Product weight, theoretical injection capacity, injection weight, product projection area, product wall thickness, cycle, raw materials, clamping force, in-mold pressure, injection rate, injection power, etc.

Theoretical injection capacity (cm3) = screw cross-sectional area (cm2) x injection stroke (cm)
Injection weight (g) = theoretical injection capacity (cm3) x raw material density (g) x specific volume ratio (about 0.86)
Density of commonly used plastics

Usually, there are 2-4 screws available for same machine.
Small screw has a large aspect ratio, high injection pressure, small injection volume, low injection rate, low melt rate, small torque required, and relatively good mixing performance, while large screw is opposite.
When selecting model, screw diameter needs to be determined according to raw materials used in product, weight of product, wall thickness of product, flow length ratio, cycle, and production requirements.
Screw speed refers to speed per minute (rpm) of machine when it is unloaded.
Screw speed (rpm) = oil pump displacement (cc/min.) ÷ hydraulic motor displacement (cc.)
Under allowable value, the faster speed, the shorter pre-plasticization time, but the worse mixing, the greater energy consumption.

Role of injection pressure is to overcome flow resistance, and role of holding pressure is to maintain density of injection molded products. Injection pressure indicated on machine sample refers to static pressure at nozzle. Dynamic pressure is variable, and there will be pressure loss during flow process.
Injection pressure required for each product is difficult to accurately estimate, and can only be simulated in advance with mold flow, or measured during molding. Common plastic injection pressure range (mpa) Plastics are easy to flow thick-walled products with medium flow General products are difficult to flow Thin-walled narrow gate products
Common plastic injection pressure range (mpa)

Injection pressure requirements for thin-walled products with a wall thickness of less than 1.0 mm (mpa)

 

Injection speed refers to maximum forward speed of screw during injection (mm/s);
Injection speed (cm/s) = oil pump displacement (cm3/s) ÷ effective cross-sectional area of ​injection cylinder (cm2);
Injection rate refers to amount of melt ejected from nozzle per unit time (g/s) Injection rate (g/s.) = product weight (g) / filling time (seconds).
Injection speed of general injection molding machines is designed to be between 100 and 150 (mm/s), and speed of thin-wall high-precision injection molding machines is designed to be between 200 and 500 (mm/s); under same injection pressure, the higher injection speed, the greater energy consumption. When injection speed exceeds 200mm/sec., it is best to add an accumulator to save energy consumption; the greater injection speed, the greater pressure loss, so generally the greater speed, the higher injection pressure.
Allowable filling time (seconds) of plastic products = wall thickness square (mm) x filling coefficient (K) Generally, for materials with good fluidity, filling coefficient can be 1, and for materials with poor fluidity, it should be relatively small.
[For example]
PP, PE, PA, PS and other materials can take 1.
For materials such as PC and PMMA, it is generally taken below 0.8.

Plasticizing capacity refers to amount of molten plastic (g/s) that machine can spit out per unit time under 0 back pressure. Plasticizing capacity (kg/h) = 1.29 * screw diameter (cm) * metering section depth (cm) * density * screw speed (rpm) * 60 ÷ 1000 * efficiency (generally 85%).
Plasticizing capacity is related to screw diameter, screw design, and screw speed.
In addition to plasticizing capacity, precision high-end products must also consider plasticizing quality, including plasticizing degree, mixing uniformity, shear heat, etc.
The total material volume of barrel of a general standard machine is about 2.4 times maximum injection weight, and packaging machine is about 2.7 times.
[For example] Diameter of A rod of 300h injection seat is 32mm, injection weight is 106 grams, and the total material volume in screw barrel is about 106 grams x 2.4 = about 254 grams.
Residence time of raw materials in barrel (minutes) = total barrel material (g) / material used per minute (g) Residence time of most raw materials in barrel is about 2 minutes at the shortest (not less than 90 seconds) and between 8 and 12 minutes at the longest. (Residence time is related to temperature of barrel)
[For example] There is a product with 30 grams per mold, PS material, 300h B screw, injection weight of 134 grams, and maximum production per minute: 134 grams x 2.4 / 30 grams / 1.5 minutes = 7.1 molds, which is equal to the fastest cycle of about 8.5 seconds, residence time is 2 minutes, and the fastest cycle is about 11 seconds.

Clamping force refers to maximum force that injection molding machine can clamp mold, also known as clamping force.
Most manufacturers use clamping force as model of machine (tons). Clamping force is generally expressed in tons (1 ton = 1000 kg) or kilonewtons (KN). Clamping force of direct press (kg/cm2) = clamping cylinder area (cm2) x hydraulic pressure (kg/cm2)
Clamping force of hinge clamping mechanism = clamping cylinder thrust x hinge mechanism magnification
Selection of clamping force
Simple judgment method for mold pressure: general products: 300kg/cm2, high-precision small products: 500kg/cm2, thin-walled packaging products: 400kg/cm2 – 600kg/cm2, thin-walled IT product appearance parts: 600kg/cm2 – 1000kg/cm2
Simple judgment method for mold pressure above 350 tons: general appearance parts: above 250kg/cm2, other thin-walled parts refer to the above.
Required clamping force (tons) ≧ product projection area (cm2) x mold pressure (kg/cm2) ÷ 0.8 ÷ 1000
Simple determination of mold pressure

Mold space should include tie rod inner distance, mold opening stroke, maximum and minimum mold thickness, and mold plate size.

 

Tie rod inner distance is inner dimension between four tie rods. If mold exceeds this dimension, it will not fit.

 

Generally, mold opening stroke required for products is 2.5 times product height, and in-mold labeling products generally require 4 to 5 times.

Ejection force: force (KN or tons) to eject product. Ejection force designed by general machine can be applied to most products. Only a few special products require a larger ejection force.
For example: PET bottle embryos require about 0.5 to 1 ton per cavity, and forced ejection of bottle caps requires about 400 kilograms per cavity.
Ejection stroke: maximum distance of machine ejection (mm)
Other ejection requirements: synchronous ejection, two-stage ejection, ejection retention, vibration ejection, delayed ejection, rotary ejection, etc.

Shooting table stroke (nozzle stroke): maximum distance nozzle moves forward and backward.
Nozzle contact force (KN): thrust of nozzle against mold. (For increased nozzle diameter, pay attention to whether thrust is sufficient)
Dry cycle (dry cycle): the shortest cycle time under no-load state measured according to European standard 6. Length of this time can determine configuration of machine, control ability of hydraulic and electronic control systems.
Motor power: power of driving oil pump or servo motor. (KW or HP) (1HP=746W)
Electric heating power: the total power of barrel electric heater. (KW)
Number of heating sections: number of points at which barrel heating can be controlled separately.
System pressure: Maximum working pressure of hydraulic system (mpa, bar, kg/cm2), general grades: 140bar, 160bar, 210bar. (All-electric models have no system pressure, which is generally limited by maximum value of individual design.)
Machine size: Mainly the overall size, as basis for factory arrangement.
Machine weight: Weight of the entire injection molding machine, as a reference for transportation and factory load-bearing.