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  • #31
    Originally posted by level3ninja View Post
    Very easy to remove. Thankfully just as easy to replace. The resulting static and velocity mean a 5cm radius around around the exit chute and below ends up covered in grinds.
    Does this mean that speed is now causing another problem, certainly have not experienced this with either the Rocky or Mini Mazzer, both slower grinders.

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    • #32


      Speed kills.
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      • #33
        This is interesting as well as informative, seems the delivery chute on the Eureka Atom is a plastic tube approx 200 mm long with a rubber front cover, both materials notorious for building and holding a static charge, hence the build up and clumping of ground coffee, as well as this they have a 90° bend for the ground coffee to negotiate as soon as it leaves the burr chamber, I doubt the makers could have chosen worse materials for fabrication of the delivery chute, even though the have rounded the bend it is a real bottle neck and compounds the problem.


        On the other hand, the delivery chute of the Mazzer is very short, approx 25mm long of metal construction contains no plastic and consequently does not build up a static charge, hence little or no clumping.

        I'm sure Lyrebird will be able to enlighten us further on this.

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        • #34
          Originally posted by Yelta View Post
          I'm sure Lyrebird will be able to enlighten us further on this
          As it happens I can.

          What you are calling static is properly called triboelectric effect: when two materials with different electron affinity are made to contact then separated, one will steal electrons from the other. Logically the higher affinity material will gain electrons and the lower affinity will lose the same amount (conservation of charge) so they will end up holding opposite charges. If the material is a conductor the charge will drain away, if it is an insulator it will not, hence the name "static electricity"

          Equally logically the larger the difference in electron affinity the larger the effect and the larger the charge. Generally polymers have high electron affinity so as you say they will cause a high degree of triboelectric effect with lower affinity materials such as coffee grounds.

          Not all polymers are equal however: PTFE is notorious for having higher affinity than just about any other material but some polymers have much lower affinities. In general this property is related to the local humidity and how hydrophobic the surface is: see this paper for more detail than you probably want.

          It turns out Eureka aren't stupid: the polymer used in the chute of my little Mignon grinder is POM (aka polyformaldehyde but no-one calls it that anymore because it sounds scary). I assume the other grinders use the same or similar material.

          POM is moderately hydrophilic and thus the electron affinity difference between it and coffee is quite low: around 10nC/J*, around 1/20th of the difference with Teflon. This and the fact that POM is easily moulded to complex shapes and very strong makes it close to the ideal material for the purpose.

          The only material I can think of that would be much better would be carbon filled POM. Carbon filled polymers and rubbers are moderately conductive, see first para regarding dissipation. The rubber components on the grinder possibly fit this category.




          * This is an educated guess: I don't have a figure for coffee so I am assuming it is somewhere around the usual level for organic materials which mostly lie between 0 and +10 nC/J**.

          POM is about -5, giving an net difference of 5 to 15, average is 10.

          Teflon is -190 giving a net difference of 190 to 200.

          Metals are by definition 0, giving a net difference of 0 to 10.


          ** The figure in nC/J is in nanocoulombs per joule, referring to the charge (in Coulombs) being transferred from a metal for a given amount of mechanical energy (in Joules). Since electrons are negatively charged, high electron affinity materials give a negative coefficient.
          Last edited by Lyrebird; 31 March 2019, 05:26 PM. Reason: clarity

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          • #35
            Originally posted by Yelta View Post
            This is interesting as well as informative, seems the delivery chute on the Eureka Atom is a plastic tube approx 200 mm long with a rubber front cover, both materials notorious for building and holding a static charge, hence the build up and clumping of ground coffee, as well as this they have a 90° bend for the ground coffee to negotiate as soon as it leaves the burr chamber, I doubt the makers could have chosen worse materials for fabrication of the delivery chute, even though the have rounded the bend it is a real bottle neck and compounds the problem.


            On the other hand, the delivery chute of the Mazzer is very short, approx 25mm long of metal construction contains no plastic and consequently does not build up a static charge, hence little or no clumping.

            I'm sure Lyrebird will be able to enlighten us further on this.
            Yelta- I actually watched this video last night. I noticed at one point they made mention of a newer style 'chute and cover that is deeper (more girth), which, for obvious reasons may be an answer. Am in the process of trying to source that item.

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            • #36
              Originally posted by Lyrebird View Post
              As it happens I can.

              What you are calling static is properly called triboelectric effect: when two materials with different electron affinity are made to contact then separated, one will steal electrons from the other. Logically the higher affinity material will steal electrons and the lower affinity will lose the same amount (conservation of charge) so they will end up holding opposite charges. If the material is a conductor the charge will drain away, if it is an insulator it will not, hence the name "static electricity"

              Equally logically the larger the difference in electron affinity the larger the effect and the larger the charge. Generally polymers have high electron affinity so as you say they will cause a high degree of triboelectric effect with lower affinity materials such as coffee grounds.

              Not all polymers are equal however: PTFE is notorious for having higher affinity than just about any other material but some polymers have much lower affinities. In general this property is related to the local humidity and how hydrophobic the surface is: see this paper for more detail than you probably want.

