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How Feeding Approach Influences Pills Accuracy

According to International practices of feeding system on pill press, 3 main categories are included: bucket feeder/boot feeder system for single punch pill press(eg. TDP-0, TDP-1.5, TDP-5), Tsukigata feeding system for low-medium speed rotary tablet press(eg. ZP-9, RTP 9,ZPW17D), and forced feeding system for high speed tablet press(eg. HZP-200).

The accuracy of pills is related with material formula, material quality, mechanical parts, and component adjustment. This paper is gonna to discuss the influence different feeding approaches make on the accuracy of pills.

★ Bucket feeder/Boot feeder

bucket feederThis feeding system, including wobble feeding and reciprocating feeding, is mainly used on some simple tablet pill press machine. Former one is used on TDP series pill press, and the latter one is mainly applied to THP flower basket single punch pill press.

The tabletting process of bucket feeder can be generalized as four movements: feeding, flatting, tabletting, and ejecting. The particles will fall into middle die as the bucket feeder wobbles. After pressing into a whole pill, then it will be ejected out by lower punch and scrap off by bucket feeder.

 

Simple operation and principle make it to be widely used. However, bucket feeding system has some weakness. The pills made by single punch tablet machine are more prone to be laminated for the materials unevenly fall down into middle die as bucket wobbles and pressed one-sided(upper punch). Furthermore, the production efficiency is low as 60 to 80 pieces of pills to be made every minute, so it is suitable for lab experiment and small batch production.

bucket feeder
Tsukigata feeding system

Tsukigata feeding is usually used on low-medium speed rotary tablet press. The Tsukigata feeder is fixed on the turntable with a certain clearance(0.05~0.1mm). When the middle die runs below the feeder, the particles in the feeder will fall into  die hole. Several separated parts on the feeder make it possible to fill powder continuously repeated. Scrapper on the end of feeder tightly closed to the turret will scrape off excessive materials so as to make tight but even pills.

bucket feeder

This feeding model is dependent on the gravity of material particles to complete filling process, so high requirement on the materials(uniform size and good fluidity) is required. Repeated filling pattern makes the pills uniform with little weight variation. Two-sided pressure from upper and lower punch evenly compact the pills. In particular, Double pressing rotary tablet presses is attached with 2 sets of filling system. Every station of tablet tooling will make 2 pills with one rotation of turret. Therefore, this kind of machine is suitable for bulk production(eg. ZP-35D double-press rotary tablet press can produce 2000 almost pieces pills per minute.)

Defects of Tsukigata feeding system comes from 2 aspects.

Strict requirement on materials. Good fluidity, uniform size and other requirements increase production cost.

‚ Particles filling needs enough time, which limits the turret speed. Too fast rotation of turret will give rise to great weight variation, insufficient filling, etc.

forced-filling-feeder-structure

★ Forced feeding system

Forced feeding system is mainly applied to high speed rotary tablet press machine, composed of hopper, motor, and forced filling feeder. Hopper is used for depositing materials, joint with the forced filling feeder. Motor creates power for filling. And the feeder was divided into gear case and feeder. Gear case transmit the power created by motor to the two impellers of feeder that spin to force materials into middle die.

Particles or powders can be pressed into pills through filling, scrapping, tabletting, and ejecting four processes. As materials are forced to fall into dies, filling time can be largely shortened, and turret speed is upgraded to 80r every minute.

Though it attracts customers with a lot of advantages, disadvantages should slao be taken into consideration:

 As turret speed is increased, more powders coming from the hopper are flying away, causing a waist of materials and cross-contamination.

‚ Some materials with poor fluidity are difficult to flow from hopper. But fast pressing process continue. So the weight of pills can not be well controlled.

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