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  • WESTERN ROOFING MARCH/APRIL 200552

    Review of Residential Roofing Materials, Part IIA Review of Methods for the Manufacture of Residential Roofing Materialsby Hashem Akbari, Ronnen Levinson, and Paul Berdahl, Heat Island Group, Lawrence Berkeley National Laboratory

    crushing various raw clay materials. For example, theraw clays used at MCA include yellow shell clay (ahighly refractory clay [i.e., having high heat resistance,permitting vertical firing without warping] with mediumplasticity); apple clay (a weakly refractory clay withhigh plasticity); and AAA clay (a medium refractory,low shrinkage clay with high iron content to make the tilered).

    The raw clays are thoroughly mixed with water andaged for 4-5 days. The aging process allows the dry mate-rial to absorb the moisture fully, improving plasticity.This increases yields from the extrusion process and thuslowers the unit production cost.

    Several extrusion machines and dies are employed toproduce clay tiles of various shapes. Prior to extrusion,the clay flows through a vacuum chamber to remove air,preventing cracking of tiles during the firing process.This process is also very important for proper vitrification(conversion to a glassy state), which makes the tile weath-er-resistant (i.e., resistant to freezing/thawing and saltintrusion) [See Clay Roof Tile Specifications: ASTM C-1167 for more detail]. An automated cutter at the end ofeach extruder cuts the tile to desired size, and trims theedges. The wet extruded tile is then dried in a sequenceof temperature-controlled chambers for about 24 hours.By reducing the excessive moisture in the tiles, this dryingprocess will reduce the probability of cracks when the tileis fired. The drying process typically starts with circulat-ing ambient air at a temperature of about 20-30C, gradu-ally increasing the temperature to about 90C using wasteheat from the kiln-cooling process. Drying reduces thetiles moisture content from 15% to less than 1%.

    roduction of shingles. Fiberglassasphalt shingles have three majorcomponents: fiberglass mat,

    asphalt (with additive fillers), and granules(colored and uncolored). In a typical plant,the fiberglass mat is fed into a roll coater thatapplies layers of stabilized coating asphalt tothe top and bottom surfaces of the webbingsheet. Stabilized coating asphalt is harderand more viscous than straight asphalt, andhas a higher softening point. The mineral sta-bilizer may consist of finely divided lime-stone, silica, slate dust, dolomite, or otherminerals.

    The filled or stabilized coating asphaltapplied at the coater is produced in the mixer,which is usually positioned above the manu-facturing line at the coater. Coating asphalt,typically at 200-270C (400-520F), is pipedinto the mixer, and the mineral stabilizer isadded. To eliminate moisture problems and to helpmaintain the temperature above 180C (360F) for propercoating consistency in the mixer, the mineral stabilizer isdried and preheated before being fed into the mixer.

    The weight of the finished product is controlled by thethickness of coating asphalt used. The coating rolls can bemoved closer together to reduce the amount of coatingapplied to the substrate, or separated to increase it. Mostmodern plants are equipped with automatic scales or pro-file scanners that monitor the sheets during the manufac-turing process and warn the operator when too much ortoo little coating is being applied.

    Colored and uncolored granules are applied in a sec-tion of the manufacturing line that usually consists of amulti-compartmented granule hopper, two parting-agenthoppers, and two large press rollers. The hoppers are fedthrough flexible hoses from one or more machine binsabove the line. These machine bins (sometimes calledsurge bins) provide temporary storage. The granule hop-per drops colored granules from its various compart-ments onto the top surface of the moving sheet of coatedweb in the sequence necessary to produce the desired col-or pattern on the roofing.

    Next, the sheet is cooled by passing it over water-cooled rollers; water may also be sprayed directly ontothe sheet to speed cooling. The final steps in the produc-tion of asphalt roofing shingles are cutting and packaging.After the shingles have been cut by machine they aremoved by a roller conveyor to automatic packagingequipment. The packaged shingles are then stacked onpallets and transferred by forklift to storage areas or wait-ing trucks.

    Clay tiles. Clay tile production begins by mixing and (Continued on Page 54)

    INSPECTING THE FINISHED PRODUCT AT A CLAY TILE PLANT.

  • WESTERN ROOFING MARCH/APRIL 200554

    Review of Residential Roofing Materials, Part II

    with colored coatings. The tiles are then covered withpost-coating polymers. The coating is a mixture of water,pigments, and polymeric additives. The coated tiles arethen dried, stacked, and packed for shipment.

