Introduction: Two Methods of Manufacturing Bar Grating
Bar grating is used for constructing work platforms, stairways, walkway bridges, cable trenches and process walkways at industrial facilities. There are two main structural types: welded and press-locked. The first is assembled from bearing bars and cross bars joined by resistance welding. The second is produced by cold pressing the cross elements into slots cut in the bearing bars under high pressure without heating. The difference in technology determines strength, appearance, corrosion resistance and price.
The choice between them is not reduced to a simple “which is better”: each technology has zones where its advantages are fully revealed. For light pedestrian areas with an aggressive environment, press-locked grating is more often chosen; for heavily loaded driveways and stairways with heavy equipment, reinforced welded series are used. Understanding the design differences helps to order exactly the type that will last for decades without replacement. Galvanized bar grating is available in the catalogue galvanized bar grating.
Comparative Table of Press-Locked and Welded Grating
| Parameter | Press-locked bar grating | Welded bar grating |
| Method of joining bars | Press-fitting of cross bars into slots in bearing bars without welding | Resistance welding of cross bars to bearing bars |
| Surface | Smooth, without weld points | Weld points are visible, sharp edges possible |
| Bending strength at equal weight | Higher: the absence of thermal influence preserves the metal | Lower: welded seams may be stress concentrators |
| Corrosion resistance | Higher: no gaps or pores, zinc lays down evenly | Medium: local zinc peeling is possible at weld points |
| Typical meshes | 33×33 mm, 33×11 mm, 34×38 mm | 33×33 mm, 33×11 mm, 34×38 mm, 34×76 mm |
| Standard series | SP, SPP | R, V |
| Permissible load | High for a distributed load | Very high with reinforced bearing bars |
| Weight of 1 m² | Slightly lower at equal strength | Slightly higher |
| Cost | Higher due to complex equipment | Lower in mass production |
| Main areas | Chemical productions, food shops, offshore platforms, pedestrian zones | Trestles, vehicle driveways, heavily loaded platforms, stairways |
Production Technology and Its Effect on Properties
Welded bar grating is manufactured according to GOST 23279-2012. Bearing bars made of steel strip are set on edge; cross bars of round or flat steel are laid between them at a certain pitch, after which the intersection points are welded by automatic resistance welding. The result is a rigid structure with a high section modulus of the bearing bars. However, thermal action at the welding points changes the metal structure: a tempering zone appears, ductility decreases, and internal stresses arise. During galvanizing, pores and gaps often remain in these places, where moisture penetrates, accelerating corrosion.
Press-locked bar grating has no welded joints. Slots are cut into the bearing bars, into which the cross bars are press-fitted. The joint is formed due to plastic deformation of the metal: the cross bar is compressed and fixed in the slot without clearance. Such grating is distinguished by a smooth face surface, the absence of thermal stresses and stable geometry. The technology makes it possible to reduce the overall weight while maintaining strength, since the bearing bars are not weakened by welding. Press-locked grating is often marked as SP — from English press-locked, although domestic designations are also found.
Strength Characteristics and Load-Bearing Capacity
The load-bearing capacity of bar grating depends on the height of the bearing bar, its thickness and the installation pitch. For the same bar height, for example 25 or 30 mm, press-locked grating demonstrates a higher yield strength in bending, since the metal has not been subjected to tempering from welding. This makes it possible, at an equal design load, to choose a smaller bar height and save weight. In practice, SP-25-33×33 press-locked grating can carry a distributed load of about 400 kg/m² at a span of 1000 mm, while welded grating of the same height withstands 10–15% less.
Welded grating compensates for this by increasing the thickness of the bearing bars. In series with reinforced bars, for example 5 mm, its strength becomes comparable or even higher, but at the cost of an increase in weight. For heavy loads, such as the passage of forklifts or laying grating on trestles with large spans, designers specify welded grating with high bearing bars — up to 100 mm. Press-locked grating is rarely produced with bars higher than 60 mm, so in extra-heavy-duty zones the choice is limited to welded.
Corrosion Resistance and Galvanizing
Hot-dip galvanizing is a mandatory stage for grating used outdoors or in an aggressive environment. The quality of the zinc coating directly depends on the cleanliness of the surface and the absence of closed cavities. In press-locked grating, the joint is tight, without gaps, so the zinc evenly covers both the outer edges and the internal slots. Such grating withstands prolonged exposure to moisture, weak acids and sea fog. That is why it is ordered for offshore platforms, chemical shops, and treatment facilities.
Welded grating after galvanizing requires inspection of the weld points. If the welded seam was made with pores or lack of penetration, the zinc will not fill the microcavities, and corrosion will start from the inside. Responsible manufacturers carry out additional treatment of the weld points before immersion in the bath. Nevertheless, operational statistics show that press-locked grating in an aggressive atmosphere lasts 3–5 years longer. For dry rooms and closed trestles, the difference is insignificant, and welded grating remains economically justified.
