Plastics Training & Technology Blog: Plastics Technology Archives

Put the Tonnage on the Mold Base...

By Andy Routsis on February 3, 2012 12:10 PM 0 Vote 0 Votes

I was at a molder the other week who had this common issue...

Engineer

Our technicians always change the clamp tonnage and it seems to cause problems with venting, actions, and wear. Even the setup guys mess it up.

My Response

Once you have determined the tonnage that should be used on a tool, I recommend you put a plaque on the side of the mold stating the tonnage to be used. If the recommended tonnage is stamped right on each tool, it is hard for a technician or setup person to miss it.

Additional Thoughts

If you are having a problem with a specific issue, such as tonnage, always look for a simplistic way to draw attention to it.

-Andy

Don't Forget the Fundamentals...

By Andy Routsis on February 3, 2012 10:00 AM 0 Vote 0 Votes

I received this comment the other day...

Manager

I understand my technicians have not had any formal process training, but what they really need is advanced training.

My Thoughts

It is common to believe that advanced training will automatically cause your employees to function at a higher level. Unfortunately, advanced training does little to change behavior if your employees lack a good understanding of the fundamentals. A great example of this is the decoupling of 1st stage filling from 2nd stage packing.

Let's presume you have a technician who has been filling the mold completely during 1st stage fill for the past 15 years. Now you send this person to a class focused on the finer points of optimizing filling and packing based on the foundation of a short shot during first stage fill. This employee would learn very little which is directly applicable to his job since he still believes filing the mold completely during 1st stage fill is the best way to process.

-Andy

Coloring Water Line Connections...

By Andy Routsis on February 1, 2012 12:25 PM 0 Vote 0 Votes

One molder asked me this question the other day...

Manager

Our setup techs always seem to connect the water lines incorrectly. We have diagrams to show the setup, but they seem to mess it up anyways.

My Response

Companies who use individual water lines rather than a manifold should color-code everything using blue lines for incoming water, red lines for outgoing water, and extra colors such as yellow for line which exit and re-enter the mold.

Once you have this established, place colored plaques on each connection of the mold. This will ensure that your employees cannot accidentally connect an in-line to an out connector.

-Andy

Setting Final Cushion...

By Andy Routsis on January 25, 2012 10:10 PM 0 Vote 0 Votes

During some classroom training the other week, a student asked me the following question...

John

What value should you set the cushion at?

My Response

A good rule of thumb is 10% of the initial shot size. For example, if the overall shot size is 100mm, then the cushion should be about 10mm. This avoids pressure losses from too much material in front of the screw, yet provides enough room in front of the screw for normal variability.

The Purpose of Cushion

Targeting Cushion Size vs. Transfer Position

-Andy

Teaching Tolerances...

By Andy Routsis on January 23, 2012 7:00 AM 0 Vote 0 Votes

I was asked this question during a recent on-site visit...

QA Manager

What is an easy was to explain tolerances to new employees?

My Response

Focus on the fact that tolerances are commonly expressed in a way which can be easily broken up into simple math equations.

Dimension: 1.00 ± 0.01

Upper Limit: 1.00 + 0.01 = 1.01

Lower Limit: 1.00 - 0.01 = 0.99

Additional Thoughts

When possible break ideas into their simplest form such as an equation or concept. Keep in mind the issue is very often math not tolerances. In this case, focus the attention on basic math and calculator usage first before moving on to part tolerances.

-Andy

PBT in Hot Runner Systems...

By Andy Routsis on January 16, 2012 8:55 PM 0 0 Vote 0 Votes

I was asked this question by a molder who was having trouble balancing a hot runner system...

Bob

We have this new mold which is running 16 cavities in PBT. Usually we can balance the mold using the drop temperatures, but that does not seem to work on this mold. Any thoughts?

My Response

Essentially, semi-crystalline polymers with a high degree of crystallinity such as PBT and nylon are not highly affected by temperature. In such a case, you will have to adjust the gates or the hot runner system itself to balance the shear of the mold.

Additional Thoughts

Cold runner systems are the best for these materials. I know many molders who use a press-side low-RPM grinder to effectively grind up the material and re-introduce PBT back into the process.

-Andy

Documentation Takes Too Long...

By Andy Routsis on January 13, 2012 9:38 AM 0 Vote 0 Votes

I was in a discussion recently with a GM and he had this problem...

