AEL Mining Services specifically designed the extrusion processes at its Initiating Systems Automated Plant (ISAP) to manufacture high quality polymeric shock tubes used in mines around the world in the initiating system assemblies for shock propagation. Suretube is expected to conform to AEL’s quality attributes and functional performance in the mines.According to Dr Samir Mukhopadhyay, a Senior Consulting Scientist at AEL’s R&D department, there are three very similar extrusion lines that are operational at ISAP currently and at the current production efficiency, these lines have the capacity to produce well over 25 million m of shock tube (commercially known as Suretube) length per month.

ISAP comprises three manufacturing units, namely shocktubing, detonator and assembly plants. These plants were developed with the aim of providing safer processes, improved product performance and high volume benefits. By December 2010 over 10-million ISAP detonators were produced per month and over 2.5-million auto assembled units were produced per month.

“In line with AEL’s promise to the industry, Suretube is expected to conform to AEL’s quality attributes and functional performance in the mines. We ensure that all extrusion processes at ISAP go through a stringent sequence of process optimisation, qualification and validation to functional performance to establish scientific evidence that these processes are capable of consistently delivering high quality products. The process of line qualification and validation to the performance also provides a mechanism of achieving less waste and reduced downtime in the manufacturing of Suretube,” he explains.

Mukhopadhyay notes that to ensure quality results, the process of line qualification and validation has to go through a number of steps involving a multidisciplinary team working over a period of seven to eight months on a single extrusion line.

“ISAP process qualification and validation work has already been completed on two extrusion lines and both lines are currently running with excellent process stability in manufacturing high quality and highly reproducible shock tubes. The process qualification work on the third extrusion line has just started and it is expected that the qualified line would be handed over to the operation team before the end of the year,” he comments.

During the process qualification work, the products are subjected to an in-depth evaluation using most of the routine and some specially assigned qualification tests that are described in the Suretube specification.

The products from a running line are sampled randomly and evaluated by determining characteristics, such as outside and inside tube diameters, distribution of core load, velocity of detonation, tube burst, breaking strength, elongation and linear shrinkage.

The products are expected to conform to all the requirements within the tightest of margins prescribed in the specifications. During the qualification run and performance validation of two extrusion lines all mechanical and thermal properties were found well within the specifications with tighter variations within and between the reels. Variation of core loading (an important function of shock wave propagation) within the tubes was successfully minimised from ±7 mg/m to ±3 mg/m during the qualification run of the two extrusion lines.

Following the process qualification run over an extended period of time, the process is expected to be validated (independently) in establishing satisfactory functional performance of the product. Process validation is also intended to assist the operators in understanding quality management system requirements. 

Validation of ISAP processes ensures that when a process is operated within specified limits, it should consistently produce shock tube complying with pre-determined requirements. 

According to Mukhopadhyay, this is extremely important especially in the explosive industry as the pre-determined requirements of shock tube can only be assured alternatively by a major destructive testing and that can be expensive. 

The principles of validation process:

• Quality, safety and efficacy are designed and built into product
• Quality should not be adequately assured merely by in-process and finished-product inspection or testing
• Each step of manufacturing process is controlled to assure that the finished product can meet all quality attributes including specifications.

Once the process qualification and validation steps are successfully executed, the qualified process line is handed over to the operation team in taking over the responsibility of on-going manufacturing of shock tube.