Compression machines are used to compress the powders or granules into tablets. The first compression machine invented was a single-punch compression machine which was used to compress a single tablet at a time.
With advancements in technology, rotary compression machines were developed. Rotary compression machines can compress many tablets in a single round. With time, many modifications were made in the rotary machines to make the process more easy, robust, and efficient.
Reasons for Improvements
The main factors for improving conventional rotary compression machines are as follows,
- Make it more efficient.
- Enhance product quality
- Reduce change over time.
- Operator safety
- Tooling safety
- Prevent cross-contamination
Main Advancements in Compression Machines.
Some main advancements of rotary compression machines are given as follow,
- Vacuum feeding
- Fill Cams
- Auto Adjustment of Weight
- Rejection Mechanism
- Online Monitoring of Weight variation
- De-dusting/Metal detector
- Visual Alarm system
- Online monitoring of punch load
Advance compression machine Tooling
Following are some examples of advanced toolings for compression machines.
- Multi tip tooling
- Exchangeable Turret
- Segmented dies
- Rota-heads
- Lined Dies
Vacuum Feeding
To start a compression operation, powders or granules are filled in machine hoppers.
Old Technique
- In Conventional compression machines, the powder or granules are filled in hoppers manually which results in dusting.
- It may result in cross-contamination.
- It may be harmful to the operator.
- Due to operator negligence hoppers may not be filled on time to supply proper feed.
- Due to poor feeding of hoppers or less hopper volume, weight variation or low hardness tablets may be produced.
Advancement
- In latest advance compression machines the Auto Feeding system is installed.
- It works on an air vacuum system in which powder or granules are automatically supplied from containers to the hoppers and rate of flow is controlled by sensors.
- It ensures timely filing of hoppers and there are no chances of empty hoppers during the compression operation.
- Due to the timely filing of hoppers, smooth feeding is ensured so weight variation and hardness problems do not occur.
- It is a close system and prevents dusting.
- It prevents chances of cross-contamination.
- It provides safety to operators.
Fill Cams
Fill cams are used to ensure the uniform weight of tablets during the compression operation.
Old Technique
- In Conventional compression machines granules or powders are filled in dies and weight is adjusted by rotating the knob of weight adjustment cam.
- By rotating the knob of weight adjustment cam it pushes the lower punch upward or downward in the die and space inside die is increased or decreased.
- When space is increased weight is increased because more granules or powders can be filled in the die cavity and vice versa.
Advancement
- In the Advance compression machines various fill cams are present.
- Fill cam is changed according to tablet weight and bulk density of powder or granules.
- Fill cams come in millimetres depths.
- Each cam can take a specific volume of granules or powders and for further increment in weight, we have to change the cam.
- Example, for cam no 2 the filling depth is 3.5 mm- to 9 mm. If our weight is not achieved meaning it is lower than the limit then we will change the filling cam to increase the filling depth to provide more space for granules or powders. we will use Cam number 3 whose filling depth is 6.5-12 mm.
Auto Adjustment of Weight and hardness
Weight variation and hardness variation are two common problems which may occur during the compression operation.
Old Technique
In conventional compression machines weight variation and hardness is controlled manually.
Advancement
In advance compression machines, servo motors are installed along with cams to adjust the weight and hardness of tablets automatically.
Rejection Mechanism
Due to powder or granules flow, problems of weight variation or hardness variation may occur.
Old Technique
In conventional compression machines, low hardness or low weight tablets are not separated.
Advancement
- In advanced compression machines, an auto rejection system is installed to separate good tablets and bad tablets.
- A range is given to the system of compression machine and any tablet above or below this range is rejected automatically through rejection chute.
- So good quality tablets and bad quality tablets are separated.
Visual Monitoring
Visual aids like graphs on HMI are used to improve product quality.
Old Technique
In conventional compression machines fluctuations in weight or hardness does not give any alerts to the operators.
Advancement
- In Advance compression machines graphical views of running parameters are displayed on HMI.
- Any fluctuation in parameters is easily observed by the operator.
- The operator can easily make changes to the parameters of the running product.
