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How to choose a second-hand injection molding machine

January 13, 2023

How to choose a second-hand injection molding machine

The important factors that usually affect the selection of injection molding machine include mold, product, plastic, molding requirements, etc. Therefore, the following information must be collected or obtained before making a selection: 1. Mold size (width, height, thickness) , weight, special design, etc.; 2. The type and quantity of plastic used (single raw material or multiple plastics); 3. The appearance size (length, width, height, thickness) and weight of the injection molded product; 4. Molding requirements, such as Quality conditions, production speed, etc. After obtaining the above information, you can follow the steps below to choose a suitable plastic injection molding machine:

1. Choose the right type:

Since there are many types of second-hand injection molding machines, it is necessary to correctly judge which type of injection molding machine or which series the product should be produced at the beginning, such as general thermoplastic or bakelite raw materials Or PET raw materials, etc., are single-color, double-color, multi-color, interlayer or mixed color, etc.

In addition, some products require high stability (closed loop), high precision, ultra-high injection rate, high injection pressure or rapid production (multi-loop), etc., and the appropriate series must also be selected for production.

2. Can fit the injection mold:

Determine whether the “big column inner distance”, “mold thickness”, “minimum mold size” and “mold plate size” of the machine are appropriate according to the mold size, so as to confirm whether the mold can be placed.

Note: ①The width and height of the mold must be smaller than or at least one side is smaller than the inner distance of the large column; ②The width and height of the mold should preferably be within the size range of the mold plate; ③The thickness of the mold should be between the mold thickness of the injection molding machine; ④The width and height of the mold must meet the minimum mold size recommended by the injection molding machine, and it is not acceptable if it is too small.

3. Take out injection molding products:

Determine whether the “mold opening stroke” and “mold ejection stroke” are sufficient for the finished product to be taken out by the mold and the finished product.

①The mold opening stroke must be at least twice the height of the finished product in the direction of opening and closing the mold, and must include the length of the vertical sprue;

②The ejection stroke must be sufficient to eject the finished product.

4. Can lock the plastic solution:

The tonnage of “clamping force” is determined by the product and plastic.

When the raw material is injected into the mold cavity at high pressure, it will generate a force to support the mold. Therefore, the clamping unit of the injection molding machine must provide enough “clamping force” to keep the mold from being stretched. The calculation of the clamping force requirement is as follows:

① Obtain the projected area of ​​the finished product in the direction of the opening and closing mold from the appearance size of the finished product; /cm2); ③The pressure in the mold varies with the raw material, and the general raw material is 350~400kg/cm2; more than double. So far, the specifications of the clamping unit have been preliminarily determined, and the tonnage of the model has been roughly determined. Then, the following steps must be carried out to confirm which injection unit has a more suitable screw diameter.

5. Shot to fill the injection mold cavity:

Determine the required “injection volume” and select the appropriate “screw diameter” based on the weight of the finished product and the number of mold cavities.

To calculate the weight of the finished product, the number of mold cavities (one mold with several cavities) needs to be considered;

For the sake of stability, the injection volume must be more than 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. Injection parameters of injection molding machine:

The conditions such as “screw compression ratio” and “injection pressure” are judged by the plastic. Some engineering plastics require a higher injection pressure and a suitable screw compression ratio design to have a better molding effect. Therefore, in order to make the finished product injection better, the injection pressure and compression ratio must also be considered when selecting the screw. . In general, a smaller diameter screw provides higher injection pressure.

7. Injection speed of injection molding machine:

Confirmation of “injection speed”. Some finished products require high injection rate and fast injection to form stably, such as ultra-thin products. In this case, it may be necessary to confirm whether the injection rate and injection speed of the machine are sufficient , whether it needs to be equipped with pressure accumulator, closed loop control and other devices. Generally speaking, under the same conditions, the screw that can provide higher injection pressure usually has a lower injection rate, and on the contrary, the screw that can provide lower injection pressure usually has a higher injection rate.

Therefore, when selecting the diameter of the screw, the injection volume, injection pressure and injection rate (injection speed) need to be considered and traded off. In addition, multi-loop design can also be used to shorten the molding time with synchronous compound actions.

If you have any questions on injection molding ,plz feel free to ask FLYSE team,we will give you best service!

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