Sturtevant Richmont 10191, Руководство пользователя

Страница: 23 / 51

Chapter 5 - Joint Simulators and Power Tool Testing
Joint Hardness
Joint hardness is the rate at which a joint develops clamping force as torque is applied to the
fastener. Any given joint may be "hard", "soft", or somewhere in between. Note: Joint
hardness is classified in accordance with the ISO 5393 standard.
A "hard" joint is one which requires very little fastener rotation to develop the joint preload
(clamping force) desired for the assembly. Stated another way, there are very few degrees
of fastener rotation, and very little time, from the moment the fastener develops a small per-
centage (10%) of the fastener preload desired to the moment the fastener develops 100% of
the desired preload.
This is depicted in the first diagram. In this diagram,
the horizontal axis is time or rotation angle, and the
vertical axis is the torque which results in clamping
force. The very rapid rise in torque and clamping
force over very little time is what defines a hard
joint.
The next diagram is of a medium joint. Notice that
the rise in torque and clamping force takes more
time - fastener rotation - than it did in a hard joint.
The angle of rotation is between 30º and 270º.
TIME/ANGLE
TORQUE
TIME/ANGLE
T
O
RQUE