Implementation of Conservation principles for Runner conduit in Plastic Injection Mould Design

DOI : 10.17577/IJERTV2IS110084

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Implementation of Conservation principles for Runner conduit in Plastic Injection Mould Design

Muralidhar Lakkanna1, Yashwanth Nagamallappa 2, R Nagaraja3

Government Tool room & Training Centre, Bangalore, Karnataka, India

Abstract

Conservation principles are used to represent all physical transformations occurring in the universe, accordingly are also adopted to design runner conduit for thermoplastic melt injection. Conservation principles for thermoplastic melt injection through runner conduit are implemented by considering cylindrical co-ordinates system relevant to its geometrical configuration for deriving governing equations. While the continuity equation ensures volumetric conservation of thermoplastic melt, the momentum equation represents equilibrium of forces on thermoplastic melt injection through runner conduit. During an injection moulding cycle heat and work done energy transformations are balanced by implementing first and second law of thermodynamics. Thermoplastic melt state change through the runner conduit for a particular cycle is appreciated by heat conduction equation. Traditionally inertia and entropy contribution is neglected to skip rigorousness, nevertheless they continue to prevail. Especially in very frequently used non-circular runner cross section conduits, their influence is highly significant. Hence the current endeavour attempts to computationally model, continuousness, equilibrium, energy balance and phase transformative runner design criteria by implementing conservation principles.

Keywords: Runner Design, Plastic Injection Mould, Conservation Principles

  1. Introduction

    Designing moulds necessitate fundamental insight into physical injection moulding behaviour of chosen melt relative to desired component characteristics as well as complementary classical principles of mechanics. Off mould design runner system is the focussed subject of investigation. Runner conduit is one

    of the integral and influential elements of injection mould design to process plastic parts [1]. Specific spatial region defining runner conduit is considered in isolation from everything else as a well-defined control surface or system boundary [2]. Non-newtonian thermoplastic melt is then injected through runner system conduit to contrive component impression space. Since runner conduit involves continuous melt injection through its inlet and exit boundary surfaces, it will be an open system often referred here afterwards as control volume [3]. Here the runner conduit is considered as a Euclidian flow field and thus thermoplastic melt properties are defined as spatiotemporal functions [4]. Hence here we consider an elemental volume of thermoplastic melt inside runner conduit and conservation laws are implemented by differential approach [5].

    The condition of thermoplastic melt at any instant of time is typically referred as its state and expressed as a function of melt characteristics [6], which are basically a non-newtonian. Though it experiences the runner conduit for fraction of cycle, it directly influences the ideal feed system design. Consequent to injection action, exclusive melt state metrics and their extents are used to design effective runner parameters by implementing mass, momentum and energy principles [7]. Thus its control volume formulation is critically important to represent overall balance [8].

    The mass conservation principle implements continuity of thermoplastic melt injection rate. The momentum conservation principle appreciates forces acting on thermoplastic melt over the entire runner conduit [9]. Similarly energy conservation principle apprehends energy change of thermoplastic melt throughout the process. Here two simultaneous modes of energy transformations are recognised, injection work and solidification heat transfer. The primary objective of mould designer is to realize maximum injection power (rate of injection work transfer) from runner conduit design criteria. The energy conservation principle articulates energy is conserved during a

