JP4085608B2 - Mold cooling water treatment method - Google Patents

Description

[0001]
BACKGROUND OF THE INVENTION
The present invention relates to a mold cooling water treatment method for preventing clogging of steam holes such as core vents opened on the mold surface in in-mold foam molding using foamable particles of thermoplastic resin. is there.
[0002]
[Prior art]
In in-mold foam molding using foamable particles of thermoplastic resin, a cylindrical core vent or the like is embedded in the entire mold surface. The core vent is, for example, a cylindrical shape having a diameter of about 10 mm, and approximately 20 columnar pores having a diameter of about 0.5 mm are formed on a circular end surface in contact with the product. There is also a type (slit type) with a groove having a width of about 0.5 mm. In the present invention, the steam passages of the steam holes provided by these are collectively referred to as pores. These pores serve as a passage for heating steam and receive the foaming pressure of the product. For example, about 1000 core vents are mounted per fish box.
[0003]
Pores of the Koabento is easily closed because thin, when closed, because as the steam is deteriorated, and insufficient heating of the product in its vicinity, partial fusion insufficient, resulting in foaming insufficiency. In order to compensate for this, if the heating time is extended, a part where heating is excessive is generated, the molding process becomes unbalanced, and the molding cycle is deteriorated.
[0004]
When the core vent is blocked, the pores are small, so removing the blockage is a laborious and very difficult task. If the occlusion is severe, the core vent will be replaced, again resulting in significant costs and time loss. Accordingly, there has been a strong demand for the development of measures to prevent pore clogging.
[0005]
[Problems to be solved by the invention]
Analyzing the pore clogging material, the main component is an additive of raw material resin such as silica (hereinafter sometimes referred to as silicic acid), mineral substances contained in mold cooling water such as calcium, and styrene resin. Some stearates. Silica is a silicate such as zinc silicate associated with zinc or calcium silicate associated with calcium, and forms a very strong scale.
[0006]
The stearate is calcium stearate or magnesium stearate, and the scale formed by these substances is hard enough to be peeled off with a spatula, but has a dense structure and is a main component that blocks pores. It has become one of the.
[0007]
Resin such as styrene resin involved in pore clogging is one that has penetrated into the pores due to foaming pressure at the time of molding and remains for some reason at the time of mold release. Once the resin remains in the pores, the resin further fuses and grows on it.
[0008]
Since the surface of the pores is a metal or polytetrafluoroethylene coated with a metal surface, the styrene resin is relatively slippery on the pore surface. It is hard to remain even if it bites into. However, when the scale adheres to the surface, fine irregularities are formed on the surface, and the resin tends to remain. Therefore, in order to prevent clogging of pores such as core vents, it is important to prevent the formation of silicate and the formation of stearate.
[0009]
[Means for Solving the Problems]
Silicate is formed when the pH is alkaline. By the way, the tempering agent added to the boiler feed water contains hydrazine as an oxygen scavenger. Since hydrazine is a volatile alkaline substance, it is accompanied by steam and reaches the mold during heating. Therefore, if the concentration of hydrazine is lowered, the formation of silicate can be suppressed because it can be prevented from becoming alkaline.
[0010]
Silicates detected as an obstruction are mainly zinc silicate, calcium silicate, magnesium silicate and the like. Zinc silicate is obtained by replacing zinc contained in zinc stearate, which is an additive for raw material beads, with calcium. Calcium silicate and magnesium silicate are a combination of hardness components in cooling water and silicic acid. Therefore, if the cooling water does not contain hardness components such as calcium and magnesium, a strong silicate will not be generated. In addition, since the sodium salt has high solubility in water, it can be expected not only to be scaled itself but also to wash away other components that are easily scaled.
