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Flow and Cure Test Methods for Molding Compounds

Hexion’s molding compounds are available in various flow settings. Essential for selecting the flow setting is the type of molded part to be manufactured and the specified processing method. This selection should be done with special care. If needed, we will make available samples of various viscosity and reactivity ranges. Our technical customer service experts can advise you in detail.

Flow/cure properties are measured according to the following test procedures:

1. Disc Flow Test – The disc flow method uses two heated plates. A specified amount of molding compound is pressed out between the heated plates to form a disc. Mold pressure and temperature are specified. Parameter for the flow/cure property of the molding compound is thickness of the pressed part to be measured at four specific points. The numerical value known to the operator as ”disc flow“ results from adding the four measuring values (in mm); this sum is multiplied by 10.

2. Orifice Flow Test (OFT) – For the OFT, a compression mold according to ISO 7808 is used. It consists of a cylindrical female mold and a specially formed punch as a male mold. The last part incorporates two channels through which a specific amount of plastic molding compound flows during the closing process, depending on the curing speed. This amount, specified as a percentage of total feed weight, is the OFT-value. Pressure, mold temperature and feed weight are specified for the test. Usual pressures are 4, 7, 12 or 19 MPa.

3. Kneader Test – For the kneader test, the molding compound is tested in a small heated blade kneader according to DIN 53764. Here, the torque on the bearing of the drive motor is measured and recorded versus time in a diagram (illustration). During the kneading process, the molding compound first melts, remains kneadable for varying lengths of time, and finally hardens. Specified for this test are the feed weight of the material, the speed of the kneader blades and the kneader chamber temperature. The course of the U-shaped curve allows a statement regarding viscosity and curing time. As viscosity, the torque at the lowest point of the curve is given. To characterize the curing time (reactivity of the molding compound), the width of the curve is used.

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