How to Specify Keyhole Slots for Chute Liner Plates
Keyhole slot drawing guide
Define the entry opening, retention slot, direction and complete fastening system before ordering a keyhole-slot liner.
A keyhole-shaped cutout can speed up positioning during a planned shutdown, but the slot geometry alone does not lock a liner in place. A reliable RFQ must describe both the finished plate and the approved fastening assembly.
Keyhole Slot Chute Liner Plates use a larger entry opening connected to a narrower directional slot. The fastener head or locating feature passes through the entry opening, then the plate moves into its retained position. This guide explains the dimensions, datums, orientation and installation information needed for a drawing-based quotation.
When is a keyhole slot useful?
Keyhole slots may be considered where maintenance teams need fast initial positioning, limited access exists behind the chute shell, or a liner must be hung temporarily before the final clamping step. The design must be reviewed for the actual load direction, vibration, impact, temperature and inspection routine.
| Project condition | Potential benefit | Engineering check |
|---|---|---|
| Short shutdown window | Faster location of the liner on prepared fasteners. | Confirm the final tightening and anti-release procedure. |
| Restricted rear access | The plate may be positioned from the wear side. | Verify the complete fastener assembly and inspection access. |
| Directional installation | The narrow slot establishes a defined retained position. | Ensure operating loads cannot drive the plate back toward the entry opening. |
| Replacement program | Repeatable drawings can support standardized spare parts. | Check worn structure and hole locations before copying the old liner. |
Important: A keyhole cutout is a positioning feature, not a complete locking system. The responsible engineer must approve the fastener head, washer or retainer, preload, anti-rotation or anti-release feature, load direction and inspection method.
Dimensions that belong on the drawing
Do not dimension a keyhole slot with one overall length and one width. The circular entry and the narrow retention section perform different functions and should be specified separately.
| Drawing item | Recommended definition | Why it matters |
|---|---|---|
| Entry opening diameter (D) | Finished diameter of the large circular opening. | Must admit the approved fastener head or locating feature with the required clearance. |
| Retention slot width (W) | Finished width of the narrow section. | Controls clearance around the shank or neck in the retained position. |
| Slot length (L) | State whether measured center-to-center, from entry center to slot end, or overall. | Avoids different interpretations of the transition region. |
| Terminal radius | Radius or full geometry at the closed end of the narrow slot. | Supports cutting, fit and stress review. |
| Transition geometry | Tangent blend, corner radius or drawing profile between the circle and narrow slot. | Prevents an uncontrolled notch or ambiguous tool path. |
| Plate thickness | Nominal grade and thickness, plus any thickness tolerance requirement. | Affects head clearance, wear life and cutting process. |
Dimension the slot from stable datums
Locate each slot from finished plate edges or another clearly identified datum. For repeated slots, use baseline coordinates rather than a long chain of hole-to-hole dimensions. Baseline dimensions reduce accumulated error and make inspection easier.
- Distance from a named end datum to the entry-opening center.
- Distance from a side datum to the slot centerline.
- Direction of the narrow slot relative to material flow and installation movement.
- Edge distance from the nearest part edge to the finished cutout.
- Pitch and quantity for repeated keyhole slots.
- Part orientation, wear face and chute-shell side.
For general replacement-liner field measurement, see How to Measure Chute Liners for Custom Replacement.
Show the retained direction explicitly
A keyhole slot is directional. Mark the plate movement from the entry opening to the retained position with an arrow, and identify upstream, downstream, top, bottom, left-hand and right-hand orientation where relevant. A photo without orientation marks can easily produce a mirrored part.
| Orientation mark | What it communicates |
|---|---|
| Installation arrow | Required plate movement after the fastener enters the large opening. |
| Material-flow arrow | Direction of abrasive material across the wear face. |
| Wear face / shell side | Which plate face is exposed and which face mates with the structure. |
| Upstream / downstream | Prevents reversing an asymmetric liner. |
| Part mark | Connects the physical liner to its drawing and installation location. |
Match the slot to the complete fastener assembly
The entry diameter should be checked against the maximum head, washer or retainer envelope, while the narrow slot should be checked against the shank, neck and required operating clearance. Also confirm the available gap behind the plate, clamp travel, tightening tool access and whether the final assembly prevents unintended reverse movement.
The drawing or RFQ should identify the approved fastener standard, material, nominal size, head style, washer or retainer, thread engagement, tightening requirement and anti-release method. Do not select slot dimensions from the bolt diameter alone.
Direction of service loads and material flow
Impact, sliding abrasion and vibration can move a liner if the fastening system loses clamp load. The installation direction should not create a simple path from the retained position back to the large entry opening under normal service loads. The equipment owner should review start-up, shutdown, blockage clearing and maintenance loads as well as steady-state flow.
If a keyhole system is not appropriate, compare Bolt-On Chute Liner Plates, Slotted Hole Chute Liner Plates, Countersunk Bolt Wear Plates, Plug Weld Chute Liner Plates and Stud-Backed Chute Liner Plates.
Tolerances and cut quality
Apply functional tolerances to the entry diameter, retention width, center location and direction. General plate-outline tolerances may not be suitable for the fastening feature. The required values should be based on the complete fit-up and inspection plan, not copied automatically from another component.
- Define whether dimensions apply before or after surface finishing.
- State whether thermal-cut edges require grinding, deburring or machining.
- Control excessive taper, dross and sharp transitions that could affect fit.
- Specify flatness only where it is functionally necessary.
- Identify critical dimensions for inspection records.
How to measure an existing keyhole-slot liner
Clean the opening and measure an unworn area whenever possible. Record the entry diameter in more than one direction, the narrow slot width at several positions, the center-to-end length, slot direction, plate thickness and the position from stable edges. Photograph the liner with a scale and orientation marks.
If the old slot is elongated, cracked or flame-cut in the field, do not treat the damaged profile as the original design. Compare it with the mating structure, fastener assembly, neighboring liners and any historical drawing. Record both the observed condition and the proposed replacement dimension.
Pre-production and inspection checks
| Stage | Recommended check |
|---|---|
| Drawing review | Confirm D, W, L, transition geometry, orientation, datums, grade and thickness. |
| Fastener review | Confirm entry clearance, retained fit, clamp range and anti-release method. |
| First-piece inspection | Measure the critical geometry and verify direction before batch cutting. |
| Fit check | Use the approved fastener or a controlled gauge representing its functional envelope. |
| Final inspection | Check quantity, part marks, burr removal, dimensional records and packing identification. |
Use the Chute Liner Inspection Checklist Before Shipment and define any required quality documents for custom chute liners in the purchase order.
Keyhole-slot liner RFQ checklist
- 2D drawing or dimensioned sketch with revision number.
- Material grade, thickness and plate quantity.
- Entry diameter, retention width, length and transition geometry.
- Slot coordinates from stable datums, pitch and quantity.
- Installation movement, material flow, wear face and shell side.
- Complete fastener assembly and required retained clearance.
- Edge finish, critical tolerances and inspection requirements.
- Working material, particle size, impact, vibration and temperature.
- Photos of the installed location and worn parts, with orientation marks.
Related resources
- Custom Processed Chute Liner Plates
- Modular Chute Liner Plates
- Conveyor Transfer Point Wear Liners
- Hopper Liners
- Manufacturing Capabilities
Send your keyhole-slot liner drawing for review
Attach the plate drawing, slot dimensions, fastener details, installation direction, material grade, thickness, quantity and service conditions. We will review the drawing as an RFQ and confirm the manufacturing scope.