[0011]
As described above, when all of the hardness components detected as hardness (ie, total hardness) such as calcium and magnesium in the mold cooling water are removed in an attempt to prevent the occurrence of pore clogging, high water softening is performed. In addition, a serious detrimental effect that the surface of the mold corrodes occurs. That is, the mold material is often aluminum, but when this aluminum is repeatedly exposed to high temperature steam for a long period of time, the surface is corroded and undesired phenomena such as a decrease in mold strength occur. This is because hardness components exist in normal cooling water, so that a thin film is formed on the metal surface of the mold, so that the surface of aluminum is protected from such corrosion, whereas the hardness due to softening of water. This is because the removal of the components eliminates the formation of such a film.
[0012]
Japanese Patent Application No. 7-252430 can be cited as a method for preventing metal corrosion as a side effect while removing the hardness component that is a cause of scale. This invention removes 100% of the hardness component of make-up water on the premise of circulating cooling water, while reducing the amount of blow water, increasing the total alkalinity and making the pH 9.0 or higher. is there. A pH of 9.0 or higher is a strong alkali, and it is difficult to say that it is an effective method because it exposes factory workers to the risk of illness and cannot be discharged as factory wastewater.
[0013]
As a result of studying a method for preventing the formation of silicate while preventing the corrosion of aluminum, the present inventors have effectively removed the hardness component concentration in the mold cooling water to 10 to 40% of the hardness of the raw water. There is. Add sodium ions. The present inventors have found that the above-mentioned problems can be solved by using knowledge such as setting the residual hydrazine concentration in boiler feed water to 0.5 ppm or less.
[0014]
That is, the present invention
1. In the mold cooling water pit, a compartment with an open top is provided, the top of the compartment is made lower than the liquid level of the pit, and the water softener is installed upstream from the mold cooling water feed pump inlet, An outlet pipe of the water softener is introduced into the compartment, and an inlet pipe for the mold cooling water is provided to feed the mold cooling water from the compartment to the mold, and the hardness of the raw water is increased using the water softener. A method for treating mold cooling water, characterized by reducing the original hardness to 10% to 40% and softening the water, and using the treated water as mold cooling water.
2. The water softener is provided with a bypass line and a valve, and by adjusting the flow rate of raw water in the bypass line by the valve, the hardness of the raw water is softened to 10% to 40% of the original hardness 1 The processing method of description.
[0016]
3. 3. The processing method according to 1 or 2 , wherein sodium ions are added to the mold cooling water.
4). The processing method according to 3, wherein sodium ions are added using a water softener.
5. The processing method according to 3 or 4, wherein an aqueous sodium salt solution is used for the addition of sodium ions.
6). 6. The treatment method according to 5 , wherein sodium bicarbonate is used as the sodium salt.
[0017]
7). 6. The treatment method according to 5 , wherein sodium hexametaphosphate is used as the sodium salt.
8). The processing method according to any one of 1 to 7 , wherein the mold cooling water is softened and the residual hydrazine concentration in the boiler feed water is 0.5 ppm or less.
9. By reducing the dissolved oxygen concentration in the boiler feed water using a membrane deoxygenator, the amount of hydrazine added to the boiler feed water is reduced, and the residual hydrazine concentration in the boiler feed water is 0.5 ppm or less. 9. The processing method according to 8 .
[0018]
DETAILED DESCRIPTION OF THE INVENTION
The present invention aims to prevent corrosion by generating a thin film of a hardness component on the mold surface while preventing formation of a silicate having a strong scale. The formation rate of silicate is roughly proportional to the product of the concentration of silicate and the concentration of the hardness component. The concentration of the hardness component that achieves appropriate film formation while suppressing the generation rate of the silicate is not determined by the concentration of the hardness component alone, and is naturally affected by the concentration of the silicic acid content. Here, the hardness component means a Ca component, an Mg component, or the like. If the concentration of the silicic acid component is about 20 ppm, it is sufficiently effective to reduce the concentration of the hardness component to 20 ppm. However, if the concentration of the silicic acid component exceeds 50 ppm, it is necessary to reduce it to about 5 ppm. From these data, if the concentration of the hardness component is lowered to a range of 10% to 40% of the concentration of the raw water, the effect of preventing the blockage of the core vent pores can be seen. Further, the effect is particularly great if it is in the range of 10% to 20%.
