Impact strip for impact pulverizers
United States Patent Kunstovny et al. Apr. 29, 1975 IMPACT STRIP FOR IMPACT 2.635.817 4/1953 Long 241/300 x PULVERIZERS 2.963.782 12/1960 Donnelly... 29/l95 A X 3.29l.653 12/1966 Eilers 29/191.2 x [75] Inventors: F rd nand Kunst ny. u k. 3.454.375 7/1969 Montgomery.... 29/191.2 Gottfried Mayerbiick; Johann 3.529.677 9/1970 Stephenson 29/191 Rossmann, both of Kapfenberg, all 3.592.l28 7/197] French 241/300 X f Austria 3.767.127 10/1973 Wood 241 300 [73] Assignee: Gebr. Biihler &amp; Co. AG, Vienna, Primary Examiner Aen B. Curtis Austrla 1 221 Filed: Sept. 21. 1973 AB TR T An impact strip for impact pulverizers for crushing [2] 1 Appl&#39; 399433 hard materials, the strip being made of an ironchromium-carbon alloy. such alloy may, for example, [52] US. Cl. 241/300 consist of 0.6 to 3.5 percent carbon to 5 to 30 percent [5 l Int. Cl. B02c 13/28 chromium, up to 2 percent nickel, up to 3 percent mo- [58] Field of Search 241/300; 29/l96.6, 191.2, lybdenum, up to 2 percent manganese, and up to 2 29/l91.6, 195 A percent silicon, the rest iron and impurities. The edges or edge regions of the impact strip to be subjected to [56] References Cited impact and wear are reinforced with plates of sintered UNITED STATES PATENTS hard metal- 2.4l4.23l l/l947 Kraus 29/195 A X 8 Claims, 2 Drawing Figures PATENTEDAPRZS I975 SHEET 2 OF 2 IMPACT STRIP FOR IMPACT PULVERIZERS The present invention relates to impact strips for impact pulverizers in which cement, rock, earth, ores, etc. are crushed.  
  Impact strips for these pulverizers are normally formed from iron-chromium-carbon alloys. Because of the high abrasion stresses, involved in the impact strips, ledeburitic cast alloys are used for this purpose, such alloys consisting of 0.8 to 3.5 percent carbon, to 30 percent chromium, up to 2 percent nickel, up to 3 percent molybdenum, up to 2 percent manganese, up to 2 percent silicon, the rest iron and minute steel impurities. Here and throughout the specification all percentages are given by weight.  
  Impact pulverizers are amongst the most modern apparatuses for preparing rocks and gravel in the mining, building, and cement industries. The enormous abrasion stresses, caused by the hard material to be processed, and the high contact speed of the pulverizing material with the abrasion sections of the impact pulverizer, have called for new wear-resistant materials. After working time of 50 to 70 hours in the case of pulverizing quartz rock, materials of the conventional type, such as, for example, ledeburitic chromium alloys, reveal defects in the impact strips which raise doubts regarding their further use. Replacement of the impact strips obviously results in time and output capacity being lost.  
  Applying hard metal alloys by welding onto the edge of the impact strip which are subject to wear had only slight success, since it was not possible to apply these wear layers in a sufficient number of strata. The wear layers proved to be too thin and were therefore soon worn out. Furthermore, with these welding attempts the composition of the body of the impact strip had to be altered in terms of quality. It was only possible to weld onto a mild, low-carbon steel which was unusable in next to the welded-on layer because it was eroded by the mineral material being ground.  
  For financial reasons, it was not possible to carry out exact field tests, so methods of testing were devised which would simulate the abrasion stresses occuring during operation in order to compare the wear of hard metal plates with that of plates made of wear-resistant iron-chromium-carbon alloys.  
  In a conventional sand-blast installation, hard metal plates (A) consisting of 85 percent tungsten, 10 percent cobalt as the bonding metal, and the rest iron and impurities resulting from manufacture, were compared with 10 steel test pieces (B) consisting of 3 percent carbon, 12 percent chromium, 2 percent molybdenum, 1 percent manganese, 1 percent silicon, the rest iron and minute steel impurities. All of the test pieces A and B were X 20 X 5mm. These test pieces were beaten or blasted with 0.5 mm chilled-cast-iron particles at a speed of 50 m/s for periods of 15 minutes. The first test period produced grit-blasted surfaces in the case of both group of test pieces.  
  The steel plates (B) after the second test period showed signs of erosion which in certain parts were up to 0.5mm deep. The hard metal plates (A) exhibited unchanged polished surfaces at the stressed parts.  
  In the case of the steel plates (B) the third test period produced individual abrasion indentations of 0.75mm. The general loss of material from such steel plates amounted to about 12 percent at the end of this test pe riod.  
