THE COPPER TUBE MINI-MILL CONCEPTS
FOR SEAMLESS COPPER TUBE PRODUCTION
by
Geoff Peirson, MRB Schumag
BACKGROUND
In the developed economies of the World the majority of copper tube is produced by large companies having high output facilities. The prime reason for this is that Billet Castors and Press manufacturers have increased their equipment capacities enabling tube plants to operate with larger coil weights, optimising yield and productivity. Further investment in Cold Drawing and Finishing equipment has allowed the establishment of tube plants with outputs of 50,000 tonnes(T) per annum and above. These fully equipped high capacity plants require high tonnage through-put, to ensure adequate return on investment.
In the developing countries copper tube is produced in either small older plants or younger companies, with a mixture of new and used equipment. In both cases, in general, working with small piece-weights and low productivity, each in turn being balanced by lower wage rates and modest capital investment, thus enabling acceptable profitability. However product quality is also of key importance and with ever increasing standards this is not always attainable on old machinery.
With this ever increasing need for high quality copper tube production there naturally becomes a demand for production facilities, however due to market conditions the majority of these production facilities exist with the production output of 10,000-20,000 tonnes (T) per annum. A further constraint is obviously capital expenditure investment. Even based on production of 10,000-20,000 tonnes (T) per annum piece-weights of a minimum of 400 KG are required to achieve any degree of efficiency. Unfortunately this is the area in a production facility that is not fully synchronised in what is known globally as a conventional production method.
The first equipment is usually a large Press incurring heavy investment and producing piece-weights of circa 500 KG. As a consequence of this the Press will be capable of production in the region of 80,000-100,000 Tonnes (T) per annum which together with downstream equipment would make initial investment potentially cost prohibitive. It is at this point that the marketplace has recognised the demand for more economical Mini-Mills for start up production and also for existing copper tube producers looking at expanding capacity and improving production levels with more acceptable investment costs.
DEFINITION OF A MINI-MILL
A Mini-Mill is a relatively low output production and distribution unit strategically located in centres of high consumption.
The production program could represent Sanitary as well as ACR tube qualities.
The Mills would be designed with equipment appropriate to the local mix of a range of finished tubes. In this context, if ACR predominates, then extra cold draw capacity would be required, as would different Finishing and Heat Treatment equipment as against the production of Sanitary Tube.
It is envisaged that several such Mini-Mills, operated by one organisation, could be sited in strategic locations within a country or continent. Export markets could be similarly serviced by having units in the heavy consumption areas, for instance, in several different countries all being co-ordinated by a single organisation, within one tube production strategy.
The Mini-Mills would be supplied with the necessary stock material from this centrally situated organisation which could also incorporate its own Mini-Mill, or specialist copper producer.
The final and perhaps most major freight cost saving is the substitution of long haul journeys to customers from the previous products facility, by local servicing from the Mini-Mills. Much shorter transport times to local customers could lead to lower copper inventory and proportionally lower capital requirement and yet again the ability to react to customer requirements more quickly.
CONCEPT A
The introduction of the Outokumpu Cast and Roll System (OTK C & R) in the early 1990's allowed new producers, for the first time, to establish small tube plants, (Mini-Mills), with piece-weights of 500 KG or more at relatively modest cost. This enables high productivity with annual outputs of up to 10,000 tonnes (T) of both ACR and Sanitary Tubing.
The Mini-Mill production route starts with feedstock tube produced by the OTK C & R System. The C & R tube is initially drawn and coiled into a basket by a linear drawing line (Schumag Cascade,) to harden the soft rolled tube and to reduce it to an adequate size. From there it is transferred to Spinner Blocks to produce a range of ACR and Sanitary tubes. Further processing is carried out on finishing equipment.
To minimise the cost of logistics it would be appropriate that the Cathode Plant was integrated with the largest Mini-Mill and be located central to the other Mills.
Scrap could be sourced locally via a centralised procurement plan again reducing overall logistic costs.
The Mini-Mill could comprise of the following main production equipment.
