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Delay Before Recovery…

In a discussion yesterday, I was asked this question…

John
Why add a delay before screw recovery? None of my guys do this, is it important?
My Response
Immediately after 2nd stage pack, there is a large amount of pressure present in front of the screw. If this pressure is not relieved, it will increase the rotational torque applied during screw rotation. To prevent screw damage, or snapping, either screw delay or screw decompression can be used.
Additional Thoughts
This concern is even greater with electric molding machines since the servo-motor can apply a great amount of torque instantaneously. This can quickly weaken, twist, or break the screw within the barrel.
-Andy

Intensification Ratio for An Electric Machine…

I received this question from a friend of mine the other day…

Ron
What intensification ratio is used for an electric molding machine? Our customer needs a value to calculate the material’s viscosity.
My Response
The Intensification Ratio is used to convert hydraulic pressure to plastics pressure. Basically, there is no intensification ratio since the electric molding machine already provides plastic pressure. Since many worksheets use hydraulic pressure, they require an intensification ratio to complete the calculation. For these situations, the intensification ratio should be 1.0.
-Andy

Basic Tensile Strength…

I received this question the other day…

Nathan
Can you please advice me the wall thickness of this Product with PP material to withstand 100kg tensile stress? The maximum thickness is 4mm.

note: the part has a round diameter in the middle, so the thickness referenced is actually a diameter.
My Response
For online purposes, we conducted this using the yield strength of a generic grade of PP at room temperature which = 120Mpa. We also used the 4mm measurement to determine acceptability.
F = 100kg = 980 N
A = pi * r^2 = 0.00001257m^2
Tensile Strength = F/A = 78,000,000 N/m^2 = 78 Mpa
In this scenario, the maximum thickness of 4mm would be acceptable assuming the application is a low-risk application where the product is stressed for a short period of time.
Additional Thoughts
Although this is a simplified example on how such a calculation could be performed since I have no specific information about the product or application.
-Andy

If I Train My Employees…

I heard this comment again the other day…

Potential Customer
OK, I know I need training, but if I train my employees, they will leave.
My Response
Some people will always believe this, and for those people, I can do little. One of the funniest responses to this I have heard is from Zig Ziglar who says ‘If you don’t train your employees… they might stay!’.
Ignorance is never a good retention policy… nor is it a good business plan. In our experience, turnover improves when you implement a ‘production-wide’ employee development system. This happens because your employees will develop a culture of learning and will begin to discuss, refer, and assist each other on a more consistent basis. The truth is, your employees want to do a good job, but they need the tools and skills to do their jobs well.
Additional Thoughts
Keep in mind, I stated a ‘production-wide’ training initiative. If you just train a couple key guys, you are likely to lose them since they are not working in an environment which caters to their desire to learn. Basically, people learn best by being trained and having the information reinforced continually over time.
-Andy

Eliminating Mold Sweat…

I received this question via email the other day…

JD
What is the best way to eliminate mold sweat?
My Response
Mold sweat, or condensation on the mold surface, occurs when the dewpoint of the air is higher than the mold temperature. When air reaches it’s dewpoint, water vapor will precipitate out of the air and accumulate on the mold surface. This condition often causes splay, blisters, or bubbles on the molded part.
To reduce condensation, the mold temperature can be increased, or the dewpoint or temperature of the surrounding air can be decreased by controlling the climate in the molding area. Blowing dehumidified air at the mold reduces the dewpoint…which lowers the possibility of condensation.
-Andy

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