Friction and corrosion issues has been involving manufacturers’ minds for centuries that made them exploit oils and other lubricants in addition to various designs, to reduce effects. Seeking the right material for sliding surfaces is also an evident attitude. Bushings are one of the most used components of a machine in terms of obtaining the best surface properties. When a shaft is required to revolve inside a hole, cylinder bushing is used.

Bushings are used for following main objectives:

1. Strength against scratch: Bushing materials are chosen in a way to prevent any harm under loads and spin of 3 axes; particularly when an imperfect oil film is formed between two surfaces or lubrication suffers or even lacks in dry condition.
2. Increase the strength against fatigue and stress: Ability to bear the loads without Crippling is an important property of such parts. Fatigue condition occurs when amount or direction of loads vary frequently. Bushing substances should confront this condition.
3. Elasticity: Elasticity saves the substance against crippling and other damages.
4. Resistance against rust: Oxidation Parameter is too much concerned. For instance, Tin in copper-tin compound secures Copper from oxidation by the sulfur content of lubricant oil.

Bushing Structure
It is believed that a bi-geminal structure of soft grains dispersed in a hard phase, results the best for bushing substance; as in Copper-Tin alloy that Tin Grains dispersed in a copper foundation. In most of the bushings a soft metal with lower melting point is used, which causes a Shearing failure in the grains while slipping happens; so that the high temperature melts the touch points of soft metal that prevents grippage. Numerous experiments confirm that soft grains control the friction, while hard substrate has no role. Bronze is one of the most common substances of bushes, which is used in bushings with medium rev and load. Observing performance conditions, Bronze bushings are demanded more than others.
No need to say that the cost and availability of the material are very crucial. Therefore and to increase economic efficiency, it is preferred to use bimetals in fabrication process. Bushing structure consists of a back layer and a lined layer stratum. Back layer is usually made of steel with high tensile strength while internal stratum possesses the criteria of bushing substance. These two textures are bond together in Sintering process in which the powder of internal substance is set on a steel substrate, cooked in especial ovens. Heat bonds powder grains together and to steel substrate in a Sintering process that gives a porous structure to internal substance. The amount of this porouses can be controlled according to different standards, depended on the size and shape of the powder grains. Capillarity of porous structure helps the formation of a perfect oil film between sliding surface. In addition to Bushings, Regulator and Gapping Trust washers are also fabricated by this method. These parts are used in cases that two shafts or disks rotate with adjoining foreheads. Tabriz PM Co is the only national fabricator of bi-metal parts by Powder Metallurgy method. Designed according to SAE, ISO, BSI, JIS standards, the products of this company could grab an immense share of the market in terms of both quantity and quality.
Seeing the various production lines of the company and referring to this fact that the technology and knowledge utilized in these methods is a result of years of experiences and researches of technical engineers of Tabriz Powder Metallurgy Co., the products of this company includes a wide range of variety; however, Bi-metal products are classified in following main categories, based on the mechanism of the formation of lubricant film between sliding surfaces Email us ( to find the complete specifications of Bi-Metal products of Tabriz Powder Metallurgy Co.
1. Bushings:

Including hereunder 5 series:

default.jpg1-1. BS products: There is no need for a thick lubricant film between Shaft and Bushing when Bushing doesn’t revolve in high speed. Therefore, no ditch considered for lubricant conduction inside the bushing and oil is conducted into sliding surfaces due to capillarity of porous texture of Sintered substance.
default.jpg1-2. BG products: To provide a thick layer of lubricant oil in bushings with a relatively high speed revolving shafts, BG products are suggested, in which the lubricant ditch is contrived in Sintered surface. From and dimensions of conducting ditches are designed in according to international standards. In this condition, lubricant streams between surfaces in a rolling motion, forming a compressed film, named Elasto-Hydrodynamic film. Oil should penetrate with pressure in between of sliding surfaces. Email us to find more details about these products.
default.jpg1-3. BM Products: Pressured Oil is not required in this product; but a certain amount of lubricant is necessary. The relative motion of the surfaces currents the oil and forms the film. This method of film formation is called hydrodynamic method. These designs are suitable for bushings with low speed revolving shafts.
default.jpg1-4. BL products: in bushings with high rev shafts, both above mentioned features are required, to achieve both a thick layer and pressure of oil.
default.jpg1-5. BT Products: in some machines and conditions, oil can’t be used for lubrication purpose; or it is impossible or noneconomic to conduct it to sliding surface. Therefore kinds of substances are brought in use with self-lubrication property, and with no need to oil. Chemistry and mechanics engineers have had many efforts upon self-lubricant material; till composing plastics with metal or non-metal material, they could overcome many problems in designation of bushings and bearings.
Plastic has an evident role in manufacturing and product of bushings. Low friction coefficient and good resistance against abrasion, corrosion and vibrations, are some advantages of Plastic, of which one of the most important and beneficial types is named: P.T.F.E. Fluor element in molecule structure, grants good friction behavior; however the low mechanical strength, low heat conduction and low volume expansion coefficient are the weak points. 
Hence, P.T.F.E can be laminated on porous structure of a Sintered Bronze to remedy these deficiencies. Tabriz PM Co. is the only manufacturer of P.T.F.E laminated Bushings in the country, in a wide range of sizes and shapes. Email us to find more details about these products and implemented standards.
In 4 series:

default.jpg2-1. WS products: In low revs of adjoining surfaces while no thick layer of lubricant is required, WS trust washers come to play in which the Porous structure of sintered substrate –due to Capillarity- circulates the oil, merely.
default.jpg2-2. WM Products: To form a permanent oil-film between adjoining surfaces, WM trust-washers have some cavities on sintered layer. Oil is collected in cavities and circulates between surfaces due to relative motion of components, frequently, that causes a permanent layer of oil.
default.jpg2-3. WG Products: WG products are used when a thick layer of pressured oil is required. Oil-conducting ditches are contrived and existed according to the international standard codes and based on the speed revolving parts.
default.jpg2-4. WL products: In high revs or under the large loads when both durance and pressure of oil is required, WL products are used, having both oil-canals and oil-cavities.