GB2196437A

GB2196437A - Adhesion tester

Info

Publication number: GB2196437A
Application number: GB08624908A
Authority: GB
Inventors: Roy Brown
Original assignee: Graphoidal Developments Ltd
Current assignee: Graphoidal Developments Ltd
Priority date: 1986-10-17
Filing date: 1986-10-17
Publication date: 1988-04-27
Anticipated expiration: 2006-10-17
Also published as: GB8624908D0; GB2196437B

Abstract

A coating adhesion tester utilises a dolly (10) glued to a coating. The tester couples to the dolly and forces a plunger (14) through a central aperture 16 therein against the substrate. The tester has a hydraulic cylinder (30) coupled to the dolly by a coupling (40) which enables attachment without relative rotation e.g. by connecting the cylinder via a swivel to a connecting piece screwed on the dolly, by a bayonet connector or as shown, by connector 40 having balls 46 urged by a spring biased releasable sleeve 48 into snug locking engagement with a groove 22 in the dolly 10. The piston (28) is attached to the plunger. The cylinder (30) is pressurised via hose 64 from a permanently attached reservoir (Fig. 1a), giving a closed hydraulic system which can be transported while filled with oil. The reservoir is pressurised by a piston driven by a manual screw. <IMAGE>

Description

SPECIFICATION Adhesion tester This invention relates to apparatus for testing the adhesion of coatings. Known testing methods include methods in which a dolly is adhered to the coated surface, after which force is applied to pull the dolly off the coating. The force which does this is measured, or a predetermined force is applied which will give a non-destructive test of a satisfactory coating.

It has been found advantageous for this purpose to use an apparatus which applies force to the substrate relative to the coating by means of a probe or plunger extending through an aperture in the dolly. An example of such apparatus is disclosed in GB-A2166875 and GB-A-2166876. This apparatus requires the cylinder to be screwed onto the dolly.

The present invention is concerned with apparatus which, like the known apparatus just mentioned, comprises a hydraulic cylinder and piston with means for attaching either the cylinder or the piston to a dolly in a manner enabling pressurisation of the cylinder to apply thrust force to a plunger extending through the dolly, with an opposite tractive force on the dolly; means for pressurising the cylinder with a hydraulic liquid and gauge means for indicating hydraulic liquid pressure. Such apparatus will be referred to as apparatus of the kind defined.

According to one aspect of the present invention apparatus of the kind defined is characterised in that the cylinder and piston and means for pressurising the cylinder are parts of a closed hydraulic system devoid of apertures permitting egress of hydraulic liquid.

It is convenient if the cylinder is attached to the dolly and the piston applies thrust force to the plunger. However, it is possible to employ the reverse arrangement in which the cylinder applies force to the plunger while the piston is attached to the dolly.

Preferably the plunger is permanently attached to, or integral with the piston.

Means for pressurising the cylinder may be a fluid reservoir connected to the cylinder, with manually operable means to force a plunger into the reservoir to pressurise the reservoir. The reservoir may be connected to the cylinder by means of a flexible hose, with this connection left intact during normal use, tran sport and storage.

According to another aspect of the invention apparatus of the kind defined is character ised in that the means for attachment to the dolly enable such attachment without more than 360" of rotation of the cylinder relative to the dolly, preferably without more than 1800 or 90" of relative rotation.

This can be implemented in various ways.

One possibility is for the cylinder to be attached through a swivel to a connecting piece which is screwed on to the dolly. Because the connecting piece is freely rotatable relative to the cylinder, the cylinder can be held still while the connecting piece is screwed onto the dolly.

Another possibility would be for the cylinder and dolly to be connectable by means of a bayonet connection, requiring only limited relative rotation of them.

In a preferred arrangement the cylinder is provided with a connector which has radially movable parts, the dolly has recessed region(s) to be engaged by the parts when in a radially inward position, and releasable locking means are provided to hold the movable parts in a radially inward position.

The recessed region of the dolly may be a circumferential groove therein. The connector may have radially movable balls and a ring axially movable to and from a position encircling the balls and locking them in their radially inward position.

An embodiment of the invention will now be described with reference to the accompanying drawings in which: Figs. 1a and 1b are views of two parts of an adhesion tester, mostly in section, and Fig. 2 is an enlarged side elevation of a dolly, with part of a connector of the adhesion tester shown in diagrammatic section.

