Keyed Bricks –Manufacturing Considerations –working document
Executive Summary
The choice of plastic/polymer is connected to the machinery needed to process and convert it. Size and shape of part are also important. Density, melting temperature, softening temperature of polymers need to be tailored to meet the physical and mechanical specifications of the part, but they also limit what type of processing equipment can be used. Using recycled plastics adds another component, as most polymers do not mix well, and tend to separate when processing, or worse, when the part is cooling, or in use. This leads to poor mechanical properties and part failure.
This report discusses design questions such as feedstock consideration, processing methods, and pros and cons for each method and recycled plastic types. Questions such as which type of feedstock is better to use, raw mixed waste or sorted segregated plastic wastes and what are the limitations of the different processing equipment will be addressed. . The latter source have been washed, sorted, and possibly already compatibilized, or at least limited to polymers that are miscible. Secondly, we will report on groups around the world who are making recycled plastic building bricks. Using these groups as models. What is their feedstock? What are their solutions to polymer limitations such as Creep, UV protection, and means of fire retardation? What manufacturing process are they using? Is it batch or continuous?
Mixed Plastic Waste versus separated plastic wastes
- Adhesion/strength/longevity considerations
- Imerplast compatibilizing catalysts for high and low density polyethylene
- Peroxides/metal catalysts for compatabilizing mixed plastic waste –are these commercially available?
- Purchasing raw mixed plastic waste versus processed plastic waste from vendor - https://www.cbinsights.com/company/hello-waste/alternatives-competitors
- Price versus properties
- Cleaned/processed/limited variability
Should we consider making the product in one shot or two?
One shot design-simple/may limit key-brick design?
- Consider more open design (more voids) with top/bottom having the keyed brick element
- Addition of filler directly with plastic for added strength in one-shot design
Two shot design –more complex
- Making the core and having the core entombed in plastic key brick element
- Injection molded? How to injection mold around a solid core?
Engineering Processes –low tech to high tech
Processing equipment from simplest to more complex include compression molding, injection molding, extrusion (profile), extrusion blow molding. Compression molding can be a simple as a reinforced box using clamps. More intricate molds are made out of metal and use muli-ton presses. This process can be automated or individually run.
- Compression molding –one-piece with composite composition using compression or injection molding
- Simple wooden mold –could be used with room temperature setting thermoset resin https://www.youtube.com/watch?v=dPLzeF_HO4g
- Rhino Machines –https://www.core77.com/posts/100357/Rhino-Machines-Turns-Plastic-Waste-and-Foundry-Dust-Into-Superior-Bricks
- Gjenge Makers –Nyrobe
https://www.youtube.com/watch?v=iFcPqXxAUWM
- K-Briq –Scotland
Injection molding –one or two piece construction –See Circular 11 - https://www.youtube.com/watch?v=hEPAmGf-0i0
The idea is that a simple core “brick” is formed and then in a second process, the key-brick design outer shell is molded around the core. Another option would be to use structural design in the brick as well as reinforcing fillers such as fibers and mineral fillers. In either case, the composition of the core needs to be considered carefully. The adhesion between the core and the casing will need to be intricate in order to maintain structural properties. A sand/plastic composite is proposed and there are bricks with this composition being manufactured (see below), but this is a one-step brick with no casing on the outside. In a two-step process, adhesion between the core and the casing may prove challenging given the different surfaces, textures, and possibly different polymers. In all cases, the casing polymer and the core polymer will need to be miscible and their melting/softening temperatures closely aligned.
Another option is to use a one-shot design. An injection-molded brick could be constructed using reinforcing fibers and fillers with a structural design that has voids to decrease density without decreasing strength.
Extrusion (profile) –See Conceptos Plasticos https://www.youtube.com/watch?v=UMl9gTQk7W8
Another idea is to make the core using profile extrusion. This process uses a single or twin screw design to melt and convey the polymer to a die that has 3 of the dimensions of the brick, and is cut to size at the end of the process. One can envision if the key-brick design is simplified, it could be used to produce the brick in a continuous process. The process would have to be tuned for using composite materials and is limited to die sizes.
Possible filler materials and/or composite matrix
- Sand –expensive/dense/possible limitations due to building shortages
- Foundry dust –light weight/waste product-circular economy product
- Rice hulls and rice glass from energy production
- Biochar
- Calcium carbonate
- Metal Swarf (metal machining wastes)
- https://www.cohenusa.com/buy-recycled-material/
- https://www.cohenusa.com/blog/what-is-swarf-recycling-your-machining-scrap-for-cash/
- metal dust and shavings from processing plants –strong/circular economy product
- presently being tested/marketed for use in low-density concrete
- Slag(a mixture of metal oxides and rock)
- Glass dust and fibers
- Building wastes (rock dust/crushed concrete blocks/rock walls, etc)
- Recycled wire from tires
https://libertytire.com/Products/Commercial-Products/Wire/
Companies presently working on making bricks out of recycled plastic and fillers
USA
- Circular 11 –mixed plastic waste –low tech injection molded parts
Injection molding/no filler –problems with creep/aging/compression strength
https://www.youtube.com/watch?v=hEPAmGf-0i0
- Lok-n-blok –PP with glass fibers, mineral and UV additives
http://lok-n-blok.com/products/
- Lok-Block –
https://lok-block.weebly.com/contact.html
Colombia
- Conceptos Plasticos
https://conceptosplasticos.com/
https://www.youtube.com/watch?v=OWNA1CjIaIw
India
- Rino Machines –Compression molding/80% filler (foundry dust (sand/metal shavings)
Scotland
- K-Briq
https://www.youtube.com/watch?v=giiTe6LzQDk
Germany
- Polycare (Smebla) -Pozzolanic material with calcium carbonate
https://www.youtube.com/watch?v=Sb2dsPlksRw
https://polycare.de/en/masonry/sembla
https://polycare.medium.com/daring-to-redefine-construction-the-geopolymer-revolution-e622322e58a8
Isreal
- Kite Bricks –concrete interlocking bricks
https://patents.google.com/patent/US20130227901?oq=kite+bricks+ltd
France
- Gablok
Toll manufacturing –Proof of concept/pilot scale
Molds are expensive. Therefore it is good know that the design is going to work before purchasing. Working with a toll manufacturer, and/or machine companies is a good way to bridge this gap. Using these resources, one can optimize and work out kinks and bugs in the system. It is good to start looking for these companies now, in these planning stages in order to have a good working relationship with them as the process evolves.
Zetar Molding –China