ARALDITE® B 41 / ARADUR® HT 903 / Mineral fillers

• Void-free epoxy resin castings exhibit outstanding resistance to mechanical, thermal and electrical stress even under long-term loading.
• Low cure shrinkage allows the manufacture of large-volume castings and the crack-free encapsulation of metal parts and conductors.

Indoor electrical insulators for medium and high voltage applications, such as instrument transformers, switchgear components and for structural parts for equipment subject to high mechanical, thermal or chemical stress.

Unmodified, Bisphenol A based epoxy resins with viscosities and reactivities closely tailored to complement the properties of the recommended hardeners. They contain no solvent and are odourless solids at room temperature
 

Carboxylic acid anhydride based curing agents which are odourless solids at room temperature.The hardeners Aradur HT 901 and HT 903CI are sensitive to moisture, absorption of which leads to the formation of acid that detrimentally affects the reactivity of the mix and the end properties of castings

 Accelerator DY 068
Low-viscosity, carboxylic acid anhydride based catalyst containing cure-accelerating agents. Addition of this accelerator to a resin-hardener combination results in a highly reactive mix primarily suitable for processing by the pressure gelation method.
 

• Conventional gravity casting process under vacuum
• The choice of the resin and hardener is determined by the application envisaged and the processing equipment available.
• Pot life and exothermic temperature rise can be controlled by appropriate selection of the resin, hardener and filler combination used.

Fillers

• The addition of powdered mineral fillers such as silica flour, microdol and aluminium oxide is recommended when manufacturing castings that will be required to withstand mechanical, electrical or thermal stress.

The incorporation of mineral fillers

• Modifies major mechanical and electrical properties;
• Reduces shrinkage and exothermic temperature rise during cure;
• Imparts a low coefficient of linear expansion;
• Improves thermal conductivity;
• Reduces unit costs.
• The reduction of elongation at break resulting from the use of filler may be a drawback under certain conditions.
• The glow heat resistance and flame-retarding properties of castings can be enhanced by substituting some part of the silica flour filler with Aluminium Oxide Trihydrate. A slight impairment of mechanical and dielectric properties is acceptable.
• Depending on processing conditions and the application for wich castings are intended, filler loadings of up to 250 parts by weight may be used.
• The data given for filled systems were determined by test specimens containing 210 parts by weight W12 grade silica flour supplied by Quarzwerke GmbH, Frechen, Germany.
• The end properties of a casting are dependent to a marked degree on the type, grade, amount and orgin of the filler incorporated, on the pretreatment it was given, and on the way it was added to the mix. For instance, silanized silica flour filler has been found to impart appreciably more durable dielectric properties to a casting exposed to tropical weathering. Filler should be predried if it is to be used in high performance castings.
• The impurity content of the filler affects the cprocesing properties of the casting resin mix. It is advisable to test the reactivity and exothermic characteristics with every new batch of filler before continuing production.
• The particle size distribution of a filler influences the flow properties of a casting mix, the gel time and the end properties of castings. Test results deviating from those quoted in this Instruction Sheet are to be expected if casting mixes are formulated using fillers other than those show.
• Coarse fillers have an undesirable tendency to settle out, ultimately promoting built-in stresses in castings. 

Electrical Properties :

Fig.8.1: Loss factor (tan δ) and dielectric constant (εr) as a function of temperature (measurement frequency: 50 Hz, IEC 60250) Systems 2 and 3

Fig.8.2: Volume resistivity (ρ) as a function of temperature (measurement voltage: 1000 V, IEC60093) Systems 2 and 3

Fig.8.3: Loss factor (tan δ) and dielectric constant (εr) as a function of temperature (measurement frequency: 50 Hz, IEC 60250) Systems 5 and 6

Fig.8.4: Volume resistivity (ρ) as a function of temperature (measurement voltage: 1000 V, IEC 60093) Systems 5 and 6

Heat ageing according to ICE 60216

• Determined on standard test specimen
• Cured for 8h at 160°C

Fig.9.1: Weight loss (DIN 16946) (limit: 1.2%) System 2

Fig.9.2: Loss of flexural strength (DIN 16946) (limit: 50%) System 2

Fig.9.3: Temperature-time curves (derivated from times for end-point criterion) System 2

Water absorption (ISO 62)

• Determined on standard test specimen(60x10x4mm)
• Cured for 16h at 140°C

Fig.9.4: Absorption of water as a function of immersion time at 20°c, 40°C, 70°C and 100°C

Tensile creep characteristics

• Determined on standard test specimen
• Cured for 16h at 140°C

Fig.10.1:Test temperature 23°C Tensile strength σz (23°C) 87 MPa ( ❒ = failure)

Fig.10.2:Test temperature 40°C Tensile strength σz (40°C) 85 MPa (❒ = failure) System 2

Fig.10.3:Test temperature 85°C Tensile strength σz (85°C) 57 MPa System 2

Determined in accordance with DIN 53444 ,The tensile specimens were loaded to give stresses equal to the indicated percentages of the initial short-term failure stresses of the material at the temperatures shown.

