GB2187560A - Apparatus for measuring surface friction - Google Patents

Abstract

Apparatus for measuring the frictional forces arising at the surface of a container comprises a mandrel 4 to support the container 6 for rotation against a weighted shoe 7. The drag forces F on the shoe which is carried by a rod 8 are transmitted by a lever 11 which acts on a transducer 15 for measurement and display or recorded on a chart. The apparatus enables the variations in drag force around the can to be plotted so that the frictional properties of various colour coatings can be compared. <IMAGE>

Description

SPECIFICATION Apparatus for measuring surface friction This invention relates to apparatus for measuring the frictional forces arising at a surface and more particularly but not exclusively to the measurement of frictional forces arising on a decorated exterior surface of a container such as a printed can body.

In the can making and packaging industry decorated cans are transported along conveyors which are provided with side guide rails in order to support the cans. The rails are covered with a polymeric section in order to abate the noise and reduce risk of scratching of the cans. During transport the cans sometimes rub along the side guides and so transport speed may be reduced by frictional engagement of the cans and side guides. Cans are also collated on collating tables from which a belt array of parallel belts take the cans between converging guide rails to transport the cans in single file to machinery.

Cans may fail to progress evenly between the converging side rails if frictional engagement of can to can or can to side rail retards the progress of the cans. The delay can manifest itdself as total stoppage of jammed cans.

Some of the decorations on cans are more slippery than others so in the past the relative slipperiness of decorative finishes on cans has been assessed by rolling two cans, having identical surface decoration thereon, against one another and measuring the force for rotation. Whilst this test gives a direct observation of the can to can friction, it is unable to analyse which colour or lacquer components of the decoration are giving rise to unacceptable friction.

An apparatus sold by ALTEK Company of Torrington, USA is sometimes used to measure the surface friction. In the Altek apparatus a loaded slider, supported on three feet is dragged along the length of the can body.

However, this apparatus only permits observation of the friction arising simultaneously at the three feet while the direction of the measurement is along the can cylindrical surface.

These mean values of friction were not in the hoop or rolling direction of the cylindrical can surface that on the conveyors, actually experiences the frictional forces.

Accordingly this invention provides apparatus for measuring the frictional forces arising at the surface of a container, said apparatus comprising means to rotate the container; a contact shoe supported for contact with the rotating surface of the container, a load to push the contact shoe onto the rotating surface; and a linkage operably connected to the shoe and indicating means to indicate the tangential drag on the shoe.

The means to rotate the container may be a rubber covered mandrel enterable into the container.

The load may be a weight resting on the contact shoe or alternatively the shoe may be supported on a rod and the weight applied to the rod at a distance from the shoe to achieve some leverage if desired.

The linkage may be in the form of a rod which supports the contact shoe at one end.

The means to indicate drag may include a spring anchored at one end and attached to the rod supporting the contact shoe, a pointer.

attached to the rod and calibrated scale or ruler against which extension of the spring is observed.

The substantially tangential strain on the shoe may be amplified by a lever. In a preferred embodiment the tangential friction force delivered by the rod is amplified by a lever operably connected to a transducer which converts the frictional force into an electrical signal.

The electrical signal, which is proportional to frictional force may be read off as a load in kilogtrams relatable to the contact load W sopermitting calculation of the coefficient of friction by the well known formula F=,uW.

The apparatus may include a disc having a' plurality of apertures arranged around it, means to rotate the disc at the same time as the can is rotated, and sensing means to relate each aperture to a corresponding point on the decoration around the container so that the frictional force arising at known points on the can decoration may be plotted graphically on a printing recorder.

The number of apertures is counted to provide the triggering signal for integration of force gauge output and termination of measurement cycle when the (printed) container has made one complete revolution.

One embodiment of the apparatus will now be described by way of example and with reference to the accompanying drawings in which: Figure 1 is a diagramatic end view of the apparatus; Figure 2 is a side view of the apparatus; Figure 3 is a graph of drag force against distance around a can; and Figure 4(a), (b) and (c) show the profile of alternative contact shoes.

In Fig. 1 the apparatus has a base plate 1 supported on three feet 2 which permit levelling which is assessed by means of a spirit level 3. A mandrel 4 is supported for rotation by a gearbox 25. A cylindrical can body 6 is supported by the mandrel which has a high friction surface so that as the mandrel rotates the can body is driven. to rotate A contact shoe 7 rests on the exterior surface of the can body. The contact shoe is supported at one end of a rod 8 which supports a weight 9 so that a load W is imposed on the shoe and hence the can surface.

The other end of rod 8 is attached at a hinge joint 10 to a lever linkage 11 supported by a pivot 12 fixed to an upright 13. The lever 11 is "L" shaped so that linear motion at the hinge joint 10 (arising from frictional drag) causes motion at the other extremity 14 of lever 11 in a perpendicular direction. If desired the lever 11 may be of a shape to amplify the drag force but in Fig. 1 the lever ratio is substantially 1:1. The extremity 14 of lever 11 bears on a force transducer 15 which converts the drag forces into an electrical sig nal proportional to the drag force.

