Handbook Of Shaft Alignment Episode 1 Part 5 pps

The vast majority of rotating machinery is either held in position by a rigid foundationmonolithic, attached to a concrete floor, installed on an inertia block, or held in position on a

It is important for the personnel who maintain rotating machinery to have a basic standing of how machinery should be supported and what problems to look for intheir foundations, baseplates, and frames to insure long-term alignment stability in theirmachinery.

under-In addition to the machinery to ground or structure interface, attention must also bedirected to any physical attachments to the machinery such as piping, conduit, or ductwork

It is desirable to insure that these attachments produce the minimum amount of force on themachinery to also insure good stability This chapter will hopefully provide the reader withthe basic foundation design principles and some techniques to check equipment in the field todetermine if problems exist with the foundation and frame, or the interface between themachinery and the foundation, or piping and conduit attached to the machine itself

3.1 VARYING COMPOSITION OF EARTH’S SURFACE LAYER

The best place to start this discussion is at the bottom of things All of us realize that there is amajor difference in stability as we walk along a sandy beach and then step onto a large rockoutcropping Different soil conditions produce different amounts of firmness Since rotatingmachinery could potentially be placed anywhere on the planet, the soil conditions at thatlocation need to be examined to determine the stability of the ground For new installations

or where foundations have shifted radically, it may be a good idea to have boring testsconducted on soils where rotating machinery foundations will be installed Table 3.1 showssafe bearing load ranges of typical soils The recommended maximum soil load from acombination of both static and dynamic forces from the foundation and attached machineryshould not exceed 75% of the allowable soil bearing capacity as shown in Table 3.1

3.2 HOW DO WE HOLD THIS EQUIPMENT IN PLACE?

I suppose someone has attempted to sit a motor and a pump on the ground, connected by theshafts together with a coupling, and started the drive system up without bolting anythingdown My guess is that they quickly discovered that the machines started moving around alittle bit after start up, then began moving around a lot, and finally disengaged from each otherhopefully without sustaining any damage to either of the machines Maybe they tried it againand quite likely had the same results I am sure they finally came to the conclusion that this

TABLE 3.1

Soil Composition

Bearing Capacities of Soils: Safe Bearing Capacity

Hardpan, cemented sand and gravel, soft rock (difficult to chisel or pick) 5–10 0.48–0.96

was not going to work for long periods of time and decided to ‘‘hold the machines’’ in theirstarting position somehow How are we going to do this exactly? What should we attach themto? How about some wood? No, better yet, something like metal or rock, something that isstrong.

Our rotating equipment needs to be attached to something that will hopefully hold it in astable position for long periods of time I have seen just about every possible configurationyou can imagine Even the scenario mentioned above The most successful installationsrequire that the machinery be attached to a stable platform that enables us to detach one

or more of the machines from its platform in the event that we want to work on it at anotherlocation Classically we attach and detach our equipment with threaded joints (i.e., bolts andnuts) You could, I suppose, glue or weld the machines to their platform, and it would just be

a little more difficult to detach them later on

The devices that we have successfully attached our machinery to are baseplates, soleplates,

or frames There are advantages and disadvantages to each choice The baseplates, plates, or frames are then attached to a larger structure, like a building, ship, aircraft andautomotive chassis, or Earth There are many inventive ways of attaching rotating machinery

sole-to transportation mechanisms (e.g., boats, mosole-torcycles, airplanes), and design engineers arestill coming up with better solutions for these types of machinery-to-structure interfacesystems Our discussion here will concentrate on industrial machinery

The vast majority of rotating machinery is either held in position by a rigid foundation(monolithic), attached to a concrete floor, installed on an inertia block, or held in position on

a frame There are advantages and disadvantages to each design There are also good waysand poor ways to design and install each of these methods to keep our machinery aligned andprevent them from bouncing all over the place when they are running In summary, machinesare attached to intermediary supports (i.e., baseplates, soleplates, and frames) that are thenattached to structures (i.e., buildings, floors, foundations) Figure 3.1 shows a typical rigid

FIGURE 3.1 Rigid foundation for induced draft fan

foundation design, Figure 3.2 shows a typica inertial block (aka floating) design, andFigure 3.3 shows a typical frame design.

