How to purchase suitable china injection machine

Generally speaking, most of the customers who have been engaged in the injection molding industry for many years, have the ability to judge for themselves and choose the suitable china injection machine to produce. However, in some cases, the customer may need the manufacturer’s help in deciding which injection molding machine to use, or even the customer may just have the sample or idea of ​​the product and then ask the manufacturer. whether the machine can be produced or which model is compared.

In addition, some special products may require special devices such as pressure accumulators, closed loops, injection compression, etc., to be produced more efficiently. It can be seen that how to determine the appropriate injection molding machine to produce is an extremely important question. The following information is provided for the convenience of readers.

Important factors that generally affect the selection of an injection machine include molds, products, plastics, molding requirements, etc. Therefore, the following information should be collected or available before making a selection:

◆ Mold size (width, height, thickness), weight, special design, etc. ;

◆ Type and quantity of plastic used (a single raw material or several plastics);

The appearance size (length, width, height, thickness), weight, etc. injection molded product;

After getting the above information, you can follow the steps below to select a suitable injection machine:1. Choose the right model: the model and series depend on the product and the plastic. Because there are many types of china  injection machines, it is necessary to determine correctly from which injection molding machine or series the product should be initially made, such as common thermoplastic or bakelite raw materials or PET raw materials. Color, two-color, multicolor, interlayer or mixed color, etc. In addition, some products require conditions such as high stability (closed loop), high accuracy, very high fire, high firing pressure or fast production (multi-loop), and a suitable series must also be selected for production.

2. It can be put down: the mold size determines whether the “large column inside distance”, “mold thickness”, “minimum mold size” and “mold plate size” of the machine are suitable to ensure that the mold can be put down.

◆ The width and height of the mold must be less than or at least one side smaller than the inside distance of the large column;

◆ The width and height of the mold must correspond to the minimum mold size recommended by the injection molding machine and is too small.

3. It can be obtained: the mold and the final product determine whether the “mold opening strokes” and “mold strokes” are sufficient to remove the final product.

◆ The opening stroke of the mold must be at least twice the height of the final product in the direction of opening and closing of the mold, and the length of the casting must be included;

4. The clamping unit that can lock the injection  machine must provide enough “clamping force” to prevent the mold from being opened. The calculation of the clamping force requirement is as follows:

◆Calculate the projected area of ​​the finished product in the direction of the switch mold from the appearance size of the finished product;

◆Mould support force = projected area of ​​the finished product in the direction of the switch mold (cm2) × number of mold cavities × pressure in the mold (kg/cm2);

◆The pressure in the mold varies with the raw material, and the general raw material is 350～400kg/cm2;

◆The clamping force of the machine must be greater than the clamping force, and for the sake of safety, the clamping force of the machine is usually 1.17 times greater than the clamping force.

5. Full shot: Determine the required “injection volume” from the weight of the finished product and the number of mold cavities and select the appropriate “screw diameter”.

◆The number of mold cavities (one mold and several cavities) should be considered when calculating the weight of the finished product;

◆For the sake of stability, the injection volume must be 1.35 times the weight of the finished product, that is, the weight of the finished product must be within 75% of the injection volume.

6. Good injection: the conditions of “screw compression ratio” and “injection pressure” are determined by the plastic. Some engineering plastics require higher injection pressure and appropriate screw compression ratio design to have better molding effects. Therefore, in order to make the finished product shot better, the injection pressure requirements and compression ratio issues must also be considered when selecting the screw. .

7.7. Shooting fast: and confirmation of “shooting speed”. Some finished products require high injection rate and rapid injection for stable molding, such as ultra-thin finished products. In this case, it may be necessary to confirm whether the injection rate and rate of injection of the machine are sufficient, and whether it needs to be equipped with pressure accumulators, closed-loop control and other devices. Generally speaking, under the same conditions, a screw that can provide a higher injection pressure usually has a lower shot speed, on the contrary, a screw that can provide a lower injection pressure usually has a higher shot speed. Therefore, when selecting the screw diameter, the injection volume, injection pressure and injection rate (injection speed) need to be cross-considered and selected.

In addition, a multi-loop design can also be used to shorten the molding time with synchronized compound actions. After the above steps, in principle, an injection molding machine that meets the requirements can be determined, but there are some special issues that must be considered:

◆The problem of size matching:

Under certain special conditions, the customer’s mold or product may have a small mold size but a large amount of shot, or a large mold size but a small amount of shot. In this case, the standard specifications set by the manufacturer may not be available. To meet customer needs, so-called “size matching” must be carried out, that is, “big wall small shot” or “small wall big shot”. The so-called “large wall and small injection” refers to the original standard clamping die unit with a smaller injection screw. On the contrary, the “small wall and large injection” refers to the original standard clamping unit with a larger injection screw. Of course, there may be several levels of difference between mold clamping and injection.

In actual use, more and more customers will ask to buy the so-called “high-speed machine” or “fast machine”. Generally speaking, in addition to the needs of the product itself, most of the goals are to shorten the molding cycle and increase the output per unit time, thereby reducing production costs and improving competitiveness. Generally, to achieve the above-mentioned purpose, there are several ways:

1. Speed ​​up the injection speed: increase the motor and pump, or add a pressure accumulator (preferably closed loop control);
2. Speed ​​up the feeding speed: increase the motor motor and pump, or reduce the feeding hydraulic motor to speed up the screw speed;
3. Multi-loop system: adopts double-loop or three-loop design to perform compound actions simultaneously to shorten the molding time;
4. Increase the mold waterway to improve the cooling efficiency of the mold.

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