Method for detecting the pitch diameter of a metric internal thread

Abstract

The application discloses a detection method for the pitch diameter of a metric internal thread, which comprises a universal toolmaker's microscope (or a flash tester), a steel ball for measurement, a strong magnet and geometric formulas. The main principle is that the steel ball is uniformly distributed in the internal thread groove, the steel ball is then attracted by the strong magnet, the measured product and the steel ball are placed under the universal toolmaker's microscope for measurement, the distance from the center of the steel ball to the center of the internal thread is measured, and finally, the pitch diameter value of the internal thread is calculated by using geometric formulas. The application has the advantages of simplicity, reliability, low cost, high popularization rate, high efficiency, high detection accuracy and precision, and suitability for scenes with strict requirements on the pitch diameter of the thread and the need for accurate data.

Description

Technical Field

[0001] This invention relates to the field of thread inspection technology, and in particular to a method for inspecting the pitch diameter of metric internal threads. Background Technology

[0002] With increasingly stringent precision requirements for threads in automotive, hydraulic, and aerospace products, significant testing and control challenges have arisen for manufacturers across the industry. This is particularly true for high-strength products requiring heat treatment, where thread deformation is a major obstacle to production control and inspection. Since thread deformation is related to heat treatment methods, material properties, material length, material diameter, and product structure, the conventional method of using standard thread plugs (rings) such as 6H, 6G, and 7H in national standards to control threads before heat treatment is no longer sufficient to guarantee that products meet national standards after heat treatment. Therefore, it is essential to precisely control the thread pitch diameter before heat treatment and to identify the patterns of thermal deformation through extensive testing to achieve the goal of controlling the thread pitch diameter quality. The biggest challenge lies in the detection of the pitch diameter of the thread. For the pitch diameter of external threads, the national standard provides a three-wire method for measurement, which is easy to implement. However, there is no effective method for detecting the pitch diameter of internal threads in my country. Currently, only the German company COTO has a patented product for detecting the pitch diameter of internal threads, which costs nearly 100,000 yuan and requires customization. It only supports the detection of internal threads with specific inner diameters and pitches, making it difficult to popularize in China. In order to solve the current problem of detecting and controlling the pitch diameter of internal threads, the inventor has invented a method that combines a universal measuring instrument, a steel ball, and a geometric algorithm to accurately measure the pitch diameter of internal threads. Summary of the Invention

[0003] The technical problem to be solved by this invention is to provide a method for detecting the mean diameter of a common metric internal thread with a tooth angle of 60°, which addresses the shortcomings of existing technologies, ensures accurate detection, is easy to implement, and has a detection error of 0.01mm.

[0004] To achieve the above-mentioned objective, the method for detecting the pitch diameter of a metric internal thread according to the present invention includes the following steps: Step 1: Place the steel balls evenly inside the internal thread of the product to be inspected, then use a strong magnet to hold the steel balls in place. Then place the product to be inspected and the steel balls on the universal inspection table and measure the distance L from the center of the steel ball to the center of the internal thread. Step 2: For metric threads, α = 60°, α / 2 = 30°. Calculate the pitch diameter D2 of the internal thread using the following formula: D2=M+D(1+1 / sin(30°))-P / 2 / ctg(30°)=M+3D-0.866P Where M = 2L - D D2: Pitch diameter of internal thread D: Diameter of the steel ball M: Minimum distance between the inner edges of the two steel balls in the direction of the internal thread diameter; The correspondence between pitch P and steel ball diameter D is shown in Table 1 below: 0.5 0.289 0.29 0.7 0.404 0.4 0.75 0.433 0.4 0.8 0.462 0.5 1 0.577 0.6 1.25 0.721 0.7 1.5 0.866 0.9 1.75 1.010 1 2 1.154 1.2 2.5 1.443 1.4 .

[0005] The detection method of this invention uses three steel balls of the same diameter, evenly distributed around the circumference of the internal thread and tangent to the internal thread, so that the contact point between the steel balls and the internal thread is just tangent to or close to the pitch diameter line of the internal thread. At the same time, a strong magnet is used to hold the steel balls firmly so that they do not fall off and remain in close contact with the thread. Then, a universal tester or a flash tester is used to measure the center distance between the steel balls and the thread axis, and the pitch diameter value is calculated using a geometric formula.

[0006] The inventive points of this invention are as follows: 1. The use of general-purpose testing equipment ensures wide adaptability; 2. Steel balls are easy to purchase and inexpensive; 3. The measurement operation is simple, fast, and accurate.

[0007] Due to the adoption of the above technical solution, the beneficial effects of the present invention are as follows: 1. Compared to imported testing equipment, this solution is simple, reliable, and low-cost; 2. Accurate and efficient detection; 3. Suitable for inspection and control of products with strict requirements on thread pitch diameter and requiring accurate data. Attached Figure Description

[0008] Figure 1 This is one of the schematic diagrams of a method for detecting the mean diameter of a metric internal thread according to the present invention.

[0009] Figure 2 This is the second schematic diagram of a method for detecting the mean diameter of a metric internal thread according to the present invention. Detailed Implementation

[0010] To more clearly illustrate the technical solutions in the embodiments of the present invention or the prior art, the accompanying drawings used in the description of the embodiments or the prior art will be briefly introduced below, but this does not limit the present invention to the scope of the embodiments described.

[0011] See Figure 1 The method for testing the pitch diameter of internal threads shown in the figure includes: 1. the internal thread product being tested, 2. a steel ball, 3. a strong magnet, and so on. Figure 2 Wan Gong Xian 4 See Figure 1 , Figure 2 Place steel balls 2 evenly inside the internal threads of the product being inspected 1, then use a strong magnet 3 to hold the steel balls in place. Finally, place the product on the inspection table 4 and press... Figure 1The geometric calculation method for the measured value L and the pitch diameter D2 of the internal thread is as follows: For metric threads, α = 60°, α / 2 = 30°, therefore: D2=M+D(1+1 / sin(30°))-P / 2 / ctg(30°)=M+3D-0.866P Where M = 2L - D D2: Pitch diameter of internal thread D: Diameter of the steel ball L: Distance from the center of the steel ball to the center of the internal thread M: Minimum distance between the inner edges of the two steel balls in the direction of the internal thread diameter. The table below shows the correspondence between pitch P and steel ball diameter D: 0.5 0.289 0.29 0.7 0.404 0.4 0.75 0.433 0.4 0.8 0.462 0.5 1 0.577 0.6 1.25 0.721 0.7 1.5 0.866 0.9 1.75 1.010 1 2 1.154 1.2 2.5 1.443 1.4

Claims

1. A method for detecting the pitch diameter of a metric internal thread, characterized in that, The steps include the following: Step 1: Place the steel balls evenly inside the internal thread of the product to be inspected, then use a strong magnet to hold the steel balls in place. Then place the product to be inspected and the steel balls on the universal inspection table and measure the distance L from the center of the steel ball to the center of the internal thread. Step 2: For metric threads, α = 60°, α / 2 = 30°. Calculate the pitch diameter D2 of the internal thread using the following formula: D2=M+D(1+1 / sin(30°))-P / 2 / ctg(30°)=M+3D-0.866P Where M = 2L - D D2: Pitch diameter of internal thread D: Diameter of the steel ball M: Minimum distance between the inner edges of the two steel balls in the direction of the internal thread diameter; The correspondence between pitch P and steel ball diameter D is shown in Table 1 below: 。

Images