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Vetra System - Articulated screws (rotules)
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introduction
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Articulated screws

We define Articulated screws the connection between supports and glass.

The operating principle of articulated screws (rotules) is the same for all versions and it consists on a spherical joint. The type of articulated screw to be use change according to the type of glass.

Articulated screws are realized by turning of stainless steel Aisi 316 L that grant an high mechanical strength, each screw has a load capacity of more than 300 Kgs, value guaranteed by testing (certificates available on request). The range includes also some fixed screws used for the realization of stairs, balustrades or indoor fixed glass structures.

The choice of articulated screws will depend on the type of glass as well as on the role required for screws on the glass sheet.

It’s possible to make straight or countersunk holes, depending on the type of constraint it gives to the glass.

The above simulation scheme shows that the tension flows are similar in both types of holes.

The difference is that when there is an over tension in the glass sheet with countersunk hole there could be a break of the glass.

When there is an over tension in the cylindrical hole there is the possibility of a further sliding movement of the glass but that could give also over tension between two or more glass sheets and so cause the breaking of more than one glass.

For this reason it is better to use cylindrical hole only for roof and covering or for horizontal glasses, in this case in fact the glass could support only perpendicular load so it will have only expansion towards its self centre without giving any over tension to other glass sheets.

The minimum glass thickness that can be used with countersunk hole is 8 mm, the use of lower thickness gives critical corner points that subject the glass sheet to easy breaking (following scheme).

With cylindrical hole it’s possible to use glass starting from 6 mm.

All the glass used have to be tempered or hardened and subjected to HST test (Heat Soak Test - process used to minimize the risk of spontaneous breaking of the glass due to the expansion of nickel sulphide following a sudden change in temperature).

introduction
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  1. Tension flow in a cylindrical hole when the articulated screw touches the inside edge of the hole, the extra-preassures conditions that could cause the breaking of the glass are clear
  2. Tension simulation with countersunk hole
  3. Tension simulation with cylindrical hole