Date
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Molding and casting
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Based on the occasional comments regarding injection molding (plastic) and die casting (metal);
I send the following link in case there are people not aware of it;
One of the best videos I have seen regarding injection molded parts (moldings), the molded on details, the tooling (molds), and the molding process. Start around minute 10 and again around minute 23.
-- Metal Diecasting is also briefly mentioned. Uses Very similar tooling (dies).
Ted Larson trainweb.org/mhrr/ -------- NASG.org -------- https://www.nasg.org/Clubs/RegionsMinnesota.php GN in 1965 |
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Jim Eager
Great video describing the very extensive, complex, labor intensive and expensive process of producing a modern state of the art model.
But I couldn't help noticing that even one of the Scale Trains guys used the word "sprue" incorrectly in the narrative. There is only one sprue in an injection molded part, and most of the time a modeller won't ever see it. It is the tapered cone formed by the sprue bushing, which mates with the injection nozzle of the molding press. It is where the molten plastic is injected into the mold. Branching off of that sprue are runners formed by the channels tooled into the mold plates to carry the molten plastic to the gates, where the plastic enters the actual part cavity. Often those runners branch several times to reach multiple cavities. It is those runners that modellers are familiar with and incorrectly refer to as "sprue". Most of the time the sprue and the largest runners are cut off of the part and set aside for regrind. You can see the press operator doing exactly this in the video. It may just be semantics to most, but the misuse of the term has always bugged me, probably because I took a program in injection mold design where the difference between a sprue and a runner was drilled into me. Rant over, back to your regularly scheduled discussion. Jim |
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John Barry
You learn something new every day. If what you say is true, it's not just modelers, but many, many kit manufacturers and tool vendors that are misusing the term. Think of the instructions to "carefully cut from the sprue" and the sellers of sprue cutting tweezers. I learned to stretch "sprue" by heating it over a candle in the early 60s. Guess I was really stretching runners. I feel your pain and outrage though. I've never seen a roofwalk referred to on a general arrangement drawing or ORER, only the running board. . . John Barry ATSF North Bay Lines Golden Gates & Fast Freights Lovettsville, VA 707-490-9696
On Saturday, February 25, 2023 at 04:27:39 PM EST, Jim Eager <jeager@...> wrote:
Great video describing the very extensive, complex, labor intensive and expensive process of producing a modern state of the art model. But I couldn't help noticing that even one of the Scale Trains guys used the word "sprue" incorrectly in the narrative. There is only one sprue in an injection molded part, and most of the time a modeller won't ever see it. It is the tapered cone formed by the sprue bushing, which mates with the injection nozzle of the molding press. It is where the molten plastic is injected into the mold. Branching off of that sprue are runners formed by the channels tooled into the mold plates to carry the molten plastic to the gates, where the plastic enters the actual part cavity. Often those runners branch several times to reach multiple cavities. It is those runners that modellers are familiar with and incorrectly refer to as "sprue". Most of the time the sprue and the largest runners are cut off of the part and set aside for regrind. You can see the press operator doing exactly this in the video. It may just be semantics to most, but the misuse of the term has always bugged me, probably because I took a program in injection mold design where the difference between a sprue and a runner was drilled into me. Rant over, back to your regularly scheduled discussion. Jim |
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Jim Eager
If what you say is true....You want I should dig out my textbooks and scan the appropriate pages for you? <g> I fully realize it is a finger in the dike exercise. Now, where did I put those gate cutters..... |
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John Barry
I believe you, but the term has been even more grossly mis-used than the bogus roof walk vice correct running board. Guess we need the Engineering Police to back up the Prototype cops. John Barry ATSF North Bay Lines Golden Gates & Fast Freights Lovettsville, VA 707-490-9696
On Saturday, February 25, 2023 at 05:32:36 PM EST, Jim Eager <jeager@...> wrote:
If what you say is true....You want I should dig out my textbooks and scan the appropriate pages for you? <g> I fully realize it is a finger in the dike exercise. Now, where did I put those gate cutters..... |
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Dennis Storzek
On Sat, Feb 25, 2023 at 03:56 PM, John Barry wrote:
You learn something new every day. If what you say is true, it's not just modelers, but many, many kit manufacturers and tool vendors that are misusing the term.Probably the confusion comes because Grandt Line and several other detail parts makers priced bulk moldings "by the sprue", meaning the complete shot. However, these parts are typically made in simple molds set up for 'parting line injection', meaning the machine nozzle fits tight against the side of the mold where it splits and shooting right into the runner. If the thing the nozzle feeds is the sprue, that makes the runner the sprue in this type of mold. I myself would rather explain the difference between a turnout and a switch than get into the semantics of injection molding. What I found surprising in the video was the use of a three plate mold with two long drops to mold bodies. Dennis Storzek |
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Jim Eager
Was that the locomotive body at 24:08 Dennis? Looks like the two deep drops feed the two sets of cross runners inside the body. The middle plate is acting as both the cavity for the roof of the hood and as a stripper plate to automatically remove the sprue, primary runner, and the two long drops that feed the core plate with the side slides that form the sides of the hood. The body had to be fed from the top because of the flaired radiators.
