Fixed Rack Exposure
 Samples on black box, fixed-rack exposure  Fixed rack exposure at 45 degree angle  Samples under glass; fixed rack exposure |
Fixed-rack exposure programs provide definitive data on material performance and weathering characteristics.
The angle of the exposure rack and its orientation are at the clients discretion. However in many cases these parameters will be defined by the test method or specification (corporate, national, in-house, etc) being followed.
And while there are many variations there are also many similarities with fixed-rack test methods. For example, construction materials and industrial coatings/products are often exposed at an angle of 45° and automotive exterior coatings and components are often exposed at 5°. The use of ‘Black Box’ exposure, now widespread, grew from an automotive test method to raise the temperature of exposed samples by using the rack as a passive ‘heat sink’. The use of 19°, Allunga’s latitude angle, is the most severe (in radiation terms) exposure option for fixed-rack exposures of 12 months or longer – and for this reason it has gradually been increasing in popularity. Horizontal and Vertical racks are also used for a wide variety of materials. It has also become more popular for materials/products to be exposed in an orientation that would parallel that of real world use.
Fixed rack exposures can be open-backed or mounted on a backing substrate such as plywood. Samples can be exposed ‘under glass’ such as with some textiles, furnishings, and automotive interior components.
As Allunga’s exposure sites are in the Southern Hemisphere, racks usually face North to maximize radiation exposure. In a few situations, for example some test methods associated with testing mould resistance, exposure racks are orientated to face south.
The most common fixed-rack exposure orientations are:
- Horizontal
- 5 degrees from the horizontal, facing North
- 19 degrees from the horizontal, facing North
- 45 degrees from the horizontal, facing North
- Vertical
Fixed-rack exposures can be:
- Open
- Under-Glass
- With or without backing substrate
- Black Box
- Black Box under GlassBlack-Box Under-Glass facilities are available with a range of internal capacities allowing for the exposure of large components eg. instrument panels, seats, doors, assemblies, shelves, etc.
Latitude Angle
For fixed-rack exposure for periods of 12 months or more, exposure at 19° (Allunga’s latitude angle) from the horizontal is the most severe option in radiation terms.
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Mounting
Samples are mounted/fixed in accordance with clients’ instructions.
In cases where large amounts of time and/or materials are involved a mounting charge may apply, though this is the exception rather than the rule.
