Metal Casting Zone

JohnCast, and of course everybody else that wants to comment.

I read your last post repeatedly to get the very most out of it I could. I sure appreciate your time and detailed responses. I expect to have some trial and error but listening to voices of experience can sure cut down on the cost.

I have a few more questions for you. One about surface finish and the other about chemical accessories. The last is on heating molds.

First to address Spad13's concern.

Do you use any of the following on a regular basis:
Flux - ammonium chloride, and how much, and how often when working with say 2 kg (4 lbs) pewter?
www.contenti.com/products/spin-casting/176-084.html

Sinthetic Silicone Mold Temp Damage Preservative and Lubricant
Fine Graphite Powder
John the latter, "Microfyne Graphite Lubricant", has a quoted -325 mesh rating. Would 325 be better than graphite rated at 205? Or perhaps you skip graphite entirely as your organic rubbers withstand heat better and you don't want to deal with the black-gray mess graphite makes?
www.contenti.com/products/spin-casting/176-059.html
www.amazon.com/Graphtek-Microfyne-Graphite-Lubricant-can/dp/B000P3W4Y2/ref=sr_1_5?ie=UTF8&s=automotive&qid=1264450460&sr=8-5

Release Agent and Lubricant
Italian Talc - Extra Fine
www.contenti.com/products/casting/176-066.html

Release Agent - Contenti said they used this primarily between rubber parting layers.
Mica Powder
www.contenti.com/products/casting/176-068.html

Mold Locaters - What do you prefer, acorn nuts, brass cones, Just cutting out cones?
www.contenti.com/products/casting/176-033.html
www.contenti.com/products/casting/176-042.html

On the subject of casting surface finish you mentioned "...silver frosted surface...is what I am after."
So even with spin casting or rapid heavy pour in gravity casting, a frosted surface is the best we should expect?

What would be the best first step to achieve a smooth polish with finely textured and smooth end pieces? Vibratory bath of ceramic media and purpose made detergent, vinegar bath, polishing with a certain rouge and muslin wheel?

I am curious if you preheat your molds or expect to pour a couple shots before the usable cast or perhaps with just the right molten temp you get it on the first shot?

I am doing both smooth globular forms for my anatomical sculpture (think arteries) as well as feather textures in jewelry. I might also latter be electroplating for final durable prototypes or simply to gold and silver plate some jewelry. Caswell seems to have some inexpensive kits to get started in electroplating and forming. Some as cheap as $35.00 (Plug N' Plate).
www.caswellplating.com/kits/

Stephen Casey

Good questions Stephen, I am awaiting the reply as well!

While eagerly awaiting any pearls of wisdom from JohnCast....

Spad13 from one newbie pewter guy to another, I just bought that Digital Thermocouple Thermometer that Jammer pointed me to. He owns one and the price was very attractive at $31 bucks out the door here in the states. I see they still have a few more of these discontinued models new and in stock. shop.ebay.com/sevensat/m.html?_nkw=thermometer&_sacat=0&_trksid=p3911.m270.l1313&_odkw=&_osacat=0

I followed John's advice and got a nice pour this morning, best yet, only a slight yellow tint to it. Still I have no idea what the temp was, and I suspect a full pot would yield a different molten metal temp than a nearly empty one. After further research I decided the IR non-contact solution while inexpensive would be problematic with the shiny sometimes dross covered molten metal although it would likely be great checking my silicon molds during resin post cure in the toaster oven. So I'll buy one of those too in a few months.

Stephen,

How does it work? Do you just hold it in the molten metal?

I have a thermometer that clips on the side of the pot and sticks the end into the molten metal... probably not as accurate as what you have. I may just pick one up!

Thanks,

Bruce

Same principle Bruce, but should read changes far faster and more accurately. But since you already have a solution maybe just work with it.

I won't get mine and a new supply of metal until mid next month. I am hoping I can leave the probe in all the time. Perhaps with a crafted holder mounted to the cool base of the unit. The probe will be submerged but not contacting the wall and toward the back of the Lee pot so as to be out of the way of added metal chunks. I will also likely buy the Lee extension that allows you to gain another couple inches of height.I am also thinking of building up a dedicated base so the pot does not move around.

Here is the specs on the this thermometer.

Specs:
* Probe Operating Range:
o 0' to 1300' F Intermittent, 0' F to 750' F Continuous
* Instrument Accuracy:
o +/- 2 degrees F 1% of reading at ambient temperatures from 68'F to 86'F
* Probe stores neatly in unit.
* Made in Florida USA by Atkins Technical Inc.

Hi Stephen and SPAD 13 and everyone

wORDS OF WISDOM I don,t know about that .experience maybe..
Got to the computer at last to answer your posts after a holiday tuesday.

