Plastic products are made and injected using small pieces of plastic. They are used in a wide range of plastic items. The quality, color, and amount of moisture on the surface of plastic particles have a direct effect on the quality of plastic products made by injecting plastic particles.
One important thing that affects the products is how wet the surface of the plastic particles is. Because injection molding is a high-temperature molding process, if a particle’s surface has a certain amount of water, the water will boil off and make bubbles during the high-temperature molding process. Plastic moisture meters are an important part of the way plastic resins like polyamide (PA) and polycarbonate are processed, how they look, and what they are made of (PC).
If plastic particles with too much water are used in production, there will be problems during processing that will eventually affect the quality of the finished product. These problems include surface cracking, reflection, and a decrease in mechanical properties like impact resistance and tensile strength. So, controlling the amount of water is a very important part of making high-quality plastic products. So, testing the amount of moisture is a necessary step in the process of making plastic.
What is the allowable moisture content of various plastic materials?
Conventional plastics:
- ABS has a maximum moisture content of less than 0.15% and a drying time of 2 hours at 80 °C.
- When the moisture content of PP is less than 0.2%, bake the material at 90 °C for 1 hour (or do not bake the material).
- PA6/66 0.1% allowable moisture content drying material at 90 °C for more than 4 hours
- The allowable moisture content of PC is less than 0.02%, and the drying material is at 120 °C for 3–6 hours.
- POM can be dried at 85 °C for 3–5 hours and has an allowable moisture content of less than 0.15%.
The drying temperature and time are used as a guide and have a strong relationship with the temperature and humidity of the air. During the Meiyu season, there is a lot of moisture in the air, which makes it hard to mold PA66 and PC materials. Dehumidification dryers are sometimes needed to get the drying effect. Nylon, for example, contains less than 0.1 percent water. In fact, it must sometimes reach 0.01 or 0.03 percent to meet the product’s requirements. If it doesn’t, there will be problems with the surface quality and there will be pores on the inside. There is also some stuff that isn’t PC. If the material gets wet, it will break down.
How will the plastic granules’ moisture affect the hot runner molding process?
The demands on plastic processing technology are getting higher and higher, and the amount of moisture has a huge effect on how plastic is processed, molded, and the quality of the product. In the plastics industry, a plastic rapid moisture meter is a tool that is used to find problems.
Many plastics can take in water from the air. The amount of water they can take in depends on the type of resin. Moisture in plastic particles, even water that has condensed on the surface, can also make molding and processing engineering plastics more difficult. This water absorption could cause problems during processing, make the surface of the product look bad, or hurt its mechanical properties. With just your eyes, it’s hard to tell if there is water or not.
How should we handle water-sensitive plastics?
- Drying plastic materials
Most engineering plastics need the particles to have less than a certain maximum amount of moisture. Whether or not the plastics need to be dried depends mostly on how sensitive the raw materials are to water. In general, the amount of moisture in plastics depends on how they are transported, how they are packaged, and how long they have been stored.
Polyamide (PA), for example, is usually moved in bags. This kind of bag is waterproofed by a layer of aluminum foil. When it’s time to use the bag, it can be opened right away to get the stuff out. But in most polyamide (nylon) processing plants, the raw resin must be dried first. However, some people think that the plastic doesn’t need to be dried if it will be used in less than an hour.
On the other hand, PET and PBT are very sensitive to moisture and need to be dried so that the impact strength of the products doesn’t change. Also, these resins will quickly soak up water again after they dry. So, in some cases, the company that processes the PBT and PET resins must be extra careful not to use open containers when transporting and sending them.
At the same time, you should think about how long the resin stays in the hopper. In a bad climate, the amount of moisture that PET can absorb in 10 minutes can be even higher than 0.02 percent of the maximum value for product moisture. Recycled materials that have been dried and crushed or granular materials that have absorbed a lot of water (like when they are put in open containers) need special care. In this case, the suggested drying time usually doesn’t work. Fully wet polyamide nylon should be dried for at least 12 hours. Under these dry conditions, the material will yellow no matter what. So, the following rules should be kept in mind:
- The runner’s recycled materials must be stored and re-crushed in a closed container.
