AIChE makes wickless candles for Engineering EXPO '99

AIChE was one of 32 student organizations that created exhibits for Engineering EXPO '99, held on the engineering campus April 16-18. Two years ago AIChE made Wisconsin W-shaped marshmallows for Engineering EXPO. They made W's again for EXPO '99, this time in the form of red, rose-scented (in honor of the UW Rose Bowl victory) wickless candles. They demonstrated the spray-cooling process of making candles and pressed the cooled wax particles into W-shaped blocks. Their exhibit, "Wicks Not Included," won an honorable mention award. (Wicks were not included due to safety concerns.)

The project sponsor, SC Johnson of Racine, Wisconsin, provided pilot-plant equipment and some technical support in addition to financial support.

The AIChE exhibit was a pilot-plant model of the process SC Johnson uses in their production of Glade® votives. The group demonstrated the following four-step process: (1) Melting. The paraffin wax was melted at around 160 degrees F, after which scent and dye were added. The kettle used for the AIChE project was heated by steam and agitated by air. (2) Spraying. The liquid wax was poured into a pressure tank which was pressurized by air to around 8 psi. The liquid wax was sent through the tower until it squirted out of twelve tiny nozzles about 0.4 mm in diameter. As the liquid wax hit the cooler air, it solidified into tiny particles which cooled further as they fell through the air, ending up at around 90 degrees F. After the particles hit the ground, they were swept around to help cool them further. In the actual SC Johnson process the particles are collected on a cooling drum and are then scraped off. (3) Pressing. The tiny wax spheres were then put in a mold and cold-pressed at 2000 pounds of force into wax blocks. The force of pressing affects the burning characteristics of the candle. Since AIChE was not interested in burning characteristics, they used a higher pressure to make the candles more solid. SC Johnson presses their candles at a lower force. (4) Overdipping. The wax blocks were then dipped in liquid wax to give them a smooth coating.

A core group of six students spent a year learning about the spray cooling process, getting their model running, obtaining materials, and setting up the press. Several of them traveled to SC Johnson in Racine, where they were shown a demonstration of the production process and talked to engineers about some of the technical aspects of the process.

As the group set up their own pilot plant they faced several challenges. They had trouble keeping the lines clear of solidified wax, which would happen any time the spray tower was shut down or if a cool spot would form in the pipe. To combat that, they installed heat tape throughout the length of the tower, but inevitable cool spots would plug the line of the tower. They also discovered that the wax needed to be an ideal temperature or it wouldn't cool properly. The temperature was controlled by the height of the spray tower. However, even in the basement of Engineering Hall with its high ceilings, they were limited in how high they could make the spray tower, and they had to filter out the clumps of wax that resulted from the wax being too hot. Another challenge was making the W mold for pressing the candles. Being chemical engineers, they knew little about tools and dies. With assistance from the Mechanical Engineering Department and SC Johnson, they were able to design and create the tool and die. The use of a press was donated by Janesville Tool and Manufacturing.

About twenty volunteers worked at the AIChE exhibit over the EXPO weekend, making wickless candles and explaining the process to thousands of EXPO attendees. One visitor remarked on AIChE's good reputation from previous EXPOs and commented that they had once again outdone themselves. Another visitor brought his granddaughter and mentioned that it was good to see women involved in their project so she could see that engineering wasn't only for men.