Under the same ratio of hole size to wire size, an increase in wire diameter will cause a sudden increase in carding force, and there exists a certain mathematical relationship between them, which is approximately a squared function. When the wire diameter increases to 10 times the original size, the carding force that a single warp thread can withstand increases to 100 times the original amount. An increase in warp and weft diameter causes a much greater increase in carding force than a decrease in the ratio of hole size to wire size under the same wire diameter conditions.
When selecting the combination of mesh size and wire diameter, in addition to ensuring that the ratio of hole size to wire size is greater than 1, the increase in carding force caused by an increase in wire diameter must also be fully considered. When carding force increases sharply, it not only causes an increase in the warp breakage rate during weaving, but also many specifications of the mesh exceed the limit of the weaving machine and steel box's bearing capacity. The closer the ratio of hole size to wire size is to 1, the thinner the steel plate thickness is compared to the wire diameter, and the lower its ability to withstand carding force. To solve the series of problems caused by the sharp increase in carding force, the weaving process often uses a twill weave to significantly reduce the carding force. Because under the same specifications, the carding force of a twill weave is approximately 1/3 of that of a plain weave.
Although weaving a twill weave can significantly reduce carding force, it also has some drawbacks. The interweaving of warp and weft of twill weave is not as firm and tight as that of plain weave, and the uniformity and stability of mesh size is not as good as that of plain weave. The rigidity of the metal mesh is also inferior due to these deficiencies of twill weave. It is only suitable for weaving high mesh counts. In order to significantly reduce carding force, for square meshes with large mesh size and thick wire diameter, the metal wire can be pre-bent and shaped before weaving.
Longitude and latitude are woven with straight wires. If the weft tension exceeds the bearing capacity of the loom, the weft wire can be pre-bent into shape before weaving (the warp wire is not pre-bent). At this time, the weft tension is about 2/3 of the original weft tension. If both the warp and weft wires are pre-bent into shape before weaving, the weft tension is reduced to 1/6 of the original weft tension, a decrease of 5/6. Therefore, some high strength and low mesh nets can only be woven using this weaving process.
Advanced industrial countries such as the UK and the US have classified different sizes of sieve net from the perspective of weft tension in the national standard for industrial square hole sieve nets. Specifications with low weft tension are classified as light-level nets; specifications with very high weft tension are classified as heavy-level nets; specifications with weft tension greater than light-level nets but less than heavy-level nets are classified as medium-level nets. In the standard, different mesh sizes are combined with wire diameters, and different types of nets are classified according to the magnitude of the weft tension. This is not only beneficial to users in selecting sieve nets, but also helps screen manufacturers to adapt to different specifications. When the sieve net manufacturer wants to produce heavy-level nets, they should first analyze the maximum weft tension that can be borne by their looms and the bearing capacity of the tool steel box at maximum weft tension in order to overcome blind investment.
When the ratio of the square hole sieve net (hole/wire) is small, the weft tension is large and not conducive to weaving. However, it also has an advantage in that it can improve the weaving accuracy of the mesh. Due to the tendency of the warp wire to slide towards the center of the hole and the greater bending angle of the weft wire after interweaving with the smooth metal wire, the tendency of the warp wire to slide towards the center of the hole is also greater, which correspondingly improves the weaving accuracy of the mesh between the warp wires. Because of the heavy weft tension, the mechanical shaking in the hand of the loom cannot be reflected significantly in the weft density, ensuring the uniformity between the weft wires. When the ratio of the square hole sieve net (hole/wire) is very large, although the weft tension is very small, it cannot strictly guarantee the weaving accuracy of the sieve net, especially when the weft tension is so small that the mechanical shaking in the hand of the loom cannot move the weaving point back by a day. It is difficult to weave the weft wires uniformly, especially on looms that use passive roll nets. Due to the small bending angle of the weft wire, the tendency for the warp wire to slide towards the center of the hole is small, so the dynamic clearance between the hole in the steel box and the diameter of the warp wire is more clearly reflected in the mesh size between the warp wires, making the mesh size between the warp wires uneven. Therefore, the ratio of the square hole sieve net (hole/wire) is an important data in the design of the sieve net and should be studied more deeply.
