I must apologize for somewhat neglecting this blog. I've been so busy with my MBA and work. I looked at some of the analytics for this blog and noticed that the most popular post seems to those around troubleshooting. If there's anything in particular you are having trouble send me an email and I'll make sure to reply directly or present a post on the topic. I also noticed that the Cobb test troubleshooting post is the most popular post. Perhaps I should write a little bit more on this topic.
Either way I will try to pay more attention to this blog and post more often. Thanks for reading.
Thursday, September 30, 2010
Monday, July 19, 2010
Troubleshooting Tips: Worms
Worms are a formation defect resulting from strings of improperly dispersed fiber.
They can be caused by an incorrect slice setting, excessive water from the breast roll shower, and poorly set deckle boards. They can also be caused by an improperly set forming board and too high of a total head.
Once the source of the worm issue is identified the proper adjustments should eliminate the worming. If the source is not known, carefully adjust probable cause areas to identify the source. Of course, you should go through the adjustments that would cause the least possibility of a break before the ones that are more likely to cause a break.
This is a fairly straight forward process. The backtender or quality person should be the ones who detect the worms. The wetend should be notified to find the cause and rectify the situation.
They can be caused by an incorrect slice setting, excessive water from the breast roll shower, and poorly set deckle boards. They can also be caused by an improperly set forming board and too high of a total head.
Once the source of the worm issue is identified the proper adjustments should eliminate the worming. If the source is not known, carefully adjust probable cause areas to identify the source. Of course, you should go through the adjustments that would cause the least possibility of a break before the ones that are more likely to cause a break.
This is a fairly straight forward process. The backtender or quality person should be the ones who detect the worms. The wetend should be notified to find the cause and rectify the situation.
Tuesday, June 8, 2010
Back to Paper
So I've been keeping up with the news and the oil spill is still a huge problem. I apologize for not posting as much lately. There are a couple of reasons for this, I wanted to leave my oil spill solution suggestion up at the top of the blog for a while and I've been a little busy of late.
Don't worry though. I'll be posting some new stuff here in the next couple weeks. I think I will talk a little about some flex roll technology being installed for some press rebuilds. I will also try to add more troubleshooting tips as these seem to be the most popular pages. If there is anything in particular you'd like to hear about just shoot me an email.
Thank you for being a part of this blog, and I hope you've found some of the information to be helpful.
Don't worry though. I'll be posting some new stuff here in the next couple weeks. I think I will talk a little about some flex roll technology being installed for some press rebuilds. I will also try to add more troubleshooting tips as these seem to be the most popular pages. If there is anything in particular you'd like to hear about just shoot me an email.
Thank you for being a part of this blog, and I hope you've found some of the information to be helpful.
Friday, May 14, 2010
Off Topic: Oil Spill Solution
This post has nothing to do with making paper. It has to do with something much more important. The current oil spill in the Gulf of Mexico is a huge environmental issue. I have thought about the problem over the past couple of days and this is what I have come up with. My hope is that it gets in front of the right people and may provide a solution or a piece to a solution to this environmental tragedy.
I am very concerned with the current oil spill in the Gulf of Mexico. Due to this concern, I would like to offer up a possible solution. This is a rough solution that can be refined for implementation.
The current issues with siphoning the oil is the formation of natural gas (methane) hydrate. In order for this hydrate to form water needs to be present in a cold and/or high pressure environment. The phase diagram below illustrates the methane hydrate relationship between depth and temperature.
As depth increases, pressure increases. A higher pressure allows the hydrate to form at higher temperatures. For example, at 1400m (~4600ft) the temperature needs to be at or below 60F for the hydrate to form.
Figure 2 shows the water temperature at various depths for the Gulf of Mexico. At a depth of 1400m, the temperature is around 5C or 41F. At this depth and temperature, with the presence of water, hydrate will form.
The proposed solution, which is illustrated on the attached page, addresses the hydrate issue. In order to reduce or eliminate the formation of hydrate, the oil should be siphoned at a point much further away from the source of the leak. The oil must be directed so that it can be concentrated and siphoned efficiently. To direct the oil, a cylinder should be placed around the source of the leak. This cylinder can be made of concrete or steel. It needs to be able to withstand the turbulence from the outflow of oil. It also needs to be heavy enough so that it can anchor a reinforced spiral ventilation duct similar to the one shown below.
The big question mark is how long the duct needs to be. It could be anywhere from a few hundred feet to a few thousand feet. However, it does not need to come all the way up to the surface. Its purpose is to direct the flow of the oil up to a depth where hydrate formation is unlikely if not impossible so that another line which will come in from the top of the duct can efficiently siphon off the oil. The duct will act as an artificial column of oil.
The attached design of the solution shows two pumps, one for siphoning the oil and the other one near the base of the cylinder around the oil leak source. The purpose of this pump is to pump out water from the column. The specific gravity of oil is lower than water so it floats. In implementing the proposed solution, some water may be trapped in the column. While some water in the column does not present a problem, a significant amount of water will reduce the efficiency of oil recovery and also increase the possibility of hydrate formation. By pumping water out of the column near the base, this will create a column of mostly oil.
A pipe or hose should be placed inside the column with a positioning ring. This ring will keep the siphoning hose or pipe in the middle of the column. The siphoning pump should be set at a rate identical to the rate of oil leaking. Once the flows are matched up the column will achieve plug flow. Under ideal plug flow conditions, 100% of the oil coming from the leak would be recovered. However, this will be difficult to achieve without automatic controls. I believe by placing cameras near the top of the column and at various points along the column an operator could monitor and control the flow and recover over 90% of the oil. If the siphoned flow is too high water will flow in from the top of the column. If the flow is too low oil may escape through the top of the column.
The big hurdle for this solution is the design of the reinforced spiral duct. The materials necessary for a viable duct are available. However, the problem may be in the production of a duct that is long enough. While the general design of this solution seems sound, the details still need to be ironed out. Note that this is not a permanent solution, but it would alleviate the oil leak until the relief wells are operational.
If you have any questions, concerns, or comments please feel free to contact me. My email address is nhiemcao@gmail.com.
I am very concerned with the current oil spill in the Gulf of Mexico. Due to this concern, I would like to offer up a possible solution. This is a rough solution that can be refined for implementation.
