Set method of screw advance time and maintenance points of heating system of injection molding machi

Time:2023-05-24 08:56:40 / Popularity: / Source:

Injection cycle

Injection molding cycle refers to time required for injection molding machine to complete a specific set of actions. Therefore, action time of each part may affect the entire cycle time. To achieve purpose of shortening cycle time and improving production efficiency, each part of action should be considered separately in order to identify part that may shorten time, which often saves a little time for each part. While this savings may be small, when these times are added together, time reduction is significant in terms of the overall percentage reduction.

Dry run time of injection molding machine

Dry run time is time it takes for an injection molding machine to complete a full cycle when it is empty, i.e. without any plastic in injection molding machine. Regardless of size and type of injection molding machine, know idle operation of injection molding machine first when you are trying to change operation, because it helps injection molder to determine whether a particular injection molding machine is capable of producing at high output or maintaining that output. . Therefore, before trying to reduce operation time, consider whether operation time can be reduced in terms of injection molding status, age and idle time.
maintenance of heating system of injection molding machine 

General injection molding machine dry run time

Cooling time factor is the longest part of injection molding cycle, but it is the one where significant savings can be made. Although it can be calculated, it is usually determined empirically, such as gradually reducing cooling time until non-deformed injection molded parts are continuously produced. During cooling phase, enough time is needed to retract screw (sometimes called screw reset or metering time) to refill shot cylinder with plastic (to place injection in mold again). Otherwise, injection molding process will not be able to proceed.

Calculate cool down

Two main effects of controlling cooldown time are:
1. Curing time of thermoplastic being processed.
2. Design of cooling pipes in mold.
Many injection molders rely on mold designer to specify type and amount of cooling that a particular mold needs from time to time, but cooling system used is simply not sufficient. Cooling energy required for mold must be calculated to obtain specified and run time.
By calculating cure time for a particular injection molded part, plastic combination, resulting value may become basic cooling requirement for a given mold.

Cooling time (seconds) for general plastics with different material thicknesses

Above calculation value is time required for material to cool to mold temperature, but in many cases this is time for material to cool to deformation resistance temperature. And this time determines that injection molded parts can be ejected without deformation. Therefore, above values can be understood as maximum value.

Setting of screw advance time (SFT)

Calculate mold fill time, add 0.5 seconds to this, and produce approximately 5 injection molded parts at this setting. Each injection molded part is weighed and/or measured, then value is indicated. Average should be calculated and then repeated as the SFT time increases (eg 0.5, 1.0, 1.5, 2.0 seconds, etc.). Time is increased until average weight or measurement of injection molded part remains same, which gives correct SFT time.

Influence of gate size on SFT

To make above process efficient, use a gate of appropriate size for each injection, and gate hole should not be so small that condensation closes gate before cavity is filled with molten plastic. On the other hand, size of gate should not be too large. This prevents cold or semi-solid plastic from being pushed through gate and into mold, which can cause pressure and cracks in gate area. For these reasons, wall thickness (depth) should be between 0.61 and 1.0t (t is wall thickness of specified part).

Maintenance points of heating system of injection molding machine

If AC contactor runs for a long time and operates frequently, its main contacts will be singed, damaged or have poor contact. Regular maintenance is essential. Contactor coil will run on electricity for a long time, which will also cause heat deterioration, noise, etc., so it needs to be replaced frequently.
Geating tube runs for a long time and has a certain period of use. But common fault is short circuit of power wire, burning out magnetic connector or terminal of heating cylinder. Short circuit of power supply is mostly caused by human factors, such as pulling of wiping machine, leakage of glue during injection molding, and loose connection point. Therefore, when replacing heating tube, it must be installed firmly and wiring is reliable. First, pre-tighten wiring of heating tube terminal, and then connect power cord. Generally, after working for a few hours, heating cylinder should be pre-tightened again to avoid loosening of connection points caused by thermal expansion and cold contraction.
maintenance of heating system of injection molding machine 
Temperature controller is heart of heating circuit. Its accuracy directly affects quality of injection molding products, especially for plastics with accurate temperature requirements, otherwise rubber will be scorched, discolored or burned. Temperature controller collects temperature signal of heating cylinder, compares it with set temperature signal, and controls whether to heat or keep warm through temperature controller.
Thermocouple is a temperature sensing element, which should be installed reliably, inserted into temperature detection hole in a proper position, connection of thermocouple lead wire should be firm and reliable. In general use, temperature control table has a certain error, and temperature control accuracy can be checked by measuring with a thermometer. Commonly used rubber compound can also be used with an error of ±10℃.
The most common fault of temperature controller is control failure, mainly due to singeing and sintering of relay contacts in watch, which causes temperature to fail, and temperature control is inaccurate. Large error range is caused by failure of dial switch or deterioration of performance of integrated circuit inside thermometer, and it can also be caused by failure of internal circuit such as Zener diode, potentiometer, precision resistor and so on. A bad thermometer head also leads to loss of control.
To repair heating circuit, you can start from power supply part to heating cylinder part, measure and adjust circuit to determine fault point and components, then replace damaged components, finally debug and correct. When replacing components, pay attention to model, shape, specification and parameters, especially graduation number of thermocouple, power of heating tube and parallel installation. Nozzle heating cylinder should try to avoid being damaged by leaking glue.

Go To Top