Leaf Disc Filters

How Melt Passes through the Disc

The pressure difference between the unfiltered melt in the housing and the filtered melt in the central collector drives flow through both faces of each disc. The diagram shows one radial half section, from the sealed outer edge to the central hub.

How a Leaf Disc Filter Works

Two Filtering Faces ● Radial Drainage ● Central Collection

Conceptual flow illustration; the approved component drawing defines the actual construction.

Melt Entry. Unfiltered polymer fills the spaces between adjacent discs and contacts the upper and lower filtering faces.

Filtration. Melt passes through the porous medium on each face. The selected medium retains contaminants; the supporting layers maintain the filtering structure.

Radial Drainage. After passing through the medium, the filtered melt enters the internal drainage core and travels radially inward towards the hub.

Central Collection. Melt passes through the hub outlets into the common collector, which carries the combined flow from the disc stack to the system outlet.

Why Sealing and Spacing Matter

The sealed outer edge and hub interface prevent melt from bypassing the medium. Correct inter disc spacing maintains access to both faces and supports consistent flow distribution.

Published Range and Rating Basis

Confirm applicability to the selected medium, disc construction and assembled stack before ordering.

Filtration Grades

5, 7, 10, 15, 20, 25, 30, 40, 60, 80 and 100 µm at βx ≥ 75

What βx ≥ 75 Means

The beta ratio compares upstream and downstream particle counts at or above size x. A ratio of 75 corresponds to approximately 98.67% removal under the applicable particle count test conditions.

Efficiency (%) = 100 × (1 − 1 / βx)

At βx = 75: 100 × (74 / 75) ≈ 98.67%

Request the test method, fluid, challenge particles and operating conditions for the quoted grade. The catalogue does not identify that test protocol.

A particle beta rating alone does not establish removal of deformable gels in a hot polymer melt.

Working Pressure and Differential Pressure

Working pressure concerns the pressurised process. Differential pressure is the pressure difference across the filter.

The published maxima are separate limits; they do not establish a combined operating envelope or a change out set point.

Specify normal and peak pressures, temperature, viscosity at the relevant shear conditions, start up transients and the approved terminal differential pressure.

Understanding D, d and H

Use these three dimensions to identify the basic disc envelope and centre opening. The plan view shows the disc face; the section shows the centre bore and axial height.

Leaf Disc Dimensions Explained

Outside Diameter ● Centre Bore ● Catalogue Height

Schematic geometry; axial thickness is enlarged for clarity. Dimensions are not to scale.

D - Outside Diameter. The overall diameter measured across the outer edge of the disc. Confirm the required clearance to the filter housing.

d - Centre Bore Diameter. The diameter of the central opening. Confirm fit and tolerances with the mating collector or shaft.

H - Catalogue Height. The axial distance between the reference planes specified for that design. Confirm whether the drawing measures across the hub, seal faces or another defined feature.

Drawing Check Before Ordering

State all dimensions in millimetres and confirm the current component drawing. H should not be assumed to equal the filter medium thickness or the assembled stack pitch.

Selected Catalogue References

Group numbers identify the catalogue sets; they are reference labels, not hub classifications.

FTD identifiers are retained for catalogue cross reference. Area values are as published. Confirm current drawings, tolerances and the effective area of the supplied component.

Select the Complete Filtration Assembly

Available Constructions

MEDIA: sintered stainless steel fibre, multilayer sintered stainless steel wire mesh, or sintered metal powder. Hub options: welded centre ring (hard hub) and centre ring (soft hub).

SINTERED FIBRE. A porous bonded fibre structure can provide depth capture. Assess the balance of contaminant capacity, retention and clean resistance for the polymer.

SINTERED MESH. Woven layers offer a defined filtration structure with supporting layers. Review the weave and full laminate, especially where hard particle contamination dominates.

SINTERED POWDER. A porous matrix of bonded particles provides another route for gel sensitive duties. Compare tested performance and resistance; media names alone do not establish equivalence

Filter Area and Surface Loading

Use the confirmed active area per disc when sizing a stack. A simple accounting example illustrates the calculation; it is not a throughput recommendation.

Total Area = 40 × 0.12 = 4.8 m²

Mass Loading = 1,200 / 4.8 = 250 kg/(m²·h)

Count each disc’s confirmed total area once. Include any excluded end faces, seals or inactive zones in the supplier’s area definition. Stack count alone does not determine hydraulic capacity.

Verify the Hydraulics

Request pressure loss data for the actual polymer, temperature, throughput and complete stack. The review should include the media, internal drainage, inter disc spaces, collector and housing.

Build the Specification Around Film Quality

Leaf disc selection should address the film’s defect limits, polymer behaviour and operating economics. Flow distribution, pressure loss and gel control should be assessed together.

Polymer and Production Duty. State resin family and grade, virgin/recycled blend, additives, melt temperature, viscosity basis, throughput range and the product being made.

Contamination and Quality Target. Describe hard particles, degraded polymer, gels and catalyst residues. Supply retained contaminant samples or microscopy where available, and define the accepted film defect measure.

Existing Assembly. Provide the OEM or housing reference, disc drawing and revision, current medium and grade, hub type, seal details, disc count, spacers, stack height and change out history.

Trial and Performance Review

Compare candidate assemblies at matched melt conditions. Record initial differential pressure, its rise with time or tonnes processed, run length, film defects, breaks and off spec output. Include pressure transients and the reason for each change out in the trial record.

Cleaning and Return to Service

Use a cleaning sequence qualified for the polymer deposits, media, hub and weld construction. Following cleaning, evaluate flow resistance and integrity against an approved baseline and acceptance criteria for that filter design.

Visual cleanliness alone does not demonstrate restored filtration performance. Keep an individual record of service cycles, cleaning history, inspection results and test disposition; retire damaged discs or those outside the agreed criteria.

Enquiry and Acceptance

Send the drawing, current filter sample details, polymer duty, required grade and quantity.

Agree material certification, dimensional inspection, sealing checks, performance evidence and packaging before finalising supply.