[0019]
A water softener is effective in reducing the concentration of the hardness component in the mold cooling water. The water softener adsorbs calcium ions and magnesium ions which are hardness components by the action of the ion exchange resin, and releases sodium ions instead.
[0020]
It is desirable that the water softener is installed at the outlet or the entrance of the mold cooling water pump to perform the water softening treatment. At this time, since the fluctuation of the flow rate of the mold cooling water is generally large, as shown in FIG. 2, it is desirable to use it together with the installation of a cushion tank 13 for absorbing the flow fluctuation using the air pressure.
[0021]
If the water pressure of the cooling water is higher than the pressure resistance of the water softener, the water softener 2 is installed at the entrance of the mold cooling water feed pump 3 as shown in FIG. 2 and FIG. It is desirable to install on the exit side. As a concrete means for adjusting the hardness component concentration of the mold cooling water to 10 to 40% of the hardness component concentration of the raw water, a line 6 for bypassing the water softener 2 is provided as shown in FIG. The concentration of the hardness component is adjusted by installing a valve and adjusting it. Adjust the opening of the bypass valve using a flow meter in the line as a guide. The hardness component concentration of the mold cooling water is measured, and the degree of water softening treatment is adjusted by adjusting the amount of water passing through the water softener and the amount of water passing through the bypass by a method such as a standard.
[0022]
A method of removing the hardness component of the water in the pit for storing the water used for the mold cooling water is also effective. However, this is not effective when the water in the pit is used in a large amount for other purposes or is discarded due to overflow from the pit.
[0023]
It is also possible to install a water softener on the line that feeds liquid to the pit, or to install a water softener by providing a line that circulates water in the pit. In the former case, it is preferable to provide a bypass line in the water softener to adjust the concentration of the hardness component. In the latter case, the concentration of the hardness component is determined by the ratio of the raw water inflow amount and the water softener passage amount. The amount of water supplied to the water softener is controlled to adjust the concentration of the hardness component.
[0024]
As shown in FIG. 2, the mold cooling water pit 4 is partitioned and a compartment 12 is provided. After the water in the cooling water pit is treated by the water softener 2, the water is stored in the compartment 12, and this is sent to the mold cooling water pump. It is also effective to send the liquid at 3. In this case, it is necessary to absorb the flow rate variation of the mold cooling water in this compartment. Increase the capacity of the compartment and absorb fluctuations, or reduce the flow rate by making the wall height of the compartment lower than the liquid level so that the mold cooling water pit and water can go in and out. I want to see that. Of course, the combined use with the method of absorbing the fluctuation of the flow rate by the cushion tank 13 using air pressure is also an effective method. In the former case, it is desirable to provide a bypass in the water softener in order to adjust the concentration of the hardness component. In the latter case, the water in the pit flowing into the compartment is almost not treated by the water softener, in other words, water that bypasses the water softener, so there is no need to provide a bypass if the compartment capacity is appropriate. .
[0025]
Since the present invention is a method of removing a certain amount of hardness component, it is natural that it is effective in a factory where the concentration of the hardness component is high and when the silica concentration in the cooling water is high, Especially effective. This is because the main components of the clogging substances that cause clogging of the pores such as mold core vents are silica-based silicic acid compounds and fatty acid salts added as a raw material to the raw material resin. This is because calcium ions are indispensable.
[0026]
When sodium ions increase in the mold cooling water, pores such as core vents are less likely to be clogged. This is because sodium salts are highly water-soluble and have a high cleaning effect. During molding, pores such as core vents are exposed to steam for heating and cooling water, so if the cooling water contains a lot of sodium salt, not only will it be difficult to scale itself, but other scale components will also be contained. The effect of washing away can also be expected.
