GB2126310A - Trimetallic cylinder - Google Patents

Abstract

A trimetallic cylinder according to the preferred embodiment of the present invention includes a mild or alloy steel cylindrical body (22) with stainless steel end rings (26) welded or otherwise suitably joined to each end of the body. A wear and corrosion resistant alloy lining (24) is provided for the composite cylinder, the combination resulting in improved corrosion resistance for the overall assembly. <IMAGE>

Description

SPECIFICATION Trimetallic cylinder This invention relates generally to steel cylinders lined with a hard, wear and corrosion resistant alloy and more particularly to such cylinders which include stainless steel end rings. Cylinders of the type described may be used in extrusion and injection molding equipment, in food processing and in a variety of other uses where cylinders having high strength and corrosion resistance are required.

Bimetallic cylinders have been employed in the plastic extrusion and injection molding industries for many years. For purposes of this specification, a bimetallic cylinder is one which includes a cylindrical body and a lining of a hard and wear and corrosion resistant metal oralloy. Bimetallic cylinders have become widely accepted because in extrusion or injection molding a screw forces a hot, molten plastic through a special shaped die and typically the plastics include abrasive filler materials. As a result of the high temperatures employed in the process, the abrasive fillers and the action of the screw itself, standard steel cylinders quickly wore or became corroded.

Kormann and Hirsch were pioneers in the development of bimetallic cylinders in the early 1930's and some oftheirwork is described in United States Letters Patent Nos. 2,049,913 and 2,046,914, each issuedjuly7, 1936. The processfor preparing bimetallic cylinders described in these patents comprises placing a steel cylinder in a horizontal position and loading the cylinder with a quantity of an alloy having a melting point of less than the cylinder itself.

The alloy hasgreaterwearand corrosion resistance propertiesthanthe cylinder. The ends ofthecylinder are closed bywelding caps overthem and the cylinder is gradually heated above the melting point of the lining material. The cylinder is rapidly spun about its axis to centrifugally spread the melted lining material overthe innersurface of the cylinder. The cylinder is then cooled gradually,theend caps are removed and laths and hones are used to finish the inside surface to the desired diameter and smoothness.

Avariety of different alloys have been used for the lining of bimetallic cylinders. Ferrous alloys were used by Kormann and Hirsch in the aforementioned Patent No.2,049,913 and by Saltzman in his U.S. Patent No.

3,658,515 issued April25, 1972. The ferrous materials have a hardness in the approximate range of 58-64 Rockwell C and exhibit good wear resistance when used in bimetallic cylinders. However, ferrous alloys are not particularly well suited for use in corrosive environments and attempts to improve corrosion resistance in ferrous alloys usually led to reduced wear resistance.

More recently, non-ferrous lining alloys have been developed for use in bimetallic cylinders. One type includes about 40% nickel, 45% cobalt 8% Chromium and 3% boron in addition to minor amounts of carbon, manganese, silicon, etc. Still more recently carbide particles have been mixed with the non-ferrous base metal to improve performance.One particularly useful carbide alloy is described in United States Letters Patent No.4,089,466 issued to the present inventors on May 1978. The latter contains 10-35% tantalum carbide ina matrixalloycomprising.16- .35% carbon, 28.5-34.6 nickel, 9.5-7.5% chromium and 28.5-42.0% cobalt (all weights being expressed in weight percent). Stil more recently, an improved alloy has been marketed which includes a mixture of at least two carbides admixed with a nickel-cobalt base alloy.

While the state of the art is well advanced in terms of lining alloys and the design thereof for particular end use applications, little attention has been directed to the performance ofthe overall cylinder. Moreover, in recent years bimetallic cylinders have been used in a variety of applications other than injection molding and extrusion. For example, such cylinders are rapidly replacing unlined orchome plates stainless steel cylinders in the food and drink processing industries.

The introduction of bimetallic cylinders for such end uses has, however, led to additional problems which have not been overcome prior to the present invention. In many food applications, the cylinders are subjected to daily acid washings, e.g. for 45 minutes at 7940C (175"F). Also, in some applications, the entire cylinder may be surrounded by a cooling fluid or heating liquid and exterior corrosion has resulted.

