Timber To Steel Decking Screws

The thread geometry parameters of Timber To Steel Decking Screws are differentially designed based on the characteristics of the two connected materials. The upper half of the thread adopts a deep tooth profile to enhance the gripping force in the wood, while the lower half uses a shallow tooth profile to reduce friction resistance when tapping in the steel plate. According to the ISO 1478 regulations on the thread size of self-tapping screws, the outer diameter of the upper thread of ST5.5 screws is 5.5 mm and the thread depth is 0.8 mm. The outer diameter of the lower thread is reduced to 5.2 mm and the thread depth is 0.6 mm. This segmented design allows the screw to penetrate the wood and enter the steel plate. When the screw penetrates the wood and enters the steel plate, its effective tapping torque is about 20% lower than that of equal diameter threads. According to DIN 7500 Part 1 Test Method for Screw-in Torque, the measured peak screw-in torque is 3.2 Nm, while the comparison sample with equal diameter thread reaches 4.0 Nm. There is a scraping groove under the screw head, which can cut a tapered counterbore when the screw sinks into the wood surface, so that the head is flush with the wood surface. According to the ASTM D143 reference method for wood cross-grain compression test, this counterbore structure can expand the compressive stress distribution range of the wood surface by about 30% under the action of pretightening force, effectively reducing the risk of local crushing of wood fibers.

 

 

In terms of construction efficiency and long-term reliability, the screw's chip flute has been optimized to separate steel chips and wood chips during the process of drilling through the steel plate, preventing mixed chips from clogging the thread flanks and affecting the bite. According to actual measurement data, when the chip flute width is 25% of the thread outer diameter, the chip removal efficiency can reach 92%, which is significantly better than 76% when the flute width is 15%. Tests have shown that the optimized chip flute reduces the average time for the continuous installation of fifty screws from 7.2 minutes to 5.8 minutes. The anti-corrosion system of the screws adopts dual protection of hot-dip galvanizing and organic coating. According to the ASTM B117 salt spray test, there is still no red rust on the coating surface after two thousand hours of exposure. At the same time, after a 48-hour test according to the ISO 9227 copper accelerated acetic salt spray test, there are no corrosion spots on the thread flanks and tips.

 

 

In view of the expansion and contraction of wood due to changes in humidity, the length of the polished rod section of the screw is based on DIN 68121 specifies the axial deformation of wooden structural connectors, which is designed to be 20% of the total thickness of the wood. This non-threaded area allows the wood to freely expand and contract along the screw axis when the moisture content changes without generating additional stress. According to simulation tests, when the wood moisture content is 100% In the process of increasing from 8% to 18%, the pretightening force attenuation rate of the connection node using the polished rod design is only 4%, which is much lower than the 12% of the fully threaded screw, thus maintaining the connection stability and structural integrity during the long-term use of outdoor terraces and landscape planks.

 

 

 

 

 

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★ Our product range includes:

► Materials: Carbon steel / Mild steel / Structural steel / Stainless steel / Aluminum / Copper, etc.

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