Advantages of electronic force proving instruments instead of force proving ring device:
Electronic force proving instruments:
It consists of a force transducer (loadcell ) and a high resolution display unit. They have become the most widespread of all force measuring systems and can be used as force transferred standard also.
Unlike proving ring devices, these force transducers are less sensitive to temperature, creep, extraneous loads, side loads and moments. Because of the high resolution and behaviour of the system a single system can be used to cover wide range of calibration atleast from (20 to 100) % of the range for class '0' and atleast (10 to 100)% of the range for Class '1' and class '2' as per IS 4169, with no loss of accuracy. Hence, less no. of loadcells (force transducers) can be used to cover wide range, which is economical in terms of maintenance and calibration costs.
Also, the advantage is with interpolation equation the force can be calculated at any given step, whereas the proving ring devices can be used at the specific forces in which they are calibrated, unless the dial gauge used is also calibrated every time the force proving ring is calibrated.
Force proving ring device:
a. Proving ring is a force measuring instrument whose shape changes as diameter deflects elastically under load which is used as a device for calibration of uni-axial testing machines. It consists of a steel ring with a Dial gauge mounted so as to measure the vertical deflection when the loads are applied through the threaded blocks at the top and bottom. Applied load is known from its load and deflection characteristics.
b. For all these years, the proving rings are considered as standard of excellence for force calibration. However, they suffer from the following adverse characteristics
1. Creep- If, we maintain the same force and continue to measure the length in the dial gauge having a very high resolution, we will see the length continues to change slightly. Deflection measurement- when the forces are applied to the proving ring, it departs from its circular shape and becomes egg- shape. The determination of the deflection of a proving ring depends on the subtraction of two large numbers, namely, the inside diameter of the proving ring and length of the Dial gauge measurement assembly. Since the difference is so small, any slight error in measuring either dimension leads to a large.
Importance of spring testing and its accuracy:
a. Springs are normally manufactured for a specific purpose. Spring reliability equals to product reliability. Hence, a spring manufacturer should ensure that the spring manufactured by him will meet his customer specification by testing with a suitable spring testing machine.
b. Most spring tests require the measurement of a load at a specific height. This requires the testing machine to measure load and height simultaneously to achieve the accurate and meaningful result. The accuracy, precision, repeatability and reproducibility of test results depend on the features and performance of the load testing machine.
c. The deflection of the loadcell and deflection of the loading frame affects test results if not compensated.
d. Calibration accuracy of load and deflection measuring system and their resolution also affects test results.
e. At Sushma we understand the challenges and have perfected the technology to manufacture high quality spring testing machines.
Importance of Torque tool calibration:
a. Controlling torque of a torque tool is important for companies to ensure proper torque being applied for their product's quality, safety and reliability and also to Maintain gauge requirements associated with ISO 9001 quality standard.
b. By regular calibration one can assure that the accuracy of a torque tool is within the specified tolerances and maintain continuous quality standards in the assembly process. The Calibration ensures the performance of a torque tool and indicates the need for any adjustment. Also the potential tooling problems can be identified before they arise, either due to tool wear and tear or broken components.
c. Hence, the torque tool calibration equipment plays an important role along with traceability to assure that all measuring results are in accordance to the National/international standards.
Importance of fastener testing:
a. Applying torque to a bolted joint is a very common practice in the industry. This has become so popular and taken for granted that, even some engineers refer to clamping force or tension of a joint in terms of torque (Nm) which is the prescribed torque to achieve the tension. It must be remembered at all times that torque is only a means of achieving tension and tension is the most critical parameter of a bolted joint.
b. The object of a threaded fastener is to clamp parts together with a tension greater than the external forces tending to separate them. The bolt then remains under constant stress and is immune from fatigue. However, if the initial tension is too low, varying loads act on the bolt and it will quickly fail. If the initial tension is too high, the tightening process may cause bolt failure. Therefore reliability depends on correct initial tension. Since tension cannot be measured directly, most practical way of ensuring this is by specifying and controlling the tightening torque. But when a threaded fastener is tightened, the induced tension results in friction under the head of the bolt and in the threads. It is generally accepted that, as much as 50% of the applied torque is expended in overcoming friction between the bolt head and the abutting the surface and another 30% to 40% is lost to friction in the threads.
c. As little as 10% of the applied torque results in useful work to tension the bolt. Given that, upto 20 % of the applied torque will be lost to friction, it follows that any changes in the coefficient of friction resulting from differences in surface finish, surface condition and lubrication can have a dramatic effect on the torque Vs tension relationships.
d. Hence evaluation of the torque to be applied depending on the joint conditions and the bolt characteristics is crucial in achieving the right tension.
e. At sushma we understand the challenges and have perfected the technology to manufacture high quality torque tension measuring system.