Manager

My technicians are not willing to take the time to document their changes. They claim it takes too long?

My Response

The issue here is not time, but education. If your employees are not taking time to document, it is likely that they do not fully understand the importance and benefits of good documentation. If they understand the ways it can simplify their job and improve their effectiveness, they would be more interested in compliance. Unfortunately, this is not a simple fix... it require the employees to not only understand the benefits, but also know what to do with the information they are given.

-Andy

The Best Way to Process...

By Andy Routsis on January 9, 2012 9:20 AM 0 0 Vote 0 Votes

I was recently at a molding facility during a training implementation was in need of some training due to a lack of fundamentals among the employees...

Company President

What is the best way to process, and why don't we just have everybody process that way starting tomorrow?

My Response

I told her that there were ways that there are many ways to process, and there are a few methods which are far superior to others. Unfortunately without a strong background in processing knowledge your employees will have no reason to understand why this method is better.

Essentially, people who have been making a living molding a particular way do not just change their entire approach to processing because someone tells them it is better. You need to educate them on plastics, machinery, materials, processing, and tooling to ensure that they know why it is a better way.

Additional Thoughts

There are always steps which your employees can take to improve the process. As they see the success they will continue to employ more cost saving, and process improving techniques. This is one of the reasons why it can be easier to teach someone who has never processed that to teach someone who has processed for years.

-Andy

Melt Temperature and Density...

By Andy Routsis on January 5, 2012 9:05 AM 0 Vote 0 Votes

I received this excellent question last week...

Saeed

In one of your videos, you state that higher melt temperatures will increase part weight. To my understanding, a less viscous material is pumped in the cavity with a relative ease thus increasing the part weight. Could you please guide me as to whether or not a decrease in density negates the above?

My Response

You are correct that you will be injecting a less dense material in this scenario… but the higher melt temperature causes many things to occur, but the 2 major factors increasing the part weight and density are listed below:

1) There will be a higher amount of material flow and in-mold pressure during packing resulting in more material entering the mold during both 1st and 2nd stage.

2) A higher melt temperature promotes an increase in part shrinkage resulting in a higher overall part density.

Additional Thoughts

This question points out how complex the interactions between the mold, machine, material, and injection molding process can become.

-Andy

Follow-Up on Increasing Injection Velocity...

By Andy Routsis on January 1, 2012 5:15 PM 0 0 Vote 0 Votes

I received an email from a blog reader about another benefit to increasing injection velocity...

Harry

Another reason we use a higher injection velocity in our facility is to increase the amount of packing that is possible.

My Comments

This is correct because of two reasons. First, the gate begins to freeze the moment the material enters the gate. The shorter time required to fill the mold allows more time for packing. The second reason is because the pressure loss within the mold cavity is decreased, allowing more packing pressure to reach the extremities of the mold during packing.

-Andy

Decreasing Energy Consumption during Injection...

By Andy Routsis on December 27, 2011 12:05 PM 0 Vote 0 Votes

I was at a company recently and the engineer was confused about how to reduce energy consumption during injection...

Engineer

I know higher injection velocities reduce variability, but a lower injection speed uses less pressure and thus reduces the overall energy consumption... right?

My Response

Actually, a higher velocity reduces overall energy consumption during injection even though the injection pressure is increased. Increasing the injection velocity decreases the material viscosity through shear thinning. As a result, the overall energy required to push the final volume of polymer necessary to fill the mold is decreased.

In an actual example performed by one of our trainers, the data from a molding process which was filled at two different times is shown below:

Slow Fill:

Fill time = 3.15sec

Transfer Pressure = 10,460psi

Fast Fill:

Fill time = 0.83sec

Transfer Pressure = 11,910psi

Although the faster fill time has a higher pressure at transfer, the molding machine applied the injection pressure for 27% of the time necessary to fill the mold at the slower speed. When you multiply the fill time by the transfer pressure you get the following effective (or relative) viscosity:

Effective Viscosity = t x psi

Slow Fill = 32,950 psi-s

Fast Fill = 9,890 psi-s

Assuming the pressure profiles are similar in shape, it can be reasonably proposed that the faster fill consumed approximately 30% of the energy necessary to fill the mold at the slower speed.

Additional Thoughts

The additional benefit to filling faster is that the polymer fills the mold and begins to cool faster. In this case the overall cycle time could drop as much as 2 seconds due to the higher injection viscosity.

