DESCRIPTION OF MANUFACTURING PROCESS AND QUALITY ASSUARANCE SYSTEM OF CMS CROSSING
Raw Material Inspection
We have two types of Raw materials:
Type – I materials for Melting
Type – II materials for Foundry
Type – I materials except Steel scrap & Ferro-allays directly goes in arc furnace. Steel scrap & Ferro-
Alloys like ferro-manganese, ferro-silicon, silica-manganese are checked / tested internally at incoming stage based on IS standards and our own specification, stipulated in QAP.
Type – II materials mainly like Olivine sand, Resin, Hardener, Mould Coat etc. are purchased only from approved suppliers with Test Certificates which are verified at in coming stage. Because of reprocessing material only Olivine sand are tested internally based on IS standard and our own specification, stipulated in QAP.
- Methoding I Pattern Making
We have established by practice the method drawings as well as Method Card Technology Card
Indicating liquid metal flow system, size & position of Runner/Riser etc. with pattern technology based on respective ROSO drawings. All these details are recorded as Method Card and are maintained by respective departments.
Patterns and cores are made by seasened teak wood & all the wear / damage prone corners of pattern are made of aluminium in pattern shop based on casting drawing dimensions including allowances as per method directives & reviewed by the Foundry Manager.
Thorough checking of pattern & core boxes are done before making moulds and recorded in pattern check record by the Process Engineering department.
‘NO BAKE’ moulding system are used for making moulds and cores instead of conventional green sand
moulding system to achieve:
• Improved surface finish.
• Consistency in quality.
• Closer dimensional accuracy.
Olivine sand with required properties are used for mould & core making. New sand are used as facing sand and reclaimed olivine sand are used as backing sand.
Organic chemical binders like resin mixed with catalyst (a-set system) are used as sand binder.
Standardized by practice at our sand laboratory, we have established the approx. ratio of sand (fresh & reclaimed),resin & catalyst to achieve the required quality of Mould & Core. These are maintained by calibrate our sand mixture for required ratio of mixing.
Sand for making moulds & cores are mixed in a 25 TPH capacity continuous mixer and fed to the mould &core boxes directly from the mixer. Once in a month one sample of mixed sand from the mixer are collected and tested at sand laboratory to calibrate the mixture. Verification of calibration are maintained per shift by same manner at sand laboratory and recorded properly. Stipulated in QAP.
Sand preparation, Mould & Core making are carried out as per the Method card. The mould for casting of crossings are made in two halves. Top & bottom mould are made separately and closed together before pouring. The top half shall act as core for making crossing mould. 10 no and few others small cores are made separately,
At the beginning of each shift the mixer machine are configured for facing and backing sand mix in
accordance with the resin and catalyst ratio against sand. Reinforcement, riser/runner sleeves and
in gets are placed before discharge of sand into mould.
Pattern stripping are done after a period of at least 1hr. after completion of moulding. Moulding time, striping time & hardness of all moulds are checked and recorded properly, and then others small cores set & painted with alcohol based magnesite paint with full coverage and proper adhesion, Once the two parts of the mould and core has been painted are dried for at least 30 rnts, followed by cleaning these are ready for closing. After proper closing by gauging pin mould shall be placed in pouring platform ready for molten metal pouring.
As per IRS T-29/2022 desired chemical composition of the finished steel is
% Mn = 11 -14
% C = 1.0 -1.4
% P = 0.06 max,
% S = 0.03 max.
% Si = 0.50 max
On the basis of desired chemical composition & targeted quantity of steel, Melting is carried out in Electric Arc Furnace with pre calculated & weighted charge-mix with Ferro alloys and etc. The charge-mix consists of different types steel scrap, and Ferro alloys consists of Ferro manganese (different types ), Ferro silicon, Silica manganese.
The characteristic and composition of the material to be used are in accordance with IS standards & Raw Material specification of the foundry, During melting with the use of the scrap, it is ensured, necessary addition of lime and petroleum coke has been made at the bottom of the charge.
During oxidation period, Oxygen blowing are started to bring down the carbon about 0,10%. Slag taken out time to time. Sufficient amount of lime and fluor spar are added and temperature are maintained at lower side to have goodde-phosphorisation, which bring down the phosphorus level about 0,010%.
