Clarifying Drives. How to Design and Manufacture the Perfect Sedimentation Drive A GLV COMPANY

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Scott Gibbs
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1 Clarifying Drives How to Design and Manufacture the Perfect Sedimentation Drive A GLV COMPANY

Introduction to Sedimentation Drives The manufacture of sedimentation drives for water and wastewater treatment has become a very competitive industry.

Engineers responsible for specifying clarifier and thickener drives must now evaluate many competing designs whose real differences are more often obscured than illuminated by the manufacturers

Starting with a detailed explanation of the our drive design, it will explain the mechanics behind the mechanism, to show the specific fixed principles of mechanical design which all geared torque

With these in mind, the discerning engineer can decide for himself which drives are most likely to fulfill the manufacturer's promise of reliable service and long life.

Manufacturers Association (AFBMA). These documents provide guidelines for the design of reliable transmission systems and a quantitative framework for assessing their capacities.

2 Introduction to Sedimentation Drives The manufacture of sedimentation drives for water and wastewater treatment has become a very competitive industry. The apparent simplicity of low-speed torque multipliers has lured many new suppliers to this field with products of widely varying merit. Engineers responsible for specifying clarifier and thickener drives must now evaluate many competing designs whose real differences are more often obscured than illuminated by the manufacturers advertising. The purpose of this brochure is to highlight those differences. Starting with a detailed explanation of the our drive design, it will explain the mechanics behind the mechanism, to show the specific fixed principles of mechanical design which all geared torque transmission systems must satisfy. With these in mind, the discerning engineer can decide for himself which drives are most likely to fulfill the manufacturer's promise of reliable service and long life. 2 A Word About Standards The accepted manuals of practice for sedimentation drive design are the standards of the American Gear Manufacturers Association (AGMA) and the Anti-Friction Bearing Manufacturers Association (AFBMA). These documents provide guidelines for the design of reliable transmission systems and a quantitative framework for assessing their capacities. When correctly applied, these formulas provide a technical basis for comparing the wear lives and strength ratings of competing drive mechanisms in a specific application. But rating formulas are not always correctly applied. AGMA and AFBMA equations for torque capacity and continuous duty service life can be used to misrepresent the utility of drives which do not comply with AGMA and AFBMA design standards. The accuracy of rating calculations hinges on a number of implicit assumptions about the construction of a drive under examination: That all mounting surfaces for gears and bearings are machined to very precise tolerances That key drive components are positively located with machined pilots or registers That the drive base is sufficiently rigid to preserve accurate gear alignment under peak design load That no welding has been required after final machining operations That the accuracy of pinion to main gear alignment is fixed with upper and lower pinion support bearings That an adequate lubrication system has been supplied to reduce friction, dissipate heat, collect condensate and contaminants and separate them from load bearing and torque transmitting surfaces.

3 Introduction to Sedimentation Drives Drive Design Eimco Water Technologies drives are designed and built specifically for long-term sedimentation service, in strict compliance with AGMA and AFBMA standards. Every piece of every drive is engineered to meet and exceed the requirements for 20-year continuous duty rating. Convenient, economical service is a design priority. With routine maintenance, many our drives are still operating after 30 and even 40 years of continuous service... with their original gears and bearings still in place. Where some drives are designed for simplicity and economy in manufacture, Eimco Water Technologies manufactures drives that are economical to own and simple to maintain. 3

The mechanism pictured above and at the right is a C-30

selection of materials, and most importantly, the methods of

Massive main gear casting 3 Worm gear intermediate reducer 4

main bearing with large diameter chrome alloy balls 6 All

lubrication for main gear and bearing set 8 Oil drains

4 The mechanism pictured above and at the right is a C-30 center column mount drive with 30-inch main gear pitch diameter. In the design of this drive s principle components, the selection of materials, and most importantly, the methods of assembly and bearing component support, perfectly represent our design philosophy. Drives Feature 1 Rigid cast base with deep oil reservoir 2 Massive main gear casting 3 Worm gear intermediate reducer 4 Fully supported one-piece pinion 5 Replaceable strip liner main bearing with large diameter chrome alloy balls 6 All bearings located in machined registers 7 Fill oil bath lubrication for main gear and bearing set 8 Oil drains located away from bearing seats 9 No seals or gaskets below oil level 10 Machined mounting shoulder to preserve pinion/main gear alignment 11 Accurate, weatherproof enclosed torque 4 control

5 The Case for Cast Iron Cast Iron is a natural choice for structures to support and enclose high-torque gears. Complex cross sections with a high degree of structural rigidity are more precisely formed than with fabricated plates, and material section is easily varied to provide massive support in high load areas. An additional advantage is the natural corrosion resistance of cast iron. The drive enclosures take maximum advantage of all these material-related opportunities. Full inner and outer walls form a deep "U" cross section, offering exceptional rigidity and an ample oil reservoir. Extra material section under main bearing, pinion bearing and intermediate reducer mounting surfaces ensures proper alignment under peak loads. Expert casting design informed by nine decades of metallurgical and manufacturing experience allows massive sections to be formed free of blowholes, voids and inclusions that might compromise the integrity of the finished drive. Machined, Registered Bearing Mounts There is no surer way to establish the quality of a drive mechanism than to examine the way in which bearings are installed. It is absolutely essential that every bearing be positively located and fully supported against deflection under all loads and moments. Every bearing in every drive is mounted on a precisely machined surface, and positively located in a machined shoulder diameter or pilot. Only when bearings are supported in this manner can accurate alignment of mating surfaces be maintained and the service life of gears and bearings reliably calculated. An additional advantage is that a drive that has been disassembled for repair can be easily and accurately reassembled in the field. Strip Liner main bearing races correctly located in precision machined registers. Machined Register locates upper pinion support bearing. Machined shoulder diameter prevents deflection of intermediate reducer. Improperly applied precision bearing with no machined support diameter. 5

