Preface
The plastic processing industry includes many and involves a wide range of knowledge. It includes knowledge in chemical engineering, molds, machinery, design, molding manufacturing and site management. There are many ways to process plastics. Common ones include injection molding, hot press molding, extrusion molding, blow molding, extrusion molding, elastomeric molding, foaming, etc. As far as single injection molding is concerned, with the continuous advancement of science, it has also developed from single-color injection molding to multi-color injection molding (also called sandwich injection molding); now there are nitrogen-assisted molding, water-assisted procedures and processes for processing thermosetting plastics. Liquid injection molding is also widely used in China. Injection molding has become the most important molding method for plastic molding today. The knowledge that our injection molding technicians or managers must master or understand mainly includes: the physical properties of plastics, the structure and function of the injection molding machine, the structure and related knowledge of the mold, the function of auxiliary equipment, and injection molding process knowledge including Problem analysis of product defects and how to improve the ability to solve practical problems. This book is mainly about injection molding process knowledge, including problem analysis of product defects and how to improve the ability to solve practical problems. It is a learning and training material written by integrating our many years of work and study experience.
Before we operate the machine, we must understand the characteristics of the materials used and the range of various process parameters of the materials. Including the physical properties of the material such as the molding temperature, drying temperature, yield rate, mold temperature, thermal denaturation temperature, etc. The physical properties of the material include the material's mechanical properties (various strengths), impact resistance, weather resistance, fatigue resistance, solvent resistance, fire protection level, fluidity, etc.
Of course, there are many factors that affect the strength of materials. These include the geometry of the plastic part, load, external force conditions, residual stress caused by unreasonable molding process and the orientation of the material itself after combination. The so-called external force conditions are tension, compression, twisting, deflection, shear, etc.
Plastics With the continuous development of science and technology, many plastics now use plastic additives to change the characteristics of the material in order to achieve certain or multiple characteristics of the material or to meet various use requirements of the product. In this way, many series of modified plastics have been derived. No matter how the product materials are updated, we can learn from the material suppliers about the physical properties, process conditions and usage methods of their materials.
1. Contents
1.1 Definition of plastic: Plastic is a natural or artificial polymer organic compound (resin) with plasticity and non-plasticity. Plastic refers to an artificial material composed of organic synthetic resin as the main component, with or without the addition of other compounding materials (plastic additives). It can usually be molded into devices with a certain shape under heating and pressure conditions. The so-called plasticity refers to the property that, like clay, it deforms when force is applied but does not return to its original shape after the external force is removed. This is the so-called plastic plastic. The so-called elasticity (elasticity) means that it deforms when a certain degree of force is applied, but returns to its original shape when the applied force is removed. This property is called elasticity (for example: rubber), and elastic objects are called elastomers (such as: elastic bands); Plastics use this plasticity produced when heated to be processed into various shapes. There are also devices that can be molded into certain shapes under heating and pressure conditions. Plastics that cannot be replasticized and reshaped later are called thermosets. Synthesis of
1.2 plastic: plastic is an important branch of organic polymer materials with various varieties, large output and wide range of uses. Plastics are also high-molecular organic compounds (polymers) formed by polymerizing low-molecular organic compounds (such as ethylene, propylene, styrene, vinyl chloride, vinyl alcohol, etc.) under certain conditions. The molecules that make up plastics have different molecular weights. There are more than 10,000 polymers, so plastics are polymer compounds (polymers). Generally, plastic molecules contain carbon (C) atoms and hydrogen (H) atoms, and some plastic molecules contain a small amount of oxygen (O). , sulfur (S) atoms. The basic raw materials of plastics are low-molecular carbon and hydrogen compounds, which are artificial resins extracted and synthesized from oil, natural gas or coal crackers.Next we will discuss the classification of plastics. Make it easier for us to recognize it, master it and use it.
1-2 Classification of plastics
1.2.1 is divided into thermoplastic plastics and thermosetting plastics according to the conditions when heated and formed.
thermoplastic is that the molecular chains of these resins are linear or branched structures, and there are no chemical bonds between the molecular chains. A physical change process that softens or melts into a fluid state when heated and hardens when cooled. Plastics that become soft or even flow when heated, and harden again when cooled, and this process is reversible and can be repeated repeatedly, are thermoplastics. Such as polystyrene, polypropylene, polyethylene, polyvinyl chloride, polystyrene, polyformaldehyde, polyamide, polycarbonate, ABS, etc. are all thermoplastics.
