Formwork Screw Jack

Formwork screw jack is an independent steel structural component used in concrete formwork temporary support systems. It consists of threaded spindle, adjusting nut and load‑bearing end fitting. The load‑bearing end can be flat base plate or U‑shaped cradle head, to satisfy bottom foundation supporting and top beam propping demands respectively. Each structural part performs separate mechanical functions, and the whole unit can complete height calibration and load‑bearing work independently without dependence on other scaffolding accessories. Carbon structural steel is adopted as primary raw material. The threaded spindle has two common structural forms: solid round steel bar and hollow seamless steel pipe. Solid spindle possesses dense metal texture, high compression and bending resistance, which is suitable for heavy‑load formwork conditions such as thick concrete slab support and large‑span formwork shoring. Hollow spindle reduces overall self‑weight while meeting medium‑load bearing requirements, lowering labor burden for manual carrying and installation at construction sites. Thread sections are mostly processed by cold rolling technology, improving surface hardness of thread teeth and reducing wear generated from frequent nut rotation during repeated turnover cycles. Adjusting nuts are manufactured by forging or casting processes, and their structural completeness determines locking stability under long‑term vertical compression load. The flat base plate enlarges contact area with supporting surface, disperses concentrated vertical pressure and reduces subsidence risk on soft ground. The U‑shaped cradle head forms a restraining groove, which can hold timber beams, H20 beams and steel beams, limiting lateral offset of horizontal load‑bearing members under concrete pouring loads. Welding joints between end fitting and spindle are key stress positions, and weld continuity shall be guaranteed during production.

Various surface anti‑corrosion treatments are available to adapt to different application environments. Hot‑dip galvanizing forms compact zinc‑iron alloy protective layers covering spindle, thread teeth and all welding seams. This coating can resist erosion caused by rainwater, humid air and salt fog, and fits long‑term outdoor exposure and marine transportation scenarios. Electro‑galvanizing produces relatively thin zinc layer on steel surface, applying to short‑cycle formwork projects with low corrosion risk. Paint finishing is prone to peeling under thread friction and mechanical impact, so it is rarely used for formwork hardware with high turnover frequency. According to installation position, formwork screw jack can be divided into base jack and U‑head jack. Base jack is arranged under vertical support uprights to bear overall vertical loads of shoring frames and compensate foundation elevation differences. U‑head jack is assembled at the top of upright members to constrain horizontal load‑bearing beams and undertake downward pressure transferred from formwork and fresh concrete.

Core dimensional parameters determine its practical mechanical performance. Spindle outer diameter is a critical indicator of load‑bearing grade, and larger diameter corresponds to higher ultimate compression capacity. Effective adjustment stroke defines valid height‑changing range. Excessively exposed threaded segments outside effective stroke scope will reduce structural rigidity and increase bending deformation risk under load. The dimension of base plate or U‑shaped cradle shall match actual site bearing conditions. Undersized load‑bearing end will lead to excessive local pressure, triggering settlement, beam slipping or component damage. This component is compatible with multiple shoring systems, including tube‑and‑coupler scaffolding, ringlock and cuplock shoring frames. Dimensional tolerances shall comply with corresponding international technical specifications to ensure reliable physical fitting during on‑site assembly.

Prior to construction application, visual inspection and sampling mechanical tests shall be implemented as independent inspection procedures. Visual examination covers spindle bending deformation, surface cracks, welding discontinuity, thread tooth damage and anti‑corrosion layer peeling. Recycled formwork screw jacks require stricter inspection standards. Even with intact outer appearance, invisible metal fatigue may accumulate after repeated load cycles and cannot be judged merely through surface observation. Sampling compression 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 formwork construction usage. Secondary modification operations including cutting, welding and hole‑drilling on finished formwork screw jack are prohibited. Arbitrary alteration will change original steel section characteristics and weaken overall load‑bearing performance of the component.

Formwork screw jack is designed for cyclic reuse. After formwork dismantling, concrete mortar, dust and foreign residues attached to spindle and thread grooves need thorough cleaning. Impurities trapped in thread gaps will cause nut jamming and interfere with normal height adjustment and locking 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 over‑extending threaded spindle, offset load placement on U‑head cradle, and applying load exceeding rated limit. These improper practices may result in component deformation and abnormal local stress distribution of formwork shoring frames. As an independent adjustable load‑bearing unit for formwork systems, its structural integrity and mechanical stability directly influence load transmission of temporary support structures, and serve as essential prerequisites for safe concrete pouring and formwork dimension control.