Lost Foam Fail on Valve Cover

Welcome Wild Irish. It's nice to be able to put metal where you want it. I'll look forward to those posts.

Best,
Kelly

 

When you make a post, just select the upload a file button at the bottom then select browse you device, select the pictures you want to upload, and upload. After they are upload you can insert them into your post one at a time wherever your cursor may be by selecting either full image or thumbnail for each photo. Selecting full image inserts them full size and thumbnail will place them as an unexpanded smaller picture that can be clicked by viewers to be expanded and viewed.

Really need to see pics of the pattern, feed system, mold orientation and result to be of help, otherwise just shooting in the dark.

Best,
Kelly

 

Fails are frustrating. Have you LF cast other parts? If not that's an ambitious first project. Don't give up!!! You've done a lot (most all) of things very well. You really need to build yourself a contact pyrometer to know your pour temp. To me it just looks like it was poured too cold.

I would have gated it pretty much like you did but without the crossbar near the bottom. Not likely needed but I do understand why and didn't likely hurt at all. Just complicates degating a bit. The fins look like cold shuts but I would have expected them to occur at the bottom of the part not the top.

Some questions:

1. What are the overall dimensions of the part?
2. What is the wall thickness on the VC sides and roof under the fins?
3. What is the thickness and depth of the fins?
4. What foam was used on pattern and sprue/gate?
5. How was positioned in the mold? Vertically?
6. Did you use a pouring cup? If so can you describe it or have a picture?
7. What's the approximate weight of the part and sprue cross section dimensions?

Sorry for all the Qs. Just trying to cut to the chase. Depending upon the answers, I think you will be able to successfully cast that part with some tweaks.

Best,
Kelly

 

+1 rocco. Start a thread in the lost foam sub forum with a "Valve Cover" or something like that in the title and lets get to success. I'll respond tomorrow but my initial impression is just more heat and a little more discussion about wall thickness.

Best,
Kelly

 

OK Irish, let's get after this. I'll make some suggestions for mods that directionally will improve the likelihood of success. It's a long reply but these are the observations.

You really need to build or buy a contact pyrometer/thermocouple. Here's a thread that discusses either build or buy. The Mifco probes are readily available. I built mine. As long as you just dip the carbon sheath versions, they will last a long time (>100 dips) before the sheath is consumed. After doing so, pour that part at 1450F. The fail could be as simple as pouring too cold.

http://forums.thehomefoundry.org/index.php?threads/cheap-pyrometer-parts-list.33/page-2#post-1043

One important question I didn't ask is your source of aluminum. If it is a casting alloy from recycled castings, fine, but if it's wrought stock, it's not fine because the fluidity of most wrought alloys will be poor and cause such failures in harder to fill features like fins.

From your fin cutter, I'm guessing you already took in the thread below. From that thread, 3/32 thickness and spacing is starting to approach where my samples displayed some fails. However, the combination of only 3/16 side wall, and 3/16" under the fins will cause the metal to have lost a lot of heat by the time it makes it to the fins since they are more isolated on the top of the VC. That combination with too low of pour temp was probably fatal (poor metal fluidity hurts too but don't know that the case). The demarcation point for sand casting thinner walled high surface area aluminum parts seems to be 1/4" thickness. I almost never have issues until I start pushing below that. If you can afford to increase the side walls and roof to that thickness, it will make probability of success higher. It may cast as is with just higher pour temp, but as mentioned, several things are stacking against you. Lastly, check to make sure your fins actually are 3/32" thick. Even though my similar cutter was set that way, they cut undersize.

http://forums.thehomefoundry.org/index.php?threads/motorcycle-cylinder-sample.1521/

There's a case to be made either way for slight lean fins upward or downward but would lean your way so there isn't an undercut/overhang on inside of VC corner.

That sprue should be ample to feed the part. You know I favor my ceramic fiber offset basins but a can with ample buffer volume should work fine. The only caveat is a metallic cup will steal heat from the melt and if you were already marginal, can contribute to cold shuts. Hard to say without knowing your pour temp, but it looks like the thin tin can is topped with a thick walled tube and that will dramatically take heat from the melt. Lastly, if that can is just on or barely below the surface you are at very high risk of a run-out. That's where the pressure of the height of metal in the cup cause a leak to the surface instead of down the sprue. It's not a contributor to this fail but could cause your next one with a short pour. Burry the can/cup to the height of metal.

I would have done it just the same. If things are right, you probably don't even need the part that attaches across the top. Doesn't hurt and I do so too for a little additional security and handling strength but often omit such for making degating a little easier, but it probably helps will chances of success. I use a cove bit to narrow down the contact with on the gate but cove, chamfer, doesn't matter. I just do it to make degating easier.

The good news is, those are definitely cold shuts. You can tell by the rounded edges where the fill is incomplete. I say good news because that's back to pour temperature but means your mold media was stable in the fins which isn't always easy, so your bed vibrators must work. Fill the flask a few inches at a time evenly on each side of the pattern continuously vibrating while the mold is still light. When the mold gets heavy, it's harder to vibe the sand but all you have is the sprue which is an easy shape to pack.

The location of the failure is a bit unusual. I'd expect it to be where the coldest metal was which would ordinarily be at the bottom of the part. BUT, that extra feed you installed may have been taking the majority of available metal from the feed system allowing the bottom to fill first. In further support of this theory, this flaw line looks like where two (cold) metal fronts met. I'd omit that extra feeder.



