February 2011 Archives

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.


Eliminating Mold Sweat...

Andy Routsis
Vote 0 Votes
I received this question via email the other day...

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.


I recently received this question...

It has been about 5 years since we trained, what is the best method to restart.

My Response
After a few years, the best way to restart a training initiative is to consider it as though you had not done any training, or a fresh start. This recommendation is because the previous training initiative has fallen through the cracks and some time has passed... your employees are almost always in the need of either retraining or a refresher.

Additional Thoughts
There is always an excuse to not train your employees, but it is never bad time to start training, or to restart a training initiative.

A blog reader emailed me some pictures regarding a product which is encountering post-molded contamination of various fibers. After some question and answer, it appears they are using a cleanroom environment and the fiber contamination is from many sources. Most of the typical precautions have been investigated and they are looking for a different opinion on the situation.

My Recommendation
From your notes, it appears you are using a blower fan on the product, if this is not an anti-static fan, we recommend upgrading to an ionizer-style anti-static fan.

On all the blower fans in the molding room, we strongly recommend that the air that is blown over the molded part be diffused or diverted afterwards. This ensures they are not sending the blown-off debris into the room’s atmosphere, or creating small air currents within the room which can pick up other debris and fibers. In one case, I have witnessed a current which actually blew up the wall and across the ceiling because many fans were aimed at the floor in the same direction.

We recommend eliminating any air nozzles on the production floor. These are often used by the employees to clean off machinery, equipment, and clothes. A vacuum with a clean filter should be used for all cleaning unless absolutely necessary.

Additionally, check all the filters in the molding area for both cleanliness as well as for fit.

I recently encountered a customer with a common concern...

Should I start all my production employees through the basic level of training?

My Response
Any company, such as this one, which lacks any structured training program, will benefit highly from a broad-based training initiative. Such an initiative should start from the top down, and begins with the basics. This creates a common knowledge and terminology as well as establish a baseline of knowledge from which everyone starts.

Additional Thoughts
Don't assume that your employees already know everything just because they don't speak up and say so. It is a rare, and extremely valuable, employee who will let you know if they lack knowledge and need instruction in a specific area.

This question addresses a common issue for many techs...

What is the best way to evaluate the performance of a check ring?

My Response
To evaluate the performance of the check ring, it is recommended that you perform the dynamic check ring repeatability test. This test consists of producing and weighing a series of ten short shots. The variation of the weights is then determined and represented as a percentage.

Additional Thoughts
Although a shot to shot variation above 3% is typically considered unacceptable, you should consider performing this test on some different processes which are functioning properly to determine a baseline of comparison for your machines and materials.


I reviewed the previous post where the blog reader asked whether electric machines are good for applications with long hold times and I wanted to add another comment...

Shut-Off Nozzles
Although some molders purchase shut-off nozzles to eliminate drooling, they are very helpful as part of an overall molding strategy. In the case of a process with a long hold time, a shut-off nozzle can be very helpful in reducing electricity consumption, improving melt capacity, and limiting strain on the hydraulic components or servo-motors.

Hold Time Strategy
In processes where the hold time is long, the shut-off nozzle can often be incorporated as an early hold time cut-off. Once the shut-off nozzle is activated, the material cannot flow back through the nozzle. In most applications with a long hold time, there is a point where a shut-off nozzle will hold the polymer in the mold cavity, allowing hold time to stop, eliminating as much as 30% of the hold time.

When implementing such a strategy, it is best to first determine the optimal hold time with a gate seal study. Once the optimal gate seal time is determined, begin a similar study, using the hut off nozzle in conjunction with a decrease in hold time. When using a cold runner system, you may need to reduce the sprue and runner thickness to help prevent back flow into the runner system. The overall reduction in hold time saves electricity, reduces long-term wear on the machine components, and allows the screw to start recovering early.

I received this as a follow-up question for a previous blog posting on The Future of Plastics...

We are adding a new machine this year and we are looking at a electric machine. Our biggest concern with electric is the hold time. Due to our thick wall parts we use extended hold times. Does anyone have any experience using extended hold time with a electric machines?

My Response
In reality, jobs with long hold and/or cooling times are very well suited for all-electric molding machines. In a hydraulic molding machine, the hydraulic pump is always providing significantly more hydraulic fluid flow than is necessary to mold the part. Even when a multiple stage, variable, or servo-driver pump is used, hydraulics are a relatively inefficient method of transferring electric energy to linear or rotary motion when compared to all-electric molding machines. These losses are amplified when you consider the added costs of water for the heat exchanger as well as additional maintenance expenses.

The latest news in all-electric molding machines is almost always focused on higher speeds, tonnages, and pressures intended to get all-electric molding machines into newer markets such as packaging and automotive where profit margins are razor-thin. As a result of this hype about the latest and greatest, the molding companies take for granted that the average injection molder already knows all the general benefits and how it applies to their own operation.

Additional Thoughts
Industries such as robotics and automation are doing a good job in teaching the consumers about the benefits of servo-motor driven components. Many molders are replacing simple items such as pneumatic sprue pickers with high-efficiency servo-motor drive versions. When I hear molders tell me things like "I'd get an electric machine if I were doing more automotive" or "My cycle times are too long to justify an electric molding machine" it shows that the industry should return to the basics and teach it's potential customers more about the fundamental benefits of all-electric molding machines.

We recently created a series of training programs focused on all-electric molding machines to help educate molders about the functionality, benefits, and optimal processing of all-electric molding machines


Recently, a potential customer mentioned this comment...

I like the idea of training my employees about extrusion, yet I need something specific to my operation and I don't have time to create it.

My Response
First off, generic extrusion training is always better than no process training at all. As one of our customers called it, "It gives them a plastics frame of mind". In most cases, supplemental systems such as on-the-job training materials can be created very easily, and most online training systems can be customized and modified easily.

Additional Thoughts
It is always better to train your employees than not train them. Whether it teaches fundamentals, or company-specific details... it helps provide the information necessary for critical decisions making.

Yesterday, I was asked this question...

My tech told me that we were getting flash as a result of a low barrel temperature. An increase in barrel temperature fixed the problem, but I don't know why, could you explain?

My Response
It may seem counter-intuitive, but flash could be the result of a low melt temperature or a high melt temperature.

If the temperature of the melt is too low, the viscosity will increase and the pressures required to fill the mold may be too high. This high pressure can exceed the clamp tonnage resulting in flash near the center of the mold or near the gate.

If the temperature of the melt is too high, the melt viscosity will drop - especially if the material degrades. This drop in viscosity may allow too much material to enter the mold during 1st stage fill, resulting in flash. A decrease in melt viscosity may also cause the material to flash during 2nd stage packing.

Additional Thoughts
Keep in mind, the focus should be on the actual melt temperature, which is a process output, instead of barrel temperature settings, which is a process input.


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This page is an archive of entries from February 2011 listed from newest to oldest.

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