-Andy

Don't Forget to Move the Temperature Probe...

By Andy Routsis on December 22, 2011 11:00 AM 0 Vote 0 Votes

I was discussing the measurement of the polymer temperature with an engineer and he explained a problem he is encountering...

Joe

Each of our technicians are getting different results when we they measure the melt temperature... especially when we measure high temperature materials like polysulfone.

note: I asked one of their techs to demonstrate how they measure the melt temperature and he purged the material, inserted a thin-style probe, and recorded the highest temperature reading. I then asked the technician to repeat the process, but when he inserted the probe I asked him to move is around slowly. The result was a temperature which was 15 degrees higher than his previous measurement.

My Response

When measuring a melt temperature, it is important to move the probe around a little. When the probe is inserted into the melt, a skin of cooled polymer forms around the probe. To ensure you are getting the temperature of the melt, you need to use the surrounding material to soften this skin and get some of the interior polymer melt in contact with the probe.

-Andy

Making Significant Changes...

By Andy Routsis on December 19, 2011 10:15 AM 0 Vote 0 Votes

As a follow-up to a previous post, I was asked to expand in the second rule of processing...

The 5 Basic Rules of Processing (from before):

Rule 1 - Make one process change at a time

Rule 2 - Make significant changes

Rule 3 - If a change does not help, change it back

Rule 4 - Document the process

Rule 5 - Document all changes to the process

Rule #2

The idea behind this is that you always want to know you are making a change which is important. Too often people will tweak different parameters without any direct knowledge as to the effectiveness of the change.

When you make a change, you want to ensure it is large enough to make a difference. Remember any change to the process can be reversed either completely or partially.

Additional Thoughts

I have seen many molders who make small adjustments with the belief it will improve the situation. A symptom of this behavior is a control panel with a large amount of numbers which do not end in either 5 or 0. For instance, if the injection profile looks like the following... V1=11.1 mm/s, V2=30.3 mm/s, V3=23.4 mm/s, V4=28.4 mm/s, and V5=12.7 mm/s. It is very unlikely that each of those velocities have been optimized and each speed in the profile can be properly justified. This type of profile is almost always the result of someone tinkering with the process until a good part came out of the machine.

-Andy

PPE for Purging...

By Andy Routsis on December 15, 2011 11:15 AM 0 Vote 0 Votes

I have seen many variations on this principle...

Steve

Here we only require our employees to wear safety glasses when purging... is that fine?

My Response

Purged plastics can cause some of the most debilitating injuries because they have a tendency to not only burn, but stick to or inject under your skin as well. When purging goes well, the conditions are relatively safe, but it is not uncommon for a explosive discharge to occur as a result of nozzle blockage or gas buildup.

If you are not wearing a face shield, heat resistant gloves, and long sleeves while purging; you are opening yourself up for serious injury.

Additional Thoughts

In all our training courses, we stress the same PPE recommended by most machine manufacturers which includes the wearing of the following when purging:

Face Shield
Heat Resistant Gloves
Long Sleeves (Cotton)

-Andy

5 Basic Rules of Processing...

By Andy Routsis on December 12, 2011 7:05 AM 0 Vote 0 Votes

I was asked this question yesterday via email...

Manager

What should I be looking for when my guys process?

My Response

There the 5 things that I always look for:

Rule 1 - Make one process change at a time

Rule 2 - Make significant changes

Rule 3 - If a change does not help, change it back

Rule 4 - Document the process

Rule 5 - Document all changes to the process

These rules apply to injection molding, extrusion, and blow molding alike.

Additional Thoughts

This list seems pretty simple, but I have found that most molders skip at least one or two of these steps whenever they process.

-Andy

More on Robots vs. Automation...

By Andy Routsis on December 9, 2011 9:55 AM 0 Vote 0 Votes

This question came up as a follow-up question to a recent blog about robotics and automation...

GH

Would a part diverter be classified as robotics or automation?

My Response

The general rule I always follow is: If it is programmable, it is a robot... if not, it is automation.

Therefore, if the diverter acted as a sort device where acceptable parts were sent one way, while defective or questionable parts were sent another way based on process or inspection data, then it could be considered robotics. If a sensor was just placed on a conveyor to sense different parts and automatically divert of orient parts in a specific manner, then it might be considered automation.

