Incomplete casting pour

detail up will put any dross in your detail , and sand can float or sink the Navy rule of thumb was always detail down

V/r HT1

 

I like detail down as gas and dross will be in cope side...just have to be sure no sand is in the drag side

While I do not disagree with what you are saying.. and it will probably be an improvement to what he has been doing...the metal fronts are often split up like that in production tooling. We have one that feeds around 160 small castings at once. Lots of times in the casting cavities metal goes a million different directions as a casting fills. It is all about time and temperature. That is partly why I do not worry about Campbells theories so much. Sometimes casting cleaning and grinding determine where the ingates are located and there is just nothing you can do to prevent metal seperation...so you speed it up and heat it up to go back into solution as well as possible. Not ideal by any means but effective. When trying to get a thin casting to pour adding the ingate to the length of the casting will put more heat into the entire casting part. Moving the runners as close the casting as possible helps get the heat into the casting faster as well. The length of the casting will sometimes cool the metal off before it reaches the end. I realize that the casting has to be cleaned after it is cast so you can slowly reduce the length of the ingate until you get misrun or you can start small and add until you get a complete casting. There are many ways to skin a cat. A long thin ingate will reduce velocity/gatewash/turbulence/inclusions/pressure defects/rough surface finish....that is why I chose it.

 

I appreciate your thoughts, Billy as it makes more sense to me than just saying it's old-fashioned.... ;-) And I know there are a lot of ways to skin a cat. The reason I suggested just starting at one end and minimizing fronts is that
1) I have had very good luck with inclined long thin molds gated at one end. That is how I cast my flask sides---24 of them in pairs with very good results.
2) The use of multiple fronts can and is done by professional casters with industrial setups all the time. But this is all new ground for the OP. Simplification is
an approach that seldom causes more trouble. I think it would be good and feel good for him to just try casting one. Make sure that his mold, gate, temperature, sprue, etc. all work
by themselves. Then try two side-by-side. When that works, go fo four. Right now some of the factors are not working and because the system is so complex, it is hard to sort out what is going wrong.

Denis

 

I agree with you except he already has his match plate made. He has made individual castings on it.

 

I guess I missed that. I see he had two fill fully on one pour where his sprue was at one end of the runner. If he would have just inclined the mold for that one, chances are all would have filled.

It is also true that if he had a large pouring basin, so metal could be dumped in rapidly, large enough runner, hot enough metal, large enough gates that enough mnetal could be run into the system so that all four would fill. But, with his current setup, if it were inclined 2 could fill and then after that two more and that would likely work as well. Lots of ways to go. I really do think I would forget the match plate for now. Hand cut the runners and gates in various configurations until a setup worked consistently. Then make it permanent in a plate. I have one straight edge pattern that I have gates and runners that have worked in 3 different configurations, trying hand cut setuops. The one I made "permanent" with a wood runner and gate pattern is the simplest of the three and works the best. I feel like the matchplate will eventually get worked out, but probably now is impeding progress as it makes experimentation more work.

Denis

 

True...I have already made the match plate as mentioned. I am considering remaking the plate but want to get it to work first. Based on some recommendations I have received from here have made changes to it without ruining the plate as well as carved out areas in the sand to try and improve flow. Today I ran another pour. Two things I changed was increased the sprue size and made a taper to the gates into the parts. Still getting froze parts on the ends where it's thin. I poured fast and hard. I do need more weight on my mold to keep it from separating next time as well. I guess all Rookie mistakes. But he'll or high water I'm going to get this figured out...with some help of course..lol Thanks to all that are helping me out here I owe you a case of beer or something.

 

Weights are commonly used. But I like to use 1/4" or so plywood tabs that span from cope to drag and are perhaps 2" wide and maybe 4" long. They help align cope on drag as well as secure cope to drag.. A square-drive drywall screw in the cope and two in the drag and the mold is locked together. Using these tabs while packing also positively prevents the occasional but frustrating separation that can occur when packing the second half of the flask on the first. I have once in a while had the cope lift off the drag when packing, for instance if I neglect to lock the cope to flask. I put the fixed side of the tabs on the drag if I pack the cope first. This also allows lifting the assembled cope and drag by grabbing onto the cope or hooking my hoist onto the cope. None of my molds weigh less than 80 pounds and most weigh more than 150 pounds. So, being able to use a hoist to lower them to the ground from the molding bench is so much easier. It's no problem to hand flip most of them on the bench. But smoothly lifting to the floor without clumsily bumping them down is just too much hassle.

You might think the unweighted sand might heave up due to metalostatic pressure. I have not had that problem, but I also do not cast plaques which I thiank would be subject to this. I do not thik this mold would be at risk of separating if the cope were locked to the drag.

I know some folks get the same locking of cope to drag using woodworking clamps. And they can place downward pressure on the sand using boards that span the cope and are held by the clamps.

Denis

 

It is hard to give up on the plate. It was not cheap to make or easy to build. I made another one that doesn't have a runner or gates installed on it yet. Going to give that a try as mentioned to cut various configurations to just see what works thanks for the info

 

I was surprised you are continuing to feed with two gates per part. Notice the metal flows nicely to the middle where the mold is thick and has less resistance to flow. Then after the middle has filled it tries to flow to the thinner ends, but the flow front has frozen. You only have so many cubic milliliters of hot metal flowing through your gate. There is not enough to go both directions. The gate would have to be significantly larger and you would need a lot more head.

