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Typical Rotary Blade

Warped or bent blade - blade tip higher than centre portion of blade. Will cause poor quality of cut and high horsepower requirement.

 

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Blade straight and parallel - blade tip lower than the centre portion of the blade. Will give good quality of cut and low horsepower requirement.

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Blade tip twisted - heel lower than the cutting edge. Will cause poor quality of cut and high horsepower requirement.
 

 

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Blade tip straight - cutting edge lower than the heel of the blade. Will give good quality of cut and low horsepower requirement.

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Typical Rotary Blade- Cutting Edge

DO NOT GRIND BOTTOM OF CUTTING EDGE

Incorrect sharpening angle will cause poor quality of cut and high horsepower requirement.

 

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GRIND TOP SIDE OF CUTTING EDGE ONLY

Correct sharpening angle will give good quality of cut and low horsepower requirement

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Correct Grind Angle for Reel Blades

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Correct Bedknife Grind Angles

Lubrication

SAE - Society of Automobile Engineers

Traditional American body, set standards for everything from horse-power ratings to nuts and bolts and oil viscosity e.g. SAE 30 engine oil and SAE 90 gear oil.

 

API - American Petrol Institute

Another body setting service ratings for engine oils. This rating is added to the SAE number e.g. SAE 30 API SE./CC. "SE" is a 1972 rating and "CC" goes back to 1961 diesel engines for moderate service, so this oil doesn't have a sophisticated additive package and is generally out of date for modern engines, but it's cheap. The highest current rating are SG/CE for most severe service with emission controls, turbochargers, long drain intervals etc. e.g. SAE 15 W 40 API SG/CE. This multigrade oil is blended to give performance over a wide range of conditions. "W" = winter: this gives easier cold starting and yet has the full protection of the heavier oil when it heats up. It is a higher detergent oil and is suitable for petrol, diesel or gas engines to reduce inventory.

 

Additives

All oil companies use additives to build products to do a job, from hydraulics to engines, compressors and gearboxes. The main ones are:- viscosity stabilisers, rust and oxidation inhibitors, anti-acid, anti-foam, detergent, dispersant, friction modifiers, extreme pressure and tacky additives. These are carefully blended in, in balanced strengths along with bonding agents to key them to the base oil. How good the base oil, blending and additives are will determine the oil's cost, performance and life. Later overdoing of the "recipe" can affect the whole package or wipe out parts of it in the long term.

 

Emulsification & Oxidation

Oil and water don't mix? Look in the rocker cover when the head gasket's blown or a pump gearbox with a worn seal. The "custard" is water absorbed into the oil. Some will settle out but some stays as part of the oil. Water breaks down the film strength of oil, causing premature wear and rusting. 0.1% water (undetectable to the eye) is the maximum limit. Regular oil analysis determines the emulsification along with wear rates in long life products. Oxidation or "burning" of the oil starts as soon as it rises above ambient temperature. Oxygen moves into the oil molecule and thickens it. The rate doubles for every 20?C increase. The smell and colour of used hydraulic oil is a good example. This hardworking product is often pushed well past giving wear protection to the system.

 

Timken OK Load Test

Developed by TIMKEN as a measure of grease and oil performance in their bearings. A product in the 40-90 lb "TIMKEN" range is regarded as "extreme pressure" e.g. SAE 90 EP or LITHIUM EP2 grease.

 

Grease Bases - "Soaps"

Metallic or clay "soaps" are used to hold oil in a grease form. Various soaps are used - calcium, aluminium, lithium and bentone are common ones giving water proofing, pumpability, high load and high temperature qualities respectively. Complex mixes give combined benefits. Gene ral purpose greases are commonly lithium based.

 

NLGI Grades - National Lubricating Grease Institute

Classify greases by thickness from semi-fluid at NLGI000 to extremely heavy at NLGI5 or 6. In practice, Grade 0 or 1 would be low temperature or high speed greases, Grade 2 is general industrial/automotive and Grade 3 suits open gears. EP and other qualities aren't compared in this grading, only relative viscosity.

 

Crude Oils

95% crude production is the Naphthenic hydrocarbon. It is solvent refined by the petro-chemical industries into fuels primarily, then oils and just about everything else. It does an acceptable job as a lubricant but has limitations, hence the increase in synthetic re-constructed (not re-refined) oils of today. The other crude, Paraffinic, is well recognised as a better, more stable lubricant but it is expensive to refine and doesn't lend itself to many other uses. Paraffins are "oilier", resist water and oxidation far better and are good "building blocks" for stronger long-life additive packages.