What Are Jaw Crusher Jaw Plates and What Do They Do?
Jaw crusher jaw plates (jaw dies) are the main wear parts that come into direct contact with the material in the crushing chamber and actually perform the crushing work. A jaw crusher has two basic jaw surfaces: one fixed and one moving. The fixed jaw is mounted on the frame and the moving (swing) jaw on the pitman. The material is reduced by being squeezed between these two surfaces. For this reason the geometry, material, fitting quality and wear condition of the jaw plates have a direct effect on capacity, product shape, power draw and total operating cost.
Jaw plates are not merely a consumable that wears out; they also define the crushing behaviour. When the right profile is not selected, plates are not fitted correctly or are not turned/replaced on time, crusher efficiency drops, material slippage increases, the chamber is loaded unevenly and undesirable stresses can develop in the frame and pitman. For a broader view of how jaw crushers work, how they are set and how they are maintained, the guide What Is a Jaw Crusher? Working Principle, Setting, Operation and Maintenance Guide is also a useful reference.
Jaw plates are mostly made of manganese steel. Depending on the application, grades with different manganese contents such as Mn13, Mn18 and Mn22 may be used. The main advantage of manganese steel is that its surface work-hardens under impact and compressive loading. This property is particularly important in applications with large feed and impact loads. However, the highest manganese content is not automatically the best choice for every application; feed structure, rock hardness, abrasiveness, moisture, fines content and the crusher setting range must be assessed together.
Design, Fastening and Profile Types
Jaw plates generally have a crushing profile on the front face and seating and clamping surfaces on the back. The fixed jaw plate is secured to the crusher frame and the moving jaw plate to the pitman with wedges and fasteners. The purpose of this fastening is to stop the plate from shifting during operation, spread the load evenly and reduce local impact on the back seating surfaces.
Clean and even seating surfaces are critical. Rock dust, crushed fines, rust scale or burrs left on the back face prevent the plate from seating fully. As a result the plate does not carry the load evenly, wedges loosen faster, bolt loads become unbalanced and the risk of breakage rises.
The main jaw plate profile types are:
- Standard profile: A balanced choice for general-purpose applications. Preferred in most quarry and aggregate applications.
- Sharp-tooth profile: Can improve grip with slippery or hard-to-grip materials and help reduce slippage with finer feed.
- Heavy-tooth profile: Can provide more aggressive grip with coarse, hard feed. Used in high-impact applications.
- Flat plate: May be preferred in certain special applications where the crushing behaviour needs to be controlled differently.
Looking only at wear life is not enough when choosing a profile. The friability of the material, the feed size, the required product, the fines content and the jaw setting must be considered together. The wrong profile can cause not only capacity loss or early wear but also material bouncing in the chamber and irregular crushing.
Wear Mechanism and the Most Common Failure Modes
Jaw plate wear usually develops from the combined effect of abrasion, high surface pressure and repeated impact loads. In a jaw crusher, material is nipped at the top of the chamber, compression increases as it moves down and crushing is completed. For this reason the heaviest wear in most applications is seen in the lower third of the plate. Especially near the discharge opening, teeth round off faster, thickness decreases and the profile deteriorates.
Typical wear and failure modes are:
- Reduced tooth height: Grip decreases and material slippage increases.
- Thinning in the lower zone: As the manufacturer’s limit is approached, plate strength decreases.
- Uneven surface wear: Can indicate poor feed distribution, one-sided loading or loose fastening.
- Cracks: Can occur due to impact loads, loose fitting, tramp metal or the plate reaching the end of its life.
- Movement or marking on the seating surface: Develops because of loose wedges, a dirty back face or incorrect torque.
- Breaking or corner fracture: Can result from sudden overload, incorrect lifting, impact during fitting or serious foreign objects.
With symmetrical jaw plates, the common practice is to turn the plate over when tooth height has fallen to roughly half. This helps use the plate life more efficiently. However, the decision to turn should not be based on visual habit alone; thickness, crack inspection, the condition of the back face and the manufacturer’s instructions must be taken into account.
