At one time, OEM turrets were manufactured as a one piece unit. When a problem occurred, in most cases, it was necessary to replace the entire turret. Scheu & Kniss developed methods of cutting the turret into separate sections and replacing only those that were out of specifications. In the end we had developed the first multi-sectional turret. As we gained experience, Scheu & Kniss started to manufacture new turrets as a product line. Today we repair and manufacture hundreds of turrets a year to fit practically every model of tablet press in the market.

Proper turret repair requires a great deal of knowledge about tablet press operation. Punch and die alignment is one of the most critical and challenging aspects of repairing a turret. In most cases, it is necessary to match a new section to another used, partially worn section.

 

Scheu & Kniss offers many options during turret repair. We pioneered the design and installation of the hardened die table wear plate. This popular option can be installed on new turrets as well as your existing turret. It is a preferred option for those compressing highly abrasive materials and in most cases can be replaced without the purchase of a new die table. Replaceable punch bushings can be installed to help when excessive punch bore wear is seen. However, this option is not available for all turrets due to the distance from one punch station to the next.
 

Scheu & Kniss can manufacture your turret sections from many different steels and alloys including: Cast Iron, Steel, Stainless Steel, Tool Steel, and even Aluminum. We can apply specialized coatings to enhance finish, corrosion resistance and wear characteristics based on the individual products that you may compress. Our staff will work with you to recommend the coatings to fit your application.

Wear Plate (back to top)

The hardened die table wear plate is a thin tool steel plate installed on the die table surface and acts as the wear surface under the feeder mechanism. The thickness of the die table is reduced to allow for installation of the wear plate, which once installed, returns the die table to its original thickness. The plate is heat treated to the specifications of the desired tool steel selected and varies by customer.

Punch and Die Alignment (back to top)

Why do you need to understand punch and die alignment? The following conditions can be attributed to poor punch and die alignment.
• Excessive tool wear
• Poor tablet quality
• Premature cam wear
• Premature turret wear

Terminology (back to top)

Punch and Die Alignment: A comparison of the axial relation / geometrical positioning of [punch and die] or [punch bore and die bore].

Punch Tip Deflection: Amount of directional change or shift in the punch tip upon entering the die.

Radial Thrust: Directional tendency of punch head to be pushed in the opposite direction of turret rotation.

Punch Barrel Clearance: Difference in diameter of punch barrel and turret punch bore.

Punch Tip Clearance: Difference in diameter of punch tip and die bore.

In order to fully understand these conditions, you must understand what affects them. Poor punch and die alignment is caused by many factors. When a new turret is put into service, it begins to wear. As the wear increases, the potential for misalignment also increases. Therefore, to manufacture a product that will provide longer service life, it must be manufactured to have near perfect alignment from the start.

A factor that affects alignment is the clearances that must be present for proper operation of the punches and dies. Punches are manufactured to allow for a specified amount of clearance between the turret punch bore and the punch barrel. Likewise, there is clearance built into the die bore and punch tip. However, the clearance of the punch barrel is greater than the tip to die clearance. This creates a situation where the punch movement inside the turret punch bore exceeds the total clearance between the punch tip and die. Even with perfect alignment, it is unavoidable for the tip to occasionally strike the die's leading edge. This is called "tipping" or tip deflection. As the turret and tooling wear, the deflection gets worse until tooling or turret need replacing. This is another reason that new or repaired turrets need to be manufactured to the closes tolerances available.

Radial thrust of the turret combined with the built-in clearances also contribute to the tip deflection of tooling. As the punches move through the cams the friction creates resistance at the punch head. Since the other end of the punch has no resistance, it causes unequal resistance forcing the punch to travel more at an angle to the true axis of the punch bore. The faster the turret turns the more the problem is seen. Some machine manufactures have tried to counter this by decreasing the punch bore clearances, only to create punch sticking problems. Again, as the turret wears, the angle increases as does the punch tip deflection.

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