Silicone hardness test is a critical quality control and R&D tool for silicone products—from soft baby bottle nipples to hard automotive gaskets. It measures a silicone’s resistance to indentation, directly reflecting its flexibility, durata, and suitability for end-use. This article breaks down the two most common test methods (Shore and Rockwell), Fattori di influenza chiave, and practical applications—with clear comparisons, step-by-step guides, and tips to ensure accurate, Risultati affidabili.
1. Common Silicone Hardness Test Methods
Silicone’s elastic properties require specialized testing methods. Below are the two primary techniques, along with their principles, procedure, e casi d'uso:
| Test Method | Principio fondamentale | Step-by-Step Procedure | Parametri chiave | Applicazioni ideali |
| Shore Hardness Test | A needle of specific shape (conical for Shore A, spherical for Shore D) is pressed into the silicone surface under a fixed load. Hardness is determined by indentation depth—shallower = harder material. | 1. Sample Prep: Cut the silicone into flat, uniform specimens (surface roughness Ra ≤ 1.6μm). Ensure no bubbles or defects in the test area.2. Impostare: Place the specimen on a rigid, flat surface (PER ESEMPIO., marble table) to avoid deformation during testing.3. Test: Align the Shore hardness tester’s needle vertically with the specimen (nessuna inclinazione). Apply pressure evenly at a speed of 1–2mm/s until the tester’s base touches the silicone surface.4. Reading: Hold the tester for 5–10 seconds (to account for silicone’s elasticity) and record the value. Repeat 3–5 times at different locations (20mm di distanza) and take the average. | – Shore a: For soft silicone (0–100 HA); indentation depth ~0.1–1mm.- Shore d: For hard silicone (0–100 HD); used when Shore A reads >90 HA.- Carico: 1kg (Shore a), 5kg (Shore d). | – Soft silicone: Baby bottle nipples (20–30 HA), custodie per telefoni in silicone (50–70 HA), cateteri medici (30–40 HA).- Silicone duro: Guarnizioni automobilistiche (80–90 HA → passa a Shore D), manici per pentole in silicone (60–80 HA). |
| Prova di durezza Rockwell | Un cono di diamante (120° angolo) o sfera in carburo (1.588diametro mm) il penetratore viene premuto nel silicone utilizzando due carichi: carico iniziale (per posizionare il penetratore) E carico principale (per creare il rientro). La durezza viene calcolata dalla differenza nella profondità di rientranza prima/dopo la rimozione del carico principale. | 1. Sample Prep: Lavorare il silicone in campioni con superficie piatta, superfici parallele (spessore ≥6mm; dimensione ≥10 mm × 10 mm). Polish the test surface to remove scratches.2. Impostare: Secure the specimen on the Rockwell tester’s stage. Select the indenter (diamond cone for hard silicone) and load (carico iniziale: 10kg; carico principale: 60–150kg, depending on hardness).3. Test: Apply the initial load first—this ensures the indenter makes consistent contact with the silicone. Then add the main load and hold for 15–30 seconds. Remove the main load (keep the initial load) and record the indentation depth difference.4. Calculation: The tester automatically converts depth difference to Rockwell hardness (HR) values (PER ESEMPIO., HRC for diamond cone, HRB for carbide ball). | – Indenter: Diamond cone (HRC scale) for hard silicone; carbide ball (HRB) for medium-hard silicone.- Loads: Initial (10kg) + Main (60kg = HRB, 150kg = HRC).- Precisione: ±1 HR unit. | – High-precision industrial silicone: Aerospace seals (90–95 HA → HRC 20–30), high-wear silicone parts (PER ESEMPIO., pump diaphragms), and silicone composites (silicone + fiber reinforcement). |
Confronto chiave: For most silicone products, IL Shore Hardness Test is preferred—it’s faster, simpler, and causes minimal damage to specimens. The Rockwell test is reserved for hard, high-performance silicones where precise, load-based measurements are critical (PER ESEMPIO., parti di macchinari industriali).
2. Key Factors Influencing Test Accuracy
Even the best test method yields unreliable results if external factors are unregulated. Below are the three most critical variables and how to control them:
2.1 Specimen Thickness & Misurare
Silicone’s elasticity means thin specimens deform under the tester’s load, leading to false low-hardness readings.
- Thickness Requirement: For Shore A tests, the specimen must be at least 10 times the indentation depth (PER ESEMPIO., if indentation is 1mm, specimen thickness ≥10mm). For Rockwell tests, spessore ≥6mm (to avoid the indenter touching the test surface below).
- Size Requirement: The specimen must be large enough to avoid “edge effects”—test points must be at least 20mm away from the specimen’s edges (edges deform more easily, skewing results).
- Esempio: A 5mm-thick silicone phone case specimen will read 5–10 HA lower than its actual hardness (30 HA → 20–25 HA) because the thin material bends under the Shore tester’s load.
2.2 Test Environment (Temperatura & Humidity)
Silicone’s molecular structure is sensitive to temperature and moisture, which alter its hardness:
- Temperatura:
- Effetto: As temperature rises, silicone softens (hardness decreases). A 10°C increase can lower Shore A hardness by 3–5 HA (PER ESEMPIO., 50 HA at 23°C → 45–47 HA at 33°C).
