Do-It-Yourself: Plastic Molding

"Why should I know how to mold my own plastic?" This isn't the first time I've heard this question. Let me explain:

You know those broken things you have laying around or even have just thrown away in the past, that when the original is pieced back together would be easy to mold a new part that could be more rigid than the broken and glued one if done correctly.

Think about how many things that you now throw away that, with a new little plastic piece, would be good as new. The statistics say that we Americans used enough plastic water bottles last year to go around the world 180 times. Most to be thrown into a land fill somewhere.

What if you had an idea to improve an existing part, or even prototyping a new part? Do you make your own jewelry from beads and such? Mold your own beads! Recycle (or upcycle in some cases) your old plastic.

Molding is the process of manufacturing by shaping pliable raw material using a rigid frame or model called a pattern. Using a pattern you create a mold. Using a mold you create a casted part, which is usually the end product.

A mold is a hollow block that is filled with a liquid-like or powdered plastic, glass, metal, or ceramic raw materials. The liquid hardens or sets inside the mold, adopting its shape. A mold is the opposite of a cast. A release agent is typically used to make removal of the hardened/set substance from the mold easier.

Using these techniques to recast old plastic can be healthier for the environment and make room for a new cottage industry that can be performed at home, as long as you do not overheat the plastic and cause more fumes that it would take to recover just throwing the plastic away.

Using a mold and fire method of polymer clay, some hobbyists are making some fantastically detailed trinkets and jewelry. Of course this is not a recycling method, it is a viable way to get started making some of the things to add detail to a piece of jewelry or art that might not be so easy with something more recyclable, such as injection or particulate molding.

Give some of these brands a try!

And the best ways to reuse them

Plastic No. 1: Includes most soft drink and water bottles, peanut butter containers, salad dressing containers and food trays that can go in the oven. Most recycling programs accept these, although only 20 percent end up getting recycled. Many drink containers can be lightly heated for vacu-forming. You could use them for particulate blending if you have already brought them down to their original size before vacu-forming in to a bottle shape. Many will shrink down to original size with only a medium amount of heat. Then pour your shavings into your mold. Typically not recommended for repour, unless you have a good system for chemically melting the plastic. This may require zoning commission and OSHA inspections, not to mention, talking to the EPA about how you intend to dispose of spent chemicals.

Plastic No. 2: Milk jugs, juice bottles, bleach, cereal box liners, shampoo bottles and many household cleaner bottles fit in this group. Most curbside recyclers take these items, but not other things in this category such as shopping and trash bags. Possible to reshrink but really not a good plastic for projects unless you find a good project to use them for.

Plastic No. 3: This is PVC, used most prominently for house siding. It's also in many bottles, wire jacketing, medical equipment, windows and piping. It's not commonly recycled. But Poly Vinyl Chloride is easily glued, seamed, and particulate molded with basic glues and heated molds. The PVC I am referring to is the hardened type, found in the siding and the plastic water pipe/electrical conduit, vinyl house siding and windows and most toys. There is also the softened type used for chew toys, rubber duckies, shower curtains and other products that we use every day. But the soft PVC isn't as easy to work with as the stiffer of the types.

Plastic No. 4: This flexible plastic is used in squeezable bottles, bread bags, dry cleaning and shopping bags, clothing, furniture and carpet. Some recycling programs accept this type of plastic, and some bags can be returned to the original store. I have a page that details how one company is making a plastic board very similar to plywood from carpet, but it isn't easy to do without a purpose built heat press or oven. But with that in mind the bread bags, shopping bags, plastic clothing, and other fabric made from nylon, can be heat set the same way on a smaller scale. I have seen enterprising people make jewelry, hand bags, art, and many other things from Wal-Mart Tumbleweeds, clothes and other styles of this plastic.

Again, bear in mind, that any time you heat plastics, you are running the risk of releasing fumes that are harmful to you and those around you. Chemically melting isn't much better. Use precaution and lots of cross ventilation!

Big name for an easy process

Particulates is a fancy word for powdered. To use a particulated product means you have first ground it into a powder. Using flour to bake bread is one easy analogy. Flour is usually ground up wheat or other grain.

While the Particulate Material industry tends to focus this application in powdered metallurgy and powdered ceramics, this technology can also be applied to plastics. Many recycling systems are now using compressed powder rather than melting the material back into the raw for transporting. Foam, aluminum, paper, iron, and organics can be done this way as well.

It is well known that the integrity of chemically dissolved plastics is much weaker than virgin material, but just like the fusion of a powdered metal forms a better bond as opposed to pour molding, so does powdered plastic, resulting in stronger parts.

Many parts in gear reduction and combustion engines are now formed from particulate materials.

How can you use this to your home advantage?

For one, there is little or no chemical smell from the reactants or the release of many toxins like the mercide compounds associated with heat melting plastic for reforming. For another, it would be fairly simple to implement a simple grinding mechanism to create plastic powders from basic recyclable products, to reform into your products.

