Why Are Molds Designed The Way They Are?

[Frank]

Just wanted to see if anyone could give me a good reason to have a mold with a 90deg port to fill a mold. I have talked to most of the mold makers and really have not gotten a good answer. On some of the molds I get bubbles in the upper most portion of the baits. Not a big deal with one color but with laminates it is. I rarely get these type of bubbles on a top pour mold, single cavity or multicavity. This is not a whos is better thing because they all make them like that. Just wanted some other thoughts on the subject. Frank

[smallmouthaholic]

Just wanted to see if anyone could give me a good reason to have a mold with a 90deg port to fill a mold. I have talked to most of the mold makers and really have not gotten a good answer. On some of the molds I get bubbles in the upper most portion of the baits. Not a big deal with one color but with laminates it is. I rarely get these type of bubbles on a top pour mold, single cavity or multicavity. This is not a whos is better thing because they all make them like that. Just wanted some other thoughts on the subject. Frank

Frank,

I have a 16 and 2 /12 cavity,custom CNC injection molds made this way. I was told the long runner was may so all the cavities have plenty of plastic to draw from as they begin to cool to eliminate dents. All three of them inject fine w/slow ,even pressure on the injector.

Al

[Frank]

So is this any differant. Both the same maker. The one on the bottom is a top pour the top one is the one in question, NOT that mold but that design. Seams to me that the baits that have larger apendages up high in the mold get bubbles. I know I am not the only one with that issue because I have talked to a few guys that have the same problem but were told they have to learn how to shoot the mold.

[powerworm]

i have heard that same thing from many many people but the only mold that has given me bubbles or i should say a bubbly was a beast mold i use somehow it just takes a different amount of pressure than the others just like it. it will leave a 3/16-1/4" elongated bubble in the top claw; so i piddled with it and piddled with it and finally got it to make consistent baits like the rest of the beast molds i have. i just believe there is that occassional mold made that for whatever reason just wants to be difficult!!

[Delw]

Just wanted to see if anyone could give me a good reason to have a mold with a 90deg port to fill a mold. I have talked to most of the mold makers and really have not gotten a good answer. On some of the molds I get bubbles in the upper most portion of the baits. Not a big deal with one color but with laminates it is. I rarely get these type of bubbles on a top pour mold, single cavity or multicavity. This is not a whos is better thing because they all make them like that. Just wanted some other thoughts on the subject. Frank

I will give you the most honest best answer I can its very simple too

because thats what the customer who asked for the first mold wanted as it was told to him by someone that IT WAS A MUST to have them at 90 degrees.

now for the detailed better explainatiion.

in most cases it makes NO difference. in some cases it does make a different, it has Nothing to do with drawing plastic from the resivour as you can see either way it will draw plastic from the resivour.

As far as the molds I make with 90's or straights is do to a few factors.

One mainly what the customer wants then also it has to do with material length. a mold with a 90 degree runner may fit in a mold 1-2 inchs less, thats 1 -2 inches less of material cost.

other reasons are alot of guys dont clamp molds down in a vice so there narrow and very tall, using a 90 degree port makes it so the can lay them down for easier shooting, and of coarse its the way I decided at the time to do it.

the paticular molds you have is that I personally like the top pour ones, but in all honesty when I first made that mold I had the stock all ready cut to length and went with it. it worked fine so I left it at that, on the side vent one as I said above the customer I made the first one for insisted on a side shot.

the big spruce size is kinda a overkill to be honest. its way way too big, spruces dont need to be more than 5/16 in width, BUT again is was something that People have been told that IS A MUST. 30 cavity nolds shoot just fine with a 1/4 - 5/16 90degreed side spruce.

for people who suck alot of air into a injector then a big spruce helps but not always.

in these 2 particular molds it doesnt make a bit of difference which way its done as I have done them both ways. both should shoot just fine, I have never heard any feed back other than people having there plastic too cold to shoot, I was always told that those 2 molds shoot flawless baits. They are shooting good right or are you saying there not and thats why the question?

I would never tell anyone to learn how to shoot so that aint coming from this shop.

Delw

[Frank]

No Del those shoot fine it was just the picture I had that was a great example of what I am talking about. Let just say the top one had a paddle at the end of the claw. That is where I get bubbles but mostly in the upper most one. But if it was made with a top sprue I have no issue at all. It is almost like the cavity fills then it trys to push the air and plastic back up to the upper most part of the mold. Thanks for the honesty Del, so it seams it is just what people want and not a design have to. I have alot of molds that I request to have top pour for this reason. Alot of them have an oversized sprue and really like that I dont have to top off. As for laminating with the top sprue, I dont have an issue with it at all. I have put an adapter on a Jacobs mold with the twinjector on top, the plastic went through all of that and down the mold then up to the baits and still gave a great laminate. Where it enters doesnt seem to matter even if it is a long way. Some work but some dont. Sucking air into the injetors when you are getting low on plastic is an art to master, you just slow down and go slow when filling. But that is not what I am talking about. Frank

[bear21211]

The main reasons we use the side ported molds is we found when shooting the molds with the port vertical they had more problems as the air was trying to come back out the same hole the plastic was going in on. Most molds when this first started like Stik baits were only vented at the bottom of the cavity. What gets filled 1st the bottom of the mold. That plugs the vent. By laying the cavity's down and injecting at 90 degrees the molds had more area to vent from. We then started using face vents which run the length of the cavity and allow the molds to vent out the top of the cavity better. Also when clamping the molds shut if using one mold the clamp would tip the mold over very easy as they were taller. Laying them on their sides make them much easier to work with in my opinion. Those are a couple of reasons that we do them this way and in no means is to conflict with why others do theirs the way they do them. We never had the option when we were using hand pour molds as we had to pour straight down the cavity. I personally do not think the 90 degree port is what is causing the bubbles. Most of our molds that have bubble issues always seems to be corrected by altering the vents and then they work fine.

Bear

[MuskyHunter]

So, what I think I heard was that venting is more important than the direction of injection.

[Frank]

Well one thing that I cant believe is that an injection mold fills from the bottom to the top. When hand pouring it is almost a must but to me I think it fills the cavity and pushes the plasitc to the end. I will have to work on that. Thanks Bear for the reasoning behind your way. That is the best reason I have heard. What if the mold is old and does not shoot well any tips on how to vent an old mold. Is there some kind of pattern? Frank

[Delw]

So, what I think I heard was that venting is more important than the direction of injection.

Yes

Well one thing that I cant believe is that an injection mold fills from the bottom to the top. When hand pouring it is almost a must but to me I think it fills the cavity and pushes the plasitc to the end. I will have to work on that. Thanks Bear for the reasoning behind your way. That is the best reason I have heard. What if the mold is old and does not shoot well any tips on how to vent an old mold. Is there some kind of pattern? Frank

Frank just grab a regular screw driver and drag it towards you away from the cavity ( dont push it) that will give you a vent line. do it a few times run some sand paper over it to clean the burr off and your good to go.

Molds DONT fill from the bottom, the push plastic from the Injection port top to the bottom push air out even if you shot it upside down.

were ever there is a vent will be the place the plastic pushs towards or pushs the air out.

[bear21211]

I was speaking more towards the Hand Pour molds as to them filling from the bottom. Not so much the Injected molds.They filled from the bottom up. Poured straight down the hole. Yes venting is way more important than the angle of the sprue.