The Bounce Page was established 11-7-99. All rights reserved.
By Isaac Orr <orr@dynamica.net>.
Home page: http://members.xoom.com/IsaacOrr/.
Please send comments, suggestions or corrections to the above email address
The following article is a summary of the experience and professional knowledge of several people reporting to the rec.juggling newsgroup. The following quotations were all taken from messages posted in December '98.
First - The Conclusions:
Judging by the personal experience of an amateur and by the professional opinion of two people with experience in the molding industry, silicone balls can not be feasibly made by an amateur. Manufacturing such balls apparently requires equipment and technique beyond the scope of a budding molder. However, a silicone layer can be usefully applied to cheap balls to enhance their texture, grip and dirt resistance: Satisfactory results were achieved with minimal equipment.
Following is a more detailed discussion of these points.
Casting Silicone Balls:
Mr. Roger W. C. Hansen has tried to cast silicone balls. Following is his report of the attempt:
"The results in my case were somewhat less than satisfactory. I made a plaster cast of a ball of the desired size, greased the inside and filled it with caulk and pressed it together. The problem is the chemistry of the caulk. Part of the curing process is exposure to moisture in the air. There is no moisture in the plaster cast and the curing is extremely slow. If you open them after only a few days, the outer shell tears, and the inside is still gooey. The inside will then start to cure with a bubble. I eventually left them in the casts for a couple of months with the casts on top of a radiator to provide gentle heating. This seemed to eventually cure them completely. It is still very easy to get disturbing air bubbles in them. These can be filled in a little and let dry. One then has to trim the material at the mold line and fill hole. I never really found a good way to do this except cutting them off with scissors. I kind of lost interest in pursuing it further because the results lacked the fine texture and bounce of the commercial product. IMHO this is not a good way to make juggling props. I think the filler and other additives added to the caulk change the product to much. I believe three HiBounce balls cost about as much as the caulk and other materials needed and work better"
Mr. David Dalton of Morningwood Laboratories (molding specialists) has some valuable information for solving this problem:
"Your problem is that you are using the wrong sort of material to make your balls. Use what's called an addition cure RTV silicone. This comes in two parts like epoxy: The smaller part B is added as a catalyst to cure the silicone. After mixing, the silicone will set up after 2-24 hours (depending on what you use). It doesn't need to be exposed to air to cure, so you wont experience the problems you've been having"
Charlie Hull has additional information on obtaining a successful mold and concludes that this might be too hard a goal for an amateur:
"To produce a really clear, clean mold one must remove all the air bubbles from the mixture before it is allowed to cure; do this with a vacuum tank (not a particularly easy thing to build). The cured rubber smells *awful*. I used to take offcuts from molds to school to wind up my friends (I must have been about eight years old) It's almost certainly easier to buy the things"
Mr. David Dalton also stresses these points, and adds several tips:
"If you have access to vacuum casting equipment, de-gas the silicone under the vacuum dome before doing your pour. This will remove all the unsightly air bubbles. You can use the same rubber for the mold and the ball, but be sure to use a release agent (like spray silicone) to keep the ball from sticking to the mold".
And closes with some discouraging remarks :
"I will warn you that the silicone will cost you over $100 a gallon. And a low end vacuum table starts at $600. Add in the difficulty inherent in casting a sphere - this is really difficult! You will ALWAYS have a sprue (little umbilical cord or rubber) coming from a point on the ball where you fill the mold, and you have to manage to fill your mold completely with no bubbles which takes skill to pour and handle properly. Unless it is the journey you are interested in, I might recommend paying the professionals to make your silicone balls"
Silicone Coating:
All is not lost on the quest for the silicone touch, however. Mr. M. Scott Dineen reports on a perhaps more feasible approach to utilizing the special properties of silicone. He tried the idea of coating existing balls with silicone to achieve the special texture, high surface grip and dirt repelling qualities of a silicone ball. His first, simpler method was applied to street hockey balls:
"All you do is cover a weighted street hockey ball (or other ball) with white silicone from a tube (use a paintbrush). The texture, of course, isn't smooth, but they have a nice grip and look decent"
A more advanced method was used to obtain smooth-skinned balls:
"I filled two halves of a 3.5" Dube stage ball with silicone and stuck a stripped tennis ball inside. When I pressed the two halves together (with the tennis ball inside) most of the silicone was pressed out. When the thing dried (I checked after two days) it had a smooth silicone surface that had just a few bubbles in it and was practically spherical. The silicone skin felt and looked good"
The Bounce Page was established 11-7-99. All rights reserved.