Additional Thougths

Under such a definition, a simple device such as a sprue picker which needs to be mechanically adjusted to alter the speed, length, and movement of the arm might be considered automation.

-Andy

Automation vs. Robotics...

By Andy Routsis on December 8, 2011 1:35 PM 0 Vote 0 Votes

I was asked the following question by a technician the other day...

Bob

What is the difference between automation and robotics?

My Response

Automation generally refers to any component which performs a basic repetitive task; such as conveying or sorting parts. In general, robotics are more complex devices which are programmed to perform advanced repetitive tasks; such as the removal, stacking, packaging, or assembly of parts.

Additional Thoughts

In the plastics industry, the terms automation and robotics both refer to mechanical pieces of equipment and are often used interchangeably.

-Andy

More About Processing PVC...

By Andy Routsis on November 23, 2011 10:25 AM 0 0 Vote 0 Votes

I received this follow-up question regarding the processing of PVC...

MT

I would like to know if it is safe to mold parts in PVC and acetal in presses that are next to each other?

My Response

It should be safe to process, but it is critical that you vent the fumes from both machines to prevent corrosion of your equipment. You should also take the time to educate your employees on the dangers of combining these materials.

Additional Thoughts

It is critical that you create a system to prevent any chance of cross contamination. This may be as simple as a color-coded system so that the color of the container matches a panel next to the machine. Personally, I would create a fool-proof system where the container for VC is not compatible with the acetal material delivery system and vice-versa.

-Andy

Caveat Emptor: Selling Older Machines...

By Andy Routsis on November 21, 2011 10:20 AM 0 Vote 0 Votes

I was recently working with a company who had an interesting tale regarding the sale of one of their larger, older, hydraulic molding machines with a very large cylinder clamping unit and corresponding hydraulic reservoir...

Engineer

When we were trying to sell one of these pieces of junk, my recommendation was to drain the oil and sell it for scrap metal or parts. Purchasing then told me they had agreed to sell the machine for a few thousand dollars, hydraulic fluid and all.

note: After a quick calculation, he explained to them that they had just lost money since the value of the hydraulic fluid currently in the machine is worth almost twice the amount they are getting for the machine.

By Andy Routsis on October 20, 2011 6:45 AM 1 Vote 0 Votes

I got this question via email yesterday...

Technician

I know we should wear safety glasses, but how can I better justify their use?

My Response

I recommend reviewing some of my previous posts on this topic:

Follow-Up on Safety Glasses...

Employees Don't Like Wearing Safety Glasses...

About Safety Glasses...

Safety Glasses on the Production Floor

-Andy

Spiral Flow Test...

By Andy Routsis on October 18, 2011 9:00 PM 0 Vote 0 Votes

I received a follow-up question regarding a post earlier this year, The Uses of MFI...,

KJ

You mentioned the spiral flow, what is this test?

My Response

The spiral flow test uses a mold with a long spiral flow channel emanating from the center. Notches are etched along the flow path to help identify the length the polymer has flowed within the mold. The mold can be filled using either a constant velocity (constant shear) or constant pressure (constant strain) to determine the polymer behavior.

The behavior of the polymer can be evaluated based on process output data such as flow length, part weight, and pressure at transfer. When using the spiral flow test, it is best to use a mold which has a channel thickness similar to the parts actually being molded.

Additional Thoughts

You might want to consider purchasing a small, inexpensive, molding machine to conduct spiral flow tests on every incoming batch of material.

-Andy

Thermoplastics vs. Thermosets...

By Andy Routsis on October 10, 2011 12:10 AM 0 Vote 0 Votes

I have read some industry discussion groups lately and have noticed some confusion on the difference between Thermosets and Thermoplastics, so I will use this post to help clarify these points...

Thermosets

Thermosets are polymerized during processing while thermoplastics are polymerized before being processed. During processing, the polymer chains in thermosets fuse together, or cross-link. Once these polymers cross-link, they undergo a chemical change which prevents them from being melted and reprocessed. An egg is an example of a natural polymer which thermosets. Once the egg is heated, it solidifies and cannot be melted again.

Thermoplastics

Thermoplastics are long polymer chains that are fully polymerized when shipped by the resin manufacturer. Thermoplastics can be re-ground, melted and re-processed while retaining most of their original properties. An example of a natural thermoplastic material is wax. It can be melted and formed. Once cooled, the hardened wax can be melted and formed again. Unlike thermosets, most plastics companies prefer thermoplastic materials because they can be reprocessed and recycled.