    process but doesnt hint anything about whether the

    process but doesnt hint anything about whether the

    Nomenclature

    m Mass Kg

    V Volume m3

    P

    Pressure

    Kgf / m2

    T

    Temperature

    K

    k

    Thermal conductivity

    W/m

    A

    Cross-section area

    m2

    U

    Ur

    Linear velocity

    Velocity in radial direction

    m / s

    m / s

    U

    Velocity in tangential direction

    m / s

    U Velocity in arbitrary direction m / s

    a Acceleration

    m / s2

    M Linear momentum Kg m / s

    1. Angular momentum Kg m / s

    2. Moment of inertia

    Kg m2

    e Specific total energy KJ / Kg

    u Specific internal energy KJ / Kg

    T Resultant torque N m

    M Resultant moment N m

    F Resultant force

    N / m2

    Fr Force acting in radial direction

    F Force acting in tangential direction

    F Force acting in arbitrary direction

    N / m2 N / m2 N / m2

    Q Rate of heat transfer KW

    q Rate of heat transfer per unit mass KW

    Wv Rate of work done by viscous forces KW

    Wp Rate of work done by pressure forces KW

    dS Entropy change KJ / Kg

    Cv Specific heat at constant volume KJ / KgK

    Cp Specific heat at constant pressure KJ / KgK

    n Unit normal vector

    r Position vector

    Greek symbols

    Density

    Specific volume

    Kg / m3

    m3 / Kg

    Angular acceleration

    m/ s2

    Surface force

    N / m2

    Shear stress

    Viscous dissipation function

    N / m2

    Angular acceleration

    m/ s2

    Surface force

    N / m2

    Shear stress

    Viscous dissipation function

    N / m2

    Angular Velocity m / s

    energy exchange is reversible or not. However in most circumstances, melt injection through runner conduit for a particular cycle is an irreversible process. So an additional quantity called entropy is required to balance energy transformations. To gain better understanding of realizable energy transformations the concept of entropy is implemented [10].

    Hence fundamental conservation of injection mechanics from mass, momentum and energy perspective is essential to realize specific relationships among chosen thermoplastic, desired component and available machine. All these relationships along with processing objectives facilitate designing an idealistic runner system.

  2. Conservation laws

    Plastic injection phenomena through runner conduit can be explained by using conservation laws. The conservation equations fundamentally seek to tell us how three important field variables are distributed in space and time. According to conservation laws any measurable property of the system does not change as the system evolves/ undergoes a change. Thus during

    any process the quantities of the system will be

    figure 1, subtending an angle d at the centre. Since thereare no sources or sinks in the conduit, we can conveniently postulate that the mass of representative melt element does not change in position and time i.e.,

    mass is conserved spatiotemporally. If U is melt velocity then Ur is velocity in radial direction, U is velocity in tangential direction and U in arbitrary

    injection direction respectively. Here is linear

    arbitrary path function in the YZ plane on machine.

    1. Conservation of Mass

      The continuity equation comes from the basic principle that matter can neither be created nor be destroyed. This principle is then applied to a small volume of thermoplastic melt under injection resulting in equation representing continuity.

      Lemma

      Melt state change at any instant within runner conduit is always equal to influx and efflux melt state change rates across the runner conduit inlet and outlet respectively

      conserved. This concept of conservation can be applied

      dV AU AU 0

      (1)

      on thermoplastic melt diffusing through runner conduit of injection mould to determine the properties of thermoplastic melt throughout runner conduit.

      Let us begin by considering a three dimensional

      rcv t

      Proof

      out in

      runner conduit of a thermoplastic injection mould in cylindrical co-ordinates system having a representative melt element between r and r dr as shown in

      Consider injection in arbitrary direction, Mass of melt entering/unit time

      Figure 1: Three dimensional runner conduit in cylindrical co-ordinates [5]

      = density × velocity in -direction × inlet cross section area

      (rUr ) ( U ) r ( U ) 0

      t r

      = U rddr

      U ( U ) 1 ( U ) ( U )

      Similarly mass of melt leaving/unit time

      r r 0

      (4)

      U

      t r

      r r

      U d rd dr

      Now by substituting vector gradient operator,

      U U 1 U U

      .U = r r

      (5)

      Thus, total change of mass in -direction/unit time

      r r r

      = mass entering – mass leaving

      U

      U

      rdrd d

      Hence equation reduces (4) to

      . U 0

      (6)

      t

      U

      dV

      The above equation is called continuity equation.

      The above equation describes that the thermoplastic melt injection is compressible and melt is conserved

      Correspondingly,

      Total change of mass in -direction/unit time

      r

      r

      1 U dV

      Total change of mass in r-direction/unit time

      Ur Ur dV

      r r

      Therefore net change of melt mass in element/unit time is

      Ur Ur dV 1 U dV U dV

      through the runner conduit [11], during complete injection moulding cycle.

