Operation Guide

To ensure safe use, it is essential to carefully read the instructions and fully comply with this guide!

1、 Prevent the silicone oil in the U-shaped tube from rushing up to the horizontal tube C

1. As long as the left valve J is open, the middle valve G must be opened first; The necessary condition for closing the intermediate valve G is that the left valve J must have already been closed, and when starting the operation, attention should be paid to temperature changes. If there is an abnormal rapid change, the intermediate valve should be opened as soon as possible.

Before releasing the vacuum, first open the middle valve G, and then slowly open the left valve J.

During the testing process, the operator should pay attention to the changes in the liquid level in the U-shaped tube L. If the liquid level on one side rises and approaches the horizontal tube, the intermediate valve G should be opened in a timely manner.

2、 Prevent vacuum pump oil from flushing out

After vacuum pumping is completed, close the left valve J. Before disconnecting the power supply of the vacuum pump, the vacuum valve F must be opened first to connect the vacuum pump to the atmosphere.

A circular buffer bottle must be inserted in the middle of the vacuum hose connecting the vacuum pump and the U-shaped tube device to avoid trouble caused by the vacuum pump oil rushing into the U-shaped glass device in case of carelessness.

3、 Prevent glass instruments from shattering

If the glass device connector needs to be inserted into a vacuum hose, it must be coated with vacuum grease in the middle.

2. The vacuum hose must not be directly removed from the glass device connector. The hose should be cut and removed.

3. Be careful when putting on the test tube. Apply an appropriate amount of vacuum grease to the mouth of the test tube and turn it dozens of times in one direction. When moving the furnace, pay attention to aligning its center position with the test tube.

4、 Prevent air leakage

1. The valve plug and valve body are matched for grinding, so it is necessary to ensure that their numbers are consistent.

2. Over time, the vacuum grease at each valve has hardened and the air tightness has decreased. It should be reprocessed: clean the valve, reapply the vacuum grease, and then rotate the valve handle in the same direction (must be!! and must also be in this direction during normal operation!!) for 50-100 turns.

3. Always be careful during operation, handle with care to prevent breakage.

5、 Prevent the temperature rise of the sample during vacuum pumping

When adding the sample to the test tube and connecting it to the testing device (differential pressure tube), and vacuuming, the bottom of the test tube should be close to the heating cylinder. To avoid heat radiation convection and affect the testing accuracy, please place a circular hollow insulation board on the heating cylinder before vacuuming and the heating cylinder rises.

6、 Replacement of thermal oil

After using the heat transfer oil for a period of time, it evaporates and ages. It should be cleaned and replaced in a timely manner to avoid the test tube from being suspended in the heat transfer oil during the heating cylinder lifting (as shown in Figure 4) due to the hardening of the heat transfer oil, which may cause lifting obstruction and even damage to the glass device.

SF-1 differential pressure method moisture determination device

operation instructions

The commonly used methods for determining trace moisture in plastic particles include differential pressure method, electrolysis method, Karl Fischer method, etc. Among them, the differential pressure method for moisture determination has been widely used in the intermediate process of the chemical fiber plastic industry due to its advantages of speed, accuracy, easy operation, and low cost of use, especially for the determination of trace moisture content in polyester chips, nylon 6, nylon 66 and other particles that have a significant impact on spinning quality after drying treatment before melt spinning. It is also applicable for the general determination of trace moisture in particles such as nylon 6 and nylon 66, as well as plastic resin. At present, there is no complete set of equipment supply in China, and it is quite troublesome for customers to customize and manufacture according to their own needs. This device refers to the methods of national and international standards (see appendix) and the usage habits of many domestic manufacturers. It is assembled as a complete set, providing users with considerable convenience and testing assurance.

The differential pressure method moisture determination device is suitable for measuring extremely small amounts of moisture bound to the internal molecular structure of raw materials, but not suitable for determining the equilibrium moisture between raw materials and the environment. Heating up and melting when there is moisture inside the material will cause degradation, resulting in a decrease in intrinsic viscosity and directly affecting product quality. Generally, it is required that the moisture content be less than 0.03% before spinning. Therefore, after drying and before spinning, the extremely low moisture content inside the raw material must be measured by pressure difference method. The moisture content of vacuum packaged plastics can also be determined using the pressure difference method.

