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2013-06-19 cropsong 103


The basic composition of injection mold

Injection mould comprises a movable mould and the fixed mould is composed of two parts, the dynamic model is installed in the mobile template for injection molding machine, mould installed on the fixed template for injection molding machine. In the injection molding die and the fixed mold closed form of gating system and cavity, during the opening of the movable mould and the fixed mould separation in order to remove the plastic products.
Although the plastic mould structure and performance of varieties, the plastic products shape and structure and the types of injection machine and may the myriads of changes, but the basic structure is the same. Mainly by die casting system, cooling system, molding parts and structural parts. The gating system and molding parts are in direct contact with the plastic parts, and varies with plastics and products, is the most complex, mold changes, requirements of part machining accuracy and finish the highest.
The gating system refers to the plastic from the nozzle into the flow passage cavity before, including the mainstream, cold material, runner and gate. Molding parts refers to various parts of the form of product shape, comprising a movable die, mold cavity, core, forming rod and the exhaust port. Typical mold structure as shown below.

1. The pouring system

The pouring system is also called the runner system, it is the plastic melt from the nozzle injection machine to the cavity of a group of feeding channel, usually composed of the sprue, runner, gate and cold material. It is directly related to the forming quality and production efficiency of plastic products.

(1). Main channel

It is a channel connecting mold injection machine nozzle to shunt or cavity. The mainstream top is connected with the nozzle to the concave. Main runner inlet diameter should be slightly larger than the diameter of the nozzle (O.8mm) in order to avoid overflow, and prevent the occur because of cohesion not intercept. Inlet diameter depending on the product size, generally 4-8mm. Sprue diameter should be enlarged to 3 ° to 5 ° angle, so that the new release channel.


(2). Cold material

It is a hole in the mainstream Road end, used to trap cold material between the nozzle end portion of the two injection, so as to prevent clogging runner or gate. If the cold material once into the cavity, the system is easy to produce stress products. Cold material diameter is about 8 lOmm, depth is 6mm. In order to facilitate the release, the bottom is often borne by the release lever. The top of the ejector pins should be designed into the winding hook or sinking groove, so that the mold can smoothly sprue pulling block.

(3). Runner

It is a channel connecting the sprue and cavity multiple slot die. As the molten material with a constant velocity with the cavity in the mold, the shunt arrangement should be symmetrical and equidistant distribution. The runner section shape and size of plastic melt flow, demolding and mold manufacturing difficulty are affected. If equal amount of material flow, the flow resistance of circular cross-section of the minimum. But because of the cylindrical channel of small specific surface, unfavorable to the cooling flow channel block, and the runner must be opened in the two modules, is time-consuming, easy alignment. Therefore, is often used in shunt trapezoidal or semicircular cross section, and the opening in the half mold with a stripper. Channel surface must be polished to reduce flow resistance for mold filling speed. The flow of size depends on the varieties of plastic products, the size and thickness of. For most thermoplastics, runner section width is less than 8m, especially up to 10 12M, small 2-3m. To meet the needs of the premise should be reduced as much as possible to avoid increasing the cross-sectional area, the shunt block and extend the cooling time.

(4). Gate

It is connected to the mainstream (or shunt) and the cavity of the channel. Area channel can and main channel (or shunt) equal, but usually smaller. So it is the smallest part of the runner system of sectional area. Effect of gate size and shape on the quality of the products greatly.
The gate is the role of:
A, control the material flow rate.
B, the injection can prevent the backflow by the molten material in this part of the early setting.
C, the molten material by the subject to strong shear and elevated temperature, thereby reducing the apparent viscosity to improve liquidity.
D, convenient products and runner system separation. Size and structure design depends on the gate shape, size and position of the nature, in plastic products. General gate section shape is rectangular or circular, cross-sectional area should be small and length should be short, which not only based on the role, but also because of the small gate becomes easier, and the big gate narrowing is very difficult. General should in the thick gate location and do not affect the appearance. Design of gate size should take into account the nature of plastic melt. The cavity is molded plastics mold space. Used as a form of cavity components are collectively referred to as molding parts. Each molded parts often have special name. A forming parts shape called die (also called die), the internal shape of formed products
(such as holes, grooves) known as the core or punch (also known as male). The design of molding parts must first to determine the overall structure cavity according to performance, plastics geometry, tolerances on dimensions and requirements. The second is determined according to the structure of parting surface, gating and exhausting hole location and demoulding mode. Finally, according to the control size of the design of each part and determine the combination between the various components of the. High pressure plastic melt into the cavity, thus forming parts should be reasonable material and its strength and stiffness. In order to ensure the smooth and clean surface of plastic products and easy demoulding, all with plastic contact surface, the roughness Ra>0.32um, and resistant to corrosion. Molding parts to improve hardness usually by heat treatment, and is made of corrosion resistant steel.

2. Temperature control system:

In order to meet the requirements of the injection process of die temperature, need to mold temperature control system for temperature regulation. For the injection molding of thermoplastic, mainly is the design of cooling system of the mold cooling. The common method is to open mold cooling cooling water channel in the die, die away by cooling water circulating heat; mold heating and cooling water channel can use hot water or steam, can also be provided with an electric heating element in the mold inside and around.

3.  Molded parts:

Molding part is composed of the core and cavity. Core form the inner surface products, die forming the outer surface shape products. After the mold core and cavity formed cavity mould. According to the process and manufacturing requirements, sometimes core and die is composed of a plurality of pieces together, sometimes as a whole, only in the easy damage, difficult machining parts use insert.
The exhaust port
It is a groove is provided in the mold shaped outlet, use gas to discharge the original and melt into the. Melt into the cavity, the original is stored in the cavity of air and gases from the melt into the stream must be in the end through the exhaust port to the die out, otherwise will make products with porosity, poor contact, filling, and due to the compression of air temperature and the product burn. In general, the exhaust hole can be located in the flow cavity melt end, can also be arranged on the mold parting surface. The latter is the creation of deep 0.03-0.2mm in the die side, shallow groove width 1.5-6mm. Injection, exhaust hole will not have a lot of the melt exudation, because the melt in the cooling and solidifying the channel blocked. Location is not opposite operator exhaust port, to prevent accidental wounding people melt. In addition, may also use the ejector and ejector clearance hole, the top block and the removal of the template and the core of the clearance to exhaust.

4. Structural parts

It refers to constitute the various parts, die structure includes: various parts of the guide, mould, core pulling and typing. Such as before and after the splint, and buckle template, bearing plate, a bearing column, a guide post, stripper plate, ejector rod and a return pole.

(1). Guide member

In order to ensure that the movable mould and the fixed mould in the mould can accurately to guide member, must be set in the mold. In the injection mold is often used in the four groups of the guide post and the guide sleeve to guide does not see, sometimes also in the die and mould are respectively arranged with each other inside, outside the cone to the auxiliary positioning.

(2). Release mechanism

In the open mold process, need to launch plastics and aggregate in the flow channel to launch or pulled out. Introduction to clamp the push rod is fixed plate and the push plate. The push rod is fixed in the general reset rod, a reset lever in the dynamic, mold is combined to push plate reset.

(3). Side core-pulling mechanism

Some with side concave or side hole to plastic products, was introduced to the former must first side parting, taking lateral core rear demould smoothly, this time need side is arranged in the mold core pulling mechanism.

(4). Standard mold

In order to reduce the heavy workload of the mold design and manufacturing, injection mold adopts the standard mold.