GB2139353A

GB2139353A - Test-piece testing apparatus

Info

Publication number: GB2139353A
Application number: GB08312441A
Authority: GB
Inventors: John David Ward
Original assignee: Froude Consine Ltd
Current assignee: Froude Consine Ltd
Priority date: 1983-05-06
Filing date: 1983-05-06
Publication date: 1984-11-07
Also published as: GB8312441D0; GB2139353B

Abstract

An ultrasonic or temperature probe (1) is sealed by an O-ring (3) inside an inner holder part (2A) which is resiliently connected to an outer holder part (2B) by a diaphragm (4) held on by end caps (5) and (6). A magnet (7) is fitted to the front of outer holder part (2B) and locates the probe (1). A ring seal (8) on magnet (7) is placed against the surface of the test-piece and a valve (12E) closed to cause pump (12) to pump water from reservoir (11) via inlet (9) and ducts into a space (16) between probe (1) and the test-piece surface, until all air has been purged from the system via outlet (10) with its non- return valve. Then valve (12E) is opened, creating suction in reservoir 11 from pump 12, and probe (1) is drawn into close contact with the test-piece surface with water between them as a fluid coupling medium, the water also serving to cleanse the surface of probe (1). <IMAGE>

Description

SPECIFICATION Test-piece testing apparatus This invention relates to test-piece testing apparatus.

Non-destructive test work using ultrasonics requires intimate contact between the ultrasonic sensor and the test piece, since high frequency sound waves (1 Mhz or thereabouts) are not transmitted through air. This problem is often solved by submerging probe and test piece in a water or oil bath or, in the case of large components, by coating the surface of the probe with grease or some other coupling medium This latter technique although suitable for manual testing where the time between tests is not important, does present difficulties when the process needs to be performed rapidly and possibly automatically. Unless the probe is cleaned between tests, its surface can become contaminated with dirt after a short while, which will affect the results. Special coupling agents are available but these are relatively expensive and may not offer any special advantages.

In the specific case of determining t.d.c.

(top dead centre) of an engine by ultrasonic means, the simple act of applying grease to the probe surface is unsuitable for product testing.

According to the invention there is provided test-piece testing apparatus comprising: a testing probe adapted to be coupled to a surface of a test-piece for testing of the testpiece; a holder for holding the probe so as to permit limited relative movement between the probe and the holder; resilient sealing means for engaging the surface of the test-piece and providing a seal between the holder and the surface of the test-piece; means for, in use, flooding a space between the probe and the surface of the test-piece with a fluid coupling medium; and means for, in use, applying suction to the flooded space so as to draw the probe towards the surface of the test-piece with fluid coupling medium there-between.

The invention will be described by way of example with reference to the accompanying drawings illustrating an embodiment of the invention with some parts shown schematicaly and other parts shown sectioned.

Referring to the drawing, the illustrated test-piece testing apparatus comprises an ultrasonic probe 1 adapted to be (ultrasonically) coupled to the surface of a test-piece as shown for ultrasonic testing of the test-piece.

For example, the test-piece may be the block of an internal combustion engine for purposes of engine testing methods as disclosed in our co-pending British Patent Applications Nos.

81.02004, 81,38431 and 82,26057, European Patent Applications Nos. 81.306010.0, Japanese Patent Applications Nos.

206336/81 and 6911/82 and U.S. Patent Applications Serial Nos. 333,387 (12-22-81).

The ultrasonic probe 1 is located in a plastics holder 2 which is in two parts, namely, an inner holder part 2A and an outer holder part 2B. The inner holder part 2A, into which the ultrasonic probe 1 is sealed by means of an "0"-ring 3, is connected to the outer holder part 2B by means of a rubber diaphragm 4 so as to permit limited relative movement between the inner and outer holder parts 2A and 2B while sealing the gap between them at their rear ends. The diaphragm 4 is clamped to the inner holder part 2A by a first screw cap 5 and to the outer holder part 2B by a second screw cap 6.

An annular magnet 7 is fastened to the outer holder part 2B and loosely surrounds a front end portion of, and magnetically locates, the ultrasonic probe 1. This magnet 7 is, in turn, surrounded by an annular rubber seal 8 forming a resilient sealing means for engaging the surface of the test-piece as shown and providing a seal between the outer holder part 2B and the surface of the test-piece. In use, pressure is applied to the outer holder part 2B so as to press the rubber seal 8 against the surface of the test-piece.

The outer holder part 2B is provided with an inlet 9 for a fluid coupling medium and an outlet 10, fitted with a non-return valve, for purged air and excess fluid coupling medium, the inlet 9 being connected as shown to a reservoir 11 for the fluid coupling medium which, in this example, is water. An air-ejector vacuum pump 1 2 is connected as shown to the top of reservoir 11 for selectively applying either suction or pressure thereto in a manner which will be described.The inlet 9 is connected by a duct 1 3 through outer holder part 2B to a frusto-conical space 14 between the inner and outer holder parts 2A and 2B, this space 14 in turn being connected by a duct 1 5 through outer holder part 2B and annular magnet 7 to a space 16 between the front end of ultrascnic probe 1 and the surface of the test-piece, so that pressure or suction, as the case may be, produced by means of pump 12 is communicated to the space 16.

