V4 Hot Press
The Sheet Press System we are going for consists of a Hot Press, a Prep Table and a Cooling Press. We discovered that getting the molds out while they are hot and pressing them further in a second press until they cooled down makes the process more efficient.
This thread is to update you on our current development of the Sheet Press System. We will be posting all the decisions we make and why and welcome you to contribute. We are Jason, Michael, Tom and Me.
V4 All about sheets – Index topic An overview of the topics so far
Sheet Press Mould Oven Oven development for cold press system
V4 Sheet-press – mould development Mold development for cold press system
V4 Sheet Pressing System Document of the first six month of development
TIME LINE This is our plan of the next 12 weeks. We are currently in week 2 and want to start building by the 3rd week of August. Currently Michael is working on the cad and we are ordering components like electronics and laser cut parts. The plan is to have everything finished by the 3rd week of October and present it during Dutch Design Week here in Eindhoven and of course online on the Precious Plastic website.
Inside the spaces between the structure, we will try using heat cartridges. They are cheap, accessible and easy to wire. Preliminary tests have also shown they are quite suitable for the application.
Attached are some thermal images of one heating element being tested over a given area. Note the largest variation in temperature difference (measured from thermocouples) on this plate is ~20 degrees at Tmax=220.
We are also taking advantage of a staggered arrangement which heats the plates from different locations on the top and bottom (not a mirrored arrangement) which should work to disperse the heat more evenly.
Graphical Circuit Diagram for the Hot press system
Just curious, how are the objectives for this effort different for the past press efforts? If you could post the requirements list for this effort, it would help clarify what you are trying to do.
Here is the CAD so far
We also have found that adding a spring to the jack assembly helps a lot in maintaining pressure on the sheets as they melt. This helps to ensure we have the highest level of heat transfer possible throughout the pressing process – this improves energy efficiency, time efficiency and overall sheet quality.
We have three different spring concepts we could go with. The first two involve a compression spring with different ways of transferring the load. The third uses two perpendicular leaf springs.
We’re leaning towards concept two, however would like to get some more thoughts/opinions first.
COOLING PRESS These are sketches of different methods to clamp the molds for cooling. One very low tech method would be clamping it between sheets of plywood with clamps. Its a very uncontrollable and slow process. Another idea is to mount toggle clamps on wood beams and clamp the plywood and molds with that. We however wanted a modular system that allows us to clamp and store multiple sheets. Do you remember the transfer problem? We also want that the mold does not need do be carried. That’s why we need something that can adjust in height where the mold can be slid over from the hot press.
We were thinking of a scissor table because it can go down all the way which means we can stack a a high amount of molds but we were not sure if it would hold the weight and be user friendly. Because of the very tight time schedule that we are in we decided to go with the mechanic that has proven to work: the bottle jack. In the second image you can see the sketch for the cooling press. It has a grid on the bottom and top to make it stable. This is a simplified version of the grid that will be stabilizing the hot press. We will post some screen shots of the cad soon.
TRANSFER METHODS To make the process of unloading the mold from the hot press as save and efficient as possible we thought about possible ways to help with that. A 1 m by 1 m, 20 mm deep mold weighs around 15 kg plus the weight of the mold and sheet metal. It needs two people to carry this and creates a lot of potential errors. In the next post I will show you with what we went.
SYSTEM BRAINSTORM Last week we had a brainstorm about the sheet press system as a whole and about the user experience during the production of a sheet. We went through every action during the process and looked at how we can optimize the workflow. I also have a detailed chard with all the actions, goals and potential errors with the according solutions. I will upload it here as well.
1.5kW is a typo, it’s definitely 15kW when heating up
So that question really depends mostly on the ambient temperature and thickness of the sheet. In our experience it would take around 20 minutes to heat up (5kWh total as mentioned before). From this point, the machine is drawing less than 15kW because the machine regulates the temp – the exact amount depends on what you throw at it and if you’re in a cool/warm climate.
Let us assume the worst – that it draws the full 15kW. Then for a 6mm sheet of HDPE (that takes around 30 minutes in the sheetpress) you would draw 7.5kWh. So to heat up and press one 6mm sheet; you’re looking at 12.5kWh, for two 6mm sheets; 20kWh etc…
Keep in mind that these are theoretical calculations based on the rating of the components. We have not measured the actual power draw – but in theory this should be a good approximation.
Hi, a kW is a rate of energy usage, not an amount of energy.
a kW is equal to 1000 joules of energy being used per second.
As the machine is rated at 15kW, you could say that the sheetpress draws 15kJ joules of energy per second. You could also say that it draws 15kWh in one hour, 30kWh in two hours etc… a kWh is usually what electricity companies use to bill you, so you can figure out your electrical costs with that 🙂
EXTRACTION HOOD This machine will come with an extraction hood. Keep in mind that always when working with molten plastic there should be extraction or ventilation, ideally an air filter system. For the hot press it will be implemented in the design and not an external feature. Here are our first concept sketches.
Concept 2 looks best to me. Other than that we’re building more likely a 70x70cm version of it due to shipping problems (I still have at hard time understand why those sheets have to be that big). Regarding the cooling press, I guess you already considered inflatable sacks or a fire-hose grid via compressor ? That’s a good way distribute pressure more evenly compared to brute force as hydraulic which involves also way more heavy structure material to avoid bending. Don’t bother if not, I am adding this variant along yours to the PP machine catalog 🙂
Btw., would be nice if you guys could compact your posts a little more. It’s hard to keep track the other posts otherwise at the moment (WordPress comes with amazing tools to author such content better, ask Dave or Mattia for ‘pages’ with dragn drop layout/widgets, with structures from templates,…).
I agree with @s2019, I also would like to see some background
hello,How many kW does Sheetpress consume per hour?
That is a great summary, thank you
The spec table for the V4 sheet press shows 1.5 KW not 15 KW do you know which is correct?
I think the basic question is how much energy is consumed to heat up the machine and then make each sheet.
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