Runner length

The function of the runner system is to transmit the molten polymer to the cavities with a minimum of material and pressure drop. Therefore, the runner length must be... 

Schematic diagram of an eight cavity mold system with various runner lengths and...

Runner length n. In knitting, the number of inches of yarn from a warp to make one rack of fabric. 

KR 2864 - easy flow, high resistance to heat deformation (articles with thin walls and/or adverse runner length/wall thickness ratios. 

Part Thickness, in. Runner Length, in. Minimum Diameter, ia Acetal Copolymer Polyester ... 

Like the runner dimensions, the viscosity of the plastic influences the magnitude of pressure losses in an HR system, and thus has a bearing on the permissible runner length. When HR nozzles are being selected a permissible pressure loss of up to 25 MPa or thereabouts is often adopted. The total pressure loss in an HR system, meanwhile, should not exceed... 

The runner length should be kept as short as possible, to reduce material wastage and to reduce pressure losses. The runners should also be balanced, i.e., the distance the material has to travel from the sprue to the gate should be the same for each cavity. This is illustrated in Figure 4.7. 

Typical runner sizes range fi-om 4mm to 7nun (0.157 to 0.276 in.) in diameter. Diameters above 7mm (0.276in) tend only to increase the cycle time and do not significantly assist in ihe filling of the mold. Runner lengths should be kept as short as possible and suitably sized ejectors positioned at runner junctions to ensure that the feed system is removed from the mold without difficulty. 

Runner length(mm) Optimized Diameter(mm) Thumbrule Diameter(mm)... 

Figure 7 Effect of runner length on runner volume...

Another possibility somce of variations between molded parts within a mold could be from dimensional differences within the molds steel. These differences conld inclnde any variations in the molds ruimer layout, actual cavity size, gate size, runner lengths, ruimer diameters or non-synunetrical venting. This study confirmed that all of these steel dimensions within the test mold were to very tight tolerance thereby minimizing this as a source of filling variations. 

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