The current issues with siphoning the oil is the formation of natural gas (methane) hydrate. In order for this hydrate to form water needs to be present in a cold and/or high pressure environment. The phase diagram below illustrates the methane hydrate relationship between depth and temperature.
Figure 1. Methane Hydrate Phases
As depth increases, pressure increases. A higher pressure allows the hydrate to form at higher temperatures. For example, at 1400m (~4600ft) the temperature needs to be at or below 60F for the hydrate to form.
Figure 2. Gulf of Mexico Water Depth Temperature
Figure 2 shows the water temperature at various depths for the Gulf of Mexico. At a depth of 1400m, the temperature is around 5C or 41F. At this depth and temperature, with the presence of water, hydrate will form.
The proposed solution, which is illustrated on the attached page, addresses the hydrate issue. In order to reduce or eliminate the formation of hydrate, the oil should be siphoned at a point much further away from the source of the leak. The oil must be directed so that it can be concentrated and siphoned efficiently. To direct the oil, a cylinder should be placed around the source of the leak. This cylinder can be made of concrete or steel. It needs to be able to withstand the turbulence from the outflow of oil. It also needs to be heavy enough so that it can anchor a reinforced spiral ventilation duct similar to the one shown below.
Figure 3. Ventilation Duct
The big question mark is how long the duct needs to be. It could be anywhere from a few hundred feet to a few thousand feet. However, it does not need to come all the way up to the surface. Its purpose is to direct the flow of the oil up to a depth where hydrate formation is unlikely if not impossible so that another line which will come in from the top of the duct can efficiently siphon off the oil. The duct will act as an artificial column of oil.
The attached design of the solution shows two pumps, one for siphoning the oil and the other one near the base of the cylinder around the oil leak source. The purpose of this pump is to pump out water from the column. The specific gravity of oil is lower than water so it floats. In implementing the proposed solution, some water may be trapped in the column. While some water in the column does not present a problem, a significant amount of water will reduce the efficiency of oil recovery and also increase the possibility of hydrate formation. By pumping water out of the column near the base, this will create a column of mostly oil.
A pipe or hose should be placed inside the column with a positioning ring. This ring will keep the siphoning hose or pipe in the middle of the column. The siphoning pump should be set at a rate identical to the rate of oil leaking. Once the flows are matched up the column will achieve plug flow. Under ideal plug flow conditions, 100% of the oil coming from the leak would be recovered. However, this will be difficult to achieve without automatic controls. I believe by placing cameras near the top of the column and at various points along the column an operator could monitor and control the flow and recover over 90% of the oil. If the siphoned flow is too high water will flow in from the top of the column. If the flow is too low oil may escape through the top of the column.
The big hurdle for this solution is the design of the reinforced spiral duct. The materials necessary for a viable duct are available. However, the problem may be in the production of a duct that is long enough. While the general design of this solution seems sound, the details still need to be ironed out. Note that this is not a permanent solution, but it would alleviate the oil leak until the relief wells are operational.
Tuesday, May 11, 2010
Troubleshooting Tip: Curl
Curl is an issue that can creep up on you from time to time. There are three types of curl to be concerned with; machine direction (MD), cross direction (CD), and diagonal.
For MD and CD curl adjustments to the jet-to-wire ratio or rush/drag can be made to alleviate the issue. Generally if you are having a MD or CD curl issue, moving the jet-to-wire ratio closer to one or moving the rush/drag closer to zero will help. This adjusts the fiber orientation to alleviate the curl issue. Reducing refining and reducing broke content will also help.
Other things to look at when dealing with MD and CD curl are the size press and coater. Make sure that the sheet is picking up the same amount at the size press. The same should be done for the coater. Also check to make sure that the mixtures in the run tanks are consistent with each other. Unless you are running out of one run tank, this can be a source of trouble.
Diagonal curl is a different animal altogether. It can come seemingly out of nowhere. The first thing to look at when this issue pops up is to see what has changed. For example, was there an outage prior to the issue and if so what was changed out during the outage that could have caused the problem. The lexan sheets in the headbox can be a source of trouble. Make sure that the new sheets are the same as the old sheets and that the manufacturer hasn't changed anything in their production process. Other causes could be uneven wear of metering blades or rods at the size press. This will cause an uneven coating that could cause diagonal curl. Uneven press loading may also cause diagonal curl.
Out of the three curl types, diagonal is the most difficult to troubleshoot. Remember, curl like any other issue is caused by a change in the process. Sometimes the change is something that can be controlled, and sometimes it is due to the raw materials you have to work with. Either way make the necessary adjustment and make a note for future reference.
For MD and CD curl adjustments to the jet-to-wire ratio or rush/drag can be made to alleviate the issue. Generally if you are having a MD or CD curl issue, moving the jet-to-wire ratio closer to one or moving the rush/drag closer to zero will help. This adjusts the fiber orientation to alleviate the curl issue. Reducing refining and reducing broke content will also help.
Other things to look at when dealing with MD and CD curl are the size press and coater. Make sure that the sheet is picking up the same amount at the size press. The same should be done for the coater. Also check to make sure that the mixtures in the run tanks are consistent with each other. Unless you are running out of one run tank, this can be a source of trouble.
Diagonal curl is a different animal altogether. It can come seemingly out of nowhere. The first thing to look at when this issue pops up is to see what has changed. For example, was there an outage prior to the issue and if so what was changed out during the outage that could have caused the problem. The lexan sheets in the headbox can be a source of trouble. Make sure that the new sheets are the same as the old sheets and that the manufacturer hasn't changed anything in their production process. Other causes could be uneven wear of metering blades or rods at the size press. This will cause an uneven coating that could cause diagonal curl. Uneven press loading may also cause diagonal curl.
Out of the three curl types, diagonal is the most difficult to troubleshoot. Remember, curl like any other issue is caused by a change in the process. Sometimes the change is something that can be controlled, and sometimes it is due to the raw materials you have to work with. Either way make the necessary adjustment and make a note for future reference.
Sunday, April 25, 2010
Brighter Brights and Whiter Whites
I was thinking about something the other day, and I thought I'd share it with you. It seems like there's always a competition between paper companies to see who can make the brightest/whitest sheet. The conventional method is by adding optical brightening agents (OBAs) or optical whitening agents (OWAs) at the wetend of the machine. This seems to work fine but you can only brighten or whiten so much before you lose the effectiveness of the OBA or OWA.
