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Frictional resistance
Published in William Bolton, Engineering Science, 2020
A screw thread is essentially just an inclined plane wrapped around a cylinder. If the whole of the thread is part of the same helix then it is known as a single-start thread. However, there are situations where two or more threads alternate and these are known as multi-start threads. Where heavy loads are to be lifted, e.g. with a screw jack, a single-start thread is used. Where the load is small but has to move quickly, a multi-start thread is used.
Common Problems Involving Friction
Published in G. Boothroyd, C. Poli, Applied Engineering Mechanics, 2018
Figure 10.12 shows a square-threaded screw where it can be seen that the nut will be resting on the inclined upper helical surface of the thread. Thus, the thread can be regarded as an inclined plane wrapped around a cylinder, the helix angle α of the thread being equal to the angle of inclination of the plane. The pitch of a screw thread is the distance between corresponding points on successive threads, as shown in Fig. 10.12.
Dry friction
Published in Anthony Johnson, Keith Sherwin, Foundations of Mechanical Engineering, 2017
Anthony Johnson, Keith Sherwin
In whatever shape or form it is found, a screw thread is merely an inclined plane which has been wrapped around a cylinder. Analysis is fairly straightforward but before continuing it is important to become familiar with some screw thread terminology.
Pneumatic piston hydrostatic bioreactor for cartilage tissue engineering
Published in Instrumentation Science & Technology, 2023
J. Hallas, A. J. Janvier, K. F. Hoettges, J. R. Henstock
The transmission body of the system was created from 6 mm aluminum sheet and machined as three separate modular components: (a) rotational connection to the motor shaft (crank), (b) linkage connection with a pivot point at each end, and (c) a rod-end connection to the pneumatic cylinder piston (Figure 1D). A secure connection to the motor was designed with a 5 mm thick slot to surround the 14 mm diameter motor shaft with a grub screw. The part was designed so that the crank radius was 40 mm. The connecting shaft was 8 mm diameter and designed to include spaces for two 0.8 mm circlips to hold the joining piece in place laterally. The pneumatic cylinder piston was connected to the system body by a 10 mm diameter female screw thread. An M10 screw thread was connected to a short cylindrical section of a 15 mm diameter cylinder which held a connecting shaft of 8 mm diameter to connect to the joining piece. This connecting shaft accommodated two 0.8 mm circlips. To link the connection pieces together, two 22 mm diameter rotational ball bearings were used to minimize the friction in the system and reduce the load acting against the motor. A 6 mm thick aluminum sheet was used as a chassis frame to align the motor and pneumatic cylinder. The sheet was fixed across the front plate of the motor and using an aluminum clamp on the pneumatic cylinder to allow for small horizontal adjustments to be made. Calculations based on the forces, pressures, and volumes of the apparatus were used to parameterize force displacement curves (Figure 2).
Local contact characteristics of threaded surfaces in a planetary roller screw mechanism
Published in Mechanics Based Design of Structures and Machines, 2020
Shangjun Ma, Linping Wu, Geng Liu, Xiaojun Fu
The threaded surface equations of the mth screw thread and can be expressed as where and are the coordinates of a point on the screw threaded surface and is the unit vector of the coordinate system is half of the thread thickness of the screw. is the initial angle of the mth screw thread in the coordinate system and is the lead of the screw.
Design and construction of long-span single-layer dome structures by direct analysis
Published in HKIE Transactions, 2018
Y P Liu, S J Pan, Simon W K Leung, S L Chan
From stages 8 to 9, a mechanical jack as shown in Figure 11(b) is pre-set at each off-loading point with short members for protection. A mechanical jack uses a screw thread for lifting or off-loading heavy weight. Once the off-loading process activates, a portion of the short members will be cut off so that the mechanical jack comes into action to support the structure. As the travel distance of the mechanical jack is adjustable, the site technician controls the displacement of the off-loading point by the specified travelling distance. In this project, 35 mechanical jacks in total are set at the off-loading points. By controlling the travel distances of jacks, which are based on the predicted displacements using SODA, the long-span structure can be progressively and safely loaded to its design position. It should be noted that the jacks need to work simultaneously with different travel distances to cater for the predicted deformed shape. By doing this, the design load path will be smoothly formed with the eventual vanishing of reactions on temporary supports because the weight and loads will then be taken by the structure.