Handbook Of Shaft Alignment Episode 1 Part 5 pps

It is important for the personnel who maintain rotating machinery to have a basic under￾standing of how machinery should be supported and what problems to look for in

their foundations, baseplates, and frames to insure long-term alignment stability in their

machinery.

In addition to the machinery to ground or structure interface, attention must also be

directed 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 the

machinery to also insure good stability. This chapter will hopefully provide the reader with

the basic foundation design principles and some techniques to check equipment in the field to

determine if problems exist with the foundation and frame, or the interface between the

machinery 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 a

major difference in stability as we walk along a sandy beach and then step onto a large rock

outcropping. Different soil conditions produce different amounts of firmness. Since rotating

machinery could potentially be placed anywhere on the planet, the soil conditions at that

location 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 tests

conducted on soils where rotating machinery foundations will be installed. Table 3.1 shows

safe bearing load ranges of typical soils. The recommended maximum soil load from a

combination of both static and dynamic forces from the foundation and attached machinery

should 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 the

shafts together with a coupling, and started the drive system up without bolting anything

down. My guess is that they quickly discovered that the machines started moving around a

little bit after start up, then began moving around a lot, and finally disengaged from each other

hopefully without sustaining any damage to either of the machines. Maybe they tried it again

and 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

Type of Soil t/ft2 MPa

Hard rock (e.g., granite, trap, etc.) 25–100 2.4–9.56

Shale and other medium rock (blasting for removal) 10–15 0.96–1.43

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

Compact sand and gravel, hard clay (chiseling required for removal) 4–5 0.38–0.58

Loose medium and coarse sand medium clay (removal by shovel) 2–4 0.20–0.38

Fine loose sand 1–2 0.10–0.20

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was not going to work for long periods of time and decided to ‘‘hold the machines’’ in their

starting position somehow. How are we going to do this exactly? What should we attach them

to? How about some wood? No, better yet, something like metal or rock, something that is

strong.

Our rotating equipment needs to be attached to something that will hopefully hold it in a

stable position for long periods of time. I have seen just about every possible configuration

you can imagine. Even the scenario mentioned above. The most successful installations

require 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 another

location. Classically we attach and detach our equipment with threaded joints (i.e., bolts and

nuts). 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, sole￾plates, or frames are then attached to a larger structure, like a building, ship, aircraft and

automotive chassis, or Earth. There are many inventive ways of attaching rotating machinery

to transportation mechanisms (e.g., boats, motorcycles, airplanes), and design engineers are

still coming up with better solutions for these types of machinery-to-structure interface

systems. 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 ways

and poor ways to design and install each of these methods to keep our machinery aligned and

prevent them from bouncing all over the place when they are running. In summary, machines

are attached to intermediary supports (i.e., baseplates, soleplates, and frames) that are then

attached to structures (i.e., buildings, floors, foundations). Figure 3.1 shows a typical rigid

FIGURE 3.1 Rigid foundation for induced draft fan.

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Foundations, Baseplates, Installation, and Piping Strain 91

foundation design, Figure 3.2 shows a typica inertial block (aka floating) design, and

Figure 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 is

not uncommon to replace structural steel with solid plate to increase the stiffness of the base

similar 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 the

anchor 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.

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92 Shaft Alignment Handbook, Third Edition