GB/T 14486-2008Dimensional tolerances for moulded plastic parts (English PDF)

3.1 Moulding shrinkage

SM

It refers to the ratio OF the difference between the dimensions of the moulding chamber Lm and those of the corresponding moulded plastic part Lp

TO the dimensions of the moulding chamber Lm at (23 ± 2) °C, expressed as percentage.

Where:

SM - Moulding shrinkage, %;

Lp - The dimensions of the moulded plastic part that has been placed in the standard atmosphere for 24h after the moulding of the plastic part, in unit of millimeter (mm);

Lm - The corresponding dimensions of the moulding chamber, in unit of millimeter (mm).

3.2 Moulding shrinkage in flow direction

SMp

It refers to the moulding shrinkage along the material flow direction during moulding.

3.3 Moulding shrinkage in transverse direction

SMn

It refers to the moulding shrinkage perpendicular to the flow direction during moulding.

3.4 Difference of moulding shrinkage in flow and transverse directions

*SM

It refers to the difference of moulding shrinkage in flow and transverse directions during moulding.

PUR-P Thermoplastic polyurethane MT4 MT5 MT7

PVC-P Plasticized polyvinylchloride MT5 MT6 MT7

PVC-U Unplasticized polyvinyl chloride MT2 MT3 MT5

SAN (Acrylonitrile-styrene) copolymers MT2 MT3 MT5

UF

Urea-formaldehyde resin

With inorganic filler MT2 MT3 MT5

With organic filler MT3 MT4 MT6

UP

Unsaturated polyester

With 30% glass fiber filler MT2 MT3 MT5

4.3 Dimensions with tolerance indications

For the tolerance grades of the dimensions with tolerance indications, SEE

Table 2. The listed numerical values correspond to the tolerance grades in

Table 1.

This Standard only specifies tolerances. The upper and lower deviations of basic dimensions can be divided according to the actual engineering needs.

For instance, the tolerance 0.8 can be divided into: , , ± 0.4, or , etc.

4.4 Dimensions without tolerance indications

For the tolerance grades of the dimensions without tolerance indications,

SEE Table 2. The listed numerical values correspond to the tolerance grades in Table 1.

4.5 Dimension a not affected by the movable parts of the mould

The dimensions not affected by the movable parts of the mould in Table 1 refer to the dimensions moulded by the same mould part in the mould. For instance, the radial dimensions of the moulded parts with integral cavities.

SEE Figure 1.

Appendix A (Normative)

Selection method for the tolerance grades of moulded plastic parts

SELECT the tolerance grades according to the shrinkage property values of moulding materials. SEE Table A.1.

Table A.1 Shrinkage Property Values of Moulding Materials and

Selected Tolerance Grades

Shrinkage property value vS

/ %

Tolerance grade

Dimensions with tolerance indications Dimensions without tolerance indicationsHigh precision General precision

> 0~1 MT2 MT3 MT5

> 1~2 MT3 MT4 MT6

> 2~3 MT4 MT5 MT7

> 3 MT5 MT6 MT7

__________ END __________