Through Wall Screw

Through Wall Screw is an independent steel tension component widely applied in concrete formwork fastening systems. It consists of main screw body, threaded sections and matching fastening nuts. Each structural part performs separate mechanical functions, and the whole assembly can complete formwork tensioning and positioning independently without additional auxiliary fittings. Carbon structural steel is adopted as primary raw material. Two mainstream structural styles are available: integral full‑thread type and assembled segmented type. Integral through wall screw is fully embedded inside concrete for single‑time usage. Assembled through wall screw is composed of middle segment and detachable outer threaded sections, and outer segments can be disassembled and recycled after concrete curing. Thread sections are processed by thread rolling technology, improving surface hardness of thread teeth and strengthening wear resistance for repeated assembly and disassembly cycles. Fastening nuts are manufactured through forging or casting processes, and their structural integrity guarantees stable clamping force under lateral pressure from fresh concrete. Positioning cones and plastic sleeves can be matched with screw body to precisely control wall thickness and simplify subsequent surface repair of concrete members. For waterproof construction scenarios, through wall screw can be fitted with welded water‑stop plate to block capillary water seepage through wall penetration points.

Multiple surface anti‑corrosion treatments adapt to diverse construction environments. Hot‑dip galvanizing forms compact zinc‑iron alloy protective layers covering screw body and thread teeth. This coating delivers stable resistance against rainwater, humid air and salt‑fog erosion, suitable for long‑term outdoor and underground construction projects. Electro‑galvanizing generates relatively thin zinc layer on steel surface, applicable for short‑cycle construction projects with low corrosion risk. Black oxide finish serves temporary dry‑condition projects without strict anti‑corrosion requirements. Paint finish is rarely selected for threaded parts, because paint layers tend to peel off under thread friction and concrete impact. Ordinary through wall screw without water‑stop plate is mainly used for non‑waterproof concrete wall structures. It bears expanding lateral force produced by pouring concrete, keeps fixed clearance between two opposite formwork panels, and prevents formwork bulging, offset and deformation during concrete pouring.

Core dimensional parameters determine practical mechanical performance. Screw body diameter is a critical indicator of tensile‑load grade, and larger diameter corresponds to higher ultimate tensile capacity. Effective overall length shall match designed wall thickness plus formwork panel thickness and on‑site operating space. Thread specifications must be fully consistent with supporting nuts. Mismatched threads will result in poor meshing, insufficient clamping force and component slipping. This component is compatible with timber formwork, steel formwork and various combined formwork assemblies. Dimensional tolerances shall comply with corresponding international technical specifications to ensure reliable physical fitting during on‑site assembly. For water‑proof modified version, water‑stop plate dimension and welding quality shall satisfy anti‑seepage requirements under designed water head.

Prior to construction deployment, visual inspection and sampling mechanical tests shall be implemented as independent inspection workflows. Visual examination covers screw body bending deformation, surface cracks, thread tooth damage and anti‑corrosion‑layer peeling. Recycled outer screw segments require stricter inspection standards. Even with intact outward appearance, invisible metal fatigue may accumulate after repeated load cycles and cannot be judged merely through surface observation. Sampling tensile tests verify ultimate bearing capacity and anti‑deformation performance. Components with permanent bending, thread slipping and structural cracks must be screened out and scrapped, and shall not be mixed into construction usage. Secondary modification operations including cutting, welding and hole‑drilling on finished through wall screw are prohibited. Unauthorized alteration will change original steel section characteristics and weaken overall tensile performance of the component.

Assembled through wall screw supports cyclic reuse. After concrete curing and formwork dismantling, detachable outer threaded segments can be unscrewed and recovered. Concrete mortar, dust and foreign residues attached to thread grooves need thorough cleaning before next installation. Impurities trapped inside thread gaps will cause nut jamming and interfere with normal assembling and clamping effect in subsequent service cycles. Finished components shall be stored in dry and ventilated surroundings, sorted and stacked by specification, avoiding long‑term rain soaking and direct contact with damp soil. Improper on‑site operations include selecting insufficient screw diameter, mismatching screw length with wall thickness, insufficient tightening of nuts and applying load exceeding rated limit. These improper practices may trigger formwork bulging, component fracture and dimension deviation of concrete walls. As an independent tension‑bearing fastening unit for formwork systems, its structural integrity and mechanical stability directly influence formwork safety and concrete forming accuracy, and constitute essential preconditions for cast‑in‑place concrete wall construction.