Description
There are two basic types of ball point pens: disposable and refillable; disposable pens are chiefly made of plastic throughout and discarded when the ink is consumed; refillable pens are metal and some plastic and tend to be much higher in price. The refill replaces the entire internal ink reservoir and ball point unit rather than actually refilling it with ink, as it takes special high-speed centrifugation to properly fill a ball point reservoir with the viscous ink. The simplest types of ball point pens have a cap to cover the tip when the pen is not in use, while others have a mechanism for retracting the tip. This mechanism is usually controlled by a button at the top and powered by a spring within the pen body, but other possibilities include a pair of buttons, a screw, or a slide.
Rollerball pens combine the ballpoint design with the use of liquid ink and flow systems from fountain pens. Compared to rollerball and fountain pens, ballpoints require more pressure to write. Ballpoints lack the free flowing supply of ink that other types have, requiring the writer to apply more pressure to the page. As a result, the ballpoint pens are less likely to leak. Their robustness makes them suitable where a firm press is required, namely for carbon copy-type forms where a layer of carbon paper transfers the writing to subsequent copies.
Because of the pen's reliance on gravity to coat the ball with ink, most ballpoint pens cannot be used to write upside down. However, Space Pens, developed by Fisher in the United States, combine a more viscous than normal ballpoint pen ink with a gas-pressured piston which forces the ink toward the point. This design allows the pen to write even upside down or in zero gravity environments. A graphite pencil can also be used in this way but produces graphite dust, requires sharpening, and is erasable, making it undesirable or unsuitable for use in some situations. Ballpoint pens also have difficulty writing on surfaces with low friction, such as plastics, shiny surfaces, and wet or oily surfaces.
Read more about this topic: Ballpoint Pen
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