How To Adjust Process Parameters

How To Adjust Process Parameters

Some of our customer always ask: How To Adjust The Injection Molding Process Parameters?

To operate plastic injection machines you need attention to these tips, it will help you to operate the injection moulding machine well.

◆    Temperature

First, It’s very important to take and control the temperature in plastic production. Although it’s comparatively easy to take these measures,

most of the injections molding machines don’t have enough temperature recovery points or lines. 

On most injection molding machines, the temperature as sensed by the thermocouple.

A thermocouple is basically composed of two different wires connected with the tails.

If one end is hotter than the other, small telecommunication will appear. The more heating, the stronger the signal becomes.

◆    Temperature control

A thermocouple is widely used as the sensor of the temperature control system.

Set the desired temperature on the control instrument and the display on the sensor will be compared with the temperature produced in the set point.

In the simplest system, when the temperature reaches the setting point,

it will be turned off, and vice versa. The system is called on-off control because it’s not on or off.

◆    Melt glue temperature

The melt glue temperature is very important. The use of the injection cylinder temperature is only guiding.

The melt glue temperature can be taken at the nozzle or by using air sparging.

The injection cylinder temperature setting depends on the melt glue temperature,

the rotational speed of the screw, the backpressure, the shot weight, and the injection molding cycle.

If you don’t have the experience of producing a special level of plastic, please start from the lowest setting.

In order to facilitate control, the injection cylinder is divided into regions, but not all of them are set at the same temperature.

If operating for a long time or under high temperatures, please set the temperature of the first region at a very low figure.

This will avoid the plastic premature melting and splitting.

Before injecting the plastic, make sure the temperature of the hydraulic fluid, the hopper sealing device, the mold and the injection cylinder at a correct temperature.

◆    Injection molding pressure

The pressure can cause plastic flow. It can be measured by using the sensor on the nozzle or hydraulic lines.

If it doesn’t have fixed figures, with the mold filling becoming more difficult,

the injection pressure increases. The injection molding line pressure is directly related to the injection pressure.

◆    The pressure of the first stage and the second stage.

In filling the stage of the injection molding cycle, it may require high injection pressure to maintain the required molding speed.

After filling, the mold no longer needs high pressure.

But in the injection process of some semi-crystalline thermoplastics (e.g. PA and POM), the sudden change of pressure will result in structural deterioration,

thus sometimes the use of secondary phase pressure may not be necessary.

◆    Clamping pressure

To counter the injection pressure, instead of automatically choosing the maximum value that can be used,

locking pressure must be applied in a bid to figure out a suitable value in terms of the projection area.

The projection area of injection molded parts is the largest area seen from the application direction of the clamping force.

For most mold injection cases, it is about 2 tons per square inch or 31 mega per square meter newton.

However, this is only a low value and should be regarded as a very rough experience value, because once the injection parts have any depth, the side walls must be taken into consideration.

◆    Backpressure

This is the force the screw produces and has to surpass when it returns back.

High backpressure is helpful to uniformed dispersion of pigment and plastic melting, but also extends the return time of the middle screw,

reduces the fiber length of the filling plastic and increases the stress of the injection molding machine; As a result, the back pressure should be as low as possible,

and does not exceed 20% of the injection pressure (the highest quota) of the molding machine in any case).

◆    Nozzle pressure

Nozzle pressure is the pressure inside the nozzle.

It roughly equals the forces that cause the plastic flowing. It does not have a fixed value,

but increasing with the difficulty of mold filling. There is a direct relationship between the nozzle pressure, the line pressure, and the injection pressure.

In the screw injection molding machine, the nozzle pressure is approximately ten percent less than the injection pressure.

However, in the piston type injection molding machine pressure loss can be about ten percent.

However, in the piston type injection molding machine pressure loss can be about 50 percent.

◆    Injection molding speed

This is the speed when the screw acts as a punch. When injection molding thin-wall products,

high molding speed must be applied in order to produce a smooth surface when the melting plastic not completely becomes solid;

During the filling process, a series of procedural molding speed is used to avoid defects such as spraying or trapped gas.

The injection can be carried out in the open-loop or closed-loop control system.

Regardless of the injection speeds, speed values together with the injection time must be recorded on a recording sheet.

Injection time refers to the time the mold to achieve the first stage of a predetermined shooting pressure,

a part of the screw rod propulsion.

All kinds of the plastic drying reference table:

Plastic materials Dryers Drying time / h Dry temperature ℃
ABS A 2-4 80-100
ABS/NOLON D 1-3 80-100
ABS/TPC D 3-4 80
POM* A 1-4 85
ACRYLIC D 2-3 70-100**
EVA A 1-2 **
NYLON6 D 2-4 80
NYLON6/6 D 2-4 80
PC D 4 120
PC/POLYESTER D 3-4 120
PC/ABS D 3-4 80-110**
PPS A 2-3 130-150
PP* A 1-2 70
PPO D 2-4 100-120**
PS* A 1-2 70-80
PSF D 4 130-140
PV D 1-4 80-100**
PBT D 2-4 120-140
PBT D 8 100
PET D -4 140
PET D 2-4 110
ELASTOMER D 2-3 80-110**
ELASTOMER A 4-6 80-110**
PVC A 2 60-80**
SAN A 2-3 80-100
TPO* A 1-2 50-70**
2019年9月24日 Industry News