Once powdered you would compact the product into your mold and heat to just under the plastics melting point making this process less toxic than even welding the plastic with a bonding agent or heat bonding. Compacting the product in layers if properly done, could make the product stronger too. Think plywood or a bullet-proof vest.

Picture this: Recycling your own pop and water bottles? Broken toys? Old computer cases? Old electronics, such as alarm clocks and microwave doors? How about making a living by stripping down a wrecked car that you buy for a few hundred dollars. There is a huge list of plastic parts in the new cars!

Kind of helps you to realize why I hated the cash for clunkers program huh?

What can you do with this new recycling stream? Form up sculptures, like the resin cast statues, to sell on Etsy or Ebay. Of course, polystyrene and the like aren't very UV light friendly so I wouldn't recommend any outdoor products unless you could purchase the inhibitors.

Setting up my own system?

First you have to put together your mold. There are several ways this can be achieved. Many people use RTV in either poly or silicon based units to create their two part molds, by making a negative of the part you are going to copy. Take for instance the question in my comments: broken lawn darts. This casting set should likely be in three pieces to allow for easy separation of each Fletch vane. I would use the best of the darts. Oil them with WD-40 or other slippery substance that silicone would not stick to. Next smear a very liberal amount of RTV on six small pieces of quarter inch paneling board. Make sure there will not be any bubbles.

Then carefully place each wet silicone piece onto the fletch vanes, making sure that all areas of the lawn dart are covered. It would be good to mark the individual pieces now with a marker. Wait a day or so for the RTV to cure. Using a utility knife, carefully separate the individual pieces. Hindsight in my own mistakes says to make sure you have also bonded the six pieces into three with a bracing piece. This can be siliconed in place as well, but make sure that your vanes are spaced evenly. Doing this properly will help in making sure your parts align properly for the next steps.

Once you have removed the original lawn dart from the mold, use your knife to open three small weep holes on the fletching edge of each vane. Next clamp your mold pieces together in the proper order. Then using a liquified plastic solution, usually created by dissolving the proper plastic into a solution of plastic weld glue. For the thin vanes of the fletching, particulate powder can be used, but being consistent in the fletching will be next to impossible. The ideal scenario would be to use the injection method after softening the injected plastic.

With this said, metal tipped lawn darts have been banned from use in the US and Canada because of injury and death. Parts can be imported, but kits and complete units are impounded by customs. This is not something to make to sell. However, this product is like the proper handling of a handgun. Education is essential for proper use. Use common sense. Anyone participating in a lawn dart game must understand that in 1988 the Trade Commission banned them after three deaths and a seven year old boy in Indiana suffered irreparable brain damage due to the metal tipped lawn darts.

Other Ideas

You could also use a ceramic or metal form to pour your liquid or powdered plastic into then heat or let set. Now let me be clear I'm not only saying a form made from metal or ceramic. I'm saying that the form could be made of anything as long as it with stood the heat of the molding process. Scrap wood can easily be shaped by standard wood working tools and made into the negative of your part. Of course, RTV Silicone mentioned above is a decently cheap method if you do not mind the smell.

For one piece molds, there are any number of ways to vacu-form your molds, using old vacuum cleaners and ovens to soften the plastic you will use for your mold. This might be handy for making a repair piece for an old doll or action figure. It is a method used often times by the plastic modelling community for numerous parts.

The four basic types of molding (particulate, pour, vacuu-forming and injection) could be used for a long time for manufacturing.

But are you going to mass produce your project? Are you going to need a quick setting system for a more rapid production?

Injection molding alone is used for many different industries. In essence, Injection Molding is using a machine to squeeze the hot or chemically melted plastic into the mold. Injection molding mated to the particulate molding process, can speed your production considerably, as well as, as mentioned before, quite possibly making a stronger product. Keeping your equipment clean helps keep the fumes at bay as well. Stray plastic material can out gas for a long time after it has melted, and every time it is heated releases even more fumes.

I had thought that by this time I would have figured out a better system but arc heating and torch/flame heating are out of the question because of keeping the fumes to a minimum. So for now I use an array of several old soldering irons that are placed strategically around the mold to help in the even heating. However, that is a very inefficient system so I have been working on a new one that uses a small chamber and direct blown heat from that chamber.

Just some more thoughts on using the polymer clay for different purposes.

Now for another simple version and a very quick method available to break into the market. The RTV mold.

Using RTV silicone to build a mold from your positive is not a new process. In fact this process is as simple as pouring the RTV into a container around your object to be copied, letting it harden, then pulling the mold apart and repouring it with new plastic reagent.

Of course you can make this process easier by pouring half of your object's mold at a time that way a proper halving or even quartering can be achieved to pull the mold apart and be ready for the next pour.

It's a simple process. Really nothing to it. The same process can be used to make ceramic molds as well.

Go ahead and try it. I guarantee you will be trying to make molds of every thing once you get some experience behind you.

By the way, unless you are really lucky the first few times, you will have some mistakes. It is all part of the learning process right?

Just wondering what you think