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Digital Density Apparatus (Specific Gravity Method) Based On Digital Weighing Balance.
International Equipments is a leading manufacturer, supplier and exporter of Digital Density Apparatus in India. Built at our Mumbai facility, our Digital Density Apparatus uses the internationally accepted Specific Gravity Method (Archimedes principle) on a precision digital weighing balance — giving fast, accurate and repeatable density measurement of plastic granules, polymer pellets, rubber, foam, film cuttings, ceramics, glass and most solid laboratory samples.
Density is one of the most fundamental and frequently tested properties in the plastic, polymer, recycled plastic and packaging industries. It is used for raw material grade verification, batch-to-batch consistency checking, recycled plastic acceptance, identification of unknown polymers, and as an essential input to MFI-to-MVR conversion calculations. Our Digital Density Apparatus delivers this critical measurement at lab-grade accuracy (1 mg resolution on a 220 g balance) at a price point accessible to every QC laboratory.
A Digital Density Apparatus — also called a Specific Gravity Tester, Density Balance or Hydrostatic Weighing Balance — is a precision laboratory instrument that measures the density of a solid sample using the Archimedes principle of buoyancy. The sample is first weighed in air on a digital balance, then weighed again while immersed in a liquid of known density (typically distilled water). The difference between the two weights, combined with the known density of the liquid, gives the density of the sample directly in grams per cubic centimetre (g/cc).
The Specific Gravity Method built into our apparatus is the international reference method specified by ASTM D 792, ISO 1183 and the relevant Indian Standards for measuring the density of plastics, polymers, recycled plastic and most solid materials. It is faster, simpler and more accurate than older displacement-volume methods, and requires no calibration of complex pycnometers — only the routine calibration of the digital balance itself.
Our Digital Density Apparatus is built around a precision 220 g digital weighing balance with 1 mg (0.001 g) resolution — the standard combination specified by ASTM D 792 for plastic and polymer density testing. The apparatus is supplied complete with a calibrated beaker, a precision stand, a stainless-steel sinker (for samples that float) and a fine thread for suspending the sample below the balance pan during underwater weighing.
The complete workflow takes less than two minutes per sample: place the sample on the pan and read the dry weight, then transfer it to the suspended sample basket immersed in water and read the wet weight. The density calculation — Dry Weight / (Dry Weight − Wet Weight) × Water Density — gives the result directly in g/cc. With the supplied sinker, the apparatus easily handles low-density samples such as LDPE film, foam and certain recycled grades that would otherwise float.
Compared to costly automated electronic density meters, our manual specific-gravity setup gives the same result accuracy at a fraction of the price, with no consumables and minimal training required — making it the standard density solution for QC labs across the polymer, plastic pipe, recycled plastic, film and packaging industries in India and abroad.
The Specific Gravity Method is based on Archimedes' principle: when a solid is fully immersed in a liquid, it experiences an upward buoyant force equal to the weight of the liquid it displaces. By measuring the sample weight in air and again under water, the density of the sample can be calculated precisely.
Place the dry, clean sample directly on the balance pan and record the weight (W₁) in grams to 1 mg resolution. This is the true mass of the sample.
Suspend the sample in the supplied beaker of distilled water using the thread, ensuring the sample is fully submerged and no air bubbles cling to the surface. Read the apparent weight in water (W₂). For low-density samples that float, the stainless-steel sinker is attached to keep the sample submerged.
Density (g/cc) = W₁ / (W₁ − W₂) × ρ_water, where ρ_water is the density of water at the test temperature (effectively 1.00 g/cc at 20–25°C). The result is the specific gravity of the sample, directly comparable with material specification sheets and ASTM/ISO standard reference values.
| Parameter | Specification |
|---|---|
| Test Method | Specific Gravity Method (Archimedes Principle) |
| Weighing Balance Range | 220 grams |
| Resolution | 1 milligram (0.001 g) |
| Accessories Supplied | Beaker, Stand, Sinker and Thread |
| Paint Finish | Powder coated |
| Power Requirement | 230 Volts, 50 Hz, single phase |
Each Digital Density Apparatus is supplied complete with the full accessory set required to perform the test from day one — no separate sourcing needed:
Precision 220 g capacity balance with 1 mg resolution, the core measurement instrument of the apparatus.
Calibrated glass beaker that holds the distilled water in which the sample is suspended during wet weighing.
Sturdy stand that holds the beaker steady at the correct height below the balance pan, ensuring the sample hangs freely in the water without touching the beaker walls.
Stainless-steel sinker for use with low-density samples that float in water (LDPE, certain foams, low-density recycled grades) — keeps the sample submerged for accurate wet-weight reading.
Fine, low-water-absorption thread used to suspend the sample below the balance pan into the water beaker.
Density is one of the most informative and most frequently tested properties in the plastic and polymer industry. Here are the main reasons every polymer QC lab needs an accurate density apparatus:
Different polymers have characteristic density ranges — LDPE typically 0.910–0.925 g/cc, HDPE 0.940–0.965 g/cc, PP 0.895–0.905 g/cc, PVC 1.35–1.45 g/cc. Density measurement is the fastest way to confirm that incoming material is the grade you ordered, and to flag any contamination or wrong-grade shipment before it enters production.
Even within a single polymer grade, density can vary by a few thousandths of a g/cc between batches. Monitoring this on every incoming batch catches process drift in the supplier's plant and prevents downstream moulding or extrusion defects.
Recycled plastic shipments often contain contamination from other polymer types — recycled HDPE may have PP or PET mixed in. Density measurement on a representative sample is the simplest first-line check that recycled material meets the required specification.
When converting Melt Flow Rate (MFR, in g/10 min) to Melt Volume Rate (MVR, in cu.cm/10 min) using your MFI Tester data, the melt density of the polymer is an essential input. The room-temperature density measured on the Density Apparatus provides the baseline value.
When a polymer is compounded with mineral fillers (talc, calcium carbonate), glass fibres or carbon black, the density rises in proportion to the filler content. Density measurement is the standard quality check that the filler loading is correct in the compounded product.
Foam products (EPS, XPS, PU foam) are sold and specified by density. Apparent density measurement using the Specific Gravity Method (with the supplied sinker) is the standard test for these products.
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