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In building formwork support systems, screw jacks—commonly called top jacks or U-head jacks in the industry—are indispensable adjustable accessories for high formwork and beam-slab formwork support. They are widely used together with scaffold steel pipes, serving to adjust support height, evenly distribute upper loads, and level the formwork system. High formwork projects such as factory buildings, basements, large shopping malls, and cast-in-place bridge structures have strict requirements for the flatness and uniform load distribution of the support system. The quality of screw jacks directly affects the effectiveness of formwork elevation control and is also related to the stability and safety of the entire support system. Recently, a batch of solid and hollow screw jack products from our company completed production, inspection, and shipment, supplying multiple high formwork projects under construction and ensuring the progress of formwork support construction.
The screw jack has a simple overall structure, mainly composed of a screw rod, adjusting nut, and U-shaped top bracket or flat base plate. It is divided into two major categories: top jacks (U-head jacks) and bottom jacks (base jacks). The top jack is placed on top of the steel pipe to support the main joist square steel of the formwork and finely adjust the beam-slab elevation; the bottom jack is placed at the bottom of the steel pipe to disperse the pressure transmitted from the scaffold to the ground and prevent the steel pipe from sinking and local foundation compression failure. On the market, screw jacks are divided into solid screw jacks and hollow screw jacks. Solid screw jacks have stronger load-bearing performance and are mostly used in high formwork areas with large loads and high heights; hollow screw jacks are lighter in weight and easier to carry, suitable for ordinary beam-slab support with conventional loads. Construction units can select the type according to the special construction plan as needed.
In terms of raw material selection, the screw rod is processed from Q235 round steel, with priority given to the round steel thread rolling process rather than cutting and turning threads. Thread rolling is an extrusion forming process for threads, in which the internal metal structure of the steel remains continuous, giving higher strength at the thread root. Under repeated pressure and adjustment conditions, problems such as thread stripping and thread breakage are unlikely to occur. The thread profile is regular, the nut rotates smoothly, and it will not seize up and become impossible to turn after long-term use. The U-shaped bracket and base plate are made of thickened steel plates and are fully welded to the screw rod—this is a key quality inspection point. Many top jack failure accidents on construction sites are caused by insecure bracket welding, where the bracket detaches under load and causes formwork settlement. After each bracket is welded, we manually inspect the weld fullness and also conduct sampling pressure tests to verify the tear resistance of the welded position, preventing poorly welded products from leaving the factory.
Anti-rust treatment is also a key process for screw jacks. Products can be finished with either spray painting or electro-galvanizing. The painted version is cost-effective and suitable for short-term turnover projects; the galvanized version has a dense coating and stronger corrosion resistance, suitable for damp basements and waterfront projects, and is not prone to rusting and thread seizing. Before finished products are put into storage, quality inspectors check the straightness of the screw rod. Screw jacks with excessive bending are directly reworked, because bent screw jacks will generate additional bending moments under load and pose a major safety hazard. At the same time, the fit clearance between the nut and the screw rod is checked—too large a clearance causes wobbling, while too small a clearance makes turning difficult—and the fit tolerance is strictly controlled.
At the on-site construction and usage level, many construction personnel tend to overlook the usage specifications for screw jacks, resulting in incorrect operations such as excessive extension length, eccentric loading, and brackets not securely supporting the main joist, which greatly reduces the safety reserve of the support. When delivering products, our sales and technical teams simultaneously communicate usage specifications to customers: the extension length of the screw jack must strictly follow the requirements of the special construction plan to avoid instability caused by excessive screw rod extension; the U-head must support the square timber in a centered manner, and eccentric loading is prohibited; the foundation at the bottom must be hardened and bearing plates laid to prevent settlement. At the same time, we remind projects to promptly clean cement dust from the screw rod after use and perform proper maintenance to extend the number of turnover cycles and reduce project consumable costs.
High formwork is a hazardous and major engineering project, and special plan approval, on-site monitoring, and accessory quality are all indispensable. Our company continues to stably supply solid and hollow screw jacks with a complete range of specifications and stable supply, continuously serving various cast-in-place formwork projects such as building construction, factory buildings, and bridges. With reliable leveling and support accessories, we help high formwork construction achieve precise elevation and stable supports.