[0027]
Addition of sodium ions is possible by treatment with a water softener. This is because the water softener has a function of using an ion exchange resin to adsorb hardness components such as calcium ions and magnesium ions and to release sodium ions.
[0028]
A method of adding a sodium salt is also desirable. As an addition method, it may be added in the form of powder, but it is desirable to dissolve in water once to make an aqueous solution and drop it with a pump. As the sodium salt, sodium chloride, sodium carbonate, sodium hydrogen carbonate, sodium sulfate, sodium nitrate, sodium acetate, sodium hexametaphosphate and the like are preferable. In any case, it is preferable to increase sodium ions by, for example, 10 ppm or more from the raw water.
[0029]
Silicate, which is one of the main components of the pore blockage, generates pH on the alkali side at a high temperature of 80 ° C. or higher. Therefore, it is effective to prevent the pH of the heated steam drain from being on the alkali side in order to suppress the formation of the plug. A boiler and oxygen scavenger are added to the water supplied to the steam generating boiler.
[0030]
As the oxygen scavenger, hydrazine is generally used. Hydrazine is a reducing agent and reacts with dissolved oxygen, while it is a volatile alkaline substance. In order to reliably reduce the dissolved oxygen concentration, an excessive amount of hydrazine is added and water is supplied to the boiler, so residual hydrazine showing alkalinity is accompanied by steam and reaches the core vent of the mold. In order to prevent this, the residual hydrazine concentration in the boiler feed water is preferably 0.5 ppm or less.
[0031]
It is more preferable to remove dissolved oxygen by a physical method without using an oxygen scavenger which is a volatile alkaline substance such as hydrazine. Examples of the physical dissolved oxygen removal method include a membrane deoxygenator and a heat deaeration method.
[0032]
【Example】
( Reference Example ) In a foamed styrene molding plant, a water softener was installed at the pump outlet of the mold cooling water feed line, a water softener bypass line was provided, and 25% was bypassed. The mold cooling water line was connected to a cushion tank filled with air at the top to absorb fluctuations in the flow rate of the cooling water. Moreover, since the boiler feed water was processed by the membrane deoxygenator, the amount of hydrazine , which is a deoxidizer in the boiler feed water, is zero. The hardness of the raw water was 20 ppm, but the hardness of the mold cooling water after the treatment was reduced to 5 ppm. And the density | concentration of the sodium salt of metal mold cooling water was 15 ppm. When the fish box was formed into 50,000 shots and the mold was evaluated, the ratio of the entire core vent in which the pores were completely blocked was 0.1%. The mold used here is 6 pieces, and the number of core vents per piece is 2500 pieces. In addition, the measurement of hardness and the like in the examples in the present invention was simply measured using “Pack Test” manufactured by Kyoritsu Riken Corporation.
[0033]
(Example 1 )
In a foamed styrene molding plant, the mold cooling water is pumped from a pit to a water softener, and treated water is sent to a cylindrical compartment having a diameter of 50 cm installed in the pit. The processing liquid in this pit is sent to the mold cooling water line. The outer edge of the cylindrical compartment is 10 cm lower than the pit liquid surface, and when using mold cooling water beyond the capacity of the water softener, the water in the pit flows into the cylindrical compartment, On the contrary, when it becomes excessive, the water processed with the water softener in the cylindrical compartment overflows into the pit.
[0034]
In addition, a cushion tank in which air is enclosed in the tank is installed at the outlet of the mold cooling water feed pump to absorb fluctuations in the mold cooling water.
[0035]
The raw water hardness was 25 ppm, the hardness of the mold cooling water after treatment was 7.5 ppm, and the concentration of sodium salt was 15 ppm. The concentration of hydrazine in the boiler feed water was 5 ppm. When a fish box was molded by 40,000 shots using the same mold as the reference example and the mold was evaluated, the ratio of the total number of core vents in which all the pores were blocked was 0.5%. .