The thing that vertical positioning has going for it is as you get deeper in the mold, the head pressure increases so the even though it's colder metal, it enjoys more head pressure to help fill the mold. I cant tell for sure how long the sprue is but longer sprue means more head pressure. I'd probably like to see something like ~>12" from the top VC features to the top of the (full) cup but don't get silly. If you don't want to cut up another steel can, I've used SonaTube (concrete forms) for flask extenders from the home improvement stores. But just a caution, if you have a sloppy pour that spills or pukes metal, like plastic buckets, the metal will compromise the wall.

It looks like you did a good job on the pattern. I know, frustrating. Don't give up. You'll get it!

Best,
Kelly

 

That's most likely decent casting stock. Just be advised though most are indeed cast, some are actually forged, which is not as desirable. Also, avoid chrome plated wheels. Wont hurt fluidity if they are cast but will foul up metallurgy.

The height of your cup also counts toward head. There's nothing magical about 12" but more height is more head at the slight expense of having to evaporate more foam on the way. When sprues get long the patterns get awkward and fragile so I add the longer sprue section with hot melt glue with the pattern buried in the mold up to that height, both coated of course. Just make sure the butt joint is nice and flat before proceeding to mold.

For the last intake manifold pour I did with the A60 and gantry, I stood on a wooden platform, not so much to control the pour, but to better see the cup. I have a steady rest on my pouring rig. Just a post and pipe at adjustable height but can set the shank handle on it. My full A20 with crucible and shank approaches 50lbs and can get a little uncomfortable at chest level with 20lbs of molten metal staring you in the face. I've seen a couple folks use pits and though it solves the pouring height issue, you must lower and retrieve the heavy mold from it. So lift the crucible or lift the mold, pick your poison.

As far as lifting equipment, I always ask, are you here to stay or just passin' through? If it's the former, you'll never regret investing time in and improving your foundry equipment, for ease of use, enjoyment, and safety. Especially for one-man show. -Just need to be able to make timely transition so you don't loose too much heat but even that can be compensated with pour temp.

If you are talking about increasing the wall thickness, I often do that with a small change in guide pin or cutter diameter with the same template. Got a picture of your pin router?

You're very welcome. Stay with it.

Best,
Kelly

 

No. You need more reach and any metal sheathed or unsheathed TC will fail when immersed in molten aluminum without a protective barrier. Here is the Mifco link.

https://mifco.com/shop/pyrometers/replacement-8-thermocouple-tip/

This TC is coated and intended for metal contact. You can build a carbon sheathed one for less than half that but the members here have good things to say about the MIFCO units. They are just a coated k-type thermocouple and most multimeters have a k-type port that that takes a mini k-type plug (search this) and will display temp directly in either C of F. You still need to run the TC wire inside a metal tube with some insulation to protect it. Look at the builds in the thread I linked and search the subject here. Some do without a TC through experience but IMO it's a must have tool.

You have a new primary candidate for cause of the valve cover failure

Got a link to it? I get a lot of questions about pin routers. I made mine (yah green sand castings) nearly 30 years ago.

Best,
Kelly

 

I just thought maybe it was still commercially available and I could refer people. Nice find. I get a few wiseacres on YT that criticize pattern making with the pin router instead of CNC. If they'd taken a minute to view my channel they'd see I do have a CNC router. I also show some basic hot wire techniques. Even if you have no machinery at all, it's surprising what can be done with just a hot wire, razor knife, abrasive paper, and a little skill and desire. Many people have woodworking skills and equipment but no CAD/CAM. As you know, that can serve quite well too.

Part of the purpose and message of my vids is LF casting is a useful tool and professional castings can be made in the home environment.......but it will take some effort. I'm not a great videographer and have no desire to become a YT star. It's less than 1% of viewers but I get these short sentence complaints about audio level. I just click mute and hide them from the channel and giggle my butt off. Why? A guy (me) posts such information on how to turn foam into professional looking castings at home and that's the most thoughtful thing they can come up with? If they are so easily defeated by the volume button, the chances they'll ever successfully cast or contribute anything useful to the channel is about nil,........and I don't like whiners and complainers, so they go bye-bye. There. That felt good! You're obviously part of the other 99%.

I see you have a mill. Do you have a lathe? I have all kinds of pins, and also collars of different diameters that insert into the table surface around the bit. They come in very handy for changing the cut dimensions from fixed patterns.

It's another Bad/Good news story. I have an elaborate hood and vacuum system I built onto my pin router. It was (initially) a disappointment. When you cut foam, it develops a mighty static charge and clings to everything.

Bad News: There is no level of velocity that can be practically achieved with a hooded dust collecting system that will overcome it.

Good News: If you keep a compressed air wand handy you can quickly blow the dust into the vacuum shoot in your hood. If you pay attention to which side of the bit you cut on, you can keep the majority of the chips ejected rearward. Still, after a session at my pin router I'm covered in foam. Wear a mask and a full face shield to avoid ingesting it and keep it out of your eyes. Blow/vacuum up the rest. -It's the life we've chosen.

Now you can try to use a brushed dust shoe like on my CNC router but it obscures your view of the cutting surface. The system I developed for my router (now) works very well, but it didn't start that way, and of course, the computer doesn't need visibility. You'd need to go to that thread for that.

http://forums.thehomefoundry.org/index.php?threads/cnc-router-up-running.1098/page-3#post-44151

I was actually going to manufacturer and sell them and even had developed owners manuals for them. I chose a different career path and sold the design package.

Best,
Kelly