Field of the Invention

The present invention relates to test apparatus and methods, and in particular to test apparatus and methods for testing the deformation of plastics elements subjected to infra-red radiation.

Background to the Invention

To date, the sun has singly supplied more energy to the planet Earth than all terrestrial energy sources combined. Capable of regularly heating Earth to over 40 degrees Celsius, the sun has provided the energy to maintain life on this planet. Sometimes the radiation from the sun can also have adverse effects.

Throughout industry, extruded and injection moulded polymer profiles are used to improve the aesthetic appearance of many products. In most cases, these profiles do not suffer any undesirable deformation throughout their life. However, in the case of laminated thin-walled, open profiles, solar radiation is known to occasionally cause significant distortion.

In the conservatory industry, numerous coloured and wood- grain effect, lamination foils are available to improve the aesthetic appearance of the completed conservatories. These foils are 0.2 mm thick and are usually made from plasticised poly vinyl chloride (PVC) . Top cap profiles have been known to undergo deformation during normal service. These profiles usually have larger ratios of leg length to leg thickness than other profiles and are also more exposed to the effects of the sun. Previous research into this phenomenon has not yielded any definite results. However, it was found that dark coloured lamination foils, particularly mahogany wood-grain effect, failed much more often than the lighter colours . There are no reports of buckling of unlaminated white extrusions during normal service.

Wood-grain foiled aluminium top caps are used in place of foiled PVC extrusions throughout the industry, as they do not undergo any adverse deformation during their lifetime. The finished product price is 20% higher than the PVC counterpart, but is merely dealing with the symptoms and not the root problem.

It appears that heat gain from solar radiation is a possible cause of the deformation.

To develop a deeper understanding of the causes and effect of solar radiation on these laminated profiles, it is desirable to provide an effective test method and create a suitable test apparatus, where the environmental variations can be controlled and monitored.

The first, and most important effect to assess, is that of solar radiation on the profile and the form and extent of any deformation which occurs. This deformation, it is believed, relates directly to the materials used, the geometric shape of the profile, and the absorptivity of the external surface and the fitting method of laminated products. By applying similar heating and cooling cycles to that experienced in everyday use, any distortion occurring would be comparable to that in normal service.

The second area of consideration is the shrinkage of the lamination foil when attached to the base material. Currently reversion and shrinkage of polymer composites are tested to UK standards, but there are no established test methods for the shrinkage of lamination foils, or shrinkage of laminated profiles as a single entity. The only test relating to the shrinkage of a foil known to the present inventor was written specifically for heat shrinkable polyethylene for use as a packaging material. This negates the accuracy of both individual tests, as neither is a genuine representation of the normal operating environment for these laminated profiles. The lamination foil is not likely to undergo the same shrinkage while attached to the base material, and the heat transferred into the base material will be altered due to the lamination foil. By developing a suitable apparatus and method it is hoped that these could be used through many industries to accurately establish the suitability of a laminated product for use in a particular environmental.

It is an aim of preferred embodiments of the present invention to obviate or overcome a disadvantage of the prior art, whether such disadvantage or prior art is referred to herein or otherwise.

Summary of the Invention

According to the present invention in a first aspect, there is provided a test apparatus for testing the deformation of a plastics element in response to infra-red radiation, the apparatus comprising a mount to locate the plastics element, an infra-red emitter capable of directing infra-red radiation at the plastics element, which infra-red emitter emits a wavelength in the range of from 0.7 to 1.5 micrometers and provides at least 500 W/m2 at the plastics element mount.

This enables the heating effect of the sun to be replicated in a test environment.

Suitably, the apparatus comprises temperature sensors and the apparatus is configured to heat a test piece to a desired temperature or range of temperatures. Suitably, the apparatus is configured whereby a temperature controller receives a temperature signal from a temperature sensor and alters the output of the infra-red emitter to maintain a predetermined temperature or temperature range at the plastics element.

Suitably, the apparatus provides from 500 W/m2 to 2000 W/m2 at the plastics element mount. Suitably, the apparatus provides from 500 W/m2 to 3000 W/m2 at the plastics element mount.

Suitably, the plastics element comprises a laminated foil on at least one surface thereof.

Suitably, the plastics element comprises a plastics profile. Suitably, the plastics profile is a conservatory profile element. Suitably, the apparatus comprises a deformation detector. Suitably, the deformation detector comprises a beam emitter aligned with a detector and means for obstructing the beam upon deformation of the test piece. Suitably, the beam emitter comprises a laser.

Suitably, there is provided a plurality of infra-red emitters. Suitably, at least two of the infra-red emitters are independently controllable.

