The Bucket Foundry

[Flettner]

The underside of the mold plate, then mold plate removed leaving cavities for the top sand mold to fill and follow the part line. Wire rods are to leave escaping gas vent holes. Also help with the CO2 gassing.

[Flettner]

I'm doing the CC601 melt first as I'm copy casting some core mold parts for one of my cylinders. CO2 sand is just too weak and to fiddly to pack the core box. Copied into metal allows me to use Shell core Sand, much stronger and easy core box fill.
Next week LM13 and some cylinders that should have been done a year ago, better late than never I guess.

[ken seeber]

Well, not a patch on Fletto's progress, but have been dabbling at brief intervals with the fish mould. So, mounted the 3D printed half on a basic pattern plate. This had 2 off 5 mm holes printed in on the back face on the centreline, these were tapped out to M6. Then on the pattern plate, 2 holes were put in for these screws and another 2 for the 2 exposed 6 mm dowels. This will mean that 2 mould halves will be made and then located together with dowels so that the 2 fish cavities will perfectly align (I bloody well hope so ), due to the symmetry of the simple shape.

Then it was waxed, not that it might have needed it, to help in the release, this being assisted by the 4 off M6 screws that are shown flush with the pattern plate. I reckon if I used plumbago it'd be everywhere but in the right place.

Then it was filled with a 50:50 mix of foundry sand and plaster of Paris. Used this cos it'll give a good finish and I don't have any sodium silicate to go the CO2 route.

With two halves being made, then it's a matter of cutting in an ingate and some small vent grooves and then filling with lead, with the secret feature being cast in during the process.

[WilDun]

Then it was filled with a 50:50 mix of foundry sand and plaster of Paris. Used this cos it'll give a good finish and I don't have any sodium silicate to go the CO2 route.

I'm a fan of the plaster/sand mix, - reckon it is a good, cheap and simple way to go - It could also actually be taken to red heat to melt out a sacrifical printed plastic pattern - saving a lot of time ( an alternative to doing it in the traditional good and well proven manner!)

[WilDun]

............. I'm copy casting some core mold parts for one of my cylinders. CO2 sand is just too weak and to fiddly to pack the core box. Copied into metal allows me to use Shell core Sand, much stronger and easy core box fill.

How do you intend to put the coresand into the hot metal mould? (sorry, using the good old Pommie/Kiwi spelling here - all very confusing these days!).

[Flettner]

See what I have to work with, bugger, this is a two piece pattern. Forgot about the second piece when packing the first mold but I'm not giving up, I'll make a special side insert that will glue on and keep the molten metal from escaping.

[Flettner]

How do you intend to put the coresand into the hot metal mould? (sorry, using the good old Pommie/Kiwi spelling here - all very confusing these days!).

Here is the process, this is the water core sand box I want to copy, I've already molded up one half.

[Flettner]

The sides of the pattern are tapered but I don't want to taper the ends so I've made straight to taper end pieces. Makes the mold more complicated with more parts but will allow for none tapered pattern.
Pack the mid section, set then one end, set, then the other end. Bottom done.

[Flettner]

Top half pack and set. Disassemble, remove pattern, reassemble and stick together with some Core Fix foundry glue. Runner and riser, ready to pour hot metal in.
This will make two replicas of my core mold but in metal so I can use the hot Shell sand mold system.

[Flettner]

Sorry Will, to answer your question, I don't have a Shell molding machine so for this one off / low run stuff I pour the fine shell sand into a cold metal mold, place in the oven at 180/200 for a time, about half an hour, then with gloves on undo the capscrews holding it together, remove sand core.
Then wait for the core box to cool off, repeat.
Sloooow but makes real nice cores.

[Flettner]

The patch up.

[ken seeber]

Did a another of the plaster/sand moulds. Came out pretty well, "smooth as a baby's bum" as they say. Dowels fit too. Still quite damp, so as it was 35 deg today, I reckon a couple of days outside will do it. I think I'll preheat them to around 100 deg prior to pouring though. Design weight is around 1.9 kg.