Thermosetting plastic can soften into a flowing state when heated for the first time (or the material itself is in a liquid flowing state). When heated to a certain extent and for a certain period of time, a chemical reaction will occur (or heated to a certain extent and under the action of a catalyst). A chemical reaction occurs within a certain period of time), resulting in cross-linking and solidification and hardening. Moreover, this process of change is irreversible. Plastics that cannot soften into a fluid state when heated again are thermosetting plastics. Usually people use the plasticization of the material to flow during the first heating to fill the mold and solidify it to obtain a product with the required shape and size. Thermosetting plastics also have a linear or branched structure before the resin is cured. After curing, chemical bonds are formed between the molecular chains to form a network structure. Not only can they not be remelted, some of them cannot be remelted in ordinary solvents. Phenolic resin, epoxy resin, silicone rubber, etc. are all thermosetting plastics.
1.2.2 According to the reaction type during resin synthesis
According to the reaction type during resin synthesis, resin can be divided into polymeric resin (usually also called amorphous resin) and crystalline resin.
1.2.2.1. Polymeric resin (non-crystalline resin) is produced by polymerization reaction. This material is generally formed by opening unsaturated double bonds, and no low molecular products are released during the reaction. Plastics such as polystyrene, polyolefin, polyoxymethylene, polyvinyl chloride, and propylene are polymeric (non-crystalline) plastics. Polymeric plastics are mostly thermoplastics. The resin macromolecules are arranged in a random arrangement. Due to the structural characteristics of the resin molecular chains, thermodynamic reasons, or the limitations of the molding process conditions, the molecular chains of this plastic will not be ordered or neatly stacked to form a crystal structure, but will appear in an irregular and random arrangement. In its pure resin state this plastic is transparent.
1.2.2.2 Crystalline plastic is a resin molecule arranged in an orderly and regular manner. During the process from the molten state to the cooling to the finished product, the molecular chains of the resin can be packed tightly in an orderly manner to produce a crystal structure. Generally, a large part of the so-called crystalline plastics are semi-crystalline plastics. In addition, crystalline plastic structures can only exist in thermoplastic plastics.
1.2.3 According to performance and application scope
Plastics can be divided into general plastics, engineering plastics and special plastics according to performance.
1.2.3.1 General plastic
General plastic refers to plastics with large production volume, large output, wide supply, low price, marketability and large-scale application.
General-purpose plastics generally have good molding process characteristics and can be molded into products of various uses using a variety of processes. But it does not have outstanding comprehensive mechanical properties and heat resistance. If the structural requirements of the product are relatively high; the load pressure of the product is relatively high; heat-resistant parts that have special mechanical requirements or work at high temperatures are not suitable for molding with general-purpose plastics. However, general plastics also have many excellent properties. For example, it has a wider range of uses and does not have such high process requirements for processing and molding. Polyethylene, polyvinyl chloride, polystyrene, polypropylene, and phenolic plastics are collectively referred to as the five major general plastics.
1.2.3.2 Engineering plastics
Engineering plastics refer to those electrical properties that have outstanding performance, heat resistance, excellent resistance to chemical reagents, solvent resistance or can maintain good insulation under changing environmental conditions.General engineering plastics can be used as load-bearing structures
Engineering plastics can generally be used as load-bearing structural parts, heat-resistant parts and load-bearing parts in rising temperatures, dielectric products and insulation supplies under rising conditions, humid conditions, and wide range of frequency conversion conditions. . The production batch of engineering plastics is small, the price is relatively expensive, and the range of uses is relatively narrow. Generally, a certain batch of materials is produced for certain special purposes. The main varieties of existing engineering plastics include polyamide, polyformaldehyde, polyphenylene ether, polysulfide, PET, PBT, polysulfide, polyphenylene sulfide, chlorinated polyether, polyimide, polyether ether, and fluoroplastics. , ultra-high molecular weight polyethylene, epoxy plastics and unsaturated polymerization, etc.
