogen, oxygen, sulphur hexafluoride, or mixtures thereof, or mixtures of any one or more with a noble gas, e.g. argon. Other gases employed in the process included, but are not limited to, carbon dioxide, ammonia and water.

CLAIMS:

1. A process for cleaning electrical contacts, the process comprising subjecting the contacts to a localised low pressure jet of an ionised plasma.

2. A process as claimed in claim 1, wherein

**WARNING** end of DESC field may overlap start of CLMS **.

Claims

**WARNING** start of CLMS field may overlap end of DESC **. SPECIFICATION Cleaning Electrical Contacts This invention relates to techniques for cleaning electrical contacts for relays and switches and to apparatus for effecting such cleaning. A problem experienced with all relays and switches is that of deteriation of the contacts with use. After a large number of operations the contact resistance may increase to an unacceptably high value thus limiting the useful life of the switch device. It has been found that one of the factors leading to high contact resistance is lack of cleanliness during initial assembly of the device. In an attempt to extend the useful contact lifetime it has become common practice to subject relay and switch contacts to some form of cleaning process. Typically the contacts are washed with an organic solvent and/or water and are then dried prior to assembly. Whilst such techniques have been reasonably successful in prolonging contact lifetime it has been found that traces of insoluble matter may still remain on the contact surface and cause subsequent deterioration. A particular problem with some relays is that the contacts require cleaning after assembly of the device. Alternatively it is sometimes desirable to clear the contacts of a relay after a period of service. Clearly in such situations the use of wet chemical techniques is precluded. The object of the present invention is to minimise or to overcome these disadvantages. According to one aspect of the invention there is provided a process for cleaning electrical contacts, the process comprising subjecting the contact to a localised low pressure jet of an ionized plasma. According to another aspect of the invention there is provided a contact cleaning apparatus, including a vacuum chamber, means for supplying one or more gases to said vacuum chamber, and means for including a localised plasma with said gas and adjacent the contacts of a switch or relay disposed within the chamber. We have found that the use of a localised plasma provides effective contact cleaning without detriment to the remainder of a switch or relay in which the contact is mounted. An embodiment of the invention will now be described with reference to the accompanying drawing in which the single figure is a schematic diagram of a contact cleaning apparatus. Referring to the drawing the apparatus includes a vacuum chamber 11 in which devices 12 to be cleaned are mounted. The chamber is sealed via a gasket 13 to an earthed conductive plate 14 which plate has openings 15 from the evacuation of the chamber via pump 16. The plate 14 has a further opening 17 provided with an insulating bush 171 which bush receives a conductive tube 18 whereby gas fed into the chamber is directed at the contacts of a relay or switch 12. Advantageously the tube 18 leads into a manifold (not shown) having a plurality of outlets one for each device 12 disposed in the chamber 11. Gases or gas mixtures are supplied to the tube 18 via an insulating tube section 181 from a gas manifold 182 comprising an array of flowmeters 183 and gas valves 184. A main control valve 185 may be used to isolate the manifold 182 during initial evacuation of the chamber 11. A plasma may be included in the chamber by the application of radio frequency power from a generator 19 via an external electrode 20 mounted on the upper part of the chamber 11, which electrode provides capacitive coupling to the gas within the chamber. Advantageously the generator imped- ance is matched to that of the chamber via a matching transformer 21. Typically we employ radio frequencies in the range 0.1 to 80 MHz and an estimated input power of 10 to 100 watts, but these valves are not critical to the process. The function of the tube 18 is to restrict the plasma to a region adjacent the tube outlet into the chamber 11, i.e. to the immediate region of the contacts of a switch or relay 12 disposed at the tube outlet. In this way plasma induced damage to the main body of the switch or relay is avoided. To effect cleaning a switch or relay is placed in the chamber 11 such that its contacts are adjacent the outlet of the tube 18. The chamber is sealed and evacuated to a pressure below 0.1 torr. A gas or gas mixture is then bled into the chamber via the tube 18 to maintain a dynamic pressure of 0.3 to 20 torr. The generator is switched on to supply radio frequency power to the chamber thereby inducing a slow discharge or plasma. We have found that using the arrangement described the plasma is confined to a region adjacent the gas inlet to the chamber, i.e. adjacent the end of the tube 18. This localised plasma is of sufficient intensity to effect contact cleaning but, as it is restricted to the contact region, it does not damage the remaining portions of the switch or relay. This localisation of the plasma can be enhanced by earthing the contacts being treated.Also means may be provided for switching the contacts during treatment. Typically the contacts are exposed to the plasma for a period of 10 to 120 seconds, this period depending on the nominal input power employed. After treatment has been completed the generator is switched off and the chamber is backfilled to atmosphere pressure with air. The switches or relays can then be removed and, advantageously, provided with a hermetic seal around the contact region. A variety of gases may be employed in the cleaning process. Typically we employ hydrogen, oxygen, sulphur hexafluoride, or mixtures thereof, or mixtures of any one or more with a noble gas, e.g. argon. Other gases employed in the process included, but are not limited to, carbon dioxide, ammonia and water. CLAIMS:

2. A process as claimed in claim 1, wherein said plasma includes hydrogen, oxygen, sulphur hexafluoride or mixtures thereof.

3. A process as claimed in claim 2, wherein said plasma contains a noble gas.

4. A process as claimed in claim 3, wherein said plasma comprises a mixture of hydrogen and argon.

5. A process as claimed in any one of claims 1 to 4 wherein said plasma is a radio frequency plasma.

6. A process as claimed in claim 5 wherein said radio frequency is from 0.1 to 80 MHz.

7. A process as claimed in any one of claims 1 to 6, wherein said plasma is maintained at a pressure of 0.3 to 2 torr.

8. A process as claimed in any one of claims 1 to 7, wherein said contacts are exposed to the plasma for a period of 10 to 120 seconds.

9. A process for cleaning electrical contacts substantially as described herein with reference to the accompanying drawing.

10. A switch or relay incorporating one or more contacts treated by a process as claimed in any one of claims 1 to 9.

11. A contact cleaning apparatus, including a vacuum chamber, means for supplying one or more gases to said vacuum chamber, and means for inducing a localised plasma within said gas and adjacent the contacts of a switch or relay disposed within the chamber.

12. An apparatus as claimed in claim 11, wherein said plasma inducing means includes a conductive tube through which the gas is directed into the vacuum chamber, the plasma being confined to a region adjacent the outlet of the tube.

13. An apparatus as claimed in claim 11 or 12, and which includes means for earthing contacts during the cleaning process.

14. A contact cleaning apparatus substantially as described herein with reference to the accompanying drawing.