Microwave curing of insulating varnish on armatures, stators and transformers

Microwave energy can accelerate the hydration of cement, which results in the rapid strength development of concrete. In this paper, prediction of later age compressive strength of fly ash cement mortars, based on the accelerated strength of mortars cured with microwave energy, was investigated. To accelerate curing properly, optimal processing parameters of microwave curing (MC) on Portland cement mortars (CM) and fly ash cement mortars (FA) were first determined and then were applied to mortars. The possible early ages for the strength prediction were found to be at 6 and 8 h for CM and FA, respectively. The error percentages for prediction of CM were ±2.22% and 2.91% for 7 and 28 d, respectively. Error percentages for FA, on the other hand, were ±4.36% and 5.20% for 7 and 28 d, respectively.

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Application of Microwave Heating for Adhesive Joining

10.1115/imece1999-0137 ◽

1999 ◽

Author(s):

Erik T. Thostenson ◽

Tsu-Wei Chou

Keyword(s):

Microwave Heating ◽

Composite Structures ◽

Material Selection ◽

Adhesive System ◽

Conventional Heating ◽

Joint Interface ◽

Microwave Curing ◽

Composite Joint ◽

High Dielectric ◽

Microwave Techniques

Abstract In conventional joining of composite materials and sandwich structures, reductions in processing time are limited by inefficient heat transfer. In conventional processing the thermal energy must diffuse through the composite layers to heat the joint interface and cure the thermosetting adhesive, and this outside-in process of heating results in excessive processing times and wasted energy. The purpose of the current work is to examine microwave heating as an alternative to conventional heating for joining of composite structures. Through proper material selection, microwaves are able to penetrate the substrate materials and cure the adhesives in-situ. Selective heating with microwaves is achieved by incorporating interlayer materials that have high dielectric loss properties relative to the substrate materials. In this study, a processing window for elevated temperature curing of an epoxy paste adhesive system (HYSOL EA 9359.3) was developed and composite joint systems were manufactured using conventional and microwave techniques and tested in shear. Microwave curing resulted in both enhanced shear strength and less scatter in experimental data.

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Numerical Simulation of Temperature Distribution in the Glass Fiber Epoxy Composites during Microwave Curing

MATEC Web of Conferences ◽

10.1051/matecconf/201820603001 ◽

2018 ◽

Vol 206 ◽

pp. 03001

Author(s):

X Zhang ◽

X L Chang ◽

R L Ma ◽

L Zhang ◽

X D Chen ◽

...

Keyword(s):

Temperature Distribution ◽

Glass Fiber ◽

Three Dimensional ◽

Coupled Model ◽

Curing Process ◽

Epoxy Ring ◽

Microwave Curing ◽

Composite Ring ◽

Initial Stage ◽

Field Temperature

A three-dimensional coupled model of electromagnetic field, temperature field and curing degree field was established. Based on this model, the simulation of microwave curing process of glass fiber epoxy ring was realized, and the temperature distribution at different time was obtained. Numerical results indicate that the temperature difference within the composite ring is mainly formed in the initial stage during microwave curing.

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Hydration and Microwave Curing Temperature Interactions of Repair Mortars

Recent Progress in Materials ◽

10.21926/rpm.2104040 ◽

2021 ◽

Vol 03 (04) ◽

pp. 1-1

Author(s):

Pal S. Mangat ◽

◽

Shahriar Abubakri ◽

Konstantinos Grigoriadis ◽

Vincenzo Starinieri ◽

...

Keyword(s):

Portland Cement ◽

Heat Of Hydration ◽

Curing Temperature ◽

Early Age ◽

Normal Density ◽

Concrete Repair ◽

Microwave Curing ◽

Polymer Addition ◽

Curing Period ◽

Repair Materials

Microwave curing of repair patches provides an energy efficient technique for rapid concrete repair. It has serious economic potential due to time and energy saving especially for repairs in cold weather which can cause work stoppages. However, the high temperatures resulting from the combination of microwave exposure and accelerated hydration of cementitious repair materials need to be investigated to prevent potential durability problems in concrete patch repairs. This paper investigates the time and magnitude of the peak hydration temperature during microwave curing (MC) of six cement based concrete repair materials and a CEM II mortar. Repair material specimens were microwave cured to a surface temperature of 40-45 °C while their internal and surface temperatures were monitored. Their internal temperature was further monitored up to 24 hours in order to determine the effect of microwave curing on the heat of hydration. The results show that a short period of early age microwave curing increases the hydration temperature and brings forward the peak heat of hydration time relative to the control specimens which are continuously exposed to ambient conditions (20 °C, 60% RH). The peak heat of hydration of normal density, rapid hardening Portland cement based repair materials with either pfa or polymer addition almost merges with the end of microwave curing period. Similarly, lightweight polymer modified repair materials also develop heat of hydration rapidly which almost merges with the end of microwave curing period. The peak heat of hydration of normal density ordinary Portland cement based repair materials, with and without polymer addition, occurs during the post microwave curing period. The sum of the microwave curing and heat of hydration temperatures can easily exceed the limit of about 70 °C in some materials at very early age, which can cause durability problems.

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