The transducer is coupled electrically to read out displays to permit reading off the drag load F in various units such as Ibs (a) Kg (b) or Newtons (c) and in chosen forms such as the damped or full signal condition selected by switch S as shown in Fig. 2. A further switch "z" is used to set the zero reading of the transducer. A suitable transducer and displays is available from SALTER ABBEY WEIGHING MACHINES LTD. A lifting cam 18 is supported for rotation on a bracket 19 attached to the upright 13. Rotation of the cam 18 by means of a knob 20 (shown in Fig. 1) lifts the rod 8 to remove the shoe 7 from the surface of the can 6. The can may then be removed from the mandrel 4.

Whilst the transducer can be arranged to display the instant reading of peak drag force the signal may be further analysed by connecting directly to a chart recorder or alternatively to processing apparatus 22 to display an instant reading or alternatively a mean or maximum reading of force. By rotation of knob 16 to drive a screw 17 against the lever 10 the transducer can be loaded for calibration with a chart recorder 23 or further processing apparatus 22.

In Fig. 2 the apparatus 22 is electrically connected to the transducer 15. The readings displayed on apparatus 22 may, if desired be plotted automatically on a chart recorder 23 connected to the apparatus 22. One such automatic recording is shown in Fig. 3 which will be discussed later by way of example.

In Fig. 2 the means to rotate the mandrel 4 include a motor 24, a gearbox 25 and a shaft 26 on which the mandrel 4 is a sleeve fit.

Rotation of screw 27 releases the mandrel from shaft 26 to permit movement of the can across the face of the shoe 7 to test other areas.

A further shaft 28 extends from gearbox 25 to support a disc 29. The disc 29 has a plurality of holes arranged on a pitch circle such that they enter a sensor unit 30 in which a light beam is directed through the holes into a photocell so that the angular orientation of the can may be related to the drag forces arising.

The sensor unit 30 is operably connected to the apparatus 22 so that the can orientation and drag forces may be plotted automatically on chart recorder 23.

The number of holes in disc 29 is counted to provide the triggering signal for integration of fore gauge output and termination of measurement cycle when the decorated container has made one complete revolution.

The rorational speed of the mandrel is controlled by adjusting the motor speed at the control knob 31.

In Fig. 3 the drag force F is plotted around the cylindrical surface of a can decorated with a base coating (HOLDEN A6293/1) over which was applied a band of red coating (MARS DENS P505252). The chart clearly shows that the drag force on the red coating is much less than the drag force on the white base coating so that the base coating is more likely to give rise to frictional interference to can transport.

(This is a result of over-curing in ovens.) Fig. 4(a) shows that the shoe 7 may be a block of metal of square cross section. Such a square cross section makes a line of contact with the cylindrical surface of a can. Whilst the shoe may be made of brass or stainless steel or other common metal, plastics materials such as nylon or polypropylene may be used. The width "d" of the shoe is typically 12 mm and the load W imposed on it is 500 gm. at the line of contact with the can surface.

Fig. 4(b) shows an alternative shoe profile which is round so that it makes a point of contact in the surface of a cylindrical can.

Fig. 4(c) shows how an experimental material, such as a polymeric material such as is fitted to a guide rail, may be mounted on the shoe 7 in order to measure the actual drag forces that willarise in use when cans travel alon a guide rail faced with the material under test.

The apparatus described permits measurement of the drag forces arising on a container surface be it coated or not. However, it is particularly useful for analysing the drag arising on printed decorations which include several ink materials.

Claims (10)

1. Apparatus for measuring the frictional forces arising at the surface of a container, said apparatus comprising means to rotate the container; a contact shoe supported for contact with the rotating surface of the container, a load to push the contact shoe onto the rotating surface; and a linkage operably connected to the shoe and to indicating.means to indicate the tangential drag on the shoe.

2. Apparatus according to claim 1 wherein the means to rotate the container is a rotatable mandrel.

3. Apparatus according to claim 1 or claim 2 wherein the load on the shoe is a weight.

4. Apparatus according to claim3 wherein the shoe is supported on a rod and the weight is applied to the rod at a distance from the shoe.

5. Apparatus according to any preceding claim wherein the linkage is a rod supporting the shoe at one end.

6. Apparatus according to claim 5 wherein the other end of the rod is attached to an anchored spring so that a pointer on the rod indicates drag force against a scale or ruler.

7. Apparatus according to any of claims 1 to 5 wherein the shoe is coupled to a transducer which converts the force into an electrical signal.

8. Apparatus according to claim 7 wherein in the tangential friction force delivered by the rod is amplified by a lever operably connected to a transducer which converts the frictional force into an electrical signal.

9. Apparatus according to claim 7 or claim 8, wherein a disc has a plurality of apertures arranged around it and means to rotate the disc at the same time as the can is rotated, and sensing means to relate each aperture to a corresponding point on the decoration around the container so that the frictional force arising at known points on the can decoration may be plotted graphically on a printing recorder.

10. Apparatus substantially as hereinbefore described with reference to the accompanying drawings.