    2. Conservation of Momentum

      We hereby develop governing equations for runner conduit design considering dynamic forces consequent to thermoplastic melt injection. According to Newtonian mechanics thermoplastic melt injection through runner conduit should obey Newtons Second Law of Motion for Conservation of Momentum. The implied momentum could be linear or angular and its

      corresponding actions are force F and moment

      Mrespectively.

      r r

      r

      U U 1 U

      U U 1 U

      U

      r r dV

      r r r

      1. Conservation of Linear Momentum Lemma

        (rU ) U

        (rU ) U

        U

        r r dV

        (2)

        At any moment resultant force acting on

        thermoplastic melt is proportional to its instantaneous

        r

        Instantaneous mass of melt within the runner conduit element = Density × Volume

        injection momentum change rates in that direction and momentum change rates across the runner conduit inlet and outlet

        mU

        = dV

        So rate of change of melt in element

        (dV)

        t

        i.e., F

        We have,

        mU mU

        t

        t

        out in

        (7)

        Since runner element volume dV is stationary and invariable with respect to time or independent of time

        change it becomes dv

        mU

        t

        UdV

        t rcv

        out

        and

        t

        Hence by applying conservation law we get,

        mU mU UUdA

        out in in

        out

        dV (rUr ) U r

        U dV 0

        (3)

        F t rcv UdV UUdA

        (8)

        t r

        in

        The term UUdA represents momentum change rates through mass transfer across runner conduit inlet and outlet.

        Proof

        The element is so small that volume integral simply reduces to a derivative term

        Therefore body forces can be neglected for runner conduit design.

        Consider stresses in r-direction,

        Resultant force acting at runner conduit entrance (boundary)/unit time rr n.rdd

        Since mass is entering into the runner control volume, unit normal vector to exit boundary n 1

        i.e., UdV UdV

        (9)

        Therefore resultant force acting at runner conduit

        t rcv t

        entrance/unit time rr rd d

        Consider rate of momentum change in r-direction

        Resultant force acting at runner conduit exit/unit time

        Rate of momentum change at inlet of runner conduit

        rr

        = Ur Urd d

        rr

        r dr n. r dr d d

        Rate of momentum change at exit of runner conduit

        Ur U

        Unit normal vector to entrance boundary, n = 1 Thus Resultant force

        = U U

        r

        r dr r drd d

        =

        • rr dr

          r drd d

          rd d

          rr r rr

          Rate of momentum change in r-direction

          U U

          = rr rr rdrd d

          U U r dr n.r drd d U Urd d

          r r

          r r r

          = rr rr dV

          r r

          Ur U Ur UdV = r. Ur UdV

          r r r

          So that the net resultant force in r-direction is given by

          dF ( rr ) 1 ( r ) ( r ) rr dV

          Similarly in and -directions

          r,resultant

          r r

          r

          Rate of momentum change in – direction

          Similarly in other directions,

          1 U U

          1

          2

          dV

          dF

          r

          r dV

          r

          ,resultant

          r r

          r

          Rate of momentum change in – direction

          r

          1

          r

          U U

          dF,resultant

          dV

          r r

          r

          dV

          Therefore net momentum change rate through mass

          Net resultant surface force due to injection/melt convection exerts stress on runner conduit boundary.

          P

          transfer

          r. Ur U

          1 U U

          U U

          ij

          rr

          r

          r

          P

          r

          dV (10)

          P

          r r

          r

          Forces acting on thermoplastic melt

          The forces acting on melt mass are body forces and surface forces. The body forces are mainly due to gravity and their contribution in momentum conservation would be very less because plastic melt within the runner conduit is a small fractio of shot volume (approximately 50 times), melt injection forces are predominantly larger (more than 100 times) than

          inertial forces and melt density itself being very less.

          Splitting this into pressure and viscous stresses, we can rewrite it as

          dV r r r r r

          dV r r r r r

          dFr P 1 (r rr ) 1 ( r ) ( r )

          Similarly in other directions,

          r r r

          r r r

          dV r r2 r r r

          dV r r2 r r r

          dF 1 P 1 (r2 ) 1 ( ) ( )

          dF P 1 (r r ) 1 ( ) ( )

          dV r r r

          Hence net resultant forces is given by

          dF P 1 P P

          This can be expanded as follows Momentum in r-direction

          dV

          r r

          P 1 (r )

          1 ( )

          ( r )

          resultant

          rr r

          1 (r rr ) 1 ( r ) ( r )

          r r r r r

          r r r r

          U U U U U U 2

          r U

          r r U

          r

          1 (r2 )

          1 ( )

          ( )

          t

          r r r

          r

          r r r

          r2 r r r

          Momentum in -direction

          1 (r r )

