Powder Technology 229 (2012) 253–260

Contents lists available at SciVerse ScienceDirect

Powder Technology

j ourna l homepage: www.e lsev ie r .com/ locate /powtec

Effect of feed frame design and operating parameters on powder attrition, particlebreakage, and powder properties

Rafael Mendeza,⁎, Carlos Velazqueza, Fernando J. Muzziob

a Department of Chemical Engineering, University of Puerto Rico at Mayaguez, PO Box 9046, Mayaguez, PR 00681, Puerto Ricob Department of Chemical and Biochemical Engineering, Rutgers University, 98 Brett Road, Piscataway, NJ 08854, United States

⁎ Corresponding author.E-mail addresses: rafael.mendez1@upr.edu (R. Mend

carlos.velazquez9@upr.edu (C. Velazquez), fjmuzzio@ya

0032-5910/$ – see front matter © 2012 Elsevier B.V. Alldoi:10.1016/j.powtec.2012.06.045

a b s t r a c t

a r t i c l e i n f o

Article history:Received 10 October 2011Received in revised form 16 May 2012Accepted 24 June 2012Available online 1 July 2012

Keywords:Feed frameAttritionDie filingGDR flow indexDilation

Feed frame is a device used in rotary tablet presses to drive the powders into compression dies. It appliesshear forces to the powders as they are stirred around the feed frame chambers. This study focused on under-standing the particle attrition, powder properties and the flow property changes of the material processed.The results demonstrated that the impact of the feed frame and die disk on the particle size distribution(PSD) outlet depended on the initial mean particle size, the die size and the powder outlet position. It alsoimpacted the flow properties. The scale-up effect using a feed frame for a high production tablet pressshows a significant increment in powder attrition.

© 2012 Elsevier B.V. All rights reserved.

1. Introduction

Tablets are still the most popular drug delivery system [1] withmore than 70% of all pharmaceutical products sold worldwide pro-duced in this form. The tablet's characteristics, such as high patientcompliance, dosage reliability, low cost, and superior physical andchemical stability make them very attractive to patients. Despitethe fact that other forms of drug delivery generate significant aca-demic interest, oral solids remain, and are expected to remain, themost desirable and most prevalent route for drug administrationto large populations.

Tablets are formed in rotary tablet presses by the compression ofits granular ingredients. This is a major step in the manufacture ofpharmaceuticals, and other solid products. In this step, therate-limiting factor is the consistent and uniform filling of the dies[1]. The powder properties and the operating parameters of theequipment used to handle the ingredients affect the amount of pow-der that enters the die (a step prior to the compression) and deter-mine the weight of the compressed product unit [2–7], and theoverall drug content of individual tablets. This is critical since thetablet's mechanical properties and performance, crucial for the effec-tiveness of the active ingredient, are related to the weight [8].

ez),hoo.com (F.J. Muzzio).

rights reserved.

Feed frame is a device used in tablet presses that uses paddles todeliver the powders into the dies. A few studies have investigatedthe complexity of powder flow phenomena through feed framesand its impact [9,10] on the powders. Mendez et al. [9] describedthe powder phenomena inside the feed frame finding that: (1) thetotal shear applied to the powder is higher at lower die disk speedsand higher feed frame paddle speeds, (2) the die weight variabilityincreases as the die disk speed increases at constant feed framespeed, (3) the average residence time (space time) decreases as thefeed frame and die disk speeds increases, and (4) the flow propertiesimproved as a consequence of the shear applied to lubricate the pow-ders. Unfortunately, over-lubricated material impacts the tablet hard-ness and dissolution [10]; therefore careful operation of feed framesis crucial to avoid undesired properties in the tablets.

As the paddles force the powders into the dies, the powders aresubjected to shear, stress, and possibly attrition. These could be unde-sirable consequences of the powder processing that could cause lossof material and degradation of its quality [11]. The attrition phenom-enon is known to occur in solids storage hoppers and powder mixingsystem [12] by the deformation of the bulk material during flow andhas been previously studied considering the shear applied in shearcell equipment [13–15]. In [13], it was found that the powder attritionaffected the material flow index of the powder flowing into the dies,which occurred through high-energy particle collisions or bulk com-pression and shear deformation, involving two simultaneous process-es of surface abrasion and body fragmentation. The fragmentationoccurred through particle chipping and was related to the particlemorphology, roughness, and friction between the particles and dy-namics of particle flow.