3． Special plastics
have certain special functions and are suitable for certain special purposes, such as conductive, piezoelectric, thermoelectric, magnetic conductive, photosensitive, anti-radiation, optical fiber, liquid crystal, polymer separation membrane, dedicated to friction and wear Uses and other plastics. This kind of plastic is also called functional plastic. The main component of special plastics is resin. Some are specially synthesized special resins, but some are made of the above-mentioned general plastics or resins for engineering plastics that have been specially treated or modified to obtain special properties.
4. Advantages
The main advantages of plastic are: ① Low density and high specific strength. It can replace wood, cement, bricks and other widely used building materials. ② It has excellent chemical corrosion resistance and can be used to make chemical equipment. ③It has good electrical insulation and heat insulation properties and is used to manufacture electronic components, comparable to ceramics and rubber. ④The friction coefficient is small, the wear resistance is good, and it has the function of silencing and damping. It can be used to replace bearings and gears made of metal and can operate at high speed without lubrication. ⑤ Easy to process and shape, easy to color, using different raw materials and different processing methods, various products that are tough, rigid, soft, light, and transparent can be produced, which are widely used in daily life and packaging materials (see Polymers for Packaging materials) and films, pipes and components for agricultural production. Plastics play a role that cannot be replaced by other materials in the aviation and military cutting-edge industries: carbon fiber reinforced plastics can replace aluminum and titanium alloys to reduce the weight of aircraft; plastics that are resistant to instantaneous high temperatures and radiation are used in rockets, missiles, artificial satellites, nuclear reactors and other plastics According to the use, it can be divided into daily plastics and engineering plastics. The so-called daily plastics refer to some plastics that are commonly used in daily life. They are produced in large quantities and have low prices. The so-called engineering plastics refer to some plastics used in engineering. These plastics generally have unique engineering properties, such as mechanical properties, electrical properties, etc. However, due to high production costs, they cannot be commonly used in daily life. However, today's engineering plastics may become daily-use plastics tomorrow. Although some are engineering plastics, once they are used in finished products, they cannot be completely separated from people's daily lives. Some plastics are both engineering plastics and daily-use plastics. Use plastic. Therefore, when this book discusses various plastics in Chapter 3, it focuses on daily plastics, but it also involves engineering plastics. It not only talks about some ordinary classic things, but also spends some words to explain some new and developing ones. Sexual stuff.
1-3 Properties of commonly used plastics
2. Basics of injection molding
2-1 Plastic
Plastic is a polymer material that can be molded and processed after heating and pressure. Plastics include natural resins and synthetic resins, generally referring to synthetic resins made from petroleum.
One of the special features of plastic is that it deforms when heated, so it can be easily mass-produced in various shapes.
Plastics are roughly divided into thermoplastic resins and thermosetting resins. Most products are made of these two plastics.
The nature of thermoplastic resin is that it melts when heated, solidifies when cooled in the mold to form a product, and melts when heated again.
The property of thermosetting resin is that although it melts when heated like thermoplastic resin, it solidifies when heated again. Once solidified, it no longer melts.
In addition, recently developed plastics called "super engineering plastics" have the same strength and heat resistance as metal, and plastics that are as soft as skin are used in various fields.
2-2 Injection molding
means heating and melting the resin in a heating cylinder, then injecting it into the mold, and then cooling the melted resin in the mold. Products are manufactured through this process.
2-3 Things needed for injection molding
1. Molding material (resin)
2. Material dryer (hot air type, dehumidification type, vacuum type)
3. Injection molding machine
4. Mold
5. Mold temperature regulator (media: Water, oil, heater)
6. Remover
7. Crusher
8. Molding technology
2-4 Five factors of injection molding conditions
1. Temperature
2.
According to the combination of the five factors, the molding conditions will be established.
time
3. quantity (position)
4. speed
5. pressure
Only five factors that are always balanced can achieve stable forming.
temperature
material drying, heating cylinder temperature, resin temperature, mold temperature, product removal temperature, indoor temperature, execution oil, cooling water temperature
time
material drying time, metering time, filling time, holding time, cooling time, cycle
Position (amount)
The amount of material put into the hopper, injection start position, injection molding forward position, injection end position, measurement start position, pressure reduction amount, injection amount
speed
metering speed (screw rotation), injection speed, Mold opening and locking speed, ejection speed, decompression speed
pressure
mold clamping pressure, filling pressure, holding pressure, metering load pressure, screw back pressure
2-5 Molding conditions
Molding conditions should confirm 5 factors. How to set, get What is the result, and confirm that the molded product can be of good quality within the set range and result range.