So what else can you do? Well you can innovate and make a better OBA or OWA. This would require some collaboration with a chemical company and could take years to develop. So I started thinking about this and here's what I came up with.
Since the OBAs and OWAs are added at the wetend they have a limited dwell time. I wonder if increasing this dwell time would allow the OBAs and OWAs to achieve greater brightness and greater whiteness. If nothing else it could improve OBA/OWA efficiency, get more brightness or whiteness with less chemicals. So now the question is where can you add it? How far back can you go?
What about the pulp mill? Why can't it be added back there? It's definitely worth a trial right? I am not a pulp mill guy though so you should talk with your pulp mill manager to gain insight into where some good addition points might be. Also remember that if you are going from a grade the requires OBAs or OWAs to a grade that doesn't require OBAs or OWAs that it might take a little while to get all the OBAs or OWAs out of the system. Ideally you would want to try this at a mill that makes OBA/OWA required paper most or all of the time.
So the concept is to base-load the chemicals in the pulp mill and add as necessary in the wetend to reach your target brightness/whiteness.
So what else can you do? Well you can innovate and make a better OBA or OWA. This would require some collaboration with a chemical company and could take years to develop. So I started thinking about this and here's what I came up with.
Since the OBAs and OWAs are added at the wetend they have a limited dwell time. I wonder if increasing this dwell time would allow the OBAs and OWAs to achieve greater brightness and greater whiteness. If nothing else it could improve OBA/OWA efficiency, get more brightness or whiteness with less chemicals. So now the question is where can you add it? How far back can you go?
What about the pulp mill? Why can't it be added back there? It's definitely worth a trial right? I am not a pulp mill guy though so you should talk with your pulp mill manager to gain insight into where some good addition points might be. Also remember that if you are going from a grade the requires OBAs or OWAs to a grade that doesn't require OBAs or OWAs that it might take a little while to get all the OBAs or OWAs out of the system. Ideally you would want to try this at a mill that makes OBA/OWA required paper most or all of the time.
So the concept is to base-load the chemicals in the pulp mill and add as necessary in the wetend to reach your target brightness/whiteness.
Friday, April 23, 2010
Start-up Checklists
I know most people hate checklists, especially operators. They have a checklist they go through when they start-up, but usually it's in their head. Implementing formal checklists for each operator is a good way to avoid costly mistakes.
Start-ups after an outage are very hectic. Everyone has been working for a long time. They're tired and ready to go home. Having a checklist helps the operators go through the necessary steps, it also keeps the operators accountable.
So how do you go about implementing these checklist? The first step is to develop the checklist. The operators should be involved in this process so that they take some ownership of the checklist. Once the checklist is finalized, it must be determined who will actually carryout the checklist. For example a supervisor can go through the checklist with the operator to make sure that the proper steps have been taken. Simply giving the checklist for the operator to go through by themselves is not a great way to implement this tedious task. Operators would soon discard the use of the checklist and go back to their old ways. Having senior operators be responsible for the checklist would be a good way to provide some accountability.
The checklist should be turned in and kept for at least the next two outages. They should also be revised from time-to-time as new equipment is installed or modifications are made to current piping and equipment.
This is a fairly simple way to improve start-up efficiencies. Remember it's all in the way you implement the checklist. Once it is executed poorly, it will be difficult for operators to buy into the program.
Start-ups after an outage are very hectic. Everyone has been working for a long time. They're tired and ready to go home. Having a checklist helps the operators go through the necessary steps, it also keeps the operators accountable.
So how do you go about implementing these checklist? The first step is to develop the checklist. The operators should be involved in this process so that they take some ownership of the checklist. Once the checklist is finalized, it must be determined who will actually carryout the checklist. For example a supervisor can go through the checklist with the operator to make sure that the proper steps have been taken. Simply giving the checklist for the operator to go through by themselves is not a great way to implement this tedious task. Operators would soon discard the use of the checklist and go back to their old ways. Having senior operators be responsible for the checklist would be a good way to provide some accountability.
The checklist should be turned in and kept for at least the next two outages. They should also be revised from time-to-time as new equipment is installed or modifications are made to current piping and equipment.
This is a fairly simple way to improve start-up efficiencies. Remember it's all in the way you implement the checklist. Once it is executed poorly, it will be difficult for operators to buy into the program.
Thursday, April 15, 2010
Troubleshooting Tip: Ring Crush Test
The ring crush test is a method for measuring the edgewise crush resistance by forming the paper into a cylinder and applying a crushing force to the edge. For more information refer to TAPPI T818.
Linerboard products are subjected to crushing forces in handling, storage and shipment. Knowledge of the edgewise compression strength is useful in controlling the manufacturing process, and in providing an indication of the compression resistance to be expected in the finished product.
Here is a list of actions that may improve Ring:
1.Rush the sheet more or drag the sheet less.
2.Optimize refining. There should a sweet spot for ring crush. There may be times when the fiber is over refined.
3.Dry up the sheet more if possible.
4.Increase basis weight.
Realize if you dry up the sheet to improve ring crush, it may reduce your tensile strength, or burst strength. Also, increasing basis weight will increase the cost of production. However, it is better than producing broke, or reject paper. The best method for optimizing refiners is to talk to your senior stock prep operators. If they've been around for a while, they generally have a pretty good idea where to start based off refiner plate wear and the grade of paper. When adjusting the rush/drag, be sure to get your machine tenders' input. Also make sure to pay attention to the draws as this can have an effect on them, you don't want to have a break due to lack of attention to detail.
Linerboard products are subjected to crushing forces in handling, storage and shipment. Knowledge of the edgewise compression strength is useful in controlling the manufacturing process, and in providing an indication of the compression resistance to be expected in the finished product.
Here is a list of actions that may improve Ring:
1.Rush the sheet more or drag the sheet less.
2.Optimize refining. There should a sweet spot for ring crush. There may be times when the fiber is over refined.
3.Dry up the sheet more if possible.
4.Increase basis weight.
