Hot plate techniques, for heating plastics components prior to welding, certainly have their place in plastics joining. But when an Industrial Member found that it created a variation in the melt depth of its components to be joined it turned to TWI for help.
The Member manufactures cartridge filters where a 56mm diameter polyester end cap is heated using a hot plate to produce a melt depth of 1.77mm. The pleated filter material is then embedded into the molten plastic hopefully producing a sound joint. Regrettably the hot plate technique produces a variation in melt depth across the end cap.
It was therefore agreed that TWI would investigate the use of infrared lamps as a potential means of melting the end caps evenly and consistently.
The objectives of TWI's work included establishing both the melt depth, and variation in melt depth, across the end cap for different infrared heating conditions, and secondly determining suitable heating conditions to create the required 1.77mm of melt depth.
Work began using TWI's Bielomatik hot plate welding machine retro fitted with an array of five medium wavelength IR lamps. Each lamp has a max power of 1.8kW and was variably controlled.
A custom built jig was manufactured which rotated the end caps parallel to the IR heaters.
How was the consistency of infrared heating of the polyester end cap to be measured? The answer.using TWI's Agema thermal imaging camera.
Heating trials confidential to the client were undertaken varying the parameters; exposure time, standoff distance, output power.
The melt depth was measured using the client's pin testing equipment.
The results clearly showed that the required end cap melt depth was achieved consistently using infrared heating. The conclusions TWI was able to draw included; IR is a very consistent, even and repeatable method of heating the end caps, it is also a potentially effective method of joining the end cap to the filter membrane. Finally TWI also advised that thermal imaging proved to be an extremely effective method of measuring the consistency of infrared heating.
For information about TWI's capabilities please contact us.