Page 100 - Machinery Component Maintenance

Machinery Foundations and Grouting 83

into the skid cavities. To reduce this fire hazard it is common to provide
openings between cavities for oil drainage. With the usual inconsistencies
in grout level, complete oil drainage is not possible. Oil degradation of
cement grouts and concrete has long been recognized. With this in mind,
skids which are to be permanently installed should be installed with ep-
oxy grout. Bond strength of epoxy grout helps to anchor internal struc-
tural members that have no anchor bolts in the concrete.
The embedment method of installing machinery is by far the oldest
method. For short crankshaft gas engine compressors in the middle
horsepower range, this method is preferred because it provides a “key”
to resist laterial movement. On long crankshaft equipment in the higher
horsepower range, thermal expansion of the foundation can cause crank-
shaft distortion problems. Foundation expansion is uneven due to heat
losses around the outer periphery of the foundation and results in center
“humping.” The effects of humping can be avoided by installing the
equipment on rails or sole plates. The air space between the foundation
and equipment provides room for thermal growth without distorting the
equipment frame. The air space also allows some heat dissipation
through convection.
Exercise caution when installing equipment on sole plates-grout
properties are taxed to the absolute maximum when sole plates are de-
signed for static loads in the 200 psi range and then installed under equip-
ment with high operating or oil sump temperatures. This is particularly
true during the first few hours of operation until the grout passes through
its period of secondary curing. Refer to the typical physical properties of
epoxy grouts as shown in Table 3-4. Rails should be as short as possible
and all rails and sole plate corners should be rounded to a 2-in. radius to
minimize stress risers in the grout.
In recent years there has been a concerted effort to replace steel chocks
with epoxy chocks. This involves the use of liquid epoxy grout which is
poured in place, and after curing, forms a nonmetallic chock. One of the
advantages of this method of installing machinery is that it is not neces-
sary to have a machined surface on the engine base in contact with the
chock. This method of engine installation has been utilized for many
years in the marine industry on diesel engines. The forces imparted by
Diesel engines driving propulsion systems are quite different from the
forces imparted by integral gas engine compressors. For example, in the
Diesel engine propulsion system, the forces are primarily those involving
torque as imparted by the crankshaft at the output end of the engine. In
integral gas engine compressors, cyclic lateral forces, created primarily
by the compressor stages, are involved. On some compressors, the lat-
eral forces are so great that the engine base is fretted by steel chocks. It