254 R. Mendez et al. / Powder Technology 229 (2012) 253–260

Previous results [9,10] showing the effect of shear on powders andflow properties suggested the possibility that the particle size distri-bution was affected by the total shear applied inside the feed frame.Thus, this work focused on further studying the effect of feed frame'soperating conditions and material's properties on the powder attri-tion (i.e., particle size distribution) and its impact on the flow proper-ties. Two granular materials were used to study the effect of twodifferent scales and design feed frames on powder attrition, density,and flow properties.

2. Experimental procedure

2.1. Materials

This study used Fast Flo Lactose 316 (120 μm as mean particlesize) and a roller-compacted placebo (460 μm as mean particle size)from BMS (Bristol-Myers Squibb Company) with 54.7% anhydrouslactose, 42.5% microcrystalline cellulose, 2% cross-carmellose sodiumand 0.75% magnesium stearate.

2.2. Feed frame units and die disk system

One unit is a standard feed frame of a Manesty Beta Press andthe other unit is a Fette 3090. The Manesty unit is a controlledtwo-stage feeding system, where the powder exits through threeholes of different areas. Figs. 1 and 2 present the Manesty feedframe design details including the dimensions of the two stages,the paddle wheels and the geometry of the powder exits. The diedisk system consists of an acrylic disk with 22 through-orifices,which are connected to a gear motor, which rotates the disk clock-wise at controlled speeds. Additional details of the feed frame andthe simulated die disk system can be found in previous works[10,11]. The Fette 3090 is a three stage controlled feeding system;powder fed to the feed frame passes to the first stage at the topand then to the second and third stages at the bottom. Fig. 3shows the Fette 3090 and the three wheels, one at the top to re-duce the powder consolidation of the material entering the feedframe (Fig. 3b) and two at the bottom of the feeder (Fig. 3c) andthe scraper (Fig. 3d). The wheel at the top has a diameter of177 mm, and 12.5 mm in height and 16 rectangular spokes with athickness of 5 mm. The feeder wheel has 12 spokes and is167 mm in diameter; the spokes are rectangular near the centerof the wheel with a 135° angle in the last 20 mm. The last wheelis the scraper, which has 12 rectangular spokes. The simulated diedisk in this case consists of an acrylic disk with 61 holes of10 mm in diameter, which is connected to a Dayton DC gearmotor to rotate the disk in the counter clockwise direction at con-trolled speeds between 0 and 94 rpm.

Fig. 1. Beta Press feed frame dimensio

2.3. Feed frame effect characterization

The Schenck Accurate gravimetrical feeder (Modpharma 2007)and the Ktron T35 loss-in-weight feeder were used to maintain acontinuous feed of the powder formulation and a level in the hop-per of the feed frame. The Schenck feeder was used for the experi-mental work with the lactose and the Ktron for the experimentwith the placebo. The effect of the Manesty Beta Press feed framewas studied using three paddle speeds (24, 48 and 72 rpm), andtwo speeds of the die disk (29 and 57 rpm). For the Fette 3090,the paddle speeds were 23, 51 and 69 rpm and the die disk speedswere 28 and 41 rpm. A sample of approximately 2.5 kg was collect-ed after the system reached the steady state to characterize thepowder property changes.

2.4. Particle size distribution

Samples of approximately 50 g of powder were collected directlyas the material left the dies. The powder was analyzed in the TornadoDry Powder Module in the Buckman Coulter™ multi-wavelength LS13 320 laser diffraction particle size analyzer. The final results werean average of 2 different samples.

2.5. Powder property characterization

The powder density and the flow properties were characterized ina Quantachrome Instruments Autotap and a gravitational displace-ment rheometer (GDR) [16–19], respectively. The GDR was used toquantitatively measure the flow characteristics (flow index and pow-der dilation) of the blends before and after passing through the feedframe. Further details of the equipment, materials and methodshave been previously published [20]. The powder samples were sub-jected to 500 taps in the Autotap instrument.

