TM 5-822-14/AFJMAN 32-1019
and fig 4-47), but most have only one. Some single
shaft mixers are equipped with a system that adds
asphalt by spraying it into the mixing chamber as
the machine moves ahead, with the amount of
spray being synchronized with the travel speed (fig
4-48). Other machines, however, must be used in
conjunction with an asphalt distributor that sprays
asphalt on to aggregates immediately ahead of the
mobile mixer (fig 4-49). Both types of machine
have the common capability of effecting a smooth
bottom cut and then blending the material with
asphalt into the mixture specified. But each type
individually is marked by certain devices and
features that enable it to perform. Machines with
built-in asphalt feeding must have the capability
for accurate metering and blending of asphalt into
the in-place materials in synchronization with a
Figure 4-44. Windrowtype pugmill travel plant.
continuous forward movement. Furthermore, they
must have spray bars that will distribute the
liquid uniformly across the mixer's width. They
must be equipped with controls for both depth of
cutting and processing and for spreading the
mixed material being laid out behind. Rotary
mixers without asphalt spraying equipment gener-
ally feature controls that permit adjustment of
cutting depth to at least a lo-inch adjustment of
tail board and adjustment of the hood itself for
aeration purposes.
Figure 4-45. Hopper-type pugmill travel plant.
ing the asphalt and adequately coating the aggre-
gate particles, thus producing a mixture that is
uniform in color. Hopper travel plants, and in
some cases, windrow plants, require devices for
ensuring accurate controls of the flow of aggre-
gates from the hopper to the pugmill so that
correct mix proportions are maintained. Feed of
asphalt to the pugmill similarly requires accurate
calibration. Typically, a positive displacement
Figure 4-46. Multiple rotary mixer.
pump is utilized to deliver asphalt to the mixing
chamber via a spray bar.
(b) Rotary-type mixers. Rotary or mechanical
on-site mixing is accomplished by what is essen-
tially a mobile mixing chamber mounted on a
self-propelled machine. Within the chamber, usu-
ally about 7 feet wide and open at the bottom, are
one or several shafts transverse to the roadbed, on
which are mounted tines or cutting blades that
revolve at relatively high speed. As the machine
moves ahead, it strikes off behind it a uniform
course of asphalt-aggregate mixture. Some rotary
mixers have up to four shafts or rotors (fig 4-46
Figure 4-47. A processing chamber of a multiple rotary mixer.
4-21
Previous Page