Describing the pump 1 2 in more detail, it is (preferably) a vacuum pump known as a ''PIAB" Vacuum pump type M32, which works on the principle of a high velocity jet of air entraining air with it. More particularly, an injector nozzle 1 2A is supplied with air under high pressure at its inlet 1 2B and squirts the air at high velocity into an outlet 12C from a chamber 1 2D which is connected as shown to a space above the liquid in the reservoir 11, which is a sealed reservoir to the extent that the only outlets are the connection to the chamber 1 2D and the connection to the inlet 9.The outlet 12C from chamber 1 2D is shown connected to a valve 1 2E which can be selectively opened or closed. When valve 1 2E is opened, the jet of air from ejector nozzle 1 2A entrains air with it from chamber 1 2D and produces suction in the space above the liquid in reservoir 11. When valve 1 2E is selectively closed, so that the air from nozzle 1 2A cannot escape through outlet 12C, pressure is built up in reservoir 11.

In use, the ultrasonic probe assembly, consisting of ultrasonic probe 1, holder 2, 0-ring 3, diaphragm 4, caps 5 and 6, magnet 7, sealing ring 8, inlet 9 and outlet 10, is placed as shown against the surface of the test-piece.

The valve 1 2E is then closed, and pump 1 2 is started, so as to build up pressure in the reservoir 11, pumping water as the fluid cou pling medium into inlet 9 and through ducts 13 and 1 5 into spaces 14 and 1 6 respectively, until all air is purged through outlet 10 from the ducts 1 3 and 1 5 and spaces 14 and 16, and water starts to issue from the outlet 10, which is a sign that air has been purged.

Then, valve 1 2E is opened, so that the pump 1 2 commences to apply suction to the space above the water in reservoir 11. Because of the non-return valve in the outlet 10, suction comes to be applied to the space 1 6, drawing the probe 1 and, with it, the inner holder part 2A. towards the surface of the test-piece, with flexure of the diaphragm 4. In this situation, the diaphragm 4, seal 8 and non-return valve in outlet 10 substantially prevent any ingress of air.If any air does enter the space 16, it tends to flow around the ultrasonic probe 1 rather than across the front face of the probe 1, because it is easier for the air to flow around the probe 1 than across its face, so that any interstitial gaps between the front face of probe 1 and the surface of the testpiece are filled with fluid coupling medium, that is, water, hence achieving a good ultrasonic coupling between the probe 1 and the test-piece. The suction is maintained throughout the test period. When testing is completed, the pump 1 2 may be switched off or alternatively the valve 1 2E closed to create pressure once again since, being water, it does not matter unduly if the fluid coupling medium goes to waste. It will be appreciated that the apparatus achieves self-cleaning of the front face of the ultrasonic probe 1. Furthermore, because the space 1 6 between the front face cf probe 1 and the surface of the test-piece is completely filled with fluid coupling medium, that is, water, it does not matter if the surface of the test-piece is very rough, as would be the cast surface of, for example, an internal combustion engine block.

Possible modifications include the substitution of oil for water as a fluid coupling medium (although water is preferred) and making the entire holder 2 as a rubber moulding, the front rim of which is impregnated with magnetic material.

In addition to use for determining top-deadcentre of an engine as mentioned abcve, the apparatus could be used for example for ultrasonic crack or flaw detection or even for contact thermometry, in which case the ultrasonic probe 1 would be replaced by a temperature probe (not shown).

Claims

1. Test-piece testing apparatus comprising: a testing probe adapted to be coupled to a surface of a test-piece for testing of the testpiece; a holder for holding the probe so as to permit limited relative movement between the probe and the holder; resilient sealing means for engaging the surface of the test-piece and providing a seal between the holder and the surface of the test-piece; means for, in use, flooding a space between the probe and the surface of the test-piece with a fluid coupling medium; and means for, in use, applying suction to the flooded space so as to draw the probe towards the surface of the test-piece with fluid coupling medium therebetween.

2. Test-piece testing apparatus as claimed in claim 1 wherein an annular magnet loosely surrounds a front end portion of, and magnetically locates, the probe.

3. Test-piece testing apparatus as claimed in claim 2 wherein the resilient sealing means is an annular seal mounted to the magnet.

4. Test-piece testing apparatus as claimed in claim 1, 2 or 3 wherein the holder comprises an inner holder part and an outer holder part interconnected by a resilient diaphragm which permits limited relative movement therebetween while sealing a gap therebetween.

5. Test-piece testing apparatus as claimed in claim 4 wherein the probe is mounted in the inner holder part and a seal is provided between the inner holder part and the probe.

6. Test-piece testing apparatus as claimed in claim 4 or 5 read as appended to claim 2 or 3 wherein the annular magnet is mounted to the outer holder part.

7. Test-piece testing apparatus as claimed in any preceding claim wherein the holder is provided with an inlet for the fluid coupling medium and is provided with an outlet including a non-return valve for purged air and excess fluid coupling medium.

8. Test-piece testing apparatus as claimed in any preceding claim wherein the flooding means and suction-applying means comprise a compressed air ejector vacuum pump which can be made to produce selectively either suction or pump.

9. Test-piece testing apparatus as claimed in any preceding claim wherein the testing probe is an ultrasonic probe.

10 Test-piece testing apparatus as claimed in any one of claims 1 to 8 wherein the testing probe is a temperature probe.