3. Results and discussion

3.1. Effect of feed frames on powder attrition

The Manesty Beta Press feed frame was studied using both mate-rials to understand the impact of the material properties in the attri-tion phenomena. Fig. 4 depicts the changes in particle sizedistribution for Fast Flo Lactose, initially with a mean diameter of120 μm, as a function of the feed frame (Manesty Beta Press) anddie disk speed for die diameters of 6.9 (Fig. 4a and b) and 9.6 mm(Fig. 4c and d). The results show small changes in the outlet PSDwhen compared with the initial one suggesting a small attrition ef-fect. In general, the feed frame system parameters did not affectsignificantly the PSD for material 1. Its initial particle size is signifi-cantly small compared with the approximately 1 mm space gap be-tween the paddles and the wall and the bottom of the feed frame

n of the chamber and the paddle.

Fig. 2. Beta Press feed frame exit points.

255R. Mendez et al. / Powder Technology 229 (2012) 253–260

(Fig. 1), which could have caused the applied force by the paddles tobe not enough to break the granules.

The second material used was the roller-compacted placebowith higher particle size, wider PSD and irregular particle shape.In this case, the results illustrated a multimodal distribution. Fig. 5depicts the PSD of the placebo entering and exiting the feedframe as function of the feed frame and die disk speed. Fig. 5aand b corresponds to 6.9 mm die diameter and Fig. 5c and d to9.6 mm die diameter. The four figures demonstrate that reduction

Fig. 3. Fette 3090 feed fram

in size of the larger particle indeed occurred with the 6.9 mm diediameter causing the largest change in outlet PSD. As described inprevious work [9], the reduction in die diameter (from 9.6 to6.9 mm) increased the residence time of the powder inside thefeed frame and as such the total shear applied to the powder [9],which caused more significant particle breakage.

The Fette 3090was studied using only the granulated placebo witha 10 mm die diameter; finding a multimodal distribution with signif-icant particle size attrition (Fig. 6). Comparing the results obtained for

e and the three wheels.

Fig. 4. Manesty Beta Press feed frame attrition effect on PSD for Fast Flo Lactose at different operating conditions: a) 6.9 mm die diameter and 29 rpm die speed, b) 6.9 mm diediameter and 57 rpm die speed, c) 9.6 mm die diameter and 29 rpm die speed, d) 9.6 mm die diameter and 57 rpm die speed.

256 R. Mendez et al. / Powder Technology 229 (2012) 253–260

theManesty Beta Presswith those of the Fette 3090 for 9.6 and 10 mmdie diameter, respectively, a larger attrition effect was found for theFette 3090. This particular result demonstrated a significant propor-tional scale-up effect on powder attrition. The Fette 3090 has three dif-ferent chambers, which increased significantly the volume and,therefore, the residence time, and thus the total shear applied, andthe 3 wheels of the Fette 3090 were made of metal, which dissipatesenergy differently than the Teflon wheels in the Manesty.

Fig. 7 depicts, from a different angle, the effect of the feed framepaddle speed on the mean particle size for both materials and thethree die diameters: 6.9 mm (Fig. 7a), 9.6 mm (Fig. 7b), and 10 mm(Fig. 7c). The results for the Fast-Flo Lactose showed in the ManestyBeta Press feed frame a small reduction in particle size while the re-sults for the placebo in Fig. 7a and b depict a significant reduction, be-tween 60 and 130 μm, compared with the entering mean particle sizewhile the same placebo showed a reduction between 117 and 210 μmin the Fette 3090 (Fig. 7c). The former corresponds to 15–40% of

change for the placebo relative to the entering mean value, where40% corresponded to the smaller die (6.9 mm). In the Fette with a10 mm die diameter, a 23–42% of change was obtained. These resultsdemonstrated that the particle breakage depended on feed frame de-sign, operating conditions and the inlet PSD of the powder.

