WO2019123485A1

WO2019123485A1 - A process of induction hardening treatment at steel cheese tube edge for high impact resistance

Info

Publication number: WO2019123485A1
Application number: PCT/IN2018/050869
Authority: WO
Inventors: Bhagwat Ramanbhai PATEL; Prashant Ramniklal GANDHI; Shailesh Ramanlal PATEL
Original assignee: Siddhi Engineers
Priority date: 2017-12-23
Filing date: 2018-12-22
Publication date: 2019-06-27

Abstract

The present invention relates to a process of induction hardening treatment at steel cheese tube edge for high impact resistance. More particularly, it relates to induction hardening treatment only at the edges of steel cheese tube used in winding flat tape yarn. Steel hardening is followed by process of heating and quenching the ends of steel tube. An induction hardening provides improved protection to the edges when the tube with filled up flat tape yarn or empty tube undergoes repeating rotations, movement, transportation, handling as well as during inserting/loading the cheese tubes on spindle winder machines. It is also cost effective in terms of repeated number of rotations in winding process. The present invention provides advantages in terms of super high strength at the ends and protection against deformation, combination of ductility and strength at the central portion of the tube, light weight, multiple usage and longer life coupled with economy per usage.

Description

A PROCESS OF INDUCTION HARDENING TREATMENT AT STEEL CHEESE TUBE EDGE FOR HIGH IMPACT RESISTANCE

Field of the Invention

The present invention relates to a process of induction hardening at ends of steel cheese tubes for high impact resistance. More particularly, the present invention relates to a process of induction hardening treatment at the edge of steel tube for winding the flat tape yam made from Polypropylene (PP) or High Density Polyethylene (HDPE). Background of the Invention

Steel cheese pipes are enticing attention in woven sacks industry and increasingly supplied to woven sack industries for winding of flat tape yarn prepared from HDPE (High Density Poly- Ethylene) or PP (Polypropylene). Steel is an alloy of iron and carbon and other elements. Due to its high tensile strength and low cost, it is a major component used in woven sacks industries. At the time of flat tape yam manufacturing process, flat tape yam packages are formed by winding flat tape yam onto flat tape yarn carriers which are rotating at speed of 800-1200 rpm. The flat tape yarn wound on the steel cheese pipes is taken to circular looms for weaving sacks which are utilized for packaging of cement, fertilizers, sugar, chemicals and food grains. Woven sacks in high density poly ethylene material are the preferred mode of carrying items of varied shapes and sizes. They are highly popular because they can easily replace expensive customized packaging of items, yet offer better protection. These sacks have many advantages over other conventional sacks materials and are quite competitive in price. They can also carry bigger volumes than bags.

Woven Sack is normally produced from P.P. (Polypropylene) and HDPE (High Density Polyethylene) materials. The choice of material among PP & HDPE is done considering the material to be packed inside HDPE as inherent tendency to shrink once wound on any object. The flat tape yarn is continuously wound on steel tubes called Cheese tubes. Conventionally Cheese Pipes are being used from cold drawn steel tubes, which are called cheese pipes since they are mounted on the cheese winder. Large numbers of cheese pipes are used simultaneously for the purpose of winding, which produces a winding pressure. Such flat tape yarn which is wound on the cheese tube is then taken to circular winding machine from which the woven sacks product comes out for further sewing, lamination etc. Some material like HDPE is hygroscopic and undergoes shrinkage due to which the cheese tubes have tendency to get compressed normally at the center and ends of tubes are likely to get damaged/deformed during handling or transportation. It is important that the portion on which flat tape yam is wound should have reasonable level ductility providing it an ability to come back to its original position once the flat tape yam is unwound, without any residual deformation.

For making flat tape yarn an extrusion plant is used, where along with PP/HDPE, a master batch is added at the extrusion input stage and thin plastic sheet comes out as output of the extrusion plant. The thin sheet is then cut into a group of parallel of strips by a multiple cutter. Such strip is then taken to the cheese winder and at a time about 250 to 300 such separate strips are wound on the individual cheese pipes. Thus, cheese pipes made from steel (mild steel) are filled up with flat tape yam of PP or HDPE material.

