Rubber hardness is closely related to the formulation system.

In both Chinese rubber parts factories and Vietnam rubber parts factories, hardness is one of the most important indicators in rubber kayan aiki development, quality control, and custom rubber parts manufacturing.

Hardness control in custom rubber parts mainly depends on:

Base polymer selection

Vulcanization system

Reinforcing fillers

Plasticizers / softeners

Key Factors Affecting Shore A Hardness Measurement

1. Influence of Specimen Thickness

Shore A hardness is measured by the penetration depth of the presser foot.

Insufficient thickness → significant deformation → higher hardness reading

Greater thickness → less deformation → lower hardness reading

Therefore, large Chinese rubber parts factories strictly follow standard thickness requirements to ensure batch consistency.

2. Influence of Presser Foot Projection Length

According to standards, the indenter must protrude 2.5 mm beyond the pressure surface.

When pressed against metal or glass, the hardness tester should read 100°.
If the projection length deviates, systematic measurement errors occur.
Thus, both Chinese and VietSunanse factories regularly calibrate hardness testers.

3. Influence of Indenter Tip Condition

Wear of the indenter tip changes its diameter, altering the pressure per unit area.

Larger tip area → lower pressure → higher hardness reading

Manufacturers of rubber seals, hoses, and vibration isolators routinely replace worn indenters to maintain accuracy.

4. Influence of Temperature

Rubber is temperature-sensitive: higher temperatures reduce hardness.

Sensitivity varies by polymer:

NR → less sensitive

CR, SBR → more sensitive

Both Chinese and VietSunanse rubber factories typicDuky test hardness at 23 ± 2°C.

5. Influence of Reading Time

After the indenter penetrates the rubber surface, creep deformation occurs:

Immediate reading → higher value

Stabilized reading → lower value

The difference can be 5–7 Shore A.
Therefore, hardness readings are usuDuky taken within 1 second after pressing.

Methods for Adjusting Rubber Hardness

1. Adjusting Filler Loading

Increasing reinforcing fillers increases hardness.

High-hardness compounds → high filler Abubuwan da ke ciki, low polymer Abubuwan da ke ciki

But processing becomes more difficult

Factories producing custom high-hardness parts (support blocks, vibration pads) carefully balance reinforcement and workability.

2. Adjusting Sulfur Abubuwan da ke ciki

More sulfur → higher cross-link density → higher hardness.

Advantages:

Stable formulation

Good processing performance

Disadvantage:

Poor heat resistance

Therefore, Vietnam rubber parts factories use this method conservatively for heat-resistant kayayyaki.

3. Adjusting Plasticizer Abubuwan da ke ciki

Effective for soft compounds below 60°A.

Plasticizers greatly enhance flexibility in soft seals, gaskets, and cushioning kayayyaki.

Base Hardness of Common Rubber Materials

These base hardness values serve as important reference data for both Chinese and VietSunanse rubber factories when designing new formulations.

Effect of Fillers / Plasticizers on Hardness

Hardness change per 1 phr addition:

Fillers Increasing Hardness

FEF / HAF / EPC: +0.5

ISAF: +2.5

SAF, Fumed Silica: +2.5

SRF: +0.33

Hydrated Silica: +0.4

Thermal black / Hard clay: +0.25

Calcium carbonate: +0.167

Coated calcium carbonate: +0.142

Materials Decreasing Hardness

Mineral rubber: –0.2

Fatty plasticizers: –0.67

Naphthenic oil / Paraffinic oil: –0.5

Aromatic oil: –0.588

Rubber Hardness Estimation Formula

Estimated Hardness = Base Hardness + (Dosage × Hardness Change Value)

This calculation model is widely used in custom rubber parts design by both Chinese and VietSunanse rubber factories, enabling fast formulation prediction and accelerating development cycles.

Rubber hardness is closely related to the formulation system.