Radiant Heat Makes Two-Piece Plastic Bottle Stopper Possible


It is often difficult to accurately calculate the wattage requirements of applications employing radiant energy. Many times the wattage can be best determined through actual testing of the material.

In one such case, a Watlow representative was helping a customer design a radiant oven. The customer was producing a three piece, plastic thermos bottle stopper that could be opened to form a pouring spout. Because of the dissimilar plastics involved, the customer was having difficulty getting a tight fit after assembly. With experimentation, the customer found that in heating the parts up, the resulting thermal expansion allowed a press fit which remained tight after cool-down.


Working with his local representative, a Watlow radiant panel was chosen for its even heat and temperature range characteristics. The representative decided further testing on the stoppers was necessary to help him make a specific wattage recommendation.

The parts required a low heat, or heat soak effect. A higher temperature source would have resulted in damage to the surface of the stopper. Although the different plastics absorbed radiant energy at different rates, Watlow was able to determine the wattage requirement by running tests on samples provided by the customer in our laboratory facilities. These tests resulted in Watlow's recommendation of radiant panels at 10 W/in2 (1.5 W/cm2). With this information, and the help of his Watlow representative, the customer built a ferris-wheel oven utilizing ten 9- by 24-inch (23 by 61 cm) Watlow radiant panels. The oven was able to process 204 stoppers per hour on a continuous basis.

As a result of using our test facility to determine a wattage for this application, a complete oven system could be confidently specified, consisting of Watlow radiant panels, basic temperature controllers, mercury displacement relays (MDRs) and thermocouples. The ferris-wheel oven is in use and the customer is very pleased with the results.