Even while transporting/handling the cheese tubes with filled up flat tape yarn or wound yarn to the circular loom or other machines, it can damage the ends of tube. Simultaneously while inserting/loading the cheese tubes on the cheese winder machines, the tubes get profoundly damaged at both the edges in terms of flattening of the ends as well as forming small grooves at the ends of tubes. It is significant to have tremendous measurement control for exact fitment on the cheese spindle.

The cheese tubes have been on a larger demand in the woven sack industries for winding flat tape yarn. Cheese tubes are most suitable and worthwhile for woven sack due to its light weight, excellent ductility and tensile strength. While at present the problem arises when cheese tubes are brought in contact with the winder machines for the circular looms once they become empty are handled in such a way that ends get damaged/deformed. It is important to mention that there are instances of deformation at the edges since the desired hardness of steel tube is not maintained.

Conventionally various processes have been carried out for the winding of flat tape yarn on cheese tubes which leads to distortion of the edges of tube. For example, in U.S. Patent. No. 5,029,762 by Behrens is directed to a yarn winding apparatus and method and discloses yam catching slots which are said to be particularly useful in connection with winders wherein the surface of an empty yarn core or tube, and the yam, move in the same direction at the time when the yarn is strung up on the empty core. In the embodiment illustrated of this patent, a portion of the start-up groove is shaped so that each wall includes saw tooth-like projecting radial edges. The radial edges on the opposed walls are displaced relative to each other, i.e. the edges are staggered. Because of this difficulties associated with the distortion of edges of steel cheese pipes for winding of flat tape yarn in textile industry, there is an inevitable requirement of protecting the edges of tubes while it can be used for repeated number of time and can be cost effective for the woven sack industries.

Hence, to overcome above mentioned problems (i.e. distortion of edges, damages and deformation of ends non accurate fitting of the tube, and very high maintenance), it is desperately needed to invent a method of manufacturing cheese pipes for woven sack industry, which will resist to the problem of deformation/damage at the ends which is not subjected to aforesaid problems. So that finally while mounting the cheese pipes on the individual locations, it is not found to be unusable while it attains super high strength edges which has desired perfunctory properties, lower upholding and high level hardness suitable for using in woven sack industry. This problem if solved, will lead to increase in the life of cheese pipes, the cheese winder will be fully loaded since the damaged pipes will not be there while loading cheese winder leading to improved productivity of the cheese winder and lesser rework to remove the damages/deformation.

Object of Invention The main object of the present invention is to provide a process of induction hardening treatment at pipe edge for high impact resistance.

Another object of the present invention is to provide a process of induction hardening treatment to achieve immense high strength and tremendous ductility on both the ends of cheese tubes.

Yet another object of the present invention is to provide a process of induction hardening treatment at the ends of cheese tubes which is made up from different grades of steel.

Further object of the present invention is to provide a process of induction hardening at the ends of cheese tubes to protect the tube against wear and tear.

Yet an object of the present invention is to provide a process of induction hardening at the edges of tube to protect the ends in terms of flattening.

Still an object of the present invention is to provide a process of hardening at ends of cheese tubes to improve protection against deformation of edges.

Another object of the present invention is to provide a process of induction hardening treatment at the ends of cheese tubes for economical and multiple use.

Further object of the present invention is to provide a process of induction hardening treatment by cold drawn welding process or cold electric welding at the ends of cheese tubes.

Summary of the Invention

The present invention relates to a process of induction hardening treatment at steel cheese tube edge for high impact resistance. More particularly, it relates to induction hardening treatment only at the edges of steel cheese tube used in winding flat tape yam. Further it provides the cheese tube to be made from specific steel grades by ERW process followed by cold drawing and then by induction hardening process at both the ends. Steel hardening is followed by process of heating and quenching the ends of steel tube. An induction hardening provides improved protection to the edges when the tube with filled up flat tape yarn goes under repeating rotations, movement, transportation, handling as well as during inserting/loading the cheese tubes on spindle winder machines. The hardened edges of steel cheese tubes provide desired strength/toughness and protection against deformation. It is also cost effective in terms of repeated number of rotations in winding process. The present invention provides advantages in terms of super high strength at the ends, combination of ductility and strength at the central portion of the tube, light weight, multiple usage and longer life coupled with economy per usage.

