Fixed Lip Slot Die Shim Adjustments: How to Optimize Lip Gap and Coating Alignment

Accurate shim adjustments are essential for controlling lip gap, coating uniformity, and flow distribution in fixed-lip slot die coating systems. Whether you're setting up a new die or fine-tuning an existing coating line, understanding how and when to adjust shims helps improve coating quality and reduce process variability. 

What Are Slot Die Shims and Why They Matter 

Die body shims are metal or plastic spacers that set the lip gap – the distance between the upper and lower die bodies where coating material exits. These shims: 

• Control the coating thickness directly
• Ensure full lip face contact for consistent fluid distribution
• Allow fine adjustments to match the desired coat width

Shims are aligned with precision dowel pins and ground flat to match the slot die bodies, ensuring a uniform lip opening and repeatable coating performance. 

How to Adjust Fixed Lip Slot Die Shims

1. Setting the Lip Gap with Die Body Shims 

The lip gap determines how much coating material is applied – and getting it right starts with selecting the correct die body shim thickness. Key steps include:

• Remove the die by separating the upper and lower bodies
• Access and replace the die body shim with the correct thickness
• Reassemble and align to ensure even gap across the die width

Proper shim selection helps balance internal manifold pressure and supports uniform flow distribution across the full coating width.

2. Fine-Tuning the Lip Offset with Offset Shims

A lip offset adjustment changes the relative position of the upper and lower lip faces. This can fix slight overbite or underbite conditions for better coating contact. The offset block system on the back of fixed lip slot dies allows these micro-adjustments:

Offset Shim Adjustment Procedure:

• Loosen, but do not remove, the die body bolts and the upper offset bolt. This frees the upper body to shift.
• Insert desired offset shims. For a zero-life face offset, a typical starting shim thickness is 0.010” (0.254mm).
• Torque the offset screws according to your operation manual to secure the upper body against the shims.
• Torque the body bolts in the specified sequence and values engraved on the die.

Following the correct sequence and torque values keeps shim pressure consistent and prevents misalignment across the die face.