Instrument for a centrifugal separator for detecting the presence of a body and rolling mill provided with such an instrument

An instrument for detecting the presence of a body, comprising a detector (2) and a housing (1) in which the detector (2) is accommodated. The housing (1) is provided with at least one guide passage (6) for transmission to the detector (2) of one or more signals originating from the body. The housing (1 ) is also provided with means for supplying a gas flow (8), for example, compressed air, and a means for discharging at least a part of said flow through the guide passage (6) in such a way that, during operation at least a part of the cleaning gas leaves the housing (1) via the transmission passage (6). At the same time the invention relates to a rolling mill provided with means for determining velocities of the products to be rolled. The means for determining recording velocity comprises at least two of the instruments above and a processing unit which is linked to receive the signals from those instruments for ascertaining the velocity of a product detected by the instruments.

The invention relates to an instrument for detecting the presence of a 
body, comprising a detector and a housing in which the detector is 
accommodated. 
One known type of instrument is based on the principle of thermal radiation 
detection from a body. However, detection methods using other wave ranges 
are also known. Such a device comprises a housing provided with a least a 
transmission passage aimed in the direction of the body to be detected 
suitable for guiding to the detector one or more signals originating from 
the body. An instrument of this type is used in the practice of continuous 
casting. Applications in rolling mill installations are also known. Also 
applications in the field of measuring temperatures in hostile 
environments are known. Reference is made to U.S. Pat. No.5,000,580 and 
DE-C-895,161. U.S. Pat. No. 5,000,580 discloses a radiation pyrometer 
suitable for detecting the presence of a body, which basically comprises a 
detector (1) in a housing having a guide passage for transmission of 
radiation from the body to be detected, and is equiped with a gas purge 
system for directing cleansing gas (air) onto a lens and down the guide. 
At the distal end of the guide an additonal gas injection system is 
arranged of which one part defines a conduit about the end of said guide, 
and another part defines a slot from which gas (air) is discharged into 
the conduit away from the housing and about the guide passage. 
A similar configuration is disclosed in DE-C-895,161. Whereas in U.S. Pat. 
No. 5,000,580 both puree and injection system are provided with 
pressurized gas, in DE-C-895,161 injection of gas takes place only via a 
separate inlet of the additonal injection system resulting in suction of 
gas through the purge system. 
Further prior art (U.S. Pat. No. 4,738,528) shows a method of cleaning a 
pyrometer lens by directing purge aire spirally inward over the lens 
surface such that a vortex is formed by the spiral air flow to increase 
effectivity of the cleaning action. 
U.S. Pat. No. 4,784,491 teaches the application of pitched grooves or screw 
threads in the walls of a gas channel to induce a swirling flow to protect 
optics against debris and moving particles in the air. 
GB-A-1,114,682 proposes the application of a head for a detection 
instrument, including tangential gas inlet for supply of cleaning gas 
along the sight-way of the instrument. 
In this application the instrument serves to detect the presence of a slab 
to be rolled out for purposes such as bringing the mill stands of the 
rolling mill up to the desired angular velocity on time and for making 
other setting adjustments. Instruments of the kind referred to in the 
preamble are also used in rolling mills provided with a reversing rolling 
unit. In a reversing rolling unit a slab is rolled out in a number of 
backward and forward motions into an intermediate product which is 
suitable for being rolled out to a desired finished rolling thickness in a 
finishing train. It is important in the use of such a reversing rolling 
unit to detect not only when the slab to be rolled is approaching the 
roller but also when it is leaving the roller. Valuable production time 
may be saved with this information, given that, for example, detecting the 
slab leaving the mill stand offers the opportunity of reversing the drive 
direction of that mill stand as early as possible. 
There is a problem in the applications mentioned above in that the 
instrument has to work in highly contaminated surroundings which adversely 
affect the operation of the instrument especially in respect of the 
temperature conditions. Consequently, the known instrument requires a 
great deal of maintenance. These aggravating conditions include the 
continual presence of surrounding air saturated with moisture as a result 
of the cooling water sprayed onto the rollers and the high pressure 
descaling water for removing the scale from the slab to be rolled. In 
addition much dirt is present in the surrounding air in the form of iron 
oxide or oil. Also associated with this is the problem that, in terms of 
measuring (recording) roller technology, the known instrument for 
detecting the presence of a body is, in itself, difficult to use in this 
application, given that the air is saturated with moisture in the form of 
steam. 
