Sponge Bar Replacement

A knitting machine sponge bar (also referred to as a needle retainer bar) is a critical maintenance component found in flatbed knitting machines (such as Brother, Singer/Silver Reed, and Toyota). It consists of a long metal channel containing a strip of polyurethane foam backed by a low-friction fabric or plastic ribbon.

The sponge bar runs horizontally across the entire width of the needle bed, sitting in a slot directly above the needle shanks. Its primary purpose is to press the needles down flat against the needle bed, providing enough tension to prevent the needles from flopping, while still allowing them to slide smoothly forward and backward during carriage passes.

Signs of a Degraded Sponge Bar

The foam inside a sponge bar naturally degrades over time, flattens out, and becomes brittle, sticky, or powdery. Running a machine with a flat or decayed sponge bar can cause severe damage. Signs that a sponge bar needs immediate replacement include:

• Floppy Needles: When needles are pushed to working position, they do not stay in place or feel loose and wobbly.
• Carriage Resistance: The carriage becomes difficult to push across the needle bed or feels like it is hitting obstructions.
• Needle Jams: Needles jump out of their tracks and jam under the carriage, which can bend the needles or damage the plastic carriage parts.
• Patterning Errors & Dropped Stitches: The carriage fails to select the correct needles for patterning (tuck, slip, or fair-isle), resulting in dropped stitches at the edges or middle of the fabric.

Replacement Frequency

A sponge bar typically needs to be replaced every 1 to 2 years for domestic machines under regular use, or whenever the machine has been stored unused for a prolonged period. Environmental factors like humidity, heat, and oil exposure can accelerate foam decay.

Step-by-Step Replacement Process

Most knitters replace the sponge strip inside the original metal bar rather than buying a whole new metal bar. Replacement foam-and-ribbon strips are widely available.

Step 1: Removal

1. Locate the ends of the sponge bar slot on the left and right sides of the metal needle bed.
2. Use a flat-head screwdriver or a knitting tool to gently push the end of the sponge bar out of one side of the slot.
3. Once the end protrudes, pull the metal bar completely out of the slot.
4. Important: As you pull the bar out, use your hands or a ruler to press the needles down flat against the bed, preventing them from springing up and catching on the metal channel.

Step 2: Cleaning the Metal Bar

1. Strip the old, decayed foam and ribbon out of the metal channel.
2. If the foam has turned sticky or gummy, use a small flat-head screwdriver to scrape the residue out of the channel.
3. Clean the inside of the metal channel thoroughly using a cloth soaked in rubbing alcohol or acetone to remove all sticky residue and dust. Allow it to dry completely.

Step 3: Installing the New Sponge Strip

1. Thread the new replacement sponge strip into the clean metal channel.
2. Ensure the strip is positioned correctly: the fabric ribbon side must face outward (pointing down when installed) and the foam side must face into the metal channel. This ensures that the metal needles will slide against the smooth ribbon rather than rubbing against raw foam, which would shred it.
3. Trim any excess foam hanging off the ends of the metal bar.
4. Replace the plastic end caps on the metal bar.

Step 4: Re-insertion

1. Before re-inserting, ensure all needles on the needle bed are pushed fully back to non-working position (A position) and are flat against the bed.
2. Slide the sponge bar back into its slot on the side of the machine, with the fabric ribbon facing DOWN towards the needles.
3. Push the bar in slowly. Keep a close eye on the needles as the bar passes over them; use your fingers or a flat ruler to keep the needles pressed down so they do not catch on the entering tip of the sponge bar.
4. Push the bar in until it is completely flush with the edge of the needle bed.