What is required on the molding condition table
1. The setting value range and final setting value should be clearly stated.
2. The result range and final result should be clearly documented.
3. The non-production parts of the product should be clearly stated.
2 molding condition setting program
2-1 Before setting the molding conditions
what is important is what kind of molding resin, product, and mold are used.
1. Confirm resin properties.
How much temperature, how much time, and how to dry it?
If drying is insufficient, not only will the molding be defective, but the physical properties of the product will also be reduced.
The temperature range within which the resin can be formed
needs to be understood at what temperature it will melt and at what temperature it will decompose. In what temperature range can the mold temperature of
be formed? What is the heat deformation temperature of
.
2. What kind of product (mold)
is the product thick or thin?
can determine the injection time, cooling time, resin temperature, and mold temperature required.
· Whether it can be demoulded when insufficient filling
can determine the injection speed, injection pressure, and amount of resin required.
· Mold temperature adjustment method
Confirm whether to use water temperature adjustment, oil temperature adjustment or heater temperature adjustment.
2-2 Molding preparation
① Resin drying
Confirm the temperature, time and method again.
② Mold installation
Confirm the up and down direction of the mold and the position of the ejector pins (number and size), and tighten diagonally from the fixed side.
③ Adjustment and confirmation of mold opening (ejector pin) action
In order to avoid cycle waste and protect speed and mold, please pay attention to the position and pressure.
④ Mold temperature adjustment (heating)
mold temperature adjustment method should be connected using the same method every time. In addition, after the temperature rises, the mold opening and locking operation needs to be confirmed again.
⑤ Cleaning in the heating cylinder
Please clean the heating cylinder when changing the material in the heating cylinder to the material to be formed. When the melting temperature of the resin to be used by
is higher than the resin used last time, set it to the lower limit temperature of the resin to be used. If the molding temperature range of
is different, temporarily switch to a stable resin with the same molding temperature of both resins, and then clean again.
When using a hot runner mold, the mold manifold needs to be cleaned after opening the mold.
3 Molding condition setting
Regarding temperature, it does not change immediately after changing the setting value. Therefore, the temperature data is directly related to the resin data and product data, and the setting value is basically fixed.
· Mold temperature
· Heating cylinder temperature (including water flow under the hopper)
· Screw rotation number → about 100r.p.m
· Screw back pressure → oil pressure: 5 to 10kg/cm2
(resin pressure: about 50 to 150kg/cm2 )
(1) Measurement value setting
is formed from an unfilled state in principle.
○ Temporary condition setting
· Measurement value (SM) is less
· Pressure reduction (SD) is about 3 to 5
It is not necessary when using a valve nozzle
· The holding pressure switching position is 10mm (holding pressure and back pressure To the same extent)
NC9300T sets
NC9000F·G in V-P and sets
·G in S5. Injection speed and injection pressure settings (based on the same speed and two pressures)
injection speed = V
injection pressure NC9300T sets
NC9000F·G in Pv. Set
in P1·Holding pressure NC9300T Set
in Pp NC9000F·G Set
in P2 and P3 The injection molding screen and other settings are set to a state where the screw position can be displayed.
○ Fill the resin into the mold in manual mode. When the screw stops moving forward, it will immediately return to the neutral state.
Please confirm where the screw has advanced at this time.
○ After a certain cooling time, open the mold and operate according to chart ① while checking the molded product. Use these operations to set the metering value settings.
Chart ①
Molded product status
Screw position
Processing
Insufficient filling
(unfilled)
Advance to below 5mm
Increase metering value
Stop between 5 and 10mm
Increase holding pressure
Stop above 10mm
Increase speed, Injection pressure
Burrs, whitening, cracks
(overfill)
Advance to less than 5mm
Reduce speed, injection pressure
Stop between 5 and 10mm
Reduce holding pressure
Stop above 10mm
Reduce metering value
○ Screw advance position Make molded products with good shape (no unfilled and burrs allowed) at about 5 to 7mm.
At this time, there is no problem if appearance defects (gate spray marks, flow marks) occur on the molded product.
○ Enter the semi-automatic mode
refer to the chart ②, temporarily set the injection time and cooling time, and perform semi-automatic operation.
