Release time：2020-01-16 18:44 Browse：
Extended self-tapping screws serve a purpose far beyond simply "nailing" objects to a wall when used in insulation layer environments. They function more as a specialized composite anchoring system. The core principle is to penetrate the soft insulation layer and transfer loads to a solid substrate (such as concrete or metal framing), while also addressing the inherent characteristics of insulation materials, which are soft and prone to compression.
Specifically, they work through the following coordinated mechanisms:
Core Working Principle: Cross-Layer Anchoring
This is the most fundamental aspect. Insulation materials (such as expanded polystyrene boards or rock wool) have low inherent strength and cannot provide sufficient holding power for screws. The extended length of these self-tapping screws is designed to pass completely through the insulation layer, allowing the threaded portion to be securely driven into the substrate wall or metal framing.
The advantage of this approach is that tensile forces (such as those from wind loads or the weight of cladding panels) are no longer borne by the fragile insulation layer. Instead, they are transferred directly to the stable substrate, achieving a reliable mechanical connection.
Key Supporting Mechanisms: Load Distribution and Structural Synergy
An extended screw alone is insufficient; the following mechanisms are also necessary to ensure long-term stability:
First, increasing the load-bearing area to prevent "crushing." Insulation layers are soft, and if only a small screw head applies pressure directly, the localized stress can easily crush the material, leading to loosening. Therefore, accompanying solutions typically include large-diameter metal or plastic washers or discs. This washer acts like a plate, distributing the compression force from tightening over a larger area of the insulation surface. This prevents the insulation from being damaged and ensures it remains securely fastened.
Second, combining components to achieve multifunctionality. In practice, extended self-tapping screws are often part of a larger system. They are frequently used to secure outer metal cladding (such as aluminum or color-coated steel sheets) to the framing, forming a sturdy "sandwich" structure over the insulation layer. For example, in thermal insulation for chemical towers or ductwork, self-tapping screws are used to fix the metal cladding, with strict spacing requirements (e.g., 150 mm). Additionally, in external wall insulation systems, they are often used in conjunction with adhesive mortars in a "bonding and anchoring" technique. The adhesive provides the primary bonding strength, while the extended screws offer critical mechanical anchoring as an additional safety measure.
Third, incorporating special designs to accommodate "thermal expansion and contraction." Insulation layers and substrates expand and contract differently with temperature changes. Some specialized insulation screws are designed with this in mind. For instance, certain patented designs incorporate elastic elements in the connector, or feature unthreaded shank sections on the screw shaft. These allow for a degree of adjustment and accommodation when minor changes occur in insulation thickness or structural thermal movement, thereby preventing connection failure due to stress concentration.
A Significant Potential Issue: Thermal Bridges
When using metal screws that penetrate the insulation layer, a key concern is the creation of thermal bridges. Metals have much higher thermal conductivity than insulation materials. Consequently, if a large number of screws pass directly through the insulation layer, they can act like bridges, creating a path for heat transfer between the interior and exterior, thereby reducing the overall effectiveness of the insulation system.
An effective solution to this problem is the use of thermal-break anchors. These anchors are designed with improvements such as plastic connecting tubes as thermal barriers or split-body configurations. These designs prevent metal components from passing entirely through the insulation layer, minimizing heat loss while maintaining anchoring strength.
