1Steel bar bending testing machinesample preparation

Sampling requirements

Raw material sampling: Cut a sample of not less than 500mm from the end of the steel bar and classify it by diameter

Diameter 8-10mm (round steel): Sampling length 200mm;

Diameter 12-25mm (threaded steel): Sampling length 300mm;

Diameter 28-36mm (threaded steel): Sampling length 400mm.

Sampling of welded joints: Samples of no less than 100mm shall be taken from both sides of the welded area, with a total length that meets the requirements of the bending test.

Straightening treatment

Coiled steel bars need to be manually straightened to ensure minimal plastic deformation (avoiding heating straightening and preventing performance changes).

After straightening, inspect the surface defects and remove non-conforming samples such as cracks and rust.

Mark the original gauge length

Use fine lines or an automatic marking machine to mark the original gauge length (L ₀) with an accuracy of ± 1%.

Mark spacing: 10d for HPB300 grade steel bars and 5d for HRB400E grade steel bars (where d is the diameter of the steel bars).

2、 Equipment preparation

Equipment inspection

Before starting up, check whether all components of the equipment are normal and whether the power supply is stable (voltage fluctuation ≤ ± 5%).

Confirm that the bending (rolling) diameter meets the standard (e.g. HRB400 steel bar bending diameter ≥ 4d).

Parameter Settings

Positive bending test: The bending angle is 180 °, and the bending center diameter is selected according to the standard (such as a 20mm diameter steel bar bending center diameter ≥ 80mm).

Reverse bending test (optional): First bend 90 ° forward, then bend 20 ° backward (applicable to special materials such as nuclear power steel).

Set the angle through the control panel of the testing machine, with an error of ≤ 0.5 °.

Sample installation

Place the sample on the inner side of the pressure roller, closely adjacent to the pressure roller, to ensure uniform force distribution.

Adjust the spacing between the support rollers, formula:

L=(D+3a)±0.5a

(D is the bending center diameter, a is the radius of the steel bar).

3、 Experimental execution

Loading control

Start the oil pump motor and slowly turn the handle of the manual directional valve to make the piston rod drive the bend forward.

Loading speed ≤ 1MPa/s (or 1 ± 0.2mm/s), to avoid result deviation caused by impact loading.

Bending process

Observe the deformation of the specimen and immediately stop loading when it is bent to the set angle (such as 180 °).

For fully automatic testing machines, the system automatically records bending angle and load data.

Reverse bending (optional)

Place the sample after forward bending on the reverse bending working axis, press it tightly, and start reverse bending.

The reverse bending angle is usually 20 °, used to evaluate the material's resistance to repeated bending.

4、 Result judgment

Visual inspection

After bending, inspect the outer surface of the sample visually or with a magnifying glass (5x).

Qualification criteria: No visible cracks, fissures, or fractures (if otherwise specified in the product standard).

特殊材料判定

High strength steel bar (HRB600): bending center diameter ≥ 3d, indentation depth after bending ≤ 0.5mm.

Stainless steel (304/316L): The bending angle can be adjusted to 90 °, and lubricating grease needs to be applied to reduce friction cracks.

Epoxy coated steel bars: If the crack length of the coating after bending is ≤ 5mm, it is qualified.

data recording

Record parameters such as bending angle, bending center diameter, and specimen diameter.

The fully automatic testing machine automatically generates Excel reports and supports QR code traceability.

5、 Precautions

safety protection

Operators should wear goggles and anti cutting gloves to prevent metal debris from splashing.

Install protective nets around the equipment to prevent the sample from breaking and causing injury.

Equipment maintenance

Regularly calibrate the testing machine (with at least level 1 accuracy) and verify the bending angle error using standard angle blocks.

Remove the bending center and connecting block after each test to avoid additional load on the piston rod.

environmental control

The experimental temperature should be controlled between 10-35 ℃ (± 2 ℃ deviation control should be used for low-temperature testing).

Sample insulation time: liquid medium ≥ 10 minutes, gas medium ≥ 30 minutes.

VISteel bar bending testing machineCase Comparison