TPT January 2008

sides of the turret. The mill changeover consists of rotating the turret through 90° or 180°.

5. There are also mills that use a combination of these technologies. For example the quick change, high quality (QHQ) mill that uses turret technology for the break down, fin pass and squeeze stands. There is also cage forming to move the strip from the breakdown to the fin passes and a sub base system for the sizing section. In all of these cases (except the flexible tooling), tooling is changed and set ready for the next job offline. In the case of flexible tooling the tooling is adjusted at the time of the job change and is relatively fast using either power adjustment or manual adjustment. This takes less time than that required to change a sub base. Converting other activities to outside work involves having enough tooling to enable internal fin cutting and external fin cutting tools to be set up offline. This ensures that all the mountings for this equipment are of a quick change variety and that they always lock into the same home position to minimise or eliminate the amount of fine adjustment that is required. Another area to consider is small improvements that add up. It is important to minimise the number of screws and bolts and to keep thread length to the minimum required to do the job. Where possible, it is important to replace screws and bolts with quick action clips and other quick change technologies. Knowledge and Information Another important aspect for efficient and low scrap changeovers is knowledge and information. There are usually a very limited number of employees on the mill that have a good solid knowledge base about how to change over and set up the mill. This is very important information that needs to be available to every one on the mill not a limited few. One of the best ways of doing this is to identify and list all of the adjustments that exist on the mill from the entry to the exit. Each adjustment must have a reliable and accurate setting method. That is digital read out, scale or some other form of identification of position. Data needs to be collected for each of these setting points in relation to pipe OD, wt, length, tensile strength and strip width.

› Figure 5 : Example of SCADA tracking mill information

In most cases the relationships are very obvious but in others it is more elusive. For each product produced a setting sheet can be developed showing the tooling requirements and all the setting points on the mill. The knowledge and information is now collected and centralised and needs to be provided to all operators in a standard form (ie set up sheets). The aim here is to make good tube first time, every time. There is no point in changing the tooling in 30 minutes if it take 60 minutes to make good tube. This also eliminates the need for the next shift to reset the mill to meet their personal preferences. On all new equipment purchases it is important to ensure that all the setting points can be adjusted easily, accurately and have indicators to ensure the repeatability of settings. This also includes the welder and ancillary equipment; basically everything that can influence the product quality, repeatability of the set up and minimise the production of scrap. During this process it is important to note which items are critical and can be monitored electronically. Collecting electronic data using a SCADA system (usually on a 1 second interval) has proved to be very beneficial in tracking quality issues when used in conjunction with inkjet printed tube that has the manufacturing time recorded on the tube. It is also a way of confirming if the settings used to make the tube are the same as that on the set up sheets. Analysis tools and work environment Analysis of downtime and the reasons for scrap start by being reasonably simple in terms of the statistics and analysis tools used. However, over time these tools need to be improved and upgraded to ensure continuous improvement is achieved each and every year; ultimately leading to a level equivalent to the internationally recognised 6 sigma program. It is extremely difficult for one person alone to achieve a highly successful outcome, so team work, involvement and commitment of all employees, staff and management is critical to ensuring a successful outcome and an ongoing environment of continuous improvement. This will always involve continuous culture change and a continuously changing work environment. It is important to ensure that all the effort and investment in the mill is directed to achieve maximum benefit. The above methodology goes a long way towards ensuring that this happens.

fi Figure 4 : Example of a setup sheet for the welding section of the mill

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J anuary 2008

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