Rotary Mower Basics PART NO.
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Rotary Mowers 1 Table of Contents Historical Background...................................................................................................... 2 Theory of Operation......................................................................................................... 4 Cutting Action .................................................................................................................. 6 Equipment Application .....................................................................
2 Rotary Mowers Historical Background The first practical concept of a rotary type mower goes back to the 1930's. The concept evolved from the need for a grass maintenance tool that could cut long grass acceptably without the cost and sophistication of a reel mower. During the 1940's improvements in engines and material brought about increased use of rotaries but it wasn't until after World War II that their use became a common sight.
Rotary Mowers 3 Improvements in engines and drive systems have resulted in the very effective commercial type rotary mowers that are presently available.
4 Rotary Mowers Theory of Operation Blade mounting and drive system Blade Deck housing There are three basic structural members to a rotary cutting unit. Cutter Deck Housing The deck housing supports the blade hubs with their drive mechanism and is shaped to carry the cut grass clippings away from the deck in an effective manner. Blade mounting and drive system The blade is normally driven directly by the engine crankshaft, a hydraulic motor or through a belt pulley system to each blade hub.
Rotary Mowers 5 Power transfer from the engine to the blades is typically done by way of belts and transfer shafts. Belt drives typically transfer a high percentage of the available horsepower to the blade and generally produce much less noise than hydraulic drive systems.
6 Rotary Mowers Cutting Action A rotary mower cuts grass by impacting the blade cutting edge against the grass blades at a very high velocity. This cutting action requires that the blade cutting edge is sharp and rotating at an adequate speed. Cutting action Cutting Blade Design Three types of cutting decks are shown here; a recycler deck, side discharge and contour deck. From left to right. Low sail, high sail, medium sail, recycler sail, and atomic mulching blade.
Rotary Mowers Rotary mower clip 7 To understand rotary cutting theory you must understand the concept of clip. Clip can be defined as the forward distance traveled by the cutting unit during one revolution of the blade. This distance is divided by the number of blade tips to arrive at the clip dimension. The dotted lines represent the cut path by the previous blade tip. Although the blade cutting edge may be 3" - 4" long the very tip is the primary contact point with the grass blades on each pass.
8 Rotary Mowers Equipment Application Rotary mowing equipment is designed for a specific application. The misapplication of rotary mowing equipment can only result in abuse, poor qualities of cut and costly downtime. The following application factors will affect the equipment requirements. Type of Grass to be cut Turf areas maintained with rotary mowers Most types of grass can be cut with a rotary mower.
Rotary Mowers Capabilities and limitations 9 Capabilities and limitations Rotary mowers will not give the manicured cut appearance of a reel mower, but will give an acceptable appearance in more varied and adverse conditions. Rotary mowers are capable of cutting much higher grass than reel mowers. When an excessive amount of grass is removed, the cut appearance can become unsightly due to the discharged grass building up in clumps and ridges.
10 Rotary Mowers The Importance of the Operator and Equipment Manager The large investment in specialized cutting equipment cannot be jeopardized by unqualified operators. Before an operator can be considered qualified to operate a piece of equipment, there should be a significant effort by the supervisor towards their training and familiarization with each product. All too frequently this procedure is not followed, with the end result being costly repairs, down time and a decrease in equipment life.
Rotary Mowers 11 Productive Equipment Operation Experience has shown that a high percentage of the problems that develop on turf equipment do not require an overhaul or disassembly type correction. In many cases a problem has developed over a period of time and it could have been corrected by adjustment, lubrication, or similar required maintenance. This requires that turf equipment be checked on a regular basis and not operated until a major breakdown occurs.
12 Rotary Mowers Wheel traction Wheel traction and hill climbing Tire pressure in the traction wheels is critical for maximum traction capability. Over-inflated tire pressure can cause spinning and tearing out of the turf in adverse conditions. if lowering the tire pressure does not correct or stop a spinning condition, adding liquid to the tires may be required. Avoid quick acceleration while operating mowing equipment because a spinning tire can seriously damage the turf.
