Hot runner mold VS Two plate mold VS Three plate mold
1.Cold Runner Mold:
Refers to the portion between the mold inlet and the product gate. The molten plastic is kept flowing in the runner under the effect of the injection pressure and its own heat. The runner only functions as part of the molding material, but is not a part of the final product. (The runner part is the residue of plastic injection molding.)
Characteristics: The advantages of the cold runner system are that it is easy to use, and able to well meet the aesthetic requirements in some circumstances. The cold runner is able to reduce the acrylate or polycarbonate used for light transmission in the injection mold runner, so as to avoid the visible strips caused by the injection molding in some parts. Disadvantages of the cold runner: (1) More waste of raw materials; (2) Additional steps in the whole production process;
the cold runner mold include two series mold: two plate mold and three plate mold
Two plate mold:
When the mold opens, the cavity plate and the core plate are separated to release the molded product. This is referred to as a single parting surface mold, AKA a two plate mold. Being most widely used, it is the simplest and most basic form of the injection mold, and can be designed as a single-cavity or a multi-cavity injection mold.
Three plate mold
Three plate mold has two parting surfaces. Compared with two plate mold, it adds a partially movable intermediate plate (also called a movable runner plate, on which the gate, runner, as well as other parts and components required for the core are designed) into the fixed mold half, so it is also known as a three-plate (cavity plate, runner plate and core plate) injection mold, which is often used for the single-cavity or multi-cavity pinpoint gate plastic injection mold. When the mold opens, the runner plate is separated from the core plate for a fixed distance on the guide pin in the core, so that the sprue can be removed from between the two plates. The three plate mold features a complicated structure, a high manufacturing cost, and difficult part processing, so usually it is not used for injection molding of large or extra large plastic products
2.Hot Runner mold
As a common part of the injection molding system, the hot runner ensures that the plastic material in the runner and gate keeps the molten state by heating. Since the heating rod and the heating ring are arranged near or in the center of the runner, the whole runner – from the nozzle of the injection molding machine to the gate – is kept in a high temperature status, so that the plastic in the runner is kept molten. Usually, it is unnecessary to open the runner to remove the sprue after shutdown. It is only necessary to heat the runner to the required temperature after the machine restarts. Therefore, the hot runner process is sometimes referred to as hot-manifold system or runner-less injection molding.
Characteristics: The hot runner technology boasts the following advantages when compared with the conventional cold runner: (1) Saving the raw material and reducing production cost; (2) Shortening the molding cycle and improving machine efficiency; (3) Improving product surface quality and mechanical properties; (4) Allowing the application of the pinpoint gate without the three-plate mold system; (5) Economically molding a single product with the edge gate; (6) Improving the degree of automation; (7) Controlling gate freezing with a needle valve gate; (8) Consistent injection molded product quality of the multi-cavity mold; (9) Improving the surface aesthetics of the injection molded product.
Disadvantages of the hot runner mold:
(1) The mold structure is complex, the manufacturing cost and maintenance cost are high; (2) It takes a certain period of time for the start-up process to be stable, resulting in more waste products; (3) When there is melt leakage or heating element failure, product quality and production schedule are greatly impacted. The 3 mentioned disadvantages can be improved through the purchase of high-quality heating elements, hot runner plates and nozzles, with careful maintenance during production.
Advantages of the Hot runner mold
(1). The diameter of a hot runner is generally larger, and the melt is kept at a high temperature in the hot runner. Therefore, the shear stress and pressure drop of the molten plastic in the hot runner are much lower than those flowing in the cold runner, thus able to deliver the homogenous (relatively identical pressure and temperature) melt to all the gates, which is advantageous for the injection molding of high quality products (especially thin-walled products), as well as the development of multi-cavity molds.
(2). The cold runner mold tends to have a too long cycle time because it is too thick compared to the product. In such circumstances, a hot runner has a shorter cycle time because it does not have to be cooled and solidified.
(3). Saving the raw material and reducing product cost are the most prominent features of the hot runner mold. In the ordinary gating system, a large number of sprues are generated, and in the production of small-sized products, the weight of the gating system sprue may exceed the weight of the product. Since the plastic is always in a molten state in a hot runner mold, the product gate does not need to be trimmed, and basically no waste is generated, so that a large amount of raw materials can be saved. Since no waste recycling, selection, crushing, dyeing or other process steps are required, it is able to save labor, time, and energy, thus reducing consumption.
(4). When combined with the valve gate, the hot runner system is able to change the filling pattern, eliminate or transfer weld lines, air traps, and the like.
(5). Simplified operation and reduced molding cycle are also important features of a hot runner mold. Compared with the cold runner, the opening and closing stroke is reduced, which not only shortens the demolding and molding cycles of the workpiece, but also facilitates automated production. According to statistics, compared with the cold runner system, the molding cycle after switching to the hot runner system can usually be improved by 30%.