GB2138699A

GB2138699A - Hammer mill for producing sterile powders

Info

Publication number: GB2138699A
Application number: GB08409422A
Authority: GB
Inventors: Richard W Walton
Original assignee: ER Squibb and Sons LLC
Current assignee: ER Squibb and Sons LLC
Priority date: 1983-04-11
Filing date: 1984-04-11
Publication date: 1984-10-31
Also published as: DE3413504A1; JPS601444U; FR2543851A1

Abstract

A mill used in the production of powders for pharmaceuticals is powered by a hydraulic motor. The hydraulic motor is driven by fluid which is pressurized by a motor and pump unit which is displaced from the hydraulic motor, whereby the sterility of the mill and of the items milled thereby is not compromised by the motor of said unit. The fluid is supplied to the hydraulic motor through a controllable valve system which includes reversing valves.

Description

SPECIFICATION Sterilizable hammer mill The present invention relates to a mill for reducing the size of particles. In particular, the present invention provides a sterilizable hammer mill comprising: (a) a hammer mill driven by a hydraulic motor; (b) a hydraulic power pack including a motor and a hydraulic pump, said hydraulic power pack being adapted to be mounted remotely from said hammer mill and being connected thereto via hydraulic lines; and (c) a valve system including valves for controlling the pressure of hydraulic fluid from said power pack to said hydraulic motor, whereby the speed of said hydraulic motor can be controlled.

The mill of this invention is particularly useful for reducing the size of solid pharmaceutical products in order that they may be made into sterile powders.

As is well known in the art, the term "Fitz mill" refers to a hammer mill of the type manufactured by The Fitzpatrick Company located in Elmhurst, Illinois. In a Fitz mill, rotating hammers, impacting against solid material, force the solid material through a screen, thereby reducing its size. Fitz mills have been used in the pharmaceutical industry for at least 40 years. Accordingly, those of ordinary skill in the art are generally well acquainted with hammer mills having that design.

The Fitz mills used heretofore had a problem when they were used in sterile environments in that Fitz mills are typically belt driven. In operation, the belts used to drive the rotating hammer mechanism break down and generate particulate matter which compromises the sterility of the environment in which the mill is used. In addition, the particulate material of the belts compromised also the quality of the powders being produced by the mills.

In addition to belt breakdown problems, the Fitz mills of the prior art also included bearings which permitted the high speed rotation of the hammer mechanism. The bearings of the type heretofore used could not be sterilized in a steam environment due to the manner in which they were constructed.

Yet another problem with the Fitz mills of the prior art was that their shaft seals included a number of sealing components which were assembled and bolted together. As with any seal arrangement, a certain amount of powder got into the seal itself. In view of the design of the shaft seals used in the Fitz mills of the prior art, a very tedious process was required in order to disassemble the shaft seals for cleaning.

In view of the foregoing design elements of the Fitz mills heretofore known, the sterility and cleanliness of such mills was compromised in operation and the mills were hard to clean thereafter.

Another problem which exists generally with motor driven mechanisms, including the Fitz mills of the prior art, is that it is very difficult to provide a sterilizable motor in view of such things as paint chips, emissions, gas production, and other factors typically associated with the operation of motors.

In addition, typical motors are constructed in a manner which make them highly resistant to cleaning with bacteriacidal solutions.

In accordance with the present invention, a fully sterilizable hammer mill is provided. The hammer mill of the present invention uses a hydraulic power pack which includes both a motor and a hydraulic pump which may be mounted remotely from the hammer mill and connected thereto via hydraulic lines. On the hammer mill itself, there is a valve system which includes a reversing lever, whereby hydraulic fluid can be pumped in either direction, thereby allowing the mill to rotate in either direction. This feature is useful to facilitate cleaning of the mill's screen without removing the mill from operation. The valves, which are comprised of micrometer head locking valves, are used also to continuously control the speed of the mill.This particular mechanism also allows for continuous variation of the speed of the mill, in a range of about 600 to about 6000 revolutions per minute, while the mill is in operation. This feature facilitates experimental determination of the quality of the product.

In addition to the foregoing features of the present invention, the seal mechanism has been considerably simplified.

In the Drawings: Fig. 1 is a schematic view of a milling process of the type used in the pharmaceutical industry, in which the present invention is shown; and FIG. 2 is a schematic representation of the present invention showing the valving used to control the hydraulic motor.

