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.
- 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.
- 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 motion of 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.