Sheet Press Mould Oven
This is my first topic, woop woop!
I am taking the lead on designing an oven which will be part of the sheet pressing system. I am working in collaboration with @markbertbach.
All information about the umbrella-project can be found here https://davehakkens.nl/community/forums/topic/v4-sheet-press-development/.
We have opted to use an oven as the heating method as we have anticipate that it is the most energy efficient way to melt the plastic as an oven allows the heat to be contained and the same air to be circulated evenly without escaping.
The alternative idea was to embed the heating elements in the bed and roof plates of the press itself but this plan was abandoned for the above mentioned reasons plus several others. With embedded heating elements the press is required to heat and fully cool during the process of making each sheet. With a separate oven a second sheet can be heated whilst the first is cooling allowing more sheets to be produced each day. This also increases energy efficiency as you do not have to repeatedly heat and cool the the heating elements and subsequent heating components, as they can stay on constantly.
We have developed a 3D model of the first prototype oven. I have attached a picture with a presentation detailing the construction process and some of the areas we still need to research.
hi how is this project coming along? i would be keen to learn more and perhaps replicate down the line. Do you intend to share or sell the plans? what is the largest sheets the machine will produce?
I have an open question for the community.
Our first design uses ceramic insinuation bricks to contain the heat. We would like to find out more about the availability of ceramic insulation bricks. Could anybody provide some information about the availability of them in low resource areas.
If people have any alternative suggestions to the ceramic bricks that would also be greatly appreciated!
Hi Richie, the project is coming along nicely, it is in early days but will be finished by October. We will open source it so you can replicate it 🙂
We have met in Underbroen (Copenhagen). My name is Asger.
We are part of an EU project, where we want to both create and test a circular model for plastic in Copenhagen, and figure out a way to locally produce recycled plastic sheets (a la Smile Plastics) that can then be processesed as we normally do with plywood.
I’m therefore following asll of these Sheet-discussions closely. Maybe we can arrange a call asap?
Please feel free to write me if you are interested to hear more: [email protected]
We are prototyping v2 of the oven which will be part of the sheet pressing system.
Does anybody have an information about insulation types that they would be able to share? We have complied a list of types available in the Netherlands but it would be great if we could know what is available in more remote parts of the world, what you guys have learned from working with these, and if you have any sugestions of alternatives?
Phar gas Plates
Thankyou for the input 🙂
We made a prototype of the proposed door mechanism for version V4.2. of the oven.
Feedback would be appreciated!
This week we are testing Insulation types!
We have built two boxes with the same size internal chamber and a portable electronics rig with a single heating element attached to a PID.
The AAC is secured from the outside walls and left exposed on the inside of the oven, this is the approach we used for V1 of the full size oven.
The mineral wool has an internal steel box to protect the insulation. I also plan to test an internal frame, instead of internal box depending on if the first results seem promising.
My first observations from building the two boxes is working with the Mineral Wool is a lot faster, cleaner process and weights a lot less than the AAC due to its ease of cutting and weight.
It is also cheaper so a thicker wall can be added and still at less expense than the AAC.
The results from the tests we will be running can be seen here.
We will be simulating a full working day for the mould oven (8 Hours).
We will be collecting data about the following parameters:
-External Surface Temp (Over Time, Regular Intervals)
-Internal Surface Temp (Over Time, Regular Intervals)
-Time to reach 220 (PID)
-Temp drop after open for 2 mins (PID)
-Time to return to 220 after open for 2 mins
-Power Consumption after 8 hours (KWH)
-Cool Time Back to 30 C
So after one week of testing the three scenarios we have made the follow observations.
The Mineral Wool insulates much better than the AAC, the external temperature of the box is actually more susceptible to the outside temperature, it dropped towards the end of the day as the sunlight dropped.
When heating the same volume of space the Mineral Wool used 0.7kwh to maintain a temp of 220’C whilst the AAC used 2.6kwh. Making the Mineral Wool more than 300% more energy efficient than the AAC.
Two layers of Mineral Wool accumulating to 140mm and one layer of AAC measuring 80mm in thickness were used to insulated identical volumes of space. The decision to use a thicker wall of Mineral Wool was made due to its lower cost, meaning the real world situation is more likely to be the same. It is also easier to overlap the two layers to prevent thermal bridges between the inside and the outside of the oven.
Although the Mineral Wool is better at insulting and has lower cost it is also weaker than the AAC it requires some additional infrastructure to secure it in place and protect it from damage. We tested two scenarios: 1.) A closed steel box and 2.) A skeletal frame with a steel plate in the bottom to protect from dripping. Both scenarios performed almost identically in terms of power consumption, insinuation and retention of heat.
This leaves us and future builders of the oven a pragmatic decision to make. The steel sheet appears more friendly and similar to a finished commercial product which we are used to seeing. It also offers more physical protection. The down side is that it adds a significant amount to the cost (750-1750) euro dependent on your location and increases the duration and complexity of the build.
Nice to see the low energy consumption with the wool. The high cost of steel sheet enclosures was surprising. With the insulation in place, the exterior could be plywood and the interior a simple bent sheet metal box, perhaps just 4 sides. Depending on size, an old CPU tower enclosure might work after you remove the paint. 4 simple column supports, either ceramic, or even steel tube or threaded rod may be sufficient. I think if you run the heat transfer calculations, the heat lost through those supports is manageable.
Test of sheet press oven door prototype V4.2.1
A little heavy but the mechanism is smooth and it closes almost perpendicular to the oven opening which allows for a snug tolerance between the inner and outer parts of insulation. We have decided to add a second layer of L extrusions to the inside of the door to protect the insulation and also considering chaning the 40×40 Ls to 20×20 to reduce weight. In This video the door sits slightly open at the top, this is because the insulation on the door (deigned to fit V4.2) is pressing against the insulation inside the oven (V4.1). If this continues to happen in the next version the 80mm horizontal tabs can be extend t o120mm so the door sits further back past the center of gravity.
The model of the oven is almost complete, just missing the electronics. The files can be downloaded here if anyone would like to give some feedback (SW2018 and STEP format)
@jasonknight, you let us know when the next iteration arrives ? otherwise we’re sending the parts as is to the laser/metal brake service by the end of the week; there are 2 crucial projects in the baleares waiting eagerly for a kit, ready to assemble. so it would be great btw. to know where or what to source for the heat elements; thanks a lot; great work btw.
The link in the post above yours contains the most recent model, this is not likley to change before October
@jasonknight now that you’ve had a chance to operate the door, what is the advantage of the linkage design as opposed to a hinged door. I think with some shaping you could get a good seal with both designs. Is the current design worth the extra lifting effort compared to a hinged door?
If it exists, it would be informative to see the thermal analysis (spreadsheet?) for the overall oven. Do you have an energy estimate per sheet?
Thank you for all the work.
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