The maximum moisture content measured by the device is 1.5mg.

When the sample contains a large amount of volatile mixed substances other than water, attention should be paid to the reliability of its test results.

The basis of this testing method is GB12006.2 Determination of Moisture Content in Polyamide, ISO 960-1988 (E) Plastics - Determination of Moisture Content in Polyamide (PA), and ISO 6188-1980 "Plastics - Determination of Moisture Content in Polyethylene Terephthalate Granules" (see appendix).

• working principle:

Figure 1

The experimental device shown in Figure 1 is an airtight system composed of glass pipes, test tubes, and glass bubbles A and B. In the U-shaped pipeline L, there is a certain amount of silicone oil. When the gas valve G is open, the system should reach a high degree of vacuum. If the entire system has good airtightness, then close the gas valve G. The pressure of D and E on the liquid surfaces on the left and right sides of the silicone oil should be the same, and the two liquid surfaces of the silicone oil should be on the same horizontal plane. If for some reason, the air pressure on the right side increases, the pressure on the right liquid surface D increases, causing the liquid level of silicone oil to rise and fall, with the right liquid surface falling and the left liquid surface rising. If a certain substance containing water is first placed in a test tube, and the water can only be released under certain conditions (such as heating), then, before the conditions for water release are reached, the liquid surface pressures of D and E are equal. After reaching the conditions for water release, the system will

Due to the effect of water vapor, the pressure inside the side pipeline increases, causing the pressure at the D liquid level to rise and the liquid level to fall, while the liquid level at E rises. The pressure difference formed by the D and E liquid levels is balanced with the pressure of the water vapor on the right side. The more water vapor there is, the greater the pressure generated, and the greater the amount of liquid level rise and fall. When the moisture content reaches a certain value, causing the water vapor pressure to reach the critical point of saturated steam, a portion of the water vapor condenses back into water (in the form of mist or droplets), and the pressure no longer increases. The moisture content corresponding to the critical point of saturated steam, which is the highest moisture content that the device may measure.

The differential pressure method is used to determine the moisture content by comparison. Using different known moisture contents to conduct experiments, identify the corresponding rise and fall of different D and E liquid levels for different moisture contents. Therefore, when testing with substances with unknown moisture contents, the moisture content can be determined based on the different rise and fall of the D and E liquid levels.

This method is commonly used by domestic manufacturers to determine the moisture content of dried polyester chips and nylon. The general test temperature is:

Polyester chip	220±5℃
Polyamide 6, 66, 69, 610, 612	195±5℃
Polyamide 11, 12	170±5℃

● Structure:

The differential pressure method moisture determination device mainly consists of the following measuring parts, vacuum pump, heating and temperature control parts:

1. Measurement section

The measuring part is shown in Figure 2, which is a combination of glass structural components, vacuum pump, and vacuum gauge, requiring good airtightness of the entire structure. The vacuum pump keeps the measuring part in a high vacuum state before testing.

2. Heating section

Composed of a heater, a furnace with a floating centering device for test tubes, and a lifting platform, the lifting platform can be moved up to insert the test tube into it and heat the sample.

The test tube is inserted into the sleeve, which is suspended in the furnace. Therefore, when the test tube M is connected to the conical port N and tilts (due to glass processing reasons, this is inevitable), it can still be placed in a free state in the furnace. The casing and furnace are thermally conducted by thermal oil (silicone oil) (see Figure 4),After a period of use, the heat transfer oil will evaporate and age, so it should be added and cleaned in a timely manner.

3. Temperature control part

Temperature is controlled by a single-chip microcomputer. Set by a touch switch, the temperature control accuracy is higher.

● Technical indicators

Moisture content of 5-500 ppm (when weighing 3g of the sample)

30-3000 ppm (when weighing 0.5g of the sample)

Corresponding to a maximum measurable moisture content of 1.5mg

Temperature range: Room temperature to 250 ℃

Display error ± 3 ℃ (170 ℃, 195 ℃, 220 ℃)

Temperature fluctuation ± 2 ℃

Vacuum degree ≤ 100Pa

Power supply 220V 50Hz 2A

Rated power 0.35kw

Figure 2

● Installation

Refer to Figure 2.