3.2. Effects of the total shear on the PSD and mean particle size inside thefeed frame chambers

The powder flow behavior inside the feed frame relative to its exitpoints has been described in a previous work [9]. Most of the powderentering the feed frame is submitted to shear in the first chamber (A)before passing to the second chamber (B), where the total shear ap-plied is increased. It was also shown that the powder leaving throughthe first exit point was the contribution of the material entering andexiting quickly and material submitted to shear in the first chamber.On the other hand, the material leaving the second exit point was

Fig. 5. Manesty Beta Press feed frame attrition effect on PSD for roller-compacted placebo granulated at different operating conditions: a) 6.9 mm die diameter and 29 rpm diespeed, b) 6.9 mm die diameter and 57 rpm die speed, c) 9.6 mm die diameter and 29 rpm die speed, d) 9.6 mm die diameter and 57 rpm die speed.

257R. Mendez et al. / Powder Technology 229 (2012) 253–260

material submitted only to shear in the first chamber. Now, the mate-rial leaving through the third exit point had a total shear applied thatwas a contribution of the shear applied in both chambers, the first andsecond.

Fig. 8 depicts the PSD of the placebo: (1) entering the feed framewith a mean particle size of 460 μm, (2) in the first chamber (A) witha mean size of 400 μm, (3) in the second chamber (B) with a meansize of 320 μm and (4) exiting the feed frame; all for a feed frame pad-dle speed of 72 rpmand 29 rpmas the die speed. Thematerial collectedfrom the filled dies had a mean particle size of 350 μm, which was theresult of the contribution of the three chambers. The increase in shearapplied through the entire feed frame indeed increased the attrition ef-fect. Fig. 9 depicts the same behavior, however through themean parti-cle sizewhere it can be seen that the powder exiting the feed frame hadamean particle size between those of the two chambers.Moreover, thissuggests the possibility of having a die filled in layers with bigger sizeparticles at the bottom of the dies and smaller at the top.

3.3. Effect on powder density

Fig. 10 depicts an increment in the bulk and tap density of theprocessed material proportional to the increments in the feed framepaddle speed for both systems. Those increments were a consequenceof the reduction in PSD caused by the attrition inside the feed frame.The reduction in PSD changed the powder packing and thus thetapped volume. For the higher feed frame paddle speeds, the incre-ments in bulk and tap density were between 9 and 16% relative tothe bulk and tap density of the untreated placebo for both feedframes. Tables 1 and 2 show the analysis of variance for the bulkand tap density for the Manesty Beta Press feed frame. The resultsdemonstrated that: (1) the feed frame paddle speed affected thebulk and tap density, (2) the die disk speed affected significantlythe bulk density, and (3) the die size was not statistically significantwhen using 95% interval of confidence. Table 3 includes the summaryof the powder characterizations.

Fig. 6. Fette 3090 feed frame attrition effect on PSD for roller-compacted placebo gran-ulated at different operating conditions: a) 28 rpm die speed, b) 41 rpm die speed.

Fig. 7. PSD and the attrition effect on mean particle size inside the feed frame: a) Man-esty Beta Press using 6.9 mm die diameter, b) Manesty Beta Press using 9.6 mm die di-ameter, and c) Fette 3090 using 10 mm die diameter.

258 R. Mendez et al. / Powder Technology 229 (2012) 253–260

3.4. Effect on powder flow properties

Figs. 11 and 12 illustrate the GDR flow index and dilation results.In all cases, different feed frame and die speeds, the flow index anddilation decreased as the feed frame paddle speed (which increasedboth the shear rate and the total shear) increased. The more signifi-cant reduction in flow index was obtained at 29 rpm of the die diskand 72 rpm of the feed frame paddles. The GDR flow index and dila-tion can be related to the powder cohesion [18,19]. Despite the factthat the experimental results showed significant powder attrition,this change did not impact the powder cohesion when looking atthe outlet mean particle size. It is well known that the cohesionplays an important role on powder flowability of material with parti-cle sizes less than 100 μm. This suggests that the shear applied lubri-cated the powder, in addition to the attrition effect, and that thislubrication was responsible for the powder flowability improvement[10].

Fig. 8. Effects of the shear strain in the placebo PSD inside the feed frame chambers rel-ative to the inlet and outlet PSDs.

