FEATURE Figure 1
100%
POWER CONSUMPTION
1
KW
KW
90%
80%
70%
2
3
4
60%
50%
40%
4
4
30%
20%
10%
x
2x
3x
4x
5x
6x
7x
8x
9x
LIFETIME OF THE DIE
10x
Complete reworking of a Die: Grind, countersink and clean Total cost, aprox 20 % of the prise for a new Die 1. Start of new Die 2. Recommended first time of reworking 3. Recommended second time of reworking 4. During normal production conditions the die have to be scrapped
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“Die holes are often found to be blocked by tramp metal or other hard material,” according to Millson Engineering so the next stage of refurbishment is clearing holes and removing any broken studs. Then the pelleting face needs to be skimmed level before re-countersinking the die holes. This is a crucial stage, as all holes need to be consistent in size. Finally, the die is treated to another pressure wash to flush out any sharp edges. In addition, sometimes dies can be externally skimmed to make them thinner which allows a more difficult product to pass through. Roll assemblies can also be given a makeover to ensure optimum wear on both dies and rolls. Replacing a roll assembly allows more material to be pushed through, improving the overall performance of the die. The roll assembly consists of a roll shell, axles, bearings, cover plate and a seal collar. Luckily, the roll shell is changeable as a tyre. “A roll shell from a Scandinavian mill will normally be ground for alignment of the production surface the first time. The second time it will be fully re-built including all inner parts, such as axles and bearings. It will be cleaned up and re-assembled including grease,” says Wolf. A die can be refurbished effectively two or three times in its lifetime (Figure 1). It is worth remembering that not all dies
will need a full refurbishment and costs will depend on the work required. “Once the roll assemblies and die have been refurbished and repositioned correctly, the press will work more efficiently as the material is being pushed through much faster,” says Millson Engineering.
The practicalities Refurbishment time depends on the size of the equipment and how worn it is. For example, At O&J HØJTRYK a full rework of a die can take between 5-30 machinery hours. One of the crucial factors which affects refurbishment time is the size and number of holes in the die. A machine with around 7,000 small holes will obviously be much quicker to recountersink than a die with 100,000 large holes. Given the size and weight of the machinery used to carried out die and roll maintenance, refurbishing work is carried out off-site. Transporting the parts for refurbishment is a major issue both in terms of cost and reliability. Some companies counter these problems by offering refurbishment packages including transport. These companies have the power to organise contracts with forwarding agents which are cheaper than ad hoc agreements negotiated by mills. In addition, freight companies with a proven track record transporting dies offer peace of mind for millers.
Another important factor to consider is location and the existing infrastructure of the country you’re in. From its base is Denmark, O&J HØJTRYK is able to service all of Scandinavia, quite a considerable sized area. This is possible due to the flexible logistic structure of the area. Wolf points out that the same business model would not be feasible in other regions.
Scheduling maintenance Deciding when to ship a die for refurbishment is “always a balance,” says Wolf. Ultimately this comes down to choice between controlled maintenance versus damaged based maintenance. “The best and cheapest method is reworking parts from a controlled production, where the mill is running controlled maintenance and parts are given in at due times, before real damages occur,” says Wolf. Failing to deal with issues are they occur can lead to greater damages and costs in the long term. “A bad or defective press will ultimately produce an inferior product. The press will have to work much harder leading to more breakdowns and down time,” says Millson Engineering. However, the advantages of die and roll refurbishment are clear. Increased lifetime of pelleting equipment, significantly reduced power usage and increased throughput should all be key concerns of the modern miller.
Die and roll re-working machines Pellet Die re-working and unblocking
www.oj-hojtryk.dk Phone: +45 75 14 22 55 Fax: +45 82 28 91 41 mail: info@oj-hojtryk.dk
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&feed milling technology
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O&J Højtryk A/S Ørnevej 1, DK-6705 Esbjerg Ø CVR.: 73 66 86 11 11/02/2013 09:09
January - February 2013 | 43