Metal detector/de-duster
During compression operation tablets are passed through a de-duster and metal detector to remove fine powders and any metal piece in tablets.
Old Technique
- In Conventional compression machines, de-dusting and metal detecting systems are separate.
- First tablets are passed through de-duster then through a metal detector.
- More space is required.
- More time is required.
Advancement
- With advancement, both these systems are combined in a single unit which performs the dual functions of de-dusting and metal detection.
- Less space is occupied and it is time-saving.
Visual Alarm system
Old Technique
- In conventional compression machines usually, no alarm system is installed and if the alarm system is present it does not give any visual indications.
Advancement
- In advance compression machines critical parts are attached with an alarm.
- It ensures the safety of operator and machine parts.
- When the alarm rings it is indicated on HMI.
- A specific area is highlighted on HMI and a defect is easily detected.
Online monitoring of punch load
- In conventional compression machines, there is no data to show the amount of load exerted on the individual punch.
Advancement
- In advance compression machines graphical data is shown on HMI for individual punch load.
- In case of overloading the punch can easily be detected from the graph.
- It shows the position of a punch according to the punch numbering system.
Advance compression machine Tooling
Many advance toolings for compression machines are used, some of them are discussed below.
Multi-tip Tooling
- As the name indicates, multi-tip tooling has more than one punch tip.
- Modifications are made in punches to enhance output.
- Dies also have more than one hole in each die.
- The advantage of multi-tip tooling is that from a single punch we can get double or triple output or as maximum as the number of tips.
- The force-feeding system is used to ensure uniform filling of dies and to prevent weight variation.
Exchangeable Turret
- The turret is named as the heart of a rotary compression machine.
- The turret is a rotating structure which contains punch holders and a die table.
- On turret, Punches are installed in punch holders and dies are installed on the die table.
- In conventional compression machines, it takes a long time for change over.
- After completion of one product, we have to weigh for 3-5 hours for change over of the next product.
- It is difficult to install punches and dies on a fixed turret.
- Exchangeable turret system is a setup in which the turret is completely replaced with another turret.
- Advance compression machines are designed in such a way that after completion of one product the whole turret is removed from the machine with all punches and dies and another turret having tooling for the next product is installed.
- Next product tooling is installed on another turret in a separate area, while compression of the first product is in process.
Advantages
- Exchangeable turrets reduce machine change over time.
- Exchangeable turrets enhance machine efficiency.
- Provide ease to operators for the changeover.
- The removed turret is cleaned in a separate area later on.
- Tool-free operation in a compression machine area.
Segmented Die Table
- Segmented die table is used to reduce set up time.
- All dies are fitted in the die table in the form of segments.
- No individual dies are required to be screwed.
- Two to three bolts are used for a complete die table change over.
- It is easy to combine 2-3 segments to complete the changeover in a short period.
- Due to the segmented die table, Change over time is reduced.
- Due to the segmented die table, machine output is enhanced.
- Tooling life is increased.
- Segmented die tables can also be used for multiple tooling.
Rota-heads
- Rota heads are the punches which have a keyed body and rotating head.
- Key is attached to the body of the punch so it remains fix and the head revolves.
- Rota head punches are used to increase the dwell time.
- The time spent by the upper punch head below the compression wheel is called the dwell time.
- Increased Dwell Time is used to remove Tablet Capping.
- In Rota head punches, the head of the punch rotates as it passes below the compression roller.
- Due to the rotation of the punch head, the contact time is increased and dwell time is also increased which is helpful to prevent tablet capping.
Lined Dies
- Lined dies are also known as insert dies.
- As the name indicates, some protective material is inserted inside the die bore.
- Usually, carbide or ceramic lined dies are used.
- These are used for corrosive materials.
- Corrosive material damage the dies and tooling life is reduced.
- Inserts give protection to dies and tooling life is increased.
- Lined dies also reduce friction during compression.
Could you please explain little more the rejection function ? How this is challenged ? Thank you in advance
Good article… can added more context like Awc with force calculations and challenge tests.. types of tooling with dimensions… MOC of different parts… metal explanations with challenge test… bilayers tablet compression also can be add… Thanks for sharing… sir ur doing good work.. best wishes.