There are two departmental ultracentrifuges located in room 230. Select the highlighted area to read detailed operating procedures for these instruments. The Beckman L8-M is shown at the left. Near the bottom of the page on the right is an picture of the Beckman L5-65 . The centrifuge is one of the more useful, and more dangerous, pieces o f equipment in the lab.
A good understanding of what it can and cannot do is essential. Centrifuges come in three general classes, low speed, up to about 5000 rpm, high speed machines of up to about 25,000 rpm and ultracentrifuges which will turn at up to 100,000 rpm. A special class of "airfuge" is in existence wherein the rotor is suspended and driven by a stream of air. These can reach over 100,000 rpm in very short times but are limited to very small sample sizes. Another form of centrifuge very common in laboratories now is the microcentrifuge or microfuge. These are simple machines used with 0.5 or 1.5 ml disposable plastic tubes. Most of these machines are single speed and generate between 10,000 and 13,000 rpm. The Department has several centrifuges. --- Many vacuum-type centrifuges are ultracentrifuges; i. e., they operate at speeds of more than about 20,000 revolutions per minute. The centrifuge rotor located inside the vacuum chamber is connected to the air-supported, air-driven turbine by a vertical, small-diameter, flexible steel shaft. Unbalanced loads bend the shaft.
The rotor of a typical vacuum-type ultracentrifuge is 18 cm (7 inches) in diameter and carries 300 milliliters (10 ounces) of liquid in a centrifugal field of more than 300,000 G. Practically all substances of importance in medicine and biology and all other substances with molecular weights of 50 Dalton (one Dalton is 1.66 10-24 grams) or more are easily purified in this type of bottle centrifuge.
The vacuum-type centrifuge may be used for the determination of the molecular weights of practically all substances in solution. In commercial vacuum-type centrifuges the air drive and support have been replaced by the more efficient and convenient electric motor drive, and the entire machine has been redesigned and made almost automatic in its operation. The present commercial vacuum-type ultracentrifuge has become an indispensable tool in laboratories where it is necessary to purify substances of importance in biochemistry.
A 1998, a Cornell campus laboratory was seriously damaged when the rotor of an ultracentrifuge failed while in use. Flying metal fragments damaged walls, the ceiling and other equipment. The shock wave blew out the laboratory's windows and shook down shelves.
Description of the Cornell Accident -- On December 16, 1998, milk samples were running in a Beckman.L2-65B ultracentrifuge using a large aluminum rotor. The rotor had been used for this procedure many times before. Approximately one hour into the operation, the rotor failed due to excessive mechanical stress caused by the "G" forces of the high rotation speed. The subsequent explosion completely destroyed the centrifuge. The safety shielding in the unit did not contain all the metal fragments. The half-inch thick sliding steel door on top of the unit buckled allowing fragments, including the steel rotor top, to escape. Fragments ruined a nearby refrigerator and an ultra-cold freezer in addition to making holes in the walls and ceiling. The unit itself was propelled sideways and damaged cabinets and shelving that contained over a hundred containers of chemicals. Sliding cabinet doors prevented the containers from falling to the floor and breaking. A shock wave from the accident shattered all four windows in the room. The shock wave also destroyed the control system for an incubator and shook an interior wall causing shelving on the wall to collapse. Fortunately the room was not occupied at the time and there were no personal injuries.
