grating

Abstract

To provide a grating that has excellent slip resistance characteristics with a BPN of 40 or more even in a wet state, and also has excellent durability.SOLUTION: A grating is a combination of bearing bars 10 and cross bars. The bearing bars 10 and the cross bars are covered with a hot-dip galvanized layer 15, and a blast treatment layer 16 is formed on the top surface of the hot-dip galvanized layer, thereby achieving a BPN (British Pendulum Number) of 40 or more in wet conditions. For the safety type, the depth of the blast treatment layer shall be 8 μm or more, and for the normal type, it shall be 12 μm or more.SELECTED DRAWING: Figure 3

Description

[Technical field]

[0001] The present invention relates to a grating having excellent slip resistance properties. [Background technology]

[0002] Gratings, which are made up of bearing bars arranged at regular intervals and cross bars perpendicular to them, have been widely used as road gutter covers, staircase treads, factory floor panels, etc. However, when the top surface of the grating becomes wet due to rainwater, it becomes slippery, and there is a risk of pedestrians and cyclists falling over. Therefore, various anti-slip measures have been implemented for gratings.

[0003] The most common anti-slip measure is to form a number of anti-slip protrusions on the upper surface of the bearing bar that constitutes the grating. For example, the grating shown in Patent Document 1 has a number of pyramidal protrusions formed in a row on the upper surface of the bearing bar, and the shoulder surface of the bearing bar is designed to be a slope so that rainwater can flow down quickly.

[0004] Also, as shown in Patent Document 2, a grating has been proposed in which a spray-coated layer made of a ceramic material is formed on the upper surface of the bearing bar instead of anti-slip protrusions.

[0005] Recently, the "Tokyo Metropolitan Government Welfare Town Planning Ordinance Facility Development Manual" and the "Asphalt Pavement Guidelines" of the Japan Road Association, a public interest incorporated association, have begun to state that "It is desirable for the skid resistance value BPN of 40 or more for road pavement on the pedestrian side." The method for measuring BPN (British Pendulum Number) will be described later, but it is the skid resistance value of the road surface measured using a test machine developed by the Road Research Institute in the UK. When the skid resistance value of conventional gratings was measured using this measuring device, it was found that while there was no problem in dry conditions, the BPN of many gratings did not reach 40 in wet conditions.

[0006] The thermal spray coating of the ceramic material shown in Patent Document 2 has the problem that the manufacturing costs are high and the thermal spray coating falls off during use, gradually reducing the anti-slip effect. [Prior art documents] [Patent documents]

[0007] [Patent Document 1] JP 2022-157731 A [Patent Document 2] Japanese Utility Model Application Publication No. 6-12585 Summary of the Invention [Problem to be solved by the invention]

[0008] Therefore, an object of the present invention is to solve the above-mentioned conventional problems and to provide a grating which has a BPN of 40 or more even in wet conditions, excellent slip resistance characteristics, and excellent durability. [Means for solving the problem]

[0009] The present invention, made to solve the above problems, is a grating combining bearing bars and cross bars, the bearing bars and cross bars being covered with a hot-dip galvanized layer, and a blast treatment layer having a depth not exceeding the layer thickness of the hot-dip galvanized layer being formed on the upper surface of the hot-dip galvanized layer of the bearing bars and cross bars, thereby making the BPN (British Pendulum Number) in a wet state 40 or more. The thickness of the hot-dip galvanized layer is preferably 80 to 140 μm.

