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ME303-308 LAB-week

The document discusses ball screw sizing and selection. It provides information on topics like axial load ratings, rolling resistances, critical speed, end fixity conditions, speed limits, and column load strength as they relate to ball screw design. Next steps include motor selection, gear sizing, and a progress report. References are provided for ball screw catalogues and the next lab will cover motor selection.

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Abdullah Mashat
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34 views15 pages

ME303-308 LAB-week

The document discusses ball screw sizing and selection. It provides information on topics like axial load ratings, rolling resistances, critical speed, end fixity conditions, speed limits, and column load strength as they relate to ball screw design. Next steps include motor selection, gear sizing, and a progress report. References are provided for ball screw catalogues and the next lab will cover motor selection.

Uploaded by

Abdullah Mashat
Copyright
© © All Rights Reserved
We take content rights seriously. If you suspect this is your content, claim it here.
Available Formats
Download as PPTX, PDF, TXT or read online on Scribd
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ME303/308 LAB

Week-6
Instructor: Mirza Murtuza Ali Baig
Todays Task
OUTCOMES
• Ball Screw Sizing and Selection
• Self-study new topic and tailor the design
process.
• How to use catalogues

Next Lab
• Motor Selection
• Gear Sizing

Progress Report Due in Week-8


Axial Load- Horizontal Mount/Orientation
Axial Load- Vertical Mount/Orientation
Coefficient of sliding friction for non-
vertical loading applications

Note: Frictional coefficients are included for reference


purposes only and may vary in accordance with actual
operating conditions.
Rolling Resistances- Castor Wheels

0.01 for typical linear rail & bearing systems


Basic Dynamic Load Rating

Ball Screw Selection


https://rockfordballscrew.com/ball-screw-catalog/?page=search&cid=mm-ball-screws
Basic Static Load Rating
• When the Ball Screw is stationary or in
motion, unexpected external force may be
applied through an inertia caused by the
impact or the start and stop.
• When ball screws are subjected to
excessive loads in static condition (non
rotating shaft), local permanent
deformations are caused between the
track surface and the steel balls.
• When the amount of this permanent
deformation exceeds a certain degree,
smooth movement will be impaired.
Screw
RPM

Length between Bearing


Supports
Critical Speed-Screw
Critical Speed is the
theoretical linear
velocity (rpm) which
excites the natural
frequency of the
screw. As the speed
of the screw
approaches the
natural frequency
(critical speed), the
screw shaft begins to
resonate which leads
to excessive vibration.
End-Fixity
Conditions Inexpensive but only
applicable for short ball
screws and/or slow
speeds.

The permissible axial load and the


permissible rotational speed vary
with mounting methods for the
screw shaft. Most commonly
used mounting
setup.

Overconstrained mounting setup for applications where high


stiffness, accuracy, and high shaft speed is required. Ball screw
needs to be prestretched to avoid buckling in the case of thermal
expansion.
Speed Limit of Nut
• Speed Limit of Nut
is rotational speed limit due to the critical ball velocity within the ball
nut for very short periods of time. Exceeding this value can have a
detrimental effect on the life of the ball screw assembly.
• n < 5000 / Dnom
n = rotational speed (rpm)
Dnom = screw shaft nominal diameter (mm)
Column Load Strength
Drive Torque Back Drive
Torque

Drive Power
Assignment
• Select Single and Three Phase AC 220 Volt motor to provide the
required power. Get 3 data sheets for each from three different
manufacturers (Total 6).

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