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Adjustable U-head Screw Jack

Jun 6th, 2019 | Categories: news
Adjustable U-head Screw Jack (3)

The adjustable U-head screw jack is a small part of a vertical pole, but it does play a decisive role in the load capacity of a single pole. Its function is that when the height of formwork at each position is not the same, it can be adjusted according to actual needs. So what should you pay attention to during actual use?

Strictly in accordance with the specification:
Adjustable U-head Screw Jack (1)

1.The material performance in the Disk Lock Steel Tubular Scaffold Component (JG/T5032016)

5.1.3 specified that the mechanical properties of steel plates of adjustable U-head screw jack and adjustable base screw jack should not be lower than GB/T700 Q235 Provisions.(JG/T5032016)

5.3.15 stipulates that both plate of base jack and U-head jack should be made of Q235 plate in 5mm thickness with ±0.3mm tolerance. The bearing surface of the steel plate’s length and width shall not less than 150mm. The bearing plate and the screw tube shall be ring welded. Stiffeners and stiffening arches shall be added. And the adjustable U-head screw jack shall be provided with an open baffle with the height not less than 40mm.

2.According to Technical specification for safety of disk lock steel tubular scaffold in construction (JGJ2312010), the extended length of formwork U-head jack over the top horizontal rod or the cantilever length of double channel steel joist shall not exceed 650mm, and the exposed length of the screw tube is strictly prohibited to exceed 400mm. The length of the adjustable U-head screw jack inserted into the vertical tube  or double channel steel beam shall not be less than 150mm.

3.According to  the Disk Lock Steel Tubular Scaffold Component (JG/T5032016), the test load P of Z type product is unloaded from 0kN to 35kN, and then from 0kN to 140kN keeping 2 minutes. Its test parts should be destroyed. For the B type product, the test load P is unloaded from 0kN to 25kN, then from 0kN to 100kN keeping 2 minutes. Its test parts shall not be damaged.

4.Construction conditions restriction: the adjustable U-head screw jack is affected by the environmental factors of the on-site construction (for example, the original design of 100mm high wooden keel is replaced by steel pipe, the ground is uneven, etc.), which is very easy to cause on-site construction and program inconsistency, for example, in the design of the scheme, the length of the cantilever is 45cm, but the actual adjustment is 65cm.

5.Gap between theoretical research and practice:  The model of theoretical research on the dick-lock scaffolding system in domestic and abroad is basically based on the condition that the adjustable U-head screw jack is pressed by axial compression (ie, the screw tube and the pole are not eccentric). However, during the implementation process, there are many situations in which the middle keel is placed eccentrically. Therefore, the bearing capacity of the adjustable U-head screw jack is far less than the assumed axial compression.)

6.Bending deformation of the screw tube: Due to the excessive bearing capacity in some engineering applications, the adjustable U-head screw jack is subjected to some degree of plastic compression and bending deformation after a long-term renting. It is difficult to recover. Therefore, the bearing capacity of U-head Jack is greatly reduced comparing with the original design.

7.Screw jack rusting: The adjustble U-head screw jack is an iron component. Its screw jack maybe rust when its surface protection is not in place or the surface protection layer is destroyed after a long-term use. It is well known that metal rust can cause changes in the material properties of the screw jack, which will finally cause a reduction in its loading bearing capacity.

8.Not strict quality control of raw material pipe and diameter: The wall thickness and tube diameter specified in the specification all refer to raw materials. However, it’s difficult to measure the wall thickness and diameter of the thread in reality. Therefore, in the inspection after the ferrule, it is difficult to identify the wall thickness of the tube diameter, which often leads to some unqualified inferior screw rods being mixed into the market. Whether the adjustable U-head screw jack is strictly enforced in the formwork supporting process is one of the key factors to ensure that the formwork supporting system is stable and will not cause the overall collapse. Adjustable U-head screw jack may be small, but it should not be underestimated!