-Andy

Drop Packing Pressure and Time...?

By Andy Routsis on October 6, 2011 3:25 PM 5 Vote 0 Votes

This question came in from a molder overseas...

HM

During process optimization, which is best, keep both the packing pressure and packing time to zero OR only holding pressure?

My Response

This is based on your machine. On most machines, you can turn the pressure down to zero and the pressure will turn off. Before you make this assumption, you should verify this by turning off the time and ensure the part looks the same.

Additional Thoughts

For some related reading, please review some of the following:

Injection Unit Inertia...

Complications With 1st - 2nd Stage Transfer...

Adjusting for Differences from Machine to Machine

1st to 2nd Stage Response Time

-Andy

Retaining Defects...

By Andy Routsis on September 26, 2011 3:25 PM 2 Vote 0 Votes

I was recently visiting a molder who was having a specific problem...

Supervisor

We are having trouble with our employees properly identifying and naming part defects... any suggestions as to how we can improve this?

note: After a couple questions, it was determined that they do not retain defective parts as they are all discarded, reworked, or reground.

My Response

It is critical that you retain current samples of each part defect your company encounters. These defects should be placed in a visible area to ensure the employees will walk by and see them on a routine basis. This make a great training tool and will help provide a common ground when defect-related questions arise.

Additional Thoughts

Please review your defect board a few times a year to ensure the parts are up to date and still defects. I have seen many parts that are so old that factors such as dust and dimensional creep will make the intended defect invisible.

-Andy

The Affect of Moisture on Injection Pressure...

By Andy Routsis on September 20, 2011 2:50 PM 0 Vote 0 Votes

The other week, I received a multiple part question regarding many aspects of materials, this is one part...

Nathan

Although the 1st stage injection time is the same, the virgin PC/ABS (<0.06% moisture) has a 1RMPa higher peak injection pressure than virgin PC/ABS (0.08% moisture). Is this change in pressure common?

My Response

Moisture in the polymer causes hydrolysis to occur. As the water molecule is heated, one of the hydrogen atoms breaks away and both the H+ and OH- ions look for pairs along the polymer chain. In hygroscopic polymers such as PC/ABS these ions break up the long polymer chains resulting in a lower average molecular weight. This drop in molecular weight results in a drop in overall material viscosity.

Additional Thoughts

Because water has a molecular weight of only 18, it alone acts as a plasticizer which reduces the overall viscosity of the material. This is one reason we often recommend molders of non-hygroscopic materials ensure they remove surface moisture from their materials.

-Andy

Determining Intensification Ratio Using Specifications...

By Andy Routsis on September 19, 2011 9:55 AM 2 Vote 0 Votes

I was asked this question during an on-site visit earlier this week...

Technician

I know this machine is rated with a maximum injection pressure of 38,000psi, but I am not sure how to convert this to an intensification ratio.

note: The intensification ratio is a factor which is used to convert the hydraulic pressure being applied to the hydraulic injection cylinders into the actual pressure being applied to the polymer melt at the front of the screw.

My Response

If you know the maximum plastic pressure (Pp-max) along with the maximum hydraulic pressure (Ph-max) for your machine, you can estimate the intensification ratio (Ri) for your machine. / =

Pp-max / Ph-max = Ri

-Andy

Attribute Data vs. Variables Data...

By Andy Routsis on September 12, 2011 9:40 AM 0 Vote 0 Votes

I have often encounter confusion on these two terms when talking to molders...

Attribute Data

Attribute data has two different outcomes. An example of such an outcome would be a GO / NO-GO gauge which is used when testing parts. This test results in only two different outcomes, Pass or Fail.

Variable Data

Variables are those aspects measured using a scale. An example of this would be a dimension measured using calipers. This device provides a wide variety, or scale, of results based on the accuracy of the instrument and ability of the person taking the measurements.

-Andy

MW vs. MWD...

By Andy Routsis on September 8, 2011 2:10 PM 0 Vote 0 Votes

I was discussing polymers with a technician and was asked this question:

John

I understand how molecular weight affects the process, but how does molecular weight distribution affect the process?