Signs of Wear and Failure
The signs most often noticed on site by operators and maintenance teams are:
- Loss of capacity and feed moving through the chamber with more difficulty
- Material slipping or bouncing back on the jaw surface
- Fluctuations in product size
- Abnormal vibration or metallic knocking noise
- Frequent loosening of wedges and fasteners
- Unbalanced amperage draw or irregular loading
- Marked thinning, cracks or edge breakage in the lower part of the plate
These signs do not always mean the plates must be replaced, but they always require a detailed inspection. For example, vibration may be caused not only by wear but also by a loose wedge, incorrect feeding, play on the pitman side or a bearing problem.
How Should Inspection and Measurement Be Done?
The biggest mistake in assessing jaw plates is deciding by eye alone. The correct approach is to interpret visual inspection, measurement, fastening checks and operating data together. The following points should be followed during inspection:
- Safe shutdown and LOTO: No inspection should be made before energy sources are isolated.
- Cleaning: The crushing chamber and access areas should be cleared of accumulated material.
- Visual inspection: Tooth profile, cracks, breaks, gouges and plate displacement are checked.
- Thickness measurement: The remaining thickness is checked at critical points with callipers, a template or the measuring method recommended by the manufacturer.
- Tooth height assessment: The time to turn symmetrical plates is determined.
- Fastening check: Wedges and bolts are checked for looseness, wear or deformation.
- Back seating marks: During removal, the seating surface is examined for uneven contact or crushing.
As a replacement criterion, replacement is generally planned when the plate thickness falls to the manufacturer’s lower limit. In many applications this limit is taken as the thickness approaching roughly 40% of the new plate thickness; however, the dimension in the manufacturer’s manual must always be the basis for the final decision. If there is a crack, noticeable movement or damage that prevents safe seating on the back face, the plate must be replaced without waiting for the thickness limit.
| Inspection point | What to look for | Method | General assessment |
|---|---|---|---|
| Tooth profile | Rounding, loss of sharpness, reduced grip | Visual check, comparison with template | On symmetrical plates, turning is considered when tooth height falls to about half |
| Lower third | Rapid thinning, grooving | Spot thickness measurement | The most critical wear zone |
| Cracks | Surface or root cracks | Visual inspection on a clean surface, further testing if needed | If there is a crack, replacement has priority |
| Wedges and bolts | Looseness, deformation, wear | Torque check, visual inspection | Check after first fitting and periodically |
| Back seating surface | Dirt, rust, crushing, incomplete contact | Surface check during removal | Poor seating can accelerate plate breakage |
| Plate position | Displacement, poor seating | Reference line and visual check | If there is movement, act immediately |
Periodic Maintenance Plan
The aim of jaw plate maintenance is not just to use the part for longer; it is to run the crusher safely and steadily. The inspection interval depends on the abrasiveness of the material, the tonnage and the shift length. Very abrasive rock requires more frequent checks. The plan below gives a general framework; for machine-specific intervals, the manufacturer’s manual applies.
| Interval | Task | Method | Note |
|---|---|---|---|
| Every shift / daily | Visual wear check | Visual inspection with the chamber clean | Focus on the lower zone and tooth profile |
| Every shift / daily | Monitoring abnormal noise and vibration | Operator observation | May indicate a loose wedge or plate movement |
| Weekly | Wedge and fastener check | Torque wrench and visual inspection | Use the manufacturer’s torque values |
| Weekly / fortnightly | Tracking thickness and tooth height | Template, callipers or reference measurement | Monitor the wear trend |
| First run after plate fitting | Re-tightening | Torque check after the first approx. 8 hours | A critical step after the new plate has bedded in |
| During planned shutdowns | Removing and checking the back face, seating area and wedges | Detailed maintenance inspection | Hidden damage is found at this stage |
Keeping maintenance records is important. If you note how fast each side wears, when the plate was turned, how much tonnage it handled in which material and how many times wedges loosened, choosing the right profile and material becomes much easier.
Can Jaw Plates Be Repaired?
Jaw plates are basically replaceable wear parts. Some operations try hardfacing or local repairs on site; however, repairing manganese steel requires care. Unsuitable welding can adversely affect the metallurgical structure, create brittle zones and cause the plate to crack unexpectedly. For this reason the main solution for a cracked or excessively thinned plate is usually replacement.
Limited repair can be considered only with the manufacturer’s explicit approval, a suitable procedure and an experienced welder. Otherwise the safe approach is to check the plate, wedges and fasteners and renew them as a set when necessary.