Realize if you dry up the sheet to improve ring crush, it may reduce your tensile strength, or burst strength. Also, increasing basis weight will increase the cost of production. However, it is better than producing broke, or reject paper. The best method for optimizing refiners is to talk to your senior stock prep operators. If they've been around for a while, they generally have a pretty good idea where to start based off refiner plate wear and the grade of paper. When adjusting the rush/drag, be sure to get your machine tenders' input. Also make sure to pay attention to the draws as this can have an effect on them, you don't want to have a break due to lack of attention to detail.
Monday, April 5, 2010
Troubleshooting Tip: Cobb Test
Paper is composed of a randomly felted layer of fiber, its structure has a varying degree of porosity. Therefore, the ability of fluids, both liquid and gaseous, to penetrate the structure of paper becomes a property that is very significant in the use of paper. The need to limit the spreading of ink resulted in "sizing" the paper with gelatinous vegetable materials, which had the effect of sealing or filling the surface pores. The term "sizing" was later applied to the treatment of paper stock prior to the formation of the sheet, with water-repellent materials such as rosin or wax. Resistance towards the penetration of aqueous solution / water is measured by Sizing or Cobb values.
The Cobb Test measures surface water absorption over 60 seconds, expressed in g/m2. The procedural Standards are explained in TAPPI T 441.
There are several actions you can take to improve Cobb Test numbers. An increase in refining can help close the sheet, which would improve Cobb results. A change in furnish can also help. You would increase broke content if possible and/or increase hardwood content. These fibers are smaller and can fill the holes or pores in the sheet. If you have alum at your disposal, increasing the addition rate could help. Also increasing pH can help close up the sheet. Be careful when carrying out any of these actions. You increase the risk of sealing the sheet by closing up the sheet.
The Cobb Test measures surface water absorption over 60 seconds, expressed in g/m2. The procedural Standards are explained in TAPPI T 441.
There are several actions you can take to improve Cobb Test numbers. An increase in refining can help close the sheet, which would improve Cobb results. A change in furnish can also help. You would increase broke content if possible and/or increase hardwood content. These fibers are smaller and can fill the holes or pores in the sheet. If you have alum at your disposal, increasing the addition rate could help. Also increasing pH can help close up the sheet. Be careful when carrying out any of these actions. You increase the risk of sealing the sheet by closing up the sheet.
Monday, March 29, 2010
Recycling in a Paper Mill
You would think recycling in a paper mill would be very simple, but it can be difficult at times. Most waste paper from the paper machine is recycled through the broke system. However, there are areas where it is not feasible to feed the paper back to the broke system.
I had the opportunity to optimize production in the converting area of a mill. During this optimization I noticed that there was lots of waste generated in this area that could be recycled. However, due to the mix of the paper and the location it was not ideal to sort the paper and feed it back through the broke system. The trash bins contained a few layers of paper from the rolls that were to be converted, cores, core plugs, cardboard, and other general trash.
The core plugs can be easily recylced by simply sending them back the line to be reused. The cores generally had some paper left on them and could not easily be sent back up the line to be used. So I contacted a recycler to come and do a study to see if there was enough waste for him to install a baler and provide a trailer to load the paper waste. His study concluded that the paper waste was of relatively good quality to him, and that he could install a baler and trailer at his cost and also pay the company for the paper waste that he was taking away to be recycled. This was not a large sum of money, but we would have been happy with him simply installing the baler and taking the waste away. The managers and employees were very happy with the result of the project. After the baler was installed the employees no longer had to take the waste to the compacter. The waste was compacted and baled on the floor which reduced the number of trips the forklift driver had to make from five or six per shift to just one or two. The trip was also shorter since the trailer was placed closer than where the baler location.
So look around for these opportunities. Companies are looking to be more green and sustainable, why not get paid a little bit for it. Just a thought.
I had the opportunity to optimize production in the converting area of a mill. During this optimization I noticed that there was lots of waste generated in this area that could be recycled. However, due to the mix of the paper and the location it was not ideal to sort the paper and feed it back through the broke system. The trash bins contained a few layers of paper from the rolls that were to be converted, cores, core plugs, cardboard, and other general trash.
The core plugs can be easily recylced by simply sending them back the line to be reused. The cores generally had some paper left on them and could not easily be sent back up the line to be used. So I contacted a recycler to come and do a study to see if there was enough waste for him to install a baler and provide a trailer to load the paper waste. His study concluded that the paper waste was of relatively good quality to him, and that he could install a baler and trailer at his cost and also pay the company for the paper waste that he was taking away to be recycled. This was not a large sum of money, but we would have been happy with him simply installing the baler and taking the waste away. The managers and employees were very happy with the result of the project. After the baler was installed the employees no longer had to take the waste to the compacter. The waste was compacted and baled on the floor which reduced the number of trips the forklift driver had to make from five or six per shift to just one or two. The trip was also shorter since the trailer was placed closer than where the baler location.
So look around for these opportunities. Companies are looking to be more green and sustainable, why not get paid a little bit for it. Just a thought.
Thursday, March 25, 2010
Troubleshooting Tip: Sealed Sheet
I know it has been a while since my last post, but I'm still here. I've just been busy. Anyhow, without further ado, sealing the sheet can be a very big problem. This is basically when the sheet is not draining properly. It seals itself and does not allow the water to drain. This problem can be quickly diagnosed by just looking at the sheet as it moves along the table.
Once the situation has been assessed, what do you do? There are several options. The simplest thing to do is to remove some broke. Broke contains lots of fines so reducing broke can alleviate the sealing. Another thing you can do is refine less mainly with the hardwood refiners. You can also adjust your furnish to increase softwood.
Those were the simple solutions. If none of those options helped then you've got to dig deeper. These are more machine specific options. You can increase the amount of water going to the headbox. This seems counter intuitive but in many cases this added water will create channels in the sheet to allow for improved drainage. Another option is to adjust the jet to wire ratio. This will change the fiber orientation which may help. One more option is to adjust the slice position which will change the delivery angle. This will effect other parameters such as the jet to wire ration, so be cautious when adjusting the slice. This will change where the jet lands on the forming board as well. Just be aware of the adjustments. Remember these are machine specific and may not apply to all machines.
I hope that helps. I know some of it is a little vague and general. Consult your process engineer and wet end operators before making these changes. They may have some insights that could prove useful in troubleshooting.
