Springs in a Mold

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 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.
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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.
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wrote:

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-)
--
Ed Huntress

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"Ed Huntress" wrote in message wrote:

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 it?s 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.
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wrote:


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.
--
Ed Huntress

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On 5/2/2019 12:37 PM, Ed Huntress wrote:
> wrote: > >> "Ed Huntress" wrote in message >> >> 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 it?s 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.
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wrote:


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.
--
Ed Huntress

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On 5/2/2019 7:49 PM, Ed Huntress wrote:

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.
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wrote:


Yeah, that rings a bell. It's been a long time since I covered toolmaking, so I'm vague on details. But I remember that the suppliers sold them color-coded for spring rate; round or square wire; and other options for which my memory fails me.
Have you looked at any of the mold-design books, Bob? I have one here somewhere (probably boxed, in the attic, or I'd look it up), and I distinctly remember that springs were a subject covered.
Good luck. If you do a little research, I think you'll find that the uses of springs in molds has been well worked out.
--
Ed Huntress

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wrote:

Rotational molds often use springs to even out the pressure of the clamps holding the lid closed. They survive many trips through a ~400 degree Fahrenheit oven... Do eventually need replacing. And we used both round and square cross section springs.
Used auto valve springs my son got for me at a junk yard for the one mold I made. http://alt-config.net/msbh/firstmold.html
--
William

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"William Bagwell" wrote in message wrote:

Rotational molds often use springs to even out the pressure of the clamps holding the lid closed. They survive many trips through a ~400 degree Fahrenheit oven... Do eventually need replacing. And we used both round and square cross section springs.
Used auto valve springs my son got for me at a junk yard for the one mold I made. http://alt-config.net/msbh/firstmold.html
--
William


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wrote:

Seems like the mold with springs would be hard to hold closed, and would likely leak. I've never cast baits, just bullets and sinkers.
Pete Keillor
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