Corrosion is most noticeable and most troublesome at the ends of the cylinder where they may be clamped or supported in the particular apparatus in which they are used. Such corrosion problems have hindered the commercial acceptance of bimetallic cylinders in new industries.

It is a primary object ofthe present invention to provide a trimetallic cylinder which overcomes the above-noted disadvantages ofthe prior art.

Another object of the present invention is to provide a trimetallic cylinder having improved corrosion resistance.

Afurther object of the present invention is to provide a trimetallic cylinder which has desirable heat transfer characteristics and corrosion resistance when the cylinder is surrounded by corrosive fluids or gases.

Astillfurtherobjectofthe present invention is to provide a trimetallic cylinder having improved corrosive resistance near the ends of the cylinder.

Howthese and other depicts ofthe invention are accomplished will be described in the following specification taken in conjunction with the drawings.

Generally, however, they are accomplished by provid ingatrimetalliccylinderwhichincludesa mild steel or alloy barrel and end rings constructed of stainless steel or other corrosion resistant material. The assembly is lined with a wear and corrosion resistant alloy, such as those which have previously been used to prepare bimetallic cylinders. Preferably, the lining is accomplished using centrifugal coating as is known to the art.

Figure 1 is a perspective view of a typical bimetallic cylinder as is known to the prior art; Figure 2 is a partial perspective view of a trimetallic The drawings originally filed were informal and the print here reproduced is taken from a later filed formal copy. cylinder prepared according to the present invention; Figure 3 is a longitudinal section through one end of the cylinder shown in Figure 2; and Figure 4 is a partial longitudinal section of a trimetallic cylinder according to the present invention showing a differentweld technique for joining the stainless steel end ring to the barrel ofthe cylinder.

Figure 1 illustrates a typical bimetallic cylinder 10 known to the prior art which includes a mild steel barrel 12 having on itsinnersurfacea lining of a wear and corrosion resistant alloy 14. Alloy steels have also been used for barrel 12 and, together with mild steels, provide a readily available, rsasonably priced backing material which provides excellent tensile strength.

Such backing materials also provide excellent heat exchange characteristics (nearly twice that of stainless steel and nearly as effective as the much higher priced nickelichrome materials used for some prior art heat exchangers).

Lining alloy 14 is added to barrel 12 by placing a predetermined amountofthe lining alloy into barrel 14 and welding end caps over each end of the barrel.

The barrel is then heated to a temperature high enough to meltthe lining alloy. The hot barrel is then rotated at high speed, centrifugally coating the interior with the stronger alloy lining. During the process, the molecules ofthe lining alloy and the backing material are believed to undergo an interchange, creating an inseparable metallurgical bond.

Following cooling, the end caps are removed and bimetal tube is finish honed and further machined or fabricated as specified. Details ofthe bimetallic cylinder preparation method will not be provided here, as such process does not in and of itself form part of the present invention. If such details are desired, reference may be had to the disclosures of the patents referred to earlier in this specification, such discloses being expressly incorporated herein by this reference.

Figure 2 shows a trimetallic cylinder 20 according to the present invention. Cylinder 20 includes a mild or alloy steel barrel 22 and a lining of a corrosion resistant alloy 24, each of which may be similarto the materials previously described. Cylinder 20 differs from cylinder 10, however, in that it includes stainless steel end rings 26 which may be located at one, but preferably are located at both ends of cylinder 20. The width of rings 26 mayvaryfrom about 1-2 inches up to much largerwidths depending on the particular use to which the cylinder is to be put. Moreover, the particulartype of stainless steel may be selected by the cylinder manufacturer depending onthefinal use and the degree of corrosive exposure.

In fabricating cylinder 20, the stainless steel rings 26 are attached to the barrel 22 priorto centrifugally casting the lining alloy 24. In this way, the lining alloy is applied to the barrel and to the end rings 26. By way of illustration, ratherthan limitation, the thickness of the lining alloy may be on the order of 0.7938to 2.3813 mm (1/32" to 3/32") to provide desirablewear protection and corrosion resistance to the inside of cylinder 20, even in applications involving screw expulsion orscraperblademovementwithinthe barrel 24. Furthermore, the overall cylinder may range from an outside diameter of only a few inches up to a foot or more and the length may range to 20 feet or even more for some applications.