Once the situation has been assessed, what do you do? There are several options. The simplest thing to do is to remove some broke. Broke contains lots of fines so reducing broke can alleviate the sealing. Another thing you can do is refine less mainly with the hardwood refiners. You can also adjust your furnish to increase softwood.
Those were the simple solutions. If none of those options helped then you've got to dig deeper. These are more machine specific options. You can increase the amount of water going to the headbox. This seems counter intuitive but in many cases this added water will create channels in the sheet to allow for improved drainage. Another option is to adjust the jet to wire ratio. This will change the fiber orientation which may help. One more option is to adjust the slice position which will change the delivery angle. This will effect other parameters such as the jet to wire ration, so be cautious when adjusting the slice. This will change where the jet lands on the forming board as well. Just be aware of the adjustments. Remember these are machine specific and may not apply to all machines.
I hope that helps. I know some of it is a little vague and general. Consult your process engineer and wet end operators before making these changes. They may have some insights that could prove useful in troubleshooting.
Tuesday, June 23, 2009
Keep Vendors in Check
The quality of the products purchased from anyone should be checked periodically. This keeps the suppliers and vendors honest. It shouldn't be that way but it is. I'll give you an example of a very big headache that occurred due to a supplier/vendor.
I was working on a fine paper machine and shortly after an outage a mysterious diagonal curl started appearing in the sheet. The thing with diagonal curl is that it's easy to diagnose but difficult to cure. The curl had not been there prior to the outage so it must have come from something that was changed out during the outage. The problem is that there are lots of the things changed out during an outage. So after a week or so of investigating the cause of the curl still couldn't be identified. The problem was that the curl was moving. It wasn't always in the same position. So whatever was causing the curl had to be a moving part. On a paper machine everything moves. So the next step was to send in the corporate engineers. The were as puzzled as the rest of us. Another week passes and still no answer. Next some paper machine experts are brought in, they are the ones that built most of this particular machine. They also supplied some parts that were routinely replaced. By this time it was about time for another outage. The paper machine is taken apart and things are be changed out as normal. Then an old machine tender is looking around at some of the headbox parts. He picks up the lexan sheet and notices something. He says, "these sheets feel flimsier than normal." He tells the machine manager who then tells the paper machine experts. They experts say no it can't be the lexan sheets, but for argument sakes lets put in a new set. Note that they supply the lexan sheets. So the machine is started back up and the diagonal curl is still there. A few days goes by and the machine tender keeps saying he thinks its the lexan sheets, there's something wrong with them. Finally the machine manager finds the old lexan sheets which had a few pieces broken off and says to put them back in. This takes about an hour and a half or so. The machine starts back up and the curl is gone. Hmmm.... The paper machine experts call back to their home office and are told that some changes to the lexan sheet production process had been made but that shouldn't have affected the sheets. After hearing of this change the mill manager makes a call and lets just say that they went back to the old way of making lexan sheets.
So trust your operators when they say something isn't right. And just because they say they're experts it doesn't mean they're always right.
I was working on a fine paper machine and shortly after an outage a mysterious diagonal curl started appearing in the sheet. The thing with diagonal curl is that it's easy to diagnose but difficult to cure. The curl had not been there prior to the outage so it must have come from something that was changed out during the outage. The problem is that there are lots of the things changed out during an outage. So after a week or so of investigating the cause of the curl still couldn't be identified. The problem was that the curl was moving. It wasn't always in the same position. So whatever was causing the curl had to be a moving part. On a paper machine everything moves. So the next step was to send in the corporate engineers. The were as puzzled as the rest of us. Another week passes and still no answer. Next some paper machine experts are brought in, they are the ones that built most of this particular machine. They also supplied some parts that were routinely replaced. By this time it was about time for another outage. The paper machine is taken apart and things are be changed out as normal. Then an old machine tender is looking around at some of the headbox parts. He picks up the lexan sheet and notices something. He says, "these sheets feel flimsier than normal." He tells the machine manager who then tells the paper machine experts. They experts say no it can't be the lexan sheets, but for argument sakes lets put in a new set. Note that they supply the lexan sheets. So the machine is started back up and the diagonal curl is still there. A few days goes by and the machine tender keeps saying he thinks its the lexan sheets, there's something wrong with them. Finally the machine manager finds the old lexan sheets which had a few pieces broken off and says to put them back in. This takes about an hour and a half or so. The machine starts back up and the curl is gone. Hmmm.... The paper machine experts call back to their home office and are told that some changes to the lexan sheet production process had been made but that shouldn't have affected the sheets. After hearing of this change the mill manager makes a call and lets just say that they went back to the old way of making lexan sheets.
So trust your operators when they say something isn't right. And just because they say they're experts it doesn't mean they're always right.
Friday, June 5, 2009
Refining
Refining in the paper making processing refines the fiber. Sounds easy enough right? It's a little more complicated than that. Refining the fibers means cutting or brushing the fibers. Too much cutting and the fibers produce too many fines which is lost during the drainage process. So we want to keep the fibers long enough to provide the strength properties we are looking for while also cutting the fibers to a length that will produce an aesthetically pleasing sheet. Too long of fibers will produce knotting and blobs in the sheet, not very uniform. The brushing part of the refining process fibrillates the fiber to produce more surface area for bonding. The more bonding that takes place the stronger the sheet. Imagine a fiber starting as a long stick. After refining the stick may be cut in half or thirds. It also will have the outside bark stripped off and look like its been chewed up a bit. That's basically what refining does.
There are different types of refiners from cones to cylinders to discs. The most common seem to be the disc models. Pulp is pumped into the refiner through a set of discs. One disc is stationary while the other spins. The plates on the disc have bars which differ depending on the refiner model and the desired results. So plates cause more cutting while others provide more brushing. As the bars from the opposing plates cross the squeeze and cut the fibers. Operators adjust the load or amount of pressure on the plates to attain a desired freeness which is the measurement used to gauge refining. The freeness is usually tested by a lab person or a utility hand.
Different plate patterns are available for different purposes, as well as different fiber species. Hardwood plates are designed for more brushing since the fibers are already relative short. Hardwood refiners are also generally set in parallel since they usually only require one pass through the main refiners. Softwood fibers on the other hand are generally set in parallel since the fibers are longer. This gives the operator more flexibility in controlling the freeness.
