Some of you wanted to know more about plastics. There are two kinds; thermosets and thermoplastics.
Thermosets are used where extreme heat requirements need to be met. An example would be the ashtray in my wife 2001 Taurus wagon. The tip of a cigarette is roughly 900 degrees F and will melt any thermoplastic. This kind cannot be remelted after it has been given a shape so that is ideal for an ashtray.
Another example for thermosets is a boat. A fiberglass boat (or a Chevy Corvette for that matter) is really a thermoset polyester structure reinforced with a woven glass mat. Boats are generally small production runs (a few hundred per model), and thermoset polyesters can be manually layered onto a pattern (typically a wooden mould) and allowed to harden to match the shape of that pattern.
Pretty much everything else is thermoplastics (that is what I work in). In thermoplastics, there are several processes. A process like rotational moulding has low tooling cost and is therefore used for low production volumes (say a few thousand parts per year). Processing costs are high (highly labour intensive).
A process like injection moulding has low processing costs per part, but when you build a mould, you may be looking at 50, 100, 150 thousand dollars, depending on the complexity. When you build one of these, you are looking at making hundreds of thousand parts per year, sometimes several millions of parts per year (imagine 64 bottle caps every 5 seconds, 24/7). A mould like that would cost a half million dollars, and would run on a million+ dollar machine.
Here is the question you all want to ask. You have this broken or missing part you want to replace, Maybe you can get together with other Pinto nuts and split the cost. Can you build a mould and do that?
Technically yes, but the tooling cost is staggering. Once you have your mould, you will be looking for a moulder to colour match and mould this part. Typically, unless you want at least 5000 parts, nobody will touch it (or you will be getting your one part, but still paying for 5000).
Plastics allow my big 2006 Chevy Impala (sorry - company car - I only get to pick the colour) to get 45 miles per gallon doing 60 on the highway. That big thing only weighs maybe 3200 lbs. It is however a disposable car, along with everything that was built since the late seventies. These modern cars will never be economically restorable (aside from taking good parts from a donor car).
When things were made out of metal, you could reproduce them if you had enough talent and patience. You did not have to spend huge amounts of money. That fabricated part was made to replace an original part which was expensive to produce; plastics changed that. However that only works when you need to mass produce something. Plastics will always beat metals for part cost when the numbers are large.
The enemy of metal is corrosion caused by oxygen and moisture. The enemies of plastics are degradation caused by oxygen, prolonged heat exposure, some chemicals (depends on the plastic), and in the case of car parts, ultraviolet rays (sunlight).
Keep your plastic questions coming. Plastics are fantastic.
What is your "take" on 2-part urethanes? I have been using these and handmade RTV rubber molds to cast model making parts, and I have to say, the stuff is extremely easy to use, VERY durable, and stands up to the elements very well. You can pre-color, paint, drill, sand, tap, carve, glue, and beat on it pretty well.
I built some small "lamp shields" 10 years ago for use on a pinball machine (these are light deflection shrouds for #555 bulbs, which generate a lot of heat), and they have held up without and deterioration or malformation whatsoever. I have also built a LOT of small 1:87 scale parts for model trains, which work extremely well.
Caveats include:
1) Tough to avoid pinholes/voids unless you go to a vacuum system
2) RTV molds can be expensive, especially where platinum systems are employed
3) Three dimensional molds are difficult (as opposed to molds where details of one side are not important
4) Copying of a part requires an intact sample with few/no flaws (as opposed to reengineering it from scratch)
5) Bulky, labor intensive
Advantages:
1) MUCH more affordable than machined injection molds
2) Does not require heat for liquefication (all solutions are at room temperature)
3) Can be catalyzed faster if heat is added to the process
4) Can be filled with glass beads to make the parts even lighter than they are, if weight is a consideration
5) Different formulations available (varying strength, desity)
6) By comparison, cheap. Small runs of a part can be cost contained (you don't need 5000 pieces to recoup a mold cost)
I am thinking of reproducing a number of items in urethane, the first being the silly dash cluster crumbling plastic mess. There are many others. I think urethanes are a very viable solution.
Chris
Anything to replace our plastic junk.....Within reason and of course PRICE.....This of course is a FREE market if you make a good part and we agree, PRICE IT WHAT YOU WILL........
popbumper
2-part urethane falls in that thermoset category. It is in fact poly-isocyanate, so make sure you don't breathe that stuff in. Nasty.
Thermosets have the advantage of allowing shaping without pressure. That is how boat hulls are made, laying by hand on a mould which can really be made of anything.
I have never worked with these; my expertise lies with thermoplastics (what the original parts are made of - the ones requiring the expensive tooling).
It certainly is worth a shot. The only caveat is that this is not a very stiff plastic, so it may be an issue if the part is load bearing. The good news is that few plastic parts were load bearing in the 1970s. They had not figured how to do this very well.