During reducing period, to lower down the sulphur about 0,020%, generally ferromanganese (HC) are added, oxygen blowing are continued and slag are taken out 2 / 3 times. The metal temperature shall be around 1550°C.
Complete slag are removed and about 10 kg of pure coke are added to the bath to remove oxygen from metal.
On the basis of chemical composition after de-oxidation at this stage necessary additions are made for the adjustments of other elements,
Again Lime and fluor spar are added at this stage. After complete fusion of lime, reducing slag mixture and pure carbonare added, Temperature at this stage shall be allowed to increase to ensure making good carbide slag. Vigorous raking are done at this stage for mixing of metal and slag. After addition of reducing slag mixture, 90% of the slag shall be taken out.
The chemistry of the metal are tested & recorded at the following stages of melting process
a) After complete melt down of scrap.
b) During and at the end of oxidations period.
c) After addition of ferroalloys.
d) Final bath analysis before tapping.
The temperature of the molten metal are checked & recorded at the following stages of melting:
a) Inside the furnace during melting.
b) Inside the furnace before tapping.
Last bath temperature are adjusted to 1470°C – 1480°C before tapping the heat.
The bottom pouring Ladle is pre heated & checked approx. 1000 °C before tapping of metal. Addition of aluminum barsare done at the bottom, before tapping starts.
Metal tapped into the Ladle between 1460°C – 1470°C and the tapping temperature are recorded. Argon gas are passed for 3 – 4 minutes to remove the oxides from steel.
Metal ready for pouring, targeted pouring temperature on 1st mould is below 1460°C
After verification of temperature of molten metal & proper position of molds, Pouring are carried out (approx.1 OOO°C) In a standardized procedure. Pouring sequence, pouring start & pouring end temperature, filling time of each moulds, chemical composition of before pouring & end of pouring samples are checked and recorded. We also are poured not more than eight crossings to ensure proper grain size of casting as per IRS T-29/2022. Test coupon ( 4 Nos. for each crossing) formation are ensured by proper pouring procedure.
- Knock Out, Fettling & Shot Blasting
After de-moulding of casting, runners/risers are detached by hammer blow, cutting of ingates are done by arc air, keeping a distance of at least 25 – 20 mm from parent metal to avoid thermal shock. Cleaning of residual sands from casting surface and removal of fins if any by mild hammering. Casting shall not be placed on shake out table under any circumstances. The casting are shot blasted thereafter for smooth visual surface inspection.
- Chemical Testing, Surface Inspection & Gross Dim. Inspection ( Stage Inspection I)
After shot blasting chemical testing are done & recorded for verification of casting chemistry. All castings thereafter are inspected visually to determine foundry defects. Major defects like cracks, lack of metal, shrinkage cavities etc. are not accepted. Detection of minor defects are done by dye penetrant method, scattered porosities with a particular dimension, no. & location are accepted as per IRS T-29/2022. Now the all major gross dimensions with straightening of each casting are checked & verified within the limit. Internally Accepted castings are offered for Stage I, ll & III inspection to RDSO. Accepted castings are ready for heat treatment.
Heat treatment Process
The castings shall be placed, with rail head down position, on the hearth of the heat treatment furnace in a length Wise manner along with integrally cast test coupons protected by proper manner.
• The heat treatment cycle shall be as below:
Operation Condition Tolerance
Rise up to 300°C. Free rise ±10°C
Rise up to 720°C. 100°C per hour ±10°C
Soaking at 720°C 2 hours Temp. ±10°C
Time ±10 minutes
Rise up to 900°C 150°C per hour ±10°C
Soaking at 900°C 2 hours Time ±10 minutes Temp. ±10°C
Rise 900°C – 1050°C Maximum rate of rise ±10°C
Soaking at 1050°C 4 hours Time ±10 minutes
Soaking at 1080°C 15 Min. Temp. max 15 min.