[0010] When the bearing bar has a large number of anti-slip projections formed on its upper surface, the depth of the blasted layer measured from the surface of the hot-dip galvanized layer is preferably 8 μm or more. When the bearing bar has no anti-slip projections formed on its upper surface, the depth of the blasted layer measured from the surface of the hot-dip galvanized layer is preferably 12 μm or more. Effect of the Invention

[0011] The grating of the present invention exhibits slip resistance characteristics of BPN 40 or more even in wet conditions due to the microscopic unevenness of the blasted layer formed on the hot-dip galvanized layer covering the upper surface of the bearing bar. In addition, since the bearing bar and cross bar are covered with the hot-dip galvanized layer, they have excellent durability, and since the depth of the blasted layer does not exceed the layer thickness of the hot-dip galvanized layer, there is no risk of the entire hot-dip galvanized layer peeling off, and there is no risk of a decrease in durability. [Brief description of the drawings]

[0012] [Figure 1] FIG. 2 is a perspective view of a grating according to an embodiment. [Diagram 2] FIG. 13 is a perspective view of a grating according to another embodiment. [Diagram 3] FIG. 2 is a conceptual enlarged cross-sectional view of a main part. [Figure 4] FIG. 1 is an explanatory diagram of a BPN measuring device. [Diagram 5] 1 is a graph showing the results of an example. DETAILED DESCRIPTION OF THE PREFERRED EMBODIMENTS

[0013] An embodiment of the present invention will be described below. Fig. 1 shows a grating according to an embodiment, which is composed of a combination of bearing bars 10 and cross bars 11 arranged at a predetermined interval. The bearing bar 10 is a steel plate-like body with an I-shaped cross section, and the cross bar 11 is a steel rod-like body arranged perpendicular to the bearing bar 10. End plates 12 are arranged around the periphery, and both ends of the bearing bar 10 and cross bar 11 are fixed to the end plates 12. The pitch of the bearing bars 10 is around 30 mm for coarse gratings and around 15 mm for fine gratings.

[0014] A large number of anti-slip projections 13 are formed on the top surface of the bearing bar 10 shown in Fig. 1. In this embodiment, the anti-slip projections 13 are trapezoidal in plan view, with their base and top sides arranged parallel to the longitudinal direction of the bearing bar 10. Also, in this embodiment, the cross bar 11 is spiral-shaped, and is arranged so that its top surface is flush with the top surface of the bearing bar 10. However, the shape of the anti-slip projections 13 is not limited to this. Furthermore, the shape of the cross bar 11 is not limited to this, and it may be a simple round bar.

[0015] Another embodiment of the grating is shown in Figure 2. This grating is also constructed by combining bearing bars 10 and cross bars 11, but the upper surface of the bearing bars 10 is flat and does not have the anti-slip protrusions 13 as shown in Figure 1. In this specification, the grating in Figure 1 is called the safety type, and the grating in Figure 2 is called the normal type.

[0016] The entire grating in these embodiments is immersed in a hot-dip galvanizing bath and is hot-dip galvanized. Therefore, the entire surfaces of the bearing bar 10, the cross bar 11, and the end plate 12 are covered with a hot-dip galvanized layer. The thickness of the hot-dip galvanized layer is HDZT63 (63 μm or more) or HDZT77 (77 μm or more) as specified in JIS·H8641, and is substantially in the range of 80 to 140 μm. This ensures sufficient weather resistance and durability. If the layer thickness is thinner than this range, the durability decreases. Furthermore, even if the layer thickness is made thicker than this range, the durability does not increase and the plating cost increases, so it is preferable to keep it within this range.

[0017] The composition of the hot-dip galvanizing is preferably one in which aluminum is contained in zinc, and more preferably one in which magnesium is further contained. In this embodiment, the composition of the hot-dip galvanizing is Zn: 94%, Al: 5%, and Mg: 1%. Hot-dip galvanizing has excellent corrosion resistance and durability because it has a pseudo-corrosion prevention effect, but if such hot-dip galvanizing is applied, the corrosion resistance and salt damage resistance are significantly improved. For example, when the thickness of the plating layer is set to 77 μm and the time until red rust occurs is measured by a salt spray test, it is about 1000 hours for hot-dip galvanizing that does not contain Al or Mg, but it is 8000 hours for hot-dip galvanizing containing Al, and it has been confirmed that red rust does not occur even after 10000 hours when Mg is further contained.

