› Screws
Non-return valves
Tie bars

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.
• Polishing
• 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, …

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