One Piece Windshield
Thanks Will. Good information. My supplier does not stock the tinted acrylic and requires full lift orders. If people want colours and coatings, I will have to shop around to find another supplier. We can cross that bridge later.
I have the plexiglas now. Next step is fabricating the oven and the glas clamps to hold the glas while it heats up. I'm going to hang the glas while heating to keep the best optical quality. I think I have the location for the oven worked out. I also have the elements and at least some of the insulation. It's relatively a low temperature oven so what I have is probably going to be overkill. I'm going to try one sided heating at first and then upgrade if that does not work out. According to the technical manual, at these thicknesses, one sided should be fine.
Hanger fabricated and track installed. Allows the plexiglas to be held vertically to keep optical properties better than horizontal heating and makes it easy to get the plexi over to the mould quickly and with minimal handling. Holds the plexi surprisingly well.
At his point the plan is to just pop them off by hand. If that proves too slow or cumbersome, I'll redesign them to be air actuated. The elements I had on hand were too high resistance so I'm replacing them. I'm not sure whether IR heating is practical. Will have to see how the new elements work. My initial plan was for an oven anyway so reverting to plan A will be simple enough.
I did a few tests using just infrared heating and it worked. The plexi was still a little cold for the trip to the mould though, so I will increase the watt density a bit and I will preheat the heating panel before exposing the plexiglas to it. Element spacing was about 3.6 inches but I'll make it 3" and that should do it. I'm calling it a heating panel instead of a kiln now because that's what it really is. 😉 I can use it to help cure paint and epoxy in the future too.
I'm waiting for a shipment of quartz tubes to mount and protect the elements. The elements tend to bend as the steel expands when hot so the tubes will keep the elements straight. This also allows me to get the plexi closer to the elements for more efficient heating. Shipping from the US of A to Canada has been slow but I'm hoping they arrive within the week.
I'm pretty confident I can make good windshields but it's gonna take some time to iron out the details.
Finally got the shipment of quartz tubes. Incredible stuff. AKA fused silica, it's melting temperature is around 3000F and it's transparent to infra red. Not only does it keep the elements in place, it insulates the elements from convective heat transfer, allowing more energy to be converted to IR. You can see the difference in the photos. The encased element is much brighter as it's not being cooled by the air flowing past it. This should make the heater much more efficient at it's job.
Any updates for 2021 on the one piece windshields?
Since the last update I have installed the quartz tubes and made some test firings. The quartz works great.
I fired two test pieces. The first one was the usual two piece windshield thickness in cell cast acrylic. It worked great. The centre was perfect but the side near the vent was a little under heated and didn’t lie flat. I’m sure that will be fixed when I go back to parallel elements.
The second test was with the .177 plexiglas which was sold to me as cell cast but turned out to be an extruded modified acrylic. It was a disaster but the supplier is allowing me to exchange the leftover since it was their mistake. I’m picking that up soon.
I just bought a few yards of high quality wool billiards fabric to cover the mold with. The flannel I was using was not suitable. It was leaving some weave pattern on the plexiglas.
I’ll make another test soon when I have the new acrylic. If that goes well, I’ll make the first full size attempt.
Cool! Thanks for the update..Looking forward to seeing a real life one piece!
Been working on the mould again. It wasn't as true as I wanted. I fixed some low spots. Now it's like glass!
Also got the heater closed in because the infrared heater was not heating as evenly as I hoped. If I used a full frame, it would probably work but I'm just hanging it off the top edge so the acrylic tends to bend away from the elements, causing uneven heating. Also installing a convection fan as recommended by the tech manual.
Going to do another test soon.
So how does that work? Do you heat is standing up in that box and then pull it out on to the mold?
The Plexi is hung from a roller track with clips and rolled into the kiln. The top part of the insulation is flopped over, closing the top and then lifts out of the way when it's up to temperature (~300F) at which time it's pulled out, in front the mould. It's unhooked and quickly draped onto the mould. The edges are clipped in place and a blanket is draped the whole deal.
Please put me down for a one piece as well. I think with the old 337 data, a DER would not have a problem signing off. Just curious, would it be possible to set up a vacuum table to draw the glass down? This may help around the wing cuff area.
I'll keep you up to date.
Vacuum should not be required. If the acrylic is evenly heated, it should lie nice and flat.