SUMMER 2023

134
THE DISTRIBUTOR’S LINK
BRUNO MARBACHER THREAD-FORMING SCREWS FOR PLASTICS from page 94
DELTA PT-SCREW
After expiration of the PT- patent, the Delta PT screw
was developed. The V-shaped thread root is shallower,
the breaking torque is therefore 50% higher. The geometry
of the Delta-PT® is the result of analysis of the material
displacement during thread-forming. Since the 20° or 30°
angle respectively causes only slight radial stress, a thinwalled
boss design can be realized. The thread flank also
guarantees optimum material flow of the formed plastic,
even in reinforced thermoplastic.
its 30° thread flank angle barely produces radial stress
during assembly. The displaced plastic flows well into the
spaces between the threads.
SPT SCREW
The STP thread geometry has flank angles and radiuses
that are optimized for strength, retention, and minimal
stress. The tread profile with a unique thread angle on one
side of the thread flank, changes from 37.5 to 30. Thus,
offering low thread forming torque, eliminates the risk of
relaxation. This thread is compatible with the Delta-PT
thread. STP screws may be used as an alternative to the
PT-screws.
Delta-PT screw is through hardened like the PT-screws.
There is a computer program available for determining the
boss geometry of the boss as well as assembly conditions.
DELTA-PT P
The new type called Delta-PT P is made of a highperformance
plastic (and is therefore suitable for
lightweight and electrically or thermally insulating threaded
joints in low strength thermoplastics.
ECO-SYN-PLAST (FORMER ECO-SYN SCREW)
The eco-syn-plast screw has the same excellent
properties as the PT-screw. It’s ideal, despite a missing
V-shaped root, for the assembly and joining into plastic. The
somewhat bigger core diameter of the thread increases its
breaking torque considerably. Thus, making it less likely
to break during installations. The eco-syn-plast screw with
HI-LO SCREWS
Each screw has a double-lead high and low thread with
the high thread having a 30°thread flank angle that further
minimizes material displacement while providing positive
thread engagement. The thread consists of a 30° thread
and a second thread with a 60° flank angle and a smaller
diameter. The helix angle of both threads is steep.
Hi-Lo screws were originally designed for the assembly
of dry walls. Due to the 30° thread, they are also used
in plastics. Here, the pilot holes should be dimensioned
in such a way that the 60° thread does not grip into the
plastic material. Their vibration resistance is extremely low
due to the high thread helix “quick in – quick out.” The
thread end makes the screws unsuitable for repetitive
assembly.
CONTINUED ON PAGE 160