Column strength
is the ability of the lift shaft to hold compressive loads without
buckling. With longer screw lengths, column strength may be substantially
lower than nominal jack capacity.
If the lift shaft is in tension only, the screw jack travel is
limited by the available screw material or by the critical speed
of the screw. Refer to the screw technical sections for critical
speed limitations. If there is any possibility for the lift shaft
to go into compression, the application should be sized for sufficient
column strength.
- Charts are used to determine the required jack size in applications
where the lift shaft is loaded in compression. To use this chart:
- Determine the mounting condition and mark a point on the “Maximum
length” line.
- Mark a point on the “Load” line, applying an appropriate design
factor.
CAUTION: chart does not include a design factor.
- Draw a line connecting the two marked points. Select a jack
above the point where the line drawn crosses the “Jack Sizes”
line.
The chart assumes proper jack alignment with no bending loads on
the screw. Effects from side loading are not included in this chart.
Jacks operating horizontally with long lift shafts can experience
bending from the weight of the screw. Consult Nook Industries, Inc.
if side thrust is anticipated, operating horizontally, or maximum
raise is greater than 30 times the screw diameter.
AVAILABLE LIFT SCREW LENGTHS As a major manufacturer of industrial
ball, acme and lead screws, Nook Industries stocks a broad selection
of screws. Nook Industries has the capacity to make long screws
for special applications. Rotating screw jacks can be built with
a larger diameter lift shaft for greater column strength or a different
lead to change the jack operating speed.
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