Technical Requirements for Grip and Delivery Rolls
The grip and delivery rolls are an essential part of many printing and converting operations due to their critical role in the sheet handling process and their impact on the quality of final product. Properly designed and constructed gripper and delivery rolls are an essential component of the sheet handling process and can improve the operational efficiency of the entire machine.
When considering the technical requirements for sizing and construction of grip and delivery rolls it is essential to understand the specific machine design, the types of materials being used, and the unique requirements for the specific application. General technical requirements must address items such as diameter, width, roll shapes, roll coverings, roll gaps, and roll compression.
Diameter
The diameter of the roll is a critical factor in ensuring proper sheet handling and sheet quality. The selection of the correct diameter prior to installation depends on both the machine configuration and the sheet materials being used. The roll diameter should be proportional to the sheet size, meaning that the diameter should increase as the sheet size increases. Similarly, the roll diameters should be different depending on the thickness of the sheet material being used as thicker materials need larger roll diameters.
Width
In addition to diameter, the width of the roll is an important consideration when designing the grip and delivery rolls. The surface width should be expanded as the size of the sheet increases to ensure that the entire sheet remains in contact with the roll. The width of the roll is also important in relation to the linear speed of the machine. Slower running machines require wider rolls in order to maintain contact with the entire sheet while faster running machines can handle narrower rolls.
Roll Shapes
The shape of grip and delivery rolls is an important factor in determining the overall performance of the machine. Generally, roll shapes should be designed to match the contours of the machine and the sheet materials being used. Most grip and delivery rolls are cylindrical in shape, however some curved and conical shaping may be beneficial for certain materials or applications.
Roll Coverings
Grip and delivery rolls should be constructed with a durable covering material that will provide superior gripping and release characteristics. Common materials used as roll coverings include felt, rubber, silicone, and polyurethane. The covering material should be selected based on the sheet material being used, the width and shape of the sheet, the line speed, and the forces applied to the sheet.
Roll Gaps
The gap between adjacent grip and delivery rolls is an important consideration when designing grip and delivery rolls. Generally, narrow roll gaps improve sheet handling and reduce marking of the sheet material, however too small of a gap can lead to sheet jams. On the other hand, larger gaps can allow the sheet to flutter and lead to excessive marking of the sheet material. The correct roll gap size can depend on the sheet material, width, length, thickness, and line speed.
Roll Compression
Finally, roll compression is an important factor in both sheet handling performance and extended roll life. Roll compression is determined by the gap between the roll and their support surfaces. Too little compression and the rolls may slip, too much and the rolls will wear out prematurely. The correct amount of compression must be determined based on the machine configuration and sheet material being used.
In conclusion, when considering the technical requirements for grip and delivery rolls, it is important to understand the machine design, the types of materials being used, and the unique requirements for the specific application. Proper sizing, construction, and materials must be considered to ensure optimal performance, extended roll life, and high-quality final products.
