Bal-tec™ Home Giant Balls
We Grind Giant Balls
Bal-tec has installed a gigantic 230-inch (5.842 meter) machine for grinding giant balls. This machine has greatly reduced the cost and dramatically shortened the delivery time for precision balls in the 6" (15.24 cm ) to 20" ( 50.80 cm ) diameter range.
This extremely versatile machine will go from grinding to lapping and then to polishing with only a change of tooling and small variations in speed and pressure. A special feature of this machine allows the spindle to be locked so a single large diameter ball can be ground individually. This unique capability can be very important when only one or just a few very large balls are required. One giant forging of a special alloy metal may cost several thousand dollars.
Safely handling these large, heavy and very slippery balls required Bal-tec to develop special slings for handling them. In use, a ball is rolled up into a cup at the bottom of the sling. Six plastic-sheathed steel cables are then inserted into the crane hook and the ball can be lifted into place without damaging the highly polished surface. On request, we will supply custom-designed and built slings for handling your giant size balls. We can also supply special containers for long distance or air freight shipment.
We usually machine the blanks for these giant balls from wrought or forged billets on spherical turning machines, but cast ingots or formed and welded hemispheres can be the raw material. If the balls require hardening, we heat-treat them after machining.
The finishing process is broken down into three steps.
- The first step is a grinding operation where the previously machined ball blanks are rounded up and brought close to final size.
- The next step is a lapping process which uses a very fine abrasive slurry and cast-iron wheels.
- Final size and sphericity are established in the polishing operation which uses extremely fine metallic oxides to impart a final luster or micro-finish to the ball.
Quality
The larger the diameter of the ball, the more difficult and expensive it is to achieve fine quality. A hard, brittle material is easier, and therefore less expensive, to finish to a fine quality than a soft ductile material.
Even the force of gravity affects the ultimate quality achievable on large diameter balls. For a ball of only 10" (250mm) diameter, made of a 300 series (18Cr 8Ni) stainless steel, the force of gravity at sea level will cause an unavoidable girth sag of 4.5 millionths of an inch (.114mm)
Although many of the large diameter balls we produce do not require extreme quality, we have produced 10" (250mm) and 12" (305mm) diameter stainless steel balls which were lapped spherical within 10 millionths of an inch (250nm). The quality of the metal itself and the force of gravity are two of the main limitations of the ultimate quality that can be achieved on large diameter balls.
