Hi everyone! Im new here! I found this place looking good sources for make my final career tesis. My background is 1 year of work in a small lost wax workshop, for that reason i know the basics, but my company there isnt very competitive. Im looking for experience, good practices and ingenious techniques that can bring me good knowledge in order to make a usefull tesis. I dont want make a mediocre and standar work. Please help me! My first question is about wax. when i worked in the company i had a lot of problems with wax, the model tend to deform or make defects like this Also some pieces were shrinking because wax properties. My second question is about slurry proces, i know that the number of layers is important but if i put too many layers then the permeability of the shell is too low and that bring to holes in the casted piece. Then i had a lot of problem with complex designs like this How it started. How it is going I have more doubts but i cant be so anoying and make a post too large. Sorry for the suffering caused for see this pictures. Im trying to make my best.
This is pretty large for conventional work, the defects I'm seeing appears to be caused by a low mold temperature. What was the mold material and how was the wax injected into the mold??
The mold was made of alluminium, i didnt control of mold temperature, but the mold trended to increase temperature in the run of the journey, then of 6 hours the inyection needed stop because mold were too hot and the wax trend to deform and shrinking, ruining the piece. The wax was inyected by pressure inyection. I dont know if that info is usefull for you.
Sounds like you've been working with the big boy toys Do you remember the injection pressure and temperature?? This defect could have been caused by the slurry not being completely dry in that area prior to recoating the next layers... Or poor slurry controll
I was looking for a video I'd seen awile back showing the wax being injected into a mold at different speeds and how it effected the wax part. I thought it was on the MPI site but im unable to find it now. I don't know if you have seen any of their stuff, but this might help you out some. https://www.mpi-systems.com/videos/
You re right! haha Inyection temperature about to 65ºC, pressure, the manual say 7MPa of maximun working pressure but i dont measured in the practice. The primary layer (80% Zirconium #325 + 16% Coloidal silica + 4% pure water) was left dry 24 hours, then the secondary layer (80% Zirconium #200 + 16% coloidal silica + 4% pure water) about 8 hours every layer. The slurry had a viscosity about 100 seconds in ford cup nº 4 in primary layer and 25 seconds in the secondary. I hope that this info is being useful. thanks!
Your certainly making me think No other additions to your slurry recipe?? Seems odd as most I've heard of contain some type of fire clay as well as wood flour... I just buy pre made slurry...
I can confirm that those are the only ingredients, the ratio can change. Is correct make a first primary layer and then secondary layers?
Yes, typically the first one or two layers use a fine sand to achieve a good surface finish, then the next layers use a coarse sand to build thickness. I'm still curios about your slurry recipe and your process to create the shell. Would you mind taking a moment to describe it in some detail??
I agree it needed more time to fully dry. Small deep spaces like that take a long time to dry. I found that blowing air into the small spaces with air bubbles or pressurized air or a shop vac helps dry out that kind of shape. I the injection mold looks like the wax is cooling quickly and trapping air against the wall of the mold. Maybe some type of oil spray or other lubricant would help break the surface tension of the wax and let it flow properly. Is the injection process fast and automated or is it slow and manual where you could spray some oil into the mold between each molding?
I'm interested to see what he's got for a slurry in Argentina as I have yet to see a home made recipe work. Surly they must be doing ceramic shell in that country right? I'm curious how are you dewaxing your shells??? This defect looks like an air bubble in the initial dip to me. A gentle mist of compressed air works great for smoothing out the very first layer. Odd how it looks like it was cast in sand instead of slurry. First layer should be super fine (50/100mesh) >>> https://shop.ransom-randolph.com/ranco-sil-a Keep at it, you'll get it eventually if you make small changes slowly. Make notes so you learn what works and what doesn't. More importantly, please report back here so others can learn too.
Important info. Actually i dont work anymore in the workshop, i needed chose between work or finish my career, i choose finish and gain the title. First we made the first 20% colidal silica solution adding 4 coloidal / 1 pure water. then we added this to a giant mixer. then continued adding the 80% of zirconium 325 mesh. finally made a viscosity control in search of 100 seconds of drop in a Ford cup number 4. EDIT: Now i remember that we also added ph neutral detergent and then butilic alcohol in order to purgue the bubles generated by detergent. That specific piece was made of fused silica. But the piece was made of stainless stell, more specific CA-15 or CF8M (the client demanded both). Now i know, reading the post in this forum, that FS only should be use in no ferrous materials. That is a important knowledge that i dont know before! Really thank you, forums and communitys are the best for learn. The process is manual, we used BLEM https://www.blem.com.ar/es-ar/all-products/blem-aerosol. We used an autoclave. This. Violent input of steam water, 8kg/cm of pressure, that is i can remember. but this stage of process was a hit in the balls, look this shit. This was the worst, this give me nightmares for some days. I dont know what was doing wrong, this is not my problem anymore, but i need well understand this if i want to make a good tesis. Our first layer used to be made of 325 mesh of Zirconium (80%), then 16% coloidal silica and finally 4% pure water.
Yeah even an autoclave isnt bullet proof. Ya might wanna check my YouTube channel and see my odd ball method for dewax. You'll never believe it until you see it.
Hi guys. Can you give me some tips related about dry the shells? i know is a critical point in the path to make a good shell. How i can measure the humidity level? or how i cant know when a shell has a good dry and is ready to the next layer? Thanks for all!
There is a couple of ways. One is if your slurry has the color indicator it changes. The other is when it stops losing weight (water has evaporated off) or it has assumed its surrounding temperature. So put it on an accurate scale or dig up the laser temp thermometer. As a side note, do not force dry your first couple of layers with fans and such. After the 3rd layer is applied, Its pretty safe to put it in front of fans. That very first layer of slurry is critical it drys slowly or it can shrink and leave a crappy surface finish.
I saw you dewax method and i dont understand how you prevented the shell fracture by the wax expansion.
The why it works is because it evenly bathes the entire shell in even heat. By doing this, it melts the wax right next to the shell and instantly comes up and out. A preheated furnace up to temp should accomplish the same thing. Compared to flash fire dewax, this works much better for me. The only variable I have found that can effect the process is large differences in wax thickness.
