So-called machine adjustment refers to continuous adjustment of various parameters of injection molding machine for a specific mold until qualified plastic parts are produced. Various parameters of plastic injection molding machine can be roughly classified as follows:

 

For a specific mold, before mold is put on, following three parameters must be considered first:
1.1 Mold size:
That is, Moho*Move*(Mothmi~Mothma) of injection molding machine. Its items must be greater than corresponding items of mold: Mwid*Mlen*Mthi width x height x thickness)
Maximum shot size:
It is maximum weight of plastic that can be injected by injection molding machine, SHWT (g). The total weight of each piece of plastic must be less than (or equal to) 85% SHWT and greater than (or equal to) 15% SHWT. (When the total weight of each piece is > 85% SHWT, injection molding efficiency will be reduced).
1.3 Clamping force:
It is maximum separation force that mold can withstand after mold is closed. Its size is approximately proportional to projected area of molded part. Rough calculation formula is as follows:
Clamping force (tons) = Projected area of cavity (inch2) * Material pressure coefficient
Among them, material pressure coefficient of PS, PE, PP is 1.7; ABS, AS, PMMA is 2: PC, POM, NYLON is 3.
For a specific mold, actual clamping force = rated clamping force of injection molding machine * 90%. Too much clamping force is not good for injection molding machine and will cause mold deformation.

Temperature in injection machine production process is set differently according to different rubber materials, and it can be divided into following types:
2.1 Partial material temperature:
During injection machine production, moisture content in raw materials needs to be dried to a certain percentage, which is called partial material. Because raw materials with a moisture content higher than a certain percentage will cause defects such as gas bubbles and delamination.
2.2 Barrel temperature:
Barrel from hopper to nozzle can be divided into: conveying section, compression section, and metering section. Heating temperature of each section is collectively referred to as barrel temperature. Barrel temperature is from low to high. In addition, nozzle temperature is usually slightly lower than temperature at metering end.
2.3 Mold temperature:
Refers to surface temperature of mold cavity. Temperature is set differently according to different shapes of various parts of mold cavity. Generally, mold temperature of parts that are difficult to glue is required to be higher, and temperature of front mold is slightly higher than that of rear mold. After temperature of each part is set, temperature fluctuation is required to be small, so auxiliary equipment such as constant temperature machine and chiller are often required to adjust mold temperature.

3.1 Screw position (S):
Segmented conversion position of injection speed and pressure of screw is called screw position. Specific segments are as follows: So-S1→S2→S3→SS. Among them, S0→SS is equal to amount of melt required for one inject, and SS cannot be less than 10mm (generally between 15-20mm); S0, S1, S2, S3, SS are screw position segments, which are specifically set according to position where molten plastic flows through mold cavity. S0→S1→S2→S3→SS is injection section. Among them, S3 and SS are pressure holding sections.
3.2 Glue extraction position (SUCK BACK):
When screw stops rotating after material is returned, screw has a backward evacuation action, which is called glue extraction, and distance of evacuation is glue extraction distance. Generally, it is less than 5mm. Purpose of evacuation is to prevent molten plastic from flowing in nozzle; glue extraction should be appropriate. Too much evacuation will cause defects such as gas flowers and bubbles in finished product.
3.3 Mold opening position:
Distance between rear mold surface and front mold surface is called mold opening distance. Its size is suitable for smoothly removing plastic parts. Too much will extend cycle time.
3.4 Ejector position:
It is distance of ejector pin of mold from rear mold surface. It is better to make product ejected from rear mold surface and be taken down smoothly. Be careful not to let ejector pin reach the end, and sufficient margin must be left to avoid breaking ejector plate of mold.

 

