Common Failures of Rotary Tablet Press and Solutions

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Common Failures of Rotary Tablet Press and Solutions

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Common Failures of Rotary Tablet Press and Solutions

Tablet press machine is the principal equipment in tablet making process. With features of stable

performance, high production, reasonable design and appropriate price, it has been widely used in

various industries, pharmacy, food, chemical, electronic, metallurgy, etc. However, once the mechanical

failure occurs, great losses is caused. Therefore, it is quite important and necessary to analyze the

common failures and promptly find precise solutions. This article is to summarize some common faults,

from the perspective of machine construction, on rotary tablet press machine, and to propose

corresponding suggestions.

1. Basic structure of rotary tablet press

A rotary tablet compression machine is mainly composed of pedestal, guide rails, rotary table(turret),

pressure roller, feeder, turbine, engine, and cover. Working principle is that the powders or particulars

will be flowing into the hole of middle die through feeder when turret is running, and then be pressed

into tablets or pills by punch tooling with pressure of rollers. Meanwhile, the upper and lower plunger

is going up and down following the track of guide rail, so as to making tablets compacted.

2. Common failures and solutions

Actually, mechanical faults usually occur in guide rails, turret, rollers, overload protection device, reduction

box, and punches and dies.

2.1 Rotary table/Turn table/Turret

Turret is one of the main parts in compression process. Punches and dies are evenly distributed on it. The

punches are going up and down along the rail track. Its common faults are listed as follows.

①Coaxiality of punches and die holes deviates from standard requirement due to long-term wear.

Misalignment of them increases friction, and even couldn’t eject a pill out if seriously wore. Then solutions

are different according to the degree of worn. Use a reamer to fix coaxiality if not badly worn, or you need

to replace a turn table.

②The turret(whole part) moves a little up, which makes it difficult to feed and eject. This is possibly

caused by looseness of lock block that is used to fix turret. You just need to lock the block on condition

that the screws are in good state, or you should replace the screws.

③As the screws that are used to fix middle die on the turret are loosening, middle die(s) go(es) up and thus

wears the feeder. In this case, you could fasten the screws to remove the trouble. However, the set screws

are easily damaged parts. Timely check and replace them if badly worn.

2.2 Guide rail

Guide rail is one of the integrant parts to guarantee the curvilinear motionof punches. Most malfunctions

of guide rail are caused by insufficient of lubrication. Possibly occurred faults and solutions are listed as

follows.

①Wear of guide rails. The punches move along the rail track by means of sliding and friction. The guide

rails are composed of upper cam track and lower cam track and other components. The wear of punches

and guide rails can be solved by polishing with oil-stones, or change the rail track if seriously worn.

②Loosening of guide rail components. Due to long time working, the components on the guide rails are

more prone to get loosened. The operator should keep an eye on all the components, promptly fasten the

problem parts.

③Wear of bridge plate on lower track leads to further wear of the principal part of guide rails. The bridge

plate of lower track play an protective role of the guide ways. If wears, recover it by applying oil-stones,

or replace it if seriously damaged.

2.3 Pressure Roller

Pressure roller is composed of two parts, upper roller and lower roller, for controlling the pressure and

working as a protective device. Common failures are illustrated as follows.

①Once outer part of the roller wears, the end portion of the punch will get stronger resistance. At this

moment you should replace on a new roller and the same treatment when the inner part of roller and

roller shaft get severe abrasion. Sometimes, the granules/powers are difficult to be pressed into a tablet,

then we will increase the pressure. But such movement will result in breaking and distortion on roller

shaft. As a result, replacing a new roller is necessary, and readjusting the pressure and materials ingredient

is also imperative.

②Insufficient lubrication or damage of roller shaft bearing. You should make a regular maintenance and

lubrication on shaft bearing, and timely change the worn parts.

2.4 Adjusting System

Adjusting system includes pressure adjustment and filling depth adjustment.

①Adjustment malfunction. In general cases, adjustment malfunction is closely related with the hand-wheel

and turbine. One possible cause is loosening of screws of hand-wheel, which makes the hand-wheel

couldn’t work. Another possible cause is that the adjusting turbine locked.

②Unstable filling. Possible reasons are as follows:

A. Materials are not uniform and with poor fluidity;

B. Abrasion of punches and dies makes the shape or the thickness of tablets a little different from time to

time;

C. Hopper is fixed at an improper position, and insufficient materials flow into feeder;

D. Front filling track gets severe worn, which causes punch skip. You just change the filling track;

E. Lift pole gets badly worn, resulting in large clearance thus causes vibration of filling track. Solution is to

replace the worn components;

F. Undersurface of feeder gets serious worn, leaving uneven clearance between feeder and turret;

G. Scraper gets badly worn, leading to uneven filling. Solution is to replace a good scraper.

③Loosening tablets and unsightly tablets. The causes of such defect tablets may be low pressure, uneven

particles.

It is better to increase pressure by adjusting hand-wheel and adjust the material formula, including the

ingredients.

④Vibration and loud sound occur when it works. It is because unbalance of pressure from both sides. you should

adjust the pressure promptly.

2.5 Feeding System

Feeding system includes feeder and hopper. Common faults and solutions are introduces as follows.

①Powder leak. Powder leak is generally caused by the large clearance between scrapper, undersurface of

feeder,

and turret. All you need to do is to control the clearance in an proper range. Large clearance will cause

powder leak, while small clearance will give rise t abrasion of rotary table.

②Overflow or inadequate of materials. No matter for the overflow or inadequate of materials, the reason

is mismatching of the material fluidity and speed of turret. You should adjust the turret speed in accordance

to the material fluidity.

2.6 Overload protective system

Common fault of overload protection system is frequent alarms for overload pressure or low set pressure of

overload protection spring. Therefore, two ways to avoid frequent alarms. One is to adjust hand-wheel to

reduce load pressure. The other is to increase the set pressure of overload protection spring.

2.7 Reduction gearbox

Reducer is composed of worm wheel, worm and housing. Oil leakage of reducer is one of the common

faults, which can be resulted from loosening of flange screws and aging of oil seal. Then the solution

comes that Tighten up the flange screws or replace the oil seal and apply sealant.

2.8 Punches and dies

Punches and dies are the quickest-wear parts, and common failures are listed as picking&sticking, capping,

chipping, lamination, weight variation, double impression, etc. These are more likely to be caused by

improper material formula. Plunger is also the most active part like guide way. Large friction and abrasion

damages them. Try to do more or regular lubrication to avoid severe worn.