1. Connect the two idle joints of the four-way tube with vacuum hoses and connect them respectively to the vacuum gauge and vacuum pump (through buffer balls). Apply some vacuum grease to the connection points. After inserting the hoses, tighten them with hose clamps to prevent air leakage.

2. Remove the glass valve G, insert the plastic tube and extend it to one end of the U-shaped tube. Use a syringe to extract a small amount of methyl silicone oil and slowly inject it into the U-shaped tube until the zero line position of the marked line is up and down (as shown in Figures 2 and 3, which have been added at the factory). Note that the closer it is to the zero line position, the slower it should be. If too much is injected, it will be troublesome to extract it. After reaching the liquid level, let it stand still for a period of time (about 1 hour). After the air in the oil escapes, the liquid level will slightly decrease. At this time, replenish it appropriately. Be careful not to let silicone oil contaminate parallel pipeline C.

Figure 3

3. Apply vacuum grease to the frosted surface of the plugs of valves G, J, and F. After inserting into the valve hole, rotate continuously in one direction until the joint surface of the plugs is sealed reliably and does not leak. Vacuum grease should not block the perforations in the plug.

4. Remove the pressure plate above the furnace, take out the copper sleeve, and add heat transfer oil (also using silicone oil). After inserting the sleeve, the oil level should rise to a margin of 5mm from overflow (after heating, the oil level should rise).

The above items 2, 3, and 4 have been properly set up when the device leaves the factory. If any problems occur due to transportation, please follow the above instructions and handle them yourself.

● Airtightness test

After the installation of the device is completed, the airtightness test can be carried out.

Apply a small amount of 7501 vacuum grease (high temperature resistant) on the outer side of the conical interface N on the right side of the glass device. After inserting the conical mouth of the dried test tube M, rotate it continuously in one direction to ensure the sealing of the interface.

Open glass valve G, close F and J, start the vacuum pump, slowly open glass valve J, and connect the vacuum pump to the entire glass system.Please pay full attention that the numbering of the glass valve plug and valve body cannot be confused, otherwise it will directly affect the vacuum degree.

After 10 minutes, place the vacuum gauge in the testing position and observe the vacuum degree. If it has not reached 100Pa, try again for a few minutes.

After the vacuum degree is reached, close valve J and valve G in sequence. At this time, valve F can also be opened and the vacuum pump can be turned off to connect the four-way pipe to the atmosphere.

Close valve J first, then valve G, and make sure not to make any mistakes. Otherwise, the silicone oil will instantly rush into the left side of the horizontal pipeline C. Rotary valve

The direction of the plug should be consistent, and the movement should be slow and light.

After maintaining for 1 hour, observe that the liquid level difference between the two oil levels on the left and right sides of the U-shaped tube L should be less than 2mm. Otherwise, it is caused by air leakage on one side, and the liquid level on the leaking side will decrease. Careful inspection should be carried out to check for poor sealing at the connection points, and to check for cracks in the glass device. Special attention should be paid to whether there are leaks in each valve. Otherwise, clean and reapply with vacuum grease before attempting again.

Attention: When replacing the silicone oil in the U-shaped tube, the instrument must be vacuumed for several hours to remove air from the new oil; New equipment or equipment that has been unused for a long time should also be vacuumed for a long time before reuse.

● Calibration

The purpose of calibration is to find the corresponding relationship between the moisture content and the liquid level difference (i.e. the liquid level difference between the left and right of the U-shaped tube) of this device, so that it can be compared and used in actual testing. Calibration is related to the glass device and the temperature of the testing environment.

Accurately weigh about 4, 8, 12, 16, and 20mg of sodium molybdate, and place them in a test tube and a drying dish for later use.

Turn on the power switch of the moisture measurement device, set the temperature to 220 ± 5 ℃, and wait for the temperature to stabilize.

Open valve G.

Insert the test tube of the test sample into the interface and seal it (apply 7501 vacuum grease, the same below).

Close valves F and J, start the vacuum pump, slowly open valve J, and evacuate to less than 100Pa, as small as possible.