The testing apparatus shown in Figs. 1a and ib is used by coupling it to a dolly 10 (Fig. 2) after the dolly's end face 12 has been glued to a substrate. When coupled, a plunger 14 of the testing apparatus extends through the central aperture 16 of the dolly 10. The testing apparatus is then used to apply thrust to the plunger 14 and hence the coating substrate while applying opposite (i.e. tractive) force to the dolly and attached coating.

The dolly 10 is turned from a suitable metal, e.g. stainless steel. As shown in Fig. 2 it has a head 20 with the end face 12, a groove 22 bonded by bevelled faces 24 at 45" to the dolly axis, and a cylindrical portion 26.

As shown by Fig. 1a the plunger 14 is integral with a piston 28 in a hydraulic cylinder 30. This is closed at one end by a cap 32 which is screwed into the end of the cylinder 30. Spanner flats 34 are provided on the cylinder 30.

The piston 28 has a sealing ring 38 fitted onto a groove in the piston. The plunger 14 extends with clearance through the centre of the cap 32.

A connector 40 is screwed into the cap 32 and enables releasable attachment of the test ing apparatus of Figs. 1a and 1b to the dolly 10. This connector is tubular with a clear central aperture through which the plunger 14 projects and which receives part of the dolly 10.

The construction of the connector 40 and the manner of its operation is shown diagram matically in Fig. 2. The main body of the con nector is a tube 42 with an externally threaded reduced diameter end portion 44 which screws into cap 32. The tube 42 has apertures at its opposite end. These apertures are distributed circumferentially around the tube 42 and each accommodates a ball 46, somewhat like ball bearings in a cage. The balls 46 can move radially in their apertures but their position is controlled by a sleeve 48 encircling the tube 42.

The sleeve 48 is spring loaded towards the position shown in Fig. 2 and may be blocked at this position by a circlip 50. In this position of the sleeve it holds the balls at their radially inward positions, at which they will fit snugly in the groove 22. If the sleeve 48 is pushed in the direction of the arrow A until it clears the balls 46, the balls are free to move radi ally outwardly, so far as permitted by the 'apertures in which they are trapped. This is sufficient radial outward movement for the balls 46 to be able to clear ridge 52 of the dolly.

Thus, the dolly can be coupled to the appa ratus of Figs. 1a and 1b by pushing the sleeve 48 in the direction of arrow A to free the balls 46, sliding the connector 40 over the dolly to the position shown in Fig. 2, and then releasing the sleeve so that it pushes the balls 46 into the groove 22. This couples the dolly to the tube 42 sufficiently strongly to permit considerable tractive force to be applied to the dolly, yet the coupling can be accom plished without requiring any relative rotation, nor any preliminary orientation to any relative rotational position.

The connector 40 is a proprietary item avail able as a hydraulic hose connector. It is avail able from Hansen Coupling Division of Tuthill Corporation, 4050 W. 150th Street, Cleve land, Ohio, USA 44135.

The portion 60 of the cylinder 30 contains hydraulic fluid delivered from a reservoir 62 shown in Fig. 1 b through a short hydraulic hose 64. The reservoir 62 is cylindrical, with spanner flats 66. It is connected to the hose 64 by a duct 68 which is intersected by a through bore; In this bore there is a rotatable plug 70 retained by a circlip 72 and sealed by O-rings 74. A circumferential groove 76 in the plug permits flow past it, while bore 78 leads to an oil pressure gauge 80 screwed into the plug 70.

The other end of the reservoir 62 is closed by a cap 82. This has a central aperture with a fine screw thread engaged by a correspon dingly threaded rod 84 whose outer end car ries a hand wheel or preferably a crossbar 86.

The inner end portion 88 of rod 84 is freely rotatable in an aperture in a piston 90. A sealing ring 92 is fitted into a groove on the piston.

As the rod 84 is screwed in through the cap 82, it bears on a domed end of a hard metal insert 94 which transfers the thrust to the (non-rotating) piston 90. This then pressurises the hydraulic fluid and hence applies force to the piston 28 and plunger 14.

In normal use and storage of the apparatus of Figs. 1a and 1b there is no need to disturb the screwed-in caps 32, 82 nor the end portion 44 screwed into cap 32 nor connections to the hose 64. All these connections are more or less permanent. Sealants and/or tapered threads may be used to keep them tight. The spaces containing hydraulic fluid constitute a closed system with no apertures such as vents through which fluid can run out.