○Enter the fully automatic mode
confirms that the product is released from the mold, sets the intermediate time, and then proceeds to fully automatic operation.
Chart ②
Molded product thickness
Injection time
Cooling time
1mm or less
5.0 sec
10.0 sec
5mm or less
15.0 sec
20.0 to 30.0sec
5mm or more
30.0 sec
40sec or more
n Depending on the resin The shape of the product is different, the above picture is for reference only. .
○ Set the injection pressure to 99% (MAX).
is set in Pv for NC9300T and
is set in P1 for NC9000F·G. In order to confirm the speed condition width in the next project and compensate for the speed, it is set to the maximum value.
The injection pressure setting value increases every 10%. According to the change conditions in chart ③, set it to 99%.
chart ③
molded product status
occurrence
processing
burrs
generated during the filling process
reduced V
generated at the end of filling
reduced P2, P3
n If no burrs etc. are generated, in order to adjust the filling time to the same level, reduce the Injection speed, while setting the injection pressure to 99%.
In the future, molded products will be evaluated for each conditional shot. Only by understanding the condition range can we determine the final setting value that can achieve stable molding.
(2) Injection speed setting
Change the injection speed and confirm the yield range of the molded product, and then determine the final speed setting value.(Related to filling time and product weight)
① Injection pressure (Pv or P1) = 99% Holding pressure conversion position (V-P or S5) = 10mm
Fixed to holding pressure (Pp or P2, P3)
② First observe the appearance of defects (burrs, burrs, Insufficient filling, flow marks, etc.), sample 5 to 10 data based on the conditions for obtaining good products.
③ The total number of samples is calculated based on N=5.
④ Converts the set data into a graph.
⑤ Looking at the figure below, the range of good products for molded products (injection speed) is 40% to 50%, the filling time is 0.79sec to 0.66sec, and the midpoint of this range is set to 45%.
If the appearance defect caused is within the allowable range, it can also be decided to shift to the safe side.
When using a mold that does not allow burrs, only the lower limit value is confirmed.
Molded product data
Speed setting (%)
Filling time (sec)
Molded product weight (g)
30
1.2
30.18
35
1
30.56
40
0.79
30.8
45
0.73
30.99
50
0.66
31.2
55
0.61
31.3
60
0.57
31. 89
(3) Setting of injection pressure (Pv or P1) (filling pressure)
After confirming the injection pressure (Pv or P1) that matches the injection speed obtained in the process (2), determine the pressure that can compensate for the speed.
(related to the filling time and injection pressure setting value)
① Injection speed (V) = 45% Holding pressure conversion position (V-P or S5) = 10mm
is fixed to the holding pressure (Pp or P2, P3)
② Injection pressure (Pp or P2, P3) dropped from 99%, and observed the changes in filling time and molded products.
③ The total number of samples is calculated based on N=5.
④ Converts the set data into a graph.
⑤ Looking at the picture below, in order to obtain a speed of 45%, the injection pressure needs to be at least 55%, so it is set to 60% after being offset to the safe side.
Molded product data
Pressure setting (%)
Filling time (sec)
Molded product weight (g)
35
1.58
29.8
40
1.2
30.18
45
0.98
30.5
50
0.82
30.8
55
0.73
30.99
60
0.73
31.05
65
0. 73
31.02
(4) Holding pressure conversion position (V-P or S5) setting
After confirming the yield range of the conversion position from injection pressure (Pv or P1) to holding pressure (Pp or P2, P3), determine the final setting position.
(Related to holding pressure conversion position and product weight)
① Injection speed (V) = 45% Injection pressure (Pp or P1) = 60%
Fixed to holding pressure (Pp or P2, P3)
② Temporarily set conditions 10mm Change to ±5 to 10 and perform sampling.
③ The total number of samples is calculated based on N=5.
④ Converts the set data into a graph.
⑤ As shown in the figure below, the range of good molded products is from 8.0mm to 12.0mm, and the midpoint of this range is determined to be 10.0mm.
Molded product data
Holding pressure conversion position
Filling time (sec)
Molded product weight (g)
7
0.78
31.35
8
0.75
31.15
9
0.74
31.08
10
0.73
31
11
0.72
30.8
12
0.71
30.6
13
0.7
30.35
( 5) Set the holding pressure (Pp or P2, P3)
Change the holding pressure (Pv or P2, P3), confirm the yield range of the molded product, and then determine the final setting value.