[Flettner]

Did a another of the plaster/sand moulds. Came out pretty well, "smooth as a baby's bum" as they say. Dowels fit too. Still quite damp, so as it was 35 deg today, I reckon a couple of days outside will do it. I think I'll preheat them to around 100 deg prior to pouring though. Design weight is around 1.9 kg.

Would that mixture be suitable for an aluminium pour?

[Grumph]

Would that mixture be suitable for an aluminium pour?

I'd doubt it - in a previous career I used plaster of paris for moulding some electrical components. It's damm near impossible to get the water content down far enough to withstand thermal shock. The sand mixture may give it better qualities but it's quite a temperature stretch from lead to aluminium.
I had several moulds crack from thermal shock - even preheated.

[ken seeber]

I sort of think Greg is right, in that some time ago we did a "lost PLA" printed casting and after a lot of heating to burn the PLA out using lots of heat with an LPG burner(and it was really smelly), the plaster did crack. But I reckon going to a 150 deg or so in a slow fashion it should be right.
In terms of gas generation I think the plaster in itself should be ok as my memory of hot plaster is that it doesn't smell, whereas shell core sand etc does smell, probably due to the binder going of, creating gases. Irrespective, being essentially non pervious, any gas that is generated must be able to escape via venting, no worse that a regular permanent mould situation.
I'll do a couple of extra moulds and when back, we have to do another piston batch pretty much straight away, as well as another lead batch, so I'll do them then.

Here’s an excerp from Wikipedia:

"Details[edit]
The plaster is not pure plaster of Paris, but rather has additives to improve green strength, dry strength, permeability, and castability. For instance, talc or magnesium oxide are added to prevent cracking and reduce setting time; lime and cement limit expansion during baking; glass fibers increase strength; sand can be used as a filler.[1] The ratio of ingredients is 70–80% gypsum and 20–30% additives.[2]
The pattern is usually made from metal, however rubber molds may be used for complex geometry; these molds are called Rubber plaster molds. For example, if the casting includes reentrant angles or complex angular surfaces then the rubber is flexible enough to be removed, unlike metal.[1] These molds are also inexpensive, reusable, more accurate than steel molds, fast to produce, and easy to change.[citation needed]
Typical tolerances are 0.1 mm (0.0039 in) for the first 50 mm (2.0 in) and 0.02 mm per additional centimeter (0.002 in per additional inch). A draft of 0.5 to 1 degree is required. Standard surface finishes that are attainable are 1.3 to 4 micrometers (50–125 μin).[1]
Process[edit]
First, the plaster is mixed and the pattern is sprayed with a thin film of parting compound to prevent the plaster from sticking to the pattern. The plaster is then poured over the pattern and the unit shaken so that the plaster fills any small features. The plaster sets, usually in about 15 minutes, and the pattern is removed. The mold is then baked, between 120 °C (248 °F) and 260 °C (500 °F), to remove any excess water. The dried mold is then assembled, preheated, and the metal poured. Finally, after the metal has solidified, the plaster is broken from the cast part. The used plaster cannot be reused.[1][2]
Advantages and disadvantages[edit]
Plaster mold casting is used when an excellent surface finish and good dimensional accuracy is required. Because the plaster has a low thermal conductivity and heat capacity, the metal cools more slowly than in a sand mold, which allows the metal to fill thin cross-sections; the minimum possible cross-section is 0.6 mm (0.024 in). This results in a near net shape casting, which can be a cost advantage on complex parts.[1] It also produces minimal scrap material.[3]
The major disadvantage of the process is that it can only be used with lower melting temperature non-ferrous materials, such as aluminium, copper, magnesium, and zinc. The most commonly used materials are aluminium and copper. The maximum working temperature of plaster is 1,200 °C (2,200 °F), so higher melting temperature materials would melt the plaster mold. Also, the sulfur in the gypsum reacts with iron, making it unsuitable for casting ferrous materials.[1][2]"