Compression machines are used to compress the powder or granules into uniform size and weight. The compression machine and tooling part are involved in the compression of tablets. So maintenance and lubrication of tooling is a very critical part of the pharmaceutical industry.
You may also read: about Tablets defects, Capsules defects, and Solid dosage form
Parts of Compression Machine:
The tablets compression machine has the following functional parts:
Hopper
Hopper is provided at the top of the compressions machine to hold or supply the bulk granules/powder to the feeder.
Feeder
The feeder feeds the granules/powder from the hopper to the dies.
Punches
Punches travel to the die to compress the powders within the dies.
Dies
Dies are used to specify the size and shape of the tablets.
Turrets
Turrets help in holding upper punches and lower punches
Cams
Cams help to guide the movements of punches
Compression Rollers
Compression machine rollers push the punches toward the die to form the tablets.
Take off blade
It is adjusted just in front of the feeder box to carry out the compressed tablets to the discharge tube.
Discharging chute
The discharging chute provides the path for tablets to travel to a Metal detector/ collection bin.
HMI
HMI is a functional part of the machine where all the parameters are set before the process.
Different stages in the tablet compression process?
Filling: Granules flow through compression tools like a punch, dia, and cavity, which are responsible for the filling of the granules according to the position of lower punches to make tablets; the volume is adjusted for the weight of the granules to be compressed.
Metering: Metering is the process of removing extra granules from the turret. The metering cam is responsible for controlling the Height of the lower punch, which helps in controlling the volume of granules.
Compression: Compression is the formation of tablets by approaching the top and bottom punch to come together by pressure within the die, resulting in the deformation of particles like Elastic deformation and plastic deformation.
Ejection: Ejection is the removal of tablets from the die wall by rising of lower punch. If inadequate lubrication results in more ejection force are required. This causes problems like sticking and picking.
Compression Machine Tooling?
Tooling is The setup of dies and punches for the compression of tablets on the machine is called tooling.
There are the following types of compression machines and tooling, depending on the sizes of punches and dies.
Chemical Composition of Tools:
Punch and Head Terminology:
Punch:
- Head: The head is the end part of a punch that guides it through the cam track of the compression machine.
- Head flat( Dwell Flat): The top area of the punch that is flat receives the compression force from the roller (in upper punches) and determines the ejection height and weight (in lower punches)
- Outside head angle: The area touched with a roller during compression.
- Inside head angle: An area that helps in pulling down the lower punches after ejection and lifts upper punches after compression of tablets.
- Neck: it’s an area between the head and barrel, which provides a path for the cam.
- Barrel: Guides the punch while punches traveling (going up and down).
- Stem: Area from the lower side of the head and extends to point up to the full diameter of the barrel begin.
- A tip is the lowest portion of the punch, which determines the profile of the tablet.
- The tip face is the area where tablets are formed; a good quality finishing is required to get the high quality of the tablet.
- Working length: working length of the punch is the distance from the head flat to the lowest area of measurements of the punch cap.
- Overall length: it is the length from punch tip to head flat.
- Key angle: influences the tablet shape and turret rotation.
- Domed heads: is responsible for tablet hardness and quality. It helps enhance dwell time.
- Dwell time: it is the travel time of the punch head over the compression roller.
- Hardness: is measured in HRC (Rockwell ‘c’ scale)
- Clearance= Die bore dia-punch tip dia
Die Terminology for Tablet Compression:
- Die. O.D.: is the outside diameter of the die, which is fitted with the die pocket in the compression press.
- Die Height: overall Height of die from top to bottom.
- Die Bore: this is the part of the die where the tablet forms; it determines both the shape and size of the tablets.
- Chamfer: is the entry angle of the die bore.
- Taper Dies: They are single(one side wider at the opening face) and double taper dies(both sides wider upper and lower) for easy ejection and to prevent capping and delamination problems)
- Die Groove: The groove outside the periphery of the die, which helps in fitting the die in the press.
- Lined Dies: it’s also called Insert dies; these dies are fitted with a linear insert made from the materials of tungsten carbide and ceramic.