According to the present invention in a second aspect, there is provided a method of testing the deformation of a plastics element in response to infra-red radiation, the method comprising the steps of locating the plastics element in a test apparatus, directing infra-red radiation at the plastics element whereby the infra-red radiation has a wavelength in the range of from 0.7 micrometers to 1.5 micrometers and power of at least 500 W/m2 at the plastics element.

Suitably, the test piece is heated to a desired temperature or range of temperatures as determined by a temperature sensor. Suitably, a temperature controller receives a temperature signal from a temperature sensor and alters the output of the infra-red emitter to maintain a predetermined temperature or temperature range at the plastics element.

Suitably, there is provided from 500 W/m2 to 2000 W/m2 at the plastics element mount. Suitably, there is provided from 500 W/m2 to 3000 W/m2 at the plastics element mount. Suitably, the plastics element comprises a laminated foil on at least one surface thereof.

Suitably, the plastics element comprises a plastics profile. Suitably, the plastics profile is a conservatory profile element .

Suitably, there is provided a deformation detector. Suitably, the deformation detector comprises a beam emitter aligned with a detector and means for obstructing the beam upon deformation of the test piece. Suitably, the beam emitter comprises a laser.

Suitably, there is provided a plurality of infra-red emitters. Suitably, at least two of the infra-red emitters are independently controllable. Suitably, the output of the infra-red emitters is varied to replicate the movement of the sun.

Brief Description of the Drawings

The present invention will now be described, by way of example only, with reference to the drawings that follow; in which:

Figure 1 is an isometric view of a test apparatus according to the present invention.

Figure 2 is an isometric view corresponding to Figure 1, but enlarged and with some parts removed for clarity.

Figure 3 is a functional flow diagram illustrating a method according to the present invention. Description of the Preferred Embodiments

Referring to Figures 1 and 2 of the drawings that follow, there is shown a test apparatus 2 comprising a frame 4, infra-red emitters 6a, 6b, 6c, a mount consisting of a mounting block 8, mounting block adjuster 10, and end- plates 12, 14. The test apparatus 2 further comprises a laser emitter 16, a laser detector 18, a power source 20 and a control device 22.

Frame 4 is made from extruded aluminium profile. This allowed for a simple, accurate and robust assembly. Frame 4 comprises two generally square ends 24, 26 joined together at their lower corners by longitudinal frame pieces 28, 30.

Three infra-red emitters 6a, 6b, 6c, acting as heating elements, are mounted on the frame 4 and are provided in a isosceles triangular array with first emitter 6a to one side of mounting block 8, second emitter 6b above mounting block 8 and third emitter 6c to the other side of mounting block 8. Each emitter 6a, 6b, 6c is independently controllable from control device 22 and is powered by power source 20. Each emitter 6a, 6b, 6c is a medium wave, twin-tube, carbon filament element that emits infra¬ red radiation in the wavelength range 0.7 to 1.5 micrometers and is operable at power levels of 100 to 1500 Watts. Gold reflectors are used to help direct the radiation from the infra-red emitters. For clarity, the mounting arrangements for the emitters 6 are omitted.

Mounting block 8 is mounted on frame 4 to support a test piece. Mounting block 8 is provided with a mounting block adjuster 10 comprising a linear slide. This allows the mounting block 8 (and hence the test piece) to be moved perpendicular to the longitudinal axis of the apparatus 2 (parallel to the line of the emitters 6) within a tolerance of 0.1 mm. To ease positioning of the linear slides, a small ball screw is provided. This system utilizes fixed connections on both the frame and the mounting section linked through a threaded screw, with an integral hand wheel. This allows the operator to precisely position the linear slides as each complete revolution of the ball screw moves the mounting section only two millimetres .

Each end-plate 12, 14 has a 10mm by 25mm hole 32 (other hole not visible) therethrough in the form of a slot to allow for horizontal adjustment of the test piece. The ■ end-plates 12, 14 are mounted on the test piece so that the holes 32 are substantially aligned along the longitudinal axis of the test apparatus. The laser emitter 16 and detector 18 are aligned on a level with the holes 32 but are mounted on plinths (not shown) at either end of the apparatus. A laser beam emitted from laser emitter 16 can pass through holes 32 and be received by detector 18 when the holes are aligned with the laser beam. When positioned within 2 mm of the test piece, any deformation of the sample causes movement of one or both of the end plates 12, 14 which interrupts the laser beam.

In the power supply 20 solid-state relays are used to reduce the switching times. Combining the fast switching operation with the slow responding heating elements lead to a system which can maintain a reasonably constant heating element temperature. This leads to an almost constant level of radiation being applied to the test piece.

