A feed mill is only as strong as its weakest link. To produce consistent high-quality feed, each machine has to work at its best. But like humans, machines do not have superpowers. Over time, they get older and slower until eventually they stop working.

1. Digital Re-print -
January | February 2013
Managing mill maintenance - Die and pelleting
equipment maintenance
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2. FEATURE
Managing mill
maintenance
Die and pelleting equipment maintenance
by Alice Neal, associate editor, Grain and Feed Milling
Technology, United Kingdom
A
feed mill is only as strong as its
weakest link. To produce consist-
ent high-quality feed, each machine
has to work at its best. But like humans,
machines do not have superpowers.
Over time, they get older and slower
until eventually they stop working.
Thanks to rising raw material and energy
costs, pelleting is an expensive process so
it makes sense to pay particular attention
to pelleting machinery. What’s more, the
benefits of investing time and money into
feed formulation can be quickly written off
if the machinery used to produce the pellets
isn’t up to scratch. United Kingdom, explains, “The main prob-
“If milling equipment, dies and rolls get lem we deal see are cracked dies because
worn, the throughput reduces, power usage of incorrect positioning of roll assemblies
increases and pellet quality is of worse or against the die.”
looser quality – in other words it gets more Before use it is beneficial to carry out a few
difficult to have controlled production,” procedures on a new die. Flushing a new die
says Leif Wolf, director, O&J HØJTRYK, will remove burrs and cleaning before pelleting
Denmark. will help ensure a good quality end product.
Warning signs
Millson Engineering estimates that the
average life expectancy of a die is anywhere
between 5000 to 15,000 tonnes. However,
this depends on usage and type of mate-
rial being used; the harder the material, the
quicker the die will wear out.
Experienced operatives will be familiar
with the performance of their equipment
Buying the best quality equipment pos- Once in use it is vital to carry out regu- and can spot when something it’s time for
sible to start with helps produce perfect lar checks to ensure the smooth running some maintenance. Wolf pinpoints reduced
pellets but dies and rollers will wear out of all machinery. “Another problem tends throughput and increased energy consump-
over time. However, unlike people, there are to be roll assemblies seizing due to lack of tion as the vital tell tale signs that something
plenty of refurbishment options to kick start grease, which means the rolls aren’t able has gone wrong.
pellet mill machines back into life. to rotate correctly within the die,” says the
Millson Engineering engineer. Refurbishment
Installation and usage It is wise to invest in several sets of dies The first stage is to clean the die and
From the start, machines need to be so that refurbishment does not mean plant check for cracks. Many refurbishment com-
installed properly with particular attention shut down. panies offer high-pressure jet washes to do
being paid to positioning the roll assem- Aside from set up, what you put into a this task. The advantage of this method is
blies correctly against the die. Failing to fit die will have an affect on its performance. that the water is strong enough to dislodge
machines properly can result in non-uniform Material that is either too wet or too dry stubborn materials without the need for
wearing on the die ring and non-uniform to pass through the machine efficiently chemicals. However, some companies prefer
pellets. Although this seems fairly common can clog holes. So feed formulation and opt for a traditional oven clear out which
sense, it is not an uncommon occurrence moisture levels are also important factors can reach temperatures of up to 90 degrees
as a senior engineer at Millson Engineering, to consider. over a 24 hour period.
42 | January - february 2013 Grain &feed millinG technoloGy

4. FEATURE
Figure 1
100% 1 KW KW
POWER
CONSUMPTION
90%
2 3
80%
70%
4
60%
50% 4
40%
4
30%
20%
10%
LIFETIME OF THE DIE
x 2x 3x 4x 5x 6x 7x 8x 9x 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
INFO@OJ-HOJTRYK.DK | WWW.OJ-HOJTRYK.DK
“Die holes are often found to be blocked will need a full refurbishment and costs will Another important factor to consider
by tramp metal or other hard material,” depend on the work required. is location and the existing infrastructure
according to Millson Engineering so the next “Once the roll assemblies and die have of the country you’re in. From its base is
stage of refurbishment is clearing holes and been refurbished and repositioned correctly, Denmark, O&J HØJTRYK is able to service
removing any broken studs. the press will work more efficiently as the all of Scandinavia, quite a considerable sized
Then the pelleting face needs to be material is being pushed through much area. This is possible due to the flexible
skimmed level before re-countersinking the faster,” says Millson Engineering. logistic structure of the area. Wolf points out
die holes. This is a crucial stage, as all holes that the same business model would not be
need to be consistent in size. Finally, the die The practicalities feasible in other regions.
is treated to another pressure wash to flush Refurbishment time depends on the size
out any sharp edges. of the equipment and how worn it is. For Scheduling maintenance
In addition, sometimes dies can be exter- example, At O&J HØJTRYK a full rework Deciding when to ship a die for refur-
nally skimmed to make them thinner which of a die can take between 5-30 machinery bishment is “always a balance,” says Wolf.
allows a more difficult product to pass hours. One of the crucial factors which Ultimately this comes down to choice
through. affects refurbishment time is the size and between controlled maintenance versus
Roll assemblies can also be given a number of holes in the die. A machine with damaged based maintenance.
makeover to ensure optimum wear on around 7,000 small holes will obviously be “The best and cheapest method is re-
both dies and rolls. Replacing a roll assembly much quicker to recountersink than a die working parts from a controlled production,
allows more material to be pushed through, with 100,000 large holes. where the mill is running controlled mainte-
improving the overall performance of the Given the size and weight of the nance and parts are given in at due times,
die. machinery used to carried out die and roll before real damages occur,” says Wolf.
The roll assembly consists of a roll shell, maintenance, refurbishing work is carried Failing to deal with issues are they occur
axles, bearings, cover plate and a seal collar. out off-site. Transporting the parts for can lead to greater damages and costs in
Luckily, the roll shell is changeable as a tyre. refurbishment is a major issue both in the long term. “A bad or defective press will
“A roll shell from a Scandinavian mill will terms of cost and reliability. Some com- ultimately produce an inferior product. The
normally be ground for alignment of the panies counter these problems by offering press will have to work much harder leading
production surface the first time. The sec- refurbishment packages including trans- to more breakdowns and down time,” says
ond time it will be fully re-built including all port. These companies have the power to Millson Engineering.
inner parts, such as axles and bearings. It will organise contracts with forwarding agents However, the advantages of die and roll
be cleaned up and re-assembled including which are cheaper than ad hoc agreements refurbishment are clear. Increased lifetime
grease,” says Wolf. negotiated by mills. of pelleting equipment, significantly reduced
A die can be refurbished effectively two In addition, freight companies with a power usage and increased throughput
or three times in its lifetime (Figure 1). proven track record transporting dies offer should all be key concerns of the modern
It is worth remembering that not all dies peace of mind for millers. miller.
Die and roll re-working machines
Pellet Die re-working and unblocking
www.oj-hojtryk.dk
Phone: +45 75 14 22 55 O&J Højtryk A/S
Fax: +45 82 28 91 41 Ørnevej 1, DK-6705
mail: info@oj-hojtryk.dk Esbjerg Ø
CVR.: 73 66 86 11
O&J_AD_QP_190x60.indd 1 11/02/2013 09:09
Grain &feed millinG technoloGy January - february 2013 | 43

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