This is a very brief overview of refining. There's much more to it. So if there is anything in particular you would like to know, just let me know.
There are different types of refiners from cones to cylinders to discs. The most common seem to be the disc models. Pulp is pumped into the refiner through a set of discs. One disc is stationary while the other spins. The plates on the disc have bars which differ depending on the refiner model and the desired results. So plates cause more cutting while others provide more brushing. As the bars from the opposing plates cross the squeeze and cut the fibers. Operators adjust the load or amount of pressure on the plates to attain a desired freeness which is the measurement used to gauge refining. The freeness is usually tested by a lab person or a utility hand.
Different plate patterns are available for different purposes, as well as different fiber species. Hardwood plates are designed for more brushing since the fibers are already relative short. Hardwood refiners are also generally set in parallel since they usually only require one pass through the main refiners. Softwood fibers on the other hand are generally set in parallel since the fibers are longer. This gives the operator more flexibility in controlling the freeness.
This is a very brief overview of refining. There's much more to it. So if there is anything in particular you would like to know, just let me know.
Tuesday, May 12, 2009
Gravity Flow
Using gravity can be economical in some circumstances. It is also very reliable since it's pretty much constant. The place where gravity flow is most often used on a paper machine is the stuff box. The stuff box provides a constant head of pressure to the basis weight valve which meters in the appropriate amount of stock.
There are other places where gravity can be used to provide pressure. In order to utilize gravity one must utilize the Bernoulli equation. One of the few equations I learned in school that I was able to use in industry. Paper machines are constructed in such a way that there are various levels that can be used to provide pressure, from the basement to the mezzanine floor. If you go into enough paper mills you will also learn the term mezzaline, which is the proper way to say mezzanine in some mills. There is usually another floor above the mezzanine which is the deculator floor or some other floor. Not all paper machines have a deculator, but they could have a floor to provide access to dryer hood vents. Of course there is also the roof. I would not recommend putting anything on the roof unless it's relatively small.
I was able to utilize gravity flow in a project that required less fluctuation in a dye flow. The dye had a relatively small flow and the pump supplying the dye had been oversized. I was given a small budget of $20,000. The reason the flow was fluctuating was due to the small orifice size on the control valves and the oversized pump. The valves worked better when they were more open in the 50% range. I calculated the pressure I needed to open the valves in this range for the necessary flow. I was able to salvage a stainless tank and set it on the mezzanine floor, the control valves were in the basement. I used the pump to fill the tank to a level setpoint. I realized that the head pressure would change when the level in the tank changed, but it was within the operating range of the control valves.
The end result was a much happier stock tender. He didn't have to worry about keeping an eye on the dye flow. The valves were stroked regularly during breaks to ensure there was no build up at the orifice. In addition to the pressure reliability, the system did not go down if the pump went down. The tank could be filled manually with totes if necessary which added more reliability to the system. So when working with a limited budget and needing a reliable pressure source, look to gravity. The pressure is only limited by how high the tank or line can go.
There are other places where gravity can be used to provide pressure. In order to utilize gravity one must utilize the Bernoulli equation. One of the few equations I learned in school that I was able to use in industry. Paper machines are constructed in such a way that there are various levels that can be used to provide pressure, from the basement to the mezzanine floor. If you go into enough paper mills you will also learn the term mezzaline, which is the proper way to say mezzanine in some mills. There is usually another floor above the mezzanine which is the deculator floor or some other floor. Not all paper machines have a deculator, but they could have a floor to provide access to dryer hood vents. Of course there is also the roof. I would not recommend putting anything on the roof unless it's relatively small.
I was able to utilize gravity flow in a project that required less fluctuation in a dye flow. The dye had a relatively small flow and the pump supplying the dye had been oversized. I was given a small budget of $20,000. The reason the flow was fluctuating was due to the small orifice size on the control valves and the oversized pump. The valves worked better when they were more open in the 50% range. I calculated the pressure I needed to open the valves in this range for the necessary flow. I was able to salvage a stainless tank and set it on the mezzanine floor, the control valves were in the basement. I used the pump to fill the tank to a level setpoint. I realized that the head pressure would change when the level in the tank changed, but it was within the operating range of the control valves.
The end result was a much happier stock tender. He didn't have to worry about keeping an eye on the dye flow. The valves were stroked regularly during breaks to ensure there was no build up at the orifice. In addition to the pressure reliability, the system did not go down if the pump went down. The tank could be filled manually with totes if necessary which added more reliability to the system. So when working with a limited budget and needing a reliable pressure source, look to gravity. The pressure is only limited by how high the tank or line can go.
Tuesday, May 5, 2009
Acid
This post is somewhat grade specific. Acid is used in some mills to control pH. In multiply linerboard it can also be used to improve drainage. However, too much will damage the fiber and lead to reduced strength. The reward of improved drainage may allow for the machine to be sped up, resulting in increased production.
Using acid on the base sheet is generally not an issue since there is plenty of flow to dilute the acid. On a secondary or top sheet controlling the amount of acid can be an issue due to the low acid addition rates. The acid addition should be controlled with a pH setpoint. The control response should be fairly quick. Some bump tests should be performed to determine how the control should be set up. This should be done with the assistance of the controls engineer and E&I personel. To improve the control, the pressure going to the control valve can be reduced to allow the valve to operate at a larger opening range.
Acid is relatively cheap. Increasing acid usage can not only increase production, but also reduce alum usage. This should not be a high priority project but is definitely worth looking at.
Using acid on the base sheet is generally not an issue since there is plenty of flow to dilute the acid. On a secondary or top sheet controlling the amount of acid can be an issue due to the low acid addition rates. The acid addition should be controlled with a pH setpoint. The control response should be fairly quick. Some bump tests should be performed to determine how the control should be set up. This should be done with the assistance of the controls engineer and E&I personel. To improve the control, the pressure going to the control valve can be reduced to allow the valve to operate at a larger opening range.
Acid is relatively cheap. Increasing acid usage can not only increase production, but also reduce alum usage. This should not be a high priority project but is definitely worth looking at.