[0036]
(Example 2)
In the foamed styrene molding plant, raw water was treated in the same manner as in Example 1, and an aqueous solution of 8% sodium hydrogen carbonate was dropped into the mold cooling water pit with a pump. The hardness of the raw water was 25 ppm and the concentration of sodium salt was 15 ppm. However, the concentration of the hardness component of the mold cooling water after treatment was 7.5 ppm, and the concentration of sodium salt was 30 ppm. The concentration of hydrazine in the boiler feed water was 5 ppm. After forming 80,000 shots of the fish box using the same mold as in Example 1 , the number of core vents in which all the pores are closed is counted, and the ratio to the total number is 0.5%. there were.
[0037]
(Comparative Example 1) In a foamed styrene molding plant, without using water softening treatment, the mold cooling water hardness is 25 ppm and the sodium salt concentration is 15 ppm. After forming 40,000 shots, the mold was disassembled for maintenance, and the number of core vents whose pores were completely blocked was measured, and the ratio was 17%. The concentration of hydrazine in the boiler feed water was 5 ppm.
[0038]
【The invention's effect】
In in-mold foam molding using foamable particles of thermoplastic resin, blockage of the core vent on the mold surface is prevented, resulting in molding defects such as uneven heating, and excessive molding time to avoid it Was able to be prevented. In addition, man-hours for maintaining the closed mold were reduced.
[Brief description of the drawings]
FIG. 1 is a layout view showing an example in which a line for bypassing a water softener is provided, while boiler supply water is treated by a deoxygenation device.
FIG. 2 is a layout view showing an embodiment of the present invention and showing an example in which a compartment is provided in a pit of mold cooling water.
FIG. 3 is a layout diagram showing an example in which sodium ions are added .
FIG. 4 is an arrangement view showing an example in which an outlet line of a water softener is connected to an inlet of a mold cooling water feed pump .
[Explanation of symbols]
DESCRIPTION OF SYMBOLS 1 Foam styrene molding machine 2 Water softener 3 Mold cooling water line feed pump 4 Mold cooling water pit 5 Mold cooling water feed line 6 Water softener bypass line 7 Molding steam line 8 Boiler 9 Boiler water supply line 10 Membrane type Deoxygenator 11 Water softener pump 12 Cylindrical compartment 13 Cushion tank 14 Air layer 15 Sodium salt aqueous solution tank 16 Sodium salt additional pump

Claims (9)

In the mold cooling water pit, a compartment with an open top is provided, the top of the compartment is made lower than the liquid level of the pit, and the water softener is installed upstream from the mold cooling water feed pump inlet, An outlet pipe of the water softener is introduced into the compartment, and an inlet pipe for the mold cooling water is provided to feed the mold cooling water from the compartment to the mold, and the hardness of the raw water is increased using the water softener. A method for treating mold cooling water, characterized by reducing the original hardness to 10% to 40% and softening the water, and using the treated water as mold cooling water. The bypass line and valve is provided in the water softener, by adjusting the flow rate of the untreated raw water bypass line by the valve, characterized by softening up to 10% to 40% of the original hardness hardness of raw water according Item 2. A processing method according to Item 1 . The treatment method according to claim 1 or 2 , wherein sodium ions are added to the mold cooling water. The processing method of Claim 3 which adds sodium ion using a water softener. The processing method according to claim 3 or 4 , wherein an aqueous solution of sodium salt is used for addition of sodium ions. The processing method according to claim 5 , wherein sodium bicarbonate is used as the sodium salt. The processing method according to claim 5 , wherein sodium hexametaphosphate is used as the sodium salt. The processing method according to any one of claims 1 to 7 , wherein the mold cooling water is softened and the residual hydrazine concentration in the boiler feed water is set to 0.5 ppm or less. By reducing the film dissolved oxygen concentration in the boiler feed water using a deoxygenation apparatus, according to claim 8 which reduces the hydrazine addition amount of the boiler feedwater, the residual hydrazine concentration in the boiler feedwater below 0.5ppm The processing method described.

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