MEASUREMENT OF SURFACE PROFILE

Abstract: The invention concerns a profile gauge for measuring or detecting changes in the surface profile of a rotatable work­ piece. The guage comprises a probe mounted for movement relative to the rotatable workpiece and connected at its end remote from the workpiece surface to the core of a transducer. The probe has an open tip through which gas under pressure can be discharged to form a film or cushion between the probe tip and the adjacent surface of the workpiece, and means are provided to couple the transducer to signal proces­ sing equipment capable of discriminating between output signals representative of several measured parameters of the workpiece profile.

Description: Improvements in and relating to the Measurement of Surface Profile This invention relates to a method of and apparatus for measuring or detecting changes in the surface profile of a rotating workpiece such as a work roll. In particular, but not exclusively, the invention concerns such method and apparatus for measuring roll surface profile as the roll is rotating and loaded by the passage of hot metal strip. In the metals industry, increasing emphasis is being placed on the control of the profile and shape of rolled hot metal strip. One important aspect of this control is the geometry of the surface of the work rolls during the rolling process. In the past, an inductance measuring systenl across an air gap has been employed to determine roll profile but this system has been found to have the disadvantage of being sensitive to the surface temp erature of the roll under inspection which means that discrimination of the variable parameters to be measured is impossible. The present invention sets out to overcome this and other disadvantages. According to the present invention in one aspect, there is provided apparatus for measuring or detecting changes in the surface profile of a rotatable workpiece comprising a transducer, a probe mounted for movement relative to the rotatable workpiece and connected at its end remote from the workpiece surface to the core of the transducer, the probe having an open tip through which gas under pressure can be discharged to form a film or cushion between the probe tip and the adjacent surface of the workpiece having a thickness related to the applied gas pressure, and means operable to couple the transducer to signal processing equip ment capable of discriminating between transducer output signals representative of several measured parameters of the workpiece profile. According to the present invention in another aspect, there is provided a method of measuring or detecting changes in the surface profile of a rotatable workpiece, which method includes the steps of maintaining a gas film or cushion between the tip of a probe movable relative to the workpiece surface and connected at one end to a transducer operable to transmit to signal processing equipment electrical signals representative of measured parameters of the workpiece profile. The workpiece may comprise a work roll whose surface, in use, is covered with a curtain of cooling water. In this embodiment, the gas forming the film or cushion is discharged from the probe tip at a force sufficient to penetrate the cooling water curtain and profile measurements are taken while the rolls are loaded by the passage of hot metal strip. The probe preferably comprises a plunger connected at one end to a transducer and formed with a central bore through which the gas (preferably air) under pressure passes to the probe tip. According to the present invention in a further aspect, there is provided a profile gauge which includes a transducer connected to respond to movements of a probe through which gas under pressure can be discharged to form at the probe tip a film or cushion or gas which, in use of the gauge, separates the probe tip from a workpiece under inspection. The invention will now be described, by way of example only, with reference to the accompanying diagrammatic drawings, in which: Figure 1 is section taken through a profile gauge in accordance with the invention; Figure 2 is a side elevational view of apparatus in accordance with the invention assembled adjacent the surface of a work roll; Figure 3 is a perspective view partly in section of the apparatus illustrated in Figure 2; and Figure 4 schematically illustrates apparatus in accordance with the invention coupled to signal processing equipment. The gauge illustrated in Figure 1 includes an L.V.D.T. transducer I mounted within a stainless steel housing 2. The movable core of the transducer is attached through a rod 4 to one end of a movable probe tip 3 supported within a collar screwed into one end of the housing 2. The housing 2 is supported within a steel yoke member 6. The housing 2 is formed with passageways 7 which place a chamber 8 of the housing in communication with the interior of the beam 5 to which compressed air is supplied from an external source (not shown). The probe tip 3 is formed with inclined entry passageways 9 and a central bore 10 which exits into a recess II formed in the probe tip end. Preferably, the probe tip is constructed from aluminium. The transducer is connected through a cable to a supply of electricity and to signal processing equipment. In Figures 2 and 3 of the drawings, the gauge illustrated in Figure 1 is shown located adjacent the surface of a work roll 12 whose profile is to be inspected. As will be apparent from these Figures, several such gauge units are housed side-by-side in the beam 5 across the full width of the roll to enable a complete display of localised wear to be made. The yoke member 6 is supported between inclined arms 13 pivotably connected to link members 14 interconnected through a pneumatic cylinder 15. The ends of the link members 14 remote from the arms 13 are pivotably mounted on fixings 16. Nonmetallic pads 17 are located on the ends of the yoke member 6 to provide a repeatable datum position for the probe units. Cooling heads 18 are provided to supply a curtain of cooling water on the surface of the work. Signal processing equipment for use with the probe units is illustrated in Figure 4. The equipment includes a head amplifier 19 connected to the gauge units through the cable 20, a signal processing unit 21, recorder 22 and microprocessor 23. In operation of the illustrated apparatus, the beam 5 is positioned adjacent the work roll 12 through operation of the cylinder 15 with the non-metallic pads 17 contacting the work roll surface to provide a repeatable datum position. The pads 17 may be constructed of a material such as nylon and are positioned one at each end of the beam. Compressed air is then passed through the beam 5 and enters the chambers 8 of the individual probe units through the passageways 7 of the housing 2. This compressed air passes into the individual probes through passageways 9 to create a film or cushion between the adjacent surfaces of the probe tip 3 and the work roll 12. In one specific arrangement, the air pressure employed was 0.7 bar to give an air film thickness of 0.127mm with a measuring accuracy of 0.01 mum. The central bore 10 of the probe in this arrangement was 2.4mm to give adequate air flow to maintain the required film thickness without generating an excessive air consumption. Air consumption was estimated at 2.54m3/min. In addition to creating an air film, the gas pressure was sufficient to clean the opposed roll surface of cooling fluid. Analogue outputs form the individual transducers are scanned at a fast rate as the roll rotates to ensure that the profile relates to a 100 or less sector of the roll. This means that a sample and hold facility is necessary so that the profile of the roll can be scanned quickly. Subsequent processing and display can, however, be carried out more slowly to provide an output for an analogue recorder or recording oscilloscope. Figure 4 shows the breakdown of units required for this facility. The output from the transducers feed directly into the head amplifier unit 19 mounted close to the beam in the vicinity of the mill stand. This output in turn can be fed to a remote sample and hold unit which also contains the multiplexer unit. The output from this processing is then suitable for direct input into the analogue recorder 22 or recording oscilloscope. The microprocessor 23 has a fast sample and multiplexing facility; the input can be taken directly from the head amplifier 19 via an analogue to digital converter to the microprocessor 23. A digital tape storage unit can then be used to programme the timing of the profile scans and the processing of the signals to provide the display required. Following use, the air cylinder 15 is operated to withdraw the beam 5 and the gauges away from the roll surface. The air cylinder 15 has an interlock valve to ensure that if the supply to the probes fails, the complete beam will be withdrawn. In addition, mechanical limit switches are provided to ensure that the beam is withdrawn during roll changes even if the operator neglects to initiate this action. ln use of the gauge, the probe tip 3 is moved relative to the roll surface under inspection with variations in roll profile (e.g. profile wear or defects). Movement of the probe is transmitted through the rod 4 to the transducer core to which the rod is connected. Thus, any changes in roll profile are detected and spurious results caused by wear or defects in the roll profile are prevented by the constant thickness air cushion. The gauge described above is capable of detecting various profile parameters, these including the initial ground profile of the work roll, the degree of roll bending under load, thermal crown and surface wear. The signal processing equipment discriminates between the respective transducer signals to give a clear measurement of the surface profile across the full width of the roll. While the invention has been particularly described with reference to the foregoing embodiments, it is to be understood that many variations of the embodiment features can be made without departing from the scope of the invention.

