In the installation of refractories (خصوصاً induction furnace linings), Pneumatic Rammers و الهزازات الكهربائية are the two core tools. They have distinctly different effects on the density distribution and the quality of interlayer bonding.
Below is an in-depth comparison of these two tools regarding كثافة و anti-lamination measures, along with practical operational recommendations:
1.Core Comparison: Impact on Lining Density
| ميزة | Pneumatic Rammer | Electric Vibrator |
| مبدأ العمل | Impact Force: Uses the reciprocating motion of a piston to generate high-frequency shock waves, physically “packing” أو “smashing” the material solid. | Vibration Force: Uses centrifugal force or linear vibration to reduce friction between particles, causing the material to “flow” and rearrange itself naturally. |
| Density Characteristics | Locally High, Overall Fluctuation: Single-point impact is immense, creating high surface hardness. لكن, it relies heavily on the operator, risking uneven density (ال “post-hole” أو “plum blossom” تأثير). | Overall Uniformity, Dead Zone Risk: Density distribution is very uniform, eliminating human error. لكن, vibration transfer may be insufficient in corners or complex shapes. |
| Segregation Risk | Risk of Grain Crushing: Prolonged fixed-point ramming can crush aggregates, destroying the particle size distribution (grading). | Risk of Particle Segregation: Excessive vibration causes large particles to sink and fines to float, forming a fine-rich layer (a breeding ground for cracks). |
| السيناريوهات المعمول بها | Furnace bottom repairs, corners, spouts/nozzles; also used for full furnace installation when specific molds are unavailable. | Large-scale standardized installation of furnace walls/bottoms; typically used with a dedicated steel former (crucible mold). |
2.Focus Analysis: Why do “Lamination Cracks” occur?
In layered construction (adding material layer by layer), Lamination Cracks are the most critical hazard. This is typically caused by the “Interface Effect”:
- ال “Hard Shell” تأثير: After a layer is rammed, a hard, smooth, and dense shell forms on its surface.
- Fines Enrichment: Especially when using vibrators, fine powder floats to the surface. This layer lacks aggregate support and has high shrinkage during sintering, leading to separation.
- Lack of Bonding: New loose material cannot embed into the already dense underlying surface—much like spreading sand on smooth ice, there is no “bite” or mechanical interlocking force.
3.الحلول: How to Prevent “Lamination Cracks”
While the specific measures differ based on the tool, the core logic for both is to break the interface.
أ. For Pneumatic Rammers (Impact Type)
Pneumatic ramming easily creates a “smooth hard shell,” so physically disrupting the surface هو المفتاح.
- Scarifying (Roughening):
- Before adding new material, you must use a pickaxe or a specialized rake to loosen/roughen the previously rammed surface (تقريبا. 10-20mm deep).
Taboo: Never add new material directly onto a smooth, hard surface.
- Angled Ramming:
- Do not only ram vertically. Adjust the angle slightly so the edge of the hammer head disrupts the surface structure, promoting the embedding of particles between layers.
- Control Layer Thickness:
- It is recommended to keep the loose material thickness under 100mm. Too thick leads to loose bottoms; too thin creates too many interfaces.
ب. For Electric Vibrators (Vibration Type)
Electric vibration easily causes “fines to float,” so managing the fine-rich layer هو المفتاح.
- Scraping off the Fine Layer: After each vibration cycle, a layer of fine powder slurry (a few millimeters thick) often forms on the surface. This must be scraped off and discarded until coarse aggregates are exposed.
- Surface Scratching: Before adding new material, use a sharp tool to create grid-like grooves (>5mm deep) on the lower layer to increase mechanical interlocking.
- التشغيل المستمر: Minimize the downtime between layers. If the next layer is added and vibrated while the previous layer is not yet fully “set,” the materials will fuse naturally via “liquefaction” caused by the vibration waves.
- De-airing (Forking): After adding material but before vibrating, insert a fork into the loose material to release air pockets, preventing an “air curtain” from forming between layers.
Summary Recommendations
- For Density: If you seek maximum overall uniformity and efficiency (especially for large furnaces), Electric Vibrator + Steel Former is the first choice.
- For Detail Control: In stress concentration areas like the bottom-to-wall connection or the taphole, use a Pneumatic Rammer for reinforcement.
- The Anti-Crack Core Rule: Regardless of the tool, “Scarifying/Scraping” هو only و إلزامي standard action to prevent lamination cracks.
