Points To Note When Choosing an Injection Molding Machine

Jan. 27, 2021


1.choose the right type:


The model and series are determined by products and plastics. Since there are many kinds of Injection Molding Machines, it is necessary to correctly judge which injection molding machine or series should be used to produce this product, such as general thermoplastic plastics or bakelite raw materials or PET raw materials, which are monochrome, bicolor, multicolor, sandwich or mixed colors. In addition, some products need high stability (closed loop), high precision, ultra-high firing rate, high firing pressure or rapid production (multi-loop), etc., and suitable series must be selected for production.


2.Put it down:


Determine whether the big column inner distance, die thickness, die * small size and die plate size of the machine are appropriate according to the die size to confirm whether the die can fit. The width and height of Plastic Mold should be less than or at least one side should be less than the distance between large columns. The width and height of the die * are within the size range of the die plate; The thickness of the mold should be between that of the injection molding machine. The width and height of the mold should conform to the * small mold size recommended by the injection molding machine, but it is too small.


Injection Molding Machines

Injection Molding Machines


3.Get:


Determine whether the mold opening stroke and mold supporting stroke are enough for the finished product to be taken out by the mold and the finished product. The mold opening stroke should be at least twice the height of the finished product in the direction of mold opening and closing, and the length of sprue should be included. The stroke of supporting die should be enough to push out the finished product.


4.Lock it:


The tonnage of clamping force is determined by products and plastics. When the raw materials are injected into the mold cavity at high pressure, there will be a force to support the mold, so the mold locking unit of the Vertical Injection Molding Machine must provide enough clamping force to prevent the mold from being opened. The calculation of clamping force demand is as follows: (1) calculate the projection area of the finished product in the direction of switching die from the appearance size of the finished product; The mold supporting force = the projected area of the finished product in the direction of opening and closing mold (cm2)× the number of mold cavities × the pressure in the mold (kg/cm2); The in-mold pressure varies with the raw materials, and the general raw materials are 350~400kg/cm2. The clamping force of the machine needs to be greater than the supporting force, and for the sake of safety, the clamping force of the machine usually needs to be more than 1.17 times of the supporting force. So far, the specifications of the mold 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 screw diameter that meets the requirements.


5.shoot full:


Determine the required shot quantity and select the appropriate screw diameter according to the finished product weight and the number of die holes. The number of die holes (several holes per die) should be considered in calculating the weight of finished products; For the sake of stability, the injection quantity should be more than 1.35 times of the finished product weight, that is, the finished product weight should be within 75% of the injection quantity.


6.Good shot:


Judging screw compression ratio and injection pressure by plastic.


Some engineering plastics need higher injection pressure and suitable screw compression ratio design to have better molding effect. Therefore, in order to make the finished products shoot better, the injection pressure and compression ratio should also be considered when selecting screws. Generally speaking, a screw with a smaller diameter can provide a higher ejection pressure.


7.Fast shooting: confirmation of shooting speed.


Some finished products need to be shot at high shooting rate and speed in order to form stably, such as ultra-thin finished products. In this case, it may be necessary to confirm whether the shooting rate and shooting speed of the machine are sufficient, and whether it is necessary to match the pressure accumulator, closed loop control and other devices. Generally speaking, under the same conditions, the screw that can provide higher firing pressure usually has lower firing rate, on the contrary, the screw that can provide lower firing pressure usually has higher firing rate. Therefore, when selecting the screw diameter, the injection quantity, injection pressure and injection rate (injection speed) need to be considered and chosen. In addition, a multi-loop design can be adopted to shorten the molding time by synchronous compound action.


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