Friday, May 1, 2009
Ropes
Ropes are used to thread the paper machine. The rope run goes through all the dryer sections and are setup so that the tail, a narrow sheet, goes through the dryers properly and reaches the reel drum. Paper machine ropes, or carrier rope, is made from nylon and other synthetic materials which are abrasion resistant.
Ropes are very dangerous. When I first started working on a paper machine the first thing the machine manager told me was if I ever heard a rope break, run. If a rope breaks and catches anyone's limb it would surely catch and pull the person through the rope run which would more than likely kill the person. This is why it is important to correctly splice the ropes. This is where the ends of the rope come around to close a loop. The splice should be overlapping at least 18 inches. Glue should also be applied to the splice for extra strength. If a rope begins to fray it should be carefully monitored. If the fray worsens, then a decision should be made to replace the rope. If a rope breaks it can not only result in a break, but also take out other ropes. If the rope is in the first section and it breaks and takes out all the other ropes down the machine this can lead to several hours of downtime. Some rope runs are fairly complicated and take some time to re route. It is much simpler to replace a rope by tying a new rope to the old rope than to have to manually guide the new rope by itself through the rope run.
It's better to be safe than sorry, so do not take unnecessary risk with the ropes, you could get burned.
Ropes are very dangerous. When I first started working on a paper machine the first thing the machine manager told me was if I ever heard a rope break, run. If a rope breaks and catches anyone's limb it would surely catch and pull the person through the rope run which would more than likely kill the person. This is why it is important to correctly splice the ropes. This is where the ends of the rope come around to close a loop. The splice should be overlapping at least 18 inches. Glue should also be applied to the splice for extra strength. If a rope begins to fray it should be carefully monitored. If the fray worsens, then a decision should be made to replace the rope. If a rope breaks it can not only result in a break, but also take out other ropes. If the rope is in the first section and it breaks and takes out all the other ropes down the machine this can lead to several hours of downtime. Some rope runs are fairly complicated and take some time to re route. It is much simpler to replace a rope by tying a new rope to the old rope than to have to manually guide the new rope by itself through the rope run.
It's better to be safe than sorry, so do not take unnecessary risk with the ropes, you could get burned.
Tuesday, April 28, 2009
Troubleshooting Tip: Holes and Busted Edges
Holes and busted edges are probably the leading cause of breaks on a paper machine. The good news is the cause is usually easy to find. Most machines have hole detectors and busted edge detectors, so the problems are automatically diagnosed. Machines that don't have these detectors must rely on dry end operators to detect the defects. Busted edges are generally easy to spot since the edges are exposed and are easily examined while on the reel. Holes on the other hand are hidden inside the reel and must be detected when the reel is being unwound at the winder. More often the holes are detected when the winder has a break which can be quite messy.
So once the issue is found, how do you find the cause of the problem? For busted edges the usual suspect is the trim squirt. The trim squirts are high pressure nozzles that are used to trim the edges off the sheet as it goes to the press section. The nozzles can get partially plugged reducing the focus of the nozzle. The nozzles can also be misaligned. Due to the position of the nozzles some buildup can form on the nozzles or nozzle apparatus. Other causes of busted edges are light edges, slice bleeds, and edge deckles. Check the weight profile to see if the edges are light and adjust accordingly. Slice bleeds can be adjusted to bring the edges up and edge deckles can be reset.
Holes can be caused by a number of things. They can be caused by material falling into the sheet, such as part of a tail that wasn't cleaned up during the previous break or a leaking shower that drips onto the sheet. The can also be caused by flaws in machine clothing or flaws in rolls on the machine. Issues with pressure screens can also cause holes. To determine the cause of the hole first examine the hole. If the hole is tear drop shaped it is likely caused by material falling into the sheet. Also see if there is some foreign material embedded in the sheet. If the hole is irregular in shape and does not appear to be caused by falling material see if there is a pattern. Does the hole occur only in one position, is there a consistent distance between holes? These are the questions that should be asked. If there is a consistency in distance, measure the distance and determine if the hole is from a roll defect or machine clothing defect. The culprit should be easily found from there unless there are multiple rolls or clothing runs that have the same circumference. If there is no pattern to the holes and it has been determined that there is no debris falling into the sheet, then further investigation is required. Stock samples should be taken at various points in the approach system to see if there are any upsets. The headbox should also be checked to see if there is anything inside that could be causing the holes.
Holes and busted edges are bad, but the causes are generally easy to find. If the cause can't be found immediately patches can be placed on holes until the next outage. However, if the problem must be solved be sure to have a checklist of areas that must be checked. Also coordinate with the maintenance crews to determine what work can be done during the downtime to shorten or delay the next scheduled downtime.
So once the issue is found, how do you find the cause of the problem? For busted edges the usual suspect is the trim squirt. The trim squirts are high pressure nozzles that are used to trim the edges off the sheet as it goes to the press section. The nozzles can get partially plugged reducing the focus of the nozzle. The nozzles can also be misaligned. Due to the position of the nozzles some buildup can form on the nozzles or nozzle apparatus. Other causes of busted edges are light edges, slice bleeds, and edge deckles. Check the weight profile to see if the edges are light and adjust accordingly. Slice bleeds can be adjusted to bring the edges up and edge deckles can be reset.
Holes can be caused by a number of things. They can be caused by material falling into the sheet, such as part of a tail that wasn't cleaned up during the previous break or a leaking shower that drips onto the sheet. The can also be caused by flaws in machine clothing or flaws in rolls on the machine. Issues with pressure screens can also cause holes. To determine the cause of the hole first examine the hole. If the hole is tear drop shaped it is likely caused by material falling into the sheet. Also see if there is some foreign material embedded in the sheet. If the hole is irregular in shape and does not appear to be caused by falling material see if there is a pattern. Does the hole occur only in one position, is there a consistent distance between holes? These are the questions that should be asked. If there is a consistency in distance, measure the distance and determine if the hole is from a roll defect or machine clothing defect. The culprit should be easily found from there unless there are multiple rolls or clothing runs that have the same circumference. If there is no pattern to the holes and it has been determined that there is no debris falling into the sheet, then further investigation is required. Stock samples should be taken at various points in the approach system to see if there are any upsets. The headbox should also be checked to see if there is anything inside that could be causing the holes.
