Operating specifications
This specification aims to provide standardized operating procedures and technical requirements for the determination of the melt flow rate of hot melt adhesives using a melt index meter. Melt flow rate is a key parameter to characterize the flow performance of hot melt adhesives at specific temperatures and loads, and has important guiding significance for material processing and application.
1. Measurement principle
The measurement of the melt index meter is based on the principle of capillary rheology. At the specified temperature, a certain quality of the hot melt adhesive specimen is loaded into the barrel, and a standard load is applied through the piston so that the molten material is extruded from the capillary mouth die of the specified diameter and length. The mass of the material extruded per unit time is the melt flow rate, usually expressed in grams per 10 minutes (g/10min). Its basic calculation formula is:
MFR = (600 × m) / t
MFR is the melt flow rate (g/10min), m is the average mass of the cut spline (g), and t is the cutting time interval (s).
2. Preparation of instruments and materials
Before operation, the following conditions must be complete:
1. Melt index meter: It must include a temperature control system, barrel, piston, standard mouth die, load weight and cutting device. The instrument must be calibrated and within the expiration date.
2. Sample material: Hot melt adhesive particles or sheet samples should be dry and free of significant impurities. Sampling needs to be representative.
3. Auxiliary tools: balance (accuracy 0.001g), timer, cleaning tools (such as gauze, special cleaning material), tweezers, etc.
4. Environmental conditions: The laboratory should be free of strong airflow interference, and the room temperature is recommended to be controlled at 23±5°C.
3. Operation steps
The following steps should be performed strictly in order:
Step 1: Instrument warm-up and setup
Turn on the instrument and set the barrel temperature to the specified value (common test temperature range is 120°C to 190°C, depending on the relevant material standard). Let the temperature stabilize within the set value ±0.5°C and hold for at least 15 minutes.
Step 2: Installation and cleaning
Put the standard die into the furnace body at the bottom of the barrel, and insert the cleaning rod to hold the die. Use gauze to clean the barrel, piston and mouth mold. Remove the cleaning rod when you're done.
Step 3: Charging and compaction
Use a feeder to add the weighed specimen (usually about 4-8g) to the barrel in batches. For each portion added, compact it with a pressing rod to remove air bubbles. Once fully filled, the piston is placed in the barrel. The total charging time should not exceed 1 minute.
Step 4: Preheat and load
Let the piston and material warm up in the barrel. The standard warm-up time is usually 4 to 6 minutes (refer to the relevant test standards). After warm-up, the selected load weight is smoothly applied to the top of the piston.
Step 5: Cutting and sampling
The timing starts when the base line under the piston rod is aligned with the upper edge of the barrel. Use a cutting device to cut the extruded strips regularly under the mouth die. After discarding the first segment, cut at least 5 bubble-free, uniform splines in a row at consistent intervals (usually 10-60 seconds).
Step 6: Weighing and calculating
Use a balance to accurately weigh the mass of each cut spline, calculate its average. Substitute the average mass into the formula to calculate the melt flow rate value.
Step 7: Cleanup
After testing, the load is removed, the piston is removed and the residual material is cleaned. Use special cleaning materials and tools to thoroughly clean the barrel, mouth mold and piston while hot.
4. Precautions
To ensure repeatability and accuracy of measurement results, the following points need to be taken into account:
| Temperature fluctuations | The barrel temperature needs to be precisely controlled, and small fluctuations can lead to significant rate changes. |
| Specimen status | Samples are hygroscopic or contain volatiles that can affect the results and should be pre-dried if necessary. |
| Charging technique | The charging speed and compaction should be consistent to avoid the introduction of air bubbles. |
| Load selection | Select the appropriate load based on the expected flow of the material and the relevant criteria. |
| Cutting timing | Discard the initial strip and start cutting and sampling once the flow is stable. |
| Instrument maintenance | Calibrate the temperature sensor and load weight regularly to keep the inner wall of the mouth die clean. |
5. Result report
The test report should clearly record the following information: material identification, test standard basis, test temperature, load size, warm-up time, cutting time interval, spline quality of each section, and calculated melt flow rate value (corrected to two significant figures). If multiple parallel tests are performed, arithmetic averages should be reported. When the relative deviation of a single measured value from the mean exceeds a certain range (e.g., 10%), the data should be rejected and retested.
6. Safety instructions
During operation, the instrument barrel, mouth die and extruded strip are all in a high temperature state, and heat-proof gloves should be worn for operation to avoid burns. The cutting action should be standardized to prevent cuts. Laboratories should be equipped with appropriate fire protection facilities. The electrical part of the instrument should be well grounded to prevent leakage.
References
1. GB/T 3682-2018 Determination of melt mass flow rate and melt volume flow rate of thermoplastics.
2. ASTM D1238-20 Standard Test Method for Melt Flow Rates of Thermoplastics by Extrusion Plastometer.
3. ISO 1133-1:2011 Plastics — Determination of the melt mass-flow rate and melt volume-flow rate of thermoplastics.