I received the following questions from a friend of yours on your behalf.
hi i would like to ask a lot about the problem in the jewelry industry especially cubic zirconia jewelry, i would like to ask the problems that are happening now in our workshop, maybe from so many friends in this community can help me to what percentage of broken stone on stone casting give suggestion and input because i just try in field
- what percentage of broken stone on stone casting
- how many lost gold per flask with 18 cm height we use yasui K2
- what percentage of lost gold is ideal on casting with casting results
- what percentage of casting defects in general, for re-casting
- what is the ideal target of seeting stone on a wax per day for one person
- if we have 100 employees how many kg can be produced for ideal
- for cz jewel industry, product lay out or layout process better we use
- on the cz industry what percentage is ideal for lost gold from the beginning of the process to the end
- for business in cz jawel industry what percentage of ideal cz content.
hopefully with a reply and input can add to our knowledge of all
My response is below:
Dear Mr. or Ms. Nos,
My, you have a lot of questions. It appears you are in need of a technical consultant. The things you are seeking to know are things that I teach for a living. Usually on Ganoskin, people are looking for answers and information from the community and that is great if you can get it and you are comfortable with the information you recieve. Not that anybody on there would tell you something that was not true but it may be an opinion or some belief based on a past experience rather than science. To be clear, I am not knocking experience, I just like to know why things work and not just that they work.
If you would like some professional help, I would be happy to help you. I am a process and product engineer for the jewelry industry. My company designs jewelry factories. We have designed and built and rebuilt factories in China, India, Mexico, the Dominican Republic, Bolivia, USA, etc… That is what we do and I think that is why Cliff Durlacher put me in contact with you. Please find the information I can easily share below: I think that most of your questions are about wax setting CZ but some of your questions also seemed to relate to diamonds so I will answer what I know about both.
What percentage of broken stone on stone casting?
a. No diamond breakage is acceptable but it happens. 95% of the time diamond breakage is due to the model. The other 5% is due to stone quality. For CZs you have the same problems you do with diamonds unless you quench your flasks too soon. CZ is a ceramic and as such, it does not transfer heat well. Thermal shock with CZ is a bad thing.
b. A small reason that diamonds break is because they are heavily included to start with. This sets up a thermal gradient in the stone that shows up during metal injection and the stress of the thermal gradient cracks the already flawed stone.
c. The much larger reason that diamond breakage occurs when diamonds touch or overlap when they are wax set.
i. During the casting process (metal injection), as the metal cools it shrinks. As it shrinks it pulls the stones closer and tighter. If the stones are already touching, one diamond will win and the loser is chipped. The same is true for CZ.
d. The model is bad because CAD people are typically designing to average size stones or imaginary millimeter sizes and are not designing to the true variance that results from stone sieving.
i. Knowing the mathematics behind sieve plates and real stone sizes for diamonds is key to making a technically correct model for wax setting.
e. If the model is bad then the wax setters are already at a disadvantage but it could also be as a result of poor training of the wax setters.
f. Stone sieving diamonds with full plates for wax setting is insane. Sorting stones with half plates below .02pt stones is also foolish. Stone buyers and company owners are typically don't like to use quarter plate sieves and that is because they don't sit and do the wax setting themselves. The smaller the stone, the more accurate the sieving must be. Hard sieving is a must! I did a research paper for the 2006 Santa Fe Symposium book that discusses this in detail.
Lost gold per flask when using a Yasui K2? That is a difficult or impossible question to answer because it depends on many factors.
a. What karat and color of gold alloys are you using and how much loss are you experiencing per that karat and color. This particular information matters…
b. Do your gold alloys contain zinc?
c. Does your gold alloys contain silicon? It is certain if you are casting 10kt or 14kt and while not likely if it’s 18kt, it is possible depending on the source of the alloy…
d. Does your Yasui melt program contain a vacuum step that continues while the metal is molten?
e. Are you doing your casting in house or sending it outside? I ask this because if you are using an outside caster that might be a factor.
What percentage of casting defects in general, for re-casting?
a. What type of casting defects are you talking about? They all have different sources and solutions. None are acceptable but you have to decide as you fix your product and process where is the point of diminishing returns. I know how to greatly reduce all of these but it is not a one size fits all solution nor is it one answer fixes all.
i. Investment inclusions
ii. Gas porosity
iii. Shrinkage porosity
iv. Oxide inclusions
vi. Hard spots
What is the ideal target of wax setting stones per day for one person?
a. It depends on how well you model is designed, how well your stones are sorted/sieved, the type of setting it is, the size of the stones, and finally the training and tools that your workers have to work with!
b. Again, this is all about product and process engineering.
If we have 100 employees how many kg can be produced for ideal?
a. Again, this is also about product and process engineering. I can probably set up an ideal factory with ideal models that can produce an equal amount of products with 50 people that a poorly engineered factory can do with 100.
b. I have doubled the output of many factories with no additional labor and in some cases, reduced labor depending on their starting point and willingness to adopt technology and understand the chemistry and physics involved with jewelry manufacturing.
Wax setting CZ has several potential issues.
a. The chemistry of the stones themselves presents the first problem. CZ or cubic zirconia is a ceramic and resist heat transfer.
i. Why this matters is because there is a limit to the thermal mass (size) and shape of a CZ that you can cast in place.
b. The reason that diamonds don’t crack very easily during cast in place is because the chemistry of a diamond is omni-directional covalent bonds of carbon.
i. Carbon transfers heat very quickly and diamonds even quicker so when the heat of the metal hits a diamond, it transfers that heat very quickly and evenly into the thicker parts of the stone so there is very little thermal gradient. As the size of the diamond increases especially for certain shapes, breaking a diamond due to thermal shock is possible.
c. With a CZ being ceramic, it resist heat movement so very strong thermal gradients occur near the point of contact with the molten metal.
i. CZ stones crack near the prongs or channel points of contact.
ii. Shapes like marquise or baguette where the prong is at the tip are very likely to break.
iii. The larger the CZ, the higher the probability that they will crack during wax setting (aka cast in place).
iv. The more metal you have in contact with a large stone, the higher the probability of cracking.
I believe that is about enough information for now. By now I’m sure you realize there are no easy answers to your questions and there are no magic powders, alloys, or consultants that can wave their hand and make all your problems go away. There is only science. If you are interested in knowing more, I look forward to hearing from you. If I have answered the questions as best I can for now. You can thank Cliff Durlacher, the Ganoskin Project for getting this party started.