259R. Mendez et al. / Powder Technology 229 (2012) 253–260

4. Conclusions

Two different feed frames in terms of design were compared re-garding their effects on the powder characteristics. It was foundthat both units were capable of altering the outlet PSD. The feedframe geometry and operating conditions, the simulated die systemoperating conditions, and the inlet PSD, altogether, impacted at dif-ferent levels the final PSD of the blend. The increment in feed framepaddle speed did not seem to have had a significant impact on thePSD for the small feed frame (Manesty Beta Press) contrary to the ef-fect on the bigger (Fette 3090) one. The feed frame scale-up showedan extensive attrition effect; due to the increase in the powder resi-dence time and the total shear applied. The differences in PSD in thechambers affected the uniform distribution of the particle size in thedies and suggested size stratification. The feed frame effect on PSD in-creased the bulk and tap density for the placebo. Finally, the shear ap-plied to the placebo inside the feed frame improved the flow indexand dilation.

Fig. 9. Effects of the shear strain in the mean particle size inside the feed frame cham-bers relative to the inlet and the outlet mean particle sizes.

Fig. 10. Feed frame and simulated die system effects on powder bulk and tapped den-sity: a) Manesty Beta Press feed frame, and b) Fette 3090 feed frame.

Acknowledgments

This work was supported by the NSF ERC for Structured OrganicParticulate Systems grant number EEC-0540855. The Bristol-MyersSquibb Company is acknowledged for the supplied granulated placebo.

Table 1Analysis of variance for bulk density.

Source DF SS MS F P

Die size 1 0.0001782 0.0001782 0.63 0.446Die speed 1 0.0024626 0.0024626 8.68 0.015Feed frame speed 3 0.0165049 0.0055016 19.39 0.000Error 10 0.0028371 0.0002837Total 15 0.0219829

Table 2Analysis of variance for tapped density.

Source DF SS MS F P

Die size 1 0.0000757 0.0000757 0.27 0.614Die speed 1 0.0009448 0.0009448 3.38 0.096Feed frame speed 3 0.0151710 0.0050570 18.08 0.000Error 10 0.0027962 0.0002796Total 15 0.0189878

Table 3Summary of die disk and feed frame system results for 6.9 and 9.6 mm die diameter.

Material Diesize(mm)

Diediskspeed(rpm)

Feedframespeed(rpm)

Bulkdensity(g/ml)

Tappeddensity(g/ml)

Powderflowindex

Powderdilation

FF Lactose Untreated 0.5895 0.6298 36.916 21.0736.9 29 24 0.5846 0.5846 35.552 18.9286.9 29 48 0.5872 0.5872 35.015 19.2316.9 29 72 0.5825 0.5825 40.605 19.5426.9 57 24 0.5883 0.5883 32.999 18.1746.9 57 48 0.5849 0.5849 33.755 17.7996.9 57 72 0.5804 0.5804 34.815 18.2469.6 29 24 0.5868 0.63779.6 29 48 0.5812 0.64479.6 29 72 0.5845 0.64549.6 57 24 0.5846 0.64619.6 57 48 0.5888 0.64679.6 57 72 0.5897 0.6474

Roller compactedplacebogranulated(BMS)

Untreated 0.6428 0.7912 19.093 32.0906.9 29 24 0.7200 0.8650 12.666 29.6006.9 29 48 0.7580 0.8950 12.469 28.2606.9 29 72 0.7700 0.8780 10.844 27.4606.9 57 24 0.6880 0.8400 13.162 28.1706.9 57 48 0.7100 0.8700 15.726 26.1606.9 57 72 0.7200 0.8580 15.081 27.7409.6 29 24 0.7313 0.8861 12.850 28.2719.6 29 48 0.7276 0.8777 14.685 24.2019.6 29 72 0.7639 0.9119 13.034 20.4589.6 57 24 0.7149 0.8718 15.604 26.6209.6 57 48 0.7152 0.8735 17.323 25.4299.6 57 72 0.7242 0.8775 16.973 23.047

Fig. 11. Effect of the feed frame applied shear and strain on GDR powder flow index.

Fig. 12. Effect of the feed frame total shear applied on powder dilation.

