How to Judge the Qualification of Fixed Jaw Plate Quality? Practical Inspection Guide for Procurement and Acceptance

1. Visual Preliminary Inspection: Rapid Screening Upon Arrival

Visual inspection requires no professional instruments and serves as the first check after delivery. It focuses on eliminating fatal casting defects. Inspection covers crushing working surfaces, tooth roots, rear mounting surfaces and areas around bolt holes where stress concentrates.

1. Crack Inspection

   No cold cracks, hot cracks or cold laps are allowed on tooth crests, corners of tooth roots, plate edges and mounting holes. Tiny cracks will keep expanding under continuous load and cause fracture during operation. A magnifying glass can be used to observe subtle linear marks; castings with linear gaps are not suitable for put-in service.

2. Hole and Inclusion Defects

   Large pores, shrinkage cavities, sand inclusions and slag holes are prohibited on working surfaces. According to relevant standards, concentrated holes with diameter greater than 3 mm are not allowed on working surfaces. The quantity and distribution of scattered small sand holes and pores shall comply with requirements specified in technical agreements. Hole areas form stress concentration points and accelerate wear and block spalling.

3. Tooth Profile and Surface Forming Condition

   The contours of tooth crests and troughs shall be intact without insufficient pouring, material shortage or protruding burrs. Distorted tooth profiles change the stress mode of material crushing, affect crushing effect and aggravate local wear. Gates and risers shall be smoothly ground after cutting without sharp edges to avoid scratching the frame during assembly.

4. Surface Treatment Condition

   Qualified castings shall be cleaned by shot blasting without thick bonded molding sand on the surface. High manganese steel fixed jaw plates feature uniform metallic luster. Large-area oxidation scale on local areas usually indicates deviation in pouring temperature and cooling process.

2. Verification of Dimensions and Geometric Tolerances to Ensure Assembly Matching

Dimension deviation is an easily overlooked indicator. Substandard dimensions lead to excessive fitting gaps between fixed jaw plate and frame, uneven bolt stress, loosening during operation and local overload impact.

1. Basic Overall Dimensions

   Calipers and tape measures are adopted to measure the total length, width and thickness of the plate. Measured values shall fall within the tolerance range specified in drawings. Uneven thickness causes stress offset and aggravated unilateral wear.

2. Mounting Structural Parameters

   Measure the aperture, hole spacing and position tolerance of mounting bolt holes; the flatness of the back plate shall be controlled within a reasonable range. Uneven back plate results in insufficient contact area, and crushing impact load concentrates on partial regions.

3. Recheck of Tooth Profile Parameters

   Detect tooth crest angle, tooth pitch and tooth height against drawings. Deviations of tooth profile parameters not only affect discharge particle size, but also change stress distribution on jaw plates. For customized fixed jaw plates, tooth profile templates must be checked to confirm forming dimensions.

Practical Tip: Dimensions of new and old jaw plates cannot be directly compared. Reasonable tolerance exists for molds of different batches. Equipment drawings or manufacturer’s technical drawings shall be taken as the benchmark for judgment.

3. Material and Mechanical Property Testing to Distinguish Raw Material Quality

Qualified appearance only reflects forming status. Chemical composition and heat treatment process determine wear resistance and impact resistance, which are also the links where inferior fixed jaw plates are prone to cutting corners. Mainstream materials on the market include ZGMn13 high manganese steel, modified Mn13Cr2 high manganese steel, bimetallic composite material and low-alloy cast steel. Acceptance indicators vary for different materials.

1. Verification of Chemical Composition

   On-site direct-reading spectrometer sampling test is recommended when conditions permit. For conventional ZGMn13 high manganese steel, manganese content ranges from 11% to 14%, carbon content from 0.9% to 1.4%; impurity elements including sulfur and phosphorus shall be controlled below standard limits. Some manufacturers reduce manganese content and use ordinary cast steel to replace high manganese steel, leading to significantly decreased wear resistance.

2. Hardness Test

• ZGMn13 high manganese steel: After standardized solution annealing treatment, the Brinell hardness of matrix reaches HB 180~230, and wear resistance is obtained through work hardening. Excessively high delivery hardness indicates unqualified heat treatment, reduced toughness and weakened impact resistance.

• High chromium cast iron and composite wear-resistant fixed jaw plates: Hardness indicators shall comply with bilateral technical agreements.

  Testing points are suggested to be scattered at tooth crest, tooth root and the middle of plate body for data comparison.

3. Metallographic Structure Evaluation (In-depth Sampling Inspection)

   The ideal metallographic structure of high manganese steel fixed jaw plate is single-phase austenite. Mass precipitation of network carbide reduces impact toughness. For bulk procurement, samples can be sent for inspection to verify whether water toughening heat treatment meets standards. High manganese steel without qualified water toughening treatment is vulnerable to fracture during service.

4. Non-Destructive Testing: Detect Hidden Internal Defects of Castings

Many fixed jaw plates have intact appearance but internal shrinkage porosity and internal cracks, which suffer sudden damage after short-term operation. For large-scale production lines and high-impact working conditions, additional non-destructive testing is recommended.

1. Penetrant Testing (PT)

   Suitable for detecting tiny surface and near-surface cracks at tooth roots and hole positions, and preferred for high manganese steel castings.

2. Ultrasonic Testing (UT)

   Detect internal shrinkage cavities, large-area shrinkage porosity and internal cracks inside the plate body. Tooth sections and thickened support areas are key testing regions. Castings with extensive internal porosity have insufficient bearing capacity.

   For small and medium batch procurement, sampling inspection can be agreed with manufacturers. For long-term bulk procurement, inspection reports can be included in delivery documents.

5. Verification of Documentation to Realize Product Traceability

Formal manufacturers shall provide complete supporting documents upon delivery, which also serve as important basis for quality judgment:

1. Material quality certificate and melting analysis report;

2. Heat treatment process records (water toughening curve shall be verified for high manganese steel);

3. Dimension inspection records and appearance self-inspection sheets;

4. Product marking: Material grade and model shall be cast on the casting body for subsequent traceability.

   Products without valid material certification documents carry risks of inconsistency between material and contract agreement.

6. Auxiliary Verification through Commissioning (Reference for Long-term Procurement)

When cooperating with new suppliers for the first time, on the basis of qualified static inspection of all items, small-batch trial operation can be carried out. Two sets of data shall be tracked continuously as reference for long-term supply:

1. Wear mode: Uniform abrasion is normal wear. Tooth root cracking and block spalling within a short period indicate insufficient toughness or internal defects. Local rapid concave wear can be analyzed for material adaptability combined with material hardness.

2. Abnormal operating noise: If abnormal impact noise occurs during crushing operation after assembly, check assembly gap, and reversely verify dimensional precision of jaw plates.

Conclusion

The qualification judgment of fixed jaw plate cannot rely merely on price or appearance. A hierarchical acceptance system shall be established: Conduct appearance and dimension preliminary inspection upon arrival; carry out hardness and material sampling inspection for important projects; add non-destructive testing under heavy-load working conditions, and complete document traceability.

Different crushed materials (limestone, granite, basalt), feed particle sizes and impact loads impose different requirements on fixed jaw plate materials. Even if all testing indicators meet standards, materials shall be selected according to working conditions.

If you are purchasing fixed jaw plates and have questions about material matching for current working conditions, drafting technical agreements for acceptance indicators, or require tooth profile parameter optimization of fixed jaw plates and estimation of wearable part replacement cycles, welcome to consult for technical solutions and quotation reference.