Overview
As a practitioner in the metallurgical industry, you must have heard that straightening is required when producing metal materials. This is mainly to keep the material in good straightness. Although it is a seldom mentioned indicator, it plays a very important role.
In this article, we will first introduce straightness and how to measure it. Then, we will introduce the equipment and principle of the straightening process. By reading, you will have a clearer understanding of it.
Straightness
What is Straightness?
Straightness refers to the degree of straight of a long strip of material (such as tubes, bars, etc.) in the straight direction. In the definition, straightness actually refers to the distance between the two points where the material deviates the most from the straight line.
Depending on the reference position, straightness can be divided into surface straightness and axis straightness. Surface straightness measures the straightness of the surface, while axis straightness measures the straightness of the center of the material cross section. The figure below shows the difference between the two types of straightness.
In this article, we mainly use surface straightness as a reference indicator.
First of all, the longer the material, the greater the probability of bending. So we must discuss straightness at the same length. Because if each material uses its own length, it will be impossible to set a unified standard. This standard length is generally 0.5 meters or 1 meter.
After determining the standard length, we determine the distance that the material deviates from the straight line in the direction of this straight line. We will take a highest point and a lowest point. The difference between them is the straightness we need.
The figure below shows the definition of straightness.
You can see that the larger the straightness value, the less straight the material is. Here is a typical representation of straightness:
It represents the deviation of a straight line over a certain length. The value after the "/" refers to the reference length, and the value before the "/" refers to the deviation.
How to Measure Straightness?
When measuring straightness, we need to determine a reference length first. Then randomly select a section on the material based on this reference length.
After selecting the segment, confirm a straight line on this segment. Then, use the gauge to measure the highest and lowest points offset from this straight line. The distance between the highest and lowest points divided by the reference length is the straightness we need.
In order to ensure the rigor of the measurement, different segments are often selected for multiple measurements.
Straightening
Why do Materials Bend?
Most materials are rolled or drawn during production. They also need to be heat treated.
During rolling or drawing, a large stress is applied to the material to deform it. This stress cannot be guaranteed to be completely uniform. The uneven stress causes the material to bend after processing.
In addition, for some hot processing, the material is heated during rolling, and the heating is sometimes not very uniform. At this time, the side with the higher temperature of the material will expand and cause the material to bend.
Finally, heat treatment can also cause the material to bend. The material softens after heating, and the softened material is placed on the bracket, and the middle part will be concave. After cooling, it cannot remain straight.
Structure of the Straightener
The straightener is a device used for straightening. Its structural diagram is as follows:
The most critical part of the straightener is the straightening roller. These straightening rollers are staggered on the upper and lower sides. They can adjust their heights to accommodate different material diameters. These straightening rollers rotate when they are working. The rotation of the straightening rollers can automatically move the material.
Principle of Straightening
Before straightening, we first adjust the position of the straightening rollers to adapt to different diameters. The adjusted straightening rollers can fit the diameter of the material exactly.
After turning on the machine, the straightening rollers will rotate. The rotating straightening rollers automatically feed the material into the straightening machine. Since the straightening rollers fit the diameter, it will limit the movement of the material and squeeze the curved parts. After squeezing, the material will become straight.
FAQ
When is straightness important?
It depends on the standard and the customer's requirements. If the standard requires straightness, then we must meet the straightness in the standard. If there is no requirement in the standard but the customer requires it, we also need to pay attention to it. In addition, if the customer needs a grinding rod, straightness becomes very important because it determines the error accuracy during grinding.
When is straightening generally performed?
Straightening is generally performed after heat treatment and surface treatment. On the one hand, heat treatment itself causes material bending. On the other hand, the material softens after heat treatment, making it easier to straighten.
If the standard does not specify straightness, is it still necessary to straighten?
Yes. Even if the standard does not specify straightness. We still need straightening to ensure the most basic straightness of the material.
Further Reading
Conclusion
Straightness refers to the degree of straight of a bar or tube in the length direction. It is usually expressed by the distance the material deviates from the straight line. In order to make the materials have good straightness, they need to be straightened. This article introduces the measurement method of straightness and the principle of the straightening machine. I believe it will help you understand these concepts better.
We strictly produce nickel alloy tubes and bars according to standards and straighten them before delivery. Please contact us for any needs.