My Response

Polymer chain mobility is highly dependent on the length, or molecular weight, of the polymer chain. If most of the polymer chains have a similar molecular weight, or smaller distribution, then they are all more likely to soften at similar temperatures typically resulting in a more narrow temperature range at which the polymer can be processed.

Adversely, a broad molecular weight distribution often results in a wider processing window due to the mobility of some polymer chains while other chains remain highly entangled.

Additional Thoughts

Semi-crystalline polymers with a narrow molecular weight distribution can often achieve a higher degree of crystallinity than polymers with a wide distribution.

-Andy

Open-Loop Molding Revisited...

By Andy Routsis on September 4, 2011 8:01 PM 0 Vote 0 Votes

I have been asked about the proper use of an open-loop molding machines...

Customer

When implementing DECOUPLED MOLDINGsm, how should we best incorporate our open-loop molding machines?

My Response

Basically, open-loop molding machines are not capable of this since open-loop molding machines cannot decouple 1st stage filling from 2nd stage packing. These machines lack closed-loop, injection velocity control and inject using pressure control instead. As a result, the screw speed decreases as the screw moves forward, resulting in an inconsistent shear rate from shot to shot. On these machines, the best approach is to fill and pack the part during 1st stage.

Additional Thoughts

More posts about this topic can be found below:

Documenting Open-Loop Processes...

Processing With Older Injection Molding Machines...

More Discussion about Open vs. Closed-Loop 1st Stage Injection...

-Andy

Mean, Median, and Mode...

By Andy Routsis on September 1, 2011 9:50 AM 0 Vote 0 Votes

I heard a quality technician make the following comment the other day...

Technician

Mean, Median, Mode... they are all the same.

Mean

The mean is the average of measurements within a particular sampling. This value equals the sum of all the numbers in a sampling divided by the number of values in the sample. For example: the mean of numbers 1.1, 1.1, 1.1, 1.3, 1.4 would be 1.2

Median

The median is the middle measurement within a sampling. This value is determined by lining up all the different measurements and the middle number is the median. For example: the median of numbers 1.1, 1.1, 1.1, 1.3, 1.4 would be 1.3

Mode

The mode is the most commonly occurring number within the measurements. This value is determined by adding up how many times each measurement occurs and choosing the value with the highest frequency. For example: the mode of numbers 1.1, 1.1, 1.1, 1.3, 1.4 would be 1.1

Additional Thoughts

In an ideal distribution, all three values should be the same. For example: For the numbers 1.1, 1.2, 1.2, 1.2, 1.3 the mean, median, and mode all equal 1.2.

-Andy

Silver Streaks with PC...

By Andy Routsis on August 30, 2011 10:30 AM 0 Vote 0 Votes

This question arrived this morning via email...

TA

We are processing polycarbonate and are having problems with short molding as well as silver streaks. The mold design is a hot runner system with three drops.

My Response

For the silver streaks, I suggest you ensure the material is properly dried. A dewpoint meter or moisture analyzer should be incorporated to ensure the material is dry enough for processing. It is also advisable to pull the screw and clan both the screw and barrel to ensure there is no buildup contaminating the material. It is also advisable to use a temperature probe to ensure the material temperature is at the manufacturer's recommended setting.

As for the short shots, you may need to develop a more robust process better capable of handling variation. for more on this, please consider reading the following:

Short Shot During 1st Stage Fill.

-Andy

Basic Gravimetric Feed Systems...

By Andy Routsis on August 29, 2011 3:45 PM 0 Vote 0 Votes

I was at an extrusion customer site last week and they were not sure whether the feed system was truly gravimetric or volumetric....

Customer

The system uses a scale to measure the material used when filling the hopper, but has a feed screw to meter the material to the feedthroat. The system can be set to a lbs/hr or RPM of the feed screw.

My Comments

Since the system can adjust the screw speed to maintain a desired lbs/hr setpoint, it can be considered gravimetric. The precision of he setpoint is not high since it has to take intermittent weight measurements as the hopper needs more material. This rate of consumption is then reevaluated each time the hopper is refilled. As a result, the system is a true closed-loop gravimetric system with a relatively long lag time.

-Andy

Keeping Basic Tools at Your Employee's Workstation...

By Andy Routsis on August 24, 2011 4:50 PM 0 Vote 0 Votes

I was at a customer site last week and we were discussing the use of math on the production floor...

