INSTRUMENT FOR DETECTING THE PRESENCE OF A BODY AND ROLLING MILL PROVIDED WITH SUCH AN INSTRUMENT

Abstract: 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.

Description: INSTRUMENT FOR DETECTING THE PRESENCE OF A BODY AND ROLLING MILL PROVIDED WITH SUCH AN INSTRUMENT 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 at 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. 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 on 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, characterised in that the housing is further provided with means for supplying a gas flow and means for discharging at least a part of said flow through the guide passage whereby during operation, at least a part of the gas flow leaves the housing via the guide passage. This system can alleviate the problems above by removing dirt particles which might be present in the housing, these particles being carried out of the housing of the instrument with the cleaning gas via the transmission guide passage. This has the additional advantage that the outflow of cleaning gas can give a clearer path for signals along the transmission passage in the direction of the body to be detected. In a specific aspect of the invention the housing is provided with a centrifugal separator for separating the cleaning gas into clean and polluted fractions. Furthermore 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. This has the advantage that the desired cleaning may be realised using cleaning gas which is itself contaminated. Such gas is present, for example in a hot-rolling mill, in the local compressed air supply network. Such a 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 fraction contaminated by pollutant (e.g. oil) may be discharged elsewhere and the lower pollutant fraction 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 separator via 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. In another aspect of the invention there is provided a device comprising a first inner element providing a central throughflow conduit which surrounds the transmission passage or an extension of the discharge flow path therefrom, and an outer element at least partially overlapping the inner element, the elements cooperating in defining a slot for a discharge of gas into said conduit in a direction away from the housing and around said passage or said extension. Surprisingly, it has been found that the line of sight for the outflow of the cleaning gas from the transmission passage, becomes greatly extended. In this way even without such an device the instrument invented is found to be capable of having a sighting range of approximately half a metre. However, when the aforementioned device is used it is found that the sight range is able to extend up to approximately three metres away from the housing. It is believed that this effect 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 towards 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 on 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 of the invention 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 results 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 in accordance with the invention 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. In another aspect of the invention the instrument is characterised in that the gas discharge means on the housing provides a supply of gas for discharge through the conduit. It is then of particular advantage if the means for discharge of the polluted fraction is connected to said device for the supply of said discharge through the conduit. This provides a very refined manner of both creating a useful application of the polluted fraction of the cleaning gas, and, when using a rigid connection, positioning the device relative to the housing as desired. 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 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. The invention further relates to a rolling mill for rolling products, for example slabs of steel into strip steel. Such rolling mills are frequently provided with means for determining velocities of the products to be rolled. The use of a measuring (recording) roller is known. However a problem with this form of measurement is that a high degree of maintenance is required. In order to maintain sufficient accuracy of the velocity recording and in order to counteract the slip of the recording roller, preventative maintenance needs to be carried out regularly. In accordance with the invention an accurate, sturdy velocity determining instrument, requiring little maintenance, is now created. The means for determining velocity comprises at least two instruments as described in the foregoing and a processing unit. The unit is linked to receive the signals from those instruments for ascertaining the velocity of a product detected by the instruments. This application is made possible because the instrument in accordance with the invention has a highly accurate recording spot. Here the recording spot is understood to be the projection of the line of sight onto the object to be detected. The invention will now be described, by way of example, with reference to the accompanying drawings. Fig 1 shows the instrument in accordance with the invention in a first embodiment. Fig 2 shows the instrument in accordance with the invention in a second embodiment. Fig 3 shows a cross-section through the centrifugal separator of the instrument in accordance with the invention. Corresponding reference numerals in the figures indicate corresponding parts of the instrument. 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 into 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 (10) comprising a first element (11) and a second element (12) which, acting jointly, define a discharge slot (13). The device (10) 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 that 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.