Referring next to Figures 3 and 4, it will be appreciated thatthe end rings may be of a slightly narrowerthicknessthan the barrel 22, orthey may be of the same thickness. It is important, however, that the inside surface of rings 26 and barrel 22 be the same to provide a smooth surface for the application of lining alloy 24. The preferred techniques for joining the rings 26 to barrel 22 is the use of a friction or inertia weld 28 (Figure 3) but a conventional weld joint 30 (Figure 4) may also be used. Following the welding operation, the fabricator should insurethatthe inside surface ofthe weld is smooth forthe reasons mentioned heretofore.Following the application of the end rings,theliningalloyis24insertedintothe cylinder and the end caps are welded to the stainless rings. In all other respects, the casting of the lining alloy and the finishing steps arethe same as for bimetallic cylinders.

As described above, a large number of lining alloys can be employed to prepare thetrimetallic cylinders of the present invention. The alloys may be oftheferrous or non-ferroustypes and may contain the carbide particles as mentioned earlier in this specification.For use with food processing equipment, a preferred lining alloy is a nickel/chromium/cobalt alloy which produces a lining having the following properties: macro-hardness 48-54 Rc, nominal tensile strength 2,460.7/3,585.7 kg/cm2 (35,000/51,000 psi), nominal compressive strength 17,577 kg/cm2 (250,000 psi), strain to fracture 0.21 % and density 8359.4kg/in3 (0.3021b/in3). The combination of such an alloy in a trimetallic cylinder provides a cylinderwhich is highly corrosive and wear resistant. The cylinder may be used with any type of scraper blades and because it has a thicker lining than chrome plated tubes previously used in the food art, wear time is greatly increased. The lining allows 100% contact of the scraper blades and which provides a metallurgical non-flaking bond to the barrel and rings as opposed to an electrolytic bond which exists in the chrome plated nickel cylinders of the prior art. The mild alloy barrel 22 provides excellent heat exchange capabilities.

While the present invention has been described with reference to a preferred embodiment and one alternate embodiment, it is notto be limited thereto, but is to be limited solely bythe claims which follow.

Claims (10)

1. Atrimetallic cylinder comprising a metal cylinder, cylindrical end ring means joined to each end of said metal cylinder, said end ring means being more corrosion resistant than said metal cylinder and said end ring means and said metal cylinder having a common bore, a lining of a wear and corrosion resistant lining alloy applied to said bore.

2. Atrimetallic cylinder according to Claim 1, wherein said metal cylinder is a material selected from the group consisting of alloy or mild steel and said end ring means are stainless steel.

3. Atrimetallic cylinderaccording to Claim 1, wherein said end ring means are welded to said metal cylinder.

4. Atrimetallic cylinder according to Claim 1, wherein said lining alloy is metallurgically bonded to said metal cylinder and end ring means.

5. Atrimetallic cylinder according to Claim 4, wherein said lining alloy comprises a nickel/cobalt/ chromium alloy.

6. Atrimetallic cylinder constructed and arranged substantially as herein described with reference to Figs. 2 and 3 or Fig. 4 of the accompanying drawings.

7. A method for making a trimetallic cylinder comprising the steps of providing a metal cylinder; welding end rings onto each end of said metal cylinder, said end rings being of a material which is more corrosion resistant than said metal cylinder, said welding step providing a cylinder having a common bore; placing in said cylinder a quantity of a lining alloy having a melting point less than said metal cylinder and said end rings; placing end caps on said cylinder and heating said cylinder above the melting point of said lining alloy; spinning said cylinder about its axis to centrifugally coat the bore of said cylinder with said lining alloy; and, cooling said cylinder, removing said end caps and finishing the inner surface of said cylinder.

8. A method according to Claim 7 wherein said metal cylinder is a material selected from the group consisting of alloy or mild steel and said end ring means are stainless steel.

9. A method according to Claim 7 wherein said lining alloy comprises a nickel/cobalt/chromium alloy.

10. A method of making a trimetallic cylinder, substantially as herein described with reference to Figs. 2 and 3, or Fig. 4, of the accompanying drawings.