Claims: CLAIMS 1. Apparatus for measuring or detecting changes in the surface profile of a rotatable workpiece characterised by a probe mounted for movement relative to the rotatable workpiece (12) and connected at its end remote from the workpiece surface to the core of a transducer (1), the probe having an open tip (3) through which gas under pressure can be discharged to form a film or cushion between the probe tip and the adjacent surface of the workpiece, and means operable to couple the transducer to signal processing equipment capable of discriminating between transducer output signals representative of several measured parameters of the workpiece profile. 2. Apparatus as claimed in claim I characterised in that the probe comprises a tubular member connected via a rod (4) to the bore of the transducer and formed at its end remote from the transducer with an enlarged recess (it). 3. Apparatus as claimed in claim 2 characterised in that the assembly of the transducer and probe is supported by a hollow structure (5) whose interior is connected to a source of gas under pressure and communicates with the open tip of the probe to place the same in communication with the aforesaid source. 4. Apparatus as claimed in claim 3 characterised in that the hollow structure supports a plurality of transducer-probe assemblies and wherein the hollow structure is movable towards and away from the surface oi the rotatable workpiece by means of a pivotably mounted frame (13 - 16). 5. Apparatus as claimed in any one of the preceding claims for detecting changes in the surface profile of a work roll whose surface, in use, is covered with a curtain of cooling fluid, characterised in that the gas forming the fizzy or cushion is discharged from the probe tip at a force sufficie:lt to penetrate the curtain of cooling fluid. 6. Apr,-ratus as claimed in any one of the preceding claims chararserised in that the gas forming the film or cushion comprises air. 7. Apparatus as claimed in any one of the preceding claims characterised in that the probe tip includes one or more protruding nonmetallic pads (17) operable, in use, to provide a repeatable datum position for locating the probe tip relative to the workpiece surface. 8. A method of measuring or detecting changes in the surface profile of a rotatable workpiece, which method is characterised by the steps of maintaining a gas film or cushion between the tip of a probe movable relative to the workpiece surface and connected at one end to a transducer operable to transmit to signal processing equipment electrical signals representative of measured parameters of the workpiece profile. 9. A profile gauge characterised in that it comprises a transducer connected to respond to movements of a probe through which gas under pressure can be discharged to form at the probe tip (3) a film or cushion of gas which, in use of the gauge, separates the probe tip from a workpiece (12) under inspection.

Inventors: MOORE, JACK MICHAEL, PARKER, DENNIS JOHN
Applicants: BRITISH STEEL PLC
Application year: 1984
Main classification: G01B7
IPC codes: G01B7, B21B38