Detailed Description of the Invention

Before explaining the present invention in detail, it is to be understood that the invention is not limited in its application to the details of the construction and arrangement of parts illustrated. The invention is capable of other embodiments, as described above and of being practiced or carried out in a variety of ways. It is to be understood that the phraseology and terminology employed herein is for the purpose of description and not to limitation. The invention may have various embodiments and they may be performed as described in the following pages of the complete specification.

Dimension and weight of the cheese tube/cheese pipe used conventionally varies as per the definitive application. Conventionally the outer diameter of the tube ranges from 34mm to 40mm whereas an inner diameter depends on the ultimate thickness and uniformity of cheese pipes. Further the length of the cheese tube ranges from 218mm to 230mm and the thickness of the cheese pipe ranges from 0.8mm to l.5mm respectively. Further based on the varying dimension, weight of the cheese pipes used in winding flat tape yam are in the range from l55gm to 300 gm.

The present invention relates to manufacturing of cheese pipes made of steel for winding flat tape yarn manufactured from PP/HDPE materials. The present invention describes method of manufacturing cheese pipe for woven sack industries which uses strips of the basic steel as feed stock. The strip of basic steel is further subjected to forming of round tube followed by Electric Resistance Welding (ERW) process. The said welding process provides seam welding by producing coalescence of surfaces, where heat is generated to form the weld by the Electric Resistance Welding (ERW). The principal behind the welding is directly based on material deformation with respect to time and the force used to hold the materials together during the complete welding process. The said welding process eventually depends on the characteristics of basic steel.

The present invention further provides different grades of steel having diverse tensile strength, hardness and percentage elongation. Further processing of the tubes is required, as basic raw material does not have requisite characteristics for manufacturing of hardened cheese pipes. The present process is scrutinized on various steel grades (i.e. SAE 1020, SAE 1026, ST 52, ST 52.3, SAE 1541, MC 11 and IS 7226 C40). These steel grades are evaluated for improvement in tensile strength, hardness and percentage elongation. The basic strips of steel are selected as feed stock or raw material. The said strips are subjected to splitting in predefined length which will undergo sealing the ends to form tube through ERW (electric resistance welded) process. The said steel grades have tensile strength in range of 400-700 MPa which is directly depended on the grades of steel. Composition and tensile strength of various steel grades is given in Table-A:

TABLE-A

* Grades are denoted as per the standards of SAE societies.

The electric resistance welded (ERW) tubes are made to cut as per desired length 218mm or as per requirement of the purchaser. Further the specific length tubes are cut, which is then subjected to induction hardening at both the ends in order to create extra hardness in about mm 25 to 30mm length of both the ends. Here if it is required, then ERW tubes are made of higher dimension compared to finished product and then subjected to further cold drawing process.

Moving further after the Electric Resistance Welded (ERW) tube, there is cold drawing step, in which an appreciative stress is developed in the steel tubes. Hence, to relieve stress, the cold drawn steel tubes are then straightened on hyperbolic 6 roller machines. This said process of cold drawing step is done with the tubes input from one end and if further required, the tube direction is reversed again to pass through the straightening machine with a view to make sure that desired straightness is achieved. After the said desired mechanical property is achieved in the resultant steel tube in longer length, tube is cut to required length. Than cut tube is taken for final process of hardening which is carried out by induction hardening at both the edges of the tube. Induction hardening process further engenders fine grains in the re-crystallization course thereby enhancing strength to the hardened portion of the edges. In the present hardening process, the steel tubes are heated for induction hardening at about 850°C -950°C. The time or duration mainly depends upon the dimension and thickness of the tubes, after which the tensile strength of the tubes go beyond 1600-1700 MPa and percentage elongation is limited to a level of 8 to 15% with reference to cold drawn steel tubes. The said hardening process is done by various methods which include perspective hardening, salt hardening and the present induction hardening. The resultant steel tubes hardened at the edges obtained by the foregoing method of the invention from various steel grades achieving higher ductility, consistent and less deformable than conventional steel tubes which are substantially suitable for woven sack industry.