- Controllare: Test at temperatura ambiente (23± 2 ° C.). If testing in hot/cold environments, let the specimen acclimate for 2–4 hours (until it reaches 23±2°C) before testing.
- Humidity:
- Effetto: High humidity (>60%) causes silicone to absorb moisture, making it slightly softer (1–3 HA decrease).
- Controllare: Store specimens in a dry environment (humidity 40%–60%) per 24 hours before testing. For high-humidity regions, use a dehumidifier in the test area.
2.3 Tester Operation & Calibrazione
Human error and uncalibrated tools are major sources of inaccuracy:
- Vertical Alignment: The tester’s needle must be perfectly vertical (±1°). A 5° tilt can increase indentation depth by 10% (PER ESEMPIO., 1mm → 1.1mm), lowering hardness by 5–8 HA.
- Loading Speed: Apply pressure at 1–2mm/s. Loading too fast (≥3mm/s) causes over-indentation (false low hardness); Troppo lento (≤0.5mm/s) lets silicone recover elastically (false high hardness).
- Calibrazione: Calibrate the tester every 3–6 months using a standard hardness block (PER ESEMPIO., 50 HA, 80 HA blocks for Shore A). An uncalibrated tester may read 10+ HA off (PER ESEMPIO., 60 HA actual → 70 HA uncalibrated).
3. Scopo & Significance of Silicone Hardness Testing
Hardness testing isn’t just a quality check—it guides every stage of silicone product development and production:
3.1 Controllo di qualità (Produzione)
- Raw Material Inspection: Test incoming silicone raw materials to ensure they meet hardness specifications (PER ESEMPIO., a baby bottle manufacturer rejects silicone with 15 HA—too soft for safe use).
- Finished Product Testing: Sample 1–5% of finished goods to verify consistency. Per esempio, a silicone gasket factory tests 10 gaskets per batch—if 2 read 85 HA (spec: 75–80 HA), the batch is reworked (adjust crosslinker dosage to soften the silicone).
3.2 Material R&D & Selezione
- Formulation Optimization: R&D teams adjust silicone formulations (PER ESEMPIO., adding fillers like silica powder) and test hardness to achieve target properties. Per esempio:
- Aggiunta 5% silica powder increases Shore A hardness by 10–15 HA (30 HA → 40–45 HA), making the silicone suitable for cookware handles.
- Reducing crosslinker dosage by 2% lowers hardness by 5–8 HA (60 HA → 52–55 HA), ideal for flexible phone cases.
- Product-Specific Selection: Choose silicone hardness based on end-use needs:
- Medical gloves: 30–40 HA (soft for comfort, durevole per uso ripetuto).
- Automotive door seals: 60–70 HA (flexible to seal gaps, Abbastanza difficile da resistere all'usura).
- Stampi in silicone: 50–60 HA (balances flexibility for demolding and rigidity to retain shape).
4. Yigu Technology’s Perspective on Silicone Hardness Testing
Alla tecnologia Yigu, Abbiamo visto 70% of silicone product failures stem from overlooked hardness issues—e.g., a client used 80 HA silicone for a baby pacifier (spec: 25–30 HA), leading to safety recalls. Il nostro consiglio chiave: Priorità Shore A testing for most applications—it’s cost-effective and aligns with consumer product needs. For industrial clients making hard silicone parts (PER ESEMPIO., aerospace seals), we recommend combining Shore D and Rockwell tests to cross-verify results. We also emphasize environmental control: A client in a tropical region (30°C+ humidity) saw 5–7 HA hardness variations until they installed dehumidifiers and temperature controllers. Finalmente, train operators on vertical alignment and loading speed—even small mistakes (PER ESEMPIO., 3° needle tilt) cost thousands in rework. Hardness testing is the foundation of reliable silicone products; cutting corners here risks product failure and brand damage.
5. Domande frequenti: Common Questions About Silicone Hardness Testing
Q1: Can I use a Shore A tester for hard silicone (PER ESEMPIO., 95 HA)?
A1: No—Shore A testers are designed for 0–90 HA. For silicone harder than 90 HA, Usa un Shore D tester—Shore A readings above 90 are inaccurate (the needle can’t indent deeply enough to measure true hardness). Per esempio, 95 HA silicone will read ~92 HA on a Shore A tester but show the correct 50 HD on a Shore D tester.
Q2: Why do my test results vary by 5–8 HA even with the same specimen?
A2: Variations usually come from three issues: (1) Edge effects: Testing too close to the specimen’s edge (must be ≥20mm away). (2) Elastic recovery: Not holding the tester long enough (wait 5–10 seconds for silicone to stabilize). (3) Difetti di superficie: Bubbles or scratches in the test area—use a new specimen or test a different location. Fix these, and variations will drop to ≤2 HA.
Q3: How thick should my silicone specimen be for a Rockwell test?
A3: Rockwell tests require a minimum specimen thickness of 6mm—thinner specimens let the indenter touch the test stage below, causing false high hardness readings. Per esempio, a 4mm-thick specimen may read 10 HR higher than its actual value. If your silicone is thinner than 6mm, layer 2–3 specimens (each ≥2mm) with a thin layer of silicone glue (to avoid separation during testing)—ensure the glued surface is flat and free of air bubbles.