3.2.1 BASEPLATES

Baseplates are typically either cast or fabricated as shown in Figure 3.4 and Figure 3.5

A fabricated baseplate is made using structural steel such as I-beams, channel iron, angle,structural tubing, or plate, cutting it into sections, and then welding the sections together It isnot uncommon to replace structural steel with solid plate to increase the stiffness of the basesimilar to Figure 3.6

3.2.1.1 Advantages

1 Most commonly used design for industrial rotating machinery

2 Provides excellent attachment to concrete foundations and inertia blocks assuming theanchor bolts were installed properly and that the grout provides good bonding

3 Can be flipped upside down and grout poured into the cavity before final installation

FIGURE 3.2 Spring isolated inertia block with motor and pump

FIGURE 3.3 Frame supporting a belt drive fan

FIGURE 3.4 Cast baseplate.

FIGURE 3.5 Fabricated baseplate

FIGURE 3.6 Weak structural steel was replaced with solid plate on this baseplate

4 Machinery can be placed onto the baseplate prior to installation and roughly aligned inthe lateral and axial directions to insure that the foot bolt locations are drilled andtapped accurately to hopefully prevent a bolt bound condition or incorrect shaft end toshaft end spacing

5 Equipment mounting surfaces can be machined flat, parallel, and coplanar prior toinstallation

6 Some designs include permanent or removable jackscrews for positioning the machinery

in the lateral and axial directions

3.2.1.2 Disadvantages

1 Usually more expensive than using soleplates or frames

2 Equipment mounting surfaces are frequently found not to be flat, parallel, and coplanarprior to installation

3 Difficult to pour grout so it bonds to at least 80% of the underside of the baseplate

4 Possibility of thermally distorting baseplate using epoxy grouts if pour is thickerthan 4 in

5 Frequently installed with no grout

3.2.2 SOLEPLATES

Soleplates are effective machinery-mounting surfaces that are not physically connectedtogether Figure 3.7 shows a soleplate being prepared for grouting on a medium-sized fanhousing They are typically fabricated from carbon steel and there are usually two or moresoleplates required per concrete foundation or inertia block Correct installation is more

FIGURE 3.7 Soleplate being prepared for grouting

tedious than baseplates due to the care required to insure that the individual soleplates are inlevel and in the same plane On larger machinery where the soleplates can be six or more feetapart, using machinist levels is not going to work effectively and either optical or laseralignment tooling is recommended to get the plates level and in the same plane Ideally thesoleplates should be level to 1 mils=ft (1 mils ¼ 0.001 in.), and there should not be a deviation

of more than 5 mils at any point on all soleplates from being coplanar Figure 3.8 shows anoptical jig transit used to level and plane the soleplates shown in Figure 3.7

FIGURE 3.8 Optical jig transit being used to level a soleplate

mounting isolators) Due to the fact that most frames are welded construction, the surfacesthat the machinery attaches to are often not coplanar or parallel to each other Figure 3.9through Figure 3.11 show a variety of rotating machinery mounted on frames.

3.2.3.1 Advantages

1 Most practical design for machinery that cannot be attached to Earth or buildingstructures

2 Used in situations where excessive floor loads are exceeded with concrete construction

3 Easier to fabricate and install than rigid foundations or inertia blocks

3.2.3.2 Disadvantages

1 Due to the low frame-to-machinery weight ratio, vibration levels are typically higherthan equipment located on rigid foundations or inertia blocks

2 Subject to more rapid deterioration from environment

3 Difficult to insure flatness of machinery-mounting surfaces during construction

4 Excitation of structural natural frequency more prevalent with this design

FIGURE 3.9 Motors and pumps sitting on structural steel frames The unistrut used for the motors isnot recommended

FIGURE 3.10 Main lube oil pump coupled to outboard end of motor sitting on a fabricated framebolted to the motor’s end bell

3.2.4 MONOLITHICRIGIDFOUNDATIONS

Rigid foundations are typically found at the ground level The basic design of a rigidfoundation is shown in Figure 3.12 Their sole purpose is to provide an extremely stableplatform for the rotating machinery with no intention of supporting any other object but themachinery that is placed on it except perhaps piping, ductwork, or conduit that attaches tothe machines in the drive system Effectively, the rigid foundation consists of a pouredreinforced concrete block with anchor bolts that have been imbedded in the concrete