The invention is intended to offer a solution to the above-mentioned 
problems and to achieve further advantages which shall be illustrated in 
the following. 
The invention provides an instrument for detecting the presence of a body, 
comprising a detector and a housing, in which the detector is 
accommodated, said housing being provided with at least one guide passage 
for transmission to the detector of signals originating from the body 
comprising means for supplying a gas flow and means for directing at least 
part thereof through said guide passage, and further comprising a device 
with an inner and an outer element, the inner element providing a central 
throughflow conduit surrounding said guide passage, and said outer element 
at least partially arranged about the inner element and cooperating 
therewith to form a slot for discharge of gas into said conduit away from 
The housing and around said passage, and is characterised in that the 
instrument is further provided with a centrifugal separator for separating 
the cleaning gas into clean and polluted fractions,whereby the means of 
supplying the cleaning gas are connected close to the outer periphery of 
the centrifugal separator and at least a part of the means for discharging 
the said cleaning gas is connected adjacent to the centre of the 
separator, whereby means for the discharge of the polluted fraction are 
connected to the said device for discharge of the said polluted fraction 
through said slot. According to the invention the desired cleaning may be 
realised using cleaning gas which itself is contaminated. Such gas is 
present, for example, in the local compressed air supply network of a 
hot-rolling mill. This supply network makes use of surrounding air present 
in the rolling mill and consequently it is contaminated, among other 
things, by oil particles suspended in the air. 
With the centrifugal separator proposed the cleaning gas coming from that 
supply network is split into a pollutant rich fraction and a fraction with 
a low pollutant level. The lower pollutant fraction obtained with the 
separator may be used for discharging via the transmission passage. 
Preferably, at the beginning of the transmission passage the centrifugal 
separator should be provided, adjacent its centre, with deflector means 
positioned transverse To the direction of the movement of the cleaning gas 
for reducing the rotational flow energy in the cleaning gas. This 
counteracts the strongly circular motion of the cleaning gas as it leaves 
The centrifugal separatorvia the transmission passage so that the cleaning 
gas is conveyed in an essentially straight path along the Transmission 
passage. 
In a preferred embodiment of the instrument in accordance with the 
invention the transmission passage is provided with a constriction 
preferably close to its end remote from the detector. Thus the cleaning 
gas attains its highest exit rate at the outer end of the transmission 
passage and consequently the entry of dirt into the housing is further 
impeded. 
It has been found that the line of sight for the outflow of the cleaning 
gas from the transmission passage is capable of having a sighting range of 
approximately three meters away from the housing. It is believed chat this 
is brought about because the gas flow which is generated by means of the 
device and which surrounds the gas flow out of the transmission passage, 
protects the latter against turbulence (reversal) caused by dirt and steam 
in the surroundings. It is preferable for the discharge slot to be 
provided on the end of the device nearer to the housing and to be directed 
away from the housing cowards the central conduit of the device. Thus the 
gas leaving the discharge slot via the central conduit of the device 
creates a local pressurised region of the side of the device closest to 
the housing. As a result; of this the surrounding air from that side is 
forced along through the central conduit of the device so that a large air 
movement occurs which surrounds the centrally situated gas flow from the 
transmission passage and protects it against turbulence. 
In a preferred embodiment the transmission passage extends through the 
central conduit of the device and terminates in the region of an end of 
the central conduit further from the housing. This embodiment is found to 
give especially good result in terms of the distance from which the 
instrument may still be used to detect a body. The reason for this is that 
in this embodiment the central line of sight, resulting from the gas 
outflow from the transmission passage, remains unchanged for a 
particularly long time by any turbulence of that flow. 
An alternative embodiment is characterised in that the device is positioned 
beyond and adjacent to the outlet mouth of the transmission passage. This 
embodiment is preferable for use in very contaminated surroundings. 
The invention described in the foregoing is as yet described only in terms 
of application with an instrument which comprises only one detector, 
though it is not limited to that. The invention is also embodied in an 
instrument in which the housing is also provided with a signal transmitter 
and a further transmission passage for directing a signal from the 
transmitter to the body to excite the signal to be received by the 
detector. The transmission passage forms at least a part of the discharge 
means for the cleaning gas flow.

