Adjustable Screw Jack

A Adjustable Screw Jack,also known as a spiral Adjustable U-Head Jack or threaded scaffolding jack,is a height-adjustable load-bearing component widely used in construction scaffolding,formwork systems,and temporary support structures.It consists of a precision-threaded steel rod,a U-shaped top plate(U-head),a rotating adjustment nut,and optionally a lock nut,utilizing a helical screw mechanism to achieve vertical positioning with high precision.This design allows for micro-adjustments to accommodate uneven surfaces or precise elevation requirements in structural support.

Core Design Components

Threaded Rod:Manufactured from high-strength carbon steel(Q235/Q345)or alloy steel(45#),with diameters ranging from 28mm to 50mm.The rod features continuous trapezoidal threads(30°profile)with pitches of 3-6mm,engineered for optimal load distribution and self-locking performance.Threads are cold-rolled to enhance surface hardness(HRB 80-90)and fatigue resistance,with a minimum thread length of 200mm for adjustment range.

U-Head Assembly:The top U-shaped bearing plate(100×150mm to 150×200mm)is either forged integrally with the rod or welded with full-penetration fillet welds(leg length≥6mm).The U-head interior is often lined with a 3mm rubber pad to prevent slippage of supported beams,while reinforcing gussets(5mm thickness)connect the plate to the rod for bending resistance.

Adjustment Nut:A heavy-duty cast iron(GG25)or ductile iron(QT450)nut with a hexagonal outer profile and knurled gripping surface.The nut’s internal thread matches the rod’s pitch and features a lead angle≤4°to ensure self-locking under static loads,preventing backsliding without additional locking devices.

Base Configuration:The lower end may feature a flat base plate(150mm diameter)for direct ground contact or a male thread(M30-M52)for insertion into scaffold standards,with a minimum engagement length of 10×rod diameter as per GB/T 15831 standards.

Mechanical Characteristics

Load Capacity:Safe Working Load(SWL)ranges from 2t to 15t,with ultimate tensile strength of the rod exceeding 400MPa.The thread engagement provides shear strength≥250MPa,while the U-head can withstand bending moments up to 5kN·m without permanent deformation.

Adjustment Precision:Vertical adjustment resolution of 1mm per nut rotation,with total travel ranging from 150mm to 800mm depending on rod length.The screw mechanism maintains positional accuracy within±0.5mm under full load.

Friction Coefficient:Thread surfaces treated with phosphate coating and molybdenum disulfide lubrication achieve a friction coefficient of 0.15-0.2,requiring adjustment torque≤60N·m for smooth operation.

Manufacturingu0026 Quality Control

Production follows ISO 9001 standards with key processes including:

Rod cold drawing for dimensional tolerance(±0.2mm on diameter)

Thread rolling with pitch accuracy of±0.1mm

Weld ultrasonic testing(UT)to detect internal defects

Hot-dip galvanizing(Zn coating 85-120μm)per ISO 1461

90%load testing at 1.5×SWL for 5 minutes