Step-by-Step Jaw Plate Replacement and Turning
Replacement should not be thought of as simply removing and refitting. Correct preparation and checks are essential for a successful installation.
- Plan the job. The new plate set, suitable wedges, bolts, nuts, washers and lifting equipment should be ready. Part numbers and left/right orientation should be confirmed.
- Stop the crusher safely. Stop the feed, empty the crushing chamber as far as possible and isolate all energy sources with the LOTO procedure.
- Make access safe. Do not start removal without a suitable platform, lifting points and a team lifting plan.
- Loosen the fasteners. Wedges and bolts are loosened in a controlled way. Seized parts should be removed with suitable equipment, not forced.
- Remove the old plate. The worn plate is lifted out using lifting lugs or approved lifting points. Chains should not be attached at random.
- Clean the seating surfaces. The back surfaces on the frame and pitman are completely cleaned of rust, rock dust, oily dirt and burrs.
- Inspect wedges and fasteners. Fitting a new plate with worn or deformed wedges is wrong. Renew them as well if necessary.
- Fit the new or turned plate. Plate orientation, top/bottom position and profile alignment are verified. If a symmetrical plate is to be turned, the condition of the back face must be inspected carefully.
- Tighten wedges and bolts according to the manufacturer’s instructions. The final tightening torque must always follow the manufacturer’s manual.
- Check clearance and seating. Confirm that the plate is fully seated, has not shifted and that the wedge is bearing correctly.
- Run a trial. Run briefly at low load and watch for abnormal noise, vibration or movement.
- Re-tighten after the first run. After a new installation, wedge and bolt torques should be checked again after about the first 8 hours of operation.
When deciding between turning and complete replacement, consider not only tooth height but also the remaining thickness, the condition of the back face and how many times the plate has already been turned.
Common Mistakes
The mistakes that shorten jaw plate life and accelerate failures are very similar from site to site:
- Turning too late: Turning after the teeth are completely rounded reduces the benefit expected from the plate’s second use.
- Running with a loose wedge: One of the most critical mistakes. Movement damages the seating surface and can cause plate breakage.
- Constantly feeding fine material: Can impair the jaw’s ability to nip the material, increase slippage and create uneven wear.
- Feeding from one side: Creates excessive local wear on one jaw or one corner of the plate.
- Fitting onto a dirty back face: The plate does not seat fully and load distribution is disturbed.
- Replacing only the plate and leaving the old wedge: A worn wedge also causes the new plate to loosen early.
- Choosing the wrong profile: Can result in lost capacity, high power draw or excessive slippage.
- Skipping re-tightening after the first 8 hours: Fastenings can loosen after the new plate has bedded in.
Troubleshooting Table
| Symptom | Possible cause | Check | Solution |
|---|---|---|---|
| Metallic knocking in the jaw chamber | Loose wedge or plate movement | Check wedges, bolts and seating surface | Tighten, replace damaged wedges/bolts, remove and reseat the plate if necessary |
| Loss of capacity | Rounded tooth profile, wrong profile, excessively fine feed | Examine tooth height and feed structure | Turn or replace, improve feeding, select the correct profile |
| Fluctuating product size | Uneven wear, plate displacement, unbalanced feed | Visual check and measurement | Correct plate fitting, direct the feed, replace the plate if necessary |
| Rapid thinning in the lower zone | Normal wear, high abrasiveness, setting and feed effects | Thickness measurement trend | Planned replacement, profile/material optimisation |
| Crack formation | Overload, loose fitting, tramp metal, end of life | Examine crack location and propagation | Replace the plate, prevent tramp metal, review the fitting procedure |
| Frequent wedge loosening | Worn wedge, wrong torque, dirty back face | Check wedge shape and contact pattern | Renew the wedge, clean the surface, apply the correct torque |
| Material slipping in the jaw | Worn profile, unsuitable tooth type, very fine feed | Profile and feed analysis | Select a suitable profile, turn/replace, improve feed conditions |
What to Look for When Selecting and Buying Spare Jaw Plates
The lowest unit price for jaw plates does not always mean the lowest total cost. The following points must be assessed to choose the right part.
