Injection Capacity (PS Equivalent)
Convert a machine's nominal injection capacity (always specified in polystyrene, PS, density ~1.05) to the equivalent capacity in another material by multiplying by the density ratio. Since the barrel has a fixed volume, the mass it injects changes with the plastic's density — denser materials yield more grams per shot. Essential to size the machine for the real material. Enter the nominal PS capacity and the material density.
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Injection capacity (PS equivalent)
There is a catch buried in the datasheet of every injection moulding machine: the shot capacity is always quoted in grams of polystyrene (PS), density ~1.05 g/cm³ — because the barrel has a fixed volume, while the figure advertised is a mass. As soon as another material runs through it, the mass per shot changes in proportion to the density: equivalent_capacity = PS_capacity · (material_density/1.05). A plastic lighter than PS, such as polypropylene (0.905), yields fewer grams per shot on the very same machine; a denser one, such as PVC or filled polyesters, yields more. Ignoring this correction means sizing the wrong machine — assuming the shot fits when it does not, or paying for a press far bigger than the job needs. That is why the process engineer always converts the nominal PS rating to the real material before the tooling project is signed off. Enter the nominal PS capacity and the density of the material.
Related Tools
Injection Shot Volume
Compute the shot volume of a plastic part by dividing the injected mass by the molten material density. The shot is the total volume of plastic injected per cycle (parts + runners), a parameter that must fit the injection barrel capacity. Together with the machine capacity, it defines how many cavities can be filled per cycle. Enter the injected mass (g) and the material density (g/cm³).
Plastic Injection Flow Rate
Compute the injection flow rate by dividing the injected volume by the fill time, in cm³/s. It is the speed at which the molten plastic enters the mold — a parameter that controls the shear rate, molecular orientation, surface finish and defects such as jetting or flow marks. High flow fills fast but may degrade; low flow may solidify before filling. Enter the injected volume and the fill time.
Cylindrical Silo Capacity
Calculate the storage capacity (mass) of a silo's cylindrical part, M = ρ · (π·D²/4) · H, from the product bulk density ρ (kg/m³), the silo inner diameter D (m) and the cylindrical body height H (m). The calculation combines the cylinder volume (section area times height) with the product's bulk density — the product mass per unit apparent volume, which includes the voids between particles and differs from the solid particle density. Bulk density varies with product and state: soybeans ~720 kg/m³, corn ~720, wheat ~770, cement ~1500, and it also changes with moisture and compaction. Capacity is a silo's most basic commercial and operational parameter: it sets how much product it stores, and thus the logistics of receiving, dispatch and stock turnover. This computes the cylindrical part; total capacity also includes the lower hopper volume and, in grain silos, the upper product cone above the transition line (formed by the angle of repose during filling). Correctly estimating capacity is essential in designing storage units, cooperatives and grain terminals. Enter the bulk density, diameter and cylindrical body height.
Injection Cycle Time
Compute the total cycle time of a plastic injection by adding the injection time (fill + pack), the cooling time and the mold open/eject time. Cooling is usually the largest share (50–80% of the cycle). The cycle time directly determines productivity: parts/hour = 3600/cycle × cavities. Reducing it is the constant focus of optimization. Enter the injection, cooling and opening times.
Shear Rate (Injection)
Compute the shear rate of the molten plastic in a rectangular channel, γ = 6Q/(W·H²), from the flow rate (Q), the channel width (W) and height (H). It is a critical parameter of polymer processing: thermoplastic viscosity drops with shear rate (pseudoplastic behavior), and excessive rates degrade the material. It guides the design of runners and gates. Enter the flow rate, the width and the height of the channel.
Mold Cavity Pressure
Estimate the pressure that actually reaches the mold cavity by multiplying the injection pressure (at the screw tip) by the pressure transmission factor, which accounts for pressure losses along the runners, nozzle and gates to the cavity. Typically only 40–60% of the machine pressure reaches the part. It is the cavity pressure that defines the clamping force and fill quality. Enter the injection pressure and the transmission factor.
The results provided by this tool are for general informational and educational purposes only and do not constitute professional, financial, medical, legal, tax or accounting advice. Always confirm important decisions with a qualified professional and official sources.