still learning, what causes this texture

[GreenTwin]

780 C = 1,436 F

The lower temperature pours seem to give a shinier smoother finish, and the higher temperature pours give a more dull coarse finish; that has been my experience.

Since your pours are shiny, I think your pour temperature is good, and I agree with McKee about the sand probably being the culprit.

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[ddmckee54]

GreenTwin, thanks..... but I think you probably meant DaleW. He was talking about the sand, I was just talking about the IR gun.

 

[GreenTwin]

LOL, I am not sure who I am referring to.........just blogging along until the third cup of coffee (tall glass actually, a cup just does not cut it) kicks in.......

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[werowance]

ill go along with not pounding that new sand hard enough for one thing. where i took a brass tube to vent the center of the wheel - that area came out smoothe as a a babys butt. when it hit the wheel form the texture was not. i mean it was much better with this new finer grain sand the ok85 i think was the number - but where i packed it around the form i think must have needed to be harder. the pushing the tube thru to vent the sand and the movement of it i think packed it harder there and that was the smoothe part. i didnt get a photo of it before i cut it off. next session ill try to pack the crap out of it and see what i get. also took a visit to my moms shut down potery business. clinch mountain pottery. she had large gas fired kilns. one was run on railroad track and the hood moved over the stacked unfired pottery and the doors shut down over it. bigger than my full size truck. she had a few pyrometers laying around. old analog ones with long leads with that white wire wrap around it. i didnt get a chance to talk to her about them but thinking of seeing if i can procure one of those and see what i can come up with.

 

[GreenTwin]

What sort of sand/clay mixture ratio are you using ?
And, if the sand is not mulled (mixed) well, you can have pockets of high/low clay content, which can affect surface finish.

myfordboy mulls his sand on the floor (requires good knees).
You can fold the tarp over the sand, and just walk around on the sand, turning the sand over, and walking, to mull it.

Edit:
The process of mulling greensand (with a mechanical muller) smears the sand and clay together, and then breaks the sand up, doing what I call "fluffing" the sand. Fluffed greensand can be compacted in the mold; non-fluffed greensand does not compact very well.

Bound sand does not work the same way.
There is no clay in bound sand; it is only sand and binder (resin or sodium silicate).
If you try to do much compacting with bound sand, you end up fracturing the sand, and causing it to shift away from the pattern and crack.
Bound sand is pressed into place tightly around the pattern, first with the fingers, then with the heels of the hands.

 

[werowance]

What sort of sand/clay mixture ratio are you using ?
And, if the sand is not mulled (mixed) well, you can have pockets of high/low clay content, which can affect surface finish.

myfordboy mulls his sand on the floor (requires good knees).
You can fold the tarp over the sand, and just walk around on the sand, turning the sand over, and walking, to mull it.

Edit:
The process of mulling greensand (with a mechanical muller) smears the sand and clay together, and then breaks the sand up, doing what I call "fluffing" the sand. Fluffed greensand can be compacted in the mold; non-fluffed greensand does not compact very well.

Bound sand does not work the same way.
There is no clay in bound sand; it is only sand and binder (resin or sodium silicate).
If you try to do much compacting with bound sand, you end up fracturing the sand, and causing it to shift away from the pattern and crack.
Bound sand is pressed into place tightly around the pattern, first with the fingers, then with the heels of the hands.

70%sand 30%clay by volume. measuring it out in pint jars. i hand mull it taking hand fulls and rubbing both hands together and letting it fall back in the batch. i use a very large pan to do it in. my fingers and hands cramp up and it definately will wear down some skin along the way. doing it in small batches of 7 pints sand and 3 pints of clay at a time. a small batch usually takes a few afternoons of my time after work before i figure its good enough

 

[ddmckee54]

I think for the initial mixing of the green sand you pretty much have to beat the crap out of it. (Or more precisely, beat the clay onto the sand.) I remember tales from years ago on Alloy Avenue, guys would cover the sand/clay mix with a tarp then drive over the tarp with their car, fold the sand over, and repeat - until all the sand was thoroughly coated with clay. If you have close neighbors they just might question your sanity, driving back and forth over a pile of sand.... But hey, if it works that's all that counts.

 

[werowance]

well, i can certainly put it on a tarp and do this. i have rammed 2 test molds without a pour and 2 test molds both with aluminum pours (discarded the burnt sand each time) but definately cant hurt to ram it more with the truck. probably better that way that sanding the skin off my hands any how

 

[werowance]

also this will hopefully be my next pour - the cho cho stack to go along with those 2 wheels i cast. below is how i plan to do the mold. is this ok? rough hand drawing with poor diminsions but hopefully close enough to represent the plan. what do you think of this setup for the mold? would it need a small vent somewhere in the middle of the stack?

 

[D and D]

I am not sure if an IR pyrometer would work correctly or not.
I will have to research using that type with aluminum.

Some folks make their own pyrometers, and that can be done on a budget.
I have not made one, but they look relatively easy to make.

The connection point of the leads to the thermocouple can affect the accuracy of the pyrometer, but it is not really necessary to have an accurate temperature reading, but rather a consistent reading, so you can find a temperature that works well, and then duplicate that temperature, regardless of what that may be.

Generally aluminum 356 pours in the 1,350 F range.
Some go a little cooler, and some a little hotter, depending on whether the casting is thick or thin.

Here is one potential pyrometer that perhaps could be adapted to be a submersible type.
I see folks purchasing a piece of graphite rod, drilling a hole partway through it, and putting the thermocoulple inside.
The graphite is attached to a piece of electrical conduit, or similar steel tubing.

The wiring that goes to the thermocouple needs to be high temperature, and I think the white braided material is high temperature.
They also have round ceramic insulators that can be used on the hot end.

No guarantees as to how well this would work.
I need to research the home-built pyrometers a bit more.

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View attachment 158552

I use one no issues, i checked it against one at work at 500 deg c and it was 8 deg low. you can get the thermocouples of Amazon for a few $.

 

[GreenTwin]

also this will hopefully be my next pour - the cho cho stack to go along with those 2 wheels i cast. below is how i plan to do the mold. is this ok? rough hand drawing with poor diminsions but hopefully close enough to represent the plan. what do you think of this setup for the mold? would it need a small vent somewhere in the middle of the stack?
View attachment 158637

Somehow I missed this post.

The "pour tube" is called the "sprue".
Not sure why you have two of those, unless you are planning on pouring from two crucibles at the same time.

The area at the bottom of the sprue is the "basin".
I have read that a basin at the bottom of the sprue should not be used, since it causes the metal to strike the bottom and splash back upward, intraining sand and air into the molten metal.

The "feeder tubes" are called "runners".

The area between the runner and the mold cavity is called the "gate".
You can have one or more gates, and the gates can be rectangular, or long thin gates called "knife gates" used on thin parts like plaques.
The runner is normally "V-shaped", but I have seen many use a "U-shaped" runner with good results.

If you are using a core in the center of the stack, then the core needs a vent hole through it, such as can be made with an 1/8" or 1/4" wood dowl, and extend the ends of the core vents up through the cope and out the top of the mold.

If you have a core, you may have to gate into one or both sides of the mold cavity.

The bottom of the sprue should transition smoothly into the runner(s), and not have a basin at its bottom.

Avoid abrupt turns in the sprue/runner system, since you are trying to get a smooth laminar flow of metal, with velocity that is not too high, and without turbulence that can intrain air and sand into the molten metal.

I use the gates to control the metal flow/metal velocity.
I put the gates at the top of the runner(s), so that they will scrape off floating slag.

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