FIGURE 3.11 Series of water bearings held in place on a dredge frame

Reinforcement rods Concrete foundation

Frost line

75% of total pedestal height

Anchor bolt imbedded in concrete

Reinforcement rods should be spaced no more than 12 in apart, using a minimum rod size of1=2 in (12.7 mm) The concrete should be rated at a compressive strength of 4000 psi for 28 d.Once the concrete has set to at least 50% cure (typically 7 d for most concrete) the baseplate orsoleplates are set into a level and coplanar condition slightly above the top of the concrete(usually 1–2 in.) The baseplate is then grouted to the concrete foundation as illustrated

in Figure 3.12

Here are some basic design ‘‘rules of thumb’’ for concrete foundations:

1 Whenever possible, mount every machine in the drive system on the same foundation

2 The mass of the foundation should be three to five times the mass of centrifugalmachinery it supports and five to eight times the mass of reciprocating machinery

3.2.4.2 Disadvantages

1 If located outdoors, eventually degradation of foundation imminent especially if located

in geographical area where climatic conditions change radically throughout the year

2 For machinery with attached, unsupported piping or ductwork, extreme forces fromimproper fits can occur causing damage to machinery

3 Potential settling of foundation causing instability and potential transmission of forcesfrom attached piping

3.2.4.3 Tips for Designing Good Foundations

1 Insure that the natural frequency of the foundation–structure–soil system does notmatch any running machinery frequencies or harmonics (such as 0.43
, 1
, 2
, 3
,

4
, etc.) with the highest priority being placed on staying þ20% away from the

operating speed of the machinery sitting on the foundation being considered Alsowatch for potential problems where running speeds of any machinery nearbythe proposed foundation might match the natural frequency of the system beinginstalled

2 In case the calculated natural frequency of the structure does not match the actualstructure when built, design in some provisions for ‘‘tuning’’ the structure after erectionhas been completed such as extension of the mat, boots around vertical supportcolumns, attachments to adjacent foundations, etc

3 Minimize the height of the centerline of rotation from the baseplate

4 Rotating equipment that will experience large amounts of thermal or dynamic ment from off-line to running conditions should be spaced far enough apart to insurethat the maximum allowable misalignment tolerance is not exceeded when the shafts

move-are located in the off-line position Refer to Chapter 16 for more details on off-line torunning machinery movement.

5 Design the foundation and structure to provide proper clearances for piping andmaintenance work to be done on the machinery, and provisions for alignment of themachine elements

6 Install removable jackscrew devices on the baseplate for moving (i.e., aligning) ment in all three directions: vertically, laterally, and axially If jackscrews will not beused, provide sufficient clearance between baseplate and rotating equipment for inser-tion of hydraulic jacks for lifting equipment during shim installation or removal

equip-7 Provide vibration joints or air gaps between the machinery foundation and the rounding building structure to prevent transmission of vibration

sur-8 If possible, provide centrally located, fixed anchor points at both the inboard andoutboard ends on each baseplate in a drive train to allow for lateral thermal plateexpansion Insure there is sufficient clearance on the casing foot bolt holes to allow forthis expansion to occur without binding against the foot bolts themselves

3.2.4.4 Tips for Installing Foundations and Rotating Machinery

1 Select a contractor having experience in installing rotating machinery baseplates andfoundations or provide any necessary information to the contractor on compaction ofbase soils, amount and design of steel reinforcement, preparing concrete joints duringconstruction, grouting methods, etc

2 If the concrete for the entire foundation is not poured all at once, be sure to chip awaythe top 1=4 in to 1=2 in of concrete, remove debris, keep wet for several hours (or days ifpossible), allow surface to dry and immediately apply cement paste before continuingwith an application of mortar (1–6 in.) and then the remainder of the concrete If notdone, the existing concrete may extract the water from the freshly poured concrete tooquickly and proper hydration (curing) of the new concrete will not occur

3 Use concrete vibrators to eliminate air pockets from forming during the pouring processbut do not over vibrate, causing the larger concrete particles to settle toward the bottom

of the pour

4 Check for baseplate distortion prior to installing the baseplate Optical alignment

or laser tooling equipment can be used to measure this Mounting pads should bemachined flat and not exceed 2 mils difference across each individual pad (i.e., machin-ery foot contact point) If there is more than one pad that each individual machine willcome into contact with, insure that those pads are coplanar within 5 mils Insure that thecontact points for each machine are parallel to the contact points for every othermachine on that baseplate within 10 mils=ft If the baseplate is slightly distorted it may

be possible to stress relieve by oven baking or vibratory shakers If the distortion isexcessive, the contact surfaces may have to be machined flat, coplanar, and parallel

