What is negative tolerance rolling?

Negative tolerance rolling means that the thickness of the final rolled product is smaller than the target thickness, but the thickness of the final rolled product is within the negative tolerance range of the finished product. Negative tolerance rolling is beneficial to improving the yield rate and reducing rolling costs, and it does not place additional requirements on equipment.

 

1. Negative tolerance rolling of ribbed steel bars and its positive significance

 

Negative tolerance rolling of ribbed steel bars means that the steel bars are produced according to the negative tolerance size requirements specified in the standard. Ribbed steel bars are rolled with negative tolerances, which will have positive significance for downstream users, middlemen and production companies. This is mainly reflected in the following three aspects.

1. Save metal, reduce the use of steel bars in the project, and reduce the project cost.

2. Middlemen or steel bar processing users can earn a certain amount of profit by delivering goods to fixed lengths based on theoretical weight.

3. Pansnail production plants meet the needs of downstream users, promote corporate sales, and improve economic benefits.

 

2. What are the difficulties of negative tolerance rolling?

 

Each production unit generally has its own production equipment and technical process conditions, so different measures must be taken, and the most important thing is measurement and testing equipment. Only with real-time and accurate product data can technicians determine and adopt different production processes and steps. Only in this way can companies produce more and better negative tolerance ribbed steel bar products.

 

3. Negative tolerance online measurement system

 

Negative tolerance rolling, online measurement, steel mill, bar production

 

Only by understanding the dimensional changes in snail production in real time can we formulate an appropriate rolling plan based on its changing trends. At the same time, when the product is unqualified, the rolling mill can be adjusted in a timely manner to reduce the mass production of unqualified products.

The online calliper detects snail information. The basic geometric size information includes inner diameter, transverse ribs, longitudinal ribs, cross-sectional area and other information. At the same time, the outer diameter and ovality dimensions of round steel can also be detected. Therefore, whether it is spiral screws, round steel, or high-line negative tolerance rolling, the calliper can be used for dimensional monitoring.

 

The content that the online caliper can detect and display

 

1. Main control room LCD:

 

1) The main interface of the round steel measurement system displays the outer contour dimensions, cross-section drawings and tolerance zones of the rolled material at the same time and section;

2) Dimensional fluctuation diagrams and defect analysis curves of each probe;

3) Real-time display of the maximum diameter, minimum diameter, average diameter, ovality of round steel and the measurement values of each probe;

4) The rebar measurement system displays the real-time measurement values of the rebar base circle, longitudinal ribs, and transverse ribs.

 

2. Embedded intelligent module:

 

Real-time display of the measurement values of each probe, equipment temperature, wind pressure, measurement centre height, etc.

 

3. On-site LED display:

 

Real-time display of the maximum/minimum diameter, ovality, and equipment working status of round steel measurements. Real-time display of the base circle diameter, longitudinal ribs, transverse ribs and equipment working status of the rebar measurement.

The online diameter gauge is an indispensable device for testing whether the quality of round and ribbed steel bars is qualified. It is a precision instrument that cannot be separated from production from trial rolling to formal rolling. It has high precision, fast speed, comprehensive detection, and system analysis. Diverse storage and data transmission provides a guarantee for high-efficiency and high-quality production.

 

4. Negative tolerance rate and weight allowable deviation

 

Negative tolerance rolling of ribbed steel bars can save metal and reduce the number of steel bars used in the project, but the savings are limited. Generally, the amount of metal saved is expressed by a negative tolerance rate. The negative tolerance rate usually refers to the percentage of the difference between the actual weight of the steel bar and the theoretical weight. The national standard “Hot-rolled ribbed steel bars for reinforced concrete” clearly stipulates the allowable deviation between the actual weight and the theoretical weight of ribbed steel bars: ribbed steel bars with a diameter of 6mm-12mm are ±7%; ribbed steel bars with a diameter of 14mm-20mm Rebar is ±5%. In actual production, the negative tolerance rate of steel bars must be controlled above the lower limit of the standard allowable weight deviation. The weight deviation is a must-protect item in GB1499-1998.

 

5. Negative tolerance products and mechanical properties of steel bars

 

Ribbed steel bars rolled with negative tolerance will change their mechanical properties. Ribbed steel bars are rolled with negative tolerances, and their actual cross-sectional area is smaller than the nominal cross-sectional area. However, Article 7.2.2 of the GB1499-1998 standard “stipulates that the calculation of steel bar strength must use…the nominal cross-sectional area.” Therefore, when ribbed steel bars are rolled with negative tolerances, the strength performance index of the product will inevitably decrease when the composition of the steel billet and the rolling process remains relatively unchanged. On the contrary, if ribbed steel bars are rolled with positive deviation, the strength performance index of the product will increase.

It can be seen that before ribbed steel bars are rolled with negative tolerances, they must have sufficient strength excess value. Otherwise, measures must be taken to improve the strength properties of the steel bars. Otherwise, scrap products will be produced.

 

6. Summary

 

1) Ribbed steel bars are rolled with negative tolerance, which has positive significance for downstream users, middlemen and production companies.

2) Negative tolerance rolling is also limited by factors such as the allowable weight deviation and the mechanical properties of the product. Therefore, do not blindly pursue negative tolerance rolling, otherwise, scrap will be produced.

3) There are many ways to pursue negative tolerance rolling and improve the negative tolerance rate of screws. Online measurement devices for dimensional monitoring are an important method. Each production unit must take different measures based on the company’s own production equipment and technical process conditions. Only in this way can the company produce more and better negative tolerance ribbed steel bar products.

 

DBM Online Rebar Weight Per Meter Negative Difference Measurement Device >>

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