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I am a hobby caster, but I have had some success with resin-bound sand, so here is a "If I were trying to cast a valve cover, this is how I would approach it" ideas.

These ideas may or may not work, but reflect some of the successful methods I have used.

1. Mix the sand for the entire cope or drag all at the same time in a cement mixing tub using a hoe, or some other method to mix the entire batch all at once.

2. Use Lino-Cure with the slowest set time on the catalyst (possibly no catalyst at all, to lengthen set time), so you have enough time to mix and ram the entire cope or drag.

3. Use a generous amount of either pattern wax or release agent on the pattern (I think you did this).

4. Use a generous amount of knife gates on either side of the mold cavity (you gating looks pretty good to me, but the gates could be longer/thinner, like is often used on thin pieces.

5. My solution for a thin casting such as this valve cover would be to use large runners down each side, perhaps 4 times larger than what you used.

I use vents/spin traps at the end of each runner, vented to the top of the cope.

The intent is to get a large mass of hot aluminum on either side of the mold cavity, in the runners, before the mold cavity begins to fill.

This may require a larger crucible or crucibles.

6. Use one or two very large sprues, and fill the sprue(s) and runners as fast as possible, letting the knife gates control flow into the mold once the runners are full.

Don't try to control flow into the mold using the runner or the sprues.

The knife gates should be at the top of the runners, and the gates should not start to feed the mold cavity until both runners are completely full.

7. I would use a series of risers across the top of the mold cavity, round, perhaps 2" diameter, 2" tall, necked down into the mold cavity to 1".

Perhaps six of these.

8. I would flame the mold cavity lightly with a propane torch, with wide soft flame, after molding it, to drive out any uncured resin.

9. I would spray on one or two coats of ceramic mold coat afer flaming the mold, burning off and lightly flaming each coat of ceramic mold coat.

This will give a superb surface finish on the casting, at least that has been my experience.

10. Superheat the aluminum more than normal, and assume that you are going to lose a significant amount of temperature when you fill the runners.

Choosing the correct amount of superheat on a thin casting is an art.

Too much superheat and you get a rough surface finish, and too little and you get an incomplete mold fill.

The ceramic mold coat will help if the aluminum is poured a little on the hot side.

I pour small molds in 356 aluminum at 1350F, and so for a large mold, you many have to be well above this.

Overheating the aluminum can cause a lot of gas pinholes, so don't get carried away with the superheat.

The superheat may be as little as 20 F additional; I am not sure.  You could experiment with a long thin rectangular test casting/mold, and see how far the aluminum will run without freezing, measuring and recording the pour temperature accurately.

11. One other thing I have started to do with thin patterns is to make the initial pattern from either a 3D print, or some other material that is not necessarily as strong as a metal pattern, and then cast a permanent aluminum metal pattern.  This assumes you have the casting process down, and you use double shrinkage on your initial pattern creation.  Any minor imperfections in the permanent aluminum pattern can either be buffed out, or filled with a good autobody filler.  If you do things correctly, you should need little or no fillers on a permanent pattern.

The beauty of using a metal pattern is that you can use it repeatedly with an automotive body-repair slide hammer, to remove the pattern from the mold, by attaching the slide hammer in various places and tapping lightly with impacts, to break the pattern/sand adhesion, without danger of damaging the pattern.  Again, mold release or wax are a must on the pattern.

For a one-off casting, the pattern only has to survive one removal from the sand, and so can be made of plastic, wood, etc.; assuming you get the first casting right.

12. If you let the pattern remain in the resin-bound sand beyond the strip time (resin bound sand has a set time, and a strip time), then you basically have glued the pattern permanently into the sand, and regardless of any mold-release agent, generally you will damage the pattern trying to remove it from the sand.

You must finish all ramming of the sand prior to the set time, else the sand will begin to set, and ramming will cause fractures.

It is essential that the entire cope or drag batch of sand be mixed and rammed at the same time, so the entire pattern can be pulled from the sand at the appropriate strip time.

Hope this helps.

Just my slant on how I would approach casting this piece, with the understanding that I am not a foundry person, but a backyard casting person, who has used quite a bit of resin-bound sand successfully with aluminum and iron.

Good luck.

You are oh-so-close to a perfect casting.

Edit:

I allow my patterns to fill upwards, and I think that is what your mold was designed to do.

I have had to vent the high points of the mold with small holes out the top of the cope, else the resin-bound sand will trap air and create large air bubbles at the high points of the mold, like 2" in diameter.

.

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On 08/06/2021 at 11:18, PatJ said:

I am a hobby caster, but I have had some success with resin-bound sand, so here is a "If I were trying to cast a valve cover, this is how I would approach it" ideas.

These ideas may or may not work, but reflect some of the successful methods I have used.

1. Mix the sand for the entire cope or drag all at the same time in a cement mixing tub using a hoe, or some other method to mix the entire batch all at once.

