Little kids naturally understand how easily balls move around. They have a blast “swimming” through a sea of balls in a ball pit. For those of us that have not experienced that pleasure, the motion of a mass of ball is not intuitive. This is probably why it is sometimes hard to explain the benefit of creating a spherical grain structure.
Rheocast aluminum is a bunch of tiny balls
Many die cast practitioners only have experience making small castings. This is because 800 ton die cast machines are what was historically found in die casting plants. Todays casting purchasers have discovered the cost advantage of combining multiple casting into one. According the castings have become larger. As always one of the challenges is getting the metal to the far end of the part before it solidifies. This is usually accomplished by rapid injection. As the fill path becomes longer it become necessary to use faster injection speeds. Faster injection speed causes flash and venting problems. I would rather use finesse. Rheocast metal with a spherical structure can be injected at 1/3 of the speed taking advantage of the way balls flow smoothly past one another. Any kid in a ball pit would understand this.
Water water everywhere but nary a drop to drink. A well known line from the poem – “The Rime of the Ancient Mariner,” by Samuel Taylor Coleridge. The mariner was bemoaning the lack of fresh water in the middle of the ocean.
Die casting got its start in the Great Lakes section of North America. There we have a treasure trove of fresh water left to us by the last ice age. Since fresh water was so plentiful and inexpensive it was natural to use a evaporative cooling tower to accomplish cooling of the die and machine hydraulics. As the majority of die casting moves away from this region this is no longer true. Many regions of the world have times of the year where there is water shortages. We really want avoid making a choice between drinking to survive and running the die cast plant to make an income.
The die casting industry is now at a cross road. New structural castings in new alloys are emerging as the dominant product. Record tonnage machines are being installed world wide to meet the demand. At the same time new die casting technologies are being invented and implemented to solve the challenges imposed by the new alloys. Historically we added iron to the die casting alloy to combat soldering. This was helpful at the expense of a less ductile casting. More precise temperature control of the die is needed to avoid soldering when casting the new structural alloys without the iron content.
Evaporative spray cooling is the historic die cast die cooling method evolving from a plentiful free water supply. Current die cast innovators are discovering that it is easier to achieve the required die surface temperature stability using internal thermal passages in the die. Other new die manufacturing technologies such as 3D printed conformal cooling inserts make this possible. Minimum lubrication water free spray release techniques such a Lubrolene are emerging to match.
This represents an opportunity for the die casting industry to make a “green” contribution. Using air fins for rejecting the heat from hot water die cooling eliminates the scale which is the bane of tower cooled water die cooling. Scale control is very important when using conformal inserts that with cooling passages that are tough to descale. Water free spray release not only reduces VOC emissions but the elimination of evaporative spray cooling prevents the humidity build-up that makes the die casting plant feel like a jungle. I will drink to that. (We will have the fresh water we need to do that)