The present method particularly provides impact resistance to deformation 5 at both the ends of the tube by following steps:

(a) The strip of basic steel grade is selected as a feed stock;

(b)The said strip is welded through Electric

Resistance Welding (ERW) to form the primary tube.

(c) The primary tube is further subjected to cold drawing and straightening 0 and cut to required length.

(d) The ERW/CDW tubes prepared after required final dimension are hardened by induction hardening at both the ends of the tubes at 900°C to achieve the desired strength at the ends.

Further with the broad point of view, the electric resistance welding for the5 tube is done in higher diameter against required finished sizes. The primary ERW tube is cold drawn to achieve the specific diameter of the tube. The said tube is further straightened on hyperbolic tube straightening machine and then transversally cut into desired length. The said tube is then hardened at both the ends of the finished cut size tube by induction hardening at 900°C to achieve the0 desired strength at both the ends of the tubes.

The test was carried out to judge the impact resistance through flattening test of the tubes shown in below table 1 with size 37.0 X 35.0 X 218.0 MM (ST- 52):

Note: Compression Length up to 16.0 mm CHT Selected.

Observation: It was observed that the load required for pressing the end hardened tube up to a level of l6mm increased by about 30% compared to normal tube. Thus, change in hardness has led to higher amount of load to deform the tube. Further spring back action for Induction hardened tube was more with compare to normal (Middle Portion of Induction Hard) tube.

Table 1

i§ RGREiSL $ END HARD

Graph: 1

Conclusion: 1. More load observed in End hardened tubes without crack.

2. Sample compression up to 16.00 mm. Here again in table 1 it is showing that hardening at the ends is improved compression load drastically and therefore the load to deform in hardened tubes required maximum than in the normal tubes. It was observed that the load required pressing the tube up to a level of l6mm increased by about 30%. Thus additionally confirming that the change in hardness has led to requirement of more amount of load to deform the tube.

Table 2

$ R-SKiAAi $ £!¾D HARD

Graph: 2

Conclusion: 1. More spring back action observed in End hardened tubes.

2. Spring back action is 3 to 4 mm more in End Hardened tubes. The Table-2 as above shows the spring back action after removal of load. Here again it is showing that hardening at the ends improve spring back drastically and therefore after removal of load, tubes with hardened end observed maximum spring back action compare to normal tubes.

Table 3

p

Conclusion: More hardness observed in End hardened tubes with compare to normal tubes. The Table-3 as above shows the hardness on Superficial Rockwell

Hardness (HR 30T) Scale. Here it is noted that since the hardening is done at the ends, the hardening measurement is done at various degrees but along the length. The tabular presentation along with graphical presentation of the hardness which is shown herewith. The overall conclusion is that hardness at both the ends increases to a level of about 55 to 60 points from normal level of 30 to 32 points.

Details of Outside Diameter observed for the Size - 37.0 x 35.0 x 218.0 mm Length Induction Hardening Cheese 3 Tubes (ST-52) at different length and different angle O

O

Tube No. 01A OUT SIDE DIAMETER - 37.0 MM

00

n H

¾ bo o o

O

00 o\ s©

2) AT 0.0 mm outside diameter increases but not found more variation. 3 o

O

3.) Variation of O.D dimension at portion of 01A observed 0.13 mm and total O.D Limits is 37.0 ± 0.07 mm (Total 0. l4mm).

Tube No. 01B 00

OUT SIDE DIAMETER - 37.0 MM

n H

¾ bo o

o

O

00 o\ s©

2) AT 0.0 mm outside diameter increases but not found more variation. 3

O

3.) Variation of O.D dimension at portion of 01B observed 0.13 mm and total O.D Limits is 37.0 ± 0.07 mm (Total 0. l4mm).

Tube No. 01A’ IN SIDE DIAMETER - 37.0 MM 00

n H

¾ bo o o

O

00 o\ s©

_)fdi ^{diii bdl} O_i A C_{b 1 I} H ^ID ^I _ttt ^ttt _seraon_:ern_conar^enn^ga^raonn^crea^sesn^eron^rovu vu u^.