Close valves J and G in sequence, open valve F to connect with the atmosphere, and turn off the vacuum pump.

be careful! After valve G is closed, close attention should be paid to the pressure changes on both sides of the U-shaped tube. When there is a significant change in the liquid level due to other reasons, the piston should be quickly opened to check if there is too much sample or if there is an issue with the air tightness.

Shake the right handle clockwise to lift the heated cylinder that has been kept at a constant temperature, and insert the test tube M into the cylinder.

Keep the sample insulated for 10 minutes or maintain a constant liquid level difference as indicated by the liquid level gauge.

Read the liquid level change value of the U-shaped tube.

Slowly and steadily open the G valve, then open the J valve (the order must not be wrong).

Lower the heating cylinder and replace the pre prepared sample for testing.

Represent the obtained data on a flat graph:

It can be seen that there is a linear relationship between the water content m · w on the left side of point e and the liquid level change value Δ h, which can be represented by the coefficient K (i.e. the slope of the line). The bending of the right line indicates that as the total moisture content increases, the change in liquid level decreases, indicating that it has entered a supersaturated state of steam. The moisture content corresponding to point e is the highest moisture content that the device can measure.

Calculate the coefficient K value of the straight line segment:

The K values obtained from different components should be consistent, as there is a linear relationship between moisture content and liquid level difference. If the total moisture content increases and the total change in liquid level decreases, it indicates that it has entered a supersaturated vapor state.

In the formula: m: sample mass (g);

w: The moisture content (g/g) in each gram of sample (such as sodium molybdate) can be calculated by molecular weight;

△ h: The change in liquid level inside the U-shaped tube before and after heating (mm).

The moisture content (w) per gram of sample is calculated by the following formula:

W (sample)=molecular weight of crystalline water/molecular weight

For example, if the molecular weight of sodium molybdate is 241.92 and the molecular weight of crystal water is 36, then

Sodium tungstate can also be used as a calibration sample, and copper sulfate was previously commonly used. Correspondingly, its moisture content is:

*At the temperature shown in the experiment, only 4 can be releasedOne.

● Measurement

The measurement method is similar to the calibration method:

Turn on the power switch of the moisture measurement device, set the temperature, and wait for the temperature to stabilize;

Open valves G and J, and close valve F;

Load about 2g of precisely weighed sample into a dry test tube (usually pre loaded and placed in a drying dish), insert the test tube into the interface and seal it;

Close valve J;

Start the vacuum pump;

Slowly open valve J and evacuate to less than 100Pa, as small as possible;

Close valve J and valve G in sequence;

be careful! After valve G is closed, close attention should be paid to the pressure changes on both sides of the U-shaped tube. When there is a significant change in the liquid level due to other reasons, the piston should be quickly opened to check if there is too much sample or if there is an issue with the air tightness.

Open valve F to connect with the atmosphere and turn off the vacuum pump;

Raise the temperature controlled heating cylinder and insert the test tube M into the cylinder;

Keep the sample insulated for 10 minutes until the liquid level difference indicated by the level gauge remains constant;

Read the liquid level change value inside the U-shaped tube;

Put down the heating cylinder and turn off the heating power if no further testing is required; Slowly and steadily open valve G, and then open valve J (the order must not be confused);

Remove the test tube.

Attention: ① When testing the powder, the piston should be slowly opened when vacuuming, and there should be a thin layer of glass wool covering the sample

Cotton is pre dried in an oven and stored in a drying dish after cooling.

② For samples with potentially high moisture content, attention should be paid to observing the liquid level gauge in the early stages of the experiment. If the liquid level changes significantly, valve G should be opened in a timely manner, the heat source should be disconnected, and the sample should be reduced before testing.

③ If the liquid level change value is too small to be easily read, the sample size can be appropriately increased.

④ Each sample should be tested twice. If there is a significant difference in the results, the air leakage should be checked before proceeding.

● Calculation:

In the formula: K: water content - liquid level difference coefficient (g/mm), calculated by calibration;

Δ h: liquid level difference in U-shaped tube before and after water release (mm);

m: Sample quality (g).

Figure 4

Observation: The reading on the thermometer observed.

T-ring: ambient temperature, calculated at the midpoint of the exposed mercury column height

② Actual temperature value: Actual value=Indication+Correction value+Dew diameter correction value

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