Hot melt wire density test: a key step to ensure product quality

Hot melt wire density test: a key step to ensure product quality

1. Introduction
In today’s globalized market, hot melt wire, as an important industrial material, is widely used in many fields such as textiles, 3D printing, and composite materials. For international wholesale buyers, product quality and performance are key factors in determining purchases. The density test of hot melt wire, as an important means to evaluate its quality and performance, is particularly important. This article will introduce in detail the methods, standards, equipment, and how to ensure product quality through these tests to help buyers make wise decisions.

2. The importance of hot melt wire density test
The density of hot melt wire is an important indicator of its physical properties, which directly affects the melting characteristics, mechanical strength, and heat resistance of hot melt wire. For example, in the textile industry, hot melt wire with substandard density may lead to insufficient bonding strength, thereby affecting the durability and functionality of clothing; in the field of 3D printing, hot melt wire with uneven density may lead to reduced printing accuracy and affect the appearance and strength of the finished product. Therefore, density testing of hot melt wire can not only ensure the quality of the product, but also improve production efficiency and reduce losses caused by quality problems.

3. Methods for testing the density of hot melt wire
(I) Archimedes buoyancy method
The Archimedes buoyancy method is one of the most commonly used density testing methods. Its principle is to calculate the volume of the hot melt wire by measuring the weight difference between the weight of the hot melt wire in the air and the weight in the water, and then obtain the density. The advantages of this method are simple operation and low cost, and it is suitable for density testing of most solid materials. The specific steps are as follows:
Place the hot melt wire sample on an electronic balance and measure its weight in the air (W1).
Immerse the sample completely in water and measure its weight in water (W2).
According to the formula: Density = W1 / (W1 – W2) × water density, calculate the density of the hot melt wire.
(II) Drainage method
The drainage method is similar to the Archimedes buoyancy method. It also calculates the density of the hot melt wire by measuring the volume change of the hot melt wire in water. This method usually requires an accurate measuring cylinder or volume measuring device and is suitable for hot melt wire samples with irregular shapes. The specific steps are as follows:
Add a certain amount of water to the measuring cylinder and record the initial water level (V1).
Completely immerse the hot fuse sample in water and record the volume after the water level rises (V2).
According to the formula: Density = Sample weight / (V2 – V1), calculate the density of the hot fuse.
(III) Electronic Densitometer Method
The electronic densitometer is a modern density testing equipment that combines the advantages of Archimedes buoyancy method and drainage method, and can quickly and accurately measure the density of hot fuses. Electronic densitometers usually have automatic calibration and data processing functions, which can reduce human errors and improve test accuracy. The steps for density testing using an electronic densitometer are as follows:
Calibrate the electronic densitometer to the standard state.
Place the hot fuse sample on the measuring table, and the instrument automatically measures its weight in the air.
Immerse the sample in water, and the instrument automatically measures its weight in water.
The instrument automatically calculates and displays the density of the hot fuse according to the built-in formula.

4. Standards for hot fuse density testing
In order to ensure the accuracy and consistency of the test results, hot fuse density testing needs to follow relevant international and national standards. The following are some commonly used standards:
(I) ISO standard
ISO 527-2: Determination of plastic tensile properties, suitable for mechanical testing of thermoplastic materials such as nylon filaments.
ISO 11357-3: Plastic DSC test method, used to determine the melting point and crystallinity of hot melt filaments.
ISO/ASTM 52900: Provisions on the diameter tolerance of wires for 3D printing, requiring the diameter deviation to be ≤±0.05mm.
(II) ASTM standard
ASTM D789: Nylon material melting point and melting heat test standard.
ASTM D638: Plastic tensile property test standard.
(III) GB/T standard
GB/T 3682: Determination of thermoplastic melt mass flow rate (MFR).
GB/T 2918: Standard environment for state adjustment and testing of plastic specimens.
V. Equipment for hot melt density testing
(I) Electronic density meter
The electronic density meter is one of the most commonly used density testing equipment at present. It has the advantages of high precision, simple operation and fast measurement speed. Common electronic density meter models include:
MZ-S300: weighing range 0.005-300g, density accuracy 0.001g/cm³, measuring time about 5 seconds.
JF-120S: weighing accuracy 0.001g, weighing threshold 120g, measuring range 0.0001g/cm³～99.9999g/cm³.
(II) Differential Scanning Calorimeter (DSC)
DSC is an instrument used to analyze thermodynamic parameters such as melting point and crystallinity of hot fuse. It can accurately measure the heat change of hot fuse during heating to determine its melting characteristics. Common DSC instrument models include:
Perkin Elmer DSC 8000: temperature range -70℃～500℃, suitable for various metals, ceramics, single crystals, glass, and hard organic materials.
METTLER TOLEDO DSC3+: Temperature range -150℃～500℃, suitable for various inorganic, organic, high molecular polymers and composite materials.
(III) Melt Indexer (MFI)
MFI is used to evaluate the melt flow properties of hot melt wire. It determines its processing performance by measuring the flow rate of hot melt wire at a specific temperature and load. Common MFI instrument models include:
ISO 1133: Applicable to the determination of melt flow rate of thermoplastics.
(IV) Laser diameter gauge
Laser diameter gauge is a high-precision measuring instrument used to measure the diameter uniformity of hot melt wire. It can accurately measure the wire diameter deviation to ensure that the size of the hot melt wire meets the standard requirements. Common laser diameter gauge models include:
Accuracy 0.001mm: Applicable to measuring the diameter deviation of hot melt wire.

5. Hot melt wire density test process
(I) Sample preparation
Randomly select samples from the hot melt wire production batch to ensure that the samples are representative.
Cut the samples into appropriate lengths, usually about 1 meter, for easy measurement.
(II) Pretreatment
The samples were balanced in an environment of 23±2℃ and 50±5%RH for 24 hours. This step is to ensure that the samples are in a standard state before testing and reduce the impact of environmental factors on the test results.
(III) Physical test
Diameter measurement: Use a laser diameter gauge to measure the diameter deviation of the sample. Usually 10 points are selected on the sample for measurement, and the coefficient of variation (CV value) is calculated to evaluate the uniformity of the diameter.
Tensile test: The sample is mounted on an electronic tensile testing machine and a tensile test is performed at a speed of 50mm/min. The tensile strength and elongation at break are recorded to evaluate the mechanical properties of the sample.

6 Thermal performance test
Melting point test: Use a differential scanning calorimeter (DSC) to scan the range of 30-300℃ at a heating rate of 10℃/min. Record the melting point and crystallinity to evaluate the thermal stability of the hot melt.
Melt index test: The melt index test is performed at 235℃/2.16kg load. Record the melt index to evaluate the flow properties of the hot melt.
(V) Data Analysis
Compare the results of three parallel tests, remove the outliers and take the average value. This step can reduce the test error and ensure the accuracy of the data.
Based on the test results, evaluate whether the density of the thermal fuse meets the standard requirements.