Advancements in a Compression machine
The Life span of the Dies and Punches:
The life span punches and dies depending on MOC( materials of construction)
- OHNS Punches and HCHC Dies- 4 Million tablets
- HCHC Punches and HCHC Dies- 7.5 Million tablets
- Complete hard chrome plating punches and HCHC dies- 8.5 Million tablets.
Punches and Dies: cleaning lubrication, wear and tear, and storage:
1. Cleaning: use 0.1% teepol solution with purified water for cleaning after the use of punches and dies, also using a soft plastic scrubber if required.
Caution: Do not use a metal scrubber; it will make scratches and marks, roughness on punches, and dies.
Rinse the punches and dies finally two to three times with hot purified water if required to do the streaming for cleaning.
After cleaning, intimate to the QA department for rinse water or swab sample to QC for testing for a residual trace of detergent and previous product( Method and cycle of cleaning of punches and dies shall be validated).
Use oil-free filtered compressed air and a suitable dry clean duster for the dry. after cleaning and drying, the disinfection of punches can be done by wiping with 70% isopropyl alcohol.
Allow to dry the punch and then lubricate the punches before storing. Polishing can also be done by using a polishing kit.
2. Lubrication: Lubrication is done by using food-grade oil like castor oil or liquid paraffin, but there is a problem with the rancidity of the oil. So nowadays, various synthetic lubricants and grease are available, which have been now used in most pharmaceutical companies.
Now some of the varieties of synthetic oil and grease, which are 100% synthetic and non-toxic, are listed in NSF and USFDA authorized. components are in accordance with FDA regulation 21CFR 178.3570
Names of some grease and oil are:
- ET- 2S grease
- ET- 10S,20S,90S,140S Lubricants
- HT- 1000G, High temperature, and non-melting grease
Store the punches and dies in their cabinet( made of a soft material to avoid damage to punches and dies)after proper greasing.
Handle punches and dies carefully to increase their life; at the time of use, wipe the punches and dies with a proper clean and dry lint-free duster with IPA 70%, then allow them to dry.
3. Wear and Tear of punches and dies: checking the punches and dies periodically for any damage and polishing termed as wear and tear.
For this follows the guidelines and use a punch inspection and maintenance kit, inspection, and maintenance of punches and dies shall be done by skilled, experienced, and knowledgeable persons with proper records.
Compression machine kit for punches and dies:
- Motorized chuck: for cleaning, and polishing of concave, the plane also punches for the cleaning of punch tip, punch barrel, and punch head.
- Double-ended Polisher: for cleaning, and polishing of all types of embossed punch tip, including break lines and shaped punch tips.
- High-speed Grinder: polishing plain concave punches and die bores.
- Bench comparator: for measurement and comparison of punch length, checking of punch tip, to barrel concentricity.
- Lapping sticks
- Fine polishing strip: use for light polishing (grit 320 and 600)
- Emery rolls: polishing of punch head 180 grit for general polishing and 320 grit for lighter polishing.
- Lapping stone: used for removing bur from punch tip.
- Nylon brushes: Used for double-ended motor for polishing all embossed punch tipe, flat beveled and shaped punch tip, and for cleaning break lines.
- Micro-polishing paste: for micro-polishing
- Chalk powder: for drying off polishing compound from punch tip.
- Lubricants for lubrication
- Brass wheel
- Turrent brushes for removing powder
- cotton wool: for cleaning.
- Magnifying Glass: for inspection
- punch holder to protect punch from tear and wear.
- Length gauge: for all length checking ( screw gauge and vernier caliper digital)
Punches wear and tear:
- Check for overall length; it should be within specified limits.
- The inside head angle should not be warned out due to friction on the cam, and it should be smooth.
- The flathead should be smooth
- Body diameter should be within limits
- The punch tip should be smooth and not warned out due to friction, and it should be intact and not damaged.
- The embossing letter and break line height and uniformity should be sharp and intact; it creates a problem during tablet ejection from dies, if not proper.
Dies, tear and wear:
- The outer diameter should be within limits.
- inside the cavity, the finishing should be mirror finished and smooth,
- Hight of the die should be within the limits
- Die grooves should be smooth and not damaged.
- The Die chamber should be proper, smooth, and appropriate; otherwise, it creates a problem in tablet ejection.
References:
- Pharma pathway book edition 2016.
- Wikipedia
- pharma Wikipedia
Very informative.