Euro-Stel overhauls and repairs screws ever since the company was established.
Used and worn screws are carefully overhauled in order to return them
to nearly new state.
The main reason why screws need overhauling is the screw wear caused by
the utilisation of the screw. Customers regularly send us screws with
mechanical ruptures as well, e.g. screws with broken return valves, whose
thread is blocked on the screw and must be recuperated or repaired in
order to enable fitting a new return valve. If possible, Euro-Stel also
repairs these mechanical ruptures.
When screws are irreparable worn out or damaged, we can offer new screws
based on the customers model or in Euro-Stel design.
There is no generally applicable description for screw wear. Screw wear
occurs in many different forms and is subject to many different causes.
Here, we will restrict us to the main form of wear, i.e. the wear of the
outer diameter due to the friction between the screw flank and the cylinder.
The active superficial pressure and the high forces causing this superficial
pressure and acting at an angle of ninety degrees with regard to the transport
direction are generally underestimated. In no way, it may be assumed that
the screw “swims” in the cylinder. In that case, the wear
models of screw and cylinder should not be congruent, as they always are.
Only the degree of wear is different: it is smaller in the cylinder, because
this component has a larger surface compared to the screw.
Abrasive additives such as glass fibre do not cause wear, but reinforce
it. The main cause for wear always is the pressure acting in the screw
part concerned, e.g. in the compression zone.
If the wear model show extreme features such as deep grooves at the bearing
surface of the flank, intensive flashing on the flank sides and a short
life, it is likely that the screw geometry is not appropriate. This could
be the reason why we discommend regeneration: the same wear symptoms would
reoccur within no time.
If “normal” wear of the basic material nitride steel occurs
– hardened steel cannot be regenerated – the screw can be
reconditioned by flank reinforcement, i.e. during the welding process,
reinforcement is applied on the topside of the flank.
The chosen reinforcement layer depends on the application. The metal
of the cylinder (matching) and the type of material to be processed (processing
temperatures) define the reinforcement layer to be welded.
The most frequent repairings are:
• Placing a new reinforcement layer with a suitable alloy on the
screw spiral. When repairing an already armoured screw we first remove
the old reinforcement layer and then place a buffer layer.
• Straighten out
• Nitrate if necessary
• Chrome or unchrome if necessary
• Repairing of screws with damage on the drive site
• Repairing of fastening non-return valve
An accurate analysis of the worn out parts must always be effectuated
when overhauling, in order to determine the most appropriate (economic
and technical) way of repairing. Euro-Stel has over 30 years of experience
on this field and can therefore certainly be considered as an expert in
overhauling screws, barrels, non-return valves, …