In FIG. 1 and 2 an instrument is shown comprising a housing (1), a detector 
(2) in the housing (1), which detector (2) is mounted behind a lens (3). 
Detector (2) is for example an infrared sensitive element which emits an 
electrical signal if it is activated by infrared radiation, The said 
electrical signal is led via a cable (4) to further processing equipment. 
On the side of the lens (3) the housing (1) is provided with a centrifugal 
separator (5) in which cleaning gas is processed in order firstly for it 
to help keep clean the surface of the lens (3) and further to help keep 
clean a transmission guide passage (6) that extends from the lens surface 
(3) to an end or mouth (7) close to an outer boundary of the housing (1). 
Cleaning gas is supplied into the centrifugal separator (5) via a feeder 
point (8). To this feeder point (8) may be connected, for example, 
compressed air that may be contaminated. In the centrifugal separator the 
compressed air supplied via feeder point (8) is brought int a circular 
motion so that any dirt particles present in the compressed air 
concentrate on the outer circumference of the centrifugal separator (5) 
and as a result of this the compressed air moving close to the lens 
surface (3) is comparatively clean and can clean the lens surface (3) 
effectively because of the rapid circular motion. 
Near the transmission passage (6) the centrifugal separator (5) is provided 
at its centre with plates (9) (see also FIG. 3) which slow down the 
circular motion of the cleaning gas supplied via feeder point (8) and 
cause an essentially straight motion of the cleaning gas into the 
transmission passage (6). The cleaning gas leaves the housing (1) via 
transmission passage (6) and its mouth (7). Preferably the mouth (7) of 
the transmission passage is also provided with a constriction in order to 
effect a higher outflow rate near to this outer boundary of the 
instrument. 
At the same time the instrument is provided with an device (19) comprising 
a first element (11) and a second element (12) which, acting jointly, 
define a discharge slot (13). The device (19) is provided with a feeder 
point (14) for a gas which can leave the device (10) in a direction away 
from the housing (1) through the discharge slot (13) and via a central 
conduit (15) of the device (10). The gas that leaves the transmission 
passage (6) is then surrounded by the gas that leaves the device discharge 
slot (13) through the central conduit (15) of the device (10). This 
creates a laminar flow whereby an extended line of sight is formed from 
the end of transmission passage (6). The line of sight corresponds with 
the gas outflow from transmission passage (6) and is maintained by the gas 
flow which surrounds the gas outflow from transmission passage (6), and 
which is induced by the gas escaping out of discharge slot (13). The 
belief is that this is particularly encouraged because the gas that leaves 
the discharge slot (13) via the central conduit (15) of the device (10) 
creates a local pressurised region on the side of the device (10) near the 
housing (1). As a result the surrounding air from that side is forced 
along through the central conduit (15) of the device (10), so that a large 
air movement occurs. This surrounds the centrally situated gas flow out of 
the transmission passage (6) and protects it against turbulence 
(reversal). 
FIG. 1 shows chat the mouth (7) of the transmission guide passage (6) opens 
out adjacent to the side of the central conduit (15) of the device (10) 
facing away from the housing (10). This embodiment is found to be 
particularly effective for .extending the sight passage over a long 
distance from the end of transmission passage (6). 
An alternative embodiment is shown in FIG. 2 whereby the mouth (7) of the 
transmission passage (6) is positioned just in front of the central 
conduit (15) of the device (10). This embodiment is found to be very 
effective in highly contaminated surroundings. 
The feeder point (14) of the device (10) is connected, by means of a rigid 
connection pipe (16) to the discharge point (17) for the relatively 
polluted fraction of the cleaning gas originating from the centrifugal 
separator (5). This makes it possible to ensure fixed positioning of the 
device (10) relative to the housing (1). 
The invention is not limited to the example embodiments described in the 
foregoing but may be applied with equal success with instruments, which, 
instead of a single detector (2), are provided at the same time with a 
signal transmitter and another transmission passage suitable for guiding a 
signal originating from the transmitter in the direction of the body to be 
detected. The transmission passage in doing so forms at least a part of 
the means of discharge of the cleaning gas. The signal is suitable for 
causing another signal to be generated from the body, this signal being 
suitable for being detected by the detector.