Supervisor

The operators always seem to have trouble counting up how many profiles are on each cart. All they need to do is use a calculator to multiply the number of profiles across by the number high.

note: During this discussion, I asked the supervisor where the operator would get a calculator for this purpose. He searched around and realized they would have to walk all the way across the production floor to locate one.

My Suggestion

Mount a calculator to each profile dump table so the operator can both count the profiles and use the calculator at the same time. Once I made the suggestion, he started to point out other tools they should also make readily accessible to improve the operator's job performance such as pens, job booklets, quality standards, etc.

Additional Thoughts

Keep in mind that many employees will often skip a step, or substitute something rather than go out of their away to locate something crucial to their job. It is your job to ensure your employees have the tools and skills necessary to succeed at their job.

-Andy

Feed Throat Cooling...

By Andy Routsis on August 22, 2011 9:25 AM 0 Vote 0 Votes

I just received this question via email...

MM

Most of the plastics raw material data sheet do not contain the Feed Zone temp. How can we keep this temp during production?

My Response

Since this cooling is used to prevent bridging most processor runs this temperature at or near the lowest setting.

The two common reasons a processors will increase this temperature is if 1) the rear heater band cannot maintain the desired setpoint, or 2) condensation is occurring inside the feedthroat.

-Andy

Another Great Use for Compressed Air Dryers...

By Andy Routsis on August 15, 2011 10:35 AM 0 Vote 0 Votes

I was in a discussion with a manager the other day. The discussion turned to material driers and the manager said this...

Manager

We don't have any compressed air driers because we process a lot of nylon and we have to dry it centrally as well as at the hopper.

My Comments

Although compressed air driers do not dry the material as quickly as desiccant driers, they can still be implemented as a cost saving alternative in many applications. Hopper-mounted compressed air driers are a great method of keeping previously dried materials from absorbing moisture.

The simplicity, low cost, and reduced maintenance of compressed air material driers make them a great option to consider for hopper-mounted drying.

-Andy

The First Step to Good Troubleshooting...

By Andy Routsis on August 8, 2011 9:30 AM 0 Vote 0 Votes

I was asked this follow-up question to a previous blog post...

NM

What is the first step in troubleshooting?

My Response

Personally, I believe the first step in good troubleshooting occurs before a defect is made. The first step is to 'Establish a Stable and Reliable Process'.

To further illustrate this point, I recommend reading the following article:

Troubleshooting: Injection Molding Seven Steps Toward Scientific Troubleshooting

Although the transition zone length is small, it is critical to ensure that a long fee zone is being used for semi-crystalline polymers. This allows the material to heat up using more energy from the heater bands to help melt the polymer with less shear. When processing these materials, it is very common to have a feed zone which is nearly half the overall length of the screw.

-Andy

By Andy Routsis on June 27, 2011 10:30 AM 0 Vote 0 Votes

I received a few questions from a blog reader the other day, this is one of them...

Nathan

Regarding the Cavity Balance Test - which is preferable, 50% or 90% full.

note: this test uses different injection speeds to determine which provides the most balanced fill during a 1st stage short shot.

My Response

It is preferable to use a 1st stage fill which provides a ~90% filled part. This provides a good representation of how the part will perform during production.

Additional Thoughts

If you have a product which require a profiled 1st stage injection, it may be a useful exercise to perform such a test at each stage in the profile. This will help you ensure the final fill balance is optimal.

For more blog entries on cavity imbalance, please feel free to review the following:

Correcting for Cavity Imbalance...

Adjusting Hot Runner Systems...

-Andy

Which Parameters to Maintain...?

By Andy Routsis on June 23, 2011 10:25 AM 0 Vote 0 Votes

I received this question this morning...

MK

After establishing the injection molding process for particular part, which parameters should we keep constant during the next subsequent production run? Whether it is Injection time, injection speed, or switch over position, or any other parameter.

My Response

Actually, the focus should not be on the machine inputs, but the actual process outputs. this is a little more complicated, but below are some examples:

Input Output

Barrel Temp Melt Temperature

Shot size 1st Stage Fill Time

Transfer 1st Stage Fill Weight

Screw RPM Recovery Time

The focus is on the outputs because the material grade or machine may change, but the process itself should have the same characteristics.

I discuss this in more detail in the following links:

Recently in Plastics Technology Category

Plastics Technology: Monthly Archives

Categories

Monthly Archives

About this Archive