Figure
34 illustrates the typical manufacturing process for producing
organic asphalt roofing shingles, mineral-surfaced rolls, and smooth
rolls. For organic products, the initial processing steps are similar
to the saturant asphalt felt line just described and include the saturator
and looper. Organic felt products pass to the saturator and then, in
some plants, on to a coater.
The coater
employs a roller-type system to apply a stabilized coating asphalt to
the top and bottom surfaces of the webbing sheet. Stabilized coating
asphalt is made up of harder, more viscous asphalt that has a higher
softening point than saturant asphalt. The mineral stabilizer*
may consist of finely divided lime, silica, slate dust, dolomite, or
other mineral materials. The softening point of saturant asphalt varies
from 104 to 165 °F (40 to 74 °C), whereas the softening point
of coating asphalt varies from 210 to 240 °F (99 to 116 °C).
The "filled"
or "stabilized" coating asphalt applied during the coater
operation is made in the coater-mixer, which is usually positioned above
the manufacturing line at the coater. Coating asphalt, typically at
400 to 520 °F (204 to 271 °C), is piped into the mixer, and
the mineral stabilizer is delivered by screw conveyor. To eliminate
moisture problems and to help maintain the temperature above 360 °F
(182 °C) in the coater-mixer, the mineral stabilizer is dried and
preheated before being fed into the coater-mixer.
The weight
of the finished product is controlled by the amount of coating asphalt
used. The coater rollers can be moved closer together to reduce the
amount of coating asphalt applied to the felt, or they can be separated
to increase it. Most modern plants are equipped with automatic scales
or profile scanners that monitor the sheets during the manufacturing
process and warn the coater operator when the product is running under
or over specifications.
Colored
granules are applied in a section of the manufacturing line that usually
consists of a multi-compartmented granule hopper, two parting agent
hoppers, and two large press rollers. The hoppers are fed through flexible
hoses from one or more machine bins above the line. These machine bins
(sometimes called surge bins) provide temporary storage. The granule
hopper drops colored granules from its various compartments onto the
top surface of the moving sheet of coated webbing in the sequence necessary
to produce the desired color pattern on the roofing. Parting agents
such as talc and sand are applied from parting agent hoppers to the
back surface of the coated sheet. Smooth-surfaced products do not require
the application of colored granules. Talc or sand is usually applied
to both sides when smooth roll roofing is made.
The next
step is product cooling and seal-down strip application. As in the case
of the saturated felt line, the sheet is cooled rapidly by passing it
around water-cooled rollers in an abbreviated looper arrangement. Usually,
water is also sprayed on the surfaces of the sheet to speed this cooling
process.
Subsequently,
the asphalt seal-down strip is applied to self-sealing coated roofings
by a roller partially submerged in a pan of hot sealant asphalt that
is usually covered. Extrusion is another method of seal-down application.
Some products are also texturized at this point by passing the sheet
over an embossing roll that forms a pattern in the surface of the sheet.
The final steps in the production of asphalt roofing shingles and roll
roofing are the finish or cooling looper (which is essentially the same
process used for saturated felts), cutting, and packaging. The sheet
destined for roll roofing is wound on a mandrel, cut to the proper length,
and packaged. When shingles are made, the material from the finish looper
is fed into the shingle cut machine. After the shingles have been cut,
they are usually moved by roller conveyor to automatic packaging equipmentalthough
manual packaging is still used for some shingle products. The packaged
shingles are then stacked on pallets and transferred by forklift to
storage areas or waiting trucks.
For fiberglass
products (which today make up about 85% of the asphalt roofing shingle
market and more than 90% of the ply sheets used in BUR),
the initial saturation operation is eliminated. As shown in Figure
35, the manufacture of fiberglass roofing products begins
(as does the manufacture of organic felts) with the feeding of the mat
through a dry looper; it then proceeds to a coater.