Linear-motion bearing
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A linear motion bearing or slide is a bearing designed to provide free motion in one dimension. There are many different types of linear motion bearings and this family of products is generally broken down into two sub-categories: rolling-element and plane.
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[edit] Rolling-element bearing
A rolling-element bearing is generally composed of a sleeve-like outer ring and several rows of balls retained by cages. The cages were originally machined from solid metal and were quickly replaced by stampings. It features smooth motion, low friction, high rigidity and long life. They are economical, and easy to maintain and replace. Thomson (currently owned by Danaher) is generally given credit for first producing [what is now known as] a linear ball bearing.
- Rolling-Element bearings can only run on hardened Steel or Stainless steel shafting (raceways).
- Rolling-Element bearings are more rigid than Plane bearings.
- Rolling-Element bearings do not handle contamination well and require seals/scrapers.
- Rolling-Element bearings require lubrication.
[edit] Plane bearing
A plane bearing/bushing is very similar in design to a rolling-element bearing/bushing, but it contains no balls. Plane bearings are further broken down into several families: Bronze bushings, Metal/Polymer Bushings and All-Polymer bushings. All metal (usually bronze) bushings were the start of of this family of bearings and these types of bearings have been used since the middle ages. Babbitt bearings also fall into this product group. These types of bearings are still commonly used today. The second category is the metal + polymer bearing. These types of bearings have been used since the early 1980's when Pacific Bearing introduced its Simplicity Self-Lubricating Linear Bearing. This type of bearing uses an Aluminum, Steel or Stainless steel outer shell and a piece of polymer or flouro-polymer as a liner. This type of liner is usually made of Teflon (to reduce friction) plus fillers (to increase life). The hard outer shell in combination with the enhanced polymer liner give this type of bearing a superior performance advantage over the other two types of bearings/bushings in this category. The third type of bushing/bearing is the all-polymer bushing. This bearing is used primarily in high-volume applications where cost is critical and the cost per bushing must be driven down to only a few pennies per part. Automated injection-molding machines allow this type of production at such a reduced cost.
- Plane bearings can only run on hardened Steel or Stainless steel shafting (raceways) OR can be run on hard-anodized aluminum or soft steel or aluminum.
- Plane bearings are less rigid than Rolling-Element bearings.
- Plane bearings handle contamination well and often do NOT need seals/scrapers.
- Plane bearings do not require oil or lubrication (often it can be used to increase performance characteristics)
The term plane bearing is of relatively recent usage and appears in technical literature such as isolated cases in Japanese Patents, and SAE document titles by Japanese authors. A search of Patent applications only returns two patents using the term and a search of SAE papers only returns a single paper with the term in its title. The term is also used by Japanese manufactures such as Yamaha and Makita in their parts nomenclature. There are also occasional mentions of the term in European publications. In American Engineering practice these bearings are referred to as journal bearings, sleeve bearings or bushing bearings and a search of index listings of engineering handbooks and reference materials for machinists will show no listings of or reference to "plane bearings". The usage has begun to appear in advertising materials from some bearing vendors only in recent years.
[edit] Linear motion slide
A linear motion system comprises bearings (plane or rolling element) and some means of moving the system from one point to another. Generally a screw or belt is used to move the system.
[edit] See also
- Linear stage, a common use for linear motion bearings
- Schaeffler Group, a manufacturer of linear motion bearings
- Pacific Bearing, a manufacturer of linear plain bearings & linear motion systems
- igus, a manufacturer of linear plain bearings
- IKO NIPPON THOMPSON, a manufacturer of linear motion bearings