Weight, Mesh Sizes and Typical Designations
The weight per square metre of grating depends on the height of the bearing bars, the thickness of the metal and the mesh pitch. For SP 33×33 press-locked grating with a height of 25 mm, the weight is about 22 kg/m²; for welded grating with the same parameters, about 24 kg/m². With a 33×11 mm mesh (narrow elongated mesh), the weight increases by 10–15%. A narrow mesh is preferable where it is necessary to prevent the fall of small objects or to facilitate the movement of wheeled equipment.
Typical designations include the type, the height of the bearing bar, the mesh pitch and dimensions. For example, welded grating may be marked as “R 30-33×33”, where R is the standard series, 30 is the bar height in millimetres, 33×33 is the pitch of bearing and cross elements. Press-locked grating is designated SP 25-33×11 or SP 30-33×33. The letter A sometimes indicates a reinforced series with thicker bars. When ordering, it is important to check the manufacturer’s drawings, since there is no single standard for marking press-locked grating in the Russian Federation.
Areas of Application: Where Each Grating Works Better
Welded bar grating, due to its high rigidity and low price, dominates at typical industrial facilities: trestles, process platforms, stair flights, passages between equipment. It is ordered in large volumes for oil and gas terminals, mining and processing plants, and the power industry. Where loads are stable and the environment is not too aggressive, the welded type provides the best balance of price and strength.
Press-locked grating is chosen in cases where aesthetics, pedestrian safety and corrosion resistance are important. It is installed on pedestrian bridges, ramps, facade passages, in the lobbies of public buildings, on ships and offshore platforms. The absence of weld points makes the surface non-slip and pleasant for walking, and the uniform zinc coating extends the service life in salty sea air. A balanced choice of grating type directly affects operating costs: overpaying for press-locked technology pays off where corrosion and appearance are critical.
When to Choose Press-Locked Bar Grating
- Facilities with an aggressive atmosphere: sea piers, chemical productions, electroplating shops, treatment facilities.
- Pedestrian zones with high requirements for appearance: shopping galleries, exhibition pavilions, entrance groups.
- Structures where minimum weight at a given strength is important: suspended walkways, light trestles.
- Conditions with strong vibration, where welded seams may fail from fatigue loads.
- Orders with increased sanitary requirements: the absence of pores and gaps prevents the accumulation of dirt.
When to Choose Welded Bar Grating
- Heavily loaded platforms and trestles for vehicle passage: high bearing bars and reinforced series are required.
- Large order volumes: mass production of welded grating reduces the price per square metre.
- Construction scaffolds, temporary walkways, shaft and well covers, where price is more important than durability.
- Reconstruction of existing facilities where welded grating is already installed and compatibility is required.
- Dry heated rooms without aggressive media: corrosion resistance is not a decisive factor.
Typical Mistakes in Selection and Ordering
- Specifying only the mesh pitch in the project without the bearing bar height. Grating with a 20 mm bar at a 33×33 mesh will not withstand the load calculated for a 40 mm bar.
- Ignoring operating conditions when choosing the technology: in a marine atmosphere, welded grating loses zinc faster at the weld points.
- Saving on galvanizing: uncoated grating or grating with cold zinc begins to rust already after a year outdoors.
- Ordering press-locked grating for the passage of a forklift. The press-locked construction does not always have reinforced series capable of withstanding point wheel loads.
- Incorrect joining of sections: the absence of fastening clamps leads to displacement of the grating and injuries.
- Confusion between type A and type R: type A is reinforced, type R is standard, and their load-bearing capacity differs significantly.
Frequently Asked Questions
What is the main difference between press-locked and welded grating?
Press-locked grating is made without welding — cross bars are pressed into the bearing bars under pressure. Welded grating is joined by resistance welding. Press-locked grating has no weld points, higher corrosion resistance and aesthetics; welded grating has a lower price and offers reinforced series for heavy loads.
What does the marking SP 33×33 mean?
SP denotes the press-locked series (press-locked), 33×33 is the mesh size in millimetres: the pitch of the bearing bars is 33 mm and the pitch of the cross elements is 33 mm. The height of the bearing bar is indicated as a separate figure before the pitch, for example SP 25-33×33.
What is the weight of 33×33 bar grating with a height of 30 mm?
Approximately 28–32 kg/m² without fasteners. The exact weight depends on the thickness of the bars and the type of grating. For press-locked grating it is 5–10% lower than for welded grating with similar parameters.
Is welded grating suitable for a marine climate?
It is suitable only with high-quality hot-dip galvanizing and inspection of the weld seams. Otherwise, corrosion quickly develops at the weld points. For offshore platforms, press-locked is preferable.
Can press-locked grating be used for a vehicle driveway?
It is not recommended. For vehicle loads, welded grating with reinforced bearing bars and a special calculation is designed. Press-locked grating may not withstand the point pressure of a wheel.
Conclusion
Press-locked bar grating is an engineering solution for environments where surface cleanliness, corrosion resistance and low weight are valued. Welded grating remains the main working tool for heavy loads and mass orders. The difference in technology does not make one type universally better: each is selected for specific conditions, based on the design load, the aggressiveness of the environment and the budget. An accurate request to the manufacturer indicating the bar height, mesh pitch and operating conditions guarantees that the grating will serve the declared period without premature replacement.
