Very few people know the basic ceramic process, and even fewer people are willing to tell others about how it works. We feel it’s in our best interest to share our knowledge with our customers so they understand what it takes to build their parts.
The ceramic material Aluminum Oxide (Alumina) comes to us in powder form with a grain size of about 100/150 microns. We then mix it with “binders” such as a food grade wax and some sintering aids (to help it bond in firing). Then we ball mill it to achieve a thorough mixing, and then spray dry it to make a powder again.
The powder can then be pressed in several different ways. In this case we will use an iso-static press. By pouring the powder into a rubber bag and sealing the bag we place the bag into the press. The press is not your typical press, instead of pressing mechanically, it uses water inside a chamber. The material is then pressed to 20,000 LBS and the water is pressing in all directions to create a block or bar of material. When we remove the block it is intact due to the waxes used in the mixing stage.
We then cut a piece off the end and machine it to be a perfectly square bar. This little piece of material is going to be a coupon to find out how much the material is going to shrink in the furnace. We measure the piece down to the tenth of a thousands .0001 in all directions and fire the coupon.
Once the coupon has been fired we measure it again to get the shrink rate on that block, and yes, we do this to every block. The material will shrink as much as 20%, our shrink numbers are 5 places 1.20354, which means we will have to multiply that number to any dimension we build from that block of material.
Now the material is ready for the job, It is soft and feels like chalk, and you can change a dimension by .001” just by brushing your finger across it. Because of its soft state we have to handle it very carefully, but at the same time we can remove material very quickly. A variety of cutters are used to form the material, from carbide to course grit grinding wheels and this is where we us our CNC (computer numerical controlled) machines to cut and form the material.
In most cases we can machine right to size, taking into consideration the shrink and the fact that we have been able to hit dimensions within .001” for every inch. But in this case we have to leave some material on the part to be ground post fire to create some finer tolerances and finishes.
The firing process is quite unique, the parts must be placed in the furnace in such a way that they will not touch each other, or they will stick together, nor will they take up to much room, for cost constraints. The firing is an awesome sight, the process usually takes about three days and reaches 1650 deg. C (over 3000 deg. F).
When the firing is complete the parts are removed and head straight for the dye room. Each part is dipped in an ultraviolet dye and inspected under a black light, if any cracks or chips are discovered the part is rejected and tagged on the spot to be reviewed by our material review board at a later time.
The parts are then taken to the grinding department where the excess material will be removed to make bring them to tolerance, in some cases within .00002” and put a finish on them that looks like glass. All machining, post fire, is done with diamonds, some are grinding wheels and some are powders, but it must be diamond or it will not remove material fast enough.
Last but certainly not least is inspection. The inspection process must be rigid, this material is still very abrasive, the material “Alumina” is basically “sand” in a much finer state, so it can grind down metal fixtures pretty rapidly. Did you know most knife sharpeners are made of ceramic? The parts are inspected visually and for all dimensions and then dye checked again to be sure no undue stress has been put on the parts during the grinding process. All the accepted parts are tagged and the rejected parts are reviewed to determine why.
The accepted parts are then cleaned and packaged for shipping. Even here we need to be careful not to put the parts together for fear of chipping during shipping.
So as you can see we have gone to great lengths to bring this wonderful material to you. It has great characteristics and a wide variety of uses. Give us a call if you have any questions or would like to see our process, we will be happy to show you around.