The controller 22 uses three temperature controllers, one for each infra-red emitter 6a, 6b, 6c, as this allows for differing levels of radiation on each face. By varying the intensity on each face, it is possible to simulate the motion of the sun and apply cyclic heating over the different faces of the profile. For instance, first infra-red emitter 6a could be at 100% for 2 hours, then switched to 50% and second emitter 6b switched on to 50%. Two hours later first emitter 6a is switched off and second emitter 6b is powered at 100% for two hours. Then second emitter 6b is switched to 50% output as third emitter 6c is energized to 50% output also for two hours. Finally, second emitter 6b is switched off and third emitter 6c is powered to 100% for two hours. The time periods and power outputs can be varied to provide the desired heat cycle.

The controller 22 includes a "failure" light 44, a light emitting diode (LED) responsive to the laser beam no longer being detected by detector 18.

Surface mounted thermocouples 42, 44, set to the temperature required on the external surface are used to provide feedback to temperature controllers in controller 22. A non-contact laser thermometer (not shown) is used to record accurate values of surface temperatures.

In Figures 1 and 2 there is shown a plastics element test piece 40 comprising a foil laminated plastics profile element, in particular a conservatory top cap profile is shown on the mounting block 8. The test piece 40 carries a glazing material 42.

With reference to Figure 3 of the drawings that follow, a test method according to an embodiment of the present invention will now be described.

In step 100, assemble the test piece 40 to be tested, as it would be assembled in normal use. In the case of a conservatory element, the glazing material used should be at least 50 millimetres shorter than the test piece to remove any effects caused by the expansion of the glazing material.

In step 102, position the test piece 40 on the mounting block 8.

In step 104 slide the end plates 12, 14 tight to the ends of the test piece 40 and fix in place.

Using the ball screw thumbwheel, in step 106 the test piece 40 is brought forward until the laser beam is broken, identified by the "Failure" light 44 on the controller 22 extinguishing.

Using the ball screw thumbwheel, in step 108 test piece 40 is moved backwards, approximately one quarter turn after the LED 44 illuminates.

In step 110, energise the infra-red emitters 6, using a start button (not shown) on the controller 22. The emitters 6 provide at least 500 W/m2 at the surface of the plastics element in receipt of the infra-red radiation. Up to 3000 W/m2 and preferably up to 2000 W/m2 can be provided at the plasties element mount 8 (and hence to the plasties element 40 also) . This range, it is believed, enables the effects of the sun to be properly replicated.

After the test piece 40 has deformed or the required period of time has elapsed, the infra-red emitters 6 are switched off (step 112) using a stop button (not shown) on the controller 22. Deformation can be detected by the laser beam being interrupted by movement of one or other end-plate 12, 14 which is detected by the controller 22. An alarm signal (audible, visual or both) can then be generated. A temperature reading can be generated from the thermometer and/or a record of the reading patters (can be generated) .

When using the test apparatus, the sample pieces when heated, showed extensive deformation, in the form of buckling. This result could be readily replicated, as could localise buckling, directly caused by incorrect assembly of the test piece.

Controller 22 can include a timer, usable both for adjusting the power of the infra-red emitters 6 over time controllably and for timing how long it takes for a deformation event to occur.

Although a deformation detector as described above is advantageous, deformation can be determined in other ways and if needs be simply by visual inspection.

Solar infra-red radiation is generally in the range 0.7 - 1.5 micrometers. It is desirable for the infra-red emitters to emit radiation substantially across this full range, but radiation emitted somewhere within the range can be sufficient .

The described embodiment does not direct radiation outside this range to the test piece 40.

The main information available from this test method is the temperature of the profile at the moment of deformation, but it is possible to measure the amount of time elapsed from initial temperature to deflection. The time measured leads to a comparison of the absorptivity of differing surface finishes.

The test method and apparatus according to preferred embodiments of the present invention aims to be suitable for the analysis of the effects of solar radiation on coloured polymers, and laminated polymer products. It is believed also to be suited to investigate the interaction between lamination foils and their base polymer product.

Attention is directed to all papers and documents which are filed concurrently with or previous to this specification in connection with this application and which are open to public inspection with this specification, and the contents of all such papers and documents are incorporated herein by reference.

All of the features disclosed in this specification (including any accompanying claims, abstract and drawings) , and/or all of the steps of any method or process so disclosed, may be combined in any combination, except combinations where at least some of such features and/or steps are mutually exclusive.

Each feature disclosed in this specification (including any accompanying claims, abstract and drawings) may be replaced by alternative features serving the same, equivalent or similar purpose, unless expressly stated otherwise. Thus, unless expressly stated otherwise, each feature disclosed is one example only of a generic series of equivalent or similar features.

The invention is not restricted to the details of the foregoing embodiment (s) . The invention extends to any novel one, or any novel combination, of the features disclosed in this specification (including any accompanying claims, abstract and drawings), or to any novel one, or any novel combination, of the steps of any method or process so disclosed.