Holes and busted edges are bad, but the causes are generally easy to find. If the cause can't be found immediately patches can be placed on holes until the next outage. However, if the problem must be solved be sure to have a checklist of areas that must be checked. Also coordinate with the maintenance crews to determine what work can be done during the downtime to shorten or delay the next scheduled downtime.
Thursday, April 23, 2009
Broke Management
Broke management sounds like what I did with my finances while I was in college. In reality it's the non postconsumer waste that is put back into the sheet. So it's kinda recycled, but not really. For reference, fiber that comes straight from wood is called virgin fiber. Back to the broke, every paper machine produces broke. Broke comes from the trim off the machine, that's the edges that are trimmed off as the sheet goes into the press section. The trim goes into the couch pit which then goes to some kind of broke thickening process to increase the consistency for ease of storage. Another source of broke is when there is a break on the machine. A sheet break is when the sheet tears or breaks and the sheet is generally put into the couch pit while the machine is being rethreaded. Since a break can last anywhere from 10 minutes to over an hour, a considerable amount of broke can be built up. The last source of broke is rejected paper. Reject paper is repulped using some kind of hydrapulper or the like. It's like a big blender.
Okay, so now we have all this broke, what do we do with it? As I said earlier it gets thickened and sent to some storage tank. From there it is sent back to the sheet. It's a little more complicated than that, but we'll keep it simple for now. Depending on the grade of paper being made the broke can be anywhere from 5% to 15%. The benefits of broke is it closes the sheet. It makes it less porous. The bad part is that it can over do it and seal the sheet which is detrimental to drainage. If that occurs more broke will be made.
So to properly manage broke levels, operators should add as much as they can since it has to be used. Dry end operators should also keep an eye on the broke level so that they don't make too much from reject rolls. This is especially important going into an outage. An outage is maintenance downtime that can last anywhere from 12 hours to forever. Maybe not forever, but sometimes it seems like it. There are times when broke storage tanks must be cleaned out or inspected, during these times broke should be reduced to the lowest levels possible. In mills where there are multiple machines the broke may be sent to the other machines if the grades being made are similar. Issues occur when the broke has chemicals such as fluorescent dye present.
So if broke is managed properly money will be saved. After all it is still fiber. It may not be virgin but it's still good.
Okay, so now we have all this broke, what do we do with it? As I said earlier it gets thickened and sent to some storage tank. From there it is sent back to the sheet. It's a little more complicated than that, but we'll keep it simple for now. Depending on the grade of paper being made the broke can be anywhere from 5% to 15%. The benefits of broke is it closes the sheet. It makes it less porous. The bad part is that it can over do it and seal the sheet which is detrimental to drainage. If that occurs more broke will be made.
So to properly manage broke levels, operators should add as much as they can since it has to be used. Dry end operators should also keep an eye on the broke level so that they don't make too much from reject rolls. This is especially important going into an outage. An outage is maintenance downtime that can last anywhere from 12 hours to forever. Maybe not forever, but sometimes it seems like it. There are times when broke storage tanks must be cleaned out or inspected, during these times broke should be reduced to the lowest levels possible. In mills where there are multiple machines the broke may be sent to the other machines if the grades being made are similar. Issues occur when the broke has chemicals such as fluorescent dye present.
So if broke is managed properly money will be saved. After all it is still fiber. It may not be virgin but it's still good.
Monday, April 20, 2009
Addition Points
The addition points of various chemicals should be analyzed from time to time to see if there are better places to add the chemicals. For example, new defoamers may be available that are less detrimental to sheet properties, but have a lower retention time. Thus, the defoamer should be added closer to the are where foam is an issue. Any chemical can be moved to improve efficiency. Optical brightening agents (OBA) or fluorescent whitening agents (FWA) may be added in more places to increase whiteness. Here's a hint look to add OBA's and FWA's further back in the system, think way back. For acid paper look at places where acid can be added to improve drainage. Too much acid will damage fiber and possibly machine clothing. Alum is another chemical that can be moved around. I was able to reduce alum usage by simply moving the addition point. Moving addition points can be easy. Setup some temporary lines and run some simple trials.
Friday, April 17, 2009
Starch
Starch is added at the wet end and at the size press. The wet end starch is cationic, has a positive charge, and bonds to the anionic pulp fibers. The wet end starch strengthens the web formed by the fibers. Wet end starches generally have solids of about 6%.
Starch is used at the size press to further strengthen the sheet. It is also used as a substrate for other chemicals. There are some important aspects of starch used at the size press that may be different from that of the wet end. The cooking of the size press starch is dependent on the product that is being cooked. The starch can be made from potatoes, corn, or tapioca. Solids and pH are other variables that also must be controlled.
In my experience wet end starch was fairly issue free. I don't recall ever having a major issue with the wet end starch. There were times when supply was an issue due to the boom in corn use for ethanol. At the size press there were problems from time to time. If not cooked properly the starch can be burned and have a brown appearance. This can affect the shade of the sheet. Increasing solids was also an issue due to the increase in viscosity as solids increased. Other issues that occurred from time to time was foaming in the starch run tanks. Defoamer was added in small amounts to help control this. Too much defoamer would hurt the sizing, reduce Cobb and HST test. Addition of fan nozzle showers in the run tanks also helped. The problems occurred during runs of special grades, such as grease resistent paper.
Starch is used at the size press to further strengthen the sheet. It is also used as a substrate for other chemicals. There are some important aspects of starch used at the size press that may be different from that of the wet end. The cooking of the size press starch is dependent on the product that is being cooked. The starch can be made from potatoes, corn, or tapioca. Solids and pH are other variables that also must be controlled.
In my experience wet end starch was fairly issue free. I don't recall ever having a major issue with the wet end starch. There were times when supply was an issue due to the boom in corn use for ethanol. At the size press there were problems from time to time. If not cooked properly the starch can be burned and have a brown appearance. This can affect the shade of the sheet. Increasing solids was also an issue due to the increase in viscosity as solids increased. Other issues that occurred from time to time was foaming in the starch run tanks. Defoamer was added in small amounts to help control this. Too much defoamer would hurt the sizing, reduce Cobb and HST test. Addition of fan nozzle showers in the run tanks also helped. The problems occurred during runs of special grades, such as grease resistent paper.
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