The Plastic Manufacturing Process

1.                            Plastic Injection Molding Process

Injection molding is one of the main methods by which parts are manufactured from plastic. The first step in the injection molding process is to feed plastic pellets into the hopper, which then feeds the pellets into the barrel. The barrel is heated and contains a reciprocating screw or a ram injector. A reciprocating screw is typically found in machines that produce smaller parts. The reciprocating screw crushes the pellets, making it easier for the plastic to be liquefied. Toward the front of the barrel, the reciprocating screw propels the liquefied plastic forward, thereby injecting the plastic through a nozzle and into the empty mold. Unlike the barrel, the mold is kept cool to harden the plastic into the correct shape. The mold plates are held closed by a large plate (referred to as a movable platen). The movable platen is attached to a hydraulic piston, which puts pressure on the mold. Clamping the mold shut prevents plastic from leaking out, which would create deformities in the finished pieces.

2.                            Plastic Extrusion Molding Process

Extrusion molding is another method of manufacturing plastic components. Extrusion molding is very similar to injection molding and is used to make pipes, tubes, straws, hoses and other hollow pieces. Plastic resin is fed into a barrel where it is liquefied. A rotating screw propels the liquefied plastic into a mold, which contains a tube-shaped orifice. The size and shape of the tube determines the size and shape of the plastic piece. The liquefied plastic then cools and is fed through an extruder, which flattens the plastic and forms the piece into its final shape.

Issues That Arise in the Plastic Manufacturing Process

A number of complications can arise during the plastic manufacturing process, including burned parts, deformities, surface imperfections and brittle parts. Parts become burned when the molds are not kept cool or if the melting temperature in the barrel is too high. Additionally, if the reciprocating screw becomes jammed or is not rotating fast enough, liquefied resin will remain in the barrel too long and become scorched. Surface imperfections and deformities occur when the surface temperature of the mold is uneven, if the molds are not clamped tightly enough or if the melting temperature is too high. Brittle pieces are formed when not enough liquefied resin is injected into the mold or if the plastic hardens before the mold can be filled. Regular testing and calibration of injection and extrusion molding machines is critical to ensure that the process runs smoothly.

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Using a Valve Gate for Injection Molding

How to Use a Valve Gate for Injection Molding

A hot runner system with a valve gate can lower the production cost of molded plastic parts.

A hot runner system offers some significant advantages in injection molding. A key component of such a system is the valve gate. The valve gate shuts off the flow of molten plastic to the mold at a specific time right at the part surface. This allows a part to be molded without a sprue or runner remaining on the part. Eliminating the sprue or runner improves the appearance of the part, may shorten cycle times, eliminates the need for a runner removal operation and eliminates the waste associated with a discarded runner or sprue.

How to use a Valve Gate in Molding

1

Size and select a valve gate in tandem with the hot runner system. The hot runner system provider will aid in the selection process. In many cases, the mold maker will coordinate this effort. The material to be molded and the overall part design will be the fundamental keys to sizing a valve gate.

2

Install the mold with a hot runner system and the valve gate in an injection press. The electronic controls for the valve gate will need to be tied to the press timer that times the injection cycle. Additionally, valve gates are often pneumatically or hydraulically actuated. Ensure that proper controls are set up to actuate the valve.

3

Determine the time in the injection cycle when the gate should be closed. This will be a function of the rate of material flow and the size of the part. Once the mold has been sufficiently filled by molten plastic to produce acceptable quality, there is no need for additional plastic to be injected. This is when the gate can be closed and the melt procedure for the next cycle can begin.

4

Set the actuator on the valve gate to shut when the injection timer reaches the time determined in the previous step.

5

Set the actuator on the valve gate to open when the injection timer is reset at the beginning of the next cycle.

6

Commence operating the injection press as per normal operating conditions.

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what's color mold? double shot molding two shot mold double injection

Color mold : two on the same plastic injection molding machine , a two- molding, but the product just only in one mold die . In general, this is also called double injection molding process. it is usually done by a mold , and need specialized color injection molding machine . Color mold growing popularity on the market today , it can make the appearance of the product is more beautiful from the process, easy to change colors and no no painting, also expensive and high technically demanding .

1 two female molds are different , each forming one kind of products, and the two male molds are the same.

2 before the mold, the mold in the center of the rotation after 180o, must match. This inspection must be done during mold design , this points have high demand for the mold base positioning  process.

3 The total thickness of the front plate plus A plate must be not less than 170mm. Please carefully review the reference data of the injection molding machines. for example, the maximum and minimum thickness of the mold, KO -hole distance etc.

4 the gate of three plates mold preferably designed to automatically release action. Particularly pay attention to the gate release of soft part..

5 when design the second injection of the female die , in order to avoid secondary mold insert ( or rub ) the first part with good product molding, can make some clearance . However, the intensity must be carefully considered . During injection ,if there will be a big injection pressure , it will cause deformation , resulting in flash problem in the second injection ?

6 during the injection , the first injection molded product may be slightly larger size , so that it can be formed in the second well tightly, in order to achieve the effect of sealing compound .

7 pls note that in the second injection , the plastic flow will impulse the first product and cause part deformation ? If there is the possibility, must find ways to improve .

8 Before A, B plate clamping , pay attention to the mold slider or lifter ,if they will be reset and the crushed product ? So , we must find ways to make the A, B plates first clamping , then make the slide or lifters reset second.

9 the water of two female molds and the male mold transport as fully and balance as possible

10 99% of the injection molded hard plastic case is the first part of the product , and then injection molded soft part . Because soft part have deformation problem .