MARS Recumbent bicycle projects

Zotefoam Manual - Heating and Forming
A project by John Tetz - April 2005

Introduction   Mold   Layout   Form   Cut   Glue   Internal Braces   Install the Trike   Tail   Door   Canopy   Turtledeck

You will need to order one sheet of Zotefoam for the top, two sheets for the sides, and one sheet for the bottom. As a backup, order a second top sheet, one extra side sheet, and an extra bottom sheet. These should be 0.5” thick LD 45. They normally come in 40 x 80”, but the green did not, so I had to weld two pieces together to make one side (the joint is the front wheel section line). See Welding on the MARS website under my VFS (Vacuum Foamshell) project, section 13.

This shows a yellow top wrapped over the mold and pulled down against the mold with many bungee cords. When heated, the Zotefoam will normally expand away from the mold. These cords provide even pulling so the Zotefoam conforms to the mold shape. The bungees I used pulled a bit too hard, causing thinning of the Zotefoam.

Cut the Zotefoam so there is about 4” of excess material below the color separation line. What often happens is there is some amount of puckering between the bungee cords because of the curvature of the mold. Puckering has to be below the color separation line.

Very important: after the top is bungeed, make a registration mark at the end (beyond the canopy end) for forward/back location, and a couple of lines for left/right position on the mold. The end of the top has to cover only part of the open cockpit - see shell layout drawing (Mold image #2). Marking is very important so the part can be accurately repositioned for trimming and assembly. Use a removable ink marking pen to make surface marks that can be removed with water. Other registration marks will be made after trimming.

Here is where the art part comes in: heating must be done with large area heaters. A hot air gun can heat only a 12 x 12” area, meaning the Zotefoam will be unevenly heated, so I used two Marvin Workshop Quartz 7060 overhead shop heaters from WB Marvin Manufacturing Co., 211 Glen Ave., Urbana, OH. The heaters can be switched from 700 to 1200 watts. Each comes with a bracket so it can be mounted on a wall or ceiling and the angle adjusted. That bracket can be modified so two heaters can be coupled together, while each heater can be adjusted independently in angle.
I hang these heaters about 18” above the mold on ropes so the height can be adjusted. I also use bungee cords from the ropes to the heaters to allow quick manual adjustment of the height while heating the Zotefoam. This is necessary to heat properly around the edges which are lower down on the sides of the mold.

This shows the lower heater rotated to heat the edges. But note how the upper heater is aimed towards the middle area. This will cause overheating in the middle. It would be better to rotate the upper heater temporarily away from the top and then rotate the entire assembly. Then the upper heater will be aimed out, away from the center. When changing the heater angle, pull it away from the mold.

The main rule is to keep the heaters moving at all times. Sweep an area about 36” long by the width of the piece to be heated. Let the heat soak in slowly. Keep the heaters about 14–24” above the Zotefoam. As the temperature of the Zotefoam rises, it changes color. Observe where this color change is occurring, and reduce the heating in this area while increasing the sweeps above the slower areas.

This shows the color change. One of the challenges is to learn what depth of heating is occurring. Once the color change occurs, no further visible change can be observed. Not until overheating - then the surface is melted and destroyed. Feeling the surface will give a clue. Smell is another. But always keep the heaters moving. Practice helps. Overheating also melts the mold; the muslin cloth and plaster help prevent this.

Because the heaters are essentially fixed in location, move the mold to cover another area. After the most of the top is heat-formed, go back over it to reduce stress from uneven heating. For this operation, it is not necessary to bring the temperature as high as the initial heating. Raise the height of the heaters with the ropes when done, because even when off the heaters radiate a lot of heat. When you disconnect the bungees, the Zotefoam should be laying uniformly up against the mold. If it isn’t, then reconnect the bungees and do another reheat.

Note as you come closer to the front, you will need to cut darts in the sides, otherwise the Zotefoam can’t bend without severe puckering.
In this photo there are not enough bungees to do a proper re-heat. To finish the nose area, use a hand-held hot air gun. This area is too small to use the large heaters.

Heat an area and hold the edges down against the mold until cooled. Don’t touch the heated area that will be the top, because the Zotefoam is soft and you will leave handprints.

I have thought about trying to use a remote-reading temperature gauge to get an idea of the Zotefoam temperature. This could possibly be mounted between the heaters and aimed at the Zotefoam. It would require some experimenting to correlate the surface temperature with the depth of heating, but it may give more reliable results. Zotefoam needs to be around 200 F. If the temperature is too high, the crosslinks stretch too much and may break, weakening the Zotefoam. Also if overheated, the surface can be destroyed. If too low, the crosslinks won’t be able to adjust and the Zotefoam won’t maintain the shape of the mold.

However, even without perfect control, the results can be quite acceptable, as shown in the VeloTrike photo (Mold image #1). You could heat and form the tail now, or wait until the main shell is finished (see Tail section).

Next: Trimming

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