          1 ( )

          ( )

          1 P 1 (r2 ) 1 ( )

          ( )

          • r

        r r

        r r r

        r

        r2

        r r r

        (11) = (U ) U

        U U U U

        U Ur U

        That is,

        t r r r r

        dF

        P dF

        (12)

        Momentum in -direction

        dV dV

        resultant

        viscous

        P 1 (r r ) 1 ( ) ( )

        dF .

        r r r

        dV

        viscous

        dF

        U

        U

        U U U U

        U

        P . (13)

        t

        r r r

        dV resultant

        The resultant force is thus the sum of the pressure gradient vector and the divergence of the viscous stress tensor.

        According to conservation law,

        Substituting (9), (10) & (13) in equation (8) we get

        Since the contribution of body forces is negligible, the rate of change of momentum of thermoplastic melt inside runner conduit is completely depended on surface forces which is a combination of pressure and viscous forces

        U r. Ur U 1 U U U U

        P .

      2. Conservation of Angular Momentum

        t

        r r

        (14)

        Equation on the right side can be split into,

        U r. Ur U 1 U U U U

        Lemma

        Resultant torque acting on thermoplastic melt at any instant is equal to instantaneous angular momentum change within the conduit and angular

        momentum change rates at runner conduit inlet & exit

        t r r

        H

        U

        . U dU

        i.e.,

        T

        H H

        t

        t

        out in

        (17)

        t dt

        Where, H Angular momentum.

        We know that, from continuity equation number (6)

        Also we have

        . U 0

        H

        r U

        t

        Hence,

        t t rcv dV

        out

        U r. Ur U 1 U U U U dU

        H H r UUdS

        out in in

        t r r dt

        i.e., dF dU (15)

        The vector cross product r Urepresents angular momentum per unit mass. Where r is position vector

        dV

        dV

        resultant dt

        Hence equation becomes,

        from origin or fixed central axis and U is linear

        dU velocity. Thus we can designate rUdV as

        P .

        dt

        (16)

        angular momentum acting on representative melt

        The above equation is also called Cauchy equation

        element. So the right hand side of equation (17) becomes

        From equation (6) we have

        .U 0

        t

        H H H

        t out in

        out

        (18)

        Thus above equation (22) reduces to

        dr U

        t

        t

        rcv r UdV r UUdS

        in

        . r dt

        (23)

        Since body torque is negligible as stated in section

        2.2.1 only surface torque acting on runner conduit accounts to net moment. Since contribution of pressure forces on angular momentum is negligible, the surface torque will mainly due to viscous torques. So left hand

        side of equation (17) becomes,

        This is called angular momentum equation

        The above equation describes that rate of change of angular momentum of the thermoplastic melt inside the runner conduit is proportional to viscous forces which causes the angular motion. Angular momentum being

        negligible in circular or axis-symmetric runner conduits

        T rcs

        r dS

        (19)

        has a significant influence particularly on parametric distribution in non-circular cross section runner

        Substituting equation (18) and (19) in (17), we get

        conduits.

        out

        t

        t

        rcs r dS rcv r UdV r UUdS

        in

        For surface integral,

        r r n. r n. r

        (20)

          1. Conservation of Energy

            Here we seek to adopt Joules energy principle to mathematically express conservation on the basis of

            By using Gauss Divergence Theorem, the left hand side of equation is converted from surface integral to

            volume integral

            rcs r dS rcs n. rdS rcv . rdV

            out

            First of law of thermodynamics by explicitly quantifying various energy entities and balancing them in accordance with the conservation notion. So in runner design we recognise melt heat, injection

            momentum work and polymers internal energy as

            Similarly,

            r UUdS

            in

            different forms of energy. In physical mould design sense, heat is thought of an energy exchange by melt in

            becomes .r UUdV

            rcv

            Thus equation (20) becomes,

            runner conduit to the surrounding in-deformable mould runner insert.

            t

            t

            . rdV

            r UdV .r UUdV

            1. First Law of Thermodynamics

              rcv

              rcv

              rcv

              Lemma

              t

              t

              . r r U .r UU

              But we have

              r U

              (21)

              The algebraic sum of thermoplastic melt heat transfer rates across runner conduit inlet and exit plus rate of injection force acting on it throughout runner

              conduit is proportional to rate of internal energy

              t .r UU

              change within runner conduit and rate of internal

              dr U

              energy changes across the runner conduit inlet and

              r U

              .U

              exit

              dt t

              dr U

              dr U

              Hence equation (21) becomes,

              Q Wv Wp t rcv edV rcs e U.ndA (24)

              r U .U . r

              (22)

              Here e is total energy and it is sum of internal and

              dt t

              kinetic energy.

