What Are the Key Differences Between Molded and Pultruded Grating?
Both molded and pultruded FRP gratings are used for industrial walkway flooring, platforms, and access floors, however, their manufacturing process and loading capabilities differ from each other. Molded grating is stronger in two dimensions and is suitable for a number of normal flooring uses. On the other hand, pultruded grating consists of load-bearing bars which can take the load along only one dimension and therefore is good for applications requiring more stiffness or longer spans.
Selection should be based upon the span distance, loading capability, chemical resistance, slip-resistance properties, and installation pattern and not only on which one is supposed to be “stronger.”
1. How are molded and pultruded gratings manufactured?
Molded FRP grating
The molded grating is produced in molds through the process of adding glass fiber to the resin. The fibers are oriented in both ways prior to the curing of the single grating panel that contains holes.
The cross-reinforced nature of this grating enables it to evenly spread the loads across and along the grating, based on the design and load table of the product.
Pultruded FRP grating
Pultruded grating consists of load-bearing bars. The load-bearing bars are produced by drawing continuous glass fibers into resin and heated mold. After that the bars are assembled with crossbars or other joining systems into grating panels.
The strength of the pultruded grating depends on the orientation of the reinforcing fibers, which is mainly longitudinal to the load-bearing bars.
2. Molded vs pultruded grating: key differences
| Feature | Molded FRP grating | Pultruded FRP grating |
|---|---|---|
| Manufacturing | Reinforcement and resin are formed and cured in a mold | Load-bearing bars are pultruded, then assembled into panels |
| Load direction | Generally carries loads in both panel directions | Carries loads mainly along the bearing bars |
| Span suitability | Often suitable for short-to-medium spans, depending on panel depth and load | Often selected for longer spans or where greater stiffness is required |
| Cut-outs | Grid layout can make some cut-outs and irregular openings easier to plan | Cutting a bearing bar can interrupt a major load path; extra support may be needed |
| Surface | Anti-slip grit or textured finishes are commonly available; confirm the supplied specification | Anti-slip finishes are available, but the surface treatment may vary by product |
| Corrosion resistance | Depends on the resin system and reinforcement; suitable grades resist many corrosive environments | Also depends on resin and reinforcement; the manufacturing method alone does not determine chemical resistance |
| Typical applications | Walkways, platforms, trench covers and access flooring | Longer-span walkways, platforms and structures requiring directional stiffness |
| Cost | May be economical for standard panel layouts | May cost more, but can be advantageous where its span or stiffness reduces support requirements |
These are general features. The actual weight capacity, deflection, open area, panel size, and cost will depend on the manufacturer and specification.
3. Which type is better for strength and load capacity?
Neither is always the stronger option. Pultruded grating is frequently the better choice if the load acts in the bearing bar direction of the panel and the span lengths are larger than usual. Molded grating has reinforcing bars in both directions, which may be an asset if load or bearing conditions change on the panel.
To make a valid comparison, consult the load tables from the manufacturer for:
- The real span length between supports
- Uniform load and wheel load (if applicable)
- Maximum allowable deflection
- Grating thickness and bearing bar sizes
- The orientation of the bearing bars and how they are supported
Never compare strength values until you verify if the span length, load type, and maximum deflection are the same. The performance of a pultruded panel may be compromised if it is installed incorrectly.
4. Where is molded grating commonly used?
FRP molded grating is usually considered for:
- Industrial walkway systems and platforms
- Drain and trench covers
- Applications where there are many directional changes or cut-outs required
Chemical processing areas where the chosen resin will be compatible with the application
The open grid structure makes it easy to use when openings are required, but any cut-outs must still be evaluated with regard to the loading capability of the panel.
Plastic Fabricators offers FRP moulded grating. Confirm the required panel depth, mesh, resin type, surface finish and load rating before specifying it.
5. Where is pultruded grating commonly used?
Pultruded FRP grating could be considered as an alternative for the following applications:
- Walkways with larger support spacings
- Structures where stiffness is significant
- Access platforms where the load is carried predominantly on the bearing bars
- Where the structural design allows the use of the directional strength of the panel
Pultruded FRP grating is available from Plastic Fabricators too. Please provide the support spacing and loading conditions for project-specific selections.
6. What about corrosion resistance and slip resistance?
Either molded or pultruded FRP gratings will be corrosion-resistant and will not be prone to rust, unlike traditional steel grating. However, it is not only about the process of manufacturing but also about the type of resins used, their concentration levels, as well as the temperature of the environment.
In addition, do not assume that all FRP gratings have an anti-slip surface. It should be specified and it should match your application needs, for example, slippery surfaces or those exposed to wet weather conditions.
7. How should you choose the right FRP grating?
Start with this straightforward approach:
- Use molded grating in situations where you need a grid panel that has strength in two directions.
- Use pultruded grating in situations where longer spans, directional loading or stiffness are more critical considerations in design.
- Compare both types if your application includes non-standard support spacing, heavy loading, cut-outs or extreme chemical exposure.
Prior to ordering, be sure to provide the following information to the grating manufacturer:
- Panel size and opening dimensions needed
- Spacing of supports and orientation of bearing bars
- Loading, including concentrated loads
- Indoor or outdoor installation and chemical exposure
- Desired surface finish and slip resistance
- Any fire, safety or project specifications
The supplier should evaluate the suitability of the grating for the specified loading conditions and design criteria.
Conclusion
While molded and pultruded FRP gratings both provide corrosive-resistant materials as an alternative to traditional metal grating, the right material will depend on the use intended. While molded grating is suitable for general purpose flooring and where the design calls for flexibility in regard to panel openings, pultruded grating may prove a better option where the design requires directional strength, stiffness, or increased span.
When making your choice, you must consider the manufacturer’s loading tables, support span, deflection requirements, resin compatibility, and surface finish. The right choice of grating should take into consideration more factors besides just the type of grating.