ARALDITE® MY 750 / ARADUR® HY 956 / ARADUR® HY 951

Casting

Casting and encapsulation of small low to medium voltage electrical and electronic components.

Moisture pickup:

1. Hardener ARADUR® HY 956 and ARADUR® HY 951 are hygroscopic – they absorb moisture when exposed to damp air. The hardeners and unCured resin-hardener mixtures are in consequence adversely affected by high atmospheric humidity, which, when the mixture is applied as a thin layer, may even prevent curing. Low ambient temperatures, which prolong curing, aggravate this effect. The mixtures should not be prepared or applied in work-areas exposed to high atmospheric humidity combined with low ambient temperature.
2. To make the effect of moist air less severe, the mixture should be allowed to stand * in the mixing container – covered with lid – so that the resin-hardener reaction is well under way when the mixture is used.

* Standing time for mixture at room temperature: ARALDITE® MY 750 + ARADUR® HY 956 EN or ARADUR® HY 951 5-10 minutes

ARALDITE® MY 750 Unmodified liquid epoxy resin

ARADUR® HY 956 EN Formulated, low viscosity polyamine hardener

ARADUR® HY 951 Low viscosity, aliphatic amine hardener

• Good mechanical strength
• Excellent Electrical Properties
• Resistant to chemical attack

• Mix resin and hardener together at room temperature, stirring thoroughly. Low ambient temperatures cause Araldite MY 750 to be viscous and difficult to mix. This is overcome by warming Araldite MY 750 prior to mixing to about 30°C. Note: Although warming Araldite MY 750 facilitates measuring and mixing, it is also shortens usable life – see Usable Life below.

A 500 g quantity of resin-hardener mixture has usable life:

However, owing to the heat generated by the exothermic reaction between resin and hardener, the usable life will be noticeably shortened if more than 500 g of mixture is allowed to stand in one compact mass – e.g. in a mixing beaker or similar “bulk container”. To minimize exothermic temperature rise, which is the cause of this shortening of usable life, the heat generated must be rapidly conducted away. The following procedure is suggested when mixing large quantities:

1. Divide the mixture into several small containers or pour into a shallow container so that the mixture spreads out to a thin layer (5-10 mm). A shallow polythene basin is recommended since this allows hardened resin residues to be removed simply by flexing. Where there is risk of exposure to damp air, containers must be covered – see Moisture Pick-up.
2. Dividing or spreading out the mixture increases its surface-to volume ratio so assisting dissipation of heat generated by the resin-hardener reaction.
3. Since usable life is limited, it is good practice to prepare only the quantity of mixture needed for immediate use – or to use automatic mixing-dispensing equipment.

• Casting mixtures Mixing and pouring under vacuum minimizes any tendency to the formation of voids. Mineral fillers may be incorporated in order to minimize shrinkage, to decrease the coefficient of expansion, to increase thermal conductivity, to decrease the exothermic temperature rise on curing.
• Quantity production Production line processing of Araldite MY 750 with Hardener Aradur HY 956 EN or Aradur HY 951 is best carried out by means of proportioning-mixing-dispensing machine. Automatic processing by these machines offers high production rates with good process control. This close control makes possible the processing of large quantities of Araldite systems with short usable life – such as ARALDITE® MY 750 with Hardener ARADUR® HY 956 EN or ARADUR® HY 951.

Minimum curing schedules

* Thin-section castings and laminates of Araldite MY 750 with Hardener Aradur HY 956 EN or HY 951 will require considerably longer than 24 hours to Cure at 25°C. To achieve full curing in reasonable time they must be Cured at a temperature above 40°C.
** Extra time must be allowed for the moulds and castings or laminates to reach the required temperature.

Cured resin
Curing schedule:
3 hours at 60°C

* Prolonged curing above 60°C will give a deflection approaching 100°C (with Aradur HY 956 EN) or above 100°C (with Aradur HY 951). For
example:

Mandatory and recommended industrial hygiene procedures should be followed whenever our products are being handled and processed.

First Aid : Contamination of the eyes by resin, hardener or mix should be treated immediately by flushing with clean, running water for 10 to 15 minutes. A doctor should then be consulted. Material smeared or splashed on the skin should be dabbed off, and the contaminated area then washed and treated with a cleansing cream (see above). A doctor should be consulted in the event of severe irritation or burns. Contaminated clothing should be changed immediately. Anyone taken ill after inhaling vapours should be moved out of doors immediately. In all cases of doubt call for medical assistance.

The resins and hardeners should be stored separately in cool dry place. Under these conditions the shelf life will correspondent to the expiry date stated on the label. The hardeners are hygroscopic and will deteriorate if allowed to absorb moisture; the containers should therefore be kept firmly closed when not in use.