5 Sandblast the underside of the baseplate If sandblasting is unreasonable, grind at least90% of the surface to bare metal If cement-based grout is going to be used, coat withinorganic zinc silicate primer as per coating manufacturers specifications to preventcorrosion and provide good bonding to cement-based grout The primer should notexceed 5 mils in coating thickness If epoxy-based grout is going to be used, do not coatwith primer and grout within 48 h of sandblasting to insure that excessive oxidation doesnot occur to the sandblasted surface

6 Insure that the baseplate has leveling jackscrews at each of the anchor bolt locations.Try not to use wedges to level the baseplate If jackscrews were not provided, weld 3=4 in

or 1 in fine threaded nuts to the outside perimeter of the baseplate near the anchor bolts

to use with jackscrews for precise leveling Optical or laser alignment equipment should

be used to check levelness particularly for medium and large machinery drive systems Amachinist level could be used on smaller baseplates but additional precautions need to

be taken to insure that all of the mounting points for each machine are coplanar (i.e., it

is possible to have two level surfaces not in the same plane)

7 For large baseplates with two or more bulkheads, grout one bulkhead section at a time.Apply grout through a 4–6 in diameter hole centrally located in each section Provide atleast 1 in diameter vent holes near the corners of each section Allow a minimum of 48 hcure time before setting rotating equipment onto base

8 Protect the foundation from any radiant heat generated from machinery, steam, or hotprocess piping by insulation or heat shields where possible

3.2.5 BASEPLATESATTACHED TOCONCRETEFLOORS

Similar in design to the monolithic rigid foundation, foundations attached to concrete floorsrequire a slightly different approach in their design and installation To a certain extent,the concrete floor now acts as the ‘‘foundation.’’ There are three different approaches toattaching machinery to concrete floors:

1 A baseplate that is grouted by traditional methods to a concrete floor or a raisedconcrete pad as shown in Figure 3.13

2 A baseplate that is pregrouted prior to installation and is then bonded to a concretefloor or a raised concrete pad as shown in Figure 3.14

3 A solid metal baseplate is bonded to a concrete floor or a raised concrete pad that is alsobonded to the concrete floor as shown in Figure 3.15

If the machinery is going to be mounted to a floor at ground level, holes (usually 4–6 in indiameter) should be cored through the concrete floor for the anchor bolts The top surface ofthe floor should then be chipped away (i.e., scarified), a form built, reinforcement rods set inplace, anchor bolts positioned, and a raised concrete block poured

Reinforced concrete floor Reinforced concrete slab

Concrete bonding glue

Anchor bolt

Protective sleeve

Fabricated structural steel baseplate

Leveling screw

Cementious grout or Epoxy grout

Air vent hole

Grout pour hole

Air vent hole

FIGURE 3.13 A baseplate that is grouted to a concrete floor or pad using traditional grouting methods

Concrete bonding glue

Anchor bolt

Protective sleeve

Fabricated structural steel baseplate

Leveling screw Air vent

hole

Grout pour hole

Air vent hole

FIGURE 3.14 A pregrouted baseplate bonded to a concrete floor or pad

Reinforced concrete floor Reinforced concrete slab

Concrete bonding glue Anchor bolt Fabricated baseplate

Solid steel plate

Protective sleeve Epoxy grout

FIGURE 3.15 Solid metal baseplate bonded to a concrete floor or pad

2 Possibility of anchor bolts pulling out, loosening, or breaking if proper precautions arenot taken during the installation of the anchor bolts

3 Possibility of baseplate (or soleplates) and the concrete slab loosening and degradingrapidly if care is not taken to properly bond the baseplate to the concrete slab to theconcrete floor

4 For machinery with attached, unsupported piping or ductwork, extreme forces fromimproper fits can occur causing damage to the machinery

5 Limited ability to isolate any vibration in the machinery from the surrounding environment

6 Possibility of absorbing vibration from other machinery in the immediate vicinity

3.2.6 ANCHORBOLTS

Figure 3.16 shows various anchor bolt designs Anchor bolts are imbedded in the concreteand serve as the device that secures the baseplate or soleplates to the concrete mass The bestdesigns incorporate a sleeve that allows the bolt to stretch properly when tightened and alsoallows for some minor positional changes if the anchor bolts do not index to the holes in thebaseplate or soleplate as shown in the bottom two diagrams in Figure 3.16 The anchor boltsshould be at least four anchor bolt diameters from the outside edge of the concrete, should be

of sufficient size and strength (ASTM A36 or ASTM A575-M1020), the anchor bolt should

be able to resist chemical attack or oxidation, the washer should conform to ANSI B18.22.1,lock washer should not be used, and nuts should be heavy hex, full size, and conform toANSI B18.2.2

Concrete

Pipe sleeve enables proper stretch on bolts and allows for slight adjustments to anchor bolt

FIGURE 3.16 Various anchor bolt designs (Courtesy of Unisorb, Jackson, Michigan With permission.)