Jim Eager |
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Steve SANDIFER
According to Mirriam-Webster: Sprue 1: the waste piece on a casting (as of metal or plastic) left by the hold through which the mold was filled. 2: the hole in which a sprue forms
Wikipedia says: Some moldmakers distinguish the sprue, the gate, and the runner. The sprue is a large-diameter channel through which plastic flows, usually around the edges of the part or along straight lines. The runner is a smaller channel from the sprue to the individual part. An analogy may be found in a water system that employs a water main (sprue) and smaller pipes (runners) to individual houses. The gate is the location at which the molten plastic enters the mold cavity and is often evidenced by a small nub or projection (the "gate mark") on the molded piece.
J. Stephen Sandifer
From: main@RealSTMFC.groups.io <main@RealSTMFC.groups.io> On Behalf Of Dennis Storzek via groups.io
Sent: Saturday, February 25, 2023 5:13 PM To: main@RealSTMFC.groups.io Subject: Re: [RealSTMFC] Molding and casting
On Sat, Feb 25, 2023 at 03:56 PM, John Barry wrote:
Probably the confusion comes because Grandt Line and several other detail parts makers priced bulk moldings "by the sprue", meaning the complete shot. However, these parts are typically made in simple molds set up for 'parting line injection', meaning the machine nozzle fits tight against the side of the mold where it splits and shooting right into the runner. If the thing the nozzle feeds is the sprue, that makes the runner the sprue in this type of mold. I myself would rather explain the difference between a turnout and a switch than get into the semantics of injection molding. What I found surprising in the video was the use of a three plate mold with two long drops to mold bodies. |
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Jack Mullen
On Sat, Feb 25, 2023 at 03:13 PM, Dennis Storzek wrote:
Probably the confusion comes because Grandt Line and several other detail parts makers priced bulk moldings "by the sprue", meaning the complete shot.Dennis, By my recollection it goes way farther back. I started building plastic models way back in the fifties, and the instructions talked about removing parts "from the sprue". Blame Revell, Aurora, or Monogram. I'll bet a lot of us learned the term that way. Jack |
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Jack,
VERY interesting info. 25 years in molding, I never saw a sprue shipped to a customer. Runners, yes. Regarding the Wikipedia sprue definition; that does not match my experience; sprue was only the tapered plastic going into the mold. Whilst talking misnomers; If a part is made with a casting process, it is a casting, and details are cast on. If a part is injection molded, it is a molding, it is made in a mold, and details are molded on.
-- Ted Larson trainweb.org/mhrr/ -------- NASG.org -------- https://www.nasg.org/Clubs/RegionsMinnesota.php GN in 1965 |
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Dennis Storzek
On Wed, Mar 1, 2023 at 06:34 AM, Ted Larson wrote:
Ted, That needs further clarification. Strictly speaking CASTING is done using only gravity to fill the mold, while MOLDING makes use of externally applied pressure. However, even industry isn't consistent in this usage; "die casting" is a pressure processes similar to injection molding. Resin kits used to be simply cast, now the bodies, at least, are vacuum cast followed by a pressure cycle. My preferred usage is plastic is molded, while resin is cast. Dennis Storzek |
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