“What are some common sources of non-passive bulb failure?”
One cause of non-passive bulb failure is often overcooling or undercooling of the bulb. Overcooling can prevent the bulb from reaching an optimal operating temperature and under cooling can allow the bulb to exceed a safe operating temperature and result in failure. Contributing factors include (but are not limited to) clogged fan filters, restricted air flow, a worn fan, an environment that is excessively cold, hot, or humid, or excessive air flow through the unit. In addition to over or undercooling, rapid temperature changes can also cause stress on the bulb. This can occur if the unit is in a warm environment and a nearby air conditioning duct or opened window allows chilled air to enter the unit.
Another common mistake is using the bulb over 2,000 hours. While it may be tempting to reset the hour meter after it indicates a necessary bulb change without actually changing the bulb, DO NOT RESET. Even if the unit still has sufficient intensity, NEVER do this. Eventually, most bulbs will fail in a non-passive manner if operated beyond 2,000 hours.
Excessive cycling can also cause bulb failure. During the bulb’s warm-up phase, the different coefficients of thermal expansion between the quartz and metal components in the bulb cause stress in the quartz. The more frequently a bulb is cycled (more than 1 power-up cycle per 8 hours), the more fatigue and stress are imparted to the bulb. Best practice is to leave the unit on as long as possible to avoid excessive power on-off cycling.
Vibrations, contamination from finger oil, or not providing proper air clearance are also common problems that can result in non-passive bulb failure.
“Will overexposure during curing have any effect on the adhesive?”
The effect of underexposure is obvious… incomplete cure. The effects of overexposure are more complex. Double and triple exposures (two to three times the dosage required to cure) typically have little effect on light-curable materials. However, significant overexposure to UV light with attendant heat may age DYMAX materials and some substrates (especially plastics). Severe aging may appear as cracking, physical distortion, changes in color, or chalking. Some physical properties such as an increase in hardness or decrease in elongation may also change. The degree of aging will depend upon several factors including intensity of the lamp, the wavelengths transmitted to the resin, temperature, exposure time, substrates, and specific formulations.
Aging from UV light is not the only concern associated with extra long exposures. Parts may get hot under UV lamps with extended exposures. Thermal aging can exhibit the same effects as UV aging. Some types of plastics may warp, scorch, or decompose from excessive heat absorption. A fan in the curing area may help keep parts cooler.
Significant overexposure of a resin to UV-curing light is unlikely to occur in a properly controlled curing process. End users should always test and validate their assembled device at the upper and lower limits of their process against the lifetime use of their device.
“One of the materials I’m using has exhibited syneresis. What is the best way to reverse the syneresis?”
A few thickened adhesives (VT and GEL grades) occasionally exhibit syneresis. Syneresis appears as a thin film or puddles of low-viscosity adhesive on top of the thicker adhesive. Sour cream and yogurt are familiar products that also exhibit syneresis. The composition of the low-viscosity syneresis liquid is chemically identical to the thickened material. It has the same chemical and bonding properties but the viscosity is much lower.
Time and colder temperatures can promote syneresis. We would recommend using a First In, First Out (FIFO) inventory control. FIFO inventory control can help control the amount of time a product is stored before use. We would also suggest that syneresis-prone materials are not refrigerated. In fact, mild heating can reverse the syneresis in some products.
Once syneresis has occurred, mixing is the most common method of returning the mixture to a homogeneous state. Mixing can be accomplished with a traditional paddle or spatula (being careful to minimize air entrapment) or mixing can be accomplished through the use of a static mixer.