If the machinery is going to be mounted on a floor above ground level where there is accessfrom underneath the floor surface, holes should be drilled completely through the floor forthe anchor bolts Whether the machinery is going to be set onto a monolithic foundation atground level, or onto a floor, properly positioning the anchor bolts is of extreme importance.

To insure that the anchor bolts maintain their desired position, it is a good idea to set thebaseplate onto a wooden template, mark where the anchor bolts will be, drill holes intothe template, and then place the template on top of the wooden form to assist in correctlypositioning and holding the anchor bolts in position when the concrete is poured

3.2.7.1 Advantages

1 If concrete slab and baseplate act as a single unit with sufficient stiffness, this designprovides a stable platform to attach rotating machinery, allowing the whole assembly tomove in the event outside forces such as piping strain are bearing on unit

2 Ability to somewhat isolate any vibration from attached machinery to surroundingstructure or other machinery in nearby area

3.2.7.2 Disadvantages

1 Slightly more difficult to construct, install, and maintain than rigid foundations

2 If excessive amount of vibration exists on machinery for prolonged periods of time,potential damage may occur to the machinery or attached piping

FIGURE 3.17 Inertia block for motor—fan drive (Courtesy of Unisorb, Jackson, Michigan Withpermission.)

3 Potential degradation of support springs or isolators

4 Frequently more difficult to align machinery and keep aligned for long periods

3.2.8 CEMENT, CONCRETE,ANDGROUTBASICS

Since rigid foundations and inertia block design incorporate concrete or other types ofpourable liquid to solid media, it is important to have a rudimentary understanding ofthese basic building materials Concrete is typically a mixture of inert materials and cement.Grout can be cement based or epoxy based Cement-based grout is typically a mixture of sandand cement Epoxy-based grout can be pure epoxy consisting of a resin and a hardener(curing agent) or it can be mixed with inert material such as sand, steel shot (small round steelballs), fly ash, etc

The inert materials in concrete are typically stone and sand but a wide variety of othermaterials can be used The word ‘‘cement’’ is from the Latin verb ‘‘to cut’’ and originallyreferred to stone cuttings used in lime mortar Lime consists of CaO (60%–67%), silica (SiO2,17%–25%), alumina (Al2O2, 3%–8%), and small amounts of iron oxide, magnesia, alkalioxides, and sulfuric anhydride Cements may be naturally occurring (lime) or manufactured

by crushing anhydrous calcium silicate–bearing rock into powder and then heated to around15008F Manufactured cement is often called portland cement There are six basic types ofcement set forth in ASTM specification C150-61, shown in Table 3.2

The cement, typically limestone, clay, or shale, acts as a glue to bond the inert materialstogether by mixing water with the cement and the aggregates When the water migratesthrough the mixture and eventually evaporates, the cement and aggregates chemically bondtogether by hydration and hydrolysis to form a continuous block The ratio of water andcement is critical to proper curing insuring that adequate strength is attained Too muchwater will cause the paste to be too thin and will be weak when hardened An U.S engineer,Duff Abrams, developed the water cement ratio law in the 1920s and it is still widely usedtoday The proportion of a typical concrete mixture is shown in Table 3.3

Compressive strengths of concrete can range from 1000 to 10,000 psi with a density ofaround 150 lb=ft3 A compressive strength for concrete typically used in foundations formachinery is between 3000 and 5000 psi

A ‘‘slump test’’ is used to determine the consistency of concrete A standard slump cone isfilled with concrete, smoothed off at the top of the cone, and then the cone is lifted verticallyclearing the top of the concrete pour allowing the concrete in the cone to slump downward.The measured distance in inches from the original to the final level of the concrete mass isthen observed Concrete slump values for concrete used in machinery foundations shouldrange from 3 to 5 in

TABLE 3.2

Types of Cements