Surgical implants - Test method for rotational torque of metal bone screws

Surgical implant metal bone screw

Test method for rotational torque

1 Scope

This standard is used to measure the torque required to unscrew metal bone screws (hereinafter referred to as "moth screws") from standard materials. The results obtained from using this standard are not directly related to the torque required to unscrew the screw into human bone. The purpose of this standard is only to confirm the consistency of the tested product.

2 Normative References

The following documents are applicable to the application of this document. For all referenced documents with dates, only the version with dates is applicable to this document. For any reference document without a date, its version applies to this document.

JJG 269 Verification Regulations for Torsion Testing Machine

3 devices

3.1 Experimental apparatus

The device shown in Figure 1 can be used for torque testing of screw in and screw out. The test device should be able to cooperate with test blocks, test block fixtures, drill sleeves, and described drill sleeve clamping fixtures that comply with ASTM F1839 materials. The test device should have sufficient rigidity to prevent deflection or deformation under test loading conditions.

3.2 Torque Sensor

A converter capable of converting applied torque into continuously recorded electrical signals, calibrated within the range used in the experiment, including YY/T 1506-2016 in both clockwise and counterclockwise directions.

3.3 Twist angle sensor

A converter that can convert the twisting angle into a continuously recorded electrical signal, calibrated according to JJG269 within the range used in the experiment, including clockwise and counterclockwise directions, with an accuracy of ± 0.3 °.

3.4 Data recording equipment

The data recording device should be able to continuously record torque and rotation angle, with torque measured in Newton meters (N.m) and rotation angle measured in degrees (°). The torque resolution should reach 10% of the maximum measured torque. The angular displacement scale should have sufficient sensitivity to record and display at least 4 cycles of data.

3.5 Drill sleeve

The drill sleeve is used in conjunction with the testing device and can be replaced, using materials that comply with ASTM F 1839. The drill sleeve should have sufficient length and rigidity to ensure that the sample is vertically rotated into the test block. The inner diameter size of the drill sleeve should ensure that the sample experiences minimal frictional resistance between its outer diameter and the inner diameter of the drill sleeve. The drill sleeve used for grinding cannot be reused.

3.6 Test block fixture

Clamps or fixing devices that can be used in conjunction with experimental equipment. The clamp should be able to maintain the pre drilled guide hole in the test block in conjunction with the test sample

Line. The fixture should avoid deformation of the test block during clamping or testing

3.7 Test Samples

The test sample should be the final product, with a length sufficient to penetrate the drill sleeve and test block.

3.8 Test Block

The test block shall be made of uniform materials in accordance with ASTMF 1839. In this test, the user can choose the appropriate foam density. For more information, see 8.6.2 of ASTMF 1839. According to the requirements of the pilot hole described in 3.9, the minimum size of the test block surface shall be 10 times larger than the screw diameter. The upper and lower surfaces of the test block should be flat, smooth, and parallel to each other (with a deviation of+0.4 mm) to ensure that when it is fixed in the fixture, its upper surface is perpendicular to the centerline of the screw. The test block should be square or other shape that ensures no relative motion or deformation during holding or testing. The thickness of the test block should not be less than 4.8 mm.

3.9 Guide holes in the test block

Before the screw in and screw out tests, guide holes should be pre drilled in the test block. The guide hole gauge should be specified by the manufacturer of the nail to be tested. If specified by the screw manufacturer, the guide hole should be tapped with a specified size tap before testing. The guide hole should be drilled perpendicular to the surface of the test block, and it should be ensured that the hole is straight and not conical Bell shaped, bucket shaped, and other situations. If there are multiple guide holes on the surface of the test block, each hole should be far enough from the edge of the test block to ensure that the test does not cause deformation of the edge of the test block. The spacing should be at least 5 times the diameter of the screw. After the test block is installed on the test device (see Figure 1), the guide holes, screws, and screw drive fixtures should be on the same axis.

4 test samples

Representative samples should be randomly selected from each batch or process quantity according to ASTME122.

5 Sample Instruments

6. Experimental steps

Install the sample into the testing device shown in Figure 1, use a matching tool of appropriate size to screw the sample into the test block, and apply torque to the screw head at a speed of 3r/min using a torsion testing machine. The screw in torque is the maximum torque recorded during the first 4 rotations of the sample. Reverse rotate the screw to measure the unscrewed torque, which is the maximum torque (N.m) recorded by rotating the test block 4 times. During the screwing in and out process, always apply an axial load not exceeding 11.17N to ensure that the driving fixture is inside the screw head.

If a larger axial load is used, the report should record the axial load used. Measure axial load using appropriate methods.

7. Report

The report should include the following information for each sample (all values in the report are in SI units):

a) Screw information refers to the national standard industry standard or ISO standard number that the screw complies with. If it does not meet the standards, the screw head form, thread form, maximum diameter/base diameter, pitch, total length of the screw, length of the head and shaft (excluding the part of the head without threads), and screw type should be provided;

b) Chemical composition of screws;

c) Surface treatment form;

d) Spinning torque:

1) Required axial load;

2) Spin depth (can be obtained through calculation or measurement);

3) The regulation on whether the guide hole is tapped, if tapped, the report should include the tap size, tap diameter, and tapping depth;

4) Screw in speed (if not in accordance with the provisions of Chapter 5);

e) Spin out torque:

1) The required axial force;

2) Spin out speed (if not in accordance with the provisions of Chapter 5);

Description of D test block material: ASTM F 1839 grade. If the drill sleeve material does not meet the requirements of ASTM F 1839, it should be reflected in the report:

1) Product name;

2) Ingredients;

3) Density;

4) Tensile strength;

5) Compressive strength;

6) Shear strength.