Friday, February 19, 2010

Stripper Ejector Construction (step by step mold design) part 8 : add return pin

In ejector system, return pin is important, i was post about ejector system, include the function of each part, see it at this link, previous post is adding ejector pin and ejector guide bush in the mold, now next step is adding return pin, when we use mold standard or mold base blank, return pin always include in those mold base blank, if you have the catalog, return pin symbol is always RP, with dimension from X direction and Y direction, see picture below, yellow pin is return pin.



picture below is standard mold base, i get from Lun Kee mold base standard we can show dimension of mold base standard 150 mm x 150 mm with flange 200 mm, return pin diameter 12 mm, with the position 57 in Y direction from 0,0. and 24 in X direction, see the green line at picture below



add the return pin between ejector plate, and ejector stripper plate, the height of return pin same with surface of core plate. make hole in Ej. plate and core plate. like picture below



Spring for Return Pin
this spring will help move back ejector plate and ejector stripper plate after ejecting process, by calculate load of ejector system we can choose the best spring for return pin, too hard spring will difficult to assembly, but too weak spring will give some problem in ejecting process, this spring also help to prevent ejector stuck after ejecting process. see the construction like picture below
some mold designer prefer make hole of spring until half of core plate. which one do you use it depend on load calculation of spring.



Next step are add ejector rod and support pillar
To prevent large deflection in center of cavity plate, we must add support pillar as much as we can, arrange it so the deflection of cavity mold when plastic injecting is minimum, deflection can make gap between cavity plate and core plate, so flashing maybe appear, maximum allowable deflection depend on material, but generally it about 20-30 micron.
In this case I put 4 support pillar symmetrically

To move ejector system, we must add ejector rods, in little mold generally use only 1 pcs of ejector rods until 80 ton still save use only 1 pcs. but if your construction more than 100 ton or mold base size more than 400 mm x 400 mm use more than one pcs of ejector rods.
picture below shown 1 pcs construction of ejector rods.

2 comments:

Excelent work.
Just a small comment; Here in Sweden we do (mostly) not like springs to return the ejector plate to it's original position, we use a mechanical coupling to the ejector cylinder so we can make more than one throw if needed.
But again, excellent work, Greetings from Sweden

thanks Steen, Europe style mostly use long ejector rods, and mechanical coupling right? I read in some book from Europe,hope you have the picture, so many people can learn it more,
thanks you very much for your comments