- If only a portion of the material is used, close the container or bag.
- The hopper must be closed.
How to dry plastic?
We must follow the drying process to make sure that the plastic products we make are of high quality. For example, you can’t dry polyester engineering plastics with simple hot air drying methods. Instead, you can use an air dryer (dehumidification dryer) that takes the moisture out of the air.
Only those pieces of equipment should be used that can dry things well and consistently in a variety of conditions. In addition to drying at the right temperature, it is important to make sure that the dew point in dry air is less than 20 °C. When using multi-container devices with different filling heights and bulk densities, each container should be able to get enough air flow.
How do you measure water content?
Some measuring tools, like the halogen rapid drying method, can tell how much water is in plastic particles. So that the measurement error doesn’t happen, the sample should be taken from the bottom of the feed hopper and put in a suitable container. The samples can be put in multi-layer bags made of polyethylene and aluminum, which can be sealed with heat, or they can be put in a sealable glass container that is used in the lab.
What kind of moisture meter can be used to measure the amount of water in plastic?
There are two kinds of fast moisture meters: those that use infrared light and those that use halogen light. Because its heating source is circular, the halogen rapid moisture tester is better for finding moisture in plastics because it can heat the plastic more evenly and won’t burn it during the testing process.
What does a moisture meter for plastic particles do?
A plastic particle moisture meter is also called a moisture meter, plastic particle rapid moisture meter, plastic particle moisture detector, moisture analyzer, water meter, and moisture detector. A moisture meter is an instrument that can measure the amount of water in different solids, liquids, gases, and other samples, both organic and inorganic. It can be split into physical measurement methods and chemical measurement methods based on how the measurements are made.
The weight loss method, the distillation stratification method, gas chromatography, and other methods are often used to figure out a substance’s physical properties. The Karl Fischer method, the toluene method, etc. are the most common chemical methods for figuring out what something is. The Karl Fischer method has been chosen as the international standard for figuring out how much trace water there is by the International Organization for Standardization.
The most common type of plastic moisture tester uses the drying weight loss method and quickly heats the sample with its heating system so that the sample’s moisture can evaporate as quickly as possible. This makes it possible to find out how much moisture is in the sample in a very short amount of time.
The utility model is good because it heats and cleans evenly, is very efficient, cuts down on work time and saves energy, and most general samples can be found in about 3 minutes. The method used is based on the same idea as the national standard oven method, and the test results can be changed. The instrument only has one button to push, which makes it easy to use and keeps human error from affecting the results of the measurements.
What kinds of plastic can be checked with the plastic moisture tester?
The plastic moisture tester can be used in PP, ABS, ASA, PVC, PET, PPS, CA, cap, PA66, PE, PA, PA6, EAE, EAA, and other plastic industries to quickly check the moisture of raw materials, semi-finished products, and finished products.
How much does a plastic moisture meter cost?
There are many ways to measure the amount of water in plastic, so there are many different kinds of instruments for doing so. There are plastic moisture measuring instruments that can be taken with you and those that are used in a lab. There are different prices. In general, the price of plastic instruments that measure moisture is between $300 and $3,000.
How to use a plastic moisture meter correctly?
- Power on: turn on the power supply and turn on the power switch at the back of the instrument;
- Self-inspection: the weight display window displays “0”, and the stable display window displays the initial value, which is generally room temperature (below 40 ℃);
- Preheating: start up and preheat for 30 minutes. The data measured after preheating is true and valid.
- Setting out: open the heating barrel, put in the sample, close the heating barrel and wait for the weight display to stabilize for 20 seconds;
- Press the test key and wait for the instrument to heat itself.
- When the alarm sounds, press the display key once to display the discrimination time, and then press the display key again to display the final water score. Continuously press the display key to view other test parameters, and then press “clear” to finish the test.
- Open the heating barrel and wait until the temperature display returns below 40 ℃before the next test.