Hydraulic, Specific, and Cavity Pressure: What's the Difference?

[@ernestkumeh3800]

Nice presentation and clarification. Keep up the great work.

[@blueduckworks]

So happy to find some intel on the nessei great machine. Would like to no if you might come out with a full maintenance video, or processing video. I've been working with this type of machine for years. Keep up the good work.

[@rjg]

Thank you! Any suggestions on a specific maintenance task? Small specific topics are best for youtube videos.

[@anfibiosyreptilesconalex9233]

Thanks so much...good información.I just have two question: what is the optimal intesification ratio in order to avoid lossing press? And the other ...it is correct that RI in an fully electric machine is 1:1?

[@woodfloor33]

I would not say there is an optimal intensification ratio. There is a relationship between the barrel size and the ratio. If you are in a situation where more shot capacity is needed then your intensification ratio will be lower in most cases. If you need a higher Ri then shot capacity will be lower. An electric technically does not have an Ri since there are no hydraulic cylinders. Some times when we are using software for hydraulic and electric machines we will input the ratio as 1:1 for the electric machines so the Specific pressures remain unchanged.

[@downbelowu1928]

Pressures in electric machines go by plastic pressure. Usually in the 26000 range

[@HAPPYTHELEAF]

Worked with theses Nissei hydraulic units good units, but working on mostly Sumitomo EV's now great repeatability with small parts

[@fardin5059]

Hi and thanks so much for the great topic, I watched your webinar on this topic and it is excellent. I know my question is not that related to this video but I found no better place to ask from you, I'm trying to make a true picture of what the injection machine does and a ask you to clarify this for me if possible, "We know that the driving force in the injection machine is hydralic or electric motor, so when we enter a value for injecion rate or injection velocity in first stage or filling stage what the machine does to maintain the value we set for velocity is it exerts a pressure to see what the resulting velocity is and in a closed loop it sets different pressures to keep the velocity on the value we have entered". What I'm pointing is actually the velocity is a result of a profile of different pressures adjusted by machine to maintain our prefered velocity. Am I correct about this? Thank you.

[@sukantasahu391]

Very nice.. in this graph ,how the green line is down side where as the value of cavity pressure is more than the hydraulic pressure.. please explain..

[@Icefisher420]

That is the peak pressure when the plastic hits the small gate. Then it drastically drops in pressure but for a fraction of a second it’s higher.

[@kurtrochlitz2567]

interesting! what's the difference between specific and back pressure?

[@sureshp644]

Do you have any table with ratio of hyd pressure vs specific pressure vs cavity pressure .. considering intensification ratio and gate sizes

[@rjg]

The relationship between hydraulic and specific pressure varies widely from machine to machine. The Ri can be anywhere from 11:1 up to 20:1. Of course there are some machines even lower or higher than that. As far as the cavity pressures, there are huge pressure losses beginning at the nozzle and continue thru the runners, gates and then across the cavity. A simulation can predict the cavity pressure generated and that info can then help determine how much specific injection pressure your machine may need. This is usually achieved by sizing the barrel correctly as the hydraulic system pressure usually remains the same.

[@kerry1111111]

So the cavity PSI requires a sensor in the mold, How reliable are those and do they require maintenance? Never worked with them. :)

[@moisesruiz7500]

Greetings. RJG sensors are very accurate and reliable. I've been working with the RJG's eDART system for a few years. It's a very useful and strong tool.

[@ronbodesheimer8232]

Kerry, as molders we make decisions based on the information we have. There's no better information to have than direct feedback as to what is happening in the cavity itself. There are definitely challenges to transitioning to monitoring cavity pressure, but it's well worth it!

[@rjg]

Yes, cavity pressure sensors are required to read the pressure , but the pressure is always there.

[@rjg]

Glad the system is working for you!

[@rjg]

Having cavity pressure data is another tool in your toolbox.

[@devendradeshmukh3989]

Hi sir, Can you tell me where u locate transducers to measure cavity pressure & specific injection pressure. I'm waiting for your reply

[@rjg]

Hello! Cavity pressure can be measured anywhere in the cavity. Near the gate and at the end of fill are the most common locations. The sensors can be indirect (under an ejector pin) or direct ( flush mount in the cavity). Specific pressure is measured in the hydraulic cylinder and converted to specific via the Ri. In electric machines, a load cell is directly behind the screw measuring the force then converted to pressure. We hope this helps!

[@almaskhancipet]

Very nice explanation

[@rjg]

We're so glad you liked it! Thank you!

[@igorrodrigues8532]

Hi Jason! Thanks for this clarifying explanation. I have one question though, which of these pressures is the one we commonly call injection pressure (I.e. on Moldflow), specific, or cavity pressure?