              U2 Therefore net rate of energy change

              i.e., e= u+

              2

              r. U U

              r

              r

              U

              = 1

              dV

              (28)

              The product

              U.ndA represents melt change rate at

              r r

              runner conduit inlet and exit

              Here rate of work done by pressure forces Wp

              p

              W = PU.ndA = P U.ndA

              Hence the equation (24) becomes

              (25)

              Net rate of heat change of thermoplastic melt in runner conduit

              To evaluate net heat change Q , we neglect radiation

              and consider only heat conduction through the

              P

              thermoplastic melt.

              Q Wv t edV e U.ndA

              (26)

              According to Fourier law of heat conduction,

              Rate of heat change per unit area is proportional to

              This is very convenient form of energy equation since pressure work is now combined with energy of thermoplastic melt leaving at runner conduit outlet; we

              gradience of temperature

              q kT

              Where k= thermal conductivity

              (29)

              no longer have to deal with pressure work.

              Q W edV m P e m P e

              (27)

              Consider rate of heat change through radial direction Rate of heat change at conduit inlet

              v t

              Proof

              out in

              qr rd d

              Consider rate of energy leaving at runner conduit exit by mass transfer in r-direction,

              Rate of heat change at conduit outlet

              q qr dr r drd d

              r r

              Let = p e

              Rate of energy change at runner conduit inlet

              Ur rd d

              By subtracting inlet term with outlet term, we obtain heat change in that direction

              Hence rate of heat change in radial direction

              Rate of energy change at runner conduit outlet

              q rd d q qr dr r drd d

              r r r

              U

              Ur

              r dr r drd d

              q drd d

              qr

              rdrd d

              r

              r r

              Therefore rate of energy change in r-direction

              rqr

              U

              r dV

              = U r dr r drd d U rd d

              r r r

              Similarly in other directions,

              U

              r. U

              Rate of heat change in tangential direction

              = Ur

              r dV =

              r dV

              1 q dV

              r r

              r

              r

              1

              1

              Similarly in " " and " " directions Rate of energy change in " " direction

              U

              dV

              Rate of heat change in longitudinal direction

              q dV

              r

              Therefore net rate of heat change on thermoplastic melt

              rqr 1 q q

              Rate of energy change in – direction

              r r

              dV

              U

              dV

              Q .qdV

              From above, rate of heat change is proportional to runner conduit volume. Thus Introducing Fourier law

              But the right hand side of the equation can be expanded as,

              of heat conduction, we have net rate of heat conducted

              e

              r. Ur

              1 U

              U

              Q .kTdV

              (30)

              t r r

              Rate of work done on thermoplastic melt due to viscous forces

              e U

              t

              e 1 U

              r r r

              e U

              e

              Net rate of work done by viscous forces on thermoplastic melt in r-direction is given by

              U U 1 U

              U U 1 U

              U

              P r r

              r r r

              r U U

              rr r 1 ( r Ur )

              r r drd d

              r. U U U

              r r

              e 1 r 1

              t r

              r r

              Similarly in and – directions

              r r U

              1 U

              U

              U

              P U

              1 P U

              P

              rdrd d

              r r

              r

              r r

              Further,

              r r U

              1 U

              U

              e

              r. Ur

              1 U

              U

              rdrd d

              r r

              t r r

              Therefore, net rate of work done by surface forces is given by

              de P.U e . U U.P

              dt t

              r rr Ur 1 ( U ) r Ur

              r r

              r r

              But . U 0

              t

              t

              Hence right hand side of equation reduces to

              r U 1 U U

              r

              rdrd d

              e

              r. Ur

              1 U

              U

              r r

              t

              r r

              r r U

              1 U

              U de

              (33)

              P.U U.P

              dt

              r r

              .U. rdrd d

              .U. dV

              (31)

