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I have been advised to roll my investment drums and redistribute the powder before I
use it. Is this required?
You recommend vacuuming until the investment rises and breaks. You say this
should take less than a minute. If it doesn’t occur in a minute’s time, should I keep the vacuum applied until it does?
Is distilled or deionized water required, rather than tap water? What is the difference?
At times, I would like to lengthen or shorten the set time of the material I am
investing. Do you have any suggestions?
Does a flask really have to set undisturbed for an hour or two before removing the
sprue base? I would like to speed up my production cycle and remove the base sooner than an hour.
Is there any easy way to increase the strength of a mold without compromising quality?
Can I add water to the powder?
Even though I think I have good vacuum, I still get nodules on my castings, caused by
excess air on the wax. Do you have any advice?
Do I need to use the entire recommended working time for your investment like other
manufacturers recommend?
Are there any differences in investment powder preparation or use if I am using
plastic, rather than wax, patterns?
How much investment should I have above the wax tree and around the sides of the
flask?
I do not use investment daily and cannot really justify buying a mixer. Can you suggest any way to mix the material well without having to spend a lot of money?
I’ve noticed that investments seem to heat up a bit while they are mixing. Why?
I have heard people refer to set time, pour time, working time and gloss off time when they speak about investments. Can you provide clear definition of these terms?
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Jewelry Questions
I have been advised to roll my investment drums and redistribute the powder before I use it. Is
this required?
The particle size of the ingredients used in R&R investments are all of a similar (and very small) particle size. Therefore, there is no separation of the ingredients. You do not need to roll the
package to redistribute materials. However, a few casters roll the package simply to decompress settled material, making it easier to scoop out.
You recommend vacuuming until the investment rises and breaks. You say this should take less than
a minute. If it doesn’t occur in a minute’s time, should I keep the vacuum applied until it does?
If the investment doesn’t rise and break quickly during the investment cycle, there is usually a problem with the vacuum. Vacuum pumps with old oil or leaks can cause the vacuum to pull less vacuum
than a well-maintained unit. An oil change often makes a significant difference.
You can check the system by placing water under vacuum. If you do not see the water boil rapidly, you should get the vacuum system checked. If the water boils and your investment does not, contact your
investment manufacturer.
Is distilled or deionized water required, rather than tap water? What is the difference?
Distilled or deionized water is recommended because it is more consistent than tap water. Impurities in tap water can change the working and set time of an investment. With distilled or deionized water,
the impurities are minimized so the investment properties are more repeatable drum to drum and batch to batch.
All of R&R’s retained batch samples are evaluated using deionized water to insure batch to batch consistency.
At times, I would like to lengthen or shorten the set time of the material I am investing. Do you
have any suggestions?
In general, waremer water and/or warmer powder will speed up the setting time. Cold water and/or powder has the opposite effect.
Does a flask really have to set undisturbed for an hour or two before removing the sprue base? I
would like to speed up my production cycle and remove the base sooner than an hour.
The investment does require at least an hour’s time to set completely. Many customers see finning and other defects associated with removing the sprue base too early. If the base is removed before
the investment has sufficient green strength, the investment is shifted and stressed when the base is removed. This can result in rough surfaces and other casting defects.
Is there any easy way to increase the strength of a mold without compromising quality?
Reducing the amount of water used will increase mold strength. Rather than using a 40/100 ratio for a gypsum investment, you may want to try 38/100 However, the increased mold strength will reduce the
ability to remove investment after casting. The permeability of the mold will be reduced when less water is used.
Can I add water to the powder?
This method of mixing is not advised since it takes too long to completely wet out the powder. The material has a set working time and it is important to keep the mix time (3 minutes or less for a gypsum
investment) as recommended so there is enough time to complete the entire process. Adding the powder to the water will allow you to mix thoroughly in the desired time.
Even though I think I have good vacuum, I still get nodules on my castings, caused by excess air on
the wax. Do you have any advice?
Often, altitude will reduce the effectiveness of even a good vacuum system. One of the tricks you might try is to add a few drops of liquid dish soap to the water before you mix your investment. The
soap will act as a surfactant and break up the air bubbles in the mix. Be careful not to add too much soap or you could cause the opposite effect and create more bubbles.
Do I need to use the entire recommended working time for your investment like other manufacturers
recommend?
Other manufacturers may advise using the entire working time as a means of eliminating water marking defects. Water marking is characterized as “rivers” of metal on the underside (as
invested) of the casting. It is caused by water separating from the investment as it sets.
Use of the entire working time is not a requirement to achieving good results with R&R investments. The working time is set to allow a large portion of the casting industry enough time to prepare
investment and fill flasks.
However, do make certain you mix the investment with water as long as recommended in the application sheets.
Are there any differences in investment powder preparation or use if I am using plastic, rather than
wax, patterns?
How much investment should I have above the wax tree and around the sides of the flask?
Plan to cover the tree with at least an inch of investment and about 1/4” of investment between the wax and the flask walls. This thickness provides good strength for casting.
I do not use investment daily and cannot really justify buying a mixer. Can you suggest any way
to mix the material well without having to spend a lot of money?
You can make a fairly good mixer using a portable hand drill, a length of threaded rod, and a rubber disk. Secure the rubber disk to the end of a rod and use the drill to mix the material. If you are
mixing a small batch of material, like 2 to 3 pounds, the disk diameter should be about 3”. For a mix of 8 to 10 pounds, increase the diameter to 6”.
I’ve noticed that investments seem to heat up a bit while they are mixing. Why?
Gypsum is somewhat exothermic. The more material you mix, the warmer the mix will become. This is not a problem because the vacuum will cool the investment and you may even notice a cooler flask after
the second vacuum step.
I have heard people refer to set time, pour time, working time and gloss off time when they speak
about investments. Can you provide clear definition of these terms?
Let’s define them from the shortes to the longest time frames. Working time starts when you add the powder to the water and ends when the material starts to thicken. For R&R’s gypsum
materials this happens 8 to 9 minutes after the start of the mix. For our phosphates, this occurs in 4 to 5 minutes.
Pour time starts with the powder to water addition and stops when the material is physically too thick to pour from one vessel to another. Gloss off again starts with the powder to water addition but ends
when you can no longer see moisture on the top of the flask. Set time starts at the same point and is timed until a Vicat needle will no longer penetrate the material more than 1 mm. deep. Our gypsum
products have a set time less than 20 minutes.
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