TPT January 2008

The application of quick change technology to high precision tube mill operation

in a just-in-time environment By Bruce Chidlow, senior tube mill operations engineer, Kusakabe Co Ltd, Japan

addition to the time lost and the number of occurrences. The cause of the downtime will come later. Conducting a Pareto analysis of the reasons for downtime will highlight the items that need to be addressed. In accordance with the Pareto principle, 20 per cent of the causes will account for 80 per cent of the downtime. Collecting good information can be a problem. If this is being done for the first time the causes will be very obvious. If this process has been going on for 5 years or more then the quality of data collection becomes an important issue as all the easy and obvious problems should have been solved. Collection of accurate data will be covered latter in this article. There will be some issues that will be difficult to overcome; they usually stem from machine reliability and machine design issues. They are a challenge but perseverance is required. These issues need to be fully understood to make sure that the same mistakes are not made on the next purchase or major modification. Downtime analysis Experience has shown that downtime can usually be separated into two categories. • Getting material to and from the mill • Things that happen at the mill Material supply and removal Getting material to the mill and getting it away from the mill is usually a larger problem than first imagined. Many mills run slower than their rating to overcome these problems. The run speed then becomes fixed and after a few years no-one knows why they run at this speed. It is assumed that it is the limit of the mill. In terms of equipment supply there are now many options that enable large improvements in productivity by overcoming these issues with the supply and removal of material from the mill. There is no reason why a mill should be stopped or run at a slow speed because the strip supply cannot keep up. Getting the steel strip to the mill involves the use of cranes and/or forklift trucks, double sided uncoilers, automatic coil loading systems, automatic shear welders and strip accumulators (loopers). If space is an issue then strip accumulators come in both horizontal and vertical versions. This type of equipment is available for the smallest to the largest tube and pipe mill. Cost justification is usually straightforward for this type of equipment as the increased uptime translates into increased volume and increased sales or reduced overtime and labour costs, operating costs and reduced scrap.

Introduction Productivity and quality improvement is an unrelenting activity for all organisations involved the manufacturing sector. Productivity and quality are key performance indictors for any organisation today and competition – both local and international – ensures it stays that way. In the tube and pipe industry, machine productivity is measured by the following sample of indicators: tonnes or (metres) per hour and percentage uptime. But in terms of quality there are more measures. There is the amount of scrap in tonnes, dollars and percentage and customer complaints issues expressed in number of incidents, dollars and metres or tonnes. Of course, the overall measure is conversion cost per tonne. Understanding the current situation It is important to establish a method to improve all of these indicators year on year. There are many factors to consider including management, labour, environment, systems, tools, training, information, knowledge and equipment. This article will concentrate on the equipment, information, knowledge and some system factors. To apply and fully utilise quick change technologies, it is best to fully utilise the existing equipment and therefore fully understand the shortcomings in the existing production environment. The tube mill itself will be the focus of this article and not the surrounding support systems. A good method that will give an indication of where the problems are, is to understand the downtime issues. It is vital to record and track downtime percentages. Downtime is calculated by working out the total time manned minus the mill run time, with the result divided by the total time manned, and multiplied by 100 to get a percentage. Reasons for downtime should also be collected, in

fi Figure 1 : Example of a tube mill downtime analysis – hours versus reason

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J anuary 2008

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