2. Use Lino-Cure with the slowest set time on the catalyst (possibly no catalyst at all, to lengthen set time), so you have enough time to mix and ram the entire cope or drag.

3. Use a generous amount of either pattern wax or release agent on the pattern (I think you did this).

4. Use a generous amount of knife gates on either side of the mold cavity (you gating looks pretty good to me, but the gates could be longer/thinner, like is often used on thin pieces.

5. My solution for a thin casting such as this valve cover would be to use large runners down each side, perhaps 4 times larger than what you used.

I use vents/spin traps at the end of each runner, vented to the top of the cope.

The intent is to get a large mass of hot aluminum on either side of the mold cavity, in the runners, before the mold cavity begins to fill.

This may require a larger crucible or crucibles.

6. Use one or two very large sprues, and fill the sprue(s) and runners as fast as possible, letting the knife gates control flow into the mold once the runners are full.

Don't try to control flow into the mold using the runner or the sprues.

The knife gates should be at the top of the runners, and the gates should not start to feed the mold cavity until both runners are completely full.

7. I would use a series of risers across the top of the mold cavity, round, perhaps 2" diameter, 2" tall, necked down into the mold cavity to 1".

Perhaps six of these.

8. I would flame the mold cavity lightly with a propane torch, with wide soft flame, after molding it, to drive out any uncured resin.

9. I would spray on one or two coats of ceramic mold coat afer flaming the mold, burning off and lightly flaming each coat of ceramic mold coat.

This will give a superb surface finish on the casting, at least that has been my experience.

10. Superheat the aluminum more than normal, and assume that you are going to lose a significant amount of temperature when you fill the runners.

Choosing the correct amount of superheat on a thin casting is an art.

Too much superheat and you get a rough surface finish, and too little and you get an incomplete mold fill.

The ceramic mold coat will help if the aluminum is poured a little on the hot side.

I pour small molds in 356 aluminum at 1350F, and so for a large mold, you many have to be well above this.

Overheating the aluminum can cause a lot of gas pinholes, so don't get carried away with the superheat.

The superheat may be as little as 20 F additional; I am not sure.  You could experiment with a long thin rectangular test casting/mold, and see how far the aluminum will run without freezing, measuring and recording the pour temperature accurately.

11. One other thing I have started to do with thin patterns is to make the initial pattern from either a 3D print, or some other material that is not necessarily as strong as a metal pattern, and then cast a permanent aluminum metal pattern.  This assumes you have the casting process down, and you use double shrinkage on your initial pattern creation.  Any minor imperfections in the permanent aluminum pattern can either be buffed out, or filled with a good autobody filler.  If you do things correctly, you should need little or no fillers on a permanent pattern.

The beauty of using a metal pattern is that you can use it repeatedly with an automotive body-repair slide hammer, to remove the pattern from the mold, by attaching the slide hammer in various places and tapping lightly with impacts, to break the pattern/sand adhesion, without danger of damaging the pattern.  Again, mold release or wax are a must on the pattern.

For a one-off casting, the pattern only has to survive one removal from the sand, and so can be made of plastic, wood, etc.; assuming you get the first casting right.

12. If you let the pattern remain in the resin-bound sand beyond the strip time (resin bound sand has a set time, and a strip time), then you basically have glued the pattern permanently into the sand, and regardless of any mold-release agent, generally you will damage the pattern trying to remove it from the sand.

You must finish all ramming of the sand prior to the set time, else the sand will begin to set, and ramming will cause fractures.

It is essential that the entire cope or drag batch of sand be mixed and rammed at the same time, so the entire pattern can be pulled from the sand at the appropriate strip time.

Hope this helps.

Just my slant on how I would approach casting this piece, with the understanding that I am not a foundry person, but a backyard casting person, who has used quite a bit of resin-bound sand successfully with aluminum and iron.

Good luck.

You are oh-so-close to a perfect casting.

Edit:

I allow my patterns to fill upwards, and I think that is what your mold was designed to do.

I have had to vent the high points of the mold with small holes out the top of the cope, else the resin-bound sand will trap air and create large air bubbles at the high points of the mold, like 2" in diameter.

.

 

This is all really great info thanks Pat.

I can implement a lot of these. I dont have control over the foundry though, so pour temperature changes probably isnt an option. I also cant pre heat the mould to help the problem.

This is what Im currently thinking for the runner. 2 sprues and runner on each side.

The in gates arnt great and they just rise up through the core becuase it was convenient. No real knife gate. 

I can try add spin traps/risers but it doesnt work well at the bellhousing end (green end)

Im going to try do the filters horizontal at the bottom of the sprue. Ive never tried this. Do you think this is a bad idea?

125109458_SumpRunner003.JPG.43f1d2f7441811ca17d2a0f72d873f4d.JPG1524900496_SumpRunner004.JPG.bcc179770af98a807506669f89865a97.JPG

 

 

Can you talk more about the 'Lino-Cure' system? Whos a good supplier? Is it a 3 part system? What strip/cure times do you think I could get? Do you have a recommendation of type to try?