2) Max Variation in ID up to 0.10 mm. 3 o

O

3) All point of O.D Dimension at 10.0 mm observed below C.L.

Tube No. 01B’ 00

IN SIDE DIAMETER - 35.0 MM

n H

¾ bo o o

O

00 o\ s©

2.) Max Variation in Inner Diameter up to 0.06 mm. 3

O

3.) I.D Dimension found in control limit.

Size: - 37.0 x 35.0 x 218.0 mm Length Induction Hardening Cheese Tubes (ST-52) 00

5 Tube No. 01 A

Thickness- 1.00 MM

n H

¾ bo o o

O

0 o0 s©\

3

O

00

n H

¾ bo o o

O

00 o\

Observation: Wall thickness under control limit. 3

O

Further the Rockwell hardness (HR30T) is measured along the length of the induction hardened cheese tubes (ST-52) and size

37.0 x 35.0 x 218.0 mm length. The following results have been shown for said Tube (End“A” to End“B”)

00

ROCKWELL HARDNESS (HR30T)

n H

¾

bo o o

O

00 os so

3 o

O

00

C/i

n H

¾ bo o o o

00 os so

Observation: 1.) Hardness increase up to length of 10.0 mm both side and also increase over all tube hardness compare to same tube of Normal condition..

2) ST-52 cheese tubes hardness before Induction hardening found 15.40 HR30T. 3) Overall tube hardness variation 35.20 HR30T from A end to B end.

4) Both ends hardness increase up to 3 times compare to normal ST-52 cheese tube hardness.

Further the stress is described that will cause a specified small, permanent extension of a tensile test piece corresponding the value which approximates to the yield stress in materials not exhibiting a definite yield point.

In some ductile materials such as Aluminum, Copper, Mild Steel, the yield point cannot be clearly defined during tension test, therefore yield stress is Unknown. For such metals design stress called PROOF stress is calculated using offset method. Moreover the Percentage Elongation calculator computes the ratio of change in length to original length.

Further the statement for which mechanical properties before and after induction hardening is mentioned. The materials from two supplier of size 37 mm OD x lmm thick (35mm ID) steel tubes is used for cheese pipes. The summary of mechanical property is shown here-under:

It can be observed that the tensile strength is in the range of 700 MPa and yield strength, which is many times considered as proof stress, is observed around 600 MPa. Further for deriving mechanical properties of induction hardened tubes, since only end hardening portion cannot provide tensile values, similar tubes which are fully induction hardened are taken and following results have been observed. It can be observed that the Tensile Strength and other properties are enhanced (increased) drastically after induction hardening.

From the above it is concluded as follows:

A) Due to induction hardened at end, the mechanical property in that particular portion is improved drastically which results into higher impact load required to damage the end portion of induction hardened tube. B) Spring back action of induction hardened tube is better compared to normal tube, which means even after applying impact load, the possibility to come back to its original position is better in case of induction hardened portion. The invention is illustrated more in details in the following example. The example describes and demonstrates embodiments within the scope of the present invention. This example is given solely for the purpose of illustration and is not to be construed as limitations of the present invention, as many variations there of are possible without departing from spirit and scope.

Example-1 a) The suitable steel strip of ST-52 grade material was taken as feed stock. b) The said strip was formed into round tube and welded through electric resistance welding on tube mill to form primary tube. c) The primary tubes were straightened on hyperbolic straightening machine and then transversally split (cut) to 218mm length. d) The straightened tubes were subjected to induction hardening at both the ends at 900°C temperature. e) The said hardened tube was subjected to water quenching to have final product awaiting surface coating/powder coating.

Example-2 a) The suitable strip of MC 11 grade material was taken as feedstock. b) The said strip was formed into round tube and welded through electric resistance welding (ERW) on tube mill to form primary tube. c) The primary tubes were straightened on hyperbolic straightening machine and then transversally split (cut) to 218mm length. d) The straightened tube was subjected to induction hardening at both the ends at 900°C temperature. e) The hardened tube was subjected to water quenching to have final product awaiting surface coating/powder coating. Example-3 a) The appropriate strip of SAE 1020 steel grade was taken as feed stock material. b) The said strip was subjected to forming followed by electric resistance welding (ERW) on the tube mill for the final size of tube. c) The said strip was welded through electric resistance welding (ERW) at flanges to form the primary tube of SAE 1020. d) The said tube was cold drawn at room temperature to have thickness in dimension of 37mm x 0.8mm thick. e) The said cold drawn tubes were straightened on hyperbolic straightening machine and then transversally split to 218mm length. f) The said tube was subjected to induction hardening at edges at the temperature of 900 °C temperature in furnace. g) The hardened tube was subjected to water quenching to obtain final product.