(Related to holding pressure and product weight)
① Injection speed (V) = 45%, injection pressure (Pp or P1) = 60%
Holding pressure conversion position (V-P or S5) is fixed at 10.0mm
② For the appearance of the molded product and Sampling was carried out by changing the weight from 5 to 10 levels.
③ The total number of samples is calculated based on N=5.
④ Converts the set data into a graph.
⑤ Looking at the figure below, the range of good molded products is 30% to 45%, and the midpoint of this range is 40%.
Molded product data
Holding pressure setting (%)
End position (mm)
Molded product weight (g)
20
7.6
30.05
25
7.2
30.56
30
6.8
30.85
35
6. 5
31.05
40
6.2
31.15
45
5.9
31.25
50
5 .5
31.32
(6) Injection molding time setting
Generally, the injection molding time is determined based on the time required to fill the resin into the mold (filling time) and the time required for the gate to solidify (pressure holding time).
① Injection speed (V) = 45%, injection pressure (Pv or P1) = 60%
holding pressure conversion position (V-P or S5) = 10.0mm, holding pressure (Pp or P2, P3) = 40%
② Compared with The filling time is the same and the injection molding time is extended every 0.5 seconds, and the weight of the product is measured.
③ The total number of samples is calculated based on N=5.
④ Converts the set data into a graph.
⑤ Looking at the picture below, although it takes 5.0 seconds for the gate to solidify, it shifts to the safe side, so it is set to 5.5 seconds.
Molded product data
Injection time (sec)
Molded product weight (g)
0.5
10.5
1
26.5
1.5
27.3
2
28.05
2.5
29.05
3
29.9
3.5
30.2
4
30.45
4.5
30.8
5
31.05
5.5
31 .07
6
31.05
6.5
31.04
(7) Cooling time setting
Cooling time setting is the time required for the resin temperature in the mold to drop to a point where it will not be affected by thermal deformation.
In general, the cooling time is determined by whether the molded product taken out from the mold is deformed (dimensions, etc.).
① The cooling time is temporarily set based on several conditions.
② The sampling number is based on N=5, and the size is measured over time.
③ The cooling time is determined based on the size measurement results.
(8) Confirmation of the final condition width
When the holding switching position changes from the temporary condition, reconfirm the lower limit and upper limit of the filling time.
(9) Stability confirmation during continuous molding
performed continuous molding about 100 times and used the display function of the injection molding machine to confirm the stability of the molding information.
regularly takes samples, measures the weight of the product, and confirms how long it will take to maintain stability.
3 Set the temperature-related conditions again
(1) Mold temperature
Measure the actual temperature of the mold regularly and write it down.
sets the value again as needed.
(2) Heating cylinder temperature
Confirm whether the actual measured temperature deviates from the set value.
① When the nozzle temperature changes,
automatically adjusts and sets the most suitable control constant.
② When the rear temperature is easy to drop,
limits the water flow under the hopper (injection molding table), and increases the temperature under the hopper to assist the thickness temperature.
(3) The number of screw rotations (VS)
is approximately set to the number of rotations at the end of the cooling time.
If the screw rotates too fast, transitional shear heat will be generated, causing the resin to scorch and decompose. Please be careful.
(4) Screw back pressure (PB)
is used as the resistance of the screw to retreat plus the screw back pressure.
Although back pressure is used to improve the resin degassing, stirring effect and resin density stability during plasticization, if the pressure is too high or the plasticization time is too long, the resin temperature will rise due to shear heat. Please Notice.
(5) Pressure reduction (SD)
When using an opening nozzle, it is for the purpose of depressurizing the resin after measurement, and as the minimum stroke, the decompression speed is changed to the retraction speed of the screw, and the resin density can be easily adjusted. Stablize.
4 Recheck other molding environments
(1) Outside the mold cooling
The molded product is not only cooled in the mold, but also cooled down to normal temperature after the product is taken out, and is also cooled as outside the mold cooling.
After taking out the product, it is also important to cool it in a certain environment.If the cooling environment outside the mold changes, dimensional changes and deformation of the product will occur.
(2) Crushing
Sprues, runners, etc. can be reused after being crushed. However, please note that if the particle size is unstable, the plasticized state will not be stable and the molding conditions will be out of balance.