The mixing of sand is the worst part of the whole thing and thats whats stopping me from getting things done.

I need to do about 300lbs in 1 batch. So if it took 1-2hours to cure that would be perfect. Also if it could be done in a concrete mixer!

My current plan is to re work the patterns and pack them at the foundry. The issue there is I dont have any control over the sand density/strength or how carefully they will pack it. From what ive seen, their resin quantity is a low as possible so its easy for them to remove after pouring. The parts they make dont have a lot of fine detail so the sand doesnt need to be strong. So ideally I would like to mix the sand myself.

If you could help figure out a good binder solution that would be awesome. Im planning to have another go at the end of next month so I would like to do some sand testing beforehand.

 

 

 

 

 

 

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Working with a Lino-Cure supplier. Thanks for the suggestion (even though you suggested it ages ago!:))

Should have some in the next couple of weeks. Work time of 50min, strip time 80mins which should be good.

Ill get a concrete mixer and see if I can do 300lbs in one go!

@PatJ What ceramic mould wash do you use? I use to use Zircon but only used it on Iron.

 

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I am just catching up on this thread.

Looks like you found some LinoCure; that stuff is the best molding product I have ever seen, and gives great results with a set time that can be varied widely.

I use Velvacoat (tm) VA 9078.

https://www.ask-chemicals.com/fileadmin/user_upload/Download_page/foundry_products_brochures/US/Coatings_USA.pdf

Be aware that some of the coating material in the above pdf I think is designed to be used to coat foam, ie: foam used in the lost-foam engine block casting process, and not necessarily to be used with sand molds like you are using (check me on that).

The Velvacoat prevents metal penetration into the sand, and would guess that it would work with aluminum, although I think it is specifically designed for use with iron.

And it looks like you got some of the good mold cement.

I bought some of that the other day.

One thing I have noticed about resin-bound sand is that it seems to trap air; ie: it is not very porous, and so I vent the high points of each mold with a very small 12" long drill bit, or a thin piece of piano wire used as a drill bit.

I ruined two good castings by trapping large air bubbles at the top of molds.

The bubbles were about 2" long.  People who have done a lot of iron castings tell me this is not possible, but then again they don't use resin-bound sand, and so they don't understand how it traps air.

 

The partial fin fill may be due to air, or may be due to too low of a pour temperature (or something else).

What pour temperature are you using.

I think I generally use 1350 F for aluminum, but for a casting the size of yours, it may have to be significantly higher.

As with all metals, the higher the pour temperature, the worse the surface finish.

 

The Linocure instructions recommend the molds sit for I think 48 hours, but it also says that if you can't wait 48 hours, then the molds can be lightly flamed to finish off the cure process and drive out any uncured resin.

I use my molds immediately after they set (within an hour), and so I lightly flame the interior surfaces with a 1" propane burner (no concentrated heat, but just a gentle flame).

Then I spray on a layer of Velvacoat, burn that off, and then lightly flame the mold interior again to drive off any residual alcohol from the mold coat.

The slightest amount of residual resin or alcohol will make a mess of the surface finish.

 

I have used a cement mixer to mix sand before, and I use it without the blades inside of it.

I use a boat paddle to help mix it.

Normally I use a large commercial kitchen food mixer, but if the mold is large enough, I have to use the cement mixer.

 

I have had excellent results with Linocure, and even better results with Velvacoat.

The filters are not a bad idea if you can get enough flow through them.

I have used filters with aluminum, but since I started used spin traps on the ends of my runners, I don't use filters anymore.

The spin traps use more metal, so filters would minimize the crucible capacity.

 

Resin bound sand releases fairly easily if you stay within the "strip time", but if you exceed the strip time, you will generally damage the pattern when removing it, since the resin after strip time becomes like glue.

And I have found that once the mold sets, it needs to remain on a very flat surface for about 30 minutes, else it will move/warp a bit, even though technically it is a solid mass.

After about 30 minutes (full set), you can do whatever to a resin mold, ie: drill, scrap, or otherwise cut/modify it, and it will not change dimensions.

 

Another trick I have seen is to use a vacuum cleaner/shop vac to somehow pull a slight vacuum on the top of a mold.

I think the vacuum works through the permeable sand.  You would not want to hook a vacuum directly into the mold cavity.

I am not sure how you would rig that on your mold, but it is a method that apparently works, and helps fill tall thin molds.

I have not had to use the vac method, but I do vent the high spots in my molds, and I get a small amount of aluminum out of them when I pour, so I know the metal is remaining fluid for the entire mold fill, and fluid enough to fill a 1/16" diameter hole at the top of the mold.

 

Once you get use to using Linocure, mold making becomes routine and relatively easy.

Once you find the right pouring temperature, you can generally get a good casting with every mold.

My success rate with resin bound sand is basically 100%.

 

Looks like you have made some serious progress, and are definitely on the right track.

.

 

 

 

 

 

 

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