Practical guide to processing 2K casting resins

PREPARATION

Before starting work, have the following items ready:

• The material, including the parts to be cast, conditioned to room temperature or the desired application temperature.

(Caution: If necessary, use extraction when working at elevated temperatures.)

• A mixing container – that is dry, clean, and preferably has a smooth bottom and walls
• Scale – for weighing portions and filling quantities
• A thermometer – for measuring the ambient temperature and the material during pouring
• Personal protection equipment – safety goggles, gloves, a smock, several cleaning rags, and a waste bin
• If possible, use a hygrometer to measure humidity.
• Stopwatch

DOCUMENTATION

• Before starting, take note of the room temperature and humidity.

An ideal temperature is 23 °C (+/- 5 °C) with a relative humidity of 50 % (+/- 10 %).

• Note the batch numbers of the resin and hardener.
• Note the weight of the empty measuring cup and each component.
• Prepare the components as you would in production. Note the batch number, material, storage conditions, and preparation of the parts.

PREPARATION

Stir the resin beforehand and try to avoid ingress of air bubbles pouring the components into the mixing vessel. If the viscosity of the components is high enough, they can be layered in the mixing vessel (hardener on top). Begin the experiment when you start mixing and press the stopwatch.

Using a wooden spatula or confectioner’s knife, mix the material thoroughly for at least one minute until it is homogeneous in color and consistency. Scrape the sides and bottom of the container at least twice. To avoid accidentally adding unmixed resin residue from the wall, you can also transfer the mixture to another container (see below).

Suitable mixing tools

If possible, resin and hardener should be mixed without ingress of air. The shape of the spatula is important for the mixing. Do not use screwdrivers or round sticks for mixing. Round shapes reduce the mixing effect. Flat, wide spatulas are much better suited for this task.

The mixing process itself generates heat, as does the curing reaction that causes polyurethanes and epoxy resins to heat up.

The stronger this effect is and the better it is mixed, the faster the material sets. Therefore, check the temperature of the mixture before pouring. The warmer the mixture, the more fluid the material. This can be important for evaluating the casting. After mixing begins, the material thickens as reaction time progresses. If there is significant additional heating, the thickening process will be faster. Determine the maximum time after which a flawless casting was possible, then note the temperature of the material in the mixing vessel. The greater the quantity mixed, the greater the effect of the reaction heat is. Therefore, large batches harden faster than smaller ones.  Hardening usually takes place „from the inside out.“

If possible, let any bubbles that were incorporated during stirring, rise to the surface before pouring. This process can be speed up by tapping the container. Any bubbles that remain on the surface of the poured mixture can be removed by carefully blowing on them with a hot air gun.

Do not scrape the mixing vessel when pouring, as inhomogenities occur on the vessel walls. This can be counteracted by repotting and mixing again.

Filling components

Avoid air pockets during casting injection. Therefore, before casting, consider the flow of the liquid through the object and select the point(s) accordingly.

Do not simply pour over cavities. It can be advantageous to fill the components from below. To do so, introduce the resin into the bottom of the component using a cannula.

For horizontal components (e.g., circuit boards), it may be advantageous to angle the components during potting. In this case, select the pouring point at the component’s lowest point.

Any air bubbles entrapped during stirring can be removed by evacuation before the processing time expires. Mechanical potting is also possible. Upon request, we can recommend suitable cleaners and rinsing agents from our range.

Store the potted parts in a dry place in a horizontal position. Make a note of the storage conditions, filling weight, and potting time. Visual documentation is advisable.

A forced hardening for example at 60 °C for 16 hours is possible after pre-hardening. If a tempered hardening is not planned in the final process, the temperature should exceed 60 °C; otherwise, an atypical hardness will be achieved. Decomposition may also be initiated at temperatures above 160 °C. If curing is carried out at elevated temperatures, air ventilation is necessary. It is best to briefly extract the air in the interior of the oven after casting opening it by connecting it to the exhaust air system. If temperature treatment is carried out immediately during production, this should also be simulated in tests to realistically reproduce the material’s flow and thermal stresses. This is particularly advisable for epoxy resins. In general, processing and curing conditions during casting tests should correspond to subsequent production conditions. Depending on the curing temperature, different curing reactions may occur. This can result in molded parts with different properties, particularly with regard to mechanical properties or thermal stresses.