[0018] Hot-dip galvanizing has also been applied to conventional gratings. However, in the present invention, blasting is further performed on the top surface of the hot-dip galvanized layer formed on the bearing bar 10 and cross bar 11. FIG. 3 is a schematic diagram showing the top surface of a safety-type bearing bar 10 including anti-slip projections 13. In this figure, 15 indicates the hot-dip galvanized layer, and 16 indicates the blasted layer. Such blasting on the surface of the plated layer is not usually performed because it damages the luster of the plated surface and reduces the thickness of the plated layer that has been formed with great care.

[0019] Blasting is a process in which the surface of a workpiece is roughened by projecting a projectile called shot or media onto the workpiece, and microscopic irregularities can be formed. Sand grains, steel balls, cut wires, etc. can be used as shots, but in this embodiment, steel balls with a size of 1.2 to 1.6 mm were used.

[0020] The depth of the blasted layer 16 can be changed by changing the processing time of the blasting. The depth of the blasted layer 16 should not exceed the thickness of the hot-dip galvanized layer 15. If the blasting is performed excessively, the hot-dip galvanized layer 15 will be removed, exposing the steel surface and reducing durability. In the case of a safety type bearing bar 10 having anti-slip protrusions 13 formed on the upper surface thereof, if the depth of the blasted layer 16 measured from the surface of the hot-dip galvanized layer 15 is 3 μm or more, the BPN (British Pendulum Number) when wet can be 40 or more.

[0021] In the case of a normal type bearing bar 10 having no anti-slip projections on the upper surface thereof, the BPN in the wet state can be made 40 or more if the depth of the blasted layer 16 measured from the surface of the hot-dip galvanized layer 15 is made 8 μm or more. The reason why the depth of the blasted layer 16 in the normal type is made deeper than that of the safety type is that the anti-slip effect of the anti-slip projections 13 is covered by the microscopic irregularities formed in the blasted layer 16.

[0022] The blasted layer 16 may be formed on the upper surface of the hot-dip galvanized layer 15 of the bearing bar 10 and the cross bar 11, and it is not preferable to form it on the side or bottom surface. This is because forming the blasted layer 16 on the side or bottom surface of the bearing bar 10, the cross bar 11, the end plate 12, etc. does not improve the slip resistance characteristics and may damage the hot-dip galvanized layer 15.

[0023] The BPN and its measurement method are explained below. As mentioned above, the BPN is the skid resistance value of a road surface measured using a test machine developed by the Road Research Laboratory in the UK. The structure of the test machine is as shown in Figure 4, with a rubber slider 22 attached to the tip of an arm 21 that can rotate around a horizontal axis 20. The arm 21 is held in the horizontal position shown in Figure 3 by a holder 23, but when a button 24 on the holder 23 is pressed during measurement, the hold is released and the arm 21 is swung downward by gravity and comes into contact with the surface of the sample 30.

[0024] A needle 25 is attached on the same axis as the horizontal shaft 20. This needle 25 is structured so that the extent to which the swung-down arm 21 rotates in the opposite direction can be read on a scale plate 26. In other words, the needle 25 rotates clockwise together with the arm 21 and stops at the maximum rotation position. The scale plate 26 has a scale from 0 to 150 marked in the counterclockwise direction.

[0025] A leveling screw 28 is attached to the base 27, and the post 29 can be adjusted so that it is vertical. A sample 30 is fixed on the upper surface of the base 27, and the height of the post 29 is adjusted by an adjustment screw (not shown) so that the swung-down rubber slider 22 comes into contact with the surface of the sample 30 over a length of 125 mm. With the sample 30 sufficiently wetted with water, the arm 21 is swung down, and the scale indicated by the needle 25 is read.

