crack of cast steel pulley

crack of cast steel pulley

Causes and Solutions for Cracks in Cast Steel Pulley Production

Cast steel pulley in the production process, each process and operation are very important, if the operation is not standardized, not in place, it will affect the quality of the product. Crack is one of the common problems in the production of cast steel pulley. So, what is the cause of the crack in the production of cast steel pulley? What are the solutions?

Reasons for cracks in the production of cast steel pulley:

The causes of cracks in cast steel pulley castings are roughly divided into the following five points:

1. The crack has no small relationship with the structure of the cast steel pulley. If the cross-section changes suddenly or the roundness of too many parts is too small, it is easy to cause cracks.

2. There are problems in the casting process, and there are more defects on the surface or inside of the cast steel pulley casting.

3. Stress relief annealing is not carried out in time after pouring cooling.

4. During the casting cooling process, the cooling speed of molten steel is too fast.

5. The section of the casting changes too suddenly, or the corner of the excessive part is too small.

The solution of the crack in the production of cast steel pulley

In order to prevent cracks in the production process of cast steel pulley, high-quality casting technology is needed, as well as the rationality of the design of the casting itself to solve this problem. The following are some solutions to cracks in the production of cast steel pulleys.

1. Improve casting wheel structure

The wall thickness of the cast steel pulley should be uniform, and the corner should be transitional rounded to reduce stress concentration. The spoke can be curved.

2. Improve the melting quality of alloy materials

Refining and initial processes are used to remove oxidizing inclusions and gases from the metal industry. Control the content of harmful impurities and adopt reasonable melting process. While preventing the formation of hot cracks, it is also necessary to prevent the formation of cold cracks, ensure the correctness of the casting process, and make the castings realize synchronous solidification.

3. Using the correct casting process is not only conducive to preventing hot cracks, but also helps to prevent cold cracks

Firstly, the position and size of the sprue should be set reasonably to make the cooling rate of each part of the casting as uniform as possible and reduce the tendency of cold crack.

Secondly, the residence time of the casting in the sand mold is determined correctly; Sand mold is a good insulation container, which can further homogenize the temperature of the thicker and thinner parts of the casting, reduce the temperature difference between them, reduce the thermal stress, and reduce the tendency of cold cracks. Prolong the residence time of the casting in the mold, so as not to cause large internal stress in the casting too early, and produce cold cracks.

The effective measures to prevent cold cracking of castings due to shrinkage stress are to increase the yield of sand mold and sand core, remove the press iron early after casting solidification, and loosen the locking device. In the process of sand dropping, cleaning and handling of cast steel pulley castings, collision and extrusion should be avoided to prevent cold cracks from gradually occurring.

4. Aging heat treatment

The pulley with large casting stress should be subjected to aging heat treatment in time to avoid cold cracks caused by excessive residual stress. Sometimes, after cutting the riser or welding, an aging heat treatment is also carried out.

Depending on the requirements, the method used will be different. The cast steel pulley is made of a suitable steel metal, melted, and then cast, and then subsequent processing. Casting production should also comply with the specifications, otherwise it will make the cast steel pulley in the production of cracks and other defects, and then cause scrap.

Scrap standard for cast steel pulleys

1. Cracks appear (shall not be repaired);

2. Uneven wear of wheel groove up to 3mm;

3. The wear of the groove wall thickness reaches 20% of the original size;

4. The diameter of the bottom of the groove is reduced by 50% of the diameter of the wire rope due to wear;

5. Other eligible for scrapping.

6. Block maintenance, single beam bridge crane to remove and repair the block, check the crack;

7. Pulley groove maintenance, shaft hole inspection, assembly, pulley shaft shall not have cracks, journal shall not wear the original diameter of 30%, conicity is not greater than 5%, more than this value should be replaced;

8. Check the groove shape of the pulley with the template, and the radial wear should not exceed 30% of the wall thickness, otherwise it should be scrapped. Shall not exceed the standard can be repaired, after overhaul check with the template, the bottom and side clearance should not be greater than 0.5mm, the deviation between the wheel groove line and the pulley line should not be greater than 0.2mm, the deviation between the rope groove and the contour end face should not be greater than 1mm;

9. After the overhaul of the single beam bridge crane, the shaft hole is allowed to have a defect of not more than 0.25 square centimeters, and the depth should not exceed 4mm; After assembly, it should be able to rotate flexibly by hand, and the lateral swing should not exceed D/1000, D is the nominal diameter of the pulley;

10. Cast steel pulley in the production will also cause scrap, resulting in defects such as porosity, shrinkage, sand holes, sand and cracks, casting defects have been the foundry industry can not avoid and difficult to solve the problem. The conventional method of repairing unqualified castings is mainly welding repair, which requires skilled workers, time consuming, and consumes a lot of materials. Sometimes affected by the material of the parts, welding will also lead to increased damage, resulting in the scrap of the cast steel pulley.

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