Answers to Frequently Asked Questions about the LED Curebox


1. Is it hard to load the composite into the tubing? It depends upon the thickness of the composite, but specimens can be prepared from even the thickest composite with this method. Injecting the composite through a syringe is an easy way to prepare the specimens. By holding the tubing with one hand and pressing the nozzle of the syringe against the end of the tubing, composite can be injected into the tubing. Another method, in which a paddy of composite is "stabbed" with the open end of the tubing, can also work on thick composites. The LED Curebox can also be made to accommodate thicker-walled tubing if cracking is a concern, or to accommodate a frame-type mold for flexural bars, fracture bars, or other specimen types.

2. Is it hard to remove the cured specimens from the glass tubing? The walls of the Vitrocom glass tubing are very smooth, and some composites will shrink enough to allow them to be slid right out. Others will stick, but if the cured specimen is placed in water, the capillary action of the water will free the bar, and it will slide out easily. Occasionally bars will resist even this method, and the thin-walled tubing must be shattered. Fortunately the expense of the tubing is minimal, about a quarter each.

3. How bright is the light in the LED Curebox? We have not measured this directly, but based on the 2000 millicandle rating of the individual LEDs, it is estimated to be about 200 mW/cm2. This is not as bright as the halogen lights typically used to prepare flexural specimens, however the spectral output of the LEDs matches the absorption spectrum of camphorquinone and other photoinitiators much more closely than output of the halogen light. The LED light provides more effective energy, as demonstrated by our lab test results.

Bars (2 x 2 x 25mm) of composite with 66wt% glass filler (ave size = 1 micron), cured with 5 overlapping spots of Bluedent halogen gun from both sides vs 60 seconds in LED Curebox. Bent to fracture on 20mm span at 10mm/min. (n=5)
Type            Flexural Modulus, GPa      Flexural Strength, MPa
                    ave, s.d.                            ave, s.d.
LED            6.6, 0.2                             118, 2
Halogen       6.6, 0.4                             116, 5

The high flexural modulus and strength values show that the LED-cured bars are just as well polymerized, and perhaps more evenly, as the halogen-cured bars.

4. Does the LED Curebox overheat? The LEDs in the Curebox are powered at their rated value, so they can run continuously without overheating. While this brightness is very effective at curing composite, the intensity controller on the LED Curebox allows the brightness to be increased beyond the rated value of the LEDs. In this case, the Curebox may need to cool briefly in between specimens.

5. What is the layout of the LEDs in the Curebox? The LEDs are mounted in four rows of nine LEDs each so that they face the fours sides of the square tubing. They are packed closely, (as shown) and are mounted about 1mm from the tubing so that their outputs overlap and provide even illumination.