Injection Shot Size, Barrel Capacity, and Residence Time

Residence time is the barrel capacity divided by the shot, multiplied by the cycle time -- so a small shot in a large barrel is not merely inefficient, it is a material problem. The usable window runs roughly 20 to 80 percent of capacity and it has a reason at BOTH ends, which is why it is a window rather than a minimum. Below the floor the melt makes too many cycles in a hot barrel before it is used; above the ceiling the screw has too little stroke and too little time to melt and homogenise the charge, and shot-to-shot consistency suffers. The consequence at the low end is what makes this worth running before a job is scheduled rather than after it has run. On a polyolefin a long residence is survivable. On PVC it is not -- the material degrades and evolves hydrogen chloride, and the damage is to the screw and barrel as much as to the parts. On acetal it is a decomposition risk, and on polycarbonate and many flame-retardant grades the properties fall away well before anything is visible. The failure mode that matters is that degraded parts often pass dimensional inspection and fail on properties, so the defect is not caught at the press and SHIPS. The residence limit is therefore a material property and is entered from the resin supplier's processing data rather than assumed. The practical use of this is machine selection: running a small part on whatever large machine is free is a decision about the material, not about the schedule, and the usable barrel range reported here is the answer to it. Where a large machine is the only one available, shortening the cycle is the lever that remains, because residence scales directly with cycle time. This is a capacity and time calculation on entered weights. It does not convert between the machine's rating basis and the material actually run (machines are commonly rated in ounces of general-purpose polystyrene, and a different density changes the figure), size the injection unit for pressure or plasticising rate, model degradation kinetics, account for the residence distribution within a screw (some material sits far longer than the average), or address purging, colour change, or barrel temperature profile. The resin supplier's processing data and the machine manufacturer's ratings govern.

residence time = (barrel capacity / shot size) x cycle time; the usable shot window is commonly 20 to 80% of barrel capacity, and the barrel range for a given shot inverts it.

Shot size and residence time as injection moulding practice states them, with the material's maximum residence ENTERED from the resin supplier's processing data because it is a material property rather than a machine one.

One ratio and one multiplication.

Estimate. AHJ and licensed professional govern.

Field names used by the API: barrel_capacity_oz, shot_weight_oz, cycle_time_s, min_pct, max_pct, max_residence_min, alt_cycle_time_s, shot_pct, shots_in_barrel, residence_min, min_barrel_oz, max_barrel_oz, alt_residence_min

• Maximum residence is entered a material property from the resin supplierthe resin processing data sheet
• Machine rating basis machines are commonly rated in ounces of general-purpose polystyrenethe machine manufacturer's rating
• Average residence some material in a screw sits far longer than the averagea residence distribution study