Rotary Mowers 13 Mowing patterns Mowing patterns It is normally beneficial to cut a given area in a pattern that will allow the grass to re discharged onto the previously cut grass area. If this is not done, the horsepower requirement increases due to the blade having to cut the discharged grass again. Debris on the Turf All debris should be removed from areas where rotary mowing equipment is being used to avoid serious damage to the cutting unit resulting in costly repairs and downtime.
14 Rotary Mowers Transporting mowing equipment Transporting mowing equipment Transporting mowing equipment requires discipline and knowledge to reduce downtime and increase equipment life. Operating the equipment in an abusive manner while transporting can only reduce its mowing efficiency.
Rotary Mowers 15 Cutting Unit Adjustments Height of cut adjustment and attitude Height of cut and attitude The height of cut is usually set by the placement of spacers on the castor wheel shafts or with the height of the rollers on contour type cutting units. The effective height of cut can be checked on the turf. This can be accomplished by inserting a narrow ruler down into the turf. Rotary cutting units are normally 1/8" - 1/4" lower at the front than in the back.
16 Rotary Mowers Inspection Maintenance and Repairs The efficiency of a rotary cutting unit is directly related to the air flow within the deck. Cutting efficiency and air flow The underside of the cutting deck should be examined periodically. The air flow is significantly affected if the deck is not cleaned out periodically. Inspect and clean out periodically to maintain air flow Blade Removal and Installation Impact gun blade removal only! Start bolt by hand and properly torque.
Rotary Mowers 17 The deck spindles usually run at approximately 2000 to 2500 RPM. They feature tapered roller bearing for impact resistance and durability. The spindles can be disassembled and repaired, or a complete assembly may be installed. Spindle assembly Pulley Matched Bearing Set Seals Housing Spacer and Seal Surface Shaft The spindle assemblies should be greased as part of a regularly scheduled maintenance program.
18 Rotary Mowers Inspecting drive belts and pulleys • Oil or grease contamination • Debris in pulleys • Damaged or rusted pulleys • Proper installation and tensioning Drive belt failures Periodically inspect drive belts and pulleys. A good time to do this is after cleaning the machine.
Rotary Mowers 19 A belt chirp is a small chirp or squeak that happens during start-up of an implement. It is caused by normal slippage an is completely normal. Never instruct the customer to use belt dressing to prevent chirps or squeaks. Do not recommend belt dressing actually for any belt problem. Belt dressing is only a band-aid and not a fix. Belt noise Chirp Belt Chirp • • • • • Chirp occurs on all types of belts. Caused by momentary slippage. Dust can be a contributing factor.
20 Rotary Mowers Rotary Blade Inspection and Sharpening To assure a quality of cut. The cutting edge of the blade must be kept in a sharp condition. A dull blade will produce a ragged cut and will require an excessive amount of engine horsepower to rotate the blade.
Rotary Mowers 21 The most common causes for rotary mowers not giving a good quality of cut are due to dull cutting edges and/or bent blades. Caution: Check cutter blade daily or before mower is used or stored and whenever mower is serviced. If bolt holding blade is loose, tighten it before using mower. If the blade is bent, the blade should be replaced. A bent blade will cause two problems. The most noticeable problem a increase in horsepower that is required to operate the mower.
22 Rotary Mowers OEM Blades • Specifically designed for the intended deck. • Meets all of the required tests. – Hardness – Object expulsion • Meets the mowing and quality demands. • Life expectancy. When discussing rotary blades, keep in mind that OEM blades are designed specifically to perform on the intended deck.
Rotary Mowers Check blade balance WARNING ! 23 After the blade has been sharpened the balance must be checked. This can best be accomplished using a commercial balancer. An unbalanced blade causes vibration damaging to adjoining parts. Warning: Always wear face shield or safety glasses when grinding or sharpening is being done. Always wear a face shield or safety glasses when grinding or sharpening.
24 Rotary Mowers Toro University Technical Training
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