Fastturbovet,
You were correct in most all of your assumptions. The 'ejector mechanism' is usually part of the mold itself. Most molds will have an ejector housing plate that have two other plates that can travel forward and back within this. The ejector housing plate is actually a plate with two shoulder rails that create a space for the ejector plate and it's back-up plate to move forward and back within. Some moldbuilders will spring load their ejector plates, and some will connect the plates to the molding machine so that the hydraulic cylinder of the mold machine will push and pull the ejctor plates.
You were correct with both of your assumptions about how the ejectors are pushed forward. Some old molding machines had a rod that pushed the ejectors forward whenever the platen came back during mold open. Most new machines have a seperate hydraulic cylinder to push the ejectors forward, either during mold open or after the mold is opened, or even push them forward several times, for parts that want to stick to the pins.
I machine 100% of the ejector pins that I buy, they come in standard lengths 5,6,7,8,10,12" etc. etc. and they need to be cut off and ground to length. If there is not a flat surface to put a pin on, you can grind the end of the pin to fit the coutour of the part. There are also other options for ejctors, instead of pins, you could use blades or sleeves. Blades are flat rectangular shaped and work basically the same as pins, however they can be places on thin ribs to help push them out (they are harder to put in because you have to create a rectangular hole that fits them, i use wired EDM for that). Ejector sleeves are used to push parts off of core pins, and they require another plate behind the ejector plates that holds the core pins in place.
As for used machines, my advice is to buy the best machine that you can afford that has all the features that you are looking for. Believe me it won't be as easy as it sounds. You will find yourself comparing many machine features and thinking, "This machine would be perfect if it had _______!"
I'll try and dig up some pictures of the ejctors side of a mold to show you what I am talking about.
Jim
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