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Examination Notes For Marine Officers: NOMENCLATURE

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Examination Notes For Marine Officers. The gear teeth are cut in a separate room which is kept at constant temperature. They are hobbled, then they are shaved ( a scrapper takes off very fine slivers and is free to follow the tooth form ) The ends and tip of the teeth are relieved. Pinion and wheel are arranged so as not to be as multiples of each other e.g. if ratio 10:250 was required the designer would use 10:251 so that there where many revolutions before two teeth repeated a mesh.

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Examination Notes For Marine Officers: HYPOID GEAR FAILURES

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Examination Notes For Marine Officers. The particular surface appearance that developed depends on the type and severity of operating conditions i.e. on the speed of rubbing and the magnitude of loading carried by the working surfaces. Furthermore it depends on the lubricity, film strength and anti weld characteristics of the lubricant. PROBLEMS FOUND DURING NORMAL USE. CALCULATION OF MAX TOOTH LOADING. BACKLASH & MATERIALS IN USE.

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Examination Notes For Marine Officers: SCORING,BREAKAGE&CORROSION

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Examination Notes For Marine Officers. Caused by foreign abrasive materials entering the mesh May appear as a score from root to tip caused by hard projection on one or more teeth penetrating oil film- this can be referred to as scoring or ridging or may appear as random scratches caused by dirt in the oil. Another form leads to a highly polished surface and is caused by very fine particles or dust in the oil. Main factors are unsuitable material , overloading and misalignement . Has four main causes;.

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Examination Notes For Marine Officers: CALCULATION OF MAX TOOTH LOADING.

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Examination Notes For Marine Officers. CALCULATION OF MAX TOOTH LOADING. Severity of tooth contact ; is generally expressed in terms of: Tangential load/face width. Alternately a 'K' factor based on the Hertzian stresses is used. K= W/Fod x mg 1/mg. W= tangential load on gear teeth ( lb ). Pinion torque/pitch radius of pinion). Fo = face width of teeth (inches). D = pitch diameter of pinion ( inches ). Mg = gear ratio; pinion speed / wheel speed. 150 max. for primary reduction ( through hardened ).

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Examination Notes For Marine Officers: BACKLASH & MATERIALS IN USE

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Examination Notes For Marine Officers. BACKLASH and MATERIALS IN USE. The backlash in a tooth is limited to oil film thickness and also to allow movement to alleviate problems caused by;. Flexibility within gear set. Up until 20 yrs ago 'through hardened' materials were widely used and still are but less frequently. These are carbon steel wheel rims and nickel steel pinions. The factors which govern the suitability of a material are;. Heat treatment is carried out after the hardening process. Providing p...

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Examination Notes For Marine Officers: GEARING FAULTS

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Examination Notes For Marine Officers. Faults associated with Spur and helical gearing. Hammer like action between teeth caused by variations in pitch or torsional vibration , may be negated by nodal drives. The mechanism for pitting is poorly understood . One theory is that it starts below the surface and parallel to it . When extended to surface oil under hydrodynamic pressure is forced in. Most severe on the pitch line or just below it , but may also be found on the dedendum. New gears suffer initial ...

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Examination Notes For Marine Officers: SCUFFING/ (WEAR)

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Examination Notes For Marine Officers. This type of failure - caused by the local breakdown of oil film as the surfaces slide over each other during mating and disengaging - led to the development of EP additives. It was also found that increasing oil viscosity was beneficial. With oil film breakdown, very high tempo are generated and welding of local high spots occurs Similar to that occurring with microseizure. These are then torn apart. Where operating conditions are more severe and boundary lubricati...

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Examination Notes For Marine Officers: PROBLEMS FOUND DURING NORMAL USE.

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Examination Notes For Marine Officers. PROBLEMS FOUND DURING NORMAL USE. In normal use, a contact area becomes polished .A wear ridge may form which may move as the bearings become worn, if new bearings are fitted then the position of the ridge will move. Problems may the occur of the teeth slipping off the ridges leading to noise and possibly removing thin shards of metal. Causes problems of overloading at the ends of teeth. PARTIAL SEIZURE OF ROTOR FLEXIBLE COUPLING. PROBLEMS FOUND DURING NORMAL USE.

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Examination Notes For Marine Officers: TIP RELIEF

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Examination Notes For Marine Officers. Fo the main gear wheel which may have more than one pinion a polygon of forces must be resolved at the wheel centre to determine resultant ahead and astern load on the bearings. Construction of Primary Wheel. The wheel cenrte is forged integral with the shaft. Wheel is stiifened by a number of axial steel tubes welded to the side plate. This type of construction is resistant to vibration. No key is fitted. The ends and tip of the teeth are relieved.