              As it happens Eureka aren't as stupid as it may seem: the polymer used in the chute of my little Mignon grinder is POM (aka polyformaldehyde but no-one calls it that anymore because it sounds scary). I assume the other grinders use the same or similar material.

              POM is moderately hydrophilic and thus the electron affinity difference between it and coffee is quite low: Of the order of 10nC/J, whereas the affinity difference with Teflon is about 200 nC/J. This and the fact that it is easily moulded to complex shapes and very strong makes it close to the ideal material for the purpose.

              The only material I can think of that would be much better would be carbon filled POM. Carbon filled polymers and rubbers are moderately conductive, see first para regarding dissipation. The rubber components on the grinder possibly fit this category.
              Lyrebird- my brain has just exploded...but thank-you though. Good info.

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              • #37
                Lyrebird thank you for such an informative reply, learnt plenty.

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                • #38
                  I'm still far from convinced, Eureka obviously perceived a problem, why design and fabricate a new improved delivery chute if this was not the case, seems all they have done is enlarge the tube in the hope that the coffee will flow and clear faster, if there is any chance of static build up nothing is going to change.

                  The bend in the tube is an obvious bottleneck and I'm not convinced that there is not a static problem, there is obviously something causing major clumping (other owners have also complained of this) if its not the material the chute is made of, or the design of the chute what is it? why are these grinders susceptible to clumping whilst grinders from other manufacturers are not.

                  Lyre Bird has explained in a manner that is way over my head, what it is not, but has not told us what the problem is.

                  What I do note is his statement "POM is moderately hydrophilic and thus the electron affinity difference between it and coffee is quite low: around 10nC/J*, around 1/20th of the difference with Teflon." quite low is not zero, so there must still be a capacity to store a charge.

                  Not trying to prove a point, simply trying to help find a solution.

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                  • #39
                    Yelta, not sure if the Atom is the clump master it is portrayed to be by whatever reviews you are reading. I have had mine nine months and have had one incident, which 100% can be put down to my inattention to get an oily roast. Totally my fault. Have probably cleaned mine 3 or 4 times in the time I have owned, relaxing ten minute job at the outside. Not sticking up for the machine, just saying from my empirical sample of one there has been no evidence of this. I think I may have the later chute as my rubber has a healthy overlap, thou the screw attachment point is the giveaway. Will check next time I clean the machine.

                    Ninja also has the same machine, how has yours been?

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                    • #40
                      Originally posted by Lyrebird
                      Interesting strategy, to state that you don't understand something then to question its validity.


                      I suppose it works for Pauline Hanson, so whatever.
                      Not sure this response was necessary, guess if it makes you feel better, why do I get the feeling you dislike your opinions being questioned.

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                      • #41
                        Beaninlove, it may be worth spending 5 minutes to take the covers off and see which chute you have? Yelta may be on to something, the older chutes obviously had some problems, my newer version seems not to. Easy to tell which you have by the screw points, the old version seemed to have tabs, the new had a larger base. The new chute may be an easy, low priced solution which takes ten minutes to fit.

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                        • #42
                          Originally posted by 338 View Post
                          Yelta, not sure if the Atom is the clump master it is portrayed to be by whatever reviews you are reading. I have had mine nine months and have had one incident, which 100% can be put down to my inattention to get an oily roast. Totally my fault. Have probably cleaned mine 3 or 4 times in the time I have owned, relaxing ten minute job at the outside. Not sticking up for the machine, just saying from my empirical sample of one there has been no evidence of this.

                          Ninja also has the same machine, how has yours been?
                          My experience matches yours 338, a couple of learning opportunities early on and otherwise no issues. It is certainly not a clumpy grinder by any stretch of the imagination. When I clean mine the chute is usually the cleanest part of the grind pathway, I remember thinking how well designed it must have been the first time I opened it up and saw it almost spotless. I suspect that the reason for the upgraded chute is not that it's design was lacking but perhaps to allow a much wider margin for error for the newly upgraded domestic user who's skills hadn't yet caught up to their equipment. I would suggest my own "learning opportunities" early on with the Atom were just that (having come from a Breville BCG820).

                          Edit to add: I definitely have the earlier smaller chute
                          Last edited by level3ninja; 31 March 2019, 11:15 PM.

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                          • #43
                            G'day Yelta...

                            While Lb's presentation of the explanation above is in a somewhat academic vein, it is right on the money and makes sense to those of us who have backgrounds related to matters Electrical/Electronics. I think Lb may have taken exception to your questioning his explanation after admitting that the topic doesn't lie within your sphere of knowledge or experience and has been construed therefore, as an insult...

                            Mal.

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                            • #44
                              Evening Mal, think I'll quietly back out of this conversation, I offered an opinion as is my right, was disrespectful of no one, certainly did not expect to be compared with Hanson.

                              If LB wants to set himself up as the forums font of scientific knowledge he can continue on his path without any input from me.

                              My interest is in making and enjoying good espresso and helping others to do the same.

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                              • #45
                                I did not intend to compare you to Hanson, it was meant as a light hearted jibe at her expense not yours. I apologise if it came across that way.

                                I have deleted the post.

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