The following is a detailed description of an exemplary embodiment of the invention: Referring generally to FIG. 1, a sterilizable hammer mill 10 of the present invention is shown schematically. As shown, a series of containers 12, 14 containing sterile pharmaceutical product are connected via a V-blender 1 6 in which material from the containers 1 2, 14 is blended together to get a blend in preblend containers 1 8.

The material from the preblend containers 1 8 goes into a feed hopper 20 on the sterilizable mill 10. The material from the feed hopper 20, is milled and dispensed into a milled blend container 22, known in the art as a "milk can".

From the milk can 22, blend is put into a V-blender 24 for final blending and for dispensing into final blend containers 26.

With continued reference to FIG. 1 , the mill 10 includes a shaft 28 which is coupled via coupling 30 to a hydraulic motor 32. The hydraulic motor 32 is part of a hydraulic circuit which includes a hydraulic pump 34 driven by a motor 36. The hydraulic pump 34 provides high pressure oil flow through a first line 38 with low pressure oil being returned to the pump through hydraulic line 40.

Through the use of a reversing valve mechanism 42 to which the high pressure and low pressure lines 38, 40 are connected the flow direction of oil into the hydraulic motor 32 can be controlled in order to provide a reversing capability. Valves 44, 46 which are mounted in the lines on either side of the hydraulic motor 32 provide the capability of controlling the high pressure oil flow rate into the motor 32. Depending upon which direction the motor 32 is rotating, one or the other of the valves 44, 46 will be on the high pressure side. The other valve 46, 44, which is on the low pressure side, is typically maintained in the fully opened position.

However, for fine adjustments, the low pressure valve may also be used.

In accordance with the present invention the pump 34 and power motor 36 are mounted as part of a hydraulic power pack which also includes an oil reservoir 48, which in the preferred embodiment of the invention contains approximately 75 gallons of hydraulic oil. The entire hydraulic power pack is preferrably mounted externally from the sterile area in which the mill 10 is operated. This constitutes an extremely important part of the present invention in that the motor 36 in the power pack can be non-sterile without compromising the sterility of the mill 10 or the product milled therein.

An additional feature of the hammer mill 10 of the present invention is the use of a split shaft seal assembly in which the top half of the split shaft seal is bolted into the lower half. Accordingly, it is very easy to unbolt the top half of the split shaft seal, remove it from the shaft to pack and clean the bearing and clean the area in which the seal is located.

In order to further maintain the sterility of the mill 10 and provide for easy cleaning thereof, the entire body of the mill 10 and the frame of the mill 10 are comprised of a readily steam sterilizable material, such as stainless steel, which is used in the preferred embodiment of the invention.

Another unique feature of preferred embodiment of the present invention is that it includes an all metal sealed bearing with high temperature grease. Heretofore, such bearings were not used in high speed hammer mills.

Claims

1. A sterilizable hammer mill comprising: (a) a hammer mill drive by a hydraulic motor; (b) a hydraulic power pack including a motor and a hydraulic pump, said hydraulic power pack being adapted to be mounted remotely from said hammer mill and being connected thereto via hydraulic lines; and (c) a valve system including valves for controlling the pressure of hydraulic fluid from said power pack to said hydraulic motor, whereby the speed of said hydraulic motor can be controlled.

2. The sterilizable hammer mill of Claim 1, wherein said valve system includes reversing valves for said hydraulic fluid, whereby hydraulic fluid can be pumped in either direction through said hydraulic motor, thereby allowing said mill to rotate in either direction.

3. The sterilizable hammer mill of Claim 1 or 2, wherein said mill is constructed of a material which is readily sterilizable.

4. The sterilizable hammer mill of Claim 3, wherein said mill is constructed of stainless steel.

5. The sterilizable hammer mill of Claim 1, 2, 3 or 4, further comprising a split shaft seal assembly.

6. The sterilizable hammer mill of any one of Claims 1 to 5, wherein said mill includes a sealed bearing.

7. The steriiizable hammer mill of Claim 6 wherein said sealed bearing includes high temperature grease.

8. The sterilizable hammer mill of Claim 6 or 7, wherein said sealed bearing is adapted to be steam sterilized.