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There are a couple general misconception regarding the benefits of all-electric molding machines…

Misconception #1 ~ All-electric molding machines will not save you money if you have a long cycle time. The truth is… The pump runs constantly on a hydraulic machine wasting energy, and causing component wear. Electric molding machine components do not run when they are not being used saving electricity and wear during idle moments.

Misconception #2 ~ For long cycle times… hybrid machines provide virtually the same energy savings as electric molding machines; since most of the energy is consumed during screw recovery. The truth is… As with #1, the cost and wear associated with running the pump during idle times will usually outweigh the initial savings during the purchase of the machine.

I recently visited a molder who purchased both a hybrid and an all-electric molding machine to compare their performance and energy savings side by side. Both machines ran the same mold and had processes with cycle times over two minutes. He claimed that he could throw away the hybrid machine, buy another electric molding machine, and still pay for both machines in less than four years just from the energy savings. This sounds extreme… buy it demonstrates the money you can save by thinking long term.

The costs savings for long cycle times is part of the reason machine manufacturers are being pressured to build larger and larger all-electric molding machines.

-Andy

The thin probe is the best method. You do not have to preheat it… and the reading is very fast. Wire probes tend to be too brittle for the production environment, while the newer thin probes are much hardier.

If you want to save a few bucks, you can usually skip the extension cable and plug the probe straight into the meter. Personally, I use the probe that way because I can take the reading with one hand.

Although there are a variety of styles, the probe adapters are pretty consistent… so you can usually plug a new probe into an older meter.

-Andy

In a previous blog entitled The 80-20 Rule For Available Shot Size I discussed the importance of processing parts where the shot size falls between 20 and 80 percent of the overall shot size capacity.

The questions all revolve around ways to get around the issues of processing shot sizes below 20% of the shot size. A typical questions is ‘Is possible to have a process control with this type of problem?’ ‘Are we going to be able to have shot to shot consistency?’ ‘I suddenly encounter shorts or flash without any warning… could this be the cause?’ ‘We are considering better process controls… will this help?’ ‘We have to purge the barrel often… might this be the cause?’

I have addresses these individually… but would also like to address this in general terms.

Basically… when you process at 20% barrel capacity, you typically have 5-10 cycles of material in your barrel. If you use 10% capacity, you have will generally have 10-20 cycles of material in your barrel. Likewise, 5% capacity jumps it up to 20-40 cycles. This means that the material will cook, breakdown, and degrade while sitting in the barrel.

Additionally, each time the screw moves forward to inject… you cause additional mixing amd material migration within and over the screw flights. This will cause an increase in the residence time distribution. This means that if you put a pellet of colorant in your barrel, the time form when you start seeing the color, to the time you stop seeing the color increases.

With the increases in both residence time and residence time distribution… you significantly increase the risks associated with degradation, viscosity variations, mechanical property loss, as well as all the related part defects that occur.

A good way to see your property losses would be to mold some parts with virgin material record the peak pressure during first stage as well as perform some mechanical tests on the parts. After this, regrind the parts, mold the parts again and compare the loss in peak pressure as well as the loss in mechanical properties. Most materials will exhibit 5-10% property loss when processed properly.

There are also other factors which affect the stability of the process… but those are the two biggest when you are processing with an over-sized molding machine.

-Andy

What is the best method for measuring mold temperature? Should I trust the thermolator measurement?

When measuring mold temperature, it is actually best to measure these two factors… coolant temperature into the controller and coolant temperature out of the controller. If these are documented when the process is molding acceptable parts, then you can better replicate the conditions in the future.

These measurements should be taken using a surface probe in contact with the in and out connectors of the temperature controller.

The return temperature provides a good indication of the mold temperature. The difference between these two numbers provides a good indication of cooling effectiveness. Higher differences may indicate a poor coolant flow, while a low difference may indicate a too much coolant… or an improperly connected coolant line.

Some molders use the thermolator measurements with good success… but these measurements should be calibrated and verified often with a pyrometer with a surface contact probe.

Mold surface temperature measurements can be helpful, but do not provide relevant data about the overall effectiveness of the mold temperature controller.

-Andy