Quenching at water Within 60 seconds from Maximum
furnace door opening
Keeping inside water bath 45 minutes. Minimum
• The following cares are taken for achieving optimum quality during heat treatment
of the crossings:
Castings shall be thoroughly cleaned before putting for heat treatment. The castings shall be arranged in such a fashion that, uniform heating of all the castings by the heat convection current is feasible.
There shall not be direct impingement of flames on the casting.
Door of the furnace is properly sealed.
For quenching, all operations after door opening to transportation and dipping into water shall be within one minute.
Water temperature before quenching shall be maintained at around 30°C, and raise in temperature of water after quenching shall not exceed 10°C.
A good quality water quenched casting shall show feeble or no magnetism, shall be verified by non magnetic test.
All the parameters related with time & temperature during Heat treatment are recorded automatically in a graph which is preserved with other parameters & details related with heat treatment & quenching.
Shot Blasting, Surface I Gross Dim. I Non Magnetic I Micrographic & Physical Inspection ( Stage Inspection II )
After separating test coupons from crossing it is shot blasted for cleaning. Again surface & Gross dim. Inspection are done in same manner which was done before heat treatment.
Non magnetic test specially on running surface of crossing are done by portable permanent magnet. Micrographic tests from test coupons are done to ensure the micro structure of the steel is single face austenite free from carbide precipitation with comparing the album of different micro photographs as per IRS T-29/2022. Impact bend test on test coupons & hardness on crossing are done to ensure physical properties of casting. In case of non conformity of any above tests there is a option of re heat treatment to achieve the desired properties. All the tests will carried out again for verification of conformity. In a proper manner all tests are done & recorded, stipulated in QAP.
- Straightening after heat treatment and after rectification of defects by welding
The straightening of the crossing are done by a hydraulic press to remove all the deformations produced in the casting during the course of heat treatment and sometimes during machining. This rectification is carried out in a hydraulic press.
The straightness is checked by piano wire and two piece steel block of 5 mm thickness placed at the ends of the crossing. Using blocks of various thicknesses ranging from 3 mm to 10 mm, the entire length of the top table of the crossing is checked. The positive & negative bends are corrected by repeated application of pressure until a tolerance of ± 1 mm is achieved, i.e. 4 mm & 5 mm blocks. pass through but 6 mm shall not pass.
Repair by Welding
Any defects if observed at different stages of processing CMS crossing are recorded in sketch. Before
welding, the defective areas are properly ground I gouged. D.P. test are carried out to check complete removal of defects and welding by specified electrodes shall be done. For welding of defects, welding procedure laid down in IRS:T 29-2022 are followed.
Marking for finishing:
Reference line for machining and fishing planes marking are drawn on each casting before placement on machine table. One marking table (6 M x 1 M) and set of marking instruments are available for the purpose.
Machine finishing of CMS crossings:
Bottom machining and finishing planes machining shall be done by Plano miller. End section of the crossing shall be machined by horizontal milling m/c. Top gauge face radius shall be machined in planing. One special drilling machine is available for drilling CMS crossing.
At this stage crossings are offered for final inspection like Visual, Dimensional, DP & Radiography tests
Following test shall be conducted as CMS crossing, as per frequents given below.
a) Visual & Dimensional – Each casting
b) Radiographic test – At a frequency of 1 : 20 for each type of CMS crossing during
production and 1 : 5 during prototype
c) Solidity test – One casting of each design during 10 & Prototype and one
casting 1 design 1000 or two years.
d) Non magnetic test – Each casting after heat treatment at any surface.
e) D.P. Test- Areas under welding rectification after removal of defects and
after welding 1 grinding. All castings at vee, up to 300 mm from nose and any area needs to be confirmed after visual
After internal acceptance finish Crossings are offered for Final Inspection to
Maintenance of records at various stages All necessary relevant records during the process of manufacturing CMS crossing are systematically documented and kept under concerned departments heads
Painting and dispatch
All the accepted castings shall be thoroughly cleaned to remove rust, scale etc. and will receive two coats of paint in accordance to IRS: T 29 – 2022 an each surface. All crossings, after acceptances and painting shall be properly dispatched duly bound with ropes in tracks I trailers to ensure that no damage occurs during transit up to purchaser’s consignee. Loose Fittings I Components shall be packed in Gunny bags for the same prepared.