[@rjg]

In simulation, injection pressure refers to the specific injection pressure. This way we can correlate that pressure to what the target machine has available and verify that the machine can generate the required pressures.

[@Diablonegro84]

Same as VP Pressure

[@downbelowu1928]

Your pressure transducer is reading the pressure of the screw pushing forward. Your intensification ration is usually around 10:1 2000 psi injection pressure means 20,000 psi. Just quit your job

[@educateyourself5650]

How is cavity pressure measured was my question, aaaaand now I'm going to look it up. Thanks!

[@rjg]

Cavity pressure has to be measured with cavity pressure transducers. These can be installed directly in the cavity or under an ejector pin.

[@educateyourself5650]

@RJG, Inc. ok that makes sense. What is RJG, A tooling program or a job shop or both?

[@rjg]

kzbin.info/www/bejne/l5XPdXiupLKMarM

[@parmanandparmanand3522]

Hi could u clear me please about this if u can thanks q=m/pt and s=4.q=22/7.r3

[@PuranSingh-ih7lc]

Sir How much force required for slider cylinder against cavity pressure how to calculate it

[@rjg]

The clamp force calculation for a slide is the slide shut off area X’s the tonnage factor then divided by the tangent of the slide angel.

[@PuranSingh-ih7lc]

Can we caiculate cavity pressure and how

[@rjg]

We can read cavity pressure with Cavity pressure transducers. A well done flow simulation is the best way to anticipate cavity pressures. This is a service that RJG provides. 😊

[@michaelzhu8460]

@@rjg cavity pressure is a good thing, however do we need the tool maker drill holes to put in the sensor, I guess this is something put away many of us adopting the cavity sensor.

[@mdegn1121md]

Why wouldn’t you want to decrease the initial spike of pressure in the cavity?

[@rjg]

If the parts are acceptable then why try and make the curve into a shape that we think is better? If this spike is not blowing the mold open and the parts are repeatable then that is perfectly ok. That spike you see there is not that uncommon when a mold has transducers in the mold to give us that data. Thanks for watching.

[@joehart103]

Awesome presentaion

[@rjg]

We're so happy you enjoyed it! Thanks for watching!

[@selvam65koodalingam]

Sir can you please explain back pressure. And how it's generated.

[@rjg]

Thanks for the suggestion. Stay tuned for a video discussing this topic.

[@user-ke7mn3sv4d]

So what about back pressure?

[@rjg]

Back Pressure is generated behind the screw. In a hydraulic machine this is done with a relief valve to generate restriction and then a certain hydraulic pressure. Electric machines do this with a load cell behind the screw and use the servo motor to provide the braking action. The most important part is to be able to convert the hydraulic pressure to specific pressure , then you know what back pressure is doing to the plastic in front of the screw tip. On the electric machines the value typed into the BP set point is already in specific pressure (plastic pressure in front of the screw tip).

[@selvam65koodalingam]

Thanks

[@sukantasahu391]

Nice

[@thomasmooney5653]

We call it melt pressure, like its ....?sister feature, melt temperature.

[@rjg]

If you are calling the pressure in front of the screw tip , then yes it is the same thing.

[@sankaranarayana2018]

Nice presentation and clarification. Keep up the great work

[@rjg]

We're glad you enjoyed it, thank you!

[@fardin5059]

Hi and thanks so much for the great topic, I watched your webinar on this topic and it is excellent. I know my question is not that related to this video but I found no better place to ask from you, I'm trying to make a true picture of what the injection machine does and a ask you to clarify this for me if possible, "We know that the driving force in the injection machine is hydralic or electric motor, so when we enter a value for injecion rate or injection velocity in first stage or filling stage what the machine does to maintain the value we set for velocity is it exerts a pressure to see what the resulting velocity is and in a closed loop it sets different pressures to keep the velocity on the value we have entered". What I'm pointing is actually the velocity is a result of a profile of different pressures adjusted by machine to maintain our prefered velocity. Am I correct about this? Thank you.

[@rjg]

Thank you for the kind words. On a hydraulic molding machine, there is a pressure limit that is set by the user. This pressure limit allows the machine to use up to that amount to achieve the flow rate. When an injection velocity is set, the hydraulic pump sees this as a certain gallons per minute. The pump will generate that GPM of hydraulic oil. The resistance of moving the screw and the plastic into the mold will start building up a dynamic pressure the further the mold is filled. The pressure limit is established 10-15 % higher than the required pressure under normal circumstances. I hope this clarifies your question.

[@fardin5059]

@@rjg Thanks so much.