RU2020478C1 - Material for protector of piezoelectric transducer - Google Patents

Abstract

FIELD: measurement technology. SUBSTANCE: material contains epoxy resin as binder, triethanolamine as hardener, plasticizer and finely divided powder of tungsten as filler in the following amounts, parts by weight: epoxy resin 99-101; tungsten powder 68-70; plasticizer MGF-9 3-4; triethanolamine 16-20. EFFECT: higher efficiency.

Description

 The invention relates to a measuring and control technique and can be used for the manufacture of piezoelectric transducers protectors designed for monitoring liquid media with frequency-time ultrasonic flow meters.

 A known material of the protector of a piezoelectric transducer containing an epoxy resin as a binder, a low molecular weight polyamide resin as a hardener, and barium ferrite powder as a filler [1].

The closest in technical essence to the proposed is (wt.%) Epoxy resin ED-5-10 [2]. Titanium Dioxide 30 Polyester MGF-9 2 Polyethylene Polyamine 1,3
However, the known material has insufficient resistance to dynamic stresses and especially to temperature changes, since the thermal coefficient of linear expansion of the tread material and the piezoceramic plate differ significantly. Another disadvantage is the difficulty in homogenizing the material during its preparation (a large amount of filler compared to the binder). When the hardener is introduced into the batch and the mass is mixed, air is captured, which is then difficult to remove from the composition (the pot life of the composition is very limited). Air bubbles remaining in the material dissipate useful energy, which leads to a loss of sensitivity of the transducer when using a known material as a tread.

 The purpose of the invention is to increase resistance to thermal shock by reducing thermal stresses, increasing sensitivity due to homogenization and deaeration of the material, increasing the manufacturability of the composition.

 This goal is achieved in that the material for piezoelectric transducers, including an epoxy resin as a binder, a filler, a plasticizer and a hardener, contains triethanolamine as a hardener and a filler of finely dispersed tungsten powder in the following ratio of components, parts by weight: Epoxy resin 99- 101 Tungsten powder 68-70 Plasticizer MGF-9 3-4 Triethanolamine 16-20.

PRI me R. Produce portsirovku component weight of the composition in parts by weight, e.g., 100 g of epoxy resin ED-20 was placed in a container, heated to a temperature of 50-60 ^{° C} and injected tungsten powder filler in an amount of 69 g. mixture was thoroughly stirred. Next, the mixture is placed in a heating cabinet and calcined at a temperature of 120-130 ^about C for one hour. The mixture was then cooled to 50-60 ^{° C} and introduced into 18 g of triethanolamine and 4 g of 9-IFG plasticizer. The resulting mixture is stirred until a homogeneous mass. The prepared mass is poured onto the surface of the piezoceramic transducer element (transducer should also be heated to a temperature of 50-60 ° ^C). Stoving must be made for 8-10 hours at 65-70 ° ^C. After the polymerization, the transducer is placed in an oven and maintained at ^75-80 for 1-1.5 h (normalization adhesive system). After curing, the tread is treated to the desired thickness. By mixing the mixture at elevated temperature, the mass is well homogenized, and a long curing time at elevated temperature helps to completely remove air bubbles from the applied layer (the mass has good fluidity). Thus, due to the homogeneous structure of the tread and the complete deaeration of the material (checked by thin section of the longitudinal section of the tread), the sensitivity of the converter increased by a factor of 1.5 (due to the exclusion of microbubbles of air on which useful elastic energy is dissipated). The content of finely dispersed tungsten powder as a filler in the selected limits while maintaining the weight ratios of the other components allows to obtain a material with evenly distributed suspensions of heavy particles of tungsten powder with a thermal coefficient of linear expansion equal to 4.5 × 10 ⁶ deg ^-1 , which is in contact with piezoceramics with thermal coefficient of linear expansion (TEC) equal to (4.5-7.5) ˙10 ⁶ , deg ^-1 .

 The approximation of the thermal coefficients of linear expansion of the tread material and the piezoelectric ceramics of the transducer significantly reduces the internal thermal stresses of the tread material at temperature differences and thereby increases the tread resistance to cyclic temperature changes.

 When the tungsten powder content is below the specified limit, less than 65 wt. h, increases the thermal expansion coefficient of the tread material, which leads to a decrease in the resistance of the tread material to temperature extremes. When the content of tungsten powder above the specified limits, more than 70 parts by weight, stresses between the filler particles and the resin volume increase, which leads to a decrease in the resistance of the material to thermal shock. When the content of the plasticizer is above 4 wt.h. moisture resistance of the tread material decreases. When kept below 3 wt.h. the plasticizer MGF-9, the internal stresses of the tread material increase (the tread becomes brittle). The hardener content of triethanolamine is less than 15 wt.h. leads to incomplete curing of the material. The hardener content of more than 20 parts by weight causes an aggressive effect on the electrodes of the piezoelectric element.

Studies of the resistance of the tread and piezoelectric ceramics of the transducer and cyclic temperature differences (holding in a heating furnace for 20 min at +80 ^о С, and then cooling at a temperature of -12 ^о С for 20 min) showed that the ultimate strength of the protector - piezoceramic element is the converter remained constant after 50 cycles (controlled by a decrease in the sensitivity of the converter in the emitter-receiver system).

 Checking the sensitivity of the proposed tread material was carried out as follows.

 Two pairs of converters with a protector of a known solution and two pairs of converters with a protector from the proposed material were manufactured. The transducers were placed in a liquid with water. The distance between the transducers was 300 mm. The protectors were made quarter-wave thickness at the resonant frequency of the Converter. The amplitudes of pulsed oscillations at the output of the emitter-receiver system are 1.5-1.8 times greater than in the case of similar converters with a protector made of the material of the prototype.

 From the above data it follows that due to the homogenization and deaeration of the tread material, the sensitivity of the material increased by more than 1.5 times.

 Thus, the proposed material for the protector of the piezoelectric transducer allows you to get good mechano-acoustic properties, namely the reduction of internal stresses at temperature extremes, increasing the durability of the piezoelectric transducer and sensitivity. The material has good manufacturability, since for a long time the mass maintains high fluidity, which ensures reliable molecular contact with the surface of the piezoceramics, good fluidity of the material makes it possible to sufficiently ensure the packing of the filler particles, as well as the output of gas inclusions during the curing time without evacuation.

Claims (1)

MATERIAL FOR A PIEZOELECTRIC CONVERTER PROTECTOR, comprising an epoxy resin as a binder, a filler, a plasticizer and a hardener, characterized in that it contains triethanolamine as a hardener and as a filler a finely divided tungsten powder in the following ratio of components:
Epoxy 99 - 101
Tungsten Powder 68 - 70
Plasticizer MGF-9 3 - 4
Triethanolamine 16 - 20