4.1 Injection pressure (IP):
Driving force given by screw to molten glue is called injection pressure. According to various sections of screw position, different screw propulsion forces can be set for molten glue. For example, S0→S1 is IP1; S1→S2 is IP2; S2→S3 is IP3. Setting of propulsion force of each section mainly depends on position of molten glue flowing through mold cavity. When shape of mold cavity through which molten glue flows is complex and glue position is thin, resistance of molten glue is large, and a larger propulsion force is required; when shape of position through which molten glue flows is simple, resistance of molten glue is small, and a small propulsion force can be set to reduce loss of injection machine.
4.2 Holding pressure (HP):
When molten glue fills mold cavity, in order to compensate for space formed in mold cavity due to cooling and shrinkage of rubber and to compact rubber, screw needs to give molten glue a certain propulsion force, which is holding pressure. Position movement of screw here is: S3-SS. Holding pressure is represented by HP. Generally, medium pressure is used for large rubber parts and low pressure is used for small rubber parts. (Under normal circumstances, HP is less than IP).
4.3 Back pressure (BACK PRESS):
When injection and holding pressure are completed, screw starts to rotate. In this way, material originally in screw groove and hopper is pressed into front end of barrel (metering chamber) through screw groove. At this time, molten glue has a reaction force on screw to force screw to retreat, which is called return material. In order to increase density of molten glue in the front end of barrel [metering chamber] and adjust speed of screw back, an adjustable thrust must be added to screw, which is called back pressure. Adjusting back pressure can adjust mixing degree of color powder and plastic raw material, affecting plasticizing effect. Appropriate back pressure can reduce defects of plastic parts such as color mixing, bubbles, and uneven gloss, but back pressure cannot be too large. Too much back pressure will cause molten glue to decompose, thereby causing defects such as discoloration and black lines in plastic parts. In addition, increasing back pressure will inevitably extend production cycle and aggravate loss of injection machine, which is generally about 10kg/cm2.
4.4 MOLD PROTECT PRESS:
Also known as low-pressure protection, it is a protective device for injection machine to mold. From mold protection position to the moment when front and rear mold surfaces are fitted, during this period of time, force of clamping mechanism pushing rear mold of mold is relatively low. At the same time, when a resistance higher than driving force is encountered during advancement process, mold will automatically open and stop cooperating. In this way, if there is foreign matter between front and rear molds during mold closing, mold can be protected. Low clamping pressure is generally larger for molds with slides than for molds without slides. Value is 10-20kg/cm2.
4.5 High clamping pressure (MOLD CONTACT PRESS):
Also known as clamping pressure, when front and rear mold surfaces are fitted together, clamping force automatically changes from low pressure to high pressure. Purpose is to have a certain pressure when front and rear mold surfaces are fitted together, so that slide of mold moves into place. Clamping pressure cannot be too high, which will damage mold surface; when adjusting, it is enough to have a certain pressure on the front and rear mold surfaces, generally 80-100kg/cm2. (Generally, whole clamping state is: slow speed → high speed → low pressure and low speed → high pressure mold closing).
4.6 Ejector pressure:
Ejection force applied by injection machine to the back of ejector plate of mold should be large enough to eject plastic parts.

5.1 Injection speed (V):
Speed at which screw pushes molten glue when injection machine is injecting. Injection speed is mainly affected by injection pressure, resistance of mold cavity to molten glue, viscosity of molten glue itself, and other factors. When injection pressure is greater than cavity resistance and viscosity of molten glue, set injection speed can be fully utilized. For example: S0-S1 is V1, at this time, molten glue fills cavity, low speed and medium pressure are required; Si-S2 is V2, at this time, molten glue fills cavity, high speed and high pressure are required: S2-S3 is V3, molten glue fills periphery of plastic part, medium speed and low pressure are required, and injection speed slowly decreases as filling resistance of mold cavity increases until it is zero. Setting of specific injection speed of each section should be determined according to shape of molten glue flowing through mold cavity.
5.2 Screw speed (R):
Speed of screw when feeding barrel metering chamber is called screw speed. It affects screw's retreat speed. When back pressure is set, the higher screw speed, the greater retreat speed. Adjusting screw speed can adjust plasticizing effect of rubber, improve uneven color tone and color mixing of product. However, too high a screw speed will cause excessive shearing of rubber and decomposition, and will also cause air to mix into the barrel, causing bubbles in product. PC, PE, PVC, POM, PMMA and other thermosensitive plastics with high viscosity are not suitable for high screw speeds. Screw speed is represented by R1 and R2. Generally, R1 is used at medium speed and R2 is used at low speed, which has a protective effect on injection machine.
5.3 Glue extraction speed (SB SPEED):
Retreat speed of screw when it is evacuated is called glue extraction speed. Generally, medium and low speeds are appropriate.
5.4 Mold opening and locking speed:
Mold opening speed is represented by: MO1, MO2, MO3. Generally, slow speed is used when front and rear mold surfaces are separated, so molds with different templates have different settings. Two-plate mold is generally set as: slow, fast, slow; three-plate mold is generally set as: medium, slow, slow. Clamping speed is represented by: MC1, MC2, MC3. Generally, slow speed is used when front and rear mold surfaces are in contact, so two-plate mold is set as: medium, fast, slow; three-plate mold is set as: medium, slow, slow.
5.5 Ejector speed (EJ SPEED):
Speed at which ejector ejects plastic part is called ejector speed. Settings for plastic parts of different structures are different, and medium speed is generally used.

 

6.1 Local material time:
Different plastic materials require different times.
6.2 Injection time (INJ-HOLD TIME):
Time required for screw to move from S0 to S3, and its setting must be consistent with screw position movement.
6.3 Holding time (HT):
Time from screw S3 to start of feeding is generally 1-2 seconds, not too long: too long will waste time.
6.4 Cooling time (COOLING TIME):
Time from screw starting to return material to mold ready to open is cooling time: cooling time cannot be less than return time.
6.5 Cycle time (CYCLE TIME):
Time required for brewing machine to start brewing from beginning to next brewing. Requirement is that the shorter inject, the better, on premise of brewing qualified rubber parts.