So a few answers..About fluxes, I use only a cleaning powder in the molten pewter when im casting .I replace the sprues into the pot from the last casting run and if i feel the pot needs a clean I heat the metal up to 50oc above its melt point and sprinkle a little cleaning powder on top and mix in then scrap of the dross. The melted pewter should have a mirror like finish I can see myself in the metal after I have done this.
The release agents is simply talc powder. When I make my moulds in the black organic mould rubber and valcanize, both rubber discs are powdered down with talc, they seperate very easly when taken from the frame, wich also receives a dusting of talc powder. When i use a RTV rubber I coat the lower half of the mould with vasaliene jelly ,,worked for me.
Mould locaters I always use the square ones if I can Some rounded but always the square ,this gives a better key. When I cut my RTV rubbers both resin and metal moulds I always cut deep square keys never round.This stops movement of the mould halfs in all directions. Round keys allow movement I feel ,and can misaline mould halfs. I haven't cut a round key in a mould for 19 years.

Silver frosted surface is probibly the best way to describe the finish on my better castings. Silver frost was a paint I used many times in my younger days, the white metal castings sure remind me of that paint finish. Aluminium rod or bar has the similar finish to, so your casting should be like that. Smooth ,no pits, no stains, no dross.
As for the heating of moulds, well just put these into your oven LOW just to warm them,place these on a pathway in the sun for 20mins or so. With my summer temps at present 20 mins in the sun gets the mould to a very good heat..
This is to just heat the mould you can drop metal into the mould and do the same.
I like to just mention here that though the moud is hot the cavities in the mould are the areas that are important . To me it is necessary to have a hot (NOT OVERHEATED)mould to cast but the important section of the mould is the mould cavities,or the holes made in the mould of your item you want to cast,if the cavities are not the correct temp the metal will react with the cold walls of the cavity and give a pitted surface. It sometime takes a long time to get the mould to a temp that gives good repeatable results. Then things can go the other way and a poor result is because of the mould being too hot, moulds needs to cool for a while. This casting is a very carefull balancing act. Hope this helps
JOHNCAST

Thanks Johncast!

Your thoughts are greatly appreciated.

Thank you John that does help.

Your descriptions are very clear and easy to visualize. I use Vaseline myself when pouring the second halves of RTV molds. It never fails to work.

What exactly is the "cleaner" you are putting in your metal, Borax perhaps or another particular brand? Your being in Australia it might not be a brand I am familiar with here in the states but I would likely be able to find out what it is made of. A proven products beats a guess any day.

Bye the way if you don't mind saying, what is in the pewter you favor?

I plan to buy a sampling of four types next week, but I am interested in what gives you good flow and results. I dig there is more craft in getting good results with these metals than my usual very low viscosity polyurethane resins. By comparison resin is a breeze. Yet I also think making core pewter armatures for some of my more delicate resin anatomical sculpture will be worth the effort. So far these are what I am planning to pick up. But I could still change it up a bit.

98 tin,1.5 bismuth,.25 copper,.25 silver - 6 pounds from Hallmark MPK.
92 tin, 7.5 antimony, .5 copper - A pound from Rotometals A/C.
99.8 tin. - A pound from Rotometals.
58 bismuth, 42 tin - A pound from Roto-, for electro-forming trials.
Atkins digital thermocouple thermometer.

Recon I should learn a bit messing about with these. I read on one site that they recommended pure tin for casting metal soldiers. I haven't read that anywhere else though. What do you think of that?

Stephen Casey

Hi Stephen

Don't know what the cleaner that I am using, the powder has a cemical in it that can rust a tin in 6 months and the lable , as it is only used a little at a time this dross remove is only the 2nd lot I have purchased in 20 yrs and have to change the container constantly.,that I keep it stored in..

These metal alloys should keep you quite busy. All high tin content, these will melt at quite a high temp 220oc plus. Probably give a good surface finish if you are intending to burnish or polish the castings you want to do. I've stuck with the Lead tin and Antiminoy alloy all my years. I did try high tin but just cost more and didn't give any better strength in the castings. JOHNCAST

Right on, its good to choose a material and go on with the process of getting good results with it.

I am working inside in an apartment building hence the lack of lead and cadmium for safety concerns. I'm buying the 5 lb of flux from Contenti then, and like you most of this will likely collect dust its coming in a plastic bucket so likely no rusting.

Today I talked with Ryan at Eastern Alloys, about zinc alloys.
www.eazall.com/gravitycasting.aspx

He recommended their Kirksite for low run molds. And ZA-8 for low run cast objects. He said Harley Davidson chrome plates a lot of ZA-8.

I understand they melt at:
707F-759F (375C-404C)

I have read that molten zinc can produce a white smoke that is noxious.
John have you used these zinc based materials?