Claims: CLAIMS 1. An instrument for detecting the presence of a body, comprising a detector (2) and a housing (1), in which the detector (2) is accommodated, said housing (1) being provided with at least one guide passage (6) for transmission to the detector (2) of signals from the body, characterised in that the housing (1) is further provided with means for supplying a gas flow (8), and means for directing at least a part of said flow through the guide passage (6) such that, during operation, at least a part of the gas flow leaves the housing (1) via the guide passage (6). 2. An instrument according to claim 1, wherein the housing (1) is provided with a centrifugal separator (5) for separating the gas into clean and polluted fractions, and the gas supplying means (8) is connected close to the outer periphery of the centrifugal separator (5), and the gas directing means comprises a connection adjacent the centre of said separator (5). 3. An instrument according to claim 2, wherein the centrifugal separator (5) is provided adjacent its centre with deflector means (9) positioned transverse to the direction of flow of the gas for reducing the rotational flow energy of the gas. 4. An instrument according to any one of claims 1,2 or 3, wherein the guide passage (6) is provided with a constriction close to its end (7) remote from the detector (2). 5. An instrument according to any one of the preceding claims wherein a device (10) comprising a first inner element (11) providing a central throughflow conduit (15) which surrounds the guide passage (6) or an extension of the discharge flow path therefrom, and an outer element (12) at least partially overlapping the inner element (11), the elements cooperating in defining a slot (13) for a discharge of gas into said conduit in a direction away from the housing (1) and around said passage (6) or said extension. 6. An instrument according to claim 5, wherein the discharge slot (13) is provided on an end of the device nearer to the housing (1) and is directed away from the housing (1) and towards the central conduit (15) of the device. 7. An instrument according to claim 5 or claim 6, wherein the guide passage (6) extends through the central conduit (15) of the device and terminates in the region of an end of the central conduit further from the housing. 8. An instrument according to claim 5 or claim 6, wherein the device (10) is positioned beyond and adjacent to an outlet mouth (7) of the guide passage (6). 9. An instrument according to any one of claims 5 to 8 wherein the gas flow directing means are provided for directing a further part of said housing gas flow for said discharge through said slot (13). 10. An instrument according to claim 2 together with claim 9 wherein means for the discharge of the polluted fraction is connected to said device (10) for said discharge of said fraction through the slot (13). 11. An instrument according to any one of the preceding claims wherein the housing (1) is provided with a signal transmitter and a further guide passage for directing a signal from the transmitter towards the body to excite said signal to be received by the detector, said further passage forming at least a part of the directing means for the gas flow. 12. A rolling mill having means for determining the velocity of a product to be rolled, including at least two instruments in accordance with any one of claims 1 to 11 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. AMENDED CLAIMS [received by the International Bureau on 21 September 1992 (21.09.92); original claims 1-12 replaced by amended claims 1-9 (3 pages)] 1. An instrument for detecting the presence of a body, comprising a detector (2) and a housing (1), in which the detector (2) is accommodated, said housing (1) being provided with at least one guide passage (6) for transmission to the detector (2) of signals from the body, and with means for supplying a gas flow (8) , and means for directing at least a part of said flow through the guide passage (6) such that, during operation, at least a part of the gas flow leaves the housing (1) via the guide passage (6) , characterised in that it is provided with a device (10) comprising a first inner element (11) providing a central throughflow conduit (15) which surrounds the guide passage (6) or an extension of the discharge flow path therefrom, and an outer element (12) at least partially overlapping the inner element (11) , the elements cooperating in defining a slot (13) for a discharge of gas into said conduit in a direction away from the housing (1) and around said passage (6) or said extension. 2. An instrument according to claim 1, wherein the discharge slot (13) is provided on an end of the device nearer to the housing (1) and is directed away from the housing (1) and towards the central conduit (15) of the device. 3. An instrument according to claim 1 or claim 2, wherein the guide passage (6) extends through the central conduit (15) of the device and terminates in the region of an end of the central conduit further from the housing. 4. An instrument according to claim 1 or claim 2, wherein the device (10) is positioned beyond and adjacent to an outlet mouth (7) of the guide passage (6). 5. An instrument according to any one of claims 1-4 wherein the gas flow directing means are provided for directing a further part of said housing gas flow for said discharge through said slot (13). 6. An instrument according to any one of claims 1-5 provided with a centrifugal separator (5) for separating the gas into a clean and a polluted fraction, and wherein the gas supplying means (8) is connected close to the outer periphery of the centrifugal separator (5), and the gas directing means comprises a connection adjacent the centre of said separator (5), wherein means for the discharge of the polluted fraction is connected to said device (10) for said discharge of said fraction through said slot (13). 7. An instrument according to claim 6, wherein the centrifugal separator (5) is provided adjacent its centre with deflector means (9) positioned transverse to the direction of flow of the gas for reducing the rotational flow energy of the gas. 8. An instrument according to any one of the preceding claims wherein the housing (1) is provided with a signal transmitter and a further guide passage for directing a signal from the transmitter towards the body to excite said signal to be received by the detector, said further passage forming at least a part of the directing means for the gas flow. 9. A rolling mill having means for determining the velocity of a product to be rolled, including at least two instruments in accordance with any one of the preceding claims 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.

Inventors: DE VISSER ROBER, LEA RICHARD WALTER, DE VISSER, ROBER, LEA, RICHARD, WALTER
Applicants: HOOGOVENS GROEP BV
Application year: 1992
Main classification: G01B11
IPC codes: B21B38, B21B39, G01B11, G01J5, G01N33, G01V8, G02B27