OEM or Aftermarket Parts
An OEM part offers an exact fit with the machine design and the manufacturer’s reference geometry. An aftermarket part can also be used successfully when produced by a reliable manufacturer with the right material, correct dimensions and proper quality control. The key point is that the aftermarket part matches not only in external dimensions but also in back seating surfaces, wedge contact areas, hole/slot positions and weight distribution.
Material Selection
The manganese steel grade should be chosen according to the application. When choosing between options such as Mn13, Mn18 and Mn22, the impact level, abrasiveness, feed size and operating regime must be considered. A very high manganese content gives an advantage in some applications, while in other conditions the expected work hardening may not develop. Material selection should be supported by operating data.
Dimensions and Tolerances
Not only the overall length and width of the plate matter, but also the flatness of the seating surface, the thickness tolerance and the wedge groove or contact surface dimensions. Seemingly small mismatches come back on site as fitting difficulties, seating with gaps or early loosening. The technical drawing reference, part code and crusher model must therefore always be matched.
Certificates and Traceability
It is good practice to ask the supplier for at least the material grade, casting/production lot information and basic quality records. Requesting certificates is especially important for operations that track tonnage regularly, as it allows performance to be compared between different lots.
When selecting parts, consider not only the plate but also the related wedges and fasteners. The product groups on the Jaw Crusher Spare Parts page can help you plan the other wear and mechanical parts that should be replaced together with the plates.
Safety: LOTO and Safe Intervention
Removing and fitting jaw plates is a high-risk maintenance task. Isolating the electrical supply alone is not enough. Mechanical movement, jammed material, lifting risks and parts under load must also be controlled.
- Apply LOTO: Isolate electrical, hydraulic, pneumatic and any other energy sources.
- Stop the feed and empty the crushing chamber: Jammed rock can create a risk of sudden falling.
- Use suitable lifting equipment: Use equipment rated for the plate weight and approved lifting points.
- Barrier off the work area: Unauthorised personnel must not approach.
- Watch out for pinch and crush points: Move in a controlled way when seating wedges and plates.
- Wear PPE: Hard hat, safety glasses, gloves, steel-toe boots and other suitable personal protective equipment are mandatory.
- Do not work alone: At least two authorised, communicating people should be present during removal and fitting.
The safety procedure should be carried out together with the site risk assessment and the manufacturer’s maintenance instructions. If the team lacks sufficient experience or suitable equipment, handing the job to a specialist service is safer and often more economical.
Frequently Asked Questions
When should jaw plates be turned?
For symmetrical plates, the general practice is to consider turning when tooth height has fallen to about half. However, the remaining thickness, any cracks and the manufacturer’s instructions must always be checked.
Is there a single thickness limit for replacing the plate?
No. In general practice, the thickness approaching about 40% of the new plate thickness can be considered critical; however, the exact limit depends on the crusher model and plate design. The manufacturer’s manual is the main reference.
Why do new plates need re-tightening shortly after fitting?
A new plate beds into its seat during the first run and the fastening system can settle slightly. That is why wedge and bolt torques should be checked again after about the first 8 hours.
Can the crusher keep running with a loose wedge?
No. A loose wedge causes plate movement and damages the seating surface. This can turn into much bigger damage in a very short time.
Why does constant fine feed cause problems?
Jaw crushers work most efficiently under certain nip and compression conditions. Excessively fine feed can make it harder for the teeth to grip the material, increase slippage and disturb the wear pattern.
Which profile is always the best?
There is no single best profile for every case. Standard, sharp-tooth, heavy-tooth or flat plates should be chosen according to material type, feed size, moisture, fines content and the target product.
Should a crack be repaired by welding?
Generally the safe solution for a cracked jaw plate is replacement. Unsuitable repair of manganese steel can create new fracture risks. Repair should only be considered with a controlled and approved procedure.
Spare Parts and Service for Jaw Crusher Jaw Plates
Based in Ankara, CSP Mühendislik supplies crusher wear and mechanical spare parts, including jaw plates for jaw crushers. Technical support can be provided on profile selection, material assessment and compatibility with your crusher model for both fixed and moving jaw plates. You can view the related product group on the JAW CRUSHERS page and our service support on the Service, maintenance and repair page.
For part replacement, on-site inspection, failure assessment or planned maintenance, it is important to consider the right plate, suitable wedges and fasteners, and fitting checks together. For a technical assessment or supply request, contact the CSP Mühendislik team via the Contact page.