- Raw material reception (Cathode/Scrap)
- Cast and Roll equipment
- 2 or 3 die Linear Drawing Lines (Schumag Cascade) with the final one coiling into a Basket
- Spinner Block/s with recirulating Basket Conveyor's
- Finishing equipment/s appropriate to the range of finished tube produced
- Heat Treatment equipment
- Automated Basket Handling system to provide the basket flow necessary to connect the units
- Inventory and despatch facility.
This C & R Mini-Mill type represents a very compact and high grade self-sufficient production unit, starting from melting via casting, mother tube rolling, break-down drawing on Schumag Cascade, Spinner Block drawing to tube finishing.
CONCEPT B
The other concept is to have Mini-Mills with only re-draw and finishing functions. These would be supplied with re-draw coils, a plant with large facility having high press and cold breakdown capacity. In this case the Mini-Mill's location would be selected in the area of high consumption away from the main manufacturing plant.
This Mini-Mill would receive re-draw tube in 'Jumbo' coil form from its main producing plant. This plant would utilise a large press and several Linear Draw machines (Schumag Cascade's,) the final one producing 'Jumbo' coils of re-draw stock. These would be re-coiled into dimensions appropriate to a standard container and to enable the maximum payload to be achieved.
For an annual output of about 12,000 tonnes (T) two transport vehicles a day are sufficient to provide the Mill with coils.
The movement of re-draw coils would be in conjunction with the master production schedule, with minimum processing time from 'Jumbo' coil arrival to despatch or to warehousing of finished tube.
The basic Mini-Mill could comprise of the following reduced list of equipment:
- Raw material reception (re-draw tube in a larger coil form, sometimes referred to as a Jumbo coil.)
- Single Die Linear Draw/Re-coil Machine to coil into baskets
- Spinner Block/s with recirculating Basket Conveyor's
- Finishing equipment/s appropriate to the range of finished tube produced.
- Heat Treatment equipment
- Automated Basket Handling System to provide the basket flow necessary to connect the units
- Inventory and despatch facility
In this concept one main Mill with one large facility of casting and extrusion can provide several Mini-Mills with pre-drawn material up to a total output of more than 100,000 tonnes (T) per annum.
Figure 1. MRB Schumag Mini-Mill concepts
NB. Finishing machines comprises equipment appropriate to finished tube type/s from following: Combined drawing/straighten/cut, pancake coiler, level wind coiler, in-line annealer, annealing furnace
OPERATION IN MINI-MILL CONCEPTS
It could be advantageous to consider a mobile second tier management structure controlling all areas. The identical nature of the equipment in the Mini-Mills provides an individual the opportunity to gain experience and expertise on one Mill and to apply it to the others.
This management concept could also be applied to maintenance engineering work and a single stock of spare parts could be held in readiness to be transported to any Mini-Mill as required.
Overall operating costs could be minimised by utilising this philosophy to cover other areas such as production/process/stock control, despatch, maintenance and also spare parts supply.
CONCLUSIONS
As stated previously the first Mini-Mill based on Concept A was established in the early 1990's utilising the OTK C & R System to produce feedstock tube and has now been accepted by several tube producers elsewhere as a cost effective method for producing feedstock tube for Mini-Mills.
The Mini-Mill Concept B has been operating already under the generic term Re-Draw Mill and is most interesting for those copper tube producers, who have spare press capacity or who want to invest in new facilities with a high annual output at modest costs.
As a supplier in the market place of drawing and finishing equipment, MRB Schumag and Schumag AG have observed the recent trend within the industry. Although discussions exist as to whether this idea is conceptual and for the future, or in reality already happening, is perhaps irrelevant. What is relevant is the need to recognise constantly changing and increasing customer requirements matched with the ability to service such demands.
In this context the companies of the Schumag Group offer complete copper tube production systems, from the drawing of the mother tube, up to the finished product, including all accessory and equipment for material handling, such as basket transport, tube storage etc. This experience has been gained over many years and many projects worldwide.
Further information :
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