Hotpress Issues, Ideas, and Solutions (click here for photos and latest documentation of the Kingston Hotpress)
At the moment the design is 60×60 cm. Do we need a larger surface? If so, what dimensions?
Larger surfaces would mean greater force needed (to maintain desired pressure) which might call for even heavier design. An occasional larger piece could be pressed in sequence, e.g. a 120×60 cm piece could be pressed in two steps by pressing the first half, then sliding the mold within the gap and pressing the second half (with small overlap). Perhaps other extensions to the current system, such as wider gap allowing more 3D features would be more feasible at the moment.
Current design uses is electricity. Carlos has asked for a gas powered design. Lesotho may need something else.
Ignazio had a nice suggestion that heating be done by a copper pipe coil running hot oil. The challenge is the elastic connections that would allow easy disconnect and bending while the lid is opened up (or even while it moves up and down). Another challenge is oil circulation, which would likely need to be forced by some kind of pump.
With natural gas (or propane), the simplest solution would be small burners, like those in a camping stove. Of course, the bottom lid is easier (flame going upwards), but there could be appropriate set of fins at the back of the top plate that would conduct heat downwards. More advanced (and much safer) solution would be flame within the tube coils…
There are issues with temperature consistency across the top and bottom plates. Darko is trying to remedy this. Where are we with this?
After refurbishing the press at Kingston (Queen’s University) I am happy to report that temperature seems uniform enough, to create nice white tiles with no signs of over- or under-heating. We replaced the original 6 mm (1/4″) steel plates with 12 mm (1/2″) aluminum plates and replaced the links between the top and bottom lid (8 square links, four on each side) with longer ones to accommodate thicker plate without reducing the gap. We kept the same gasket material between the plates and the lids (3 mm “cork rubber”, commonly used for on engine block – between the intake manifold and the block, between the oil pan and the bottom of the block, etc.). It provides nice thermal barrier reducing heat loss, while helping distribute pressure evenly. While replacing the plates we slightly modified the way the plates are attached to the metal frame. Originally, a set of 36 flat-head screws was screwed directly into the threaded holes in the lid. Now, they are replaced with 36 flat-head bolts (screws with washers and nuts), passed through 1 mm larger holes. The nuts are lightly tightened, to prevent plate bulging when the gasket is squeezed around the perimeter, while not in the middle, pushing the plate center out.
Agreed that we need a much larger gap between the top and bottom plates in order to make more 3D objects and to arrange the elements that we heat/press more precisely. Darko, have you managed this in the new design? Opening the top lid like a clam shell would allow for more 3D designs to be pressed, assuming that the flat plates are replaced with appropriate shapes, or that a highly thermally conductive thick mold is used (i.e. aluminum). Opening can be assisted either by “gas springs” which we use in Kingston – the devices typically used to lift the back door of a minivan, or heavy cantilever wights affixed to the top lid, protruding back. In either case, one steel rod (pin) needs to be taken out to disengage one end of the lid. We use tight tolerance between the rod and the sleeves (made of pipe sections), with only 0.25 mm clearance. This makes the disengagement difficult. There are two remedies possible. Use larger gap on this connection only (even 1 mm could work O.K.), or cut the top half of the pipe segments on the lid, since these “bearings” are only loaded downwards. In any case, if this is routine step in production, the four links should be connected by a cross-bar, so that they stay together when the pin is pulled out. This detail is certainly worth further contemplation and I invite others to come with suggestions.
Fire retardancy; gas emissions; pollutants in final products.
Carlos is asking for increased production capabilities. Is this possible with the present design? (Ancillary question: do we really want to support assembly line production?)
The following recommended changes are from David Zitnick based on user experience at RISD:
These are all suggestions and a concerted look at the design may make some of them not valid. Also I’m sure some of these have been addressed. I’m thinking about putting some more instrumentation on our press to better analyze what’s going on. Primarily I’d like to visualize the forces with some strain gauges we collect data from. For RIS moving forward if we can build another press we look at build a press that is more technically advance that we can gather these kinds of forces and thermal information from to help inform everyone for a more effective, simpler end press.
The Following is an evaluation of the hotpress on Appropredia
In conjunction with a winter semester 2010 course being taught by Joshua Pearce at Queens University, MECH 425 – Engineering for Sustainable Development, senior Nate Preston is reviewing, evaluating, and illustrating the hotpress design via an appropredia wiki. His insights are very significant, and can be found here: http://www.appropedia.org/Kingston_Hot_Press:_Process_Improvements
The Following two videos show the revised hotpress built by Derek Goad at the University of Western Australia. Many of the above issues have been addressed in this new build. Derek added 2 additonal heating coils to the top and bottom sections of the press to aid heat distribution; he used automotive insulating material from http://www.novussealing.com/products1.htm#; and he reduced heat loss by adding insulating the top of the press with MDF.