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The Uses of MFI…

I was asked this question yesterday…

HG
We get MFI data from the supplier, how can we use this data to our advantage?

My Response
Th Melt Flow Index, MFI, is take under pressures and shear rates which do not represent the actual conditions the material will see during processing. As a result, the MFI is not a good representation of the material processing characteristics. For these reasons, many people completely ignore this data, yet it can be helpful for scheduling and the anticipating potential changes.
For example, if you are processing a lot of material which has a MFI of 5, and you have to decide whether to change to a lot with an MFI of 6 or a lot with an MFI of 10… it is more likely that the lot with a 6 MFI is more likely to process similar to the lot currently processing.
Additionally, if you have to change from a lot with an MFI of 5 to a lot with an MFI of 10, the technician can be warned that the next lot is likely to have a lower viscosity.
Additional Thoughts
I have found MFI data to be a moderately helpful tool when no other rheological data is available. Whenever possible, it is helpful to have more relevant rheological data such as that from a spiral flow, capillary rheometer, or a dual plate rheometer.
-Andy

Costs of Hands-On Training…

I recently heard this statement…

Potential Customer
We save money by just using shadowing to train our employees.

My Response
Personally, I believe that shadowing alone has shown to be the most costly for any company to rely on for many reasons. First, the best you can hope for is that the employee learns the minimal information necessary to perform their job. Second, any success relies on the knowledge of the guiding person and their ability to convey this information properly. Third, constant retraining and reminding is always needed since the minimal information is conveyed to begin with. Forth, this process requires the labor of two employees, the training cots add up quickly.
Additional Thoughts
Since people only learn the ‘how’ of a process, they lack the full understanding as to why an action, procedure, or step is required. As a result, the employees seldom put little emphasis on adherence to procedures in such scenarios. The result is generally a higher level of csrap and damage than that of a well-trained workplace.
-Andy

Follow-Up on Safety Glasses…

A blog reader posted a response to a post on safety glasses, and I believe it deserves a little more attention…

TJ
I think safety glasses should be used in tool room and maintenance area as Personal Protection Equipment, there is no need in quality lab and warehouse.

My Response
I agree with the Tool Room and Maintenance… As for the lab and warehouse, many eye related accidents actually occur in these areas.
In the lab, many companies do dangerous activities such as perform mechanical testing, use chemical agents, cut samples, and even perform rheological tests. Many of the activities in a quality lab can be dangerous and each company should take a look at this before making a judgement.
As for the warehouse, many eye injuries occur when someone is looking up while something is falling down. It is very common for dust, debris, and pellets to accumulate on the top of boxes, molds, and containers stored within a warehouse. When these are pulled from the upper storage racks the employee is looking up while all this dust and debris is falling down.
Additional Thoughts
In many situations, safety glasses are not required in the lab or warehouse, but your company should truly assess the risks before making a decision.
-Andy

Mold Bolt Specifications From Supplier…

I received this question from a recent customer…

Jim
{Our supplier} cannot supply specification documentation that the mold clamp bolts they supply are Grade 8. This is one of the reasons why we are looking at other suppliers.
note: Jim included the name of the supplier, but it was omitted for the purpose of our blog.
My Response
Since these bolts are being used to hold down the mold, the bolt class specifications are not as critical as you might think. When used for mounting injection molds, the bolts are torqued to values siginifcantly lower than their maximum. Since the company you are purchasing from is reputable, you should be fine.
Additional Thoughts
The more important factor is to use a toque wrench to secure the bolts while minimizing any excessive loads. Using the appropriate torque values will be most important in manitaining the long term integrity of the bolts, nuts, and t-slots.
For more on torque values, please feel free to read:
-Andy

Understanding Hydrolysis…

I was discussing material dying with a technician and was asked this question…

Bob
What is Hydrolysis? I looked it up online, but I don’t understand the technical jargon.

My Response
Basically, water molecules are formed with two hydrogen atoms and one oxygen atom (H2O). This is a relatively stable relationship under room conditions. When heated during processing, one of the hydrogen atoms can become easily dislodged from the molecule creating a positively charged hydrogen atom H+. This will also leave a negatively charged alcohol molecule OH-.
Additional Thoughts
What is important about this process is that many polymers are attacked by the results of the hydrolyzed water molecule causing polymer chain degradation. This is why properly drying hygroscopic materials is so important.
-Andy

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