[0026] If the surface of the sample 30 is smooth and frictionless, the arm 21 rotates approximately 180 degrees from the initial position shown in FIG. 3, and the needle 20 stays at the 0 mark on the scale. In this case, BPN=0. However, if the surface friction of the sample 30 is large, the kinetic energy of the swung-down rubber slider 22 is attenuated, so the maximum rotation position of the arm 21 drops and the BPN increases. Measurements are performed five times, and the average or median value is taken as the BPN. As shown in the following examples, it has been confirmed that the BPN of the conventional grating does not reach 40 when wet, but that the BPN of the grating of the present invention when wet is 40 or more. EXAMPLES

[0027] The BPN was measured using a "normal mesh groove cover" grating, a product of the applicant company. Two types of gratings were used: a safety type with the shape shown in Figure 1, and a normal type as shown in Figure 2. Both were entirely covered with a hot-dip galvanized layer with a composition of Zn: 94%, Al: 5%, Mg: 1%. The BPN was measured five times in a wet state before blasting treatment, and the average value for the safety type was 34.3, while the average value for the normal type was 25.8, neither of which reached 40. For reference, the BPN measured in a dry state was 45 or higher in both cases.

[0028] Next, the top surface of this grating was shot blasted, and the BPN was measured after treatment times of 30 seconds, 1 minute, 3 minutes, and 5 minutes. The shot blasting was performed by projecting balls with a diameter of 1.2 mm from above the grating using air pressure, forming a blasted layer on the surface of the hot-dip galvanized layer. The thickness of the hot-dip galvanized layer was 80 to 90 μm, and the depth of the blasted layer was 8.0 μm after a treatment time of 30 seconds, and 11.9 μm after a treatment time of 1 minute.

[0029] The relationship between the shot blasting time and the BPN in a wet state is shown in Table 1 and Figure 5. In the case of the normal type, after only 30 seconds of shot blasting, the BPN in a wet state was 34.7, which did not clear 40. However, after one minute of shot blasting, the BPN was 41.2, exceeding 40. In the case of the safety type, after only 30 seconds of shot blasting, the BPN was 46.6, clearing 40. Also, after one minute of shot blasting, the BPN rose significantly to 52.2.

[0030] The graph in FIG. 5 also shows data for shot blasting for 3 and 5 minutes. In this way, if the shot blasting time is further extended, the depth of the blasted layer becomes deeper and the BPN also increases. However, there is no particular meaning in making the BPN 50 or more, and since it will lead to an increase in processing costs, blasting for 3 minutes is sufficient under the conditions of this example. It is considered that the depth of the blasted layer is preferably 8 to 14 μm, but since it is a rough surface, accurate measurement during processing is difficult, and in practice, it is preferable to manage it based on the blasting time.

[0031] [Table 1]

[0032] As explained above, the grating of the present invention uses the unusual method of blasting the top surface of the plating layer, which gives it a BPN of 40 or more even in wet conditions, excellent slip resistance properties, and excellent durability. [Explanation of symbols]

[0033] 10 Bearing bar 11 Crossbar 12 End plate 13 Anti-slip protrusions 15 Hot-dip galvanized layer 16 Blasting layer 20 horizontal axis 21 Arm 22 Rubber Slider 23 Holder 24 Buttons 25 needles 26 Scale plate 27 Base 28 Leveling screw 29 Posts 30 Samples

Claims

1. A grating that combines bearing bars and cross bars, The bearing bar and the cross bar are coated with a hot-dip galvanized layer, A grating characterized in that a blast treatment layer having a depth not exceeding the layer thickness of the hot-dip galvanized layer is formed on the upper surface of the hot-dip galvanized layer of the bearing bars and cross bars, thereby making the BPN when wet 40 or more.

2. The grating according to claim 1, characterized in that the thickness of the hot-dip galvanized layer is 80 to 140 μm.

3. The grating according to claim 2, characterized in that the bearing bar has a number of anti-slip protrusions formed on its upper surface, and the depth of the blast treatment layer measured from the surface of the hot-dip galvanized layer is 8 μm or more.

4. The grating according to claim 2, characterized in that the bearing bar has no anti-slip protrusions formed on its upper surface, and the depth of the blast treatment layer measured from the surface of the hot-dip galvanized layer is 12 μm or more.

Images