General instructions for preparing prefilled resin systems

• Long pot life is desirable in the processing of any ARALDITE® casting resin system.
• The ARALDITE® resin melted to 120-150°C, together with the dried filler and eventually further additives, will be first premixed under vacuum in the premixer.
• Internsive wetting of the filler is extremely important. Proper mixing will result in:
• Better flow properties and reduced tendency to shrinkage
• Lower internal stresses and therefore improved mechanical properties on object
• Improved partial discharge behaviour in high voltage applications.
• The quantity of premix needed for a casting operation will be transferred to the final mixer and the appropriate quantity of the ARADUR® hardener (at room temperature) will be added.
• After reaching appr. 5 mbar of vacuum, the vacuum pump has to be turned off. Following, the mixer is turned on. After intensive mixing of appr. 15 min the casting resin system is ready.
• The temperature will decrease to appr. 100-120°C and the vacuum did regulate itself to appr. 8 mbar. Now it can be casted directly into the preheated moulds in the autoclave at 100-120°C and under a vacuum of appr. 10-15 mbar.
• The mixing time of the premix (ARALDITE® resin and filler) can vary from 2 to 6 hours, depending on mixing temperature, quantity, mixing equipment and the particular application. The required vacuum is 0.5 to 3 mbar. The vapour pressure of the individual components should be taken into account.
• In the case of electrically highly stressed parts, we recommend checking the quality consistency and predrying of the filler. The moisture content should be ≤0.2%. 
• The mixing time of the premix (ARALDITE® resin and filler) can vary from 2 to 6 hours, depending on mixing temperature, quantity, mixing equipment and the particular application.
• The required vacuum is 0.5 to 3 mbar. The vapour pressure of the individual components should be taken into account. In the case of electrically highly stressed parts, we recommend checking the quality consistency and predrying of the filler. The moisture content should be ≤0.2%.

Specific Instructions

• The effective pot-life of the mix is about 1 hour at temperatures below 120°C. Conventional batch mixers should be cleaned once a week or at the end of work.
• Viscosity increase and gel time at various temperatures.

• For castings with big volume (exothermic reaction, interal mechanical stresses) or encapsulation of heat sensitive active parts could be cured at appr. 80°C.
• To determine whether crosslinking has been carried to completion and the final properties are optimal, it is necessary toc arry out relevant measurements on the actual object or to measure the glass transition temperature.
• Different geling anc cure cycles in the manufacturing process could lead to a different crosslinking and glass transition temperature respectively.

Mix ratios

* A filler loading of up to 250 part pbw (64%) would be feasible

Pretreatment of resin, addition of filler

ARALDITE® B41 or B46 is heated to obtain a clear, liquid melt to which the, usually, preheated and degassed filler and the required amount of colouring paste are added. This mix is degassed under constant stirring prior to adding the hardener. The following guidelines apply :

Addition of cold hardener

Hardener Aradur HT 901 or HT 903-1CI is added when the mixer is stopped. The mixing chamber is then again put under a vacuum, the vacuum line closed off, and the mixer put in motion. To ensure rapid and complete melting of the hardener the following requirements should be met.

Addition of liquefied hardener

• Hardener ARADUR® HT 901 and Hardener ARADUR® HT 903CI can be liquefied at 130-135°C and 90-110°C respectively prior to being added to the resin-filler mix, the temperature of which should be reduced accordingly. Use of liquefied hardener makes it easier to control the temperature of the casting mix.

• Viscosity versus time and temperature
• Systems 2 and 3 at 120°C

• Viscosity versus time and temperature
• Systems 5 and 6 at 120°C, System 5 at 100°C

• Geltime as a function of temperature (ISO 9396)
• Systems 2 and 3

• Geltime as a function of temperature (ISO 9396)
• Systems 5 and 6

• Glass transition temperature as a function of the cure time (isothermic reaction, ISO 11357-2)
• Araldite B41/B46:HT 901:Silica (100:30:200 pbw)

• Glass transition temperature as a function of the cure time (isothermic reaction, ISO 11357-2)
• Araldite B41/B46:HT 903CI:Silica (100:40:200 pbw)

Mechanical and Physical Properties

• The components have to be stored under dry conditions, in tightly sealed original containers.
• Product specific advise regarding storage can be found on product label.
• Under these conditions, the shelf life will correspond to the expiry date stated on the label.
• After this date, the product may be processed only following reanalysis.
• Partly emptied containers should be closed tightly immediately after use.