The Factors Affecting the Bolt Strength Test Results.


Tolerance and bolt deviation are the parameters used to assess the quality of bolts, and often, they are not given enough attention. This article will clarify some aspects for you. Please delve into the article's content to learn more.

The main factors influencing the mechanical test results of bolts are as follows:

1. Intrinsic Factors: Thành phần (hàm lượng cacbon, Si, Mn, S, P…) và cấu trúc của mẫu test.

These factors primarily originate from the heat treatment process of the specific product, particularly the quenching and tempering processes, which can affect the mechanical properties of the product, such as its strength and ductility. (Refer to the KPF heat treatment process). 

2. External Factors:

Accuracy of the testing machine: The testing machine must be calibrated according to ISO 7500-1 and should meet at least Class 1 or better.
Testing conditions:
The rate of stress increase affects the strength of the test sample, and it must conform to the specified rate as per the provided table.

The most straightforward way to understand it is that the pulling speed must be ≤ 25mm per minute, and slower pulling speeds provide more accurate force measurements.
Clamping Method: Test samples are held in place using nuts, bolt clamps, or clamps with serrations. The test samples must be positioned as vertically as possible without tilting or skewing.

  • The testing machine must be in good working condition and not adversely affected by common usage conditions, such as wear and tear or defects in guiding parts of the movable pulling head or clamping devices. This includes any slack in machine column assembly and in the fixed slide.
  • The machine should not be affected by the surrounding environmental conditions (vibrations, power supply interference, corrosion effects, localized temperature variations, etc.).
  • Accurate determination of mass can be achieved using removable mass pendulums.

Test Samples: There should be a minimum of three test samples because the material may have non-uniform properties, and its strength is determined as the average strength of a group of samples.
Bolt Clamping Principle: According to the table below, the bolt must be clamped with a minimum of three complete nut turns..

Samples that are not suitable, such as bolts and nuts, do not have the same strength.

3. Load-bearing Chart of Bolt Nuts When Subjected to Load:

Several criteria are used to evaluate bolts.
  • A complete bolt manufacturing process with effective management that ensures no steps are skipped.
  • The input materials used for bolt manufacturing must be controlled in terms of mechanical properties and chemical characteristics (C, Mn, S, P, Cr, Al, etc.) to meet standards, facilitate machining, and enable easy welding.
  • Bolts should undergo experimental testing based on various criteria such as minimum tensile strength, minimum yield strength, and impact testing for ductility and toughness.
  • Bolts should have resistance to wear, oxidation, and corrosion, with hardness ensuring the required performance.
  • The finished surface of the bolt must withstand environmental factors without rusting, corroding, or oxidizing. They should be able to withstand high-temperature environments.
  • Bolt dimensions should comply with regulations and standards to ensure compatibility with various types of machinery and equipment available in the market.

We hope the information provided by CTEG here helps you gain a better understanding of bolts and make informed choices for your specific needs. For inquiries, please contact Hotline at 0914117937

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Cuong Thinh Company (abbreviated CTEG) is a leading provider of bolts and screws, manufacturing, importing, and distributing wholesale and retail products to businesses, factories... in a variety of fields and industries.

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