    Metal Roofing. Metal production for the roofing indus-try may be divided into two phases: (1) metallic and/orcoil coating plants, where raw metal coils are cleaned,metallic coated, primed, and coated with paint (somefacilities can both metallic-coat and paint, while othersonly apply paint); and (2) metal-forming plants, where thecoated coils are either used to produce flat metal panels,or pressed into shapes that simulate non-metal roofingproducts (e.g., shake, slate, or tile).

    Coil Coating Plants. Coil coaters produce rolled metalsin the thickness, width, metal-coating type, and colorspecified by their customers, which include but are notlimited to members of the roofing industry. An advancedmetal coil plant typically has four major production lines:a pickle line, where the hot band coil (hot band coils are theresult of steel slabs being elongated and rolled into coiledsheet of finite width and thickness; the temperature andamount of processing determine mechanical properties ofthe coil) is uncoiled and cleaned of oxides, edges aretrimmed to customer requirement, and the coil is oiled inpreparation of further processing; a cold mill line, wherethe pickled bands are reduced in thickness 65-80% to meetordered thickness, and rolled to a suitable shape, and tex-ture is applied to the surface; a metallic coating line, wherethe coils are cleaned again, a layer of metallic coating isapplied, and the surface is treated for either painting orbare metal application; and a paint line where primer andfinish coatings are applied. Many coil coaters consist ofonly a paint line; they do not process their own substrate.In addition to steel, aluminum can also be coated via thecoil process.

    Pickle line. The raw material for this industry is typical-ly a thick metal steel coil. The hot-band coil is pickledwhen it first arrives at the coating plant. There it is

    The dry raw tiles are inspected for defectsbefore they are sprayed with glossy or matteglazes. The glazing is a mixture of water,pigments and clay additives. For the glossyfinish, frits (glassy silicates), clay, and color-glazed materials are added to the glazingmixture. The glazed tiles are positioned invertical stacks or in a standing up posi-tion, with typically 1.25 cm (12) spacers toallow an even heat distribution in the kiln.Even heating yields evenly colored tileswith good mechanical properties.

    The glazed tiles are then passed througha kiln, fired for 14-20 hours, dependingupon the production schedule. The kiln hasthree stages: preheat, heating, and cooling.In the preheating zone, the tiles are gradual-ly heated to about 700C by warm drawn airfrom the heating zone. In the heating zone, the tiles aredirectly fired for about four hours by gas flame, reachinga maximum temperature of about 1050C. Then the tilesare gradually cooled to about 300-400C by drawing out-side air through the kiln. The clay tile is ready to ship assoon as it is removed from the kiln - no curing is required.The clay tile colors are permanent and do not fade withexposure to the sun.

    Concrete tiles. Sand, cementitious materials, limestonefillers, and water are the main ingredients (by mass) ofconcrete tiles. Pigments are added for color and polymersare used as a water-resistant coating on the tile surface.Pigments are typically added to the surface in a slurrycoat comprised of pigment, cement, silica and water. Fin-ished concrete tiles may also be painted. The major com-ponents contributing to the cost are cementitious materi-als, sand, polymer coating, and pigments.

    Concrete tile production begins by mixing aggregate(sand) and fillers. Sand is pre-washed to remove dirt con-taminants. Recycled aggregates and quarry waste arealso used in the mixture, and milled calcium carbonate isused as filler (calcium carbonate filler is an inexpensivematerial that improves the quality of concrete). Then theaggregate and filler mix are mixed with cementitiousmaterials before water is added to the mixture. The per-centages of calcium carbonate filler added to the mix varyfrom facility to facility. At this stage, pigments may beadded to color the concrete mix. The ingredients are com-pletely mixed before being fed to the molding machine.

    Several machines and molds are employed to produceconcrete tiles of various shapes. The mold and the wetconcrete tile run on a conveyor where the tiles are partial-ly dried and polymeric coating is applied to the surfacebefore curing. The tiles and the mold are packed in a cur-ing chamber for about four hours, where the concrete tileis cured and dried. The molds and tiles run through aseparator that removes the molds from the tiles. The dryraw tiles are inspected for defects before they are sprayed

    (Continued from Page 52)

    CONCRETE TILE EXTRUSION MACHINE.

  • WESTERN ROOFING MARCH/APRIL 2005 55

    uncoiled and cleaned in a series of acid baths to ensurethe proper surfac