Sliding strip for collector with rupture detection device

A carbon sliding strip for a collector has a rupture control device, comprising a pressure line (9) incorporated directly in the carbon strip (1), a device (13) for producing increased pressure in the pressure line and a pressure detector (15), which detects the sudden drop in pressure which occurs if the channel begins to leak. Since at least part of pressure line wall is made directly from the carbon material, the pressure control device responds even to small cracks in the carbon and immediately shows wear and rupture.

The present invention relates to a sliding strip for a collector comprising 
a carbon strip mounted on a carrier and a rupture or crack detection 
device for sensing ruptures or wear in the carbon strip. 
It is essential to take modern collectors out of service as quickly as 
possible when their carbon sliding strips are damaged by wear or cracking. 
Thus, a rupture detector known from U.S. Pat. No. 4,578,546, for example, 
automatically lowers the collector when wear or a rupture in the sliding 
strip is detected. Wear or cracking in the carbon sliding strip is 
detected by placing an internally pressurized hose inside the sliding 
strip which extends in the longitudinal direction of the strip. Damage to 
the hose results in a sudden pressure drop which is used for triggering an 
alarm or automatically lowering the collector. 
However, such conventional pressure controllers have not been sufficiently 
reliable. The hose does not necessarily wear down with the carbon strip 
and cracks in the strip are either not sensed at all or they are sensed 
with a time delay. 
It is therefore an object of the present invention to provide an improved 
carbon sliding strip of the aforementioned kind in which excessive wear 
and cracking of the carbon are detected instantaneously and with greater 
reliability. 
The objective is achieved as set forth in claim 1. The subclaims relate to 
further advantageous embodiments of the invention. 
The pressure conduit of the present invention is not formed by a hose but 
directly by the carbon strip material or a coating applied thereto. Hence, 
the pressure conduit will begin to leak due to a rupture of or even a thin 
crack in the carbon, wear of the carbon strip, or when the strip is jolted 
loose from its carrier. In each case there is a rapid pressure drop which 
either triggers a warning signal in the conventional manner and/or is 
utilized to automatically lower the collector. The degree of 
responsiveness may be controlled by appropriately varying the thickness of 
a coating applied to the walls of the pressure conduit.

FIGS. 1 and 2 show a sliding strip made of a carbon strip 1 and a carrier 3 
for the requisite mechanical strength and which is also used on 
conventional collectors as a conductor. A copper layer 5 is galvanically 
applied to the underside of carbon strip 1 which is cemented to carrier 3 
by means of an adhesive layer 7. For purposes of illustration the 
thickness of both copper layer 5 and adhesive layer 7 are exaggerated in 
FIGS. 1 and 2. 
A groove 9 is milled or press formed into the underside of carbon strip 1. 
Copper layer 5 bridges over groove 9 to define an air-tight pressure 
conduit enclosed on three sides by the carbon and on a fourth side by 
copper layer. The interior walls of the groove formed by the carbon may 
also have an air-tight coating of, for example, a thin lacquer or a 
pyrolytically applied carbon layer. 
As seen in FIG. 2, at one end of the carbon strip, a hose 11 is cemented 
into pressure channel 9. A compressed air pressure line from a source, 
such as, for example, a compressed air tank 13, is connected to the hose 
and the pressure in channel 9 is monitored with a sensor 15. At the other 
end of carbon strip 1 (not shown in FIG. 2) pressure channel 9 is sealed 
in a suitable manner. 
When the material of which carbon strip 1 is made becomes worn, damaged or 
ruptures, a leak occurs in pressure channel 9, producing a drop in 
pressure which is measured by a pressure sensor 15. Pressure sensor 15 may 
function in a conventional manner to trigger a warning signal and/or to 
disengage the collector. 
Though not shown in the present embodiment, the galvanically applied copper 
layer 5 may also cover the walls of groove 9. Here too, the advantages of 
the present invention are realized because excessive wear or a rupture of 
the carbon immediately damages the thin copper layer, thereby causing it 
to leak. 
Carbon strip 1 together with pressure channel 9 is preferably made 
utilizing the following advantageous method. A groove 9 is milled into the 
undersurface of carbon strip 1 and is then filled with a material so that 
it is flush with the undersurface. Plastic materials are ideally suited as 
a filler, e.g. in the form of a plastic strip that is laid into groove 9. 
Next, a copper layer 5 is galvanically applied to the undersurface of 
carbon strip 1. It expands across and completely bridges over the filler 
disposed in groove 9. It is advantageous to select a filler that adheres 
poorly to the copper layer. After the copper layer is applied, the plastic 
or other filler material is removed, e.g. by pulling it out of or melting 
it in groove 9, leaving behind an airtight pressure conduit 9. 
In a modified embodiment of the present invention a copper layer 5 is 
applied on each side of groove 9 and, if desired, to the interior walls of 
the groove, but it does not bridge over the groove. In this case the 
portion of the groove 9 facing carrier 3 remains open and it is sealed off 
when the carrier is cemented to carbon strip 1, thereby forming an 
airtight seal. An advantage of this embodiment is that the detector 15 
also senses a separation or leakage occurring at any given point along the 
adhesive connection between carbon strip 1 and carrier 3. 
In the embodiment of FIG. 3 the carrier is constructed with side sections 
in the form of curved, horn-like extensions 3a for guiding an electric 
wire approaching the collector from the side towards the center portion of 
the sliding strip. Carbon strip 1, with the pressure channel 9 described 
above, is placed over the straight or only slightly curved center section 
of carrier 3. Extensions 3a are also covered with a carbon layer 1a to 
provide wear protection. Each layer 9a is considerably thinner than carbon 
strip 1 and is preferably manufactured and applied separately from carbon 
strip 1. An adhesive joint 17 connects the two and forms an airtight seal. 
A pressure conduit 9a is also formed within each layer 1a and is connected 
to pressure conduit 9 of carbon strip 1 with a hose section 19 that 
bridges joint 17. Pressure channel 9a of layer 1a, and with that pressure 
channel 9 of carbon strip 1, are joined by means of a fitting 12 to a 
compressed air tank (not shown) and to a pressure sensor. A connector 14 
serves, for example, to secure the sliding strip, to the pantographs of 
the collector, and to establish electrical contacts.