I love this picture. Which two pieces cast the best? And which two were mimicked in your last pour?



What am I missing? Pour from one end but cut your runner down to half size after the first set of gates takes off their flow.

I use bar clamps to hold my flasks together. It looks like you had some gap or the end of the flask floated. Bronze is heavy.

 

You definitely had float here. Your gates are big and have a nice transition. But the flow was trying to go both ways and fill everything at once.



Notice the shrinkage under the thick center. Is that OK or do you wand to eliminate it?

You notice the mold closest to the sprue filled? Others will chime in but I think you need to step your runner down from gate to gate to keep flow going all the way to the end. Plus you don't really have a gate. I would have a half size gate between the runner and the stem of the yoke. There just wasn't enough metal getting to the far end fast enough and it cooled.



Keep trying. You are almost there. It might be worth it to cut this match plate apart and get rid of the dead real estate between patterns. It could be half as long or less. Good pull on the patterns, by the way.

 

John, you have had a few patterns fill completely and we can see the backs of two of them. The two we can see do have shrinkage. Do the others also have shrinkage? I think HT1 mentioned the possible need for cores to prevent this. Good chance he is right or some form of risering will be needed. All you need is one more complication...

You also mentioned the trouble and expense of making the matchplate. Understood. And the matchplate sort of limits your options. One possible workaround for that might be to just grab some plywood, dowel, and bondo and make up a couple loose patterns of the same thickness and overall dimensions. You could then use them to simulate the problem less the fancy carving. You could also pretty easily make one with provision for a core and try casting it with a core. I can see that the design does not lend itself to easy inclusion of a simple spool-like core. But for testing purposes you could just use a simple spool and pin it down in the sand with wires to prevent it from floating. I used such a technique in this post

Casting Windmill Parts from Original Cast Parts. Celastic for Adding Draft

If you decide a core is needed, making a nicer core that fits well into a well designed coreprint and would need no pinning would be practical for production work. But to just try it out a time or two, this might be an option.

FWIW
Denis

 

Denis as far as the shrinkage...I didn't get any when I gated to the center of the part where it's thicker. Which would be the best way to make the parts for ease of cleanup, less grinding.
I have thought about a core and actually a friend with a CNC is making me a core box for this. Not sure how to set this up in the moulds but I may end up doing this because I don't want a riser to have to cut and grind.
I have several older parts made in the late 1800s and early 1900s that I have inspected with no signs of grinding or cleanup on the backs which leads me to believe they were made gated to the centers.
So I will keep plugging away at this. Definitely appreciate all the feedback.

 

I dont like to have the gating made with the pattern...never know when you may change a process or maybe even the metal you are making it out of and need the flexibility to make changes to the gating.
I like Dennis's method of locking the cope with screws but I am used to using weights and commonly use old fire brick for weights as I can also double them as a backsplash or if I stack them right almost double as a pouring basin..with the intent of it draining into the mold. There is a chance that you can knock sand into the mold or drop the cope with too much weight in the wrong place and his method eliminates that. If you had excessive finning on the casting you lost hydraulic pressure on the gating that may have kept you from making a complete casting.
As far as feeding into the heavy area...if you are not seeing shrinkage it is not necessary to feed it. Let the cold metal flow into the thick parts and keep the hot metal in the thin parts.

 

You don't need to do any grinding with a blind riser. You just put it in the gate a short distance from the pattern. For this flat emblem it took a large gate to eliminate shrinkage. I think just a blind riser a short distance from your pattern would serve you well. Ignore the aluminum feed system in this video to eliminate oxides in the casting.



Adding a core is super easy. Just make your core long and cylindrical and add core prints on each end. Lay it in just before you close the mold to pour.

 

I really respect your experience Billy.

I love gating in the pattern because I don't have ot remember how to gate it and I get consistent results. Maybe not good results but at least they're consistent. I have made 85 of those little plaques and they all came out fine time after time.

 

Usually ores a really easy. But, in this case the center of the core will not be on the part line. It will be well above the part line. So, rather than just having a half cylinder core print in cope and riser, he will need a cylindrical core that has truncated triangular ends that will set into correspondingly shaped prints. Maybe there would be an easier way, but this is what I was thinking.


Denis

 

Thank you! That may have came out wrong though...I use gating on the pattern.. I dont cast the gating with the pattern but add it later, so changes can be made easily. I even 3D print gating separately on my 3D printed patterns so they can be changed easily. When it comes to gating...sometimes we put way too much effort worrying about it when keeping the processes in range will make us much more consistent than gating alone. I see that here more than anything...if we have scrap there is usually a process that has been neglected. If all processes are golden...then it may be a gating issue.

 

Good point! I missed that seemingly unimportant detail.

However after looking again, I think his match plate does go to the parting line on the centerline of the cylinder, so it is just a matter of adding core prints and adjusting the parting line.

 

I'm with you now. I never cast patterns.