Thermal Effect of Polymer Materials Under Ultrasound

Although the thermal effect of polymer materials under power ultrasound was found earlier, the principle of its action has not been fully understood so far. This article mainly discusses the thermal behavior of polymer materials under ultrasound, and points out that the conclusion of the paper is worthy of confirmation.

2 experimental device Experimental equipment, see, during the experiment, the sample was placed flat on the frequency of 1.7MHZ, sound intensity of 18w/c2 ultrasound, a variety of polymer materials (such as plastic sheet, organic glass, foam, plastic film And so on) in different locations, such as A, B or C, etc., and perform temperature recordings at different locations.

3 experimental results and basic characteristics of the experiment 1. When the sample is a thickness of 3mm plastic plate and a thickness of 6mm plexiglass, under the A ultrasonic effect, the temperature rising melting process can be used to describe. Time-temperature curve, one side of the backwater is a Logistic curve, the maximum temperature is 210C, and the water side is a constant 21C. Under the ultrasonic action of B and C, the polymer material will melt.

In the 0.2 mm plastic film, no dissolution occurred at A, B, and C. And at the position of ultrasound at A, the time curve of the backside of the polymeric material is 0.5, the curve of the 0.2mm plastic film is constant, and the temperature of the O.Simn rises slightly to 56°C. constant.

The original plastic was 3mm and the total ultrasonic time was 30 seconds.

In the early and middle stage, m齄-m―organic glass was originally 6mm, and the total ultrasonic time was 30 seconds. S3 Experiment 3. When the sample is a thickness of 3m plastic plate and a thickness of 0.2 plastic film, when the plastic plate is close to the plastic film, the plastic The film was placed on the side A by water, and the results of experiments 1 and 2 occurred on the plastic plate and the plastic film. That is, the plastic plate melted, and the plastic film did not melt. However, it is mainly pointed out that plastic plates sometimes melt and sometimes melt.

Experiment 4. When the sample is foamed, the foam plate does not have a thermal effect at A.

Experiment 5. Comparative test, the current wind welding machine was used to test the above-mentioned high-molecular materials (plastic plates, plexiglass, plastic films, and foam plastics) in the air by blowing hot air between water and gas. When the air temperature of the welding torch was 210C, no matter Polymers in the air, or in water and gas, must melt. It is particularly pointed out here that when the plastic plate is heated, the plastic plate is melted from the surface of the air blow layer by layer, and the temperature at the other end of the melt is not changed. When the side of the heated plastic plate melts from the beginning to the middle of the material, the temperature on the other side remains unchanged. The above experimental phenomena are in accordance with the basic laws of physics, that is, when the outside world heats the object, the heat is transferred from the object to the object.

From the above experimental results, we can wait for the melting temperature of the plastic plate not to pass it to the high temperature material of the plastic plate, because the temperature of air and water is lower than the melting temperature of the plastic plate, because the plastic plate melts the heat under ultrasound, inside the plastic plate. The resulting melting speed of the polymer material is related to the sound pressure and frequency of the ultrasonic wave. The temperature distribution of the melting time is related to the material, and the temperature has an upper limit. The occurrence of melting is related to the thickness of the material. When the thickness of the material is less than or much less than the ultrasonic wave length, no melting phenomenon occurs. Water is the medium that transmits ultrasound, so plastic films can transmit ultrasound without melting. We believe that the conclusion that this kind of melting phenomenon is mainly attributed to the burning effect of concentrated ultrasonic cavitation is unreliable.

4 Analysis of thermal effects The mechanical behavior of thermal effects caused by polymer materials under ultrasound is mainly related to the viscosity of the material and heat conduction. Under the action of ultrasonic pressure, the high-molecular material undergoes ultrasonically passing through the object, and a periodically varying stress (or strain) is generated inside the object under the action of the longitudinal wave. Let sinusoidal stress be expressed as: = = coffee + sin, where is the absolute value (amplitude) of the stress expressed in the complex form, and the angular frequency (rad/s) is the phase. The polymer material is now regarded as a viscoelastic body. If a Maxwell model is used, 7 is the strain, and 7/ is the viscosity, (3 is the elastic modulus. Let 7 be based on G = (T/y relation, +g complex model can be obtained) Quantity, kinetic angle tangent.Functions determined from the above knowledge G, Gn.

From the physical point of view, when the viscoelastic body is subjected to a sinusoidal stress, a part of the work done by the external force on the system will be consumed to overcome the inter-molecular friction within each week. In other words, in a cycle, the system must absorb a certain amount of energy (Q) from the outside world and convert heat energy. This is the reason why the polymer material generates heat under the action of strain force, that is, the energy loss reaches a maximum at the time of l.

From the above analysis, under the effect of high-molecular material ultrasound, the pressure of longitudinal ultrasonic waves generates cyclically changing stress, which causes the polymer material to generate heat internally, but when the thickness of the polymer material L is smaller than the ultrasonic wave length A=c//=1.5 When xl05/1.7xl06=0.088cm, the internal stress of the polymer material is not significant, and therefore the heat generation is not significant. This conclusion is consistent with experiment 2. Ultrasonic fever threshold conditions. Followed by the long ultrasonic conditions, the relative density of the foam is low, more than the hole, the wall between the hole and the hole is very thin, it is much smaller than 0.088cm, so the foam does not heat in the ultrasonic effect.

Sense i-shot Li Huamo provided information and help.