Steel Screw Jack

Steel screw jack is an independent steel structural element deployed for building temporary scaffolding and formwork shoring. It is assembled from threaded steel spindle, adjusting nut and load‑bearing end piece. The load‑bearing end can be flat base plate or U‑shaped head to satisfy bottom support and top propping requirements respectively. Each component part undertakes separate mechanical functions, and the whole unit can perform height calibration and load‑bearing work without dependency on additional scaffolding accessories. Carbon structural steel serves as the primary raw material. The spindle is manufactured in two mainstream forms, solid steel bar and hollow seamless steel pipe. Solid spindle owns dense metal texture, outstanding compression and bending resistance, suitable for heavy‑load working conditions such as high‑rise formwork and large‑span beam temporary support. Hollow spindle cuts down overall self‑weight while meeting load requirements of conventional medium‑load construction scenarios, lowering physical burden for manual handling and installation. Thread sections are mostly treated by cold rolling process, improving surface hardness of thread teeth and mitigating wear caused by frequent nut rotation during repeated cyclic usage. Adjusting nuts are produced via forging or casting, and their structural soundness governs locking stability under sustained vertical compression. The flat base plate expands contact area with supporting surface, disperses concentrated pressure and reduces subsidence risk on soft ground. The U‑shaped head forms a clamping groove to hold horizontal steel tubes or wooden beams, transferring downward loads generated by formwork and poured concrete.

Multiple anti‑corrosion surface treatments are available to adapt to diverse service environments. Hot‑dip galvanizing generates compact zinc‑iron alloy protective layers covering spindle, thread teeth and welding seams. This coating delivers stable resistance against rainwater, humid air and salt fog erosion, applicable for long‑term outdoor exposure and ocean‑going transportation. Electro‑galvanizing produces a relatively thin zinc layer on steel surface, matching short‑cycle construction projects with low corrosion exposure. Paint finishing tends to peel off under thread friction and mechanical collision, so it is seldom selected for construction hardware with high turnover frequency. According to installation positions, steel screw jack can be categorized into base jack and U‑head jack. Base jack is positioned beneath vertical support uprights to bear frame vertical loads and offset foundation elevation deviations. U‑head jack is mounted on the top of support members to restrain horizontal load‑bearing parts and withstand pressure from formwork assemblies.

Key dimensional parameters define its practical mechanical performance. Spindle outer diameter is a critical performance indicator, and larger diameter corresponds to higher ultimate compression capacity. Effective adjustment stroke sets the valid range for height variation. Over‑exposed threaded segments outside valid stroke scope will reduce structural rigidity and raise deformation risk under loaded condition. The dimension of base plate or U‑head should match actual site bearing conditions. Undersized load‑bearing end will trigger excessive local pressure and further lead to settlement or displacement. This steel component can adapt to various scaffolding systems, including tube‑and‑coupler scaffolding, ringlock, cuplock and frame‑type shoring structures. Dimensional tolerances need to comply with relevant international technical standards to guarantee reliable physical fitting during field assembly.

Prior to on‑site application, visual inspection and sampling mechanical tests should be conducted as independent inspection workflows. Visual examination checks spindle bending deformation, surface cracks, welding discontinuity, thread tooth damage and anti‑corrosion layer peeling. Recycled steel screw jacks require stricter inspection criteria. 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 capability. Units with permanent bending, thread slipping and structural cracks must be screened out and scrapped, and shall not be mixed into construction deployment. Secondary modification such as cutting, welding and hole‑drilling on finished steel screw jack is prohibited. Arbitrary alteration will change original steel section characteristics and weaken overall load‑bearing performance of the component.

Steel screw jack is designed for cyclic reuse. After dismantling of support frames, concrete mortar, dust and foreign residues attached to spindle and thread grooves require thorough cleaning. Impurities trapped inside threads will cause nut jamming and disturb normal height adjustment and locking performance in subsequent service cycles. Finished components shall be stored in dry and ventilated space, sorted and stacked by specification, avoiding long‑term rain soaking and direct contact with damp soil. Improper site operations include over‑extending threaded spindle, placing load‑bearing end on uneven ground or scattered debris, and applying load exceeding rated capacity. These improper practices may result in component deformation and abnormal local stress distribution of shoring frames. As an independent steel adjustable load‑bearing unit, its structural integrity and mechanical stability directly influence stress status of temporary support structures, and form essential prerequisites for safe operation of scaffolding and formwork shoring systems.