              Substituting (33) in equation (32), we get

              dt

              dt

              .kT .U. de .PU

              U2

              Hence from conservation law, Substituting (28), (30) &

              d u 2

              (31) in equation (27), we get

              .kTdV .U. dV

              .kT .U. .PU

              dt

              dt

              From equation of mechanical energy,

              (34)

              e

              r. Ur

              1 U

              U

              U2

              dV

              d

              t r r

              2

              dt

              dt

              .PU P.U .U. : U

              (35)

              .kTdV .U. dV

              Subtracting equation (35) from equation (34) we get,

              e

              r. Ur

              1 U

              U

              (32)

              du

              dV

              .kT P.U : U

              (36)

              t r r dt

              The above equation describes that rate of change of

              . q and irreversible 1 q.T effects of heat

              T T2

              internal energy of the thermoplastic melt inside runner

              conduit is proportional to amount of energy added to

              transfer.

              the thermoplastic melt via heat and work done.

              Hence equation (41) becomes,

              dS . q 1 q.T

              (42)

            2. Second Law of Thermodynamics

              Lemma

              Rate of injective work done on thermoplastic melt across the runner conduit inlet and outlet is proportional to thermoplastic melt energy change rates within the runner conduit and rate of entropy change across the runner conduit inlet and outlet

              Entropy change (dS) gives us,

              TdS de Pd

              dt T T2 T

              This is called Equation of Entropy

              The above equation describes that rate of change of entropy during the injection moulding cycle is proportional to energy added to the thermoplastic melt during that cycle.

          2. Volumetric Heat Absorption

        Thermoplastic melt state change for a particular

        Substituting specific volume 1

        TdS de P d

        2

        we get,

        (37)

        cycle through the runner conduit of an injection mould is considered. Accounting to runner conduit configuration heat transfer is dominant in radial direction compared to that of heat transfer in the

        Since injection moulding is a dynamic process, we now differentiate above equation (37) for a small representative interval to get,

        dS de P d

        direction of injection which is very less and hence neglected. This provides us with an advantage of considering heat conduction in radial direction alone.

        T

        dt dt 2 dt

        (38)

        runner volume element with heat transfer taking place

        Equation of internal energy is given by,

        de .q P .U

        dt

        where = Viscous dissipation function

        in r-direction alone. Since the runner geometry is best explained by cylindrical co-ordinate system, the same is taken to derive heat conduction equation.

        Lemma

        de

        dt

        .q

        P.U

        (39)

        Rate of volumetric thermal energy absorbed across thermoplastic melt core and conduit interface wall is proportional to difference between net rate of

        Equation (6) can also be written as,

        d .U dt

        Substituting (39) & (40) in equation (38) we get,

        T dS .q

        (40)

        heat conducted radially across runner conduit cross- section and rate of internal energy change throughout an injection cycle

        Proof

        dt

        By rearranging we get,

        The rate of volumetric heat absorbed across thermoplastic melt core and conduit wall interface is

        dS

        dt

        .q

        T T

        (41)

        given by

        qvh rdr

        (43)

        Using vector calculus the term

        .q T

        is split as

        Let the rate of heat conducted into differential runner

        element in r-direction

        • .q . q q .T to separate reversible Q k T r

        T T T2

        r r

        Let the rate of heat conducted away from differential

        Where, Ttrans

        is the glass transition temperature which is

        runner element in r-direction

        almost a linear function of pressure [13].

        Q

        Ttrans b5 b6P

        (51)

        Q Q r dr

        r

        r

        rdr

        Hence governing equations are:-

        Continuity equation

        Hence governing equations are:-

        Continuity equation

        r

        t

        Linear momentum equation

        t

        Linear momentum equation

        . U 0

        . U 0

        Thus net rate of heat conducted into differential runner element in r-direction

        Q Q

        1 kr T rdr

        (44)

        r rdr

        r r

        r

        dt

        Angular momentum equation

        dt

        Angular momentum equation

        P . dU

        P . dU

        The rate of internal energy change of thermoplastic melt is given by

        C

        T rdr

        v

        v

        t

        (45)

        dt

        First law of thermodynamics

        dt

        First law of thermodynamics

        Hence from equations (43), (44) and (45) we have

        .r d r U

        .r d r U

        du .kT P.U : U

        du .kT P.U : U

        q rdr 1 kr T rdr C T rdr

        vh r r

        r

        v t

        dt

        Second law of thermodynamics

        dt

        Second law of thermodynamics

        dS . q 1 q.T

        dS . q 1 q.T

        Neglecting the volume terms and expanding the above terms, the equation becomes

        dt

        dt

        T

        T

        T2

        T2

        T

        T

        2T k T T

        Volumetric heat absorption

        Volumetric heat absorption

        T

        T

        2

        2

        C

        C

        k

        k

        T T

        T T

        t

        t

        qvh k r2 r

        r Cv t

        (46)