Example-4 a) The suitable steel trip of ST 52 grade material was taken as feed stock. b) The said strip was subjected to forming followed by electric resistance welding on the tube mill for the final size of tube. c) The final size strip was welded through electric resistance welding (ERW) at flanges to form the primary tube of ST 52. d) The said tube was cold drawn at room temperature to have thickness in dimension of 37mm x 0.8mm thick. e) The said tubes were straightened on hyperbolic straightening machine and then transversally split to 218mm length. f) The said tube was subjected to induction hardening at temperature of 900 °C temperature in furnace. g) The said hardened tube was subjected to water quenching to have final product. Advantages of the process:

The present invention relates to manufacturing of cheese pipes made of steel for winding flat tape yam made from PP/HDPE materials. The present invention provides light weight and strong ends as well as good ductile body. The steel tubes are subjected to induction hardening treatment particularly at the edges for higher impact resistance and hardness of an alloy. The said treatment results in formation of hardened ends and therefore there is an increase in tensile strength.

The process in the above case provides advantage in terms of remarkable high strength at the ends, combination of strength and ductility at the central portion of the tube, light weight, multiple usage capability compared to conventional process and longer life even after repeated usage for winding flat tape yam.

While various embodiments of the present invention have been described in details, it is apparent that modification and adaptation of those embodiments will occur to those skilled in the art. It is expressly understood, however, that such modifications and adaptations are within the spirit and scope of the present invention as set forth in the following claims.

Claims

We Claim: -

1. A process of induction hardening treatment at steel cheese tube edge for high impact resistance used in winding flat tape yam comprising following steps: a) manufacturing cheese pipes by Electric Resistance Welding (ERW) formed by strips of basic steel as feed stock; b) cutting as per required length of the electric resistance welded tubes obtained in step (a); c) hardening by induction process at both the ends of tubes obtained in step (b) to create extra hardness on both ends; d) drawing of said steel tubes obtained in step (a) at a room temperature to reduce the cross section area of said steel cheese tubes; e) straightening the cold drawn steel tubes obtained in step (d) at a room temperature to remove stress generated during step (d); f ) cutting as per required length of the electric resistance welded tubes obtained in step (e) g) carrying out induction hardening treatment at both the ends of finished cut size cheese tubes obtained in step (b) and (f) to further improve the mechanical strength and percentage elongation in straightened steel cheese tubes.

2. The process for induction hardening treatment at steel cheese tube edge for high impact resistance as claimed in claim 1, wherein steel cheese tube grade is selected from SAE 1020, SAE 1026, ST 52, ST 52.3, SAE 1541, MC 11 and IS 7226 C4.

3. The process for induction hardening treatment at steel cheese tube edge for high impact resistance as claimed in claim 1, wherein at step (a) welding of tubes is done by cold drawn welded or cold electric welded.

4. The process for induction hardening treatment at steel cheese tube edge for high impact resistance as claimed in claim 1, wherein step (c) is carried out at 900°C for induction hardening to create extra hardness in 25 to 30 mm length at both ends.

5. The process for induction hardening treatment at steel cheese tube edge for high impact resistance as claimed in claim 1, wherein step (e) is carried out by hyperbolic 6 roll machine.

6. The process for induction hardening treatment at steel cheese tube edge for high impact resistance as claimed in claim 1, wherein step (g) is carried out at 900°C for induction hardening to achieve the desired strength.

7. The process for induction hardening treatment at steel cheese tube edge for high impact resistance as claimed in claim 1, wherein the mechanical properties includes improvement in tensile strength and percentage elongation, reduction in weight and less deformable suitable for woven sack industry.