Injection weight Injection weight is an important param […]
Injection weight is an important parameter of the injection molding machine. It is the most frequently used parameter when selecting an injection molding machine, expressed in ounces or grams. Although this parameter is simple and easy to understand, it is easy to be misunderstood. The reason is very simple. When the plastic is selected, the injection molder can determine the weight of the plastic part, so they can easily choose the machine by this injection weight. In fact, the injection weight is defined as the weight of the plastic injection when an empty injection (not injected into the mold) is measured, rather than theoretically calculated. The compound used is usually a general hard rubber with a specific gravity of 1.05. When the plastic of the plastic part is different from PS, the injection weight of the specification can be used after the following conversion. Injection weight of non-PS plastic = c*b/1.05, (b = specific gravity of plastic and c = injection weight expressed in PS.) For example: the specific gravity of Saigang is 1.42, it is in one injection weight (calculated as PS) 8 oz.
(1) Choose an injection molding machine with a sufficient injection weight - you should not choose an injection molding machine with an injection weight just equal to the weight of the plastic part plus the weight of the flow channel plastic. In less demanding injection molding, such as toy portraits, the total weight should be 85% of the injected weight. In demanding injection molding, such as crystal supplies, 75%. The injection weight measured in the empty injection is small at the injection pressure, and the high injection molding requires a high injection pressure.
For example, when using a rigid polyvinyl chloride (UPVC) with a specific gravity of 1.38 to mold a toy portrait, the plastic part and the runner plastic weigh 4 ounces, and the injection molding machine needs to be injected. The injection weight characterized by PS = 4*1.05/0.38 =3.04 oz. Using the 85% guide, the required injection injection weight = 3.04 / 0.85 = 3.58 oz.
(2) Injection molding machines with excessive injection weights should not be used. The total weight of plastic parts and runner plastics should be between 35% and 85% of the injection weight. The lower limit is due to three considerations: the bending of the stencil, the residence time of the plastic in the barrel and the power consumption per kg of the injection molded part.
The use of a small mold for a small injection molded part can cause the template to bend excessively, causing him to scratch (affecting product quality) and even rupturing the template.
Injection molding of small plastic parts with an oversized injection molding machine, too long a residence time of the melt will cause the plastic to decompose.
The use of a multi-cavity or larger die size can solve some of the problems of molding small plastic parts with large machines. Reducing the temperature of the barrel also eases the decomposition of the speech due to the long dwell time.