Fiberglass Grating Explained
The two primary manufacturing processes used to produce Marco Fiberglass Reinforced Plastic (FRP) Grating products are Open Molding and Pultrusion. Both processes produce high quality, uniform construction.
High quality, well designed, Pultruded Grating, which resembles metal bar grating, is stronger, lighter, equally corrosion resistant, and in most cases, is less expensive than molded grating. Additionally, pultruded grating comes in larger panels and can be built to custom panel sizes. In most applications, pultruded fiberglass grating will represent the best product and the lowest price.
Molded Grating has equal strength in both directions and is made with square or rectangular grid patterns. Since it was developed much earlier than pultruded grating, it is widely used and performs well in many applications.
Molded Fiberglass Grating
Imagine a giant 4′ x 12′ waffle iron (mold). Liquid resin and continuous fiberglass roving are systematically laid in the mold, layer after layer manually, to produce the desired thickness and panel dimensions. The finished molds are set aside for a predetermined time to allow the panel to cure. The panel is then ejected from the mold. The molds are cleaned and prepared for the process to begin again.
The one piece interwoven square mesh construction of molded grating produces two primary benefits: maximum corrosion resistance and high strength.
Because the grating is “cast” in one piece, there is no mechanical joint between bearing bars, unlike the pultruded grating where the glued joints can give way in heavy continuous traffic or after prolonged service.
The high percentage of resin (65%) in molded grating offers superior corrosion resistance. The molded grating with a square mesh pattern offers increased load capacity and panel utilization due to this bi-directional trait.
Cutting access holes in the molded grating does not weaken the panel and does not require additional or costly supports (unlike pultruded grating that must be re-supported and edge-banded).
- Isophthalic: Your choice against acids and other chemicals commonly found in most industrial and chemical processing applications. Flame spread rating is Class I, 25 or less when tested in accordance with ASTM E84. Isophthalic Base.
- Vinyl Ester: The strongest resin system available to protect against caustics and acids found in the toughest environments. Flame spread rating is Class I, 25 or less when tested in accordance with ASTM E84. Vinyl Ester Base.
- Food Grade: A resin designed for USDA food processing applications. Flame spread rating is ClassII, 75 or less when tested in accordance with ASTM E84. Isophthalic Base.
- Extra Fire Retardant: Used when the lowest flame spread rating is required. Flame spread rating is Class I, 10 or less when tested in accordance with ASTM E84. Isophthalic Base.
Pultruded Fiberglass Grating
The pultruded grating product is a mostly mechanized process. Fiberglass of different shapes such as: strand, mat and veil are pulled through a liquid resin bath and a heated die where the bar is shaped and the resin is cured. These pultruded bars can be cut into 12′, 15′ or 20′ lengths. The bars are then taken to a workstation and drilled (6″ or 12″ on center) on the sides to accept the crossbars. The drilled bars are spaced proportionally for the width of the panel; 3′, 4′ or 5′. The final step is to seal the entire cross bars and holes with corrosion resistant epoxy resin.
The pultruded grating provides increased load capacity with moderate levels of corrosion resistance. The components (bearing bars and cross bars) are pulled by machine to have a higher glass content. Its superior load capacity to molded grating is a result of the higher glass to resin ratio (65% glass to 35% resin). However, the lower resin content reduces the corrosion resistance as compared to the molded grating.
The pultrusion process is automated and produces a consistent, high quality finished product.
Assembled from bars, the pultruded grating can offer a wide variety of panel sizes and substantially reduce “scrap loss” not always possible from molded grating panels.
- Isophthalic: Good corrosion resistance in moderately corrosive industrial areas. Flame spread rating is Class I, 25 or less when tested in accordance with ASTM E84. Isophthalic Base.
- Vinyl Ester: Highly resistant to both acidic and alkaline environments. Flame spread rating is Class I, 25 or less when tested in accordance with ASTM E84. Vinyl Ester Base.
- Food Grade: USDA approved resin for food processing applications.
- Phenolic: Good corrosion resistance and excellent fire and smoke resistant. ASTM E84 Class I, flame spread rating of 15 or less and smoke developed of 50 or less.
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