  In the case of the hard metal plates (A) the fourth test period resulted in the edges being rounded off to a noticeable extent. The impact surfaces themselves were metallically smooth without any noticeable defects. After the fourth test period the steel plates (A) had suffered quite noticeable uneven erosion, a weight check showing an increasing weight loss in the range from 15 to 20%.  
  In view of the advanced erosion of the steel plates (B) experiments were only continued with the hard metal plates (A).  
 Further Tests with the Hard Metal Plates (A) In the case of the hard metal plates, only after the tenth test period were the first noticeable through a loss in weight in the range of 3 to 7 percent.  
  Two further test periods, thus after the twelfth period, showed no further noticeable erosion defects. Weight measurements, relating to all 10 plates (A), showed a total loss of 6 percent.  
  On the basis of these experiments it can thus be assumed that impact strips reinforced with hard metal plates (A) can be produced with a much longer working life under extreme erosion stresses, compared with the conventional wear-resistant steel.  
  The present invention thus provides an impact strip for impact pulverizers for crushing hard materials, the  
 strip being made of an iron-chromium-carbon alloy.  
 Such alloy, for example, may consist of 0.6 to 3.5 percent carbon to 5 to 30 percent chromium, up to 2 percent silicon, the rest iron and impurities, the edges or edge regions to be subjected to impact and wear being reinforced with plates of sintered hard metal. The hard metal plates are preferably fastened to the wear-resistant upper edge by hard solder or dovetail recesses through the use of turn screws. Depending upon the kind of pulverizer and the speed of pulverization, it is possible to replace the hard solder by metal adhesive, bearing in mind the local temperature rises. In the case of smaller pulverizers the hard metal can also be fastened to the impact strip merely by adhesion and without any turn screw or&#39;screws.  
  The invention will be described further, with reference to the accompany drawings, in which:  
  FIG. 1 is a fragmentary view in perspective of a reinforced impact strip; and  
  FIG. 2 is a vertical cross-section through part of the strip shown in FIG. 1.  
 FIG. 1 shows a preferred embodiment of a hard metal reinforcement for an impact strip for an impact pulverizer which rotates in the direction of the arrow. Plates 1, 2, 3 of hard metals are mounted on an impact strip 5.  
  FIG. 2 is a vertical cross-sectional view through the hard metal reinforced wear edge of the impact strip 5. The hard metal plates 1, 2, 3 are arranged as shown. The screw head 4 of a turn screw 6 and a spring washer 7 fix each plate on the body of the impact strip 5. The hard metal plate 2 is fastened on the screw head 4 by means of hard solder. The plates 1 and 3 are received within dovetailed recesses, as shown, the plates 1 and 3 being held fast in the body 5 by means of surface pressure excited thereon by screw 6 acting through plate 2.  
  Although the invention is illustrated and described with reference to one preferred embodiment thereof, it  
 is to be expressly understood that it is in no way limited to the disclosure of such a preferred embodiment, but is capable of numberous modifications within the scope of the appended claims.  
 What is claimed is: I  
  1. An impact strip for impact pulverizers having an impact edge with two sides defining an apex region, which is covered with plates of sintered hard metal, said impact strip having a recess at both sides thereof, a plurality of lateral sintered hard metal plates mounted in said recess at both sides of said impact edge, a plurality of bolts threadably mounted on said impact strip, each bolt having a head portion which overlaps the adjacent lateral plates and thus holds them in position in said recess.  
  2. The impact strip as set forth in claim 1, wherein said impact strip has a corresponding plurality of threaded bores in which said plurality of bolts are mounted and lock-washer means disposed between said bolts and impact strip.  
  3. An impact strip as claimed in claim 1, wherein the hard metal plates consist of 85 percent tungsten, percent of the bonding metal cobalt, and the remainder 4 iron and impurities, all percentages being by weight.  
  4. An impact strip as claimed in claim 1 wherein the impact strip has a body made of an alloy consisting of 0.30 to 0.70 percent carbon, 0.] to 2 percent silicon, up to 3 percent tungsten, up to 3 percent chromium, up to 3 percent molybdenum, up to 2 percent manganese, and up to 0.5 percent vanadium, the remainder being iron and impurities, all percentages being by weight.  
  5. The impact strip as set forth in claim 1, wherein said head portions of said bolts are soldered to lateral hard metal plates.  
  6. The impact strip as set forth in claim 1, wherein said recess is dovetailed and said hard metal plates have mating dovetailed shapes.  
  7. An impact strip as claimed in claim 1, in which said bolt includes a spring washer and further includes an additional plate fastened onv the bolt head by being soldered thereto.  
  8. An impact strip as claimed in claim 7, wherein said lateral plates are received in dovetailed recesses in the body of the impact strip, and parts of the said additional plate overlie portions of said lateral plates.