Smooth Rubber Research Articles

Rolling friction and adhesion between smooth solids

Rolling friction has been explained in terms of crack propagation through an adhesive joint. The contact between a smooth cylinder and flat has been regarded as an adhesive junction bounded by two cracks moving in the same direction at the same speed, one crack continually opening and one closing. Propagation of these cracks requires a force which is calculated from crack theory and shown to be equal to the friction. The theory has been verified experimentally using glass cylinders rolling on smooth rubber. Results show that rolling friction is closely connected with peel adhesion. Moreover, this adhesion interpretation of rolling friction between smooth surfaces explains several observations: (a) the existence of a static rolling friction, (b) the unusually high value of friction and its independence from load and roller radius, (c) the marked effect of lubricant or dust.

The adhesion and friction of smooth rubber surfaces

In an earlier study of adhesion between smooth rubber and rigid surfaces time effects were apparent. It now appears that under non-equilibrium conditions these effects largely determine the magnitude of the force required to separate adhering surfaces. This paper presents an optical study of contact area time effects between such surfaces and shows in a simple way how these optical observations may be used to predict the rate of rolling of a ball bearing on smooth rubber, the time taken to detach itself under gravity and its resilience when bouncing on smooth rubber. The friction when a rigid surface slides over smooth rubber under conditions where Schallamach waves are generated is also shown to be quantitatively related to their mutual adhesion.

Kinetics of Contact between Smooth Solids

Abstract The diameter of the circular contact region formed between a smooth rubber sphere and a glass plate has been studied as a function of time under a variety of loading conditions. Theoretically, the system is viewed as a circular crack which can move through the glass-rubber interface in two directions: one to form the contact and the other to break it. Discussion centres principally on the speed at which the crack propagates, and on a sudden stopping of the crack which leads to adhesive hysteresis.

The shear of thin liquid films

Optically smooth rubber pressed against glass provides a microconforming contact between which a thin uniform film of liquid can be sandwiched. The contact largely overcomes the problem of asperity interaction between surfaces. The rubber surface could be slid relative to the glass plate under controlled conditions and in this way it proved possible to study the shear properties of liquid films as thin as 40 Å. Results for water show that down to film thicknesses of 70 Å there is no increase in shear strength of the liquid. Below this thickness asperity interaction increasingly confuses the interpretation of measurements.If the water film contains a surface active agent, monolayer protection does much to reduce the friction between surfaces when the film is less than 70 Å. In the absence of monolayers the friction rapidly rises with decreasing film thickness towards the dry value.

The turbulent boundary layer over a wall with progressive surface waves

An experimental study of the interaction of a turbulent boundary layer with a wavy wall was conducted in a wind tunnel. A smooth neoprene rubber sheet comprising a portion of the floor of the tunnel was mechanically deformed into 12 sinusoidal waves which progressed upwind or down at controlled speed. The turbulent layer thickness was a little less than the wavelength. The mean velocity profile was linear on a semi-log plot over a substantial range of vertical height.The wall pressure was observed to be asymmetrical about the wave profile, resulting in a pressure drag. Flow separation was not the cause of the drag. The drag was found to be larger than that predicted by the inviscid wave generation theory. The measurements indicate that the waves strongly modulate the turbulent structure. The phase of the turbulent stresses with respect to the waves varies with wave speed, indicating that the dynamical reaction time of the turbulence is not negligible in comparison with the wave period.

Recent studies of short range forces

This paper describes recent studies of the forces between surfaces for separations of the order of tens to hundreds of angstroms. The first part deals with the direct measurement of forces between molecularly smooth mica sheets and shows that normal van der Waals' forces operate for separations less than 100 Å, retarded van der Waals' forces for separations greater than 200 Å. The second part describes a direct study of the repulsive forces exerted by charged double layers residing on solid surfaces. By using the contact between a soft optically smooth rubber hemisphere and a flat glass surface repulsive forces of the order of 10 5 dyne/cm −2 have been measured for film thicknesses of about 150 Å. The equilibrium film thickness decreases with increasing ion concentration and the results are in broad agreement with measurements by Mysels and others on black soap films.

Simple Method for Constructing Obturators and Prosthetic Patches of Prevulcanized Latex

Th e mechanical replacement of ana­ tomic tissues and structures is an ever present problem in the general dental practitioner’s treatment planning. Pros­ thetic procedures require evaluation of conditions with particular reference to location, type of structure lost, pathologic change and mechanical limitations. Recent publicity has stressed the need for early diagnosis and possible surgical treatment of malignant lesions. In view of the fact that many of these lesions in­ volve the hard and soft palate, cheeks and other parts of the face, the demand for obturators and surgical prosthetic patches is greater now than ever before and will continue to increase in the future. In lesser numbers, presented for cor­ rection are such malconditions as cleft palates, syphilitic and other pathologic fistulas, unhealed tooth sockets involving maxillary sinuses and scar tissue areas in the hard and soft palate. • Defects such as these require early prosthetic treatment, for the untreated patient is handicapped when eating, drinking and speaking. Patients suffer­ ing these handicaps may develop a men­ tal condition that results in their with­ drawing as much as possible from their normal surroundings and associates. In the past, efforts have been made with varying success to correct such mal­ conditions by constructing obturators and complex hinged appliances from cast metal, vellum rubber, vulcanite rubber or solid rubber, all attached to some type of denture. From experience gained in the treat­ ment of mouth wounds of World War II veterans, a very simple process has been developed whereby it is possible to con­ struct obturators of any type, separate and independent of any other prosthetic appliance. These obturators are retained by undercuts or adhesives, and may be inserted or seated at any time after sur­ gical intervention. They will be tolerated by the most sensitive tissues, even postoperatively. The first consideration in developing these appliances was to find a material that could be used to simplify their con­ struction. O f all the well known dental materials such as vellum rubber, elasto acrylics and various types of metal, pre­ vulcanized latex has proved superior in length of service, creation of sure seal, toleration by tissue and ease in manipula­ tion, fabrication and insertion. Prevulcanized latex is an aqueous solu­ tion composed of about 65 per cent rub­ ber solids and 35 per cent water. When this aqueous solution is dehydrated, a pure, smooth rubber deposit results. An obturator or prosthetic patch can be fab­ ricated to any thickness desired by the application and dehydration of successive coats of the solution. Prevulcanized latex is a well known commercial item and may be obtained from any reputable chemical or drug firm.