Inherent Friction Research Articles

Estimation of the inherent friction factor per main‐chain friction unit of liquid low‐molecular‐weight unsaturated polyesters

AbstractThe temperature dependence (at 323–443 K) of the zero‐shear viscosity η of about 30 nonfractionated samples of an unsaturated polyester (300 < Mn < 1500) was analyzed and the parameters of the Vogel equation describing the η(T) dependence were estimated. Their dependence on the molecular weight is discussed. The inherent friction factor per main‐chain friction unit, ξo, has been evaluated for 15 < Zn < 70 (where Zn is the number‐average number of main‐chain friction units) and compared with the values available for other polymers.

The viscosity of an unsaturated polyester

AbstractThe zero‐shear viscosities of the fractions of an unsaturated polyester were determined by using a rotation viscosimeter with cone‐and‐plate measuring system. The polyester was prepared by the generally known melt condensation of maleic anhydride, phthalic anhydride, ethylene glycol, and cyclohexanol. The viscosity–temperature relationship and the viscosity‐molecular weight relationship are given. The low value of the critical molecular weight as well as rather high value of the inherent friction factor are probably caused by high forces between polar groups of the chains of an unsaturated polyester.

A clinical evaluation of the differential force concept as applied to the edgewise bracket

A study was conducted to retest the hypothesis of “differential force” as stated by Begg and to determine if this concept would apply to the edgewise bracket. Two recognized limitations in this study were that neither the tipping of teeth nor the inherent friction between the edgewise bracket and archwire was measured. An acrylic jig or matrix was constructed to fit over the central incisors. By placing a metal bar in the matrix with a point indented into the metal bar, a reference point for measuring distances to the canine and molars was established. The factor of friction should be mentioned relative to this investigation because in sliding an edgewise bracket over an arch wire, varying degrees of friction impede tooth movement. Friction is relevant in making an absolute comparison between conclusions of the differential force concept found in this study and the differential force concept stated by Begg. The conclusions of this investigation are as follows: (1) When using the Siamese edgewise bracket with continuous arch wires, it does not always follow that with 100 to 150 Gm. of applied force only the canine and not the buccal segment or anchor unit will move. Conversely, it does not always follow that with 400 to 500 Gm. of applied force only the buccal segment or anchor unit will move forward and the canine will not move. (2) Using the sliding mechanics of this study, the percentage of greater rates of tooth movement happening coincident with greater forces was found to be 0.857. (3) When the edgewise bracket and sliding mechanics were used, the curves showed that, in general, reciprocal forces cause reciprocal tooth movement with varying and relative rates of space closure. (4) Subjectively, no relationship was found between pain and increased forces; that is, pain in this study was found just as often on the side with 100 to 150 Gm. of applied force as on the side with 400 to 500 Gm. of applied force. This is not to say that there is not more tissue damage found with the use of heavier forces.

Discussion of “A means for studying mandibular movements”

Each link in the entire chain can affect the accuracy of reproduction. The attachment of the face-bow to the teeth, the deflection of the face-bow due to static load, the inherent friction of the ball joint of the transducer, the instability of the light source and solar cells, the conversion of light energy to an electric pulse, and, finally, the quality of the tape itself can contribute individually and in total to exceed the measurement limits imposed by the dental profession. As the measuring instrument has been engineered and constructed, the accuracy of the tape recording is 0.0025 inch. If this figure is doubled to include the playback, we will still have an over-all error of less than 0.15 mm.

Externally Pressurized Bearings With Inherent Friction Compensation

Inherent friction compensation can be obtained by grooving one of the bearing surfaces in such a way that the through-flow of lubricant (oil or gas) exerts viscous forces in the direction of motion. In this study, theoretical and experimental data have been presented and many applications suggested. An experiment concerning an application as a continuous viscometer has been successful.