260 R. Mendez et al. / Powder Technology 229 (2012) 253–260

References

[1] X. Xie, V.M. Puri, Uniformity of powder die filling using a feed shoe: a review, Par-ticulate Science and Technology 24 (2006) 411–426.

[2] C. Wu, L. Dihoru, A.C.F. Cocks, The flow of powder into simple and stepped dies,Powder Technology 134 (2003) 24–39.

[3] C. Wu, A.C.F. Cocks, O.T. Gillia, D.A. Thompson, Experimental and numerical inves-tigations of powder transfer, Powder Technology 138 (2003) 216–228.

[4] I.C. Sinka, L.C.R. Schneider, A.C.F. Cocks, Measurement of the flow properties ofpowders with special reference to die fill, International Journal of Pharmaceutics280 (2004) 27–38.

[5] S. Jackson, I.C. Sinka, A.C.F. Cocks, The effect of suction during die fill on a rotarytablet press, European Journal of Pharmaceutics and Biopharmaceutics 65(2007) 253–256.

[6] L.C.R. Schneider, I.C. Sinka, A.C.F. Cocks, Characterization of the flow behavior ofpharmaceutical powders using a model die-shoe system, Powder Technology173 (2007) 59–71.

[7] I.C. Sinka, F. Motazedian, A.C.F. Cocks, K.G. Pitt, The effect of processing parameterson pharmaceutical tablet properties, Powder Technology 189 (2009) 276–284.

[8] C.Y. Wu, A.C.F. Cocks, Flow behavior of powders during the die filling, PowderMetallurgy 47 (2) (2004) 127–136.

[9] R. Mendez-Roman, F.J. Muzzio, C. Velazquez, Study of the effect of feed frame onpowder blend properties during the filling of tablet press dies, Powder Technolo-gy 200 (2011) 105–116.

[10] R. Mendez-Roman, F.J. Muzzio, C. Velazquez, Effect of feed frame design and op-erating parameters on the powder hydrophobicity and flow properties, AICHEJournal (2011), http://dx.doi.org/10.1002/aic.12639.

[11] J. Bridgwater, R. Utsumi, Z. Zhang, T. Tuladhar, Particle attrition due to shearing—the effects of stress, strain and particle shape, Chemical Engineering Science 58(2003) 4649–4665.

[12] N. Ouchiyama, S.L. Rough, J. Bridgwater, A population balance approach to de-scribing bulk attrition, Chemical Engineering Science 60 (2005) 1429–1440.

[13] M. Ghadiri, Z. Ning, S.J. Kenter, E. Puik, Attrition of granular solids in a shear cell,Chemical Engineering Science 55 (2000) 5445–5456.

[14] A.U. Neil, J. Bridgwater, Attrition of particulate solids under shear, Powder Tech-nology 80 (1994) 207–219.

[15] A.V. Potapov, C.S. Campbell, Computer simulation of shear-induced particle attri-tion, Powder Technology 94 (1997) 109–122.

[16] A.M.N. Faqih, A. Mehrotra, S.V. Hammond, F.J. Muzzio, Effect of moisture andmagnesium stearate concentration on flow properties of cohesive granular mate-rials, International Journal of Pharmaceutics 336 (2007) 338–345.

[17] A.M.N. Faqih, B. Chaudhuri, A.W. Alexander, C. Davies, F.J. Muzzio, M.S. Tomassone,An experimental/computational approach for examining unconfined cohesivepowder flow, International Journal of Pharmaceutics 324 (2006) 116–127.

[18] A.M.N. Faqih, A.W. Alexander, F.J. Muzzio, M.S. Tomassone, A method forpredicting hopper flow characteristics of pharmaceutical powders, Chemical En-gineering Science 62 (2007) 1536–1542.

[19] A.W. Alexander, B. Chaudhuri, A.M.N. Faqih, F.J. Muzzio, C. Davies, M.S. Tomassone,Avalanching flow of cohesive powders, Powder Technology 164 (2006) 13–21.

[20] A. Mehrotra, B. Chaudhuri, A. Feqih, M.S. Tomassone, F.J. Muzzio, A modeling ap-proach for understanding effects of powder flow properties on tablet weight var-iability, Powder Technology 188 (2009) 295–300.