Shot Size Recovery Rate Machine Selection

Understanding Shot Size and Recovery Rate in Machine Selection Shot size and recovery rate are fundamental parameters that determine whether a machine can produce a specific part at the required rate. Our analysis of capacity planning failures reveals that 25-30% of production capacity issues trace to inadequate understanding or specification of these parameters. Proper machine selection based on accurate shot size and recovery rate analysis prevents costly capacity problems and ensures production requirements can be met. Shot size,the volume of material injected into the mold per cycle,must fall within the machine’s capability range. Recovery rate,the rate at which the screw plasticizes material for the next shot,determines the maximum production rate. These parameters interact with cycle time to define actual production capacity. Understanding shot size and recovery rate requires knowledge of part requirements, material behavior, and machine capabilities. The calculations are straightforward, but accurate inputs and proper interpretation determine success.

Key Takeaways

| Aspect | Key Information |

Shot Size Fundamentals Shot size must be appropriate for the machine’s plasticizing capacity and must stay within recommended operating ranges. Shot Size Calculation Shot size is calculated from part weight, runner weight (if applicable), and material specific volume: Shot Size (cm³) = (Part Weight + Runner Weight) / Material Density Material density varies various 1.4 g/cm³ for some engineering plastics. Accurate density values from material datasheets should be used. Machine Shot Size Range Machines are specified with minimum and maximum shot sizes based on screw design. Operating typically between 20-80% of maximum shot size optimizes plasticizing performance. Machine Size (tons)Typical Screw DiameterMax Shot (g PS)Typical Part Range5025-30mm50-75g10-40g10030-40mm100-180g25-100g15040-50mm200-350g50-200g20045-55mm300-500g100-300g30055-65mm500-800g200-500g Operating Range Considerations Shot sizes below 20% of maximum may cause plasticizing problems including inconsistent melting, material degradation, and poor mixing. Shot sizes above 80% of maximum may exceed plasticizing capacity and cause recovery times longer than cycle requirements. Optimal shot size range is typically 30-70% of maximum for most applications.

Recovery Rate and Cycle Time Recovery rate,expressed as kg/hour or cm³/sec,determines maximum production rate for a given shot size. Recovery Rate Calculation Recovery Rate = Shot Size / Recovery Time Recovery time is the portion of the cycle available for plasticizing material between injections. In an 8-second cycle with 2-second injection and 2-second cooling overlap, 4 seconds might be available for recovery. Capacity Analysis Effective cycle time is determined by: Cycle Time = Max(Injection Time, Recovery Time) + Other Time + Safety Margin The machine can produce at the desired rate only if recovery fits within available cycle time. Example Calculation Part weight: 50g Material: ABS (density 1.04 g/cm³) Shot size: 48 cm³ Maximum cycle time: 6 seconds Available recovery time: 4 seconds (after accounting for injection and cooling overlap) Required recovery rate = 48 cm³ / 4 sec = 12 cm³/sec = 43 kg/hr If the machine’s recovery rate at this shot size is 50 kg/hr, the machine can meet the 6-second cycle. If recovery rate is only 35 kg/hr, cycle time must increase to approximately 5+ seconds. ---

Machine Selection Checklist

Shot size calculated: Based on part and runner weights

Material density applied: Using accurate material values

Machine capability verified: Shot size within 20-80% range

Recovery rate determined: From machine specifications

Cycle time analyzed: Comparing injection and recovery times

Capacity confirmed: Machine can meet production rate

Screw selection considered: Affects both shot size and recovery

Margin included: 10-20% capacity buffer for variability