Chain and Sprocket Primary Reduction Initial reduction on all our drive mechanisms is accomplished with a

In addition to mechanical simplicity and durability, this arrangement has the advantages of allowing final rake

Worm Gear Intermediate Reducer Worm and gear sets provide high reduction ratios in a compact arrangement,

Moving parts are reduced to an absolute minimum in a simple design that is easily maintained and repaired in the

Alloy steel worms and bronze gears are individually matched, and the reducer is designed so that the relatively

Accurate alignment between the intermediate reducer and main gear set is preserved through the use of a

Fully Supported One-Piece Pinion Our drives employ a precision machined, one-piece pinion to transmit power

6 Chain and Sprocket Primary Reduction Initial reduction on all our drive mechanisms is accomplished with a reliable chain and sprocket assembly. In addition to mechanical simplicity and durability, this arrangement has the advantages of allowing final rake speed to be changed simply and inexpensively by changing the diameter of the motor output shaft sprocket. Worm Gear Intermediate Reducer Worm and gear sets provide high reduction ratios in a compact arrangement, delivering smooth power transmission with no pulsations in output speed. Moving parts are reduced to an absolute minimum in a simple design that is easily maintained and repaired in the field. Alloy steel worms and bronze gears are individually matched, and the reducer is designed so that the relatively low-cost worm gear or key will yield before other, more expensive components. Accurate alignment between the intermediate reducer and main gear set is preserved through the use of a precision mounting register machined in the drive base. Fully Supported One-Piece Pinion Our drives employ a precision machined, one-piece pinion to transmit power between the intermediate reducer and main gear, without resort to couplings or keyways that might compromise the strength and accuracy of this linkage. Two support bearings, one located above and one below the main gear, ensure accurate alignment of the gear faces. It should be noted that AGMA standards provide no procedure for rating overhung pinions. Strength and service life claims for drives with unsupported pinions should be evaluated carefully. 6

7 Deep Tooth Faces on Main and Pinion Gears Our Drives are designed with deeper tooth faces on main and pinion gears than any other competing mechanism. Greater tooth surface area means wider distribution of contact stresses, resulting in longer gear life or higher torque rating for a given pitch diameter. Separate Main Gear and Bearing Can Be Replaced Independently The Eimco Water Technologies drives are designed so that the main gear and bearing can be separately replaced. Downtime and repair expenses are greatly reduced and service life can be extended substantially. Forty-year-old drives are in service today, following strip liner replacement and normal maintenance. High Quality Main Bearing Rates 20+ Year B10 Life Eimco Water Technologies wastewater drives utilize high quality (super clean) induction hardened alloy steel strip liners and large diameter chrome alloy steel balls. B10 ratings for these bearings far exceed the 20-year calculated service life of the gears they support. 7

8 Oil Bath Lubrication Adequate lubrication is essential to the achievement of optimum gear and bearing life. All our drives are oil bath lubricated for maximum friction reduction and reliable dissipation of heat. Every bearing is fully submerged and all gears deeply immersed for 100 percent reliable lubrication. The dual-wall base is designed with a deep oil reservoir, providing ample room for condensate and contaminants to settle away from bearings and gears. Cast construction eliminates the need for seals or gaskets below oil level, ensuring reliable containment. Oil drains have been placed away from the lower pinion pocket to prevent bearing contamination during lubricant changes. No other drive delivers equal lubrication and protection from oil contaminants. Sealed Mechanical Torque Monitor Torque load is positively measured through worm shaft movement against a precisely rated compression spring. This linear movement is converted to visual information by a cam and follower arrangement connected on the worm gear housing for convenient visual reference. Safety switches activate an audible high torque alarm and cut drive power when torque exceeds maximum design levels. The mechanism is completely protected from weather, corrosion and tampering by a sealed NEMA 4 X/7 housing. In Summary This brochure has outlined some key design issues for clarifier and thickener drives as identified in AGMA and AFBMA standards, including: 1 Sufficient base rigidity for reliable component support 2 Correct use of machined pilots or registers to prevent deflection of load bearing and torque transmission components under load 3 An ample lubricant reservoir, uncompromised by submerged seals or gaskets, with adequate settling area for condensate and other contaminants No other drive manufacturer addresses these criteria as thoroughly as Eimco Water Technologies. We provide mechanisms that perform reliably in long-term sedimentation service. Copyright 2007 GLV. All rights reserved. ETE008 For more information visit us at

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