Use of the apparatus is accordingly convenient. The dolly is first glued to a coating to be tested. The apparatus of Figs. 1a and 1b then coupled to it, as described, without rotation. The flexible hose 64 facilitates use in almost any position and the plug 70 allows the gauge 80 to be turned to a position where the operator can use it.

Turning the rod 84 pressurises the hydraulic fluid to apply force to the coating under test, and the fluid pressure is observed on the gauge 80. The fine thread on rod 84 facilitates close control of the pressure applied.

After the test has been performed, the rod 84 is unscrewed somewhat. Return of plunger 14 and piston 28 pushes fluid back to the reservoir 62, pushing back its piston 90.

The methods of testing the coating can be the destructive or non-destructive tests described in GB-A-2166875 and 6, but these are accomplished with a hydraulic system which remains closed throughout.

A spring 96 may be provided between the piston 28 and cap 32, for returning the piston. Fluid pressure will be needed to compress the spring during a test, but the amount may be too small to give a serious error.

Moreover, the positioning of a doily in the connector 44 is repeatable. Hence the compression of this spring before the coating is stressed should also be repeatable, (so that the necessary pressure can be subtracted from the value observed on the gauge, if desired).

While the dolly is glued to a coating its central aperture must be kept clear. To do this the aperture is blocked with a close fitting peg of polytetrafluoroethylene (ptfe) until the adhesive is no longer fluid.

Claims

1. Coating testing apparatus comprising a hydraulic cylinder and piston with means for attaching either the cylinder or the piston to a dolly in a manner enabling pressurisation of the cylinder to apply thrust force to a plunger extending through the dolly, with an opposite tractive force in the dolly; means for pressurising the cylinder with a hydraulic liquid and guage means for indicating hydraulic liquid pressure, characterised in that the means for the attachment to the dolly enable such attachment without more than 360" of rotation of the cylinder relative to the dolly.

2. A coating testing apparatus according to claim 1 wherein the means for attachment to the dolly enable such attachment without more than 1800 or 90" of relative rotation.

3. A coating testing apparatus according to claim 1 or claim 2 wherein the cylinder is attached through a swivel to a connecting piece screwed onto the dolly, and the connecting piece is freely rotatable relative to the cylinder so that the cylinder can be held still while the connecting piece is screwed onto the dolly.

4. A coating testing apparatus according to claim 1 or claim 2 wherein the cylinder and dolly are connected by means of a bayonet connection, which requires only limited relative rotation of the cylinder and dolly.

5. A coating testing apparatus according to claim 1 or claim 2 wherein the cylinder is provided with a connector which has radiallly movable parts, the dolly has recessed region(s) to be engaged by the parts when in a radially inward position, and releasable locking means are provided to hold the movable parts in a radially inward position.

6. A coating testing apparatus according to claim 5 wherein the recessed region of the dolly is a circumferential groove.

7. A coating testing apparatus according to claim 5 wherein the connector has radially movable balls and a ring axially movable to and from a position encircling the balls and locking them in their radially inward position.

8. Coating apparatus comprising a hydraulic cylinder and piston with means for attaching either the cylinder or the piston to a dolly in a manner enabling pressurisation of the cylinder to apply thrust force'to a plunger extending through the dolly with an opposite tractive force on the dolly; means for pressurising the cylinder with a hydraulic liquid and gauge means for indicating hydraulic liquid pressure, characterised in that the cylinder and piston and means for pressurising the cylinder are parts of closed hydraulic system devoid of apertures permitting egress of hydraulic liquid.

9. A coating testing apparatus according to claim 8 wherein the cylinder is attached to the dolly and the piston applies thrust force to the plunger.

10. A coating testing apparatus according to claim 8 wherein the piston is attached to the dolly and the cylinder applies force to the plunger.

11. A coating testing apparatus according to claim 8, 9 or 10 wherein the plunger is permanently attached to, or integral with the piston.

12. A coating testing apparatus according to claim 8, 9, 10 or 11 wherein the means for pressurising the cylinder is a fluid reservoir connected to the cylinder, with manually operable means to force a plunger into the reservoir to pressurise the reservoir.

13. A coating testing apparatus according to claim 12 wherein the reservoir is connected to the cylinder by means of a flexible hose, enabling this connection to be left intact during normal use, transport and storage.

14. A coating testing apparatus substantially as described herein and with reference to and as illustrated in the accompanying drawings.