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Bob La Londe[_7_] Bob La Londe[_7_] is offline
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Default Springs in a Mold

On 5/2/2019 7:49 PM, Ed Huntress wrote:
On Thu, 2 May 2019 15:02:46 -0700, Bob La Londe
wrote:


On 5/2/2019 12:37 PM, Ed Huntress wrote:
On Thu, 2 May 2019 11:53:04 -0700, "Bob La Londe"
wrote:

"Ed Huntress" wrote in message
...

On Wed, 1 May 2019 13:27:47 -0700, Bob La Londe
wrote:

Typo corrected below ***

On 5/1/2019 1:23 PM, Bob La Londe wrote: Yesterday I had a customer
request I add springs to a mold at the last
minute. (Literally at the last minute. I had just sent him a screen
shot
of the cut simulation and was getting ready to take it to the

machine.)

Other than the irritation and disruption of last minute changes on

fully
approved designs I'm not against doing it, but I don't think I've seen
that before. Now, I am not talking about ejector pins. I am familiar
with them, although the types of molds I make don't make use of

them. He
was talking about springs to help open the mold. I can't

** help but

think about
how I would do it, but I'm not sure its really of any use. Most hand
injected or hand poured molds are just easily pried apart. For

most of
what I do the media doesn't not have any significant bond to the mold
material and a release agent is not even used. Sure for some resins a
release agent is used, but again the mold opens fairly easily.

I don't think I'd use springs in any automated operation either. The
molds halves are just attached to the platens (?) of the hydraulic

press
portion of the injection machine. Hydraulic pressure pushes them
together and hydraulic pressure pulls them apart. What purpose would
springs serve?

I explained that adding a new feature at the last minute would

delay his
order and increase the cost. I also asked him if he had seen that
before and how it was used. He decided to go with the original

design,
never answered if he had seen that before, but he did specify he

wanted
that on future molds. Ok... more money for me I guess.

Have any of you seen a mold with springs built in to assist with

opening
the mold? I visualize them in the types of molds I make and I

just see
them being an encumbrance.

Bob, return springs for injectors and springs to open molds were
common not many years ago, when I was covering the field. The
mold-opening springs were being replaced by hydraulics at the time so
maybe they're gone now.

But I'm not sure what kind of molding you're doing. Injection molding?
If so, there's plenty of design data around for mold springs. I just
did a quick check on Google to make sure I haven't lost my mind - yet.
d8-)


My work is 99.99% cold low pressure (100 psi peak maybe if somebody

is ham
handed and puts their body weight on the injector) injection or low temp
(under 1000F) casting molds. Split about 50:50. I have done a

handful of
"high pressure" molds for ABS and other thermo plastics, but its not my
primary market. This particular one was for a low pressure cold

silicone
media. They also have a very heavy steel core which is removed after
injection media has fully cured. The core will probably eject the

molding
from its weight alone. This customer also wants some ABS molds down

the road, so maybe that's what he was thinking of.

I sometimes make master molds from which I make silicone molds for

various
things. Candy molds, resin casting molds, etc. Molds to make

molds, but
this is my first mold to make a final product from silicone.

Ok. I guess I could see using springs in a mold that is used in a vise
under a table top injection machine. Still unless its a speed vise I
suspect it would be better to attach the mold to the vise jaws just

like you
do on a hydraulic clamping system on a bigger injection machine.

Opening
the vise opens the mold. I figured out how I would do it anyway,

and I will
make the springs easily removable. Then if he decides they are more

trouble
than they are worth he can just popped them out and pitch them.

When you shop for mold springs (they're still made by several
companies, as I learned when I Google-checked for my mental health and
declining memory), you'll note there are round-wire springs and
square-wire springs. Square wire is preffered; They're stronger and
can fit in a slightly tighter space.


Since its new to me I figured I'd just use springs from my junk
collection and measure the force of the springs. Then order springs to
suit after that. I set up a little jig a while back to measure travel
of springs under weight on a platform for calculating spring force. I
was doing some airgun modifications. Its a pretty simple tool and easy
to make.

I never would have thought to look for "mold springs" or "square mold
springs." Thanks.

Since there is some heat in when injecting thermo plastics I was
concerned about spring life.


I'll bet that heat is a consideration in applying mold springs. In the
end, you'll probably want to get some made for the job.


Just for the heck of it I searched on the McMaster Carr website for
"mold springs" and they produced several results for "die springs"
including long section that can be cut to length as needed.