        The above equation represents the melt state change during a particular injection moulding cycle through the runner conduit.

  3. Equation of State (Tait Equation)

    Thermoplastic melt specific volume streaming through runner conduit at any instant is represented as a function of its pressure P (t) and temperature T (t). This equation is popularly known as Tait equation [12].

    qvh

    k r2 r r

    v

    qvh

    k r2 r r

    v

  4. Conclusion

The authors have earlier proposed spatiotemporal conservation principle to design runner system for a plastic injection mould [14]. Accordingly governing equations for thermoplastic melt inside runner conduit

T, P

T Cln 1 P

T, P

(47)

throughout an injection moulding cycle has been

0 1 BT t

obtained after implementing conservation principles.

Where C=0.0894 is a universal constant.

Further set of equations tabled above are then used to

0 T is given by,

T b m b m T b , if T > T

(48)

derive a computational model to design the ideal runner conduit size for feeding thermoplastic melt relative to

specific combination of injection moulding machine

0 1 2 5 trans,

Where, subscripts (m) represent molten state of the polymer.

B (T) is given by

available, characteristics of thermoplastic material chosen and desired features of component being moulded.

BT b m exp b m T b , if T > T

(49)

3 4 5

trans

5. References

For thermoplastic melt streaming through runner conduit under general injection moulding processing

conditions,

  1. K. Lee and J. Lin, Design of the runner and gating system parameters for a multi-cavity injection mould using FEM and neural network, International Journal

    t T, P 0

    (50)

    of Advance Manufacturing Technology, pp. 1089-1096, 2 March 2005.

  2. J. Jones, Engineering Thermodynamics: An Introductory Textbook, 2nd ed., Wiley, 1986.

  3. G. Batchelor, An introduction to fluid dynamics, Cambridge: Cambridge university press India Pvt.Ltd, 2007.

  4. M. D. Raisinghania, Fluid Dynamics with complete Hydrodynamics and Boundary Layer Theory, 10th ed., Muzaffarnagar, UP, 2011, p. 2.1.

  5. F. M. White, Fluid Mechanics, 6th ed., Tata McGraw Hill, 2008, p. 227

  6. E. F. Obert and R. L. Young, Elements of thermodynamics and heat transfer, 2nd ed., Mcgraw Hill.

  7. P. Zdanski and M. Vaz.Jr, Polymer melt flow in plane channels: Effects of the Viscous Dissipiation and Axial Conduction, An International Journal of Computation and Methodology, pp. 159-174, 2006.

  8. F. A. Morrison, Constitutive modelling of viscoelastic fluids, RHEOLOGY, vol. 1.

  9. Y. A. Cengel and J. M. Cimbala, Fluid Mechanics fundamentals and applications, McGraw Hill, 2006, p. 173.

  10. M. A. Boles and Y. A. Cengel, Thermodynamics: An Engineering Approach, McGraw Hill, 2005.

  11. L. Taura, I. Ishiyaku and A. Kawo, The use of continuity equation of fluid mechanics to reduce the abnormality of the cardovascular system: A control mechanics of the human heart, Journal of Biophysics and Structural Biology, vol. 4, no. 1, pp. 1-12, March 2012.

  12. R. Zheng, R. I. Tanner and X. J. Fan, Injection moulding: Integration of theory and modeling methods, Sydney: Springer-Verlag, 2011.

  13. H. Meijer and J. d. Toonder, "Specific volume of polymers," 2005.

  14. M. Lakkanna, R. Kadoli and G. C. Mohan Kumar, Governing Equations to Inject Thermoplastic Melt